Symposium Organizers
Steve Dunn, Queen Mary University of London
Brian Rodriguez, University College Dublin
Henry Sodano, University of Michigan
Matjaz Valant, University of Nova Gorica
ES03.01: Session I
Session Chairs
Monday PM, November 27, 2017
Hynes, Level 3, Room 300
8:30 AM - *ES03.01.01
Environmentally-Friendly Synthesis of Metal Chalcogenide Nanomaterials for Energy Conversion Devices Employing Supercritical Fluid Processing
Yuta Nakayasu 1 , Takaaki Tomai 1 , Itaru Honma 1
1 , Tohoku University, Sendai Japan
Show AbstractFor the development of sustainable science and technology, it is important to develop energy device materials composed of abundant resources. Particularly, the metal sulfides and selenides have promising properties for energy conversion devices. However, the synthesis process of the metal chalcogenides requires high temperature, long process time, and the use of highly toxic raw materials. From the viewpoint of sustainability, the development of environmentally-friendly synthesis processes is important challenge.
In recent years, we have been developing the novel sulfurization and selenization process for metal oxide precursors using supercritical reducing condition. By using the supercritical fluid (SCF) environment where the solvent properties can be easily controlled by pressure and temperature, relatively low-temperature and high-rate processes without toxic solvents. For fabrication of CuInS2 and Cu2ZnSn(S,Se)4 thin films via sulfurization and selenization from amorphous oxide precursor films, by using supercritical ethanol condition, less toxic materials such as sulfur and selenium as chalcogen sources were utilized, and reaction temperature and reaction time were relatively low 350−400°C and relatively short 25−40 min, respectively.
In addition, we applied this SCF chalcogenization process for the synthesis of flower-like MoS2(1−x)Se2x (x:0−1) with edge-rich structure and few-layer thickness for electrocatalytic hydrogen evolution reaction (HER). As a result, we succeeded in the synthesis of Mo(S,Se)2/reduced graphene oxide (rGO) composite in one-pot process for 1 hour. These original sources are elemental sulfur, selenium, MoO3 and graphene oxide, and solvent is ethanol dissolving NaBH4, which are facile and environmentally friendly chemicals. In cyclic-voltammetry measurements for HER, flower-like MoS2(1−x)Se2x showed onset potentials of about 100 mV (vs RHE) and operating potentials in the range of 210−300 mV (vs RHE) at a cathodic current density of 10 mA/cm-2. The Tafel slopes between 36 and 82 mV/decade were obtained. In the latter case, Mo(S,Se) /rGO showed an onset potential of about 80 mV (vs RHE) and a very low operating potential of about 160 mV (vs RHE) at a current density of 10 mA/cm-2 and Tafel slope of 44 mV/decade were obtained, suggesting very high HER catalytic activities.
In summary, the utilization of SCF condition for the synthesis of metal sulfides and selenides energy materials has many advantages, shorter reaction time and lower reaction temperature. Moreover, SCF processing is quite suitable for using nontoxic precursors to produce chalcogenide compounds. The SCF processes studied in this work can open sustainable chemistry to the fabrication of multicomponent, hard-to-synthesize compound into thin films, nanocrystals and nanoporous materials for versatile applications to catalysts, solar cells, secondary batteries, hydrogen production, nanoelectronics and biomaterials.
9:00 AM - ES03.01.02
Highly Conducting Metallic MoS2 for Energy Storage
Hongli Zhu 1 , Yucong Jiao 1 , Xiumei Geng 1 , Alolika Mukhopadhyay 1
1 Department of Mechanical and Industrial Engineering, Northeastern University , Boston, Massachusetts, United States
Show AbstractBenefit from its different Mo and S atom coordination of octahedral structure with dense active sites, metallic phase MoS2 owns the electrical conductivity of 5 orders magnitude higher than that of semiconducting MoS2. This high intrinsic conductivity can significantly advance the metallic MoS2 electrode electrochemical performance on energy storage. Until now, little work has been done to investigate the electrochemical mechanism of metallic phase MoS2 as an anode on lithium-ion and sodium-ion batteries and ultrafast supercapacitors. In this work, the metallic, intrinsic multilayer, and pure metallic MoS2 has been investigated for use in supercapacitors. An ultrafast rate supercapacitor with extraordinary capacitance using a multilayer M-MoS2-H2O system is first investigated. Intrinsic M-MoS2 with a monolayer of water molecules covering both sides of nanosheets is obtained through a hydrothermal method with water as solvent. The super conductivity of the as-prepared pure M-MoS2 is beneficial to electron transport for high power supercapacitor. Meanwhile, nanochannels between the layers of M-MoS2-H2O with a distance of ~1.18 nm are favorable for increasing the specific space for ion diffusion and enlarging the surface area for charge storage. Furthermore, three-dimensional hollow metallic MoS2-graphene-MoS2 sandwich electrode will be introduced. The MoS2-graphene-MoS2 electrode exhibit excellent electrochemical performance. The freestanding, lightweight, porous, hollow metallic MoS2-graphene-MoS2 sandwich electrode highly facilitates electron/ion transportation during the charge/discharge for high performance sodium ion batteries.
9:15 AM - ES03.01.03
Evidence for Sulfur Vacancies as the Origin of N-Type Doping in Pyrite FeS2 Single Crystals
Bryan Voigt 1 , Mike Manno 1 , Jeffery Walter 1 , David Carr 2 , Eray Aydil 1 , Chris Leighton 1
1 , University of Minnesota, Minneapolis, Minnesota, United States, 2 , Physical Electronics, Chanhassen, Minnesota, United States
Show AbstractPyrite FeS2 has long been considered an ideal candidate as a light absorber in thin film solar cells. However, disappointingly low power conversion efficiencies, predominantly due to low open circuit voltages, have prevented pyrite from becoming a serious contender as a photovoltaic material. This failing is widely acknowledged to be due to fundamental problems with pyrite’s surface, and to a lack of control over doping in this material. One important unanswered question has been the origin of the n-type behavior exclusively seen in unintentionally-doped pyrite single crystals. Here, we present the strongest evidence to date that sulfur vacancies (VS) are the n-type dopants in pyrite. Single crystals with experimentally indistinguishable lattice parameters, mosaic spread, and nominal stoichiometry, grown via chemical vapor transport under different sulfur vapor pressures, show significantly different electron densities and mobilities. Specifically, crystals grown under high sulfur vapor pressure exhibit semiconducting behavior with temperature-dependent electron densities giving an activation energy of 400 meV. Decreasing the sulfur vapor pressure during crystal growth decreases this activation energy, increasing the electron density, and eventually leading to an apparent insulator-metal transition. This is consistent with higher concentrations of VS in pyrite crystals grown under decreased sulfur vapor pressure. These trends are independent of transition metal impurity concentrations in our pyrite crystals. Moreover, the electron concentrations are too large to be explained by trace amounts of transition metal impurities. All evidence thus implicates VS as the n-type dopant in pyrite.
9:30 AM - ES03.01.04
Above 10 % Efficient Earth-Abundant Cu2ZnSn(S,Se)4 Solar Cells with Introducing Alkali Metal Fluoride Electron-Selective Contacts
Cheng-Ying Chen 1 , Bandiyah Sri Aprillia 1 2 3 , Wei-Chao Chen 1 , Yen-Ching Teng 1 3 4 , Chih-Yuan Chiu 1 3 , Kuei-Hsien Chen 1 3 , Li-Chyong Chen 1
1 , National Taiwan University, Taipei Taiwan, 2 Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei, Taiwan, Taiwan, 3 Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan, Taiwan, 4 Institute of Optoelectronic Sciences, National Taiwan Ocean University, Keelung, Taiwan, Taiwan
Show AbstractCu2ZnSn(S,Se)4 (CZTSSe) is the earth-abundant/non-toxic alternative compounds for the commercialized metal chalcogenides (i.e., CdTe and Cu(In,Ga)(S,Se)2) thin-film solar cells. To boost the performance of CZTSSe based photovoltaics, many efforts have been applied to improving the quality of absorbers, band alignments, front and back interfaces/contacts. [1,2,3]
In this work, we demonstrated the high efficient CZTSSe solar cells by simply introducing an interfacial alkali metal fluoride (AMF) layers (~ several nm NaF, LiF) between the buffer layer (i.e., CdS) and the front transparent conductive electrode (i.e., ITO) without extra 50nm ZnO layers. In the statistically studies (10 cells), the AMF layers increase power conversion efficiency from 5.77±0.54 % to 9.68±0.5 %, short circuit current density (Jsc) from 30.1±0.3 mA/cm2 to 32.2±0.2 mA/cm2 and open circuit voltage (Voc) from 400±20 mV to 480±10 mV, resulting from the front AMF modified ITO as electron-selective contacts. After the AMFs modification, the kelvin probe measurement confirmed that the work function of the front ITO decrease from 4.82 eV to 3.39 eV (NaF)/ 3.65 eV (LiF), which causes the beneficial band alignment for electron collection (/hole blocking) on top electrodes. According to the temperature-dependent current density-voltage measurement, the AMF based devices reduce the contact voltage loss, leading to the larger implied Voc of 900 meV compared with 740 meV of pristine devices. After the thickness dependent studies of AMFs, a 10.4 % efficient CZTSSe solar cell with Voc of 490 mV, Jsc of 32.8 mA/cm2 and fill factor (FF) of 63.2 % was obtained.
The morphology, elemental composition, and distribution of the absorber layers are being examined by X-ray diffraction (XRD), X-ray fluorescence spectrometry (XRF), Raman spectroscopy, and by combining transmission electron microscopy (TEM) with electron energy loss spectroscopy (EELS).
References
[1] V. Tunuguntla, W.C. Chen, P.H. Shih, I. Shown, Y.R. Lin, C.H. Lee, J.S. Hwang, L.C. Chen and K.H. Chen, J. Mater. Chem. A, 2015,3, 15324-15330
[2] Y.R. Lin, V. Tunuguntla, S.Y. Wei, W.C. Chen, D. Wong, C.H. Lai, L.K. Liu, L.C. Chen and K.H. Chen, Nano Energy, 2015, 16, 438
[3] W.C. Chen, C.Y. Chen, V. Tunuguntla, S.H. Lu, C. Su, C.H. Lee, K.H. Chen and L.C. Chen, Nano Energy, 2016, 30, 762-770
9:45 AM - ES03.01.05
Electrochemical Active Chlorine Generation Catalyzed by Earth-Abundant Metal Oxide Nanocatalysts for Efficient Water Treatment
Heonjin Ha 1 , Kyoungsuk Jin 1 , Sunghak Park 1 , Kang Hee Cho 1 , Ki Tae Nam 1
1 , Seoul National University, Gwanak-gu, SE, Korea (the Republic of)
Show AbstractElectrochemical water treatment utilizing oxidants produced by electrochemical oxidation reactions in water has been an alternative method overcoming the limitations of conventional water treatment methods. While the conventional biological and chemical treatments have difficulty of bio-refractory pollutants elimination and safety issues for transportation and storage, respectively, the electrochemical treatment has high elimination capacity and cost-effectiveness due to the direct production of oxidizing species from water to be treated. Among the possible disinfectants generated from water molecules (ozone generation) or dissolved ions in water (active chlorine generation), active chlorine including aqueous Cl2, HClO and ClO- has been widely applied with a variety of advantages such as effective capability to eradicate microorganisms, cheap cost and long residence time for water treatment.
Due to the fact that the active chlorine is generated by chlorine evolution reaction (CER) competing with oxygen evolution side reaction (OER), electrocatalysts exhibiting high selectivity for CER are required to achieve efficient water treatment and a dimensionally stable anode (DSA) comprising of RuO2 has been regarded as a highly efficient catalyst for CER. Indeed, the DSA has been intensively investigated for decades, focusing on improving its catalytic performance and understanding chlorine evolving mechanism. However, the mechanistic investigations for CER have not been sufficiently understood due to the lack of in-depth experimental analyses such as verification of reaction intermediates. Moreover, in spite of expensive material cost of the DSA, earth-abundant metal based electrocatalysts for cost-effective active chlorine generation have been rarely introduced and most of reported works have been conducted under acidic brine condition (lower than pH 4) to suppress the OER and enhance the efficiency for CER, which is far from the neutral condition where the active chlorine generation is operated. Therefore, attempts to replace the precious DSA with transition metal oxide based electrocatalysts and understand the active chlorine generating mechanism under neutral brine condition are crucial to achieve efficient active chlorine generation.
Herein, we applied transition metal oxide nanocatalysts for the first time to the electrochemical active chlorine generation system and investigated active chlorine generating mechanism of our nanocatalysts under neutral brine condition using in situ spectroscopic and electrokinetic analyses. We found our transition metal oxide nanocatalysts exhibited comparable catalytic performance to the commercial DSA with high efficiency and stability. Furthermore, we suggested reaction mechanism of our nanocatalysts and verified the reaction intermediates for the active chlorine generation. This works would provide a new insight into designing efficient electrocatalysts for water treatment system utilizing the active chlorine.
10:30 AM - ES03.01.06
Water Splitting Electrodes Based on NiFe Alloy Foil Produced by Roll-to-Roll Processing
HoonKee Park 1 , Ho Won Jang 1
1 , Seoul National University, Seoul, SE, Korea (the Republic of)
Show AbstractWith the rapid increase of global temperature and depletion of fossil fuels, developing sustainable energy resources is crucial nowadays. Among the various renewable energy source generation approaches, water splitting has attracted increasing attention for clean energy generation and efficient energy storage. Electrochemical production of hydrogen from solar electricity is also an attractive option for generating energy in the form of a hydrogen which could be used at a later stage for electricity. Over the past decades, despite of significant achievements have been obtained, the solar-to-hydrogen (STH) efficiency is still too low for practical applications. Low solar to hydrogen (STH) conversion efficiency is due to the suppressed water splitting reactions by high overpotential, especially oxygen evolution reaction. Due to relatively high overpotential than hydrogen evolution reaction(HER), the oxygen evolution reaction(OER) is a key reaction in water splitting. To overcome this problem, current studies are focused on development of efficient, abundant and inexpensive OER catalyst. Although Nickel/iron(NiFe)-based compounds have been known as active OER catalysts for decades, NiFe-based materials such as NiFe layer double hydroxide(NiFe LDH). Herein we report an approach to improve efficiency of water splitting electrodes based on flexible NiFe-based foil. Anodic oxidation method is applied to enhance the oxygen evolution activity of NiFe alloy foil. The anodized NiFe alloy foil exhibit significant higher activity than the corresponding Ni foam in base conditions. The anodic oxidation method generate NiFe oxide and hydroxide layers on NiFe alloy surface, act as electrocatalyst. Spontaneously, the anodic oxidation method widen the specific surface area of water splitting electrodes. Increased reaction sites and catalytic behavior of NiFe hydroxide is the reason of improved water splitting property. Because Ni based alloy like NiMo is remarkable hydrogen evolution catalyst, similar to noble metal, electrodeposition method is applied to enhance the hydrogen evolution activity of NiFe alloy foil. NiMo electrodeposited NiFe alloy foil exhibit highly enhanced activity than pure NiFe foil. Using anodized NiFe alloy foil as anode and using electrodeposited NiMo as cathode, PV-EC cell shows around 15% STH.
10:45 AM - ES03.01.07
Turnip-Inspired BiVO4/CuSCN Heterojunction Photoanode for Highly Efficient Photoelectrochemical Water Splitting
Truong-Giang Vo 1 , Jian-Ming Chiu 1 , Yian Tai 1 , Chia-Ying Chiang 1
1 Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei Taiwan
Show AbstractInspired by the functions and structures of the root and stalk of a turnip, a novel BiVO4/CuSCN heterojunction was constructed for photoelectrochemical water splitting, by initially fabricating bulky BiVO4 film (the root) and subsequently depositing p-type CuSCN nanorods (the stalk) on top. This BiVO4/CuSCN photoanode produced an enhanced photocurrent density of 1.78 mA cm-2 and hole injection efficiency of 82% at the potential 1.23 V vs. RHE. About 40% increase in photocurrent density coupled with a dramatic cathodic shift (~220 mV) in onset potential compared with bare BiVO4. The heterojunction also possesses external quantum efficiency of approximately 33% in the range from 350-450 nm with fairly high solar energy conversion efficiency (0.5%). The unique electrode architecture design favors the facile water splitting process over conventionally fabricated electrode by providing the more active sites and facilitates transportation and consumption of photoinduced holes, open a new route for the high-efficiency photoanodes.
11:00 AM - ES03.01.08
Electrocatalysis of Polysulfide Conversion by Sulfur-Deficient MoS2 Nanoflakes for Lithium-Sulfur Batteries
Haibin Lin 1
1 Chemical and Biomolecular Engineering, National University of Singapore, Singapore Singapore
Show AbstractLithium-sulfur batteries are promising next-generation energy storage devices due to their high energy density and low material cost. The efficient conversion of lithium polysulfides to lithium sulfide (during discharge) and to sulfur (during recharge) is a performance-determining factor for the lithium-sulfur batteries. Here we show that MoS2-x/reduced graphene oxide (MoS2-x/rGO) can be used to catalyze the polysulfide reactions to improve the battery performance. It was confirmed, through the microstructural characterizations of the materials, that sulfur deficiencies in the surface participated in the polysulfide reactions and significantly enhanced the polysulfide conversion kinetics. The fast conversion of soluble polysulfides decreased their accumulation in the sulfur cathode and their loss from the cathode by diffusion. Hence in the presence of a small amount of MoS2-x/rGO (4 wt% of the cathode mass), the sulfur cathode improved its high rate (8 C) performance from a capacity of 161.1 mAh g-1 to 826.5 mAh g-1. In addition, MoS2-x/rGO also raised the cycle stability of the sulfur cathode from a capacity fade rate of 0.373% per cycle (over 150 cycles) to 0.083% per cycle (over 600 cycles) at the typical 0.5 C rate. These results provide the direct experimental evidence for the catalytic role of MoS2-x/rGO in promoting the polysulfide conversion kinetics in the sulfur cathode.
11:15 AM - ES03.01.09
Feasible and Non-Expensive Photocathodes Based on Kesterites for Water Splitting
Carles Ros 1 , Sergio Giraldo 1 , Edgardo Saucedo 1 , Teresa Andreu 1 , Juan Morante 1
1 , IREC, Catalonia Institute for Energy Research, Sant Adria del Besos Spain
Show AbstractAn important approach towards an efficient and sustainable economy is storing solar energy into chemical fuels through photoelectrochemical (PEC) water splitting. Solar hydrogen, as a clean source instead of hydrocarbon steam reforming, can be used in CO2 hydrogenation for its conversion, among others, to methanol or synthetic natural gas as vector for chemical energy storage and contributing to the circular economy. Cheap and earth abundant materials, optimal band gap and electrolyte adaptability is mandatory for large scale industrialization and deployment of PEC technology.
Mathematical calculations have shown that dual absorber tandem photocathode/photoanode configurations, coupling a medium band gap photoelectrode (around 1.9 eV) with a small one (1.0 eV) could overcome the required efficiencies for large scale industrialization[1]. Chalcopyrite CI(G)S, and its earth abundant similar, kesterite CZTS/Se, offer a thin film low cost alternative to traditional silicon. Chalchogenide solar cells bandgap can be tuned from 1.0 to 1.5 eV with stoichiometric modification[2], with state of the art efficiencies ranging over 20 %. This versatility makes them very interesting to be implemented in PEC water splitting[3]. In this work, we present a high throughput CZTS/Se based photocathode for water splitting with MoS2 catalyst, protected from degradation by TiO2 for wide range of pH.
We demonstrate that titanium dioxide grown by ALD can be used as a transparent protective and conductive layer and MoS2 nanostructures as HER catalysts to obtain a kesterite CZTS/Se fully based on earth abundant materials photocathode with tunable band gap. Solar-to-Hydrogen half-cell stable efficiencies over 7% have been obtained with earth-abundant CZTS/Se, with room for photopotential improvement by deeply understanding band gap tunning. These photocathodes have been tested in electrolytes with pH ranging from 0.3 to 14, presenting no degradation over one hour stability in the harshest environments and high current throughput over 30 mA/cm2 both decorated with Pt and MoS2.
[1] S. Hu, C. Xiang, S. Haussener, A. D. Berger, and N. S. Lewis, “An analysis of the optimal band gaps of light absorbers in integrated tandem photoelectrochemical water-splitting systems,” Energy Environ. Sci., vol. 6, no. 10, p. 2984, Sep. 2013.
[2] S. Giraldo, M. Neuschitzer, T. Thersleff, S. López-Marino, Y. Sánchez, H. Xie, M. Colina, M. Placidi, P. Pistor, V. Izquierdo-Roca, K. Leifer, A. Pérez-Rodríguez, and E. Saucedo, “Large Efficiency Improvement in Cu2ZnSnSe4 Solar Cells by Introducing a Superficial Ge Nanolayer,” Adv. Energy Mater., vol. 5, no. 21, pp. 1–6, 2015.
[3] C. Ros, T. Andreu, S. Giraldo, Y. Sánchez, and J. R. Morante, “Conformal chalcopyrite based photocathode for solar refinery applications,” Sol. Energy Mater. Sol. Cells, pp. 1–5, 2016.
11:30 AM - ES03.01.10
Delafossite Oxides for High Temperature Thermoelectric Applications
Yining Feng 1 , Ian Ferguson 2 , Na Lu 1 3 4
1 Lyles School of Civil Engineering, Sustainable Materials and Renewable Technology (SMART), Purdue University, West Lafayette, Indiana, United States, 2 College of Engineering and Computing, Missouri University of Science and Technology, Rolla, Missouri, United States, 3 School of Materials Engineering, Purdue University, West Lafayette, Indiana, United States, 4 Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States
Show AbstractThe use of nanostructured delafossite oxides in thermoelectric (TE) applications has attracted much interest due to their high performance and long-term stability at elevated temperatures. Cuprous delafossites CuMO2 (M= Al, Cr, Fe, Ga, Mn), compared to conventional TE materials, such as BiTe, PbTe and SiGe, are non-toxic and more earth abundant. In particular, CuAlO2 compound shows a great potential for high performance thermoelectric materials. First principle calculations have indicated that it can achieve a figure-of-merit of ZT > 1 at 800 K.
In this work, a systematic study of TE properties of cuprous delafossite materials will be reported. The optimization of the TE property has been realized by controlling nanostructure size from 20-50nm. Reducing the particle size of nanostructured bulk materials decouples interdependent electron and phonon transport and results in lattice thermal constant decrease without deteriorating electrical conductivity. This has yielded high power factorresulting in an enhanced figure of merit, ZT. CuAlO2 powder has been prepared using solid state synthesis method at ~1100 oC in argon atmosphere. The nanostructure size was controlled by high energy ball milling process. Temperature dependent TE properties, including Seebeck coefficient, electrical conductivity, and thermal conductivity are analyzed. The processing-structure-property correlation of these materials will be discussed.
11:45 AM - ES03.01.11
Correlating the Local Structure and Electronic Properties of Nanoparticulate NixFe1-xO with the Electrochemical Oxygen Evolution Activity via Operando X-Ray Absorption Spectroscopy
Daniel Abbott 1 , Emiliana Fabbri 1 , Mario Borlaf 2 , Francesco Bozza 2 , Robin Schäublin 3 , Thomas Graule 2 , Thomas Schmidt 1
1 Electrochemistry Laboratory, Paul Scherrer Institut, Villigen Switzerland, 2 Laboratory for High Performance Ceramics, Empa - Swiss Federal Laboratories for Materials Science and Technology, Dübendorf Switzerland, 3 Scientific Center for Optical and Electron Microscopy, ETH Zurich, Zurich Switzerland
Show AbstractMixed Ni-Fe metal oxides currently represent some of the most attractive anode catalysts for alkaline water electrolysis due to their low overpotentials for the oxygen evolution reaction (OER) in alkaline electrolytes and at near-neutral pH conditions. Here we demonstrate a practical flame-spray pyrolysis technique capable of producing high quantities of nano-scale Ni-Fe oxides (Ni1-xFexO) with high surface areas (SABET ≈ 20 - 75 m2/g). The research presented herein further focuses on expanding the fundamental understanding of how the local electronic and surface structures influence the OER activity of Ni-Fe oxide through operando X-ray absorption spectroscopy investigations. The resulting operando XANES and EXAFS analyses of the Ni and Fe K-edges permit useful insight into the nature of the valence states and rearrangements in local structure that occur under real operating conditions. Combined with a broad range of ex-situ physical characterization techniques, we then relate the structural, electronic, and morphological changes to the observed electrochemical OER activity. Ultimately we identify critical changes that occur in both the local and electronic structures that are linked to the observed enhancements in OER activity as compared to pure nickel oxide.
ES03.02: Session II
Session Chairs
Monday PM, November 27, 2017
Hynes, Level 3, Room 300
1:30 PM - *ES03.02.01
The Energy Efficiency of Electrocaloric Oxides for Cooling
Neil Mathur 1
1 Materials Science, University of Cambridge, Cambridge United Kingdom
Show AbstractElectrocaloric oxides undergo thermal changes in response to changes of applied electric field that drive and undrive ferroelectric phase transitions. I will describe strategies for improving the energy efficiency that may be achieved with such materials.
2:00 PM - ES03.02.02
MOCVD of SnS for Thin-Film Photovoltaics
Andrew Clayton 1 , Stuart Irvine 1 , Cecile Charbonneau 1 , Wing Tsoi 1 , Peter Siderfin 1
1 , Swansea University, St. Asaph United Kingdom
Show AbstractTin Sulphide (SnS) has received attention in recent years for solar cell applications, but to date the highest certified conversion efficiency has only reached 4.4%. Small grain sizes have been determined to be a contributing factor for low cell efficiencies, with high density of grain boundaries where defects acting as recombination centres typically reside. Post-growth annealing of SnS thin films results in grain growth and improves photovoltaic (PV) cell efficiencies. SnS thin films are typically deposited by thermal evaporation, spray pyrolysis, atomic layer deposition (ALD) and plasma enhanced chemical vapour deposition (PE-CVD).
Metal organic chemical vapour deposition (MOCVD) offers an alternative deposition process, employing higher growth temperatures than other processes necessary for achieving large SnS film grain sizes in one step. This eliminates the need for the post-growth annealing step, which can introduce undesired phases in addition to SnS. In the study presented in this paper, MOCVD of SnS thin films was carried out with a hydrogen carrier and using the chemical precursors tetraethyltin (TET) and ditertiarybutylsulphide (DtBS). Film characterisation was carried out using energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM) and X-ray diffraction (XRD) to determine composition, grain size and crystal structure.
A hydrogen (H2) carrier was necessary for radical formation leading to precursor decomposition to achieve film deposition. It was not possible to obtain SnS films with use of a nitrogen (N2) carrier, which is inert, even at high process temperatures. In situ mass spectroscopy was used to determine the exhaust gas species after injection of chemical precursors, comparing the use of either N2 or H2 as carrier gas, to determine the reaction chemistry.
Different chemical precursor concentration ratios were used through partial pressure control by varying the vapour pressure for Sn and S for different temperature regimes. Composition of the SnS films were measured with EDX and phase was assessed using XRD. S/Sn ratio varied in film composition, as measured by EDX, correlating to input partial pressures of the chemical precursors. This allowed the required ratios to be determined for achieving 1:1 SnS stoichiometry. This varied for different temperature regimes, where larger S partial pressures were needed for desired SnS stoichiometry at higher temperatures due to the higher vapour pressure of S relative to Sn. Higher growth temperatures led to films with larger grains, determined by SEM, with grain size ≥ 1 μm.
MOCVD has been shown in this study to be a process with excellent control for achieving as-grown single phase SnS with desired stoichiometry. Large grains were obtained at the higher process temperatures, which is essential for producing a thin film absorber layer with low density of grain boundaries and fewer potential carrier recombination centres. Solar cell performances will be presented.
2:15 PM - ES03.02.03
CuCo Hybrid Oxides as Bifunctional Electrocatalyst for Efficient Water Splitting
Min Kuang 1 , Peng Han 1 , Gengfeng Zheng 1
1 Laboratory of Advanced Materials, Fudan University, Shanghai China
Show AbstractThe solar-driven water splitting is a promising approach for renewable energy, where the development of efficient and stable bifunctional electrocatalysts for simultaneously producing hydrogen and oxygen is still challenging. In this work, copper-cobalt oxides nanowires (CuCoO-NWs) consisting of Cu2O, CoO and CuCo2O4, were developed as an integrated 3D array electrode for overall water splitting including both the HER and OER reactions in the same electrolyte. The excellent electrocatalytic capability of CuCoO-NWs may be primary attributed to the following two aspects: (1) the incorporation of excess Cu+ and Co2+ into CuCoO-NWs enhance the catalytic activity owing to the increasing of active sites and oxygen vacancies; (2) the uniformly 1D porous architecture of CuCoO-NWs endow it with high exposed surface area, efficient electron, and enhanced mechanical stability. When serving as both anode and cathode catalysts in a two-electrode water electrolysis system, the CuCoO-NWs only required a potential of 1.61 V to offer a current density of 10 mA cm-2. Further combining with a commercial silicon photovoltaic allows the direct use of solar energy for spontaneous water splitting with high efficiency and excellent stability, thus suggesting the potential as a promising bifunctional electrocatalyst for efficient solar-driven water splitting.
2:30 PM - *ES03.02.04
Switchable Surface Chemistry and Catalysis on Ferroelectric Surfaces
Sohrab Ismail-Beigi 1
1 , Yale University, New Haven, Connecticut, United States
Show AbstractThe heterogeneous catalytic activity of a given materials surface is governed by the Sabatier principle: the highest activity occurs for moderate surface-molecule interaction strengths. However, when the bulk of the material has a non-volatile order parameter, an interesting question is if and to what extent its surface chemistry can be affected by the order parameter. If the order parameter can be switched and the two resulting surfaces have significantly different chemical activities, then one can cycle the surface between strongly adsorptive and strongly desorptive regimes to drive a reaction to completion. This approach allows one to circumvent many of the limitations imposed by the Sabatier principle.
We have used first principle density functional theory to show that oxide ferroelectric surfaces provide poignant examples of this idea. We describe how cyclical polarization reversal in PbTiO3 can catalyze important reactions that are difficult for existing catalysts based on precious metals or rare elements. We will focus primarily on two examples: direct reduction of NOx molecules in oxygen rich environments and hydrogen production via water splitting.
3:30 PM - ES03.02.05
Pseudohalide-Exchanged Quantum Dot Solids Achieve Record Quantum Efficiency in Infrared Photovoltaics
Bin Sun 1 , Oleksandr Voznyy 1 , Hairen Tan 1 , Philipp Stadler 1 , Mengxia Liu 1 , Grant Walters 1 , Sjoerd Hoogland 1 , Edward (Ted) Sargent 1
1 , University of Toronto, Toronto, Ontario, Canada
Show AbstractColloidal quantum dots (CQDs) are promising materials for use in solar cells due to their tunable bandgap, via the quantum size effect, that enables broadband harvesting of the solar spectrum. Although only thin films of CQD absorber layers are required for capturing most of the solar spectrum, extraction of photo-excited carriers generated throughout the entire length of CQD films is limited by carrier trapping. Since as-prepared PbX (X = S, Se) CQDs are nonstoichiometric and lead-rich, they are particularly susceptible to having mid-gap trap states. In the latest record-performing devices, improvements have arisen mainly from judicious management of the CQD surface stoichiometry. Halide anions (Cl-, Br-, I-) and molecular halides (Cl2, I2) have been used to reduce trap state densitiy, leading directly to improved power conversion efficiencies.
We took the view that the success of halides in chalcogenide quantum dot passivation merited renewed explorations of the potential for pseudohalides (SCN-, CN-, N3-) to achieve greater performance by reducing trap states. Preliminary evidence also indicated that mixed-anionic-passivant strategies can outperform strategies that rely only on a single class of ligands. In our study, we combined the thiocyanate (SCN) anion with halides during solution exchange to achieve a hybrid surface passivation. Pseudohalides, as hybrid passivating agents, offer strong chemical interactions with the CQD surfaces, as evidenced by observations of the thiocyanate stretching transition in the infrared spectra for exchanged CQDs. The hybrid surface passivation effects on CQD films were investigated using a suite of field-effect transistor studies. We extracted the density of trap states from measured transfer characteristics and found that the trap density of the hybrid film was 1.6±0.3 ×1016 cm-3, which was ~ 4 times lower than that of CTL films (7.6±0.8 ×1016 cm-3). The reduced densities enhanced transport lengths and so enabled us to fabricate record-thickness high-performing CQD films. These devices exhibited the highest external quantum efficiency (EQE) at the excitonic peak – an EQE of 80% - compared to previous reports of CQD solar cells. The corresponding power conversion efficiency reached 11.2%.
3:45 PM - *ES03.02.06
Polar Surface Domains on Non-Polar Surfaces
Gregory Rohrer 1 , Paul Salvador 1
1 , Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractPolar semiconductors have recently received significant attention because their internal fields separate photogenerated electron-hole pairs and reduce recombination. On surfaces with polar domains, electrons are attracted to positively terminated domains where they promote reduction reactions and holes are attracted to negatively charged domains where they promote oxidation. We have found that polar domains can be created on the surfaces of non-polar materials, including BiVO4, WO3, and SrTiO3. In the cases of WO3 and BiVO4, polarity arises from the flexoelectric effect. On SrTiO3, polarity arises from polar terminations on different terraces. For SrTiO3, it is possible to control the fraction of the surface terminated by positive or negative charges by annealing the surfaces in environments with an excess or deficit of strontium. In this talk, the use of polar domains to control photochemical reactions on the surfaces will be described.
4:15 PM - ES03.02.07
Efficient and Stable Antimony Chalcogenide Planar Thin-Film Solar Cells
Shengjie Yuan 1 , Hui Deng 1 , Haisheng Song 1 , Jiang Tang 1
1 Wuhan National Laboratory for Optoelectronics (WNLO), Huazhong University of Science and Technology, Wuhan China
Show AbstractAntimony chalcogenide has attracted great research interest very recently as a promising absorber material for thin film photovoltaics because of their unique optical and electrical properties, binary compound and easy synthesis. Firstly, Sb2S3 planar solar cells from evaporation method without hole-transport layer (HTM) assistance suffer from sulfur deficit vacancy and high back contact barrier. Thus we developed a post-surface selenization treatment to Sb2S3 thin film in order to improve the device performance. The XRD, Raman and UV-vis spectra indicated the treated film kept the typical characters of Sb2S3. TEM/EELS mapping of treated Sb2S3 film revealed that only surface adjacent section was partly selenized and formed Sb2(SxSe1-x)3 alloy. In addition, XPS results further unfolded that there was trace selenium doping in the bulk of Sb2S3 film. The treated HTM-free Sb2S3 based solar cells were fabricated and an improved efficiency of 4.17 % was obtained. The obtained VOC of 0.714 V was the highest and the power conversion efficiency also reached the top value among HTM-free planar Sb2S3 solar cells. The back alloying could suppress the rear contact barrier to improve the fill factor and carrier extraction capability. The bulk Se-doping helped to passivate the interface and bulk defect so as to improve the CdS/Sb2S3 heterojunction quality and enhance the long-wavelength photon quantum yield.
Secondly, Sb2S3 film based solar cells are limited to wide bandgap ~ 1.7 eV. Thus it need Se incorporation to extend the absorption spectra. For absorber screening, we developed a high-throughput experimental method to successfully deposit continuous composition spread Sb2(SexS1-x)3 library at one time. The obtained film composition showed wide distribution with x value of Se content evolved from 0.09 to 0.84 by a series of complementary characterizations. As the increase of Se content, the conversion efficiency first increased from 1.8% to 5.6% and then decreased to 5%. The champion device with the composition of Sb2(Se0.68S0.32)3 achieved the Voc and Jsc trade-off exceeding the performances of Sb2S3 (2.43%) and Sb2Se3 (4.97%) devices. The present continuous composition spread Sb2(SexS1-x)3 film and their deposition techniques were expected to efficiently screen materials and promote the development of antimony chalcogenide solar cells.
4:30 PM - ES03.02.08
Core Shell ZnO Nanowire Heterostructures for Extremely Thin Absorber Solar Cells
Romain Parize 1 , Thomas Cossuet 1 , Atanas Katerski 2 , Inga Gromyko 2 , Odette Chaix 1 , Laetitia Rapenne 1 , Herve Roussel 1 , Erki Karber 2 , David Muñoz-Rojas 1 , Estelle Appert 1 , Malle Krunks 2 , Vincent Consonni 1
1 , Université Grenoble Alpes, CNRS, Grenoble INP, LMGP, Grenoble France, 2 Department of Materials and Environmental Technology, Tallinn University of Technology, Tallinn Estonia
Show AbstractZnO nanowire (NW) arrays are promising building blocks for a variety of devices, including extremely thin absorber (ETA) solar cells. A ZnO NW-based core shell p-n heterojunction is typically formed using a direct p-type semiconductor as absorber layer and following the type-II band alignment. Increasing interest has been dedicated to this radial architecture owing to efficient light trapping and charge carrier management together with the use of a low amount of materials [1]. Antimony trisulfide (Sb2S3), as a p-type semiconductor with a 1.7 eV band gap energy and a high absorption coefficient, has been integrated into mesoporous-TiO2-based dye-sensitized solar cells, showing power conversion efficiency (PCE) as high as 7.5 % [2]. It is usually grown by low-cost, low-temperature chemical deposition techniques, which still make its combination with ZnO NWs difficult owing to their instability in acidic conditions. In this work, the crystallization process of Sb2S3 thin films is investigated by in situ x-ray diffraction and in situ Raman spectroscopy, revealing the intermediate formation of a metallic antimony phase and showing the optimal annealing temperature of 270°C [3]. Furthermore, an 8 nm-thick TiO2 protective layer is grown by atomic layer deposition onto ZnO NW arrays grown by chemical bath deposition. Sb2S3, as an absorbing shell, is subsequently deposited by spray pyrolysis onto ZnO/TiO2 NW arrays. The Sb2S3 conformal shell with high crystalline quality covers the ZnO/TiO2 NW arrays from the bottom to the top. The photovoltaic performance of the ZnO/TiO2/Sb2S3 core shell NW heterostructures using P3HT as hole transporting material results in a promising PCE of 2.3 % [4]. The use of low-cost, surface scalable chemical deposition techniques for their whole fabrication open the way for new strategies to improve the performances of ZnO NW-based ETA solar cells.
[1] E. C. Garnett et al., Annual Review of Materials Research 41, 269-295 (2011).
[2] Y. C. Choi et al., Advanced Functional Materials 24, 3587-3592 (2014).
[3] R. Parize et al., Materials & Design 121, 1-10 (2017).
[4] R. Parize et al., The Journal of Physical Chemistry C 121, 9672-9680 (2017).
ES03.03: Poster Session I
Session Chairs
Tuesday AM, November 28, 2017
Hynes, Level 1, Hall B
8:00 PM - ES03.03.01
Zinc Oxide Nanorod P-N Junction Piezoelectric Energy Harvesters—Mechanism, Developments and Applications
Joe Briscoe 1 , Pelin Yilmaz 1 , Petr Novák 2 , Nimra Jalali 1 , Steve Dunn 1 3
1 , Queen Mary University of London, Cranfield United Kingdom, 2 New Technologies Research Centre, University of West Bohemia, Plzen Czechia, 3 , Deregallera Ltd, Caerphilly United Kingdom
Show AbstractOriented films of ZnO nanorods can be coated easily using low temperature solution methods onto a wide range of substrates, including flexible plastics and fabrics. This offers the prospect of developing a range of energy harvesting devices which can access large mechanical deformations for conversion to electrical energy. Although in principle not an ideal material for piezoelectric energy harvesting for reasons such as low coupling coefficients and high internal losses, the ease of production of ZnO nanostructures on flexible substrates gives an incentive to investigate how to maximise performance of these devices.
We have developed piezoelectric energy harvesters based on ZnO nanorod p-n junctions on flexible substrates, using the p-type conducting polymer PEDOT:PSS to coat the nanorod tips, acting both as a top contact surface and reducing the screening effect that can limit the efficiency of ZnO-based devices. Furthermore, by coating the nanorods with the p-type semiconductor CuSCN, or layer-by-layer deposited polyelectrolytes, the internal carrier density can be reduced, leading to a significant increase in power output. We have also found that by tailoring the ZnO ‘seed’ layer at the base of the nanorods, and further adding ultra-thin insulating layers, the output from the devices can be further increased. All of these improvements can be related to reductions in screening of the piezoelectric polarisation by free carriers.
Through all of these improvements the output of the devices has been increased from tens of mV for early devices to up to ~1.5 V. Although this voltage is relatively low compared to some piezoelectric energy harvesters, we show that due to the low internal impedance (~10 kΩ) the power output is higher than equivalent ZnO-based devices incorporating insulating layers to limit screening. When tested using continuous vibration of a resonant cantilever, continuous power output of the devices is measured up to tens of micro-Watts. To make use of this power output, we are investigating the use of these devices in wireless sensor nodes for helicopter health monitoring, and the progress and challenges for practical implementation of these devices will be discussed.
8:00 PM - ES03.03.02
Synthesis of “Cubic-Phase” SnS Thin Films by Simple Sulfurization for Earth-Abundant Solar Cells
Taichi Tousuke 1 , Mutsumi Sugiyama 1
1 , Tokyo University of Science, Chiba Japan
Show AbstractTin monosulfide (SnS), a cost-effective and earth-abundant inorganic material, is considered to be a promising candidate for fabrication of next-generation solar cells. However, although the theoretical conversion efficiency of SnS-based solar cells is high, the experimental efficiencies of such cells are still low. In the past, most research on SnS for solar cells has been conducted using “orthorhombic phase (Pnma)” SnS thin films. The reasons for the low efficiencies of these films include the poor crystal quality of the SnS layers, and contamination by extra phases. Recently, studies using “cubic phase (P213)” SnS thin films with a large lattice constant (a = 1.15–1.17 nm) have been reported [1]. Because cubic SnS has a large band gap (1.5–1.7 eV) compared to that of orthorhombic SnS, cubic SnS thin films are appropriate as photo-absorbers for earth-abundant solar cells. However, the growth mechanisms of SnS, and the appropriate band offsets of SnS-based solar cells, have not yet been fully investigated. In particular, there have been few reports on the synthesis of cubic SnS using the simple sulfurization technique. In this presentation, the fabrication of “cubic-phase” SnS thin films using the conventional sulfurization technique will be presented. We will examine the relationship between growth conditions and contamination by extra-phase crystals such as orthorhombic SnS or SnS2. In addition, band offsets between “cubic-phase” SnS and various n-type semiconductors will be investigated to determine the appropriate buffer-layer material.
Metal Sn or Sn-S pre-mixed precursors were deposited using conventional RF sputtering on Mo coated soda-lime glass (SLG) substrates and were sulfurized in a quartz tube in a N2 and S vapor atmosphere. The time and temperature of the sulfurization were controlled. Conventional SnS solar cells were fabricated using an Al/ZnO:Al/ZnO/CdS/SnS/Mo/SLG structure. For the conventional sulfurization condition [2], both cubic and orthorhombic SnS films were obtained. This indicates that the formation energy of cubic SnS is small and the same as that of orthorhombic SnS [3]. Therefore, it is difficult to obtain single-phase cubic SnS is difficult by using optimization of a sulfurization and/or post-thermal process. For this reason, pre-processing before sulfurization is important. We obtained cubic SnS films by sulfurization using a Sn precursor deposited at 200 °C. Compared to the unintentionally heated deposition precursor, the heated deposition precursor tends to be dense. Various properties of cubic SnS thin films and the associated solar cell properties will also be investigated.
[1] Rabkin et al., Nano Lett. 15 (2015) 2174. [2] Sugiyama et al. Thin Solid Films, 615 (2016) 25. [3] Segev et al., Cryst. Eng. Com. 19 (2017) 1751.
8:00 PM - ES03.03.03
Transparent Conducting N-Type ZnO:Sc—Synthesis, Optoelectronic Properties and Theoretical Insight
Sebastian Dixon 1 , Sanjayan Sathasivam 1 , Benjamin Williamson 1 , David Scanlon 1 2 , Claire Carmalt 1 , I.P. Parkin 1
1 , University College London, London United Kingdom, 2 , Diamond Light Source Ltd., Didcot, Oxfordshire, United Kingdom
Show AbstractTransparent conducting oxide (TCO) thin films are essential components in virtually all optoelectronic devices such as digital information displays and photovoltaic cells, in which the unique properties of these films enable their use as transparent electrodes. The most prevalent of these is typically tin-doped indium oxide (ITO), however work is ongoing to seek more earth-abundant alternatives. This work represents a joint theoretical-experimental study of scandium-doped zinc oxide (ZnO:Sc), one of the lesser-investigated TCOs, in which a computational model has been constructed using density functional theory methods (DFT) to provide a rational basis for experimentally-observed phenomena concerning growth conditions, n-type dopability and electronic properties. Thin films of transparent and electrically conducting ZnO:Sc were synthesised via a one-pot chemical vapour deposition method from a methanolic solution of cheap, air-stable, readily available precursors over a range of dopant concentrations. The aim of the work is to better understand this promising material, by (i) mutual validation of the theoretical and experimental studies by direct observation of the predicted properties, (ii) obtaining an optimum dopant quantity for minimal resistivity, and (iii) demonstrating for the first time that electrically conductive transparent ZnO:Sc thin films can be synthesised by the industrially-relevant chemical vapour deposition technique.
8:00 PM - ES03.03.04
Earth-Abundant ns2-md0 Oxides for Solar Energy Conversion
Zhehao Zhu 1 , Pranab Sarker 2 , Ronald Grimm 1 , Muhammad Huda 2 , Pratap Rao 1
1 , Worcester Polytechnic Institute, Worcester, Massachusetts, United States, 2 , The University of Texas at Arlington, Arlington, Texas, United States
Show AbstractEarth-abundant metal oxides with moderate band gaps are desired for efficient solar energy conversion via photovoltaic production of electricity or photoelectrochemical (PEC) production of fuels. The ternary oxide BiVO4 is a top-performing PEC material due to a combination of moderate band gap (Eg ≈ 2.4 eV) and relatively long carrier lifetimes. However, the band gap of BiVO4 is still much larger than desired. Among the complex oxides, certain ternary oxides (AxByOz) in which A is an ns2 metal cation (Bi3+, Sn2+, Sb3+) and B is an md0 metal cation (Nb5+, Ta5+, Mo6+, W6+), of which BiVO4 is an example, are particularly interesting. Materials in this class often have moderate band gaps due to hybridization of the ns2 cation orbitals with O 2p orbitals, and relatively high charge carrier mobilities due to the formation of large-polaron carriers by the hybridization of the md0 cation orbitals with O 2p orbitals. Another ternary metal oxide in this category is α-SnWO4. In α-SnWO4, hybridized Sn 5s and O 2p orbitals contribute to the valence band and the W 5d orbitals principally contribute to the conduction band. We recently reported an α-SnWO4 photoanode synthesized by hydrothermal conversion of WO3 films, that achieves photon to current conversion at wavelengths up to 700 nm (~1.78 eV) (ACS Appl. Mater. Interfaces, 2017, 9 (2), 1459-1470). This photoanode is promising for overall PEC water-splitting because the flat-band potential and voltage of photocurrent onset are more negative than the potential of hydrogen evolution. Furthermore, the photoanode utilizes a large portion of the solar spectrum. However, the photocurrent density reaches only a small fraction of that which is theoretically-possible. Density functional theory-based thermodynamic and electronic structure calculations were performed to elucidate the nature and impact of defects in α-SnWO4 prepared by this synthetic route, from which hole localization at Sn-at-W anti-site defects was determined to be a likely cause for the poor photocurrent. Alternative synthetic methods are suggested to avoid the formation of this defect, and thereby improve the solar energy conversion efficiency of this α-SnWO4 material.
8:00 PM - ES03.03.05
Hierarchical Mesoporous NiO-NiMnOx@PANI Core/Shell Microspheres Highly Efficient and Stable Bifunctional Electrocatalysts for Oxygen Evolution and Reduction Reactions
Junkai He 1 , Mingchao Wang 1 , Wenbo Wang 1 2 , Ran Miao 1 , Wei Zhong 1 , Sheng-Yu Chen 1 , Shannon Poges 1 , Steven Suib 1
1 , University of Connecticut, Storrs, Connecticut, United States, 2 Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou China
Show AbstractWe report on the new facile synthesis of mesoporous NiO-NiMnOx in one-step by modifying inverse micelle templated UCT (University of Connecticut) methods. The catalyst shows excellent electrocatalytic activity and stability for both the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR) in alkaline media after further coating with polyaniline (PANI). For electrochemical performance, the optimized catalyst exhibits a potential gap, ΔE, of 0.75 V to achieve a current of 10 mA cm-2 for the OER and -3 mA cm-2 for the ORR in 0.1 M KOH solution, better than the majority of reported bifunctional electrocatalysts, including Ir/C (0.95 V), Ru/C (1.01 V), and Pt/C (1.18 V). Extensive characterization methods were applied to investigate the structure-property of the catalyst for correlations with activity (e.g. XRD, BET, SEM, HRTEM, FIB-TEM, XPS, TGA, and Raman). The outstanding electrochemical performance of the catalyst closely relates to its good electrical conductivity, high surface area, as well as the synergistic effect of the specific core/shell structure. This work opens a new avenue for the rational design of core/shell structure catalysts for energy conversion and storage applications.
8:00 PM - ES03.03.06
Vertically-Aligned Metallic CoS2 Nanowires on Current Collectors for Supercapacitors with Excellent Cycling Performance
Ren Ren 1 , Matthew Faber 2 , Rafal Dziedzic 2 , Zhenhai Wen 3 , Song Jin 2 , Shun Mao 4 , Junhong Chen 1
1 , University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, United States, 2 , University of Wisconsin–Madison, Madison, Wisconsin, United States, 3 , Fujian Institute of Research on the Structure of Matter, Fuzhou China, 4 College of Environmental Science and Engineering, Tongji University, Shanghai China
Show AbstractEarth-abundant pyrite-phase transition metal disulfides especially cobalt pyrite (CoS2) is one of promising alternative electrocatalysts for energy related applications. In this study, vertically-aligned metallic CoS2 nanowires (NWs) were prepared directly on current collecting electrodes, e.g., carbon cloth or graphite disc, for high-performance supercapacitors. These vertically-aligned CoS2 NWs have a variety of advantages for supercapacitor applications. Because the metallic CoS2 NWs are synthesized directly on the current collector, the good electrical connection enables efficient charge transfer between the active CoS2 materials and the current collector. In addition, the open spaces between the vertical NWs lead to a large accessible surface area and afford rapid mass transport. Moreover, the robust CoS2 NW structure results in high stability of the active materials during long-term operation. Electrochemical characterization reveals that the CoS2 NWs enable large specific capacitance (828.2 F/g at a scan rate of 0.01 V/s) and excellent long term cycling stability (0-2.5% capacity loss after 4,250 cycles at 5 A/g) for pseudocapacitors. This example of vertically-aligned metallic CoS2 NWs for supercapacitor applications expands the opportunities for transition metal sulfide-based nanostructures in emerging energy storage applications.
8:00 PM - ES03.03.08
Density of States of CZTS by Molecular Modelling and Tight Binding
Jarvist Frost 2 1 , Suzanne Wallace 2 , Aron Walsh 2
2 Department of Materials, Imperial College London, London United Kingdom, 1 , University of Bath, Bath United Kingdom
Show AbstractCopper Zinc Tin Sulphide (CZTS, Cu2Zn2Sn4S8) is a promising earth-abundant thin film photovoltaic material. Current devices have disappointing open circuit voltages considering the band gap of the material. At open circuit all charges are recombining; the open circuit voltage is set by the degree of recombination.
From studies of the photoluminescence, there appears to be significant band-gap tailing even in high quality bulk CZTS material.
Independent of the source of disorder, the device physics are particularly affected due to the low dielectric constant of this material.
In this work we combine electronic structure calculations with different representations of disorder. We write custom Monte Carlo codes to simulate both substitutional disorder; and sample positional disorder with both molecular dynamics and lattice dynamics (phonons). These temperature-dependent models of structural disorder we then combine with simple models of the electronic structure based on tight binding to simulate the band tailing.
We estimate the band tailing effect on device physics, and predict experimental observables for the different models.
8:00 PM - ES03.03.09
Dual-Stretchable Rubber/CNT/MnO2 Fiber Supercapacitors
Jihwan Kim 1 , Changsoon Choi 1 , Seon Jeong Kim 1
1 , Hanyang University, Seoul Korea (the Republic of)
Show AbstractNecessities for improved energy storage performance and stretchable fiber or yarn-based supercapacitors for wearable energy storage devices have become an urgent issue. Highly stretchable fiber supercapacitors structure remaining their storage performances under large tensile deformations are demonstrated here using dual-stretchy structure. The dual-stretchable structure consists of macro-sized coil and micro-sized buckle, leading high stretch-ability and high energy storage capability of a fiber supercapacitor. The macro-sized coil provides initial stretch by increasing the inter-coil distance. After that, micro-sized buckles become unfolded over a higher strain range. Pseudo-capacitance material, MnO2, is deposited on dual-stretchable fiber electrode (rubber/CNT) to increase specific capacitance. The flexibility and high stretch-ability, the dual-stretchable fiber supercapacitor can be woven into commercial textile for wearable textile energy storage.
8:00 PM - ES03.03.10
Highly Deformable Fiber Supercapacitors
Jaemyeong Lee 1 , Changsoon Choi 1 , Seon Jeong Kim 1
1 , Hanyang University, Seoul Korea (the Republic of)
Show AbstractResearch on highly deformable one-dimensional (1D) devices are needed for next-generation wearable applications due to the complex combinations of human motions. Here, twistable, stretchable, and bendable fiber redox supercapacitor is demonstrated by novel structure, which comprises a stretchable rubber fiber and buckled carbon nanotube electrodes which are loaded on each side of core fiber. On the macroscopic scale, the core fiber acts as an effective elastic substrate that gives stretchability and prevents the electrical shorting or irreversible displacements of CNT electrodes during severe mechanical deformations. On the microscopic scale, buckled CNT electrodes formed on the opposite sides of the core fiber effectively absorb the tensile or shear stresses while providing constant electrical conductivity. Due to high deformability, the fiber supercapacitor can be woven into commercial textile for wearable applications. Consequently, fiber supercapacitor provide exceptionally high structural, mechanical, and electrical stabilities against severe mechanical deformations, including bending, stretching, and twisting.
8:00 PM - ES03.03.11
Earth-Abundant Cu2ZnSn(S,Se)4 Solar Cells with 9.75% Efficiency via Interface Engineering of Double Buffer Layers CdS/Zn(O,S)
Cheng-Ying Chen 1 , Yen-Ching Teng 1 2 3 , Wei-Chao Chen 1 , Bandiyah Sri Aprillia 1 2 4 , Chih-Yuan Chiu 1 2 , Shao-Sian Li 5 , Kuei-Hsien Chen 1 2 , Li-Chyong Chen 1
1 Center For Condensed Matter Sciences, National Taiwan University, Taipei Taiwan, 2 Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan, Taiwan, 3 Institute of Optoelectronic Sciences, National Taiwan Ocean University, Keelung, Taiwan, Taiwan, 4 Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei, Taiwan, Taiwan, 5 Department of Materials Science and Engineering, National Taiwan University, Taiwan Taiwan
Show AbstractThe over 20% efficient thin-film solar cells have been realized by the rare-metals/toxic chalcogenides, such as Cu(In,Ga)(S,Se)2 (CIGSSe) and CdTe. In terms of the production cost and sustainable development, there is a clear quest for developing alternative earth-abundant/nontoxic compounds, such as Cu2ZnSn(Se,S)4 (CZTSSe). [1-3] However, one of the main issues in the kesterite based solar cells is the deficit of open circuit voltage (Voc) due to interface defects / band alignments near p-n heterojunction.
In this work, we demonstrated the high efficient CZTSSe solar cells by interface engineering of inserting a transition Zn(O,S) buffer layer between the window layer (i.e., ZnO) and the n-type layer (i.e., CdS). In the statistically studies, the transition Zn(O,S) buffer layer increase open circuit voltage (Voc) from 450±10 mV to 480±10 mV and short circuit current density (Jsc) from 30.11±0.01 mA/cm2 to 31.51±0.63 mA/cm2, possibly resulting from the suppression of interface defects, suitable band alignment and enlarged depletion region. The reverse saturation current and the interface defect related crossover behavior were reduced by inserting an extra Zn(O,S) buffer layer. Finally, a 9.75% efficient CZTSSe solar cell with Voc of 490 mV, Jsc of 32.14 mA/cm2 and fill factor of 62.2 % was obtained, which is about 50% enhancement compared with the control devices without the transition Zn(O,S) buffer layers.
The morphology, elemental composition, and distribution of our thin films are being examined by scanning electron microscopy (SEM), time-of-flight secondary ion mass spectroscopy (TOF-SIMS), Raman spectroscopy, and drive level capacitance profile (DLCP) measurement, and by transmission electron microscopy (TEM) combined with Energy-dispersive X-ray spectroscopy (EDX)
References
[1] V. Tunuguntla, W.C. Chen, P.H. Shih, I. Shown, Y.R. Lin, C.H. Lee, J.S. Hwang, L.C. Chen and K.H. Chen, J. Mater. Chem. A, 2015,3, 15324-15330
[2] Y.R. Lin, V. Tunuguntla, S.Y. Wei, W.C. Chen, D. Wong, C.H. Lai, L.K. Liu, L.C. Chen and K.H. Chen, Nano Energy, 2015, 16, 438
[3] W.C. Chen, C.Y. Chen, V. Tunuguntla, S.H. Lu, C. Su, C.H. Lee, K.H. Chen and L.C. Chen, Nano Energy, 2016, 30, 762-770
8:00 PM - ES03.03.12
Controlling Grain Size in Bismuth-Doped CuGaS2 Thin Films
Marcos Antonio Santana Andrade Junior 1 , Lucia Mascaro 1
1 , Universidade Federal de São Carlos, São Carlos Brazil
Show AbstractChalcogenides thin films solar cells compete to achieve as high efficiencies as than that obtained by crystalline silicon solar cells1. The ternary copper sulfides are among promising materials to be applied as absorber layer in solar cells. CuGaS2 is a chalcogenide with a broad band gap, and exactly due to this large band gap this chalcogenide has been arousing interest to be applied in third generation solar cells. The CuGaS2 band gap value allows intercalation of an intermediate band driven to absorption of photons with lower energy than the gap 2. Theoretically, the maximum efficiency of intermediate band solar cells can reach up to 60 %. This is not so simple, and to walk in a way to achieve this goal, researchers must put some effort to develop new material and devices. In this work, it is shown a formation of an intermediate band in CuGaS2 by doping this semiconductor with 1.1, 1.7, and 4.4 % of bismuth. The materials were prepared from a mixture of appropriated molar concentrations of Cu(I), Ga(III), Bi(III) and S precursors in oleylamine at 240 °C under nitrogen atmosphere 3. The nanoparticles were dissolved in hexane and the resulting solution was used to prepare thin films on FTO by spray method. Bi:CuGaS2 thin films were calcined and sulfurized at 500 ° C during 1 hour. X-rays diffractograms of CuGaS2 and Bi:CuGaS2 (with 1.1, 1.7 and 4.4 % of Bi) show three distinct peaks at 29°, 48.5° and 57.5° 2θ attributed to the planes (112), (220) and (116) of chalcopyrite. No secondary phases are observed in the diffractograms. The elemental quantification was obtained by EDX and XPS analyses, where this last one shows the presence of the metal dopant into the chalcopyrite structures with the peaks at 159 and 164 eV. The band gap was calculated based on the spectra of absorption in the UV-Vis-NIR region: CuGaS2 presented a band gap of 2.55 eV (the same reported in literature) and Bi:CuGaS2 (1.5 and 1.0 eV, due to the presence of the intermediate band as expected). The scanning electron microscopy and transmission electron microscopy images showed thin films of CuGaS2 and 1% Bi-doped CuGaS2 comprised by nanoparticles of 10-25 nm. Increasing the concentration of bismuth up to 4.4. % in the chalcopyrite, the film presented grains sized in up to 500 nm. In literature, it is shown the same effect of grain growth caused by Sb-doping in CuGaInS2 4. The ability to improve growth control and quality of the grain structures, and the presence of intermediate band highlights Bi-doped CuGaS2 to be applied in thin film solar cells.
References
1. Luque, A. et al. Sol. Energy Mater. Sol. Cells 115, 138–144 (2013).
2. Chen, P. et al. Phys. Status Solidi Appl. Mater. Sci. 210, 1098–1102 (2013).
3. Chang, S.-H., Chiu, B.-C., Gao, T.-L., Jheng, S.-L. & Tuan, H.-Y. CrystEngComm 16, 3323 (2014).
4. Yuan, M. et al. Chemistry of Materials 285–287 (2010).
8:00 PM - ES03.03.13
Highly Efficient Nanostructured Electrocatalysts for Oxygen and Hydrogen Evolution Reaction in Alkaline Media
Sung Mook Choi 1 , Kyu Hwan Lee 1
1 , Korea Institute of Materials Science, Changwon Korea (the Republic of)
Show AbstractThe hydrogen has been recognized as a clean, nonpolluting and unlimited energy source that can solve fossil fuel depletion and environmental pollution problems at the same time. Water electrolysis has been the most attractive technology in a way to produce hydrogen, because it does not emit any pollutants compared to other methods such as natural gas steam reforming and coal gasification etc. In order to improve efficiency and durability of the water electrolysis, comprehensive studies for highly active and stable electrocatalysts have been performed. The platinum group metal (PGM; Pt, Ru, Pd, Rh, etc.) and its oxide catalysts indicated a higher activity and stability compared with other non-precious catalysts in operating condition. It is necessary to develop non-precious catalysts with high activity and durability because the PGM catalysts are expensive materials with insufficient it’s reserves. In the water electrolysis area, the numerous researchers have been focused on the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) because the OER and HER are a key process (slow kinetics) compared with other resistances such as bubble, electrolyte, diaphragm, membrane, etc. On a point of view of a catalyst, slow kinetics and the use of precious metal (platinum group metal) for high performance should be solved to popularize water electrolysis.
The target of this study is the development of non-precious catalysts with high activity via simple and efficient synthesis method that is a wet-chemical based method. The nanostructured catalysts were synthesized through the co-precipitation. The catalysts were characterized by various physicochemical analyses such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). To investigate electrocatalytic properties of prepared catalysts, we carried out electrooxidation activity measurements such as cyclic voltammetry (CV), linear sweep voltammetry (LSV), long-term stability test, and electrochemical impedance spectroscopy (EIS). The relationship between their physicochemical properties and electrocatalytic activities will be explored and discussed.
8:00 PM - ES03.03.14
Highly Stretchable Fiber-Based Single-Electrode Triboelectric Nanogenerator for Wearable Devices
Jiwon Park 1 , A Young Choi 1 , Chang Jun Lee 1 , Dogyun Kim 1 , Youn Tae Kim 1
1 , Chosun University, Gwangju Korea (the Republic of)
Show AbstractFiber- or thread-based triboelectric nanogenerators are applicable to wearable electronics such as clothes embedded with communication devices and other electronic textiles. Unfortunately, previously reported fiber-based triboelectric nanogenerators had poor stretchability because of which their use was limited to weaving applications. We have proposed a new structure of a fiber-based single-electrode triboelectric nanogenerator (FSTENG). FSTENG consists of a silicone rubber as the negatively charged component and a conductive thread as the electrode. The conductive thread is coiled around the silicone rubber frame, and it serves as a flexible single electrode. The electrical output of the FSTENG is generated through the continuous contact and separation process that occurs between human skin and the silicone rubber. The FSTENG showed an electrical output of 28 V and 0.56 μA when in contact with human skin and exhibited a high strain of up to 100%. We also fabricated a woven structure with dimensions of 45 mm × 45 mm with the FSTENG and confirmed its power generation capabilities using an LED and electronic watch. Therefore, the FSTENG can be applied to various products ranging from wearable and stretchable energy harvesters to smart clothing by enabling the manufacture of large textiles.
8:00 PM - ES03.03.16
Characterisation and Analysis of CZTS and CZTSe Single Crystals
Oliver Hutter 1 , Theodore Hobson 1 , Ken Durose 1
1 , University of Liverpool, Liverpool United Kingdom
Show AbstractCZTS (Cu2ZnSnS4) and CZTSe (Cu2ZnSnSe4) have the potential to offer low cost and low toxicity photovoltaics, however they currently suffer from a large voltage deficit of around 40% of the max Voc. One possible candidate for the cause of this issue is the grain boundaries in these devices, and thus fundamental information on CZTS and CZTSe single crystals is required.
In this work, CZTS4xSe4-x in varying compositions has been synthesised from elemental precursors and characterised by power X-ray diffraction, raman spectroscopy, energy dispersive x-ray analysis, differential scanning calorimetry, and optical microscopy among others.
Single crystals have been grown using tin and salt solvents with a variety of growth conditions. These crystals are large in size and phase pure. Characterisation of these single crystals reveals that they are Kesterite with very little secondary phases. In addition to this we also report on the ongoing investigations into the electrical properties of these single crystals.
Analysis of these crystals yield insights into the bulk properties of these important emerging photovoltaic materials.
8:00 PM - ES03.03.17
Solventless Synthesis of Antimony Sulfide, Bismuth Sulfide and Antimony-Bismuth Sulfide Solid Solutions Using Novel Single Source Route
Tahani Alqahtani 1 , Malik Khan 2 , Mohammad Azad Malik 1 , Paul O'Brien 1
1 , University of Manchester, Manchester United Kingdom, 2 , University of Zululand, Empangeni South Africa
Show AbstractAbstract
Antimony sulfide (Sb2S3) is an earth abundant useful binary chalcogenide with low toxicity. Sb2S3 has a direct band gap and ranges between 1.5 to 2.5 eV, depending on the shape, size, and crystallinity of the nanostructure. Moreover, it has exceptional semiconducting and photoconductivity properties that allows potential applications in solar energy conversion, optoelectronics, and thermoelectric devices.1 Similarly, Bismuth sulfide (Bi2S3) has attracted considerable attention owing to its remarkable properties such as a direct band gap, which lies between 1.2 to 1.7 eV, and a high absorption coefficient. Bi2S3 nanoparticles and thin films can find various applications in gas sensors, thermoelectric, photovoltaic, electronic and optoelectronic devices.2
The crystal structures of Sb2S3 and Bi2S3 are similar, with orthorhombic unit cell dimensions differing by a maximum of 3.5%. The similar charge and comparable sizes of bismuth and antimony atoms favour the formation of Bi-Sb-S system, in almost all the ratios from Bi2S3 end to Sb2S3 end, as both antimony and bismuth can be used interchangeably in the crystal lattice.3
In this work, we investigate the use of antimony(III) ethylxanthate and bismuth(III) ethylxanthate as a single source precursor for the solventless synthesis of Sb2S3 and Bi2S3. The thermogravimetric analysis (TGA) reveals that both precursors exhibit complete decomposition in similar temperature range. Therefore, the mixture of these precursors can be used to produce solid solutions of Bi-Sb-S between the two phases (Bi2S3 and Sb2S3). A series with varying stoichiometry was synthesized by using different molar ratios (i.e. Sb/Sb+Bi = 0.2, 0.4, 0.6 and 0.8).
The XRD peaks at all ratios correspond well to the orthorhombic crystals, where the peaks fall in between those of orthorhombic Bi2S3 and orthorhombic Sb2S3 for Bi-Sb-S system. The gradual splitting and shift in the peaks position confirms the successful incorporation of antimony into bismuth sulfide. The inclusion of antimony was further confirmed by change in lattice parameters and is in good agreement with the literature values. A decrease of almost 3.5 % in volume was observed as moving from Bi2S3 to Sb2S3. A change in all lattice parameters indicates that the substitution is random and not in any specific direction. The elemental compositions of all the samples were examined via EDX analysis and ICP- OES, which shows uniform distribution of elements in all samples. The morphology for all the samples was observed using SEM, revealing different morphologies as the composition changes from Bi2S3 to Sb2S3.
References:
1 S. Messina, M. T. S. Nair and P. K. Nair, Thin Solid Films, 2007, 515, 5777–5782.
2 V. Kaltenhauser, T. Rath, W. Haas, A. Torvisco, S. K. Müller, B. Friedel, B. Kunert, R. Saf, F. Hofer and G. Trimmel, J. Mater. Chem. C, 2013, 1, 7825–7832.
3 K. Atsushi and K. Mitsuyoshi, Am. Mineral., 2004, 89, 932.
8:00 PM - ES03.03.18
CuS Thin Films Obtained by CBD Using Amino Acids as Complexing Agents and Investigation of Their Behavior as Counter Electrodes in QDSSCs
Daniela Ortiz Ramos 1 , Luis Gonzalez 1 , Arturo Martinez 1
1 , CINVESTAV Saltillo, Saltillo Mexico
Show AbstractQuantum dot-sensitized solar cells (QDSSCs) have the properties like the potential to achieve efficiency beyond the Shokley-Queisser limit through multiple exciton generation, large intrinsic dipole moments, low cost and direct hot carrier collection to multiply the current generation. The QDSSCs are composed of a TiO2 photo anode, a sensitizer, a redox electrolyte and a counter electrode (CE). The role of the CE in a solar cell is to collect electrons from external circuits and to regenerate the holes by catalyzing the reduction of the oxidized species in the electrolyte and keep the cell working. CuS is a promising material for device applications. Chemical bath deposition (CBD) is a low temperature, simple and low cost method for depositing CuS thin films. For the reaction solutions we used Cu (NO3)2 as source of Cu ions, Thiourea as source of S ions and amino acids as complexing agent. KOH was used to adjust the pH. The temperature was 60°C, and the deposition time was 45 minutes. The influence of each amino acid on the growth, morphology, and microstructure, elemental content, optical and electrical properties are also discussed. The resultant XRD analysis showed low-crystalline structure, the Raman spectroscopy showed that covellite structured of the CuS prevails, the XPS analysis confirm the presence of the CuS on the thin films and the presence of oxygen and carbon are due to the atmosphere. The morphology of the CuS using amino acids as complexing agents are composed of flakes with flower shaped CuS clusters. The elemental content as %At are almost stoichiometric using alanine, glycine and serine as complexing agents in the CuS thin films. The optical properties id the CuS thin films showed an optical transmittance between 37-51% according to the amino acid used as complexing agent, the CuS thin films using glycine as complexing agent showed the lower transmittance. The energy ban gap value goes from 2.0 to 2.13 eV, the PL spectra we calculated a more accurate energy band gap, the values goes from 1.943 to 1.949 eV , similar to the obtained in the graphic method. The electrical properties showed values of resistance of 182.05 to 954.09 Ω/■ according to the amino acid used as complexing agent. The obtained CuS thin films were used as counter electrodes in a QDSSCs, using a TiO2 photo anode, CdS as quantum dot-sensitizer and a polysulfurated electrolyte. To evaluate the photoelectrochemical performance of the CuS as the CEs of the QDSSCs using TiO2/CdS as the working electrode. The J-V curves of the CuS were obtained, also the photovoltaic parameters including the short-circuit current density, open-circuit voltage, fill factor and photovoltaic conversion efficiency. Also the stability of the CEs were studied, the CEs showed a good stability in the electrolyte during the measurement in prolonged times, the stability depends on physical, chemical, pH, electrolyte composition, temperature, time and photocurrent density.
8:00 PM - ES03.03.19
A One-Pot Ease Methodology to Synthesis MoSe2 Nanostructures for Rechargeable Batteries
Dhanasekaran Vikraman 1 , Sajjad Hussain 2 3 , K Prasanna 7 , K Karuppasamy 1 , A Kathalingam 6 , Jongwan Jung 2 3 , Hui Joon Park 4 5 , Hyun-Seok Kim 1
1 Division of Electronics and Electrical Engineering, Dongguk University - Seoul, Seoul Korea (the Republic of), 2 Graphene Research Institute, Sejong University, Seoul Korea (the Republic of), 3 Institute of Nano and Advanced Materials Engineering, Sejong University, Seoul Korea (the Republic of), 7 Electrochemical Energy Storage and Conversion Lab (EESC), Kyung Hee University, Yongin Korea (the Republic of), 6 Millimeter-wave Innovation Technology (MINT) Research Center, Dongguk University - Seoul, Seoul Korea (the Republic of), 4 Division of Energy Systems Research, Ajou University, Suwon Korea (the Republic of), 5 Department of Electrical and Computer Engineering, Ajou University, Suwon Korea (the Republic of)
Show AbstractEnergy storage and conversion is playing the vital role in our routine life. Among the various candidates, lithium-ion batteries (LIBs) are considered the most promising energy storage systems and have been used widely in portable electronic devices and electric vehicles (EVs), owing to higher energy density, long lifespan, no memory effect, and environmental benignity. Layered transition metal dichalcogenides MX2 (M = Mo, W, Ti; X = S, Se, Te), a class of graphene-like two-dimensional (2D) materials, have attracted significant interest for their wide range of applications including energy storage, catalysis, and sensors. Among metal dichalcogenides, molybdenum di-selenide (MoSe2) and their hybrid materials have been extensively investigated for their use in lithium-ion batteries because of their high theoretical capacities. MoSe2 has the three stacked atom layers (Se–Mo–Se) held together by van-der Waals forces which is favored for the intercalation/extraction of Li ions. In this work, we have developed a facile one-pot chemical approach, ease of processing and low cost, for the synthesis of MoSe2 nanostructures to use as anode materials in LIBs. X-ray diffractograms (XRD) studies were revealed their hexagonal structure along with (004) preferential lattice orientation of MoSe2. SEM and TEM analyses were evidently proved their nano-sizes of grains with uniform shapes. Raman scattering and photo luminescence (PL) analyses showed their characteristics peaks of MoSe2. We found that the MoSe2 nanostructures are capable of delivering the higher initial discharge capacity of 843 mAh g–1 at the current of C/10 rate. Also, quantum efficiency was observed at 99.9% after 100 consecutive cycles. The electrochemical results showed that our MoSe2 nanostructure holds great potential as anode materials and it would be a promising candidate for high performance Li-ion batteries.
8:00 PM - ES03.03.20
Patterned Ferroelectric Lithium Niobate for Spatial Control of Photochemical Reduction Reactions and Metallic Nanoparticle Deposition
N. Craig Carville 1 , Sabine Neumayer 1 , Michele Manzo 2 , Katia Gallo 2 , Brian Rodriguez 1
1 , University College Dublin, Dublin Ireland, 2 Department of Applied Physics, KTH - Royal Institute of Technology, Stockholm Sweden
Show AbstractNon-centrosymmetric materials such as ferroelectric lithium niobate have a switchable spontaneous polarization that can be exploited to drive local spatially-resolved reduction reactions at the crystal surface. Under super-band gap illumination, photogenerated electrons, subjected to internal fields, can be used to reduce metallic salts from solution at the solid-liquid interface. Considerable progress has been made to understand the photoreduction of metallic nanostructures at the surface of uniformly and periodically poled lithium niobate and other ferroelectric materials. Here, we use proton exchange to replace lithium ions in the lithium niobate crystal with hydrogen ions from a proton source (benzoic acid) periodically through 1D mask openings to create regions with high (lithium niobate) and low (proton exchanged lithium niobate) polarization. The periodic proton exchange process yields three distinct regions (RIE – reactive ion etch, LD – lateral diffusion, and LN – lithium niobate). The proton exchange region comprises the RIE region surrounded on either side by LD regions. Reactive ion etch is used to create the mask opening for proton exchange. The exposed surface is directly exposed to the benzoic acid; however, proton exchange also proceeds laterally under the mask to form the LD proton exchange region. The influence of this spatial modulation of polarization on the charge separation and photoreduction of silver and gold nanostructures will be discussed. Whereas the silver nanoparticles generally deposited preferentially along the LD regions independent of the AgNO3 concentration, the location of gold nanoparticle deposition was found to depend strongly on HAuCl4 concentration, allowing the deposition location to be tailored. Under certain conditions, gold nanoparticles were deposited directly on the RIE region and subsequent deposition of silver resulted in parallel arrays of gold and silver nanoparticles. The role of pH and argon ion implantation during reactive ion etching on the gold deposition will be discussed and biocompatibility and biosensing applications of the resulting templates will be highlighted.
8:00 PM - ES03.03.21
The Role of Heterojunctions on the Water Oxidation Performance in Mixed a-Fe2O3/Fe3O4 Hybrid Film Structures
Jennifer Leduc 1 , Yakup Gonullu 1 , Thomas Fischer 1 , Sanjay Mathur 1
1 , University of Cologne, Cologne Germany
Show AbstractIn our recent work, we have examined the effect of directed post-deposition plasma-chemical reduction of hematite to increase its photoelectrochemical performance. Via variation of the temperature used during hydrogen plasma treatment, different proportions of Fe3O4 (mixed valent Fe+2/Fe+3) in the resulting Fe3O4/a-Fe2O3 nanomaterials could be achieved. Even though Fe3O4 had been reported to be photo-inactive, the mixed Fe3O4:a-Fe2O3 photoanodes showed a better PEC performance (photocurrent density of 3.5 mA/cm2 at 1.8 V vs. RHE and onset potential of 1.28 V vs. RHE) than the respective pristine hematite samples. This was ascribed to a reduced band gap energy and higher carrier density resulting from the generation of additional charge carriers upon reduction of Fe3+. In this work, we report on mixed a-Fe2O3/Fe3O4 heterostructures generated via the single-step chemical vapor deposition of [Fe(OtBu)3]2. The mixed hybrid film structure showed an increased water oxidation activity despite a film thickness of 11 µm. This enhancement is attributed to the improved electron transport resulting from the higher magnetite content towards the bottom of the layer and the increased light absorption of the hematite layer mainly located at the top of the film. To the best of our knowledge, this is the first report on efficient hematite-based water oxidation catalysts with a layer thickness of higher than 10 µm.
8:00 PM - ES03.03.22
Microstructure Alteration of Molybdenum Trioxide in Reduction—An In Situ Transmission Electron Microscopy Investigation
Jian Chen 1
1 , National Institute for Nanotechnology, Edmonton, Alberta, Canada
Show Abstracta-MoO3 is attractive as a pseudocapacitor due to its layered structure which offers a superior ion intercalation capability. However, low electrical conductivity (e.g. semiconductivity) and modest reaction kinetics of a-MoO3 prevent its widespread use. Since multiple valence states are the prominent feature for molybdenum, efforts are devoted to overcome the low electrical conductivity by introducing oxygen vacancies [1-3]. When the valence state of molybdenum oxide changes from 6+ to 4+, molybdenum oxide changes from semiconductor (a-MoO3) to metallic MoO2. As the first step of a series of investigations, here, we report the microstructure evolution of a-MoO3 when heated in a vacuum by employing the H-9500 Environmental Transmission Electron Microscopy (ETEM).
The change sequence of the selected area electron diffraction (SAED) pattern is obtained at different temperatures. When the specimen was heated up to 400oC, new features emerged, overlapping the original [010] zone axis reflections of a-MoO3 (see red arrowed reflection in Figure 1(A)). This stems from the short-ordering of oxygen vacancies formed by the partial removal of Van der Waals force connected oxygen atoms between the consecutive double layers parallel to the (010) plane. In contrast to (100), there is no sharp satellite appearing beside (001). Instead, a symmetrical diffuse reflection emerges (see green arrow indicated reflection in Figure 1(A)). This relates to the rigid chains of edge-sharing octahedra within the double layers. The diffuse reflection zone becomes bigger (Figure 1 (B)) at 570oC, suggesting more oxygen vacancies generated in the double layers. At 950oC, MoO2 forms a weak ring pattern, implying that the original a-MoO3 transfers to small MoO2 particles with random orientations.
Since oxygen vacancies formed during the heating process as indicated by SEAD patterns, the electron energy loss spectroscopy (EELS) was employed to investigate the oxygen K-edge because O K-edge is very sensitive to the oxidation state changes. Figure 2 shows the in-situ EELS spectra obtained at intervals between SEAD pattern collecting. The evolution of O K-edge is interpreted as the transition of oxygen 1s to 2p. In a-MoO3, the crystal field splitting leads to separations of the low part of the conduction band into t2g and eg symmetry bands [4], as indicated by peak 1 and the arrowed shoulder shown in the spectrum at room temperature. There are six empty t2g and four empty eg orbitals for octahedron [MoO6] in a-MoO3. O 1s electrons can be excited into these orbitals. In MoO2, the t2g orbitals are filled with two electrons, which results in the increase of the weight of eg orbitals as well as the decrease of the weight of t2g orbitals, hence the decrease in peak 1 and increase in the arrowed shoulder observed in the spectrum at 450oC and 916oC. That indicates the valence decreasing trend, which confirms the electron diffraction observations.
8:00 PM - ES03.03.23
Packaged Triboelectric Generator with a Sponge-Like Structure Embedded with Ferroelectric Barium Titanate Oxide Nanoparticles
Daehoon Park 1 , Sung-Ho Shin 1 , Junghyo Nah 1
1 , Chungnam National University, Daejeon Korea (the Republic of)
Show AbstractTriboelectric nanogenerators (TENGs) have gained much attention as it can convert various physical stimuli to electricity. To date, various approaches, including micro/nano surface patterning, surface functionalization, and modulation of dielectric permittivity, have been actively investigated to improve the output power of TENGs. However, most of the TENGs require a separation gap between electrodes to generate electricity, hindering to develop compact device structure.
In this work, we report the packaged TENG with spontaneously polarized porous surface. The hydrophobic sponge structure with embedded ferroelectric BaTiO3 (BTO) nanoparticles (NPs) was integrated with the counter electrode layer, forming less than few tens of um separation distance. Due to this reduced contact separation gap between two friction surfaces, the output power of the TENG can be significantly reduced. Here, this limitation was overcome by employing sponge-like porous structure and ferroelectric-polymer composite structure. Specifically, the porous polymer structure was prepared by mixing and curing polydimethylsioxane (PDMS), sugars, and BTO NPs, followed by dissolution of sugars in water. The role of sponge structure is two-folds. First, it decreases effective thickness during the contact motion, which in turn increases capacitance and can induce more charges on the facing electrode when they separate. Second, sponge-based structure has hydrophobicity and is thus less sensitive to humid condition. Besides, it also provides flexibility. Next, coupling effect of spontaneous electric dipoles of BTO NPs inside the porous structure also contributed to enhance the output power of TENG. The packaged TENG reported in this work generates the output voltage up to ~60 V and current density up to ~4uAcm-2, respectively. The approached introduced here is simple, effective, suitable for high performance TENG in harsh conditions.
8:00 PM - ES03.03.24
Carrier Dynamics and Ultrafast Zero-Bias Photocurrents in SnS2 Single Crystals
Erin Morissette 1 , Kateryna Kushnir 1 , Maggie Kuck 2 , Curtis Doiron 2 , Ronald Grimm 2 , Lyubov Titova 1
1 Physics, Worchester Polytechnic Institute, Worcester, Massachusetts, United States, 2 Chemistry and Biochemistry, Worchester Polytechnic Institute, Worcester, Massachusetts, United States
Show AbstractModerate band gaps, high carrier mobility, and environmental stability make layered transition metal dichalcogenides attractive for optoelectronic and solar energy conversion applications. Of these materials, SnS2 demonstrates promise as a photocatalyst for visible light water splitting and in field-effect devices, with reported on-off current ratios >106 and carrier mobilities up to 230 cm2 V–1 s–1 [1,2]. Further progress in application of this emergent material requires the understanding of the dynamics of photoinjected carriers and optical excitations.
We present the synthesis of single-crystal SnS2 and its subsequent characterization by terahertz (THz) spectroscopy of carrier dynamics with sub-picosecond time resolution. Chemical vapor transport (CVT) yielded 2–5 mm2 flakes of SnS2 from elemental precursors. Photoelectron spectroscopy confirmed the presence of Sn and S with a small concentration of iodine, as well as the stability against oxidation followed by prolonged exposure to an air ambient.
The THz spectroscopy experiments characterized carrier dynamics, frequency-resolved conductivity, and photoinduced ultrafast currents in SnS2 crystals. Above band gap excitation generated long-lived free carriers, and transient photoconductivity followed a bi-exponential decay with ~21 ps and ~168 ps decay times that suggest the presence of two distinct free carrier trapping events. Applying the Drude model to the complex transient conductivity results yielded free-carrier mobility values as a function of time.
Finally, THz emission spectroscopy probed photoinduced ultrafast currents in single-crystal SnS2. Inversion symmetry breaking can result in generation of shift currents, or zero-bias photocurrents as the excitation of an electron from the valence to the conduction band yields a spatial shift of the electron charge density [3,4]. We observed in-plane ultrafast shift currents by detecting terahertz electromagnetic pulses emitted by the photoexcited SnS2 single crystal without external bias, and quantified a dependence of the shift current on the orientation of the SnS2 with respect to the polarization of the excitation pulse. The observation herein of zero-bias photocurrents indicates the viability of SnS2 nanosheets for third generation shift current photovoltaics [3].
We acknowledge funding from the Clare Boothe Luce Foundation.
[1] Huang, Sutter, Sadowski, Cotlet, Monti, Racke, Neupane, Wickramaratne, Lake, Parkinson, and Sutter, ACS Nano 8, 10743 (2014)
[2] Sun, Cheng, Gao, Sun, Liu, Liu, Lei, Yao, He, Wei, et al., Angew. Chem., Int. Ed. 51, 8727–8731 (2012)
[3] Tan, Zheng, Young, Wang, Liu and Rappe, npj Computational Materials 2, 16026 (2016)
[4] Kushnir, Wang, Fitzgerald, Koski, and Titova, ACS Energy Letters, 1429-1434 (2017)
8:00 PM - ES03.03.25
Synthesis and Characterization of CeO2 Doped with Sm2O3 and Eu2O3 for the Use in SOFCs
Alena Borisovna K. 1 , Moises Hinojosa Riviera 1 , Oxana Kharissova 1
1 , UANL, Monterrey Mexico
Show AbstractTo free ourselves from the use of fossil fuels that are highly polluting, life-threatening and not easily regenerated, new technologies are being developed to obtain alternative energy sources more efficiently. Among these technologies, there is the option to improve the performance of solid oxide fuel cells (SOFCs) to make them highly energy efficient. Solid oxide fuel cells (SOFCs) have attracted much attention because of they are environmentally benign, sustainable, generate low emissions and have relative low cost. However, conventional SOFCs with yttria-stabilized zirconia (YSZ) electrolyte require high operation temperature (800-1000°C), which often lead to material degradation problems. Given that the greatest disadvantage of SOFCs is their high operating temperature, samples of CeO2 were synthesized by spray pyrolysis method and doped with Sm2O3 and Eu2O3 to improve the ionic conductivity of the electrolyte so that it can operate at lower temperatures without losing its efficiency. The samples were analyzed using SEM, EDS, EIS and DRX and tested in a SOFC prototype.
8:00 PM - ES03.03.26
Synthesis and Characterization of Zn2SnO4 Nanoparticles by Microwave Chemical Synthesis
Odin Vallejo 1 , Sebastian Joseph 1
1 Materials Research Department, IER-UNAM, Temixco, Morelos, Morelos/Temixco, Mexico
Show AbstractZn2SnO4 (ZTO) is an n-type oxide semiconductor with an inverse spinel structure. It presents outstanding optical and electrical properties for optoelectronic applications. The low visible absorption, relative low refractive index (~2.0 in the visible region) and wide band gap in the range of 3.6 to 3.8 eV combined with its high electron mobility (10-30 cm2/Vs) make it suitable for photoelectrical applications, chemical sensors, functional coatings and transparent conducting electrodes. Besides, the conduction band edge position makes it potential candidate photoelectrode for solar cells technologies, such as, Perovskite solar cells. Another attractive attribute of crystalline ZTO is its chemical stability to acid/base solution and polar organic solvents, for solution processing1.
It is reported that ZTO compared with TiO2, promotes a higher quality crystallization of Perovskite layers, which enhances the performance of the solar cell achieving higher efficiencies, exhibiting negligible electrical hysteresis and high stability without encapsulation. This is attributable to the excellent ZTO/Perovskite interface2.
We report an easy and fast microwave chemical route to synthetize Zn2SnO4 nanoparticles. The effect of temperature, oxidizing agent and time were analyzed trough X-ray diffraction, Raman Spectroscopy, Scanning Electron Microscopy, Transmission Electron Microscopy, Fourier Transform Infrared and UV-Vis Spectroscopy. The secondary phases SnO, SnO2 and ZnO are predominant at temperatures lower than 200 C, while above to 200 C the ternary phase Zn2SnO4 is predominant. The concentration of oxidizing agent is primordial to achieve pure ternary phase of ZTO, the low concentration of oxidizing agent promotes the presence of secondary phases. High crystalline ZTOnanoparticles are synthetized at times longer than 40 minutes. Crystalline ZTO nanoparticles present low absorption in the visible range and wide band gap (> 3.2 eV), which make it suitable for being tested as transparent layer in photovoltaic solar cells.
1.- Shin, S. S., Yang, W. S., Noh, J. H., Suk, J. H., Jeon, N. J., Park, J. H., ... & Seok, S. I. (2015). High-performance flexible perovskite solar cells exploiting Zn2SnO4 prepared in solution below 100 [thinsp][deg] C. Nature communications, 6.
2.- Bera, A., Sheikh, A. D., Haque, M. A., Bose, R., Alarousu, E., Mohammed, O. F., & Wu, T. (2015). Fast crystallization and improved stability of perovskite solar cells with Zn2SnO4 electron transporting layer: interface matters. ACS applied materials & interfaces, 7(51), 28404-28411.
8:00 PM - ES03.03.27
Cu2O Thin Films by Microwave-Assisted Chemical Bath Deposition
Odin Vallejo 1 , Sebastian Joseph 1
1 , IER-UNAM, Temixco, Morelos Mexico
Show AbstractCuprous oxide (Cu2O) is a p type semiconductor with a direct band gap of 2.0-2.7 eV. Cu2O is very attractive because of its excellent optical and electrical properties, which combined with its natural abundance, non-toxic nature and growth by scalable production techniques makes it attractive candidate for solar cell application. The high hole mobility, high minority carrier diffusion length and high absorption coefficient in the visible region have promoted its application in the conversion of solar energy into electrical or chemical energy, photochemical decomposition of water into O2 and H2 under visible-light irradiation, as photocatalyst for degradation of organic contaminants, as hole transporting material in photovoltaic technology and for gas sensing and magnetic storage.
Cu2O thin films are commonly deposited by thermal oxidation of copper thin films, which are deposited previously by sputtering or evaporation. Thermal oxidation is an expensive technique because of high temperatures and consequently due to the great consumption of energy. The Chemical Bath Deposition (CBD) is an economic, easy-handling and scalable deposition technique, which has been used for thin film deposition of different semiconductors. However, Cu2O has presented poor adherence by CBD. Previously, we have proposed the use of complexing agents to promote adherence and crystallinity. Now we present Cu2O thin film deposition through novel microwave-assisted chemical bath deposition (MACBD). We have analyzed the effect of temperature and deposition time by X-ray diffraction, Scanning Electron Microscopy, UV-Vis Spectroscopy and electrical characterizations. Compared with regular CBD at the same deposition conditions, the films deposited through MACBD present preferential orientation along the (111) plane, while in the case of CBD they are oriented along the (200) plane. The films deposited by MACBD present thickness around 200 nm, half of that achieved by CBD. The conductivity of thin films by MACBD is around 10 Ω-1cm-1 considerably higher than that deposited through CBD. These characteristics make thin films deposited by MACBD suitable as charge transport layer in photovoltaic technology.
1.- Yu, W., Li, F., Wang, H., Alarousu, E., Chen, Y., Lin, B., ... & Wang, X. (2016). Ultrathin Cu 2 O as an efficient inorganic hole transporting material for perovskite solar cells. Nanoscale, 8(11), 6173-6179.
2.- Hossain, M. I., & Aïssa, B. (2017). Effect of Structure, Temperature, and Metal Work Function on Performance of Organometallic Perovskite Solar Cells. Journal of Electronic Materials, 1-5.
8:00 PM - ES03.03.28
Triboelectric Charging Modulation via Chemical Surface Functionalization Using Aminated- and Halogenated-Molecules
Sung-Ho Shin 1 , Min Hyung Lee 2 , Junghyo Nah 1 , HyoJae Yoon 3
1 , Chungnam National University, Daejeon, SE, Korea (the Republic of), 2 Applied Chemistry, Kyunghee University, Young-In Korea (the Republic of), 3 Chemistry, Korea University, Seoul Korea (the Republic of)
Show AbstractTriboelectric nanogenerators (TENGs), converting various kinetic energy in our living environmentto electricity through friction between the materials with different triboelectric properties, have received much attention thanks to their relatively high output power density and simple fabrication process. Until now, different approaches such as physical surface nano-/micro-patterning and various device structures have been mainly attempted to modulate the triboelectrically-generated output charges on polymeric surfaces. However, these approaches have been hindere by limited materials choices in triboelectric series, entailing processing issues.
In this work, we report a simple and effective chemical surface functionalization method to widely modulate triboelectric surface charging. Using our method, triboelectric properties of the polymeric friction surfaces are easily adjusted, providing tunable output power of functionalized TENGs. Specifically, polyethylene terephthalates (PETs) were functionalized by synthetic halogenated (Cl, F, and Br)-molecules to render negative charging surface. For the positive charging, the surfaces of PETs were functionalized using several aminated-molecules. We thoroughly investigated the triboelectric charging behavior of distinct 20 contact pairs using Kelvin probe microscopy, electrometer, and density functional calculation, functionalized surfaces. Noticeably, output voltage of ~520 V and current density of ~110 mA/m2, were achieved using TENG functionalized with contact pair (Cl-PET:PEI(b)-PET), corresponding power density of ~55 W/m2. Our results demonstrate the formation of wide spectrum on triboelectric charging using proposed method. Also, the introduced method here that is simple and effective can be adopted for developing energy harvesting devices and sensors based on the triboelectric effect.
8:00 PM - ES03.03.29
BaTiO3 Nanopillar Array via Nanoimprint Lithography-Assisted Sol Gel for High Output Performance Piezoelectric Nanogenerator
Sung-Ho Shin 1 , Daehoon Park 1 , Seong-Young Choi 2 , Min Hyung Lee 2 , Junghyo Nah 1
1 , Chungnam National University, Daejeon, SE, Korea (the Republic of), 2 Applied Chemistry, Kyunghee University, Gyeonggi Korea (the Republic of)
Show AbstractPiezoelectric nanogenerators (PENGs) using perovskite oxide BaTiO3 (BTO), which has non-centrosymmetric tetragonal phase at room temperature have been actively investigated, thanks to its high piezoelectric coefficient and environmentally-safe nature. Up to date, consistent efforts to realize high performance BTO-based PENGs have been made by aligning the BTO nanostructures on flexible substrates. To this end, various methods such as chemical synthesis, electrospinning, and spacer lithography have been attempted. However, above approaches have been inhibited for practical application, caused by processing issues on controllability, throughput, and mulitstep process.
In this work, we report high performance PENG using highly-ordered BTO nanopillar array by combining soft nanoimprint lithography and sol-gel. The dense and uniform one-dimensional (1D) BTO nanopillar patterns were easily and quickly formed onto indium tin oxide (ITO)/polyethylene terephthalate (PET) substrate after coating of synthesized BTO gel, followed by imprinting step using PDMS template. In the end, under the applied force of 0.3 MPa, the PENG (active area: 1 cm × 1 cm) fabricated using BTO nanopillars with 100 nm in diameter, 200 nm in height, and 400 nm in pitch, exceed the output and current density exceed the ~10 V and ~1.2 µA cm-2, respectively. Consequently, two orders of magnitude higher output voltage and 6-fold higher output current density were achieved, compared to the flat film BTO PENG without imprinting process. In addition, by easily enlarging the size of the device, we demonstrate the reliability of the BTO array patterned using adopted method by measuring different areas in a device under the same applied force. Consequently, the results clearly show the suitability of sol-gel for nanoimprint lithography and introduced method here is simple, time-efficient, reproducible, and scalable for high performance 1D BTO based PENGs.
8:00 PM - ES03.03.30
Synthesis of TiO2 by Pechini Method—Effect of Temperature and Ratio of Polymeric and Chelating Agents in the Formation of Anatase and Rutile Phase
Yesica Castillo 1 , Luis Gonzalez 1
1 , CINVESTAV Saltillo, Saltillo Mexico
Show AbstractThe titanium dioxide is a compound of great interest, because of this photocatalytic properties and particles size. It is a type n semiconductor sensitive to visible light that absorbs electromagnetic radiation, mainly in the UV region. It has a high refractive index (2.4-2.5). This compound present three different crystallographic forms: rutile, anatase, brookite. The titanium dioxide in anatase phase is widely used as a photocatalyzed and photoactive electrode (for solar cells) for its optical and electronic properties, low cost, chemical stability and low toxicity. The photocatalytic properties of TiO2 derive from the photogeneration of charge carriers (electrons and holes) that occurs upon the absorption of ultraviolet (UV) light in the band gap of 3.2 eV. In this work, the polymeric precursor method (Pechini method) was used to synthesize titanium dioxide. The Pechini method stands out among several chemical synthesis methods because it allows for the use of different temperatures and proportions of polymeric agent/chelating agent, enabling controlled particle and/or agglomerate stoichiometry and morphology and compositional homogeneity This process allowed a bigger control on the purity of the oxide and the crystalline phase present in the material. A chelating agent (Ethylenediaminetetraacetic acid (EDTA)) and a polymeric agent (ethylene glycol) having a ratio of 2:1 and 4:1 (Polymeric agent: chelating agent) were used to obtain the ceramic powders. For other hand, the TiO2 powders were treated at different temperatures (400, 450 and 500° C) for the obtaining the anatase phase. The ceramic powders were characterized using x-ray diffraction (XRD) and scanning electron microscopy (SEM). The results of XRD indicated that the 4:1 sample containing two phases anatase and rutile. The 2:1 samples contained only anatase phase at 400-450°C, the rutile phase occurs at 500 ° C. In the XRD patterns the characteristic peaks of the anatase phase at 25.2°, 37.8°, 47.9°, 53.8°, 55.05° and 62.7° corresponding to the planes [101], [004], [200], [105] and [211] respectively can be observed. The crystallite size of sample 2:1 was smaller than 20 nm, indicating the formation of anatase nanoparticles.
8:00 PM - ES03.03.31
Simple Synthesis of MgCO3 and Na2Mg(CO3)2 through Alkali Metal Nitrate Medium
Kyung-Ryul Oh 1 , Ah-hyeon Park 1 , Jin-Su Kwak 1 , Young-Uk Kwon 1
1 , Sungkyunkwan University, Suwonsi Korea (the Republic of)
Show AbstractMgCO3 and Na2Mg(CO3)2 are anhydrous forms of magnesium carbonate, which are hard to synthesize in aqueous solution at ambient temperature and pressure because of large hydration energy of magnesium ion. Molten salt provides liquid medium at higher temperature than normal solvents, therefore various kinds of metal oxides have been synthesized by molten salt method. Furthermore, alkali metal nitrates are used as promoting agents for MgO-based CO2 absorbent at intermediate temperature (200-500 °C). Based on these backgrounds, we successfully synthesized anhydrous MgCO3 and Na2Mg(CO3)2 using hydromagnesite (MCH) and alkali metal nitrate at 325 °C under CO2 flow. Water of hydration decomposes and Mg(OH)2 converts into MgCO3 at given condition. The existence of Na2CO3 determines the products being MgCO3 or Na2Mg(CO3)2. It was confirmed that neither of MCH nor a mixture of MCH and Na2CO3 produces MgCO3 or Na2Mg(CO3)2 at same condition. Every kind of alkali metal nitrate successfully acted as a reaction medium, giving different particle morphology. The characterization of samples were performed by powder X-ray diffraction measurements (XRD), thermogravimetric analyzer (TGA), and field emission scanning electron microscopy (FE-SEM), which verified that the synthesized products are pure anhydrous rhombohedral MgCO3 and Na2Mg(CO3)2.
8:00 PM - ES03.03.32
Flexible Piezoelectric Generators Using BaTiO3 Sol-Gel
Seong-Young Choi 1 , Sung-Ho Shin 2 , Junghyo Nah 2 , Min Hyung Lee 1
1 , Kyung Hee Unversity, Yongin-si, Korea, South, Korea (the Republic of), 2 , Chungnam National University, Daejeon Korea (the Republic of)
Show AbstractPiezoelectric generators (PEGs), using piezoelectric effects to produce electrical output from mechanical deformation, are promising sustainable energy-harvesting devices that can create electrical energy from the abandoned pressure and vibrational energy in everyday life. Their electric output, however, is usually too small to be used in real applications.
Here, we demonstrate compositional and structural control of materials to overcome low output voltage and current of PEGs. Barium titanate (BaTiO3), which is lead-free and has high piezoelectric coefficient, is main component of our PEGs and Fe ions were doped to increase the conductivity of BaTiO3. In order to increase the power of PEGs, a high-voltage poling process was carried out to improve the dipole alignment, and patterning BaTiO3 into 1D nanopillars also helps to maximize the effect of the dipole alignment.
8:00 PM - ES03.03.33
Investigation of High Oxygen Reduction Reaction Catalytic Performance on Mn-Based Mullite SmMn2O5
Jieyu Liu 1 , Weichao Wang 1 2
1 , Nankai University, Tianjin China, 2 , University of Texas at Dallas, Richardson, Texas, United States
Show AbstractThe most investigated ternary oxides with efficient oxygen reduction reaction (ORR) activities have primarily adopted perovskite (ABO3) or spinel (AB2O4) structures, where generally A represents an alkaline-earth metal or rare-earth metal ion, and B denotes a transition metal ion.1, 2 Here, we proposed mullite, a class of catalyst for NO oxidation with the formula AB2O5,3 to be applied for catalyzing ORR.4,5 Take SmMn2O5 as a prototypical representative. There are two different Mn coordinations (octahedral Mn4+ and pyramidal Mn3+) as well as the Mn-Mn chains in mullite SmMn2O5, making the local surface structures plentiful and facilitating the tunability of electronic structure.6
We combined density functional theory (DFT) based calculation and experiment to systematically explore oxygen reduction kinetics on SmMn2O5 surfaces on the atomic and molecular scales. Theoretical calculations are performed to investigate the bulk phase diagram, as well as the stability and electrocatalytic activity of ORR under alkaline condition for SmMn2O5 (001) surfaces, which are passivated by nitrogen atoms to avoid any spurious interference. The adsorptions of relevant ORR species (O*, OH*, OOH* and OO*) tend to compensate the coordination of manganese atoms to form Mn-centered octahedral or pyramidal crystal fields, and the corresponding binding energies fulfill linear relations. Oxygen molecule prefers to be reduced to OH- via a four-electron pathway and this prediction is verified by electrochemical measurement on the as-prepared SmMn2O5 catalyst with nanorod structure. Volcano curves are obtained to describe trends in theoretical ORR activity as a function of a single parameter, i.e. the oxygen binding energy. An overpotential of 0.43 V is calculated at the O* binding energy around 3.4 eV, being close to the experimental observation (0.413 V) in this work. SmMn2O5 mullite performs favorable ORR activity and superior stability towards commercial Pt/C, making it a promising candidate for cathode catalyst.
1. M. Kuang and G. Zheng, Small, 2016, 12, 5656-5675.
2. K. Zhang, X. Han, Z. Hu, X. Zhang, Z. Tao and J. Chen, Chem. Soc. Rev., 2015, 44, 699-728.
3. W. Wang, G. McCool, N. Kapur, G. Yuan, B. Shan, M. Nguyen, U. M. Graham, B. H. Davis, G. Jacobs, K. Cho and X. Hao, Science, 2012, 337, 832-835.
4. Y. Li, X. Zhang, H.-B. Li, H. D. Yoo, X. Chi, Q. An, J. Liu, M. Yu, W. Wang and Y. Yao, Nano Energy, 2016, 27, 8-16.
5. C. Dong, Z. W. Liu, J. Y. Liu, W. C. Wang, L. Cui, R. C. Luo, H. L. Guo, X. L. Zheng, S. Z. Qiao, X. W. Du and J. Yang, Small, 2017, 13, 1603903.
6. H.-B. Li, W.-H. Wang, X. Qian, Y. Cheng, X. Xie, J. Liu, S. Sun, J. Zhou, Y. Hu, J. Xu, L. Li, Y. Zhang, X. Du, K. Gao, Z. Li, C. Zhang, S. Wang, H. Chen, Y. Zhao, F. Lu, W. Wang and H. Liu, Catal. Sci. Technol., 2016, 6, 3971-3975.
8:00 PM - ES03.03.35
Two-Dimensional SnO Anodes with a Tunable Number of Atomic Layers for Sodium-Ion Batteries
Fan Zhang 1 , Jiajie Zhu 1 , Daliang Zhang 1 , Udo Schwingenschlogl 1 , Husam Alshareef 1
1 , King Abdullah University of Science and Technology (KAUST), Jeddah Saudi Arabia
Show AbstractWe have systematically changed the number of atomic layers stacked in 2D SnO nanosheet anodes and studied their sodium ion battery (SIB) performance. The results indicate that as the number of atomic SnO layers in a sheet decreases, both the capacity and cycling stability of the Na ion battery improve. The thinnest SnO nanosheet anodes (two to six SnO monolayers) exhibited the best performance. Specifically, an impressive reversible capacity of 665 mAh g–1 after 100 cycles at 0.1 A g–1 and 452 mAh g–1 after 1000 cycles at a high current density of 1.0 A g–1 was observed, with excellent rate performance. As the average number of atomic layers in the anode sheets increased, the battery performance degraded significantly. For example, for the anode sheets with 10–20 atomic layers, only a reversible capacity of 389 mAh g–1 could be obtained after 100 cycles at 0.1 A g–1. Density functional theory calculations coupled with experimental results were used to elucidate the sodiation mechanism of the SnO nanosheets. This systematic study of monolayer-dependent physical and electrochemical properties of 2D anodes shows a promising pathway to engineering and mitigating volume changes in 2D anode materials for sodium ion batteries. It also demonstrates that ultrathin SnO nanosheets are promising SIB anode materials with high specific capacity, stable cyclability, and excellent rate performance.
8:00 PM - ES03.03.36
Tuning the Overpotential for NiO Nanocatalyst for Water Splitting
Zhen Qiu 1 , Amitava Banerjee 1 , Sudip Chakraborty 1 , Tomas Edvinsson 1
1 , Uppsala University, Uppsala Sweden
Show AbstractDesigning highly efficient and cost-effective nanocatalysts for water electrolysis by the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) has been considered as a promising route to develop sustainable hydrogen production. In our study, nickel, cobalt, and iron oxides and their double hydroxides/sulfide have been extensively investigated as nanocatalysts for water splitting. We show that the surface energies of lattice planes during synthesizing NiO nanostructures can be altered and an enhanced crystal growth in different crystalline direction can be controlled by a hydrothermal method with the variation of the pH conditions of the precursor solution. Based on the different pH, the morphology of NiO nanostructure can also be varied according to the different surface charge, which results in different catalytic performance. Moreover, by Fe doping, NiO could be tuned into higher OER performance by changing the local electronic structure as well as making the nanocatalyst bi-functional with respect to the OER and the HER processes under alkaline conditions. The 3D Fe-NiO nanocatalyst is fabricated by the facile chemical bath deposition (CBD) method on nickel foam templates. In order to identify the composition of the active phase on the surface of Fe-NiO/Ni foam, in situ Raman spectroscopic measurements are carried out for both the OER and HER reactions under alkaline conditions. The results show that the Fe doping plays a critical role for the catalytic property. Density functional theory (DFT) calculations show that Fe changes the local electron density, shifting the energetically preferable adsorption site of H from oxygen in NiO onto Ni in Fe-NiO in the hydrogen evolution reaction. In addition, the effects of the heteroatoms (S or Se) in the same group as oxygen are investigated as new, efficient nanocatalysts.
Symposium Organizers
Steve Dunn, Queen Mary University of London
Brian Rodriguez, University College Dublin
Henry Sodano, University of Michigan
Matjaz Valant, University of Nova Gorica
ES03.04: Session III
Session Chairs
Martyn McLachlan
Xudong Wang
Tuesday AM, November 28, 2017
Hynes, Level 3, Room 304
8:00 AM - ES03.04.01
P2 - Sodium Layered Transition Metal Oxides as a Cathode for Sodium-Ion Batteries—Understanding the High Voltage Phase
James Somerville 1 , Nuria Tapia Ruiz 2 1 , Urmimala Maitra 1 , Peter Bruce 1
1 Materials Department, University of Oxford, Oxford United Kingdom, 2 , Lancaster University, Lancaster United Kingdom
Show AbstractThe world needs more energy storage to facilitate the integration of renewable energy sources into the electrical grid.1 Although the cost of lithium ion batteries is slowly decreasing to match the required price for this application2, the Na-ion chemistry has been suggested as a potentially lower cost alternative. P2-type (P: Trigonal Prismatic, 2: ABBA Oxygen Stacking) sodium layered transition metal oxides (eg. Na2/3MnxNiyMzO2, M = Li, Mg, Fe, Co, Ti, etc., x + y + z = 1) are a particularly promising prospect for Na-ion battery cathodes given their relatively high average voltage and large capacities.3 However, due to the stabilization of an alkali metal layer composed of trigonal prismatic sites rather than octahedral sites, complex layer gliding events arise at high states of charge often leading to capacity fading.4 In these layer gliding phase transitions, there are two equally probable glide vectors which causes much of the long range interlayer order to be lost. This makes the so-called high voltage phase notoriously hard to probe with traditional diffraction techniques.5 In this talk, we will examine the first electrochemical charge/discharge cycle for a P2-type compound and detail the mechanism at the high voltage region. Only by first understanding the process do we then hope to uncover a path to combat the degradation process, which will aid the continued development of this class of material.
References:
1. Dunn, B., Kamath, H. & Tarascon, J.-M. Electrical Energy Storage for the Grid: A Battery of Choices. Science (80-. ). 334, 928–935 (2011).
2. Blomgren, G. E. The Development and Future of Lithium Ion Batteries. J. Electrochem. Soc. 164, A5019–A5025 (2017).
3. Xiang, X., Zhang, K. & Chen, J. Recent Advances and Prospects of Cathode Materials for Sodium-Ion Batteries. Adv. Mater. 27, 5343–5364 (2015).
4. Kubota, K., Yabuuchi, N., Yoshida, H., Dahbi, M. & Komaba, S. Layered Oxides as Positive Electrode materials for Na-ion batteries. MRS Bull. 39, 416–422 (2014).
5. Nazar, L., Talaie, E., Duffort, V., Smith, H. & Fultz, B. Structure of the High Voltage Phase of Layered P2-Na2/3-x[Mn1/2Fe1/2]O2 and the Positive Effect of Ni Substitution on its Stability. Energy Environ. Sci. (2015). doi:10.1039/C5EE01365H
8:15 AM - ES03.04.02
The Role of Intrinsic and Extrinsic Point Defects in Controlling the Conductivity Properties of the Mixed Ion-Electron Conductors LaFeO3 and LaCoO3
John Buckeridge 1 , Felicity Taylor 1 , C. Richard Catlow 1
1 , University College London, London United Kingdom
Show AbstractThe search for suitable cathode materials for intermediate temperature solid oxide fuel cells has led to the study of complex oxide perovskites such as LaCoO3 and LaFeO3. To understand the ionic and electronic transport properties of this material, it is essential to model accurately the relevant defect structures. Here we present results on the formation energies of intrinsic and extrinsic defects in both systems, and determine their effect on the ionic and electronic conductivity properties by considering relevant charge compensation schemes. We determine the ground state structures and defect formation energies using plane-wave density functional theory including a Hubbard U parameter to describe localised levels on transition metal ions. Moreover, we determine equilibrium defect concentrations and the self-consistent Fermi level for a range of temperatures relevant to experiment. In particular, we find the surprising result that, given certain growth and environmental conditions, cation vacancies, usually overlooked in these systems, play a significant role in the defect chemistry and can account for the observed conductivity properties of real samples. Our results explain observed trends on the efficacy of different dopants.
8:30 AM - *ES03.04.03
Ferroelectric Heterostructures and Ultrathin Oxides Thin Films for High-Performance Photoelectrochemical Electrode Development
Xudong Wang 1
1 , University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractRecent discovery of the piezotronic effect revealed that when a strain is experienced by a piezoelectric semiconductor material or device, it can introduce interfacial charge redistribution and lead to significant performance gain or new functionality. In this talk, we will discuss the coupling of ferroelectric polarization and the intrinsic electric field in a space charge region for the purpose of tuning charge transport behaviors in the oxygen evolution reaction (OER) in photoelectrochemical (PEC) systems. A largely enhanced PEC performance was obtained by ferroelectric polarization-endowed band engineering on the basis of TiO2/BaTiO3 core/shell nanowires. Tuning the conductivity of the ferroelectric layer could further balance the polarization and charge transport. Thus, further enhancement was discovered in TiO2/SrTiO3 core/shell nanowires, where the SrTiO3 offered an improved charge transport property. Numerical model was established to calculate the potential distribution across the catalyst/ferro(piezo)electric/electrolyte heterojunction and reveal favorable electronic band bending as a result of internal electric polarization. This research opens a new route for engineering the catalytic properties of conventional catalysts via internal electrical polarization.
In addition, we will present a new development of nanometer-thick oxides thin films for PEC electrode applications. Ionic layer epitaxy (ILE) technique was used to synthesize large-area crystalline oxide nanosheets from solution using a monolayer of ionized surfactants at water-air interface as a flexible template. Various types of oxides nanosheets, including CoO, NiO, and RuO2 were synthesized at the wafer scale with a thickness of only 1-2 nm. Due to the large surface atom ration and short cross-plane charge diffusion path, these nanosheets exhibited substantially higher catalytic property towards OER compared to their bulk form. These nanosheets also exhibited extremely large mass activity owing to their ultrasmall thickness, presenting a promising solution for efficient catalytic material utilization.
9:15 AM - ES03.04.05
Nano-Structuring Effects on the Local Structure of V2O5 Probed by Temperature Dependent X-Ray Absorption Spectroscopy
Wojciech Olszewski 1 2 , Carlo Marini 1 , Naurang Saini 3 , Laura Simonelli 1
1 , Alba Synchrotron Light Facility, Cerdanyola del Valle Spain, 2 Faculty of Physics, University of Bialystok, Bialystok Poland, 3 Dipartimento di Fisica, Universitá di Roma, Rome Italy
Show AbstractVanadium pentoxide (V2O5) is an attractive multifunctional material used in widespread applications related to lithium-ion batteries [1], catalysis [2], gaschromic devices [3], sensors [4], actuators [5], etc. V2O5 possesses an outstanding structural versatility and can be manufactured into nanostructures with superior properties [1, 3, 5].
Among the potential cathode materials, V2O5 has been extensively studied because of its low cost, abundance, as well as its high energy efficiency and relatively high theoretical capacity [6]. However, due to its slow electrochemical kinetics and poor structural stability, two major problems for this electrode material are its low rate and limited long-term cycling stability [7]. Many efforts have been made in nanostructuring of V2O5 to extend its electrochemical performances [6-7].
In particular, one-dimensional nanostructures, i.e., the nanowires, have attracted considerable attention due to importance in basic scientific research and potential technological applications [5, 8]. In this case, correlation between the modulation of structure and functional properties is of large interest. In particular, it is of prime importance to understand how the chain structure, that has a direct implication on the V2O5 properties, is affected by nanostructuring.
We have investigated the local structures of bulk, nanoparticles and nanowires of V2O5 by temperature dependent V K-edge x-ray absorption spectroscopy. We confirm that the extended x-ray absorption fine structure measurements show different local displacements in the three morphologically different V2O5 samples with nanowires that have a significantly ordered chain structure in comparison to the V2O5 bulk, and nanoparticles, that have larger interlayer disorder [9]. The temperature dependent data reveal in general a lower expansion coefficient in the nanostructured samples, with a clear anisotropic effect for the V2O5 nanowires. The results highlight the differences in the five V-O bonds (in function of nanosizing) that are at the basis of the peculiar V2O5 properties.
References:
[1] J. J. Yu et. al, Electrochim. Acta 89, 292 (2013).
[2] M. Ponzi et al., Appl. Catal., A 169, 373 (1998).
[3] C. L. Dong et al., EPL 101, 17006 (2013).
[4] G. Micocci et al., J. Vac. Sci. Technol. A 15, 34 (1997).
[5] T. Zhai et al., Adv. Mater. 22, 2547 (2010).
[6] S. Q. Wanget al., Energy Environ. Sci. 4, 2854 (2011).
[7] J. Muster, J et al., Adv. Mater. 12, 420 (2000).
[8] W. Avansi et al., J. Nanopart. Res. 13, 4937 (2011).
[9] B. Joseph et al., Applied Physics Letters 103, 251910 (2013).
9:30 AM - ES03.04.06
Candidate Photoferroic Absorber Materials for Thin-Film Solar Cells from Naturally Occurring Minerals—Enargite, Stephanite and Bournonite
Suzanne Wallace 2 1 , Katrine Svane 2 , William Huhn 3 , Tong Zhu 3 , David Mitzi 3 4 , Volker Blum 3 , Aron Walsh 1 5
2 Chemistry, University of Bath, Bath United Kingdom, 1 Materials, Imperial College London, London United Kingdom, 3 Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina, United States, 4 Chemistry, Duke University, Durham, North Carolina, United States, 5 Materials Science and Engineering, Yonsei University, Seoul Korea (the Republic of)
Show AbstractTo build on the success of other mineral systems employed in solar cells, including kesterites (Cu2ZnSnS4) and herzenbergite (SnS), and mineral-inspired systems such as lead halide perovskites (CH3NH3PbI3), we have searched for photoactive minerals with the additional constraint that a polar crystal structure is adopted. Macroscopic electric fields provide a driving force to separate electrons and holes in semiconductor devices, while spontaneous lattice polarization in polar semiconductors can facilitate microscopic photo-carrier separation to enhance carrier stability and lifetimes [1]. We identify enargite (Cu3AsS4), stephanite (Ag5SbS4), and bournonite (CuPbSbS3) as candidate materials and explore their chemical bonding and optoelectronic properties using a first-principles quantum mechanical approach. To assess if the candidates are likely to be able to rival the success of solution-processed CH3NH3PbI3 solar cells, whilst being unlikely to suffer from the same instability issues, we use design principles for defect-tolerance suggested from studies on other solar absorber materials to predict the likely defect-tolerance of the candidate absorber materials [2-5].
[1] M. R. Morris, S. R. Pendlebury, J. Hong, S. Dunn and J. R. Durrant, Advanced Materials, 2016, 28, 7123-7128.
[2] S. B. Zhang, S.-H. Wei, A. Zunger and H. Katayama-Yoshida, Physical Review B, 1998, 57, 9642–9656.
[3] R. E. Brandt, V. Stevanovic, D. S. Ginley and T. Buonassisi, MRS Communications, 2015, 5, 265–275.
[4] A. Zakutayev, C. M. Caskey, A. N. Fioretti, D. S. Ginley, J. Vidal, V. Stevanovic, E. Tea and S. Lany, The Journal of Physical Chemistry Letters, 2014, 5, 1117–1125.
[5] Brandt, R. E.; Poindexter, J. R.; Kurchin, R. C.; Gorai, P.; Hoye, R. L. Z.; Nienhaus, L.; Wilson, M. W. B.; Polizzotti, J. A.; Sereika, R.; Zaltauskas, R.; et al. Chemistry of Materials. 2017.
10:15 AM - *ES03.04.07
Low Temperature Processing of Metal Oxide-Organic Composite Films for Interlayer and Electrode Applications in Organic Electronics
Martyn McLachlan 1
1 , Imperial College London, London United Kingdom
Show AbstractMetal oxide semiconductors play a significant role in enhancing the performance and stability of a wide range of optoelectronic devices, particularly as charge selective interlayers in both organic photovoltaics(OPV) and organic light emitting diode (OLED) platforms. The attraction of metal oxides lies in the unique combination of superior optical and electronic properties combined with the wide-range of deposition routes that can be implemented for thin film growth. In many applications low-temperature processing routes are desirable to ensure the functionality of the active layer materials are preserved. For many oxide materials interesting new, low-temperature processing routes have emerged that facilitate low-temperature conversion of various precursor species, dissolution of oxide materials in various solvent systems and even routes for processing compact oxide films from nanoparticle systems. With many of the emerging processes excellent device performances have been achieved- however issues relating to reproducibility, possible toxicity and material/processing costs persist.
Here I will discuss some recent developments from our laboratory of low-temperature solution processed interlayers based on ZnO and MoOx and with the same materials blended with common conducting polymers. Observed changes in OPV/OLED performance are correlated to variation in interlayer composition, microstructure and electrical properties. The use of these interlayers is further explored by incorporating into lead halide perovskite solar cells where our studies of the composition, structure and electronic properties are combined to explain the observed performance enhancements and considering the nature of the near surface species explain the observed instability in the perovskite cells.
10:45 AM - ES03.04.08
Tubular Monolayer Superlattices of Hollow Mn3O4 Nanocrystals by Confined Epitaxial Assembly and Their Efficient Oxygen Reduction Activity
Tongtao Li 1 , Angang Dong 1
1 Department of Chemistry, Fudan University, Shanghai China
Show AbstractApart from the flexibility in tuning the composition and structure, the ability to tailor the mesoscale morphology of nanocrystal (NC) superlattices is of paramount importance for extending their range of applications. Despite tremendous progress on the growth of 2D or 3D NC superstructures, the self-assembly of NC superlattices with a mesoscale tubular geometry is still challenging because of the difficulty to achieve the superlattice growth on a curved surface. Here, tubular superlattices were constructed by confining the self-assembly of colloidal NCs within anodized aluminum oxide (AAO) channels through an epitaxial assembly strategy. We demonstrate this concept by fabricating freestanding, carbon-coated tubular monolayer superlattices comprising hollow Mn3O4 nanoparticles by the confined assembly of MnO NCs followed by controlled oxidation, in situ ligand carbonization, and selective etching. Benefiting from their unique and advantageous hierarchical structural features, such tubular monolayer superlattices could be used as high-efficiency electrocatalysts for oxygen reduction, with the catalytic performance superior to that of most manganese oxide-based catalysts reported previously.
11:00 AM - ES03.04.09
Understanding Photoelectrochemistry on Epitaxial Oxide Surfaces
Kelsey Stoerzinger 1 , Scott Chambers 1 , Yingge Du 1
1 , Pacific Northwest National Laboratory, Cambridge, Massachusetts, United States
Show AbstractThe intermittent nature of renewable energy sources requires a clean, scalable means of converting and storing energy. One Earth abundant storage option is water electrolysis, storing energy in the bonds of O2 and H2. Photoelectrochemical (PEC) cells based on semiconductor/liquid interfaces can convert sunlight to chemical fuels without external circuitry, such as “splitting” water into O2 and H2 upon illumination of a photoabsorber and catalyst. Tuning the location of the band edges of a semiconductor tailors the wavelength of photoabsorption and the charge transfer to adsorbed species. The efficacy of conversion depends in part on the rectifying properties of semiconductor–electrolyte junctions, as the band bending present in the semiconductor space-charge region from Fermi level equilibration drives the separation of electron–hole pairs. This can be impacted by the use of Earth abundant oxide materials as protective coatings for traditional semiconductor absorbers, where ideal band alignment and transport of charge carriers through the heterostructures might enable water splitting without the use of precious metal catalysts.
In the particular case of the semiconductor Ge, favorable conduction band alignment with the hydrogen evolution reaction (HER) suggests the potential for efficient solar-to-hydrogen conversion with visible light. However, material instability in aqueous environments and the potential for photocorrosion limits its utility in PEC applications. In order to protect the photoabsorber surface while maintaining favorable alignment of the conduction band, we epitaxially grow SrTiO3 on top of p-Ge. We will present studies of such model oxide photoelectrodes grown by molecular beam epitaxy (MBE) on single crystal substrates that display a known crystallographic orientation, surface area, path for charge transport, and strain. Photoelectrochemical measurements on these heterostructures can establish the intrinsic activity of oxide catalysts in a way that cannot be realized with polydisperse nanoparticle systems. Insight into the band bending between the substrate and oxide overlayer, as well as at the semiconductor surface, can be obtained from X-ray photoelectron spectroscopy (XPS).1 Measurement of XPS at ambient pressures (AP-XPS) can further elucidate the relationship between adsorbates and surface band bending in situ.2 This fundamental insight will build understanding necessary for the design of active, earth-abundant photocatalysts that can be integrated into PEC devices for efficient conversion of solar energy into chemical fuels.
References
1. S.A. Chambers, Y. Du, R.B. Comes, S.R. Spurgeon, P.V. Sushko, Applied Physics Letters, 110, 082104 (2017).
2. K.A. Stoerzinger, R. Comes, S.R. Spurgeon, S. Thevuthasan, K. Ihm, E.J. Crumlin, S.A. Chambers. J. Phys. Chem. Lett. 8, 1038 (2017).
11:15 AM - ES03.04.10
Strongly Enhanced Photovoltaic Performance and Defect Physics of Bismuth Oxyiodide (BiOI) Solar Cells
Robert Hoye 1 , Lana Lee 1 , Rachel Kurchin 2 , Tahmida Huq 1 , Kelvin Zhang 1 , Melany Sponseller 2 , Lea Nienhaus 2 , Riley Brandt 2 , Joel Jean 2 , Alex Polizzotti 2 , Ahmed Kursumovic 1 , Moungi Bawendi 2 , Vladimir Bulovic 2 , Vladan Stevanovic 3 , Tonio Buonassisi 2 , Judith MacManus-Driscoll 1
1 , University of Cambridge, Cambridge United Kingdom, 2 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 , Colorado School of Mines, Golden, Colorado, United States
Show AbstractBismuth-based compounds are gaining increasing attention as a promising class of materials for photovoltaics. This is because bismuth is a heavy-metal cation that has demonstrated very little evidence of toxicity and can replicate many of the features of lead thought to enable defect-tolerance. Defect-tolerance is the ability of materials to achieve long charge-carrier transport lengths despite the presence of defects and is critical for optoelectronic performance, as exemplified by the hybrid lead-halide perovskites. However, many of the bismuth-based semiconductors predicted to be defect-tolerant have demonstrated limited photovoltaic efficiencies. Herein, we explore in detail through experiment and computations one such compound: bismuth oxyiodide (BiOI) [1]. We demonstrate BiOI thin films to be air-stable for at least 197 days (>4700 hours). Through computations we find BiOI to be tolerant to antisite and vacancy defects. We develop an all-inorganic thin film device structure: ITO|NiOx|BiOI|ZnO|Al, and achieve external quantum efficiencies of up to 80%. Our devices exhibit negligible hysteresis, with short-circuit current densities and power conversion efficiencies nearly double previous reports of not only BiOI, but also other bismuth halide and chalcohalide photovoltaics recently explored by many groups. To provide direction for future research to build upon our work, we analyze the losses in our devices through optical analysis, photoemission spectroscopy and device modeling. Our work raises the distinct possibility of realizing a bismuth-based solar absorber that is lead-free, air-stable, defect-tolerant and efficient.
[1] R. L. Z. Hoye, et al., Adv. Mater., 2017, In Press. DOI: 10.1002/adma.201702176
11:30 AM - ES03.04.11
Improved Efficiency of Photoelectrochemical Water Oxidation Using Tin Disulfide Photoanodes
Binod Giri 1 , Pratap Rao 1
1 Mechanical Engineering, Worcester Polytechnic Institute, Worcester, Massachusetts, United States
Show AbstractTin disulfide (SnS2) is a promising material for photoelectrochemical (PEC) water splitting and tandem photovoltaics due to its high optical absorption coefficient, moderate band gap, and conduction and valence band edges that straddle the reduction and oxidation potentials of water. SnS2 is derived from earth abundant elements that are non-toxic, and unlike SnS and Sn2S3, is stable under ambient atmosphere. SnS2 has CdI2-type 2D crystal structure consisting of layers of SnS2 held together by Van der Waals forces. This is known to reduce the number of defects at the crystal surface and allow efficient heterogeneous charge transfer.
Several reports have been published explaining various synthesis methods for SnS2, however very few reports have successfully realized SnS2-based devices. In this work, photoanodes consisting of vertical nanoflakes of SnS2 were synthesized on fluorine doped tin oxide-glass substrates using close space sublimation, and exhibited a direct bandgap of 2.32eV. The SnS2 photoanodes were measured in aqueous sodium sulfite electrolyte with pH7 buffer. Photocurrents up to 3.4mA/cm2 were obtained at 1.23 V vs. the reversible hydrogen electrode under simulated sunlight. SnS2 was found to be more stable in non-aqueous iodide/triiodide electrolyte, hence sandwich-type photovoltaic cells with platinum counterelectrodes were also constructed and characterized.
11:45 AM - ES03.04.12
Rapid Growth of P-Type NiOx by Atmospheric Pressure Chemical Vapour Deposition for Perovskite Solar Cells
Lana Lee 1 , Baodan Zhao 1 , Robert Hoye 1 , Dawei Di 1 , Judith MacManus-Driscoll 1
1 , University of Cambridge, Cambridge United Kingdom
Show AbstractNickel oxide (NiOx) is a wide band-gap p-type semiconductor that has recently attracted attention as a stable hole-transport/electron blocking layer in inverted lead-halide perovskite solar cells, demonstrating power conversion efficiencies of over 17%. However, the highest-performing NiOx hole transport layers were synthesized using high-temperature, batch processes. It is essential to synthesize perovskite solar cells using low-cost, high throughput methods in order to be compatible with large-scale manufacturing for the commercialisation efforts that are already underway. Atmospheric pressure chemical vapour deposition (AP-CVD) is one such method that can synthesize high-quality oxide films with high throughput on an industrial scale. Here, we report for the first time the growth of NiOx by AP-CVD and investigate the materials properties and performance in inverted perovskite solar cells. We achieve compact methylammonium lead iodide perovskite films on NiOx. From devices, we demonstrate a champion efficiency of 15.9% without hysteresis, highly competitive with the best devices using un-doped NiOx and exceeding the performance of sister devices made on PEDOT:PSS. We note that the efficiencies were measured under 1 sun illumination, whereas our EQE analysis shows that the mismatch factor was 1.12, suggesting the efficiency of our devices are higher when corrected for spectral mismatch. Critically, from transient photocurrent data we find photocurrent decay to be faster than 10 ns, suggesting remarkably high charge extraction rates. Additionally, from JV measurements we measure an ideality factor close to 1, showing that non-radiative recombination pathways in devices are insignificant. To understand the cause of high charge extraction rates, we characterize the surface chemistry of the NiOx films using X-ray photoemission spectroscopy, as well as the mobility of the NiOx using Hall measurements and electrochemical impedance spectroscopy. X-ray diffraction and atomic force microscopy also show that our AP-CVD NiOx thin films give sharp diffraction peaks and a compact, pinhole-free morphology. Through these measurements, we can increase our understanding of the desirable properties of hole transport materials to aid future design of materials for improved perovskite devices.
ES03.05: Session IV
Session Chairs
Steve Dunn
Elvira Fortunato
Tuesday PM, November 28, 2017
Hynes, Level 3, Room 304
1:30 PM - ES03.05.01
Optoelectric Properties of Chemical Vapor Deposited Niobium doped ZnO Thin Films for Transparent Conducting Oxide Applications
Sanjayan Sathasivam 1 , Benjamin Williamson 1 , David Scanlon 1 , Claire Carmalt 1 , I.P. Parkin 1
1 , University College London, London United Kingdom
Show AbstractTransparent conducting oxide (TCO) thin films have both high visible light transparency and low electrical resistivity. Typically they have n-type conductivity where extrinsic and/or intrinsic defects contribute electrons to the conduction band. At the moment, despite the high cost of indium, the most popular TCO is Sn doped In2O3 (ITO) due to its low resistivity in the 10-4 and even 10-5 Ω.cm order as well as visible transparency above 80%. Effort is underway to find alternative systems with comparable properties to ITO. Here, we report on the TCO properties of Nb doped ZnO grown via CVD from ZnEt2 and Nb(OEt)5. The theory being that each Nb5+ replacing Zn2+ would be able to donate up to three electrons for conductivity. The films grown were highly transparent (80%) with band gaps at 3.3 eV and resistivities were as low as 5.9 x 10-4 Ω.cm for low Nb concentrations, the lowest ever for ZnO:Nb films. With increasing Nb concentration a decrease in the electron mobilities was seen due to increased ionized impurity scattering. Hybrid density functional theory calculations of the defect chemistry of ZnO:Nb have uncovered that Nb acts as 4+ dopant in ZnO, donating 2 electrons to the conduction band. This work highlights that under a low doping levels ZnO:Nb can be a high performance, earth abundant TCO.
1:45 PM - ES03.05.02
Single Crystal Thin-Film Earth-Abundant Element Heterovalent Nitride Semiconductors
Robert Makin 1 , Krystal York 1 , Steven Durbin 1 , Nathaniel Feldberg 2 , Patrice Miska 2 , Nancy Senabulya 3 , James Mathis 3 , Christina Jones 3 , Emmanouil Kioupakis 3 , Roy Clarke 3
1 , Western Michigan University, Kalamazoo, Michigan, United States, 2 , Universite de Lorraine, Nancy France, 3 , University of Michigan–Ann Arbor, Ann Arbor, Michigan, United States
Show AbstractInterest in earth-abundant element compound semiconductors has yielded a sizeable number of candidate materials suitable for optoelectronic devices, including those intended for photovoltaic applications. One interesting family of potential materials is analogous to III-V semiconductors in the same way that CIGS is analogous to the II-VI compounds, in that pairs of column III metallic elements are replaced by a column II and column IV element. In particular, the nitride members of this class of materials has attracted attention recently, with ZnSnN2 showing promise as an alternative to indium-rich InGaN. Given that a significant portion of the US domestic consumption of zinc and tin comes from reclamation activity instead of new mining, such a material has both environmental and economic advantages over compounds which contain indium and/or gallium. We have recently succeeded in growing high-quality single crystal thin films of this material using plasma-assisted molecular beam epitaxy (MBE), and demonstrated the ability to alter the degree of cation disorder (and consequently, switching between orthorhombic and wurtzite lattice structures) by carefully controlling growth parameters [1]. Intriguingly, in a fashion similar to what has been observed in other cation disordered compounds, the band gap of the material changes significantly between the two lattice structures, with a predicted range of approximately 1 to 2 eV. Experimentally, we have already observed optical band gaps in the range of 1.3 to 2.3 eV, although both values are affected by the Burstein-Moss effect as the ~150 nm thick samples are degenerately n-type. While the majority of films have been grown on (111) YSZ, we will also report the results of experiments using LiGaO2, which has a closer lattice match to the orthorhombic structure and appears to stabilize that symmetry more easily. It is worth noting that in addition to MBE, a number of groups have successfully deposited high-quality thin films using other techniques [2], including sputtering.
Beyond ZnSnN2, which is of interest for terrestrial photovoltaics depending on the crystal structure and corresponding electronic band gap, there are also several closely related materials which could be of interest for short wavelength applications. Among these is ZnGeN2, which has been estimated to have a band gap of approximately 3.3 eV (very close to that of GaN). We have recently conducted preliminary growth experiments on this material using several substrates including YSZ, and noted that growth behavior appears to mirror that of ZnSnN2.
[1] Makin et al., J. Vacuum Science and Technology B35 (2016) 02B116; Senabulya et al., AIP Advances 6 (2016) 075019.
[2] Lahourcade et al., Advanced Materials 25 (2013) 2562; Quayle et al., Physical Review B 91 (2015) 205207; Fioretti et al., J. Materials Chemistry C 3 (2015) 11017; Qin et al., Applied Physics Letters 108 (2016) 142104; Kawamura et al., Crystal Research and Technology 51 (2016) 220.
2:00 PM - *ES03.05.03
Metal Oxide Materials as a Sustainable and Viable Alternative to Low Cost Electronics
Elvira Fortunato 1 , Rodrigo Martins 1
1 , FCT-UNL, Caparica Portugal
Show AbstractMetal oxide electronic materials are quite attractive since they provide a large variety of different and possible applications due to the diverse spectrum of properties ranging from thin films to nanostructures.
Concerning applications they are becoming increasingly important in a wide range of applications like transparent electronics, optoelectronics, magnetoelectronics, photonics, spintronics, thermoelectrics, piezoelectrics, power harvesting, hydrogen storage and environmental waste management.
In terms of production tecnhiques rf magnetron sputtering has been well established and has demonstrated high performance devices, however these require complex high vacuum equipment which is a major drawback, especially if we are targeting low cost applications. In contrast, the solution process has many advantages such as large-area deposition, roll-to-roll capability, easy control of composition, atmospheric processing, and low cost.
In this work we will present some advances on solution based conductors, dielectrics and semiconductors all based on metal oxide and their application to electronic devices.
2:30 PM - ES03.05.04
Lithium Titanate/Carbon Nanotube Thin-Film Electrodes for High Power Lithium-Ion Batteries
João Coelho 1 , Anuj Pokle 1 , Sang Hoon Park 1 , Valeria Nicolosi 1
1 School of Physics/CRANN, Trinity College Dublin, Dublin Ireland
Show Abstract
Nowadays, nanomaterials are considered optimal candidates for energy storage applications, as they present a higher electrode/electrolyte contact area per unit mass and reduce the diffusion paths for both electrons and ions.1 From several synthesis techniques, solution-phase processing of materials in water or organic solvents upon ultrasound irradiation has been regarded as a very promising method for nanomaterials preparation.2,3 However, this route has been mainly applied to layered bulk samples, such as graphene.2,3
In this work, the authors demonstrate that liquid phase processing can be extended to non-layered bulk materials, in this case spinel lithium titanate (LTO). Nanoparticles were prepared via ultrasonic irradiation (37 kHz for 3 hours) in different solvents. A detailed structural characterization revealed that the obtained particles do not suffer any phase change upon processing. Moreover, the dispersions revealed to be highly stable, according to a zeta potential measurement (- 67 mV).
The obtained dispersions (in 2-propanol) are then mixed with single wall carbon nanotubes and sprayed onto copper disc electrodes (2.54 cm2), following a cost-effective spray deposition technology, suitable for the fabrication of both semi-industrial scale and laboratory size thin film electrodes. By testing electrodes with different mass fractions of carbon nanotubes it was found out that the electrochemical utilization is enhanced for a nanotubes load of 15% (wt). These electrodes (2 µg.cm-2) present an outstanding capacity of 92 mAh.g-1 at a relatively high current of 3.30 mA.cm-2 (100C). Besides the high rate capability, the nano LTO/carbon nanotubes composites also present a good stability and coulombic efficiency when cycled for 1000 cycles at 1C (35 µA.cm-2).
References
(1) Haetge, J.; Hartmann, P.; Brezesinski, K.; Janek, J.; Brezesinski, T. Chemistry of Materials 2011, 23, 4384
(2) Coleman, J. N.; Lotya, M.; O’Neill, A.; Bergin, S. D.; King, P. J.; Khan, U.; Young, K.; Gaucher, A.; De, S.; Smith, R. J.; Shvets, I. V.; Arora, S. K.; Stanton, G.; Kim, H.-Y.; Lee, K.; Kim, G. T.; Duesberg, G. S.; Hallam, T.; Boland, J. J.; Wang, J. J.; Donegan, J. F.; Grunlan, J. C.; Moriarty, G.; Shmeliov, A.; Nicholls, R. J.; Perkins, J. M.; Grieveson, E. M.; Theuwissen, K.; McComb, D. W.; Nellist, P. D.; Nicolosi, V. Science 2011, 331, 568.
(3) Hernandez, Y.; Nicolosi, V.; Lotya, M.; Blighe, F. M.; Sun, Z.; De, S.; McGovern, I.; Holland, B.; Byrne, M.; Gun'Ko, Y. K. Nature Nanotechnology 2008, 3, 563.
2:45 PM - ES03.05.05
Tuning the Interlayer Region of NiFe Layered Double Hydroxide for Enhanced Water Oxidation via Cobalt Confinement
Akila Thenuwara 1 2 , Nuwan Attanayake 1 2 , Qimin Yan 3 2 , Evert Elzinga 4 , Daniel Strongin 1 2
1 Chemistry, Temple University, Philadelphia, Pennsylvania, United States, 2 , Center for the Computational Design of Functional Layered Materials (CCDM), Philadelphia, Pennsylvania, United States, 3 Physics, Temple University, Philadelphia, Pennsylvania, United States, 4 Earth and Environmental Sciences, Rutgers, The State University of New Jersey, Newark, New Jersey, United States
Show AbstractDevelopment of low overpotential (or energy efficient) oxygen evolution reaction (OER) catalysts holds the key for enabling numerous renewable energy technologies including rechargeable metal-air batteries, carbon neutral hydrocarbon generation via CO2 reduction and H2 generation. Here, we utilize a novel design strategy of metal confinement in the interlayer region of NiFe layered double hydroxide (NiFe LDH) to improve its catalytic properties towards OER. In this contribution, we show that cobalt insertion into the NiFe LDH through both substitution and intercalation lead to enhancement in OER activity. Electrochemical measurements show that the cobalt-modified NiFe LDHs exhibit an enhanced activity relative to the unmodified material (~ 290 mV overpotential at 10 mA cm-2 for cobalt substituted NiFe LDH and ~265 mV overpotential at 10 mA cm-2 for cobalt intercalated NiFe LDH). Overpotential calculations (via density functional theory) reveal that the origin of the enhancement in catalytic activity in these cobalt-modified NiFe LDHs is due to the tuning of the electronic structure so that optimal binding of OER reaction intermediates is reached.
3:30 PM - ES03.05.06
Carbon Nanodot Solar Cells from Renewable Precursors
Joe Briscoe 1 , Adam Marinovic 1 , Lim Kiat 2 , Steve Dunn 1 3 , Maria-Magdalena Titrici 1
1 , Queen Mary University of London, London United Kingdom, 2 , National University of Singapore, Singapore Singapore, 3 , Deregallera Ltd, Caerphilly United Kingdom
Show AbstractIt has recently been shown that waste biomass can be converted into a wide range of functional materials, including those with desirable optical and electronic properties, offering the opportunity to find new uses for these renewable resources. Photovoltaics is one area where finding the combination of abundant, low-cost and non-toxic materials with the necessary functionality can be challenging. A new and growing area of research is to use carbon-based nanoparticles, sometimes called carbon nanodots or carbon quantum dots, derived from renewable precursors, as sensitizers in a nanostructured solar cell based on the dye-sensitised solar cell structure.
We report the synthesis of carbon nanodots derived from a wide range of biomaterials obtained from different biomass sources and their performance as sensitizers for TiO2-based nanostructured solar cells. Polysaccharides (chitosan and chitin), monosaccharide (D-glucose), amino acids (L-arginine and L-cysteine) and raw lobster shells are all used to produce carbon nanodots via hydrothermal carbonisation. This involves the treatment of the precursor materials at moderate temperatures (200 °C for 6 hours) under elevated pressure. We demonstrate through TEM, XPS, FTIR and XRD analysis that this produces nanoscale carbon materials (2-20 nm diameter) with graphitic cores and surface functionality that is retained from the precursor material. Nanostructured TiO2 electrodes were then soaked in solutions of the carbon nanodots, and UV-Vis analysis shows increased absorption of light in the visible spectrum, though the dominant absorption is still in the UV.
The highest solar power conversion efficiency (PCE) of 0.36 % was obtained by using L-arginine carbon nanodots as sensitizers, while lobster shells, as a model source of chitin from actual food waste, showed a PCE of 0.22 %. By comparing this wide range of materials, we have correlated the performance of the solar cells with the materials characteristics by carefully investigating the structural and optical properties of each family of carbon nanodots. This indicated that the combination of amine and carboxylic acid functionalisation in amono acids is particularly beneficial for the solar cell performance. We propose routes to improve the performance of these solar cells via such guided selection of precursors to achieve the desired functionality, but particularly the visible absorption of the carbon nanodots needs to be significantly improved to raise the solar cell efficiency.
3:45 PM - ES03.05.07
Thin-Film Solar Cells of 5% Efficiency Using Antimony Sulfide-Selenide of Varying Composition
Geovanni Vazquez Garcia 1 , Eira Anais Zamudio Medina 1 , Laura Guerrero Martinez 1 , Ana Karen Peñaloza 1 , M.T. Santhamma Nair 1 , P.Karunakaran Nair 1
1 , Universidad Nacional Autonoma de Mexico, Temixco Mexico
Show AbstractAntimony sulfide selenide thin film solar cells with a conversion efficiency (η) of 5-6 % efficiency are currently being fabricated by vacuum thermal evaporation of antimony sulfide, antimony selenide or a mixture of these two. Either CdS or ZnO thin films have served as n-window films for the cells. While η of the cells achieved so far has not reached the threshold for technological viability, the Sb2SxSe3-x absorber films have some outstanding qualities to lead to a viable photovoltaic technology: (i) for a composition x = 1.4 to 1.6, the films have direct band gap (Eg) of 1. 45 – 1.55 eV (placed between 1.1 eV of Sb2Se3 and 1.88 eV of Sb2S3) with light generated current density near 30 mA/cm2 attained for a film of thickness 350 nm; (ii) the annual production of antimony exceeds 150, 000 tons and selenium requirement is nominal; (iii) constituent elements are of relatively low toxicity. Solar cell of CdS/Sb2S0.65Se2.35 has open circuit voltage Voc of 0.46 V, short circuit current density Jsc, 21.6 mA/cm2 and η of 5.6%; CdS/Sb2S2.2Se0.8 has Voc 0.54 V; Jsc, 13.7 mA/cm2; and η, 3.1%. We shall present how graded composition cells of Sb2SxSe3-x such as CdS/Sb2S0.65Se2.35…. Sb2S2.2Se0.8 as well as CdS/Sb2S2.2Se0.8…. Sb2S0.65Se2.35 would behave. With a substrate temperature of 425-450 oC, such graded composition cells are produced through sequential thermal evaporation from two crucibles containing Sb2S3-Sb2Se3 powder mixtures in distinct molar ratios. Window films of resistive tin oxide produced through the oxidation of chemically deposited SnS thin films and/or of chemically CdS thin films are used. The characteristics of individual films as well as those of the solar cells will be presented. We consider that this methodology for the cell fabrication would help increase η above 6%.
4:00 PM - ES03.05.08
Physical and Chemical Applications of Photodoping in Electrodeposited Cuprous Oxide Thin Films
James Lowe 1 , Robert Coridan 1
1 , University of Arkansas, Fayetteville, Arkansas, United States
Show AbstractExternal fields can be used to regulate the morphological and chemical properties of electrochemically synthesized materials. Examples include emergent morphological patterns in electrodeposited thin films or plasmon-induced shape control in nanocrystals. These illustrate the principle of phototropism, where the coaction of light absorption and carrier generation can induce controllable variations in the material as it grows under illumination. Here we describe the photoelectrodeposition of photocathodic cuprous oxide (Cu2O). Illuminating the growing film with photon energies larger than the band gap of Cu2O results in nanoscale morphological changes in the structure of thin films and intrinsically dopes the material during growth. The result is a ‘black’ Cu2O film that is chemically distinct but crystallographically identical an ordinary film grown in the dark. The flat band potential of the film is controlled by the growth illumination intensity and the photodoping is reversible under thermal oxidation. We explore the nature of the intrinsic dopant as evidenced by the emergence of nanocrystalline Cu metal inclusions in the Cu2O matrix. Finally, we explore the potential of for this effect to be used in new semiconductor heterostructures prepared by light-directed fabrication.
4:15 PM - *ES03.05.09
Earth Abundant Metal Oxides, Sulphides and Selenides for Energy Systems and Devices
Enzo Peccerillo 1 , Peter Yates 1 , Laurie Phillips 1 , Jon Major 1 , Ken Durose 1
1 Department of Physics, Stephenson Institute for Renewable Energy, University of Liverpool, Liverpool United Kingdom
Show AbstractThe agenda to discover and develop sustainable materials for photovoltaics builds on the 1970’s ‘thin film’ paradigm, in which cheap, impure polycrystalline materials are formed into active p-n junction devices by exploiting native defects to enact the doping. While CdTe and CIGS have been successful in this regard, they are more complex to handle than originally envisaged. Hence development of alternative chalcogenides must be mindful of potential complications down the line.
A potentially important group of compounds for sustainable PV is the family of Cu – (Sb or Bi) – S sulpho-salts and their Se analogues. They offer the possibility to engineer the copper vacancy to give control of p-doping, together with a rich phase chemistry that gives many opportunities to discover and tune the materials for use in devices.
Of the many phases possible, the best known are: CuSbS2 (chalcostibite Eg ~1.5 eV), Cu3SbS3 (skinnerite, Eg 1.6 – 1.8 eV) their bismuth analogues (Eg = 1.65 and 1.2 – 1.41 eV respectively). All four have selenium and tellurium analogues of course. While the earliest literature on these is mineralogical they have attracted increasing interest for photovoltaic applications - but the amount of data on them declines rapidly through the series in the order presented above. Experimental and theoretical results will be reviewed briefly and our recent experimental efforts with CuSbS2 will be described. Our sulphurised metal films had a band gap in the expected range, absorption of ~104 – 105 cm-1, p-conductivity and mobilities of ~ 10 cm2.V-1.s-1. Systematic studies of devices made with undoped and NaF-, Zn-, and In-doped material along with window layers comprising CdS, ZnS and ZnSe will be reported. Although voltages of up to 0.56 V could be achieved, the photocurrents and fill factors limited the devices severely.
An ongoing controversy concerning thin film solar cells concerns the role of grain boundaries and whether they harm or assist with light harvesting. We present evidence that some significant electron beam induced current studies are subject to a systematic error, and that grain boundaries always act to reduce PV efficiency. One possible way to avoid this is by using oriented films of Sb2Se3 which comprises van der Waals joined covalently bonded ribbons: in such films vertical conduction would not be affected by wrong bonds as is the case in conventional tetrahedrally bonded semiconductors.
4:45 PM - ES03.05.10
Preparation of Cu2ZnSn(S,Se)4 Thin Films by Selenization of Cu2ZnSnS4 Layers and Suppression of By-Products Formation
Shunya Taki 1 , Kota Moriuchi 1 , Aya Uruno 1 , Masakazu Kobayashi 1 2
1 Department of Electrical Engineering and Bioscience, Waseda University, Tokyo Japan, 2 Kagami Memorial Research Institute for Materials Science and Technology, Waseda University, Tokyo Japan
Show AbstractCu2ZnSnS4 (CZTS) and Cu2ZnSn(S,Se)4 (CZTSSe) are materials based on the earth abundant elements, and they are promising absorber materials for low cost thin film solar cells. CZTS layers were prepared using CZTS nanoparticles; CZTS nanoparticles were prepared by the ball milling of stoichiometric CZTS powder. CZTSSe thin films were prepared by annealing CZTS layers under the Se vapor (selenization). The annealing was performed using a two zone annealing furnace. Although uniform layers could be successfully prepared, various problems were discovered. Some samples have exhibited n-type conduction or semi-metallic. It was confirmed that Cux(S,Se) as by-product was formed in selenized films. It was known that CuxS and CuxSe have metallic properties, and CuxSe is formed as an intermediate during the selenization process at a certain temperature range. Therefore, the variation of temperature ramp up speed would affect the formation of CuxSe.
In this paper, we have varied the ramp up speed from 5 oC/min to 30 oC/min and the suppression of the by-product formation was explored. The film quality of the CZTSSe was characterized by X-ray diffraction (XRD), Raman spectroscopy and Hall measurements. It is expected that Raman scattering signal would be originated from the surface area of the sample (up to 50 nm from the surface). We have also fabricated CZTSSe solar cells consisting of ZnO:Al / ZnIn2S4 / CZTSSe / Mo / Glass.
When the temperature ramp up speed was 5 oC/min or 8 oC/min, a broad peak resolved into 2 components was observed from the XRD measurement. It was considered that one component was originated from CZTSSe and the other was from the by-product. Raman scattering measurement suggested that a strong peak of CuxSe and a week peak originated from Cux(S,Se) were observed. The Raman signals originated from CZTSe and CZTS were very weak. These results suggested that Cux(S,Se) was formed at the surfase area of the film. On the other hand, a sharp peak consisted from one component was confirmed from XRD measurements when the temperature ramp up speed was 30 oC/min. Raman scattering measument showed the decrease of CuxSe and Cux(S,Se) signals. When the temperature ramp up speed was slow, desorption of Sn was serious and the formation of CZTSSe was limited since the formed CuxSe was not changed to CZTSSe. It was concluded that the formation of CuxSe and Cux(S,Se) was supressed by increasing the temperature ramp up speed. It was because the desorption of Sn was supressed by shortening the time to across the “Sn desorption temperature range”. It was also examined that Sn was supplied during the selenization process.
The authors would like to acknowledge Mitsui Mining and Smelting Co.This work was supported in part by Waseda University Research Initiatives, by Waseda University Grant for Special Research Project, and by JSPS Research Fellowships for Young Scientists.
ES03.06: Poster Session II
Session Chairs
Wednesday AM, November 29, 2017
Hynes, Level 1, Hall B
8:00 PM - ES03.06.01
Edge Enriched 2D MoS2 Thin Films Grown by Chemical Vapor Deposition for Enhanced Catalytic Performance
Sha Li 1 , Shanshan Wang 1 , Matteo Salamone 1 , Alex Robertson 1 , Simantini Nayak 1 , Heeyeon Kim 2 , Edman Tsang 3 , Mauro Pasta 1 , Jamie Warner 1
1 Department of Materials, University of Oxford, Oxford United Kingdom, 2 , Convergence Materials Laboratory, Daejeon Korea (the Republic of), 3 Department of Chemistry, University of Oxford, Oxford United Kingdom
Show AbstractChemical vapor deposition (CVD) is used to grow thin films of 2D MoS2 with nanostructure for catalytic applications in the hydrogen evolution reaction (HER). Tailoring of the CVD parameters results in an optimized MoS2 structure for HER that consists of large MoS2 platelets with smaller layered MoS2 sheets growing off it in a perpendicular direction, which increases the total number of edge sites within a given geometric area. A surface area to geometric area ratio of up to ~ 340 is achieved, benefiting from the edge-exposed high porosity network structure. Optimized thickness of the MoS2 film is determined for maximum performance, revealing that increasing thickness leads to increased impedance of the MoS2 film and reduced current density. Current density of the optimum sample reaches as high as 60 mA/cm2geo (normalized by geometric area) at an over-potential of 0.64 V vs. RHE (in 0.5 M H2SO4) with corresponding Tafel slope of ~ 90 mV/dec, which demonstrates the high-porosity edge-exposed MoS2 network structure is promising as a HER catalyst.
8:00 PM - ES03.06.02
Atomic-Layer Deposited MoS2 on Si Heterostructures for Highly Efficient Photoelectrochemical Water Reduction
Seungtaeg Oh 1 , Jun Beom Kim 2 , Jun Tae Song 3 , Soo-Hyun Kim 2 , Jihun Oh 1
1 Graduate School of Energy, Environment, Water, and Sustainability (EEWS), Korea Advanced Institute of Science and Technology (KAIST), Daejeon Korea (the Republic of), 2 School of Materials Science and Engineering, Yeungnam University, Gyeongsangbuk-do Korea (the Republic of), 3 KI Institute for NanoCentry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon Korea (the Republic of)
Show AbstractMolybdenum disulfide (MoS2) have attracted intensive attention as an earth-abundant and low-cost hydrogen evolving electrocatalyst that can substitute precious metal catalyst materials, such as Pt[1,2]. Furthermore, it is well-known that MoS2 can form the type-II heterojunction with Si for enhanced charge collection[3]. Therefore, the combination of MoS2 and Si is suitable for implementing a highly efficient and cost-effective photoelectrochemical (PEC) water reduction device. Atomic-layer deposition (ALD) is a versatile deposition process with precise control of film thickness and excellent uniformity in wafer-scale[4].
Herein, we present the highly efficient and stable ALD MoS2/Si photocathodes for PEC water reduction reaction[5]. As-grown ALD MoS2/Si photocathodes reduce about 450 mV of overpotential for producing 10 mA/cm2 of photocurrent density for hydrogen evolution reaction (HER) compared to bare Si. In addition, we demonstrate that the post-sulfurization at high temperature dramatically enhances the electrocatalytic performance of ALD MoS2 by tuning stoichiometry and crystallinity of MoS2. As a results, sulfurized ALD MoS2/Si photocathodes exhibits an additional 180 mV overpotential reduction compared to as-grown ALD MoS2. Our ALD MoS2/Si photocathode exhibits a photocurrent density of 21.7 mA/cm2 at 0V .vs RHE operates continuously for 24 hours without degradation. The role of post-sulfurization and ALD cycles MoS2 on PEC HER will be presented in detail.
Reference
1 Jaramillo, T. F. et al. Identification of active edge sites for electrochemical H2 evolution from MoS2 nanocatalysts. Science 317, 100-102 (2007).
2 Kibsgaard, J., Chen, Z., Reinecke, B. N. & Jaramillo, T. F. Engineering the surface structure of MoS2 to preferentially expose active edge sites for electrocatalysis. Nature materials 11, 963-969 (2012).
3 Tsai, M.-L. et al. Monolayer MoS2 heterojunction solar cells. Acs Nano 8, 8317-8322 (2014).
4 Browning, R. et al. Atomic layer deposition of MoS2 thin films. Materials Research Express 2, 035006 (2015).
5 Oh, S., Kim, J. B., Song, J. T., Oh, J. & Kim, S.-H. Atomic Layer Deposited Molybdenum Disulfide on Si Photocathodes for Highly Efficient Photoelectrochemical Water Reduction Reaction. Journal of Materials Chemistry A, 5, 3304-3310, (2017).
8:00 PM - ES03.06.03
One-Step Chemical Vapor Deposition of MoS2 Nanosheet Catalysts for Enhanced Hydrogen Evolution Reaction
Seung-Deok Seo 1 , Jae-Wan Lee 1 , Gwang-Hee Lee 1 , Dong-Wan Kim 1
1 , Korea University, Seoul Korea (the Republic of)
Show AbstractRecently, the efficient production of energy is the most important issue for humanity due to large energy consumption by the rapidly grown population. Most countries are still producing electricity using fossil fuels, which cause various types of air pollution and global warming from carbon dioxide emissions. H2 has been widely considered for clean energy cycle by their high energy density of 140 MJ kg-1, carbon-free energy cycle, and sustainability. [1] Especially, the sustainable production of hydrogen via water splitting is a promising approach because water exists everywhere around us. The hydrogen evolution reaction (HER) acts as the most important stage in both electrochemical and photoelectrochemical water splitting. The Pt is the best known pure metal catalyst for HER but has a high cost due to their scarcity and difficulty in mass production. In this respect, low-cost and earth-abundant transition metal chalcogenides are of great interest. [2] MoS2 is one of representative metal-chalcogenides material, which intrinsically has weakly coupled two-dimensional layered nanosheets structure like graphene. They has large band-edge excitation of the metal centered d-d transition that can give rise to unique electronic features, which serves an advantage for numerous applications such as HER catalyst, hydrogen storage, and elastic and coating materials for Li batteries. [3]
In this research, we prepared the MoS2 nanosheets array (NA-MoS2) using one-step chemical vapor deposition (CVD) process for HER catalysts. The NA-MoS2 was synthesized using thermal evaporation of commercial MoO3 and S powder, carried by Ar/H2 mixed gas under low-pressure using rotary pump. The deposition was performed at 800°C using Ti foil as a substrate. The edge-exposed, directly assembled NA-MoS2 was grown on Ti foil and evaluated as an HER catalyst electrode in three-electrode beaker cell using acid electrolyte (0.5M H2SO4 solution, pH: 0.38). The as-obtained NA-MoS2 electrode was highly efficient for HER, compared with commercial MoS2, exfoliated MoS2 electrodes. The excellent electrocatalytic HER activity can be originate from the edge-exposed nanostructures of directly grown NA-MoS2, offering large surface area and rich defects.
[1] Y.-J. Yuan et al. ChemSuSChem 2015 8, 4113
[2] H. Wang et al. Nano Res. 2015 8, 566
[3] Z. He et al. Appl. Mater. Today 2016 3, 23
8:00 PM - ES03.06.05
Structural Water Engaged Disordered Vanadium Oxide Nanosheets for High Capacity Aqueous Potassium-Ion Storage
Daniel Charles 1 , Mikhail Feygenson 3 , Katharine Page 4 , Joerg Neuefeind 4 , Wenqian Xu 2 , Xiaowei Teng 1
1 , University of New Hampshire, Durham, New Hampshire, United States, 3 , Juelich Centre for Neutron Science, Juelich Germany, 4 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractAqueous electrochemical energy storage devices using potassium-ions as charge carriers are attractive due to their superior safety, lower cost and excellent transport properties compared to other alkali ions. However, the accommodation of potassium-ions with satisfactory capacity and cyclability is difficult because the large ionic radius of potassium-ions causes structural distortion and instabilities even in layered electrodes. Here we report that water induces structural rearrangements of the vanadium-oxygen octahedra and enhances stability of the highly disordered potassium-intercalated vanadium oxide nanosheets. The vanadium oxide nanosheets engaged by structural water achieves high capacity (183 mAh g-1 in half cells at a scan rate of 5mV s-1, corresponding to 0.89 charge per vanadium) and excellent cyclability (62.5 mAh g-1 in full cells after 5,000 cycles at 10 C). The promotional effects of structural water on the disordered vanadium oxide nanosheets will contribute to the exploration of disordered structures from earth-abundant elements for electrochemical energy storage.
8:00 PM - ES03.06.06
Fabrication of SnS-Based Thin-Film Solar Cell Using Novel Precursor, Sn(dmamp)2
Young Kuk Lee 1
1 , Korea Research Institute of Chemical Technology, Taejon Korea (the Republic of)
Show AbstractTin sulfide (SnS)-based thin film solar cells were fabricated using Sn(dmamp)2 (dmamp, di-methyl-amino-methyl-propanolate). SnS thin films were deposited by MOCVD (metal organic chemical vapor deposition) in the temperature range 150–300 °C. Effect of post annealing temperature and atmosphere on the cell efficiency were investigated. Also, n-type buffer, Zn(O,S) were optimized by estimation of band structure. X-ray diffraction (XRD) showed that formation of the pure SnS phase was observed on the sample grown at 200 °C and partial pressure of H2S at 10 Torr. Transmission electron microscope (TEM) images showed that metallic thin precipitates in the films were observed to disappear at moderate annealing condition. Maximum cell efficiency was measured up to ~3.0%.
8:00 PM - ES03.06.07
Investigating Vapor-Phase Defect Passivation in NiO by Targeted Atomic Deposition and its Effects on Solar Cell Performance
Aaron Taggart 1 , Taylor Moot 1 , Shannon McCullough 1 , Lenzi Williams 1 , John Papanikolas 1 , James Cahoon 1
1 , University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States
Show AbstractIn the last two decades, metal oxide semiconductors have gained enormous attention as photocathodes, photoanodes, and charge transport layers in solar energy devices. However, defects innate to these materials promote charge recombination and limit their efficiencies. Nickel oxide (NiO) is the state of the art material for p-type dye-sensitized solar cells (DSSCs), dye-sensitized photoelectrosynthesis cells, and hole transport layers; yet, it contains many defects, largely arising from nickel vacancies. In order to passivate these defects, we substitute Group 3A elements into the nickel vacancies using a kinetically-controlled gas phase treatment called Targeted Atomic Deposition (TAD). By varying the deposition time, we achieve sub-monolayers of passivating elements. Therefore, the TAD treated NiO films maintain good charge transfer across the interface while removing defects. TAD treatments can increase the short circuit current density of NiO DSSCs by 150% and increase the open circuit voltage by 200%. Density of states maps extracted from cyclic voltammetry measurements show that TAD of Al and TAD of Ga significantly passivate trap states. Ultrafast transient absorption results indicate that TAD treatment reduces charge recombination across the NiO interface, leading to long lived charge carriers and more efficient devices. These results demonstrate a surface treatment that dramatically improves the electronic properties of NiO films for photocathode and hole transport layer applications.
8:00 PM - ES03.06.08
Theoretical Investigation of the Catalytic Activity of Iron Oxyhydroxide(FeOOH) for the Electrochemical Water Oxidation
Taehyung Lee 1 , Ho Won Jang 1
1 , Seoul National University, Seoul Korea (the Republic of)
Show AbstractRecently, to replace the expansive noble metals in electrocatalyst, transition metals with low cost and comparable performances are chosen as substitutes. Among transition metals, iron, which is one of the most abundant metal in the earth crust, is relatively out of the attention as an electrocatalyst. Due to its earth abundance and well-organized production system, iron has the one-tenth price of nickel, and even one-fiftieth price for cobalt. Considering that the ultimate goal of the water electrocatalysis system is an integrated system with a photovoltaic cell which demands the scale-up processing, the cost competitiveness can be maximized for the commercialization.
To enjoy the strong cost competitiveness of the iron, the poor catalytic property of the iron based electrocatalysts, particularly its low current density should be enhanced. According to several studies, it is known that certain phase, iron oxyhydroxide, can have much higher current density than existing iron-based electrocatalysts. Especially, iron oxihydroxide (FeOOH) belongs to thermodynamically stable form among iron oxides and presented to have enhanced catalytic property by experiments. Though, there are not enough theoretical investigations on its catalytic activity.
Herein, we investigate the water oxidation mechanism on the Iron oxyhydroxide(FeOOH) electrocatalysts using first-principles calculations based on Density Functional Theory. With calculations of relative surface stabilities and adsorbate coverages, the most stable low-index surfaces of FeOOH will be determined. Next, with the determined FeOOH surfaces, we will compare the theoretical overpotentials achieved by calculating each oxygen evolution reaction steps. For each step, the magnetic and charge state will be checked for the explanation of oxygen evolution reaction process. Furthermore, impacts of the various dopants such as Mn, Zn, Ni, Co will be also investigated. With the calculation using hybrid functional, the electronic structure of the iron oxyhydroxide, with and without dopants, will be obtained and it will gives the explanation of different OER catalytic activity shown by iron oxyhydroxide with different dopants.
8:00 PM - ES03.06.10
Earth-Abundant and Non-Toxic V-VI-VII Semiconductors for Solar Cells
Alex Ganose 1 2 , Keith Butler 3 , Scott McKechnie 4 , Pooya Azarhoosh 4 , Jarvist Frost 5 , Mark van Schilfgaarde 4 , Aron Walsh 5 6 , David Scanlon 1 2
1 , University College London, London United Kingdom, 2 , Diamond Light Source, Harwell United Kingdom, 3 , University of Bath, Bath United Kingdom, 4 , Kings College London, London United Kingdom, 5 , Imperial College London, London United Kingdom, 6 , Yonsei University, Seoul Korea (the Republic of)
Show AbstractBismuth-based solar absorbers are of interest due to similarities in the chemical properties of bismuth halides and the exceptionally efficient lead halide hybrid perovskites. Both Pb2+ and Bi3+ possess a similar soft polarisability and form a wide range of compounds with rich structural diversity, such as BiX6 clusters, 1D ribbons, and layered perovskite type structures. Whilst both are composed of earth-abundant materials and experience the same beneficial relativistic effects acting to increase the width of the conduction band, bismuth is non-toxic and non-bioaccumulating, meaning the impact of environmental contamination is greatly reduced.[1]
Here, we use hybrid density functional theory, with the addition of spin orbit coupling (SOC), to examine a range of bismuth containing V-VI-VII candidate photovoltaic (PV) absorbers.[2-5] We show that BiSI and BiSeI possess electronic structures suitable for photovoltaic applications. Furthermore, we calculate band alignments against commonly used hole transporting and buffer layers, which indicate band misalignments are likely to be the source of the poor efficiencies reported for devices containing these materials. Based on this, we have suggested alternative device architectures expected to result in improved power conversion efficiencies. Lastly, we explore the defect properties of BiSI and suggest ideal growth conditions for optimised film properties.
References
[1] A. M. Ganose, C. N. Savory and D. O. Scanlon, Chem. Commun. 53, 20–44 (2017)
[2] K. T. Butler, J. M. Frost, and A. Walsh, Energy Environ. Sci. 8, 838 (2015)
[3] A. M. Ganose, K. T. Butler, A. Walsh, and D. O. Scanlon, J. Mater. Chem. A 4, 2060 (2016)
[4] A. M. Ganose, M. Cuff, K. T. Butler, A. Walsh and D. O. Scanlon, Chem. Mater. 28, 1980 (2016)
[5] D. S. Bhachu et. al., Chem. Sci. DOI: 10.1039/C6SC00389C (2016)
8:00 PM - ES03.06.11
Synthesis and Photoelectrochemical Caracterization of ZnO-Ionic Liquid Films for DSSC Type Devices
Aline Trench 1 , Letícia Guerreiro da Trindade 1 , Gabriela Bosco Minervino 2 , Maria Helena Carvalho da Costa 1 , Marcelo Assis 1 , Máximo Siu Li 3 , Ernesto Chaves Pereira 1 , Tatiana Mazzo 2 , Elson Longo 1
1 , Federal University of Sao Carlos, Sao Carlos Brazil, 2 Department of Marine Sciences, Federal University of São Paulo, Sao Paulo Brazil, 3 , University of Sao Paulo, Sao Carlos Brazil
Show AbstractThe search for alternative sources of energy has grown in recent years due to the possibility of depletion of fossil fuels and the great environmental impact caused by their excessive use. Among renewable energy sources, solar energy stands out because it is inexhaustible both as a heat source and as a light source. In this context, The electrochemical energy conversion device that stand out are the dye-sensitized solar cells (DSSCs) because they are simple manufacturing devices, with low cost of production and ecofriendliness. Nowadays, several researches have indicated that zinc oxide nanoparticles (ZnO) are a candidate to replace the TiO2 in DSSCs because of its band gap of approximately 3.4 eV, and much higher electron mobility that reaches values of 7 orders of magnitude higher than TiO2. Ionic liquids (ILs) are a class of novel solvents that exhibit interesting properties that make growing the interest in testing them as electrolyte solvents and into the electrolyte for DSSCs. In this present work, ZnO nanoparticles synthetized by the microwave assisted hydrothermal method were sensitized by incorporation of the 1.3-dimethylimidazolium iodide (MMI.I) ionic liquid, the amount of IL in the composite were varied. Sensitized and unsensitized ZnO nanoparticles films were characterized by XRD analyses, Field Emission Gun-Scanning Electron Microscopy (FEG-SEM) micrographs, Ultraviolet-visible (UV–vis) absorption spectra, Photoluminescence (PL) measurements at different temperatures and by photoelectrochemical measurements. The zoom of (101) plane of the XRD data, showed a shift in the peak positions that suggest that the IL had already entered in the crystal structure of ZnO nanoparticles. The FEG-SEM micrographs showed that the addition of the IL in the nanoparticles does not change the micro flower-like morphology. However, the addition makes the nanoparticles coalesce causing changes in the diameter and in the thickness size of the particles and reduces the band gap values of 3.16 eV of pure ZnO to 3.14 eV and 3.09 eV for ZnO/IL20 and ZnO/IL35,respectively. This decrease in the band gap value and the shift in the peak positions observed in the XRD data with the increase of the IL concentration suggest that structural defects such as distortions and/or strains in the ZnO lattice is caused by the substitution of MMI+ cations at the Zn+2 sites leading to an appearance of intermediary levels between the valence and conduction bands. These changes in nanoparticles become more evident with the results of PL measurements that showed the changed of the shallow defects to deep defects and in the photoelectrochemical data, where it was observed that the photocurrent density of ZnO/IL films increases significantly. The photocurrent density increased from 0.05 mA cm-2 for pure ZnO nanoparticles to 0.51 mA cm-2 when the ZnO film contains 20% in mass of the IL and to 1.07 mA cm-2 when the film contains 35% in mass of the IL at 1.08 V.
8:00 PM - ES03.06.12
The Influence of Nanoparticle Size on the Synergistic Catalytic Properties of α-Ni(OH)2-FeOCPc@rGO Composite for Water Oxidation
Josué Gonçalves 1 , Tiago Matias 1 , Lucas Saravia 1 , Mauro Berttoti 1 , Koiti Araki 1
1 Department of Fundamental Chemistry, University of São Paulo, São Paulo, São Paulo, Brazil
Show AbstractOxygen evolution reaction (OER) is a key step of water splitting that holds an ultimate potential to cater the energy demand on a global scale. OER proceeds through sluggish multistep proton-coupled electron transfer processes where a catalyst is fundamental to enhance the O2 evolution rate under low overpotentials[1]. The most active OER catalysts are based on scarce and high cost precious metals such as Ir and Ru[2]. Thus low cost and highly active Ni-based materials are interesting alternatives[1], especially when in the more active alpha phase (α-Ni(OH)2)[1], whose performance was further improved by combining graphene, improving the electric conductivity and the catalytic activity while providing larger surface areas[2]. Thus, herein described are materials based on α-Ni(OH)2nanoparticles with different sizes deposited on reduced graphene oxide (rGO), whose electrocatalytic activity for OER was further enhanced by combining iron-octacarboxy phthalocyanine (FeOCPc), generating a ternary α-NiFeOCPc@rGO nanocomposite, that were characterized by DLS, XRD, AFM, TEM, and its potential for OER was evaluated. The size of α-Ni(OH)2 NPs was found to be significantly dependent on the alkaline metal (Na+ or K+) hydroxide used in the synthesis, where KOH produced larger NPs than NaOH, that were more positively affected by incorporation of rGO and FeOCPc, suggesting significant effect of nanocrystallites size. The results were confirmed by the Tafel plots in which the slope decreased significantly for K-derivatives. The reason for the higher reactivity for OER in the composites decorated with α-Ni(OH)2-K may be related to the larger spacing in between rGO sheets favoring the diffusion, enhancing the mass and charge transport and thus the electrocatalytic activity. In fact, it was able to sustain a stable current of 15 mA cm-2 during 10 h of continuous electrolysis at 0.62 V, in 1.0 mol dm-3 KOH solution, showing good perspectives as electrode material for OER.
References
1. M. Gao, et al. J. Am. Chem. Soc., 2014, 136, 7077-7084.
2. D. H. Youn, et al. J. Power Sources, 2015, 294, 437-443.
Acknowledgments
This work was supported by FAPESP, CNPq, SisNANO, LNNano@CNPEM.
8:00 PM - ES03.06.13
Enhancement of Oxygen Evolution Activity for the cObalt Oxide Catalyst by Addition of Organic Molecules
Tomoki Hiue 1 , Masaaki Yoshida 1 , Hiroshi Kondoh 1
1 , Keio University, Yokohama Japan
Show Abstract1. Introduction
Electrochemical water splitting by renewable energy is one of the promising methods for the future sustainable hydrogen production. The oxygen evolution reaction (OER) limits the efficiency of overall water splitting due to the large overpotential. Thus, the development of highly active OER catalyst is required. In recent years, Nocera and co-workers reported cobalt-phosphate-based OER catalyst (Co-Pi) functions as the efficient OER catalyst.[1] Meanwhile our group found that amino acids integrate nickel oxide clusters adding amino acids to nickel catalyst and enhance the catalytic activity.[2] Herein, we examined whether the OER activity improve by addition of organic molecule to Co-Pi, and the function of the organic molecule was investigated using in-situ UV-vis absorption, in-situ X-ray absorption fine structure (XAFS) and in-situ infrared absorption spectroscopy in an attenuated total reflection mode (ATR-IR).
2. Experimental
A Teflon electrochemical cell was equipped with a Pt wire counter electrode and a Ag/AgCl reference electrode for all electrochemical experiments. Cobalt oxide thin films were electrodeposited on an indium tin oxide (ITO), a Pt/Pd thin film, or a Au thin film in 0.1 M potassium phosphate (K-Pi) containing 0.4 mM Co(NO3)2 and 6.4 mM organic molecule such as glycine (Co-Gly), ethylenediamine (Co-EDA), and ethylamine (Co-EA). The prepared sample was measured using in-situ UV-vis absorption, in-situ XAFS and in-situ ATR-IR.
3. Result and discussion
Constant potential electrolysis of water was conducted in a K-Pi aqueous electrolyte. The OER current of Co-Gly was higher than that of Co-Pi, indicating that the glycine molecule enhances the OER activity of Co-Pi. To assess the film thickness of these catalysts, in-situ UV-vis absorption spectra were measured. The broad peak intensity of UV-vis absorption spectrum for Co-Gly was higher than that for Co-Pi, demonstrating that the glycine molecule promotes the electrodeposition of cobalt oxide catalyst. To investigate the local structure of Co species in the Co-Gly, extended X-ray absorption fine structure (EXAFS) spectra were taken for Co-Gly, Co-Pi and CoOOH reference powder. This results suggest that the local structure of Co species in the Co-Gly is composed of an edge-sharing CoO6 octahedral clusters a few nanometers in size. To observe the glycine molecule adsorbed in Co-Gly, in-situ ATR-IR spectra were obtained. As the catalyst was electrodeposited, the two upward bands emerged. These bands are assignable to NH3+ asymmetric deformation mode and COO- symmetric stretching mode, which exhibits that the glycine molecule adsorbed in Co-Gly. In conclusion, we found that the glycine molecule combined between cobalt oxide clusters composed of CoO6 octahedral structure and the OER activity improved because the number of active reaction sites increased.
[1] D. G. Nocera et al., Science. 2008, 321, 1072.
[2] M. Yoshida*, S. Onishi et al., J. Phys. Chem. C, 2017, 121, 255.
8:00 PM - ES03.06.14
Influence of Ammonium Sulfate Concentration on Optical Property of Zn(S,O,OH) Thin Films
Hiroki Ishizaki 1 , Hironori Haga 1
1 , Saitama Institute of Technology, Fukaya, Saitama Japan
Show AbstractRecently, CuIn1-xGaxSe2 thin film solar cells with alternative buffer layers have high efficiencies over 19%,. CuIn1-xGaxSe2 thin film solar cells typically consisted of glass substrate, molybdenum back electrode, CuIn1-xGaxSe2 absorbent layer, CdS buffer layer and transparent conductive oxide. However, CdS buffer layer with bandgap energy of 2.4eV was highly absorbing for wavelengths below 520nm. In order to improve the short-circuit current of the CuIn1-xGaxSe2 thin film solar cells, the buffer layer material with wide bandgap energy need be developed. Thus, Zn(S,O,OH) thin film with a wider bandgap energy than those of ZnO and CdS paid many attention for CuIn1-xGaxSe2 thin film solar cell field. However, the conduction band offset exited in the interface between the Zn(S,O,OH) buffer layer and CuIn1-xGaxSe2 thin film and this conductive band offset was influenced with the efficiency of CuIn1-xGaxSe2 thin film solar cell4. As the conduction band minimum of the buffer layer was 0.0-0.4eV higher than that of CuIn1-xGaxSe2, a higher efficiency of the CuIn1-xGaxSe2 thin film solar cell was obtained, referring of the theoretical analysis . Thus, the CuIn1-xGaxSe2 thin film solar cell, connected with a functionally graded Zn(S,O,OH) buffer layer with changing the bandgap energy in the thickness would be expected to reduce the conduction band offset.
The preparation of Zn(S,O,OH) thin films by chemical bath deposition presents several advantage over the physical vapor deposition techniques; (1) the thickness and morphology of film can be controlled by chemical parameters, (2) the thin films can be obtained on substrates with melting point below 373K such as polymer, (3) the equipment is not expensive . In order to grow a functionally graded Zn(S,O,OH) buffer layer with changing the bandgap energy in the thickness, we proposed that the O/S atomic ratio of Zn(S,O,OH) buffer layer would be controlled by adding a sulfate into the CBD- Zn(S,O,OH) aqueous solution.
For the aim of this investigation, the bandgap energy and the O/S atomic ratio of Zn(S,O,OH) thin film would be controlled by ammonium sulfate concentration.
8:00 PM - ES03.06.15
Fabrication of Zinc Oxide Films by New Electrochemical Reaction
Akira Yamamoto 1 , Hironori Haga 1 , Hiroki Suzuki 1 , Shumpei Ogawa 1 , Hiroki Ishizaki 1
1 , Saitama Institute of Technology, Fukaya Japan
Show AbstractRecently, Dye-sensitized solar cells will easily manufacture and have low cost. However, Dye-sensitized solar cells with lower conversion efficiency than silicon solar cells are not widespread. Therefore, it is necessary to improve the conversion efficiency by improving the photocatalytic layer. Since zinc oxide has excellent properties such as electrical characteristics and optical characteristics, this ZnO has attracted attention as a photocatalytic. In this investigation, the speedy preparation of Zinc Oxide film at low temperature was developed by using a zinc sulfate aqueous solution containing citric acid and hydroxylamine, and the electrical and optical properties for these ZnO films was evaluated. As a result, growth rate of ZnO films and the optical bandgap energy was controlled by changing the cathode potential.
8:00 PM - ES03.06.16
Few-Layer Thickness of MoSSe Alloy by RF Sputtering—CVD route for Enhanced Hydrogen Evolution Reaction
Sajjad Hussain 1 4 , Kamran Akbar 2 , Dhanasekaran Vikraman 3 , Hyun-Seok Kim 3 , Seung-Hyun Chun 2 , Jongwan Jung 1 4
1 Graphene Research Institute, Sejong University, Seoul Korea (the Republic of), 4 Institute of Nano and Advanced Materials Engineering, Sejong University, Seoul Korea (the Republic of), 2 Physics, Sejong University, Seoul Korea (the Republic of), 3 Division of Electronics and Electrical Engineering, Dongguk University-Seoul, Seoul Korea (the Republic of)
Show AbstractSustainable, cost-effective and efficient hydrogen production through water splitting for clean energy source has been considered as a promising candidate to replace fossil fuels and also gained remarkable attention to fulfill the global energy demand as well as overcome the environmental issue. The central challenge is to explore new advanced earth-abundant, highly catalytical materials with a high current density at a low overpotential to replace scarce and precious platinum (Pt) and noble metal oxides. 2D transition metal dichalcogenide (TMDs, MoS2, WS2, MoSe2, etc.) have attracted special attention due to low cost catalyst alternatives for HER electrocatalysts because of their earth abundant nature and high electrochemical activity.
Herein, we present the synthesis of few-layer thickness molybdenum disulphoselenides (MoSSe) alloy onto FTO with maximally exposed active edges to possess high electrocatalytic activity for hydrogen evolution reactions (HER) compared to pristine few-layer MoS2. Raman scattering and X-ray diffraction (XRD) analyses were confirmed the MoSSe alloy formation. MoSSe film thickness and their layer structure were evidently demonstrated using atomic force microscope (AFM) and transmission electron microscope (TEM) tools. The few-layer MoSSe alloy showed the enhanced excellent HER catalytic activity in an acidic electrolyte with an onset overpotential potential of 141 mV @ 10 mAcm-2 and Tafel slope of 79 mV decade-1. Moreover, MoSSe alloy film exhibited long time stability over 20 h in acidic solution as electrocatalytic material for HER. Our methodology is provided to synthesis of tunable MoSSe alloy atomic layers which would be open up exciting opportunities for their applications such as in energy storage, electrocatalytic and photo-electrochemical.
8:00 PM - ES03.06.17
Ab Initio Evaluation of Co-Doped TiO2 as a Sustainable Intermediate Band Photovoltaic Material
Katherine Inzani 1 , Sverre M. Selbach 1
1 , Norwegian University of Science and Technology, Trondheim Norway
Show AbstractA global research effort has been dedicated to developing materials based on titanium dioxide (TiO2) for light-driven energy applications. Expanding on this, the stable, non-toxic and low-cost semiconductor TiO2 has here been evaluated as a candidate intermediate band host with co-dopants chromium and nitrogen for third-generation photovoltaics.
The intermediate band concept is one of the most favored for solar cells exceeding the single-gap efficiency limit at a low device cost. A narrow intermediate energy band within a wide-band gap allows efficient utilization of both high and low energy photons with only one additional layer to a conventional p-n junction device. The wide-band gap and high photocatalytic response of the anatase phase of TiO2 place it as a promising host for an intermediate band solar absorber.1 In order to form a mid-gap band, a suitable dopant and high doping concentration are required, but this means that non-radiative recombination is a considerable issue.2 One solution is to utilize co-doping of donor-acceptor combinations, in essence providing built-in passivation.3 Here, chromium and nitrogen are paired as a photoactivity enhancing and reasonable cost first choice.
In order to explore defect engineering in co-doped TiO2, ab-initio methods provide an unparalleled insight into the material properties. We use a multi-level approach to calculate the effect of Cr and N substitution on the anatase and rutile phases of TiO2. The electronic structure is calculated for a range of dopant concentrations using density functional theory with hybrid exchange-correlation functionals to give accurate band structures. Optical properties are evaluated by calculation of the dielectric function and absorption spectra, with local field effects included beyond the random phase approximation (RPA). Furthermore, the relative stabilities of anatase and rutile phases are considered with changing dopant concentration by including high-order correlations in the adiabatic connection fluctuation–dissipation theory with RPA.
Evaluation of effective dopant levels and phase stability is currently being used to guide material synthesis. In addition, this work provides optical constants for input to device level models for solar cell design. There is also a broader scope to this work arising from the implications to complimentary solar energy conversion systems.
1. F. Wu, H. Lan, Z. Zhang & P. Cui, J. Chem. Phys. 137, 104702 (2012).
2. Y. Okada, N.J. Ekins-Daukes, T. Kita, R. Tamaki, M. Yoshida, A. Pusch, O. Hess, C.C. Phillips, D. J. Farrell, K. Yoshida, N. Ahsan, Y. Shoji, T. Sogabe & J.-F. Guillemoles, Appl. Phys. Rev. 2, 021302 (2015).
3. W. Zhu, X. Qiu, V. Iancu, X. Chen, H. Pan, W. Wang, N.M. Dimitrijevic, T. Rajh, H.M. Meyer III, M.P. Paranthaman, G.M. Stocks, H.H. Weitering, B. Gu, G. Eres & Z. Zhang, Phys. Rev. Lett. 103, 226401 (2009).
8:00 PM - ES03.06.18
Growth Mechanism of LiNi1/3 Mn1/3 Co1/3O2 Precursor Particles
Mengyuan Chen 1 , Zhangfeng Zheng 1 , Yubin Zhang 1 , Yan Wang 1
1 Department of Materials Science and Engineering, Worcester Polytechnic Institute, Worcester, Massachusetts, United States
Show AbstractWith the rapid development of mobile devices and electric cars, lithium-ion batteries (LIBs) attract lots of attention. LiNi1/3 Mn1/3 Co1/3O2 (NMC 111), with the advantage of low cost, good stability and high capacity, has been commercialized as cathode material. During the process of synthesize NMC 111, which is characterized by co-precipitation reaction, however, the growth mechanism of precursor particles (Ni1/3 Mn1/3 Co1/3(OH)2) has not been understood well. Here we show the mechanism is that the precursor particles (secondary particles) are formed by the agglomeration of primary particles. X-ray diffraction (XRD) pattern and inductively coupled plasma optical emission spectrometry (ICP-OES) are used to determine the presence of precursor particles. With the development of reaction, the growth mechanism of particles is revealed by tap densities and scanning electron microscope (SEM) images. Our results reveal a general idea of how the precursor particles are formed. We anticipate that this is a starting point of understanding the growth mechanism of co-precipitation reaction. By a clearer view of this reaction, the synthesis of NMC 111 can have better control, and this will keep reducing the production cost and accelerate the development of mobile devices and electric cars.
8:00 PM - ES03.06.19
Layered Sodium Iron Manganese Oxide as a Cathode Material for Sodium-Ion Batteries
Shin Gwon Lim 1 , Mi-Sook Kwon 1 , Kyu Tae Lee 1
1 School of Chemical and Biological Engineering, Seoul National University, Seoul Korea (the Republic of)
Show AbstractLi-ion batteries are one of the most popular power sources for electric vehicles (EV) and large-scale energy storage systems (ESS) because of their excellent electrochemical performance. However, as the cost of Li-ion batteries recently increases, Na-ion batteries have been considered as one of the promising candidates to replace expensive Li-ion batteries. Although Na-ion batteries have a potential advantage in terms of price, the cost per energy ($/Wh) of the current Na-ion batteries is comparable to that of the commercialized Li-ion batteries because the energy density of the current Na-ion batteries is lower than that of Li-ion batteries. Therefore, it is necessary to develop electrode materials with a high reversible capacity to improve the cost per energy of Na-ion batteries. [1-3]
Various layered iron manganese oxides have recently attracted attentions as a promising cathode material for Na-ion batteries because of their high reversible capacities and low cost. The redox couples of sodium iron manganese oxides are Mn3+/Mn4+ and Fe3+/Fe4+, delivering about 180mA h g-1 at relatively high redox potentials. However, their cycle performance is poor because of the phase transition to the Z-phase during charging.
In this presentation, we introduce a new P3-type sodium iron manganese oxides suppressing the phase transition to the Z-phase during cycling. This material showed excellent electrochemical performance including high reversible capacity (~180 mAh/g) and stable cycle performance over 100 cycles. Moreover, we demonstrate the reaction mechanism of the new P3-type sodium iron manganese oxides through ex situ XRD analysis and also clarify the effect of dopants on the reaction mechanism.
Reference
[1] M. Kwon, S. G. Lim, Y. Park, S. Lee, K. Y. Chung, T. J. Shin, K. T. Lee, ACS Appl. Mater. Interfaces, 9 (17) (2017), 14758–14768
[2] Y. Kim, K. H. Ha, S. M. Oh, K. T. Lee, Chem. Eur. J., 20 (2014), 11980
[3] S. Y. Hong, Y. Kim, Y. Park, A. Choi, N. S. Choi, K. T. Lee, Energ. Environ. Sci., 6 (2013), 2067
8:00 PM - ES03.06.20
Sonochemical Preparation of Extremely Small and Amorphous NiFe-based Nanoparticles as Superior Electrocatalysts for Oxygen Evolution Reaction
Ah-hyeon Park 1 , Kyung-Ryul Oh 1 , Hyun-Uk Park 1 , Young-Uk Kwon 1
1 , Sungkyunkwan University, Suwon Korea (the Republic of)
Show AbstractHighly active and durable electrocatalysts are required for the development of water electrolysis for renewable energy conversion and storage. Herein, cheap and abundant NiFe-based nanomaterials have been prepared via the one-pot syntheses for oxygen evolution reaction (OER) in alkaline media. By using a simple sonochemical route, we achieved the preparation of amorphous and composition tunable NiFe-based nanomaterials which are received lots of attentions as desirable and novel electrocatalyst with low overpotential for OER. Through the structural characterization, we found that these materials have extremely small particle size and homogeneous elemental compositions. Electrochemical analysis also showed that the OER activity of samples exhibit the volcano-type trend according to adjusting of Fe content. Among them, Ni70Fe30 sample showed overpotential of 292 mV at 10 mA cm-2geo and Tafel slope of 30.4 mV dec-1, which outperform that of IrOx/C (326 mV, 41.7 mV dec-1). Chronopotentiometry at 10 mA cm-2geo for 2 h of samples for durability test reveals that Ni70Fe30 sample maintains the steady-state potential compared with that of IrOx/C, meaning an excellent durability of our samples. This work demonstrates that sonochemical syntheses could be novel approach to prepare superior and durable OER electrocatalyst for water electrolysis and metal-air battery.
8:00 PM - ES03.06.21
Crystal and Electronic Structure of Quaternary Narrow Gap Oxide Semiconductor Cu2ZnGeO4 with a Wurtzite-Derived Structure
Masao Kita 1 , Issei Suzuki 2 , Makoto Inoue 1 , Takahisa Omata 3
1 Department of Mechanical Engineering, National Institute of Technology, Toyama College, Toyama City Japan, 2 Institute of Materials Science, Technical University of Darmstadt, Darmstadt Germany, 3 Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai Japan
Show AbstractTernary I–III–O2 semiconductors with a wurtzite-derived β-NaFeO2 structure have recently attracted attention as the oxide semiconductors, of which the band gap covers wide wavelength region from near-infrared to ultraviolet [1,2]. Among them, β-CuGaO2 is a promising material as thin-film solar cell absorbers because of its direct and 1.47 eV of energy band gap that matches the required energy to achieve the theoretical maximum conversion efficiency for a single-junction solar cell [3]. In this work, we further explored new materials applicable to solar cell absorbers in multinary oxides with wurtzite-derived structure, and found quaternary Cu2ZnGeO4 that possesses 1.4 eV of energy band gap. Its crystal structure was refined by Rietveld method, and the electronic structure was studied by the first principles calculations.
Three types of structure, which differ each other in cation ordering patterns, is known as the quaternary wurtzite-derived structure, such as wurtz-kesterite type (space group P1c1), Lithium cobalt slicate type (space group Pna21), and wurtz-stannite type (space group Pmn21). The Rietveld analysis assuming wurtz-kesterite structure, in which divalent Zn2+ and tetravalent Ge4+ ions occupy the trivalent cation site in β-NaFeO2, gave the best fit among these three types of structure. The structural distortion of MO4 tetrahedra (M=Cu, Zn, Ge) from the regular tetrahedron in the Cu2ZnGeO4 was large as compared to that in ZnO and β-CuGaO2, because this material consists of three kinds of cation with different sizes. This suggests indirect band gap of the Cu2ZnGeO4 based on the relationship between the tetrahedral distortion and band gap nature in multinary wurtzite oxide semiconductors [4].
In terms of the electronic structure, the conduction band minimum (CBM) of Cu2ZnGeO4 is located at Γ point while the valence band maximum (VBM) is located at intermediate point between Γ and B points. Cu2ZnGeO4 is, therefore, an indirect semiconductor as suggested its crystal structure unlike the β-CuGaO2 [5]. However, the energy difference between the VBM and the Γ point in the valence band is very small as 0.001 eV. This suggests that Cu2ZnGeO4 exhibits intense light absorption near the band edge. These features indicate that the quaternary Cu2ZnGeO4 is applicable to thin-film solar cell absorber.
[1] Omata et al., Sci. Technol. Adv. Mater., 16 (2015) 024902
[2] Suzuki and Omata, Semicond. Sci. Technol., 32 (2017) 013007
[3] Omata et al., J. Am. Chem. Soc., 136 (2014) 3378
[4] Nagatani et al., Inorg. Chem., 54 (2015) 1698
[5] Suzuki et al., J. Appl. Phys., 119 (2016) 095701
8:00 PM - ES03.06.22
Molten Salt Assisted Self-Assembly—Synthesis of Mesoporous Transition Metal Oxide Thin Films
Muammer Yaman 1 , Omer Dag 1 , Nesibe Akmansen 1 , Assel Amirzhanova 1 , Irmak Karakaya 1
1 , Bilkent University, Ankara Turkey
Show AbstractTransition Metal Oxides (TMO) have wide application fields including catalysis, energy conversion and storage, and sensoring (1). There are lots of attempt to make TMOs mesoporous, because they have high surface area and open pores. Using soft templating (evaporation-induced self-assembly (2), true liquid crystal templating (3)) and hard templating method (4), some of mesoporous TMOs powder have been synthesized. Here, we introduce a new process (Molten Salt Assisted Self-Assembly (MASA)), which is a unique and more practical method for synthesis of mesoporous TMO thin films. In MASA approach, two surfactants (cetyltrimethylammonium bromide (CTAB) and 10-lauryl ether (C12EO10)) as templating agent and transition metal salts in molten phase are used. After coating the clear solution over substrate (glass, FTO), liquid-crystalline mesophase forms with only molten salts and surfactants. At high temperature, the surfactant molecules burn out and the mesoporous thin films of TMOs (Fe2O3, NiO, CuO and ZnO) are obtained. The particle size of the TMOs is around 10 nm with a high surface area. However, iron oxide forms smaller pores, around 3nm with a pore wall of around 3-4 nm, which is optimum for the hole diffusion length of iron oxides (LD = 2–4 nm). Calcination temperature control the crystallinity and porosity of products. Formation mechanism of iron oxide has been evaluated by monitoring nitrate peaks in IR spectra. The materials, in all stages of fabrication, were characterized using XRD, UV-Vis absorption, FT-IR, Raman, SEM, TEM, N2 sorption techniques.
1) Ren, Y.; Ma, Z.; Bruce, P. G. Ordered Mesoporous Metal Oxides: Synthesis and Applications. Chem. Soc. Rev. 2012, 41, 4909−4927
2) Brinker, C. J.; Lu, Y.; Sellinger, A.; Fan, H. Evaporation-Induced Self-Assembly: Nanostructures Made Easy. Adv. Mater. 1999, 11, 579− 585
3) Huo, Q.; Margolese, D. I.; Ciesla, U.; Feng, P.; Gier, T. E.; Sieger, P.; Leon, R.; Petroff, P. M.; Schuth, F.; Stucky, G. D. Generalized Synthesis of Periodic Surfactant/Inorganic Composite Materials. Nature 1994, 368, 317−321
4) Petkovich, N. D.; Stein, A. Controlling Macro- and Mesostructures with Hierarchical Porosity through Combined Hard and Soft Templating. Chem. Soc. Rev. 2013, 42, 3721−3739
5) Kennedy, J. H.; Frese, K. W., Photo oxidation of Water at Fe2O3 Electrodes J. Electrochem. Soc. 1978, 125, 709–714
8:00 PM - ES03.06.23
Pyrophosphate Based Materials as a New Oxygen Evolution Catalyst
Hyunah Kim 1 , Jimin Park 2 , Ki Tae Nam 1 , Kisuk Kang 1
1 , Seoul National University, Seoul Korea (the Republic of), 2 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractSplitting water into hydrogen and oxygen molecules via solar energy has been considered as one of the most environmentally-friendly ways to effectively utilize renewable energy resources from harvest to redistribution. Although it has been studied for more than a half century, oxygen evolution reaction (OER) are still regarded as a bottleneck in integrating overall water splitting system. The noble-metal catalysts such as Pt and IrOx showed outstanding OER catalytic activity, however the high costs remain as limitation. In this regard, the development of cost-effective, abundant-element based, and efficient OER catalyst is highly demanded.
Inspired from the Mn4CaO5 cluster in nature which shows remarkable catalytic performance, previous researches pointed out the importance of Mn(III) in water oxidation reaction. However, it is hard to know the role of manganese valency itself, because the structure of the catalyst always changed significantly as the valency changed. Herein, we selected a new pyrophosphate-based manganese compound as a model system, and obtained Li2-xMnP2O7 by delithiation with minimal crystallographic change. We observed that as the averaged oxidation state of manganese increases from 2 to 3, the catalytic performance enhanced. Therefore, we were able to observe the effect of valency state itself on catalysis.1
Moreover, although the coordination of the transition metal in the catalysts is believed to greatly affect the catalytic activity, there is a lack of systematic information relating the local cobalt coordination to the OER catalysis. Therefore, we selected four cobalt-based phosphate catalysts with various cobalt- and phosphate-group coordination as a platform to better understand the catalytic activity of cobalt-based materials. While they exhibit various catalytic activities during water oxidation, Na2CoP2O7 with distorted cobalt tetrahedral geometry shows high activity, along with high structural stability. First-principles calculations suggest that the surface reorganization by the pyrophosphate ligand induces a highly distorted tetrahedral geometry, where water molecules can favorably bind, resulting in a low overpotential.2
In conclusion, through a combination of experiments and density functional theory calculations, we observed the roll of transition metal valency state in water oxidation reaction. Also, we observed the importance of local coordination in the catalysis and were able to suggest the possible effect of polyanions on the water oxidation chemistry. We expect that our study provides valuable guidelines for developing an efficient oxygen evolution catalyst under neutral conditions.
References
1. Hyunah Kim et al. A new water oxidation catalyst: lithium manganese pyrophosphate with tunable Mn valency. J. Am. Chem. Soc. 136, 4201–4211 (2014).
2. Hyunah Kim et al. Coordination tuning of cobalt phosphates towards efficient water oxidation catalyst. Nat. Commun. 6, 8253 (2015).
8:00 PM - ES03.06.24
In Situ Observation of Phosphate and Borate Ions Adsorbing onto Cobalt Oxygen Evolving Catalysts
Hirokatsu Kurosu 1 , Masaaki Yoshida 1 , Hiroshi Kondoh 1
1 Chemistry, Keio University, Yokohama, Kanagawa, Japan
Show AbstractIntroduction
Recently, the cobalt phosphate (Co-Pi) and cobalt borate (Co-Bi) were reported as efficient and inexpensive OECs.1 Although the difference between Co-Pi and Co-Bi is only buffer solutions for electrodeposition and electrochemical measurements, Co-Bi clusters are larger and more active on water oxidation reaction than Co-Pi clusters.1 It is suggested that electrolyte relates with the OER activity and catalyst formation.2 In this study, we investigated the behavior of phosphate and borate anions adsorbed on Co-OECs during water oxidation reaction by in-situ P K-edge XAFS and attenuated total reflection infrared spectroscopy (ATR-IR) measurements in the scope of elucidating the role of electrolytes.
Experimental
Co-Pi and Co-Bi were electrodeposited on the working electrodes in potassium phosphate (KPi) and potassium borate (KBi) buffers (pH 9.0), respectively, containing 0.5 mM cobalt nitrate at the applied bias of 1.7 V vs. RHE. After exchanging the electrolyte solutions to those not containing cobalt ion, in-situ XAFS and ATR-IR measurements were performed at BL-9A in Photon Factory (PF) with fluorescence mode and using a fourier transform infrared spectrometer, respectively.
Results and Discussion
To investigate the relationship between electrolytes and OER activity, the catalytic activities for Co-Pi and Co-Bi OECs were examined by exchanging electrolyte solutions from KPi to KBi and from KBi to KPi, respectively. In the case of Co-Pi OEC, the OER activity was almost the same between KPi and KBi buffers. On the other hand, in the case of Co-Bi OEC, the OER activity decreased by exchanging the electrolyte solution from KBi to KPi buffer.
Next, we measured in-situ P K-edge XAFS and ATR-IR spectra for Co-Pi OEC. The peaks attributed to phosphate ion were observed for both measurements and the peak positions slightly shifted by changing the applied electrode potential, indicating that phosphate ion adsorbs on the Co-Pi clusters even during the OER process. In the similar way, the peak attributed to borate ion was also observed by in-situ ATR-IR measurements for Co-Bi.
Moreover, to discuss the difference of adsorption force between phosphate and borate ions, we exchanged the electrolyte solution of in-situ ATR-IR measurement for Co-Pi or Co-Bi from KPi to KBi or from KBi to KPi, respectively. In the case of Co-Pi, the peak of adsorbed phosphate ion did not change even though the electrolyte solution was exchanged from KPi to KBi. Meanwhile, in the case of Co-Bi, the peak of adsorbed borate ion was partially replaced to that of adsorbed phosphate ion, probably implying that the adsorption force of phosphate ion was stronger than that of borate. Therefore, we think that phosphate ion is likely to inhibit the OER by binding to the terminal of Co-OECs because of the strong adsorption force.
References
1. S. J. L. Billinge et al., J. Am. Chem. Soc., 2013, 135, 6403-6406.
2. D. G. Nocera et al., J. Am. Chem. Soc., 2012, 134, 6326-6336.
8:00 PM - ES03.06.25
Ternary FeNiP with Hierarchical Nanoarchitecture Wrapped Seamlessly in Conductive Carbon Network for Water Electrolysis
Bowei Zhang 1 , Shan Hu 1
1 Department of Mechanical Engineering, Iowa State University, Ames, Iowa, United States
Show AbstractThe electrolysis or photoelectrolysis of water to generate oxygen and hydrogen gas is a promising way to convert intermittent renewable energy into fuels for effective energy storage and delivery. For efficient (photo)electrochemical water splitting, there is a critical need for highly active, robust, and earth-abundant electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) to replace the expensive Pt/Ru based catalysts. Herein, we fabricated ternary iron nickel phosphide (FeNiP) (Fe/Ni mole ratio ~ 0.4) with hierarchical porous structure for OER and HER catalyst. The unique structure of the FeNiP is built on Ni foam (NF) and consists of flower-like spheres supported on nanosheets array, all of which is wrapped seamlessly inside a conductive carbon shell (FeNiP@C/NF). The conductive carbon shell provides direct electron transport path to the porous 3D-structured catalyst. Several beneficial effects are provided by this unique structure, including large active surface area, fast charge transfer between the electrolyte and catalyst, interconnected channels for facile mass transport, and open structure for rapid release of final gas products. The FeNiP@C/NF shows enhanced HER and OER performances in 1M KOH compared to FeNiP/NF, making it among the most efficient earth-abundant catalyst for water electrolysis.
8:00 PM - ES03.06.26
Low Bubble-Escape Resistance of Non-Woven Stainless Steel Fabrics for Efficient Water Splitting
Ling Wang 1 , Xiaolei Huang 1 , Jun Min Xue 1
1 , National University of SIngapore, Singapore Singapore
Show AbstractWater electrolysis has been considered as one of the most efficient approaches to produce renewable energy, while the development of highly efficient and durable bifunctional electrocatalysts for both hydrogen and oxygen evolution is still challenging. Appropriate pore structure design and efficient removal of gas bubbles attached onto the electrode surface could further improve the efficiency of water oxidation. Herein, a novel designed strategy is developed to improve electrocatalytic activity through reducing contact area between as-obtained bubbles and electrode. The prepared superaerophobic electrode with thin stainless steel fibres could fastly remove bubbles on the electrode during the process of water splitting, and exhibites excellent electrocatalytic performance for both OER and HER, with low overpotentials of 230 and 110 mV at the current density of 10 mA cm-2 in 1 M KOH for OER and HER, respectively. And there is almost no current drop after long-time durability test. In addition, its performance for full water splitting is superior to those reported catalysts, with a voltage of 1.56 V at current density of 10 mA cm-2.
8:00 PM - ES03.06.27
Printable Additive Free Manganese Dioxides Based Na-Ion Battery Anodes with Aesthetic Versatility
Jiasheng Qian 1 , Shu Ping Lau 1
1 , Hong Kong Polytech University, Hong Kong Hong Kong
Show AbstractDue to the abundant and even distribution of Na reserves as compared to Li, Na-ion batteries are potential alternative for the current dominant Li-ion batteries. A mass production of the Na-ion battery anode with low cost, satisfied discharge capacity, long- term cyclic life as well as high rating capability is highly sought. We report an additive free Na-ion battery anode based on the MnO2 thin film on commercially available substrates by spray-printing technique. The as-prepared thin films exhibit aesthetic versatility and exceptional endurance to various common solvents. The MnO2 anode can reach a discharge capacity of 177 mAh g-1 at 1 A g-1 after 500 cycles and remain at 130 mAh g-1 even at 10 A g-1. The long-term cyclic performance and enhanced rating capability could be attributed to the nano-sized MnO2 and the merits of the ether based electrolyte. The unprecedented electrochemical properties of the MnO2/Na cell pave the way for the large-scale production of future printable, rechargeable and high performance power sources.
8:00 PM - ES03.06.28
High-Temperature Semiconductor Behavior in Disordered Ferromagnetic Fe-Tb-Dy-Oxide (FTDO) Thin Films
Alexandra Waters 1 , Tatiana Allen 1 , Humaira Taz 2 , Tamil Sakthivel 3 , Sudipta Seal 3 , Ramki Kalyanaraman 2 4 5
1 Department of Chemistry and Physics, University of Tennessee, Chattanooga, Chattanooga, Tennessee, United States, 2 Bredesen Center, University of Tennessee, Knoxville, Knoxville, Tennessee, United States, 3 Advanced Materials Processing and Analysis Center (AMPAC), NanoScience Technology Center (NSTC), Materials Science and Engineering (MSE) Department, Orlando, Florida, United States, 4 Department of Materials Science and Engineering, University of Tennessee, Knoxville, Knoxville, Tennessee, United States, 5 Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Knoxville, Tennessee, United States
Show AbstractIron oxide is one of the most prevalent oxides on Earth. Recently, iron–based oxide thin films containing two lanthanides, terbium and dysprosium, have been reported to show a remarkable combination of amorphous microstructure with very high optical transparency, electrical conductivity, and Hall mobility [1, 2]. In addition, room temperature ferromagnetism can also be obtained by tuning the R-value, the atomic ratio of iron to the two lanthanides, during the deposition [2]. This makes the material a potential candidate for a wide range of applications in energy conversion, electronics, photonics, and spintronics.
Here we report the evolution of transport behavior in highly disordered thin films prepared by e-beam evaporation and having R-values of up to 21, as confirmed by energy dispersive X-ray spectroscopy. The conductivity evolved from metallic to semiconductor behavior, over the course of repeated thermal cycling between 300 to 700 K under a low pressure of 5 mTorr. This metal to insulator transition was attributed to oxidation of the films, as verified by measuring the metal cation states and oxygen state by x-ray photoelectron spectroscopy.
For the films with R=21, the temperature dependence of resistivity in the semiconductor state between 300 K to 700 K showed evidence for intrinsic, extrinsic and ionization regimes. In the same temperature range, the Hall mobility showed a maximum at ~500 K that is reminiscent of the temperature-dependence of scattering observed in semiconductors. The carrier concentration changed from a weak temperature dependence below 500 K to a strong one above it, analogous to the change from an extrinsic to intrinsic charge carrier behavior. The Hall mobility of the semiconductor state indicated p-type carriers with a room temperature value of 27 cm2/V-s. The semiconductor state also displayed room temperature ferromagnetism measured by surface magneto-optical Kerr effect, and retained its largely disordered microstructure confirmed by grazing incidence x-ray diffraction.
This work provides evidence for an interesting class of disordered materials made from the iron-lanthanide-oxygen system. The material appears suitable to be used as a high temperature disordered semiconductor with exceedingly high Hall mobility and p-type conductivity. It could find applications in high temperature environments as well as in harsh environments, such as in space, where the combination of disordered structure and high temperature stability could reduce the risk of radiation damage.
1. Malasi A. et al. Novel Iron-based ternary amorphous oxide semiconductor with very high transparency, electronic conductivity, and mobility. Sci. Rep. 5, 18157; doi:10.1038/srep18157(2015).
2. Taz, H. et al. Transparent ferromagnetic and semiconducting behavior in Fe-Dy-Tb based amorphous oxide films. Sci. Rep. 6, 27869; doi: 10.1038/srep27869 (2016).
8:00 PM - ES03.06.29
Impact of Sn Addition on Crystal Structure and Optical Properties of Chemically Deposited Sb2S3 Thin Films
Enue Barrios Salgado 1 , Judith Moraga 1 , Yamilet Rodriguez 1 , Juan Pablo Pérez-Orozco 2 , Sarah Messina 1
1 , Universidad Autonoma de Nayarit, Tepic Mexico, 2 Ingeniería Química y Bioquímica, Instituto Tecnológico de Zacatepec, ZACATEPEC, MORELOS, Mexico
Show AbstractSb2S3 thin films were successfully deposited on SnS thin film by chemical bath deposition and heated in argon atmosphere to produce Sb2S3:Sn thin films. Their structural and optical properties were studied by X-ray diffraction and transmittance and reflectance measurements in the wave length range 190–1100 nm. X-ray diffraction (XRD) patterns indicate the polycrystallinity of the films after heating. All the samples show high absorption coefficient of almost 104 cm-1 in the visible region, which is a good advantage for solar cell application. The optical bandgap of the Sb2S3:Sn thin films is between 1.64 and 1.92 eV depending on the quantity of Sn and heating temperature. The electrical conductivity is in the range of 10-8 to 10-7 Ω−1 cm−1. We present a novel approach for the addition of tin in antimony sulphide thin films for photovoltaic application.
8:00 PM - ES03.06.30
Structural and Optical Properties of PbSe Thin Films Grown by Microwave Technique
Yamilet Rodriguez 3 , Enue Barrios Salgado 3 , Sarah Messina 3 , Eliseo Llamas 1 , Rocio Castaneda 2 , Jose Campos Alvarez 4
3 , Universidad Autonoma de Nayarit, TEPIC Mexico, 1 , Instituto Tecnologico de Tepic, Tepic Mexico, 2 , Universidad de Guadalajara, GUADALAJARA Mexico, 4 , Instituto de Energías Renovables, Universidad Nacional Autónoma de México, Morelos Mexico
Show AbstractPbSe thin films were obtained by microwave assisted chemical bath deposition. To promote adhesion to the substrate a very thin film of ZnS was chemically deposited previously. PbSe samples were prepared at different temperature and deposition time. Their structural and optical properties were studied by X-ray diffraction, XRD, transmittance and reflectance measurements and energy-dispersive X-ray spectroscopy, SEM-EDS. The surface morphology was analyzed by atomic-force microscopy, showing that the layers have uniform surface morphology and good quality over the entire sample. The thermoelectric measurements have shown p-type conductivity. Optical measurements show that thin films have relatively high absorption coefficients between 104 and 105 cm-1 in the visible range. The optical band gap was found to be increase from 0.5 to 2.0 eV as particle size decreases.
8:00 PM - ES03.06.31
Kinetic Models of the Hydrogen Evolution Reaction on Transition Metal Phosphide Surfaces
Chenyang Li 1 , Hao Gao 1 , Wan Wan 1 , Tim Mueller 1
1 Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractThe hydrogen evolution reaction (HER) constitutes half of the water splitting reaction, which could produce H2 from renewable energy resources, and therefore reduce the demand for fossil fuels. Transition metal phosphides (TMPs) have emerged as promising HER catalysts made from earth-abundant materials. TMP surfaces typically have a variety of symmetrically distinct sites that may be catalytically active, and the hydrogen adsorption energy, an important descriptor of catalytic activity, has been shown to strongly depend on the coverage of adsorbed hydrogen on these surfaces. However the structure of hydrogen adsorbed on TMP surfaces is largely unknown, limiting our understanding of the catalytic properties of these surfaces. To address this problem, we have used cluster expansions to determine the atomic-scale structure of hydrogen on four different TMP surfaces: FeP(011), Fe2P(100), CoP(101), and Co2P(101). For reference, we also constructed a cluster expansion for hydrogen adsorption on the widely-studied Pt(111) surface. These cluster expansions allow us to identify the structure and energetics of adsorbed hydrogen as a function of temperature, applied potential, and hydrogen chemical potential. We present the results of cluster-expansion-based kinetic models that allow us to better understand the catalytic properties of TMP surfaces.
8:00 PM - ES03.06.32
Selenobenzoate Metal Complexes for Synthesis of Anisotropic Metal Selenide Nanomaterials and Thin Films by AACVD—Potential Materials for Water Splitting
Neerish Revaprasadu 1 , Malik Khan 1 2 , Mohammad Azad Malik 2
1 , University of Zululand, Empangeni South Africa, 2 , The University of Manchester, Manchester, Lincolnshire, United Kingdom
Show AbstractThe development of reliable and efficient strategies for artificial photosynthesis is an intensive research focus over the last decade. Water splitting using nanostructures avoiding precious metals such as platinum, gold and ruthenium is highly desirable to meet the competitive market demands. The development of materials with surface chemistry that can have better charge carrier life times and electrical capabilities is very significant for H2 production from water.1,2 Anisotropic semiconductors such as, SnSe, Sb2Se3 and Bi2Se3 are abundant in geosphere and have attractive thermoelectric and electrical conductivity properties.3,4
Herein, we report an efficient synthesis of new seleno-benzoate complexes of tin, antimony and bismuth, the X-ray structure of tris(selenobenzoato)antimony(III) and their use as single source precursors for the synthesis of the corresponding metal selenide nanoparticles by the hot injection method and thin films were deposited by aerosol assisted chemical vapor deposition. Sb2Se3 nanorods and Bi2Se3 nanosheets were used as low cost nanomaterials for the photoelectrochemical (PEC) production of H2 from water under sunlight illumination. When simulated solar light was illuminated at the Sb2Se3/FTO or Bi2Se3/FTO surface, cathodic photocurrents were generated for H2 generation. At open circuit potential (OCP) photo-cathodic current generated with the Sb2Se3/FTO electrode was in the range of -44.8 to -52.1 μA.cm-2 while with Bi2Se3/FTO the photo-cathodic generated was in the range -48.5 to -56.3 μA.cm-2. The current generated at OCP was only due to the illuminated light and not due to any intrinsic properties of the Sb2Se3 nanorods or Bi2Se3 nanosheets.
References
[1] J. Azevedo, S. D. Tilley, M. Schreier, M. Stefik, C. Sousa, J. P. Araújo, A. Mendes, M. Grätzel and M. T. Mayer, Nano Energy, 2016, 24, 10-16.
[2] M. G. Walter, E. L. Warren, J. R. McKone, S. W. Boettcher, Q. Mi, E. A. Santori and N. S. Lewis, Chem. Rev., 2010, 110, 6446-6473.
[3] K. Zeng, D.-J. Xue and J. Tang, Semicond. Science Technol., 2016, 31, 063001.
[4] R. J. Mehta, C. Karthik, W. Jiang, B. Singh, Y. Shi, R. W. Siegel, T. Borca-Tasciuc and G. Ramanath, Nano Lett., 2010, 10, 4417-4422.
8:00 PM - ES03.06.33
Fabrication of NiO-Related Invisible Solar Cells Supplying Power for Integrated Invisible Gas Sensors Using NiO and SnO2
Ryo Tanuma 1 , Hikaru Haga 1 , Yusuke Ohteki 1 , Mutsumi Sugiyama 1
1 , Tokyo University of Science, Noda Japan
Show AbstractTransparent conducting oxide (TCO) films such as NiO and SnO2 exhibit p-type and n-type conductivity, respectively, and are composed of earth-abundant and less-toxic elements. In addition, these TCOs are chemically and environmentally stable. In recent years, we have been studying NiO based p-type TFTs [1] and visible-light-transparent solar cells [2] installed on the walls or ceilings of buildings and greenhouses. It is possible to create a power-supplying device for invisible multi-functional devices using TCOs. We have proposed a combined device called “intelligent window” or “intelligent greenhouse,” where invisible solar cells [2] supply a small amount of electrical power for invisible sensors. Among them, the invisible gas sensor is an essential device for realizing the system. For example, a CO2 sensor is important to control air-quality and growth of plants. NiO and SnO2 thin films have been fabricated using various methods. Among these methods, sputtering is the most suitable for economically depositing large-area films with well-controlled compositions. In this presentation, we propose an integrated device with a NiO-based solar cell, SnO2-based CO2 sensor, and NiO-based H2 sensor, deposited using conventional RF sputtering.
Polycrystalline 5-20-nm-thick NiO:Li and 500-nm-thick ZnO thin films were deposited by sputtering NiO:Li and ZnO ceramics, respectively. A mixture of Ar and O2 gases was used as the sputtering gas. Invisible solar cells with PEDOT:PSS/NiO:Li/ZnO/TCO/soda-lime glass were fabricated. For integrated CO2 and H2 sensors, polycrystalline undoped n-type SnO2 and p-type NiO thin films with a thickness of approximately 50–400 nm were deposited on the glass, respectively. Then, several types of catalyst solutions were spin-coated on the oxide semiconductors, and they were heated at 100-500 °C for 10–120 min and/or UV-treated.
The fabricated solar cells exhibited a photovoltaic effect under illumination. In addition, an optical transmittance of the solar cell, and several of the sensors, greater than 80% was obtained in the wavelength range of 400–800 nm. These results are attractive because the optical transparency of the sensors and solar cells allow for greater flexibility in their installation locations. The resistivity of the CO2 and H2 sensors that were fabricated using Ag/Au/SnO2 or NiO:catalyst/soda-lime glass, respectively, changed under CO2 or H2 atmosphere. The sensitivity of the sensor changed by varying the catalyst solution concentration. These “invisible solar cells” can supply a small amount of electrical power for several integrated invisible sensors and provide an energy harvest.
[1] Our Group, MRS Fall Mtg., (2014) O9.37.
[2] Our Group, J. Appl. Phys., 52 (2013) 021102.
8:00 PM - ES03.06.34
Effect of Lightweight Porogen Addition on the Microstructure of Tape-Casted MCFC Electrodes
Karol Cwieka 1 , Tomasz Wejrzanowski 1 , Jaroslaw Milewski 1
1 , Warsaw University of Technology, Warsaw Poland
Show AbstractThe microstructure of molten carbonate fuel cell (MCFC) electrodes is characterized by open porosity, mean pore size and its distribution, particularly in terms of sufficient transport of gaseous reactants, removal of products into pore space, and degree of infiltration with the electrolyte. The combination of porosity and mean pore size results in the specific surface area. Moreover, it affects the total length of the triple phase boundary (TPB) – the region where the electrode reactions occur during MCFC operation.
MCFC electrodes are commonly manufactured using tape casting method of nickel powder suspended in the polymeric slurry with additives, followed by firing process in reducing atmosphere. The resulting high porosity and inhomogeneous pore size distribution is intentional in the case of MCFC cathode, since small pores are infiltrated with the electrolyte by capillary forces and large pores provides sufficient mass-transport properties. Porosity and pore size dispersion characteristics can be tailored by addition of appropriate fraction of porogen with defined particle size distribution.
In the present study, we analyzed the addition of polymeric microspheres – a lightweight filler – as the porogen. Polymeric microspheres have several features making them advantageous for this application. The spherical shape makes them easy to characterize through particle size measurements and resemble desired pore shape in the microstructure of MCFC electrodes. Low polymeric content is expected to provide low carbon residue after firing. Thus, several nickel electrodes varied in porogen addition were manufactured herein and then were examined by electron microscopy observations and porosimetry measurements. Single cell performance tests were conducted in operating conditions. The power density of fuel cells with new electrodes is analyzed with respect to their microstructure and the results are presented herewith.
8:00 PM - ES03.06.35
Effect of Sn Composition on Optical and Electric Properties of Amorphous Zn-Sn-O Transparent Conducting Films Prepared by Radio Frequency Magnetron Sputtering
Seol Hee Oh 1 , Aziz Dinia 2 , Abdelilah Slaoui 3 , Gerald Ferblantier 2 , Emilie Steveler 2 , Thomas Fix 2 , William Jo 1
1 , Ewha Womans University, Seoul Korea (the Republic of), 2 , IPCMS, CNRS-Universite de Strasbourg, Strasbourg France, 3 , ICube, CNRS-Universite de Strasbourg, Strasbourg France
Show AbstractZinc tin oxide (Zn-Sn-O, ZTO) multicompound have received extensive attention due to their high optical transmission and high electrical conductivity. In this study, we investigated the compositional dependence on optical and electrical properties of ZTO thin films. The ZTO thin films were prepared by radio frequency (rf) magnetron sputtering at different Sn rf power of 10, 20, 30, 50, 60, and 70 W on glass and p-silicon wafers at 300oC substrate temperature. Crystallinity and composition of ZTO thin films were investigated by symmetric and asymmetric X-ray diffraction θ-2θ scans and scanning electronic microscopy equipped with energy dispersion spectroscopy, respectively. The optical transmittance over 70% in the visible region for all the ZTO films was observed by means of a UV-visible spectrometer. The optical band gap of the ZTO films were changed as a result of the competition between the Burstein-Moss effect and renormalization. The dependence of binding energy was examined by a X-ray photoelectron spectroscopy. An electron concentration in the films and surface work function distribution were measured by a Hall measurement and Kelvin probe force microscopy, respectively. We finally constructed the band structure which contains band gap, work function, and band edges such as valence band maximum and conduction band minimum of ZTO thin films. Our results suggest that ZTO thin film is competitive compared to indium tin oxide, a representative material of transparent conducting oxide in application of optoelectronic devices.
8:00 PM - ES03.06.37
Generalized Geometric Descriptors for Oxygen Reduction Activity on Transition Metal Sulfides
Dilip Krishnamurthy 1 , Venkatasubramanian Viswanathan 1
1 , Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractSabatier-type activity volcano plots have been used to determine optimal adsorption characteristics for maximizing catalytic activity. The rational way to designing catalysts involves identifying the active sites for optimal adsorption strength and then engineering catalyst materials with target active sites. It has been shown that the variation in binding energies across heterogeneous surface sites is strongly dependent on the local environment1. Therefore, catalyst discovery can be accelerated through structure-energy-activity relationships, which allow us to formulate the active site design as merely finding the optimal local coordination environment that maximizes activity. Recently, structure-activity relationships have been developed for metals12, and we extend this approach to obtain a structure-energy-activity relationship for transition metal sulfides. Transition metal sulfides represent an attractive class for ORR3 and their rich phase diagram allows tunability of activity. We employ density functional theory (DFT) to study ORR activity on various transition metal sulfides including nickel, cobalt, molybdenum, ruthenium and titanium sulfides.
We illustrate the robustness of the geometric descriptor for an example class of nickel sulfides4. As observed on metals and metal oxides, we show that there exists scaling between oxygen intermediates, that leads to a volcano relationship for the limiting potential in the OH* adsorption energy. We identify a simplest geometric descriptor using a least-squares approach to obtain the structure-energy descriptor: GOH=0.29(CNS+0.06CNNi), which has excellent predictability (RMSE = 0.16 eV). Therefore, to a first approximation, a simple counting of neighboring atoms around the surface site can be used to screen catalysts. Our analysis suggests that having 3 nearest-shell sulfur atoms leads to high activity for Ni-based sulfides.
We will discuss a generalization of this structure-energy descriptors for transition metal sulfides and the trends in the coefficients will be discussed to formulate a generalized structure-activity descriptor for the transition-metal sulfides class. These coefficients are expected to strongly depend on metal-metal and sulfur-metal bonding characteristics. Identification of structure-activity relationships for classes of compounds allows for rapid identification of candidates and robust activity quantification. This approach will allow for rapid screening within material classes for a variety of reactions.
References:
Calle-Vallejo, F. et al. Science, 350 185 (2015).
Friebel, D., Viswanathan, V. et al. (2012). J. Am. Chem. Soc. 134 9664 (2012).
Behret, H. et al. G. Electrochim. Acta, 20 111 (1975)
Yan, B., Krishnamurthy, D., Hendon, C., Deshpande, S., Surendranath, Y., Viswanathan, V., arXiv:1706.04090 (2017)
Symposium Organizers
Steve Dunn, Queen Mary University of London
Brian Rodriguez, University College Dublin
Henry Sodano, University of Michigan
Matjaz Valant, University of Nova Gorica
ES03.07: Session V
Session Chairs
Joe Briscoe
Robert Sinclair
Wednesday AM, November 29, 2017
Hynes, Level 3, Room 304
8:00 AM - *ES03.07.00
The Versatility of Mesoscopic Solar Cells
Anders Hagfeldt 1
1 , Laboratory of Photomolecular Science, Swiss Federal Institute of Technology Lausanne (EPFL), Lausanne Switzerland
Show AbstractIn our work on solid-state dye-sensitized solar cells (ssDSSC) we have recently [1] shown that copper phenanthroline complexes can act as an efficient hole transporting material. We prepared ssDSCs with the organic dye LEG4 and copper(I/II)-phenantroline as redox system and achieved power conversion efficiencies of more than 11%. Our follow up work on electron transfer studies and device optimization will be presented at the meeting.
In our work on perovskite solar cells (PSC) we have achieved efficiencies above 20% with a mixed composition of iodide/bromide and methyl ammonium/formamidinium [2]. For cells larger than 1 cm2 we recently certified a record efficiency of 19.6% [3], replacing the anti-solvent step in the perovskite film formation with a vacuum flash treatment. With the use of SnO2 compact underlayers as electron acceptor contacts we have constructed planar perovskite solar cells with a hysteresis free efficiency above 20% [4]. Recently, we have taken the cation mixing of the perovskite film further by including the Cs+ in a so-called ‘triple cation’ composition, i.e. Cs/FA/Ma. Larger grains grown in a monolithic manner are observed and for example reproducibility and device stability are improved [5]. At the meeting we will discuss our follow up works [6] and present our champion data; up to 22% efficiency with an external electroluminescence of 4%, and an outstanding open-circuit voltage of 1.24 V at a band gap of 1.63 eV entailing one of the smallest loss-in-potential of 0.39 V ever measured for any solar cell material. Furthermore, we will report a breakthrough in stability at 85 oC for 500 h under full solar illumination and maximum power point tracking (during which 95% of the initial performance was retained).
References
[1] Freitag et al., Energy & Envir. Sci., DOI: 10.1039/C5EE1204J
[2] Bi et al., Science Advance, DOI: 10.1126/sciadv.1501170
[3] X. Li et al., Science, DOI:10.1126/science.aaf8060
[4] Correa et al., Energy & Envir. Sci., DOI:10.1039/C5EE02608C
[5] M. Saliba et al., Energy & Envir. Sci., 2016, DOI: 10.1039/C5EE03874J
[6] M. Saliba et al., Science 10.1126/science.aah5557 (2016)
8:30 AM - *ES03.07.01
Achieving High Visible-Light Activity for ZnS Photoelectrodes
Judy Hart 1 , Fran Kurnia 1 , Collin Park 1 , Jeremy Bogovac 1 , Yun Hau Ng 2 , Nagarajan Valanoor 1
1 School of Materials Science and Engineering, University of New South Wales, Sydney, New South Wales, Australia, 2 School of Chemical engineering, University of New South Wales, Sydney, New South Wales, Australia
Show AbstractPhotoelectrochemical water splitting is a promising method for allowing solar energy to be stored in chemical form. ZnS is an appealing photoelectrode material for water splitting because it has high activity for hydrogen evolution without requiring the assistance of a precious metal co-catalyst [1]. However, it has a band gap that is too large for absorption of visible light and hence it has low efficiency under sunlight.
In this work, thin films of ZnS have been fabricated by pulsed laser deposition. The effect of deposition conditions, particularly background gas pressure, on the the film’s mophology and optoelectronic properties have been investigated. It is found that the presence of background gas during deposition can lead to films with increased surface roughness that contain defects. These defects can allow absorption of visible light, which in combination with the high surface roughness, result in good visible-light photoelectrochemical activity [2].
Based on previously published density functional theory calculations, which showed that the addition of a small amount of GaP to ZnS could significantly reduce the band gap [3], we have also investigated the photoelectrochemical activity of ZnS-GaP multilayered films. It is found that the presence of interfaces between layers of GaP and ZnS can enhance the photocurrent produced under visible-light irradiation.
1. J.-F. Reber and K. Meier. J. Phys. Chem., 1984, 88, 5903-5913.
2. F. Kurnia, Y. H. Ng, R. Amal, N. Valanoor, and J. N. Hart, Sol. Energy Mater. Sol. Cells, 2016, 153, 179-185.
3. J. N. Hart and N. L. Allan, Adv. Mater., 2013, 25, 2989-2993.
9:00 AM - ES03.07.02
A High Performance Lithium-Oxygen Battery Working in Real Air Environment
Baharak Sayah Pour 1 , Pedram Abbasi 1 , Mohammad Asadi 1 , Larry Curtiss 2 , Amin Salehi-Khojin 1
1 , University of Illinois at Chicago , Chicago, Illinois, United States, 2 , Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractEnergy storage has become a global concern due to ever-growing demand for reliable, large-scale and safe energy resources. Current constraints of traditional energy resources specifically environmental concerns have led to increasing need to clean energy resources. Lithium-air batteries are considered as a promising alternative to Lithium-ion batteries due to their high theoretical specific energy1. However, the cyclability and stability of Li-air batteries still remain an issue in presence of the air components such as nitrogen, oxygen, carbon dioxide, and humidity; due to slow kinetics and clogging in air cathode, degradation of anode, and decomposition of electrolyte2,3.
Here, we present an integrated Li-air battery system consisting of a protected anode, a bi-functional air cathode based on Molybdenum disulfide catalyst, and a mixture electrolyte working in presence of the real air components (N2, O2, CO2, and H2O). This system shows a high cyclability up to 550 cycles with the capacity of 500 mAh/g. Different characterizations including differential electrochemical mass spectroscopy (DEMS), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy on the cathode reveal that the only discharge product in our system is lithium peroxide (Li2O2) without any evidence of side products e.g., lithium hydroxide (LiOH) and lithium carbonate (Li2CO3). Nuclear magnetic resonance (NMR) results also show the stability of the electrolyte after 550 cycles. DFT calculations show that there is no reaction involving other species such as CO2 and H2O due to the combination of MoS2 cathode and mixture electrolyte which make the system kinetically favorable for Li2O2 formation.
The Li-air system studied here is a key step toward the development of next generation of lithium batteries with higher energy density.
References:
1. Aurbach, D., McCloskey, B. D., Nazar, L. F. & Bruce, P. G. Advances in understanding mechanisms underpinning lithium–air batteries. Nat. Energy 1, 16128 (2016).
2. Geng, D. et al. From Lithium-Oxygen to Lithium-Air Batteries: Challenges and Opportunities. Adv. Energy Mater. 201502164, 1–14 (2016).
3. Gallagher, K. G. et al. Quantifying the promise of lithium–air batteries for electric vehicles. Energy Environ. Sci. 7, 1555 (2014).
9:15 AM - ES03.07.03
Mechanism of Heterogeneous Catalysis in the Solar Thermochemical Decomposition of SO3—An Uncommon Energy Storage Opportunity
Levi Irwin 1
1 ManTech International Corp., Contracted to US DOE, Washington, District of Columbia, United States
Show AbstractThe chemical mechanism by which SO3 is thermally decomposed into SO2 is critically examined. As a surface-catalyzed heterogeneous process the impact of catalyst identity, catalyst and support configuration, as well as the character of energy input to this endothermic reaction is described through relation to other modern works. The insight thus provided, especially from the ‘frustrated rotation’ mechanism for decomposing formate in the fuel cell industry, allows us to put forth several strategies for enhancing a solar thermochemical reactor’s capability to selectively ‘crack’ SO3 into SO2. Achieving this enhancement, whilst preserving a high energetic and exergetic reactor efficiency, could open a significant opportunity to meet the renewable energy needs of the United States via a National Solar Thermochemical Cycle.
Sulfur is a good choice for a National Solar Thermochemical Cycle. It binds a renewable energy source (solar thermal) into a form that is easy to transport and easy to store (indefinitely); it also leverages infrastructure that already exists on a national scale. There are major sulfur/sulfuric acid operations in 29 of the United States. These plants create sulfuric acid by combusting sulfur. Sulfur combustion is an incredibly exothermic process (; -300 kJ/mol) and the ‘waste heat’ is typically converted to steam that is used for other industrial processes, which includes providing thrust to drive antiquated steam turbines to produce electricity [1]. Consequently, many sulfuric acid plants are already connected to the national electricity grid. Chemically looping sulfur/sulfuric acid through a solar thermal process that has solar thermal cracking and combustion as antipodes in the cycle could covert the industrial heartland of the United States into an array of giant thermochemical batteries driven, in part, by solar energy.
Sulfur is domestically abundant, easy to transport, and it has the potential to proliferate in natural match to growth in the Agricultural and Industrial sectors. The United States Geological Survey has suggested that sulfur reserves in the US are virtually limitless. The US is already engaged in more than 14% of the human-directed sulfur manipulation on the planet [2]. The broad use of sulfuric acid means that few other solar thermal energy storage options offer such opportunity for a natural, market-based pull for their continued advancement. Indeed, a country’s degree of industrialization may be directly correlated to the amount sulfuric acid it produces [2]. New materials and their thoughtful configurations could allow us to exploit the chemical mechanism by which SO3 is ‘cracked’ into SO2 enabling us to bind a source of dispatchable solar thermochemical energy to the very act of industrializing a nation.
[1] Irwin, L. J.; Le Moullec, Y. Science, 356 (6340), 805-806, 2017.
[2] http://minerals.usgs.gov/minerals/pubs/commodity/sulfur
9:30 AM - *ES03.07.04
Environmental Transmission Electron Microscopy of Chemical and Phase Evolution of Amorphous Molybdenum Sulfide Catalysts
Robert Sinclair 1 , Sangchul Lee 1 , Jesse Benck 2 , Ai Leen Koh 1 , Thomas F. Jaramillo 1
1 , Stanford University, Stanford, California, United States, 2 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractAmorphous MoSx is a highly active, earth abundant catalyst for the electrochemical hydrogen evolution reaction (HER). Previous studies have revealed that this material initially has a composition of MoS3, but after electrochemical activation, the surface is reduced to form an active phase resembling MoS2 in composition and chemical state. However, structural changes in the MoSx catalyst and the mechanism of the activation process remain poorly understood. In this study, we employ aberration-corrected transmission electron microscopy (TEM) to image amorphous MoSx catalysts activated under two hydrogen-rich conditions: ex situ in an electrochemical cell and in situ in an environmental TEM. For the first time, we directly observe the formation of crystalline domains in the MoSx catalyst after both activation procedures as well as spatially-localized changes in the chemical state detected via electron energy loss spectroscopy (EELS). It is found that the presence of hydrogen is critical for enabling the restructuring process. Our results suggest that the surface of the amorphous MoSx catalyst is dynamic: while the initial catalyst activation forms the primary active surface of amorphous MoS2, continued transformation to the crystalline phase during electrochemical operation could contribute to catalyst deactivation. These results have important implications for the application of this highly active electrocatalyst for sustainable H2 generation. The role and utility of the environmental TEM will also be discussed.
10:15 AM - ES03.07.05
Ultrafast Carrier Dynamics in BiVO4 Photoanode Material—Interplay between Free Carriers, Trapped Carriers and Low-Frequency Lattice Vibrations
Keith Butler 2 , Benjamin Dringoli 1 , Lite Zhou 1 , Pratap Rao 1 , Aron Walsh 3 , Lyubov Titova 1
2 , University of Bath, Bath United Kingdom, 1 , Worcester Polytechnic Inst, Worcester, Massachusetts, United States, 3 , Imperial College London, London United Kingdom
Show AbstractBiVO4 is an emergent photoanode materials that has a moderate bandgap, high photochemical stability, and band edge positions favourable for water oxidation [1-4]. However, its reported solar-to-hydrogen conversion efficiency BiVO4 photoanodes is still significantly lower than theoretically predicted. The two most important performance limiting factors are significant carrier recombination and low carrier mobility (~ 10-2 cm2/Vs) which is a consequence of strong carrier-phonon coupling, which favors formation of polarons [3].
Understanding the effects of carrier-phonon coupling on dynamics of photoexcited carrier is therefore critical for addressing those limitations and designing higher efficiency photoelectrochemical cells. We have applied time-resolved THz spectroscopy and first-principle phonon spectrum calculations to study ultrafast carrier dynamics and interactions of carriers with lattice vibrational modes in BiVO4[4]. We find that photoexcited holes form bound polaron states. This is accompanies by a lattice distortion and suppression of the Ag phonon mode associated with opposite motion of Bi and VO4 molecular units, which manifests in bleaching of THz absorption by Ag phonons at excitation fluence higher than 1 mJ/cm2. Concurrently, we find that population of polaron states surpasses critical Mott concentration, and a short-lived excess free carriers exhibit Drude conductivity with mobility on the order of 200 cm2/Vs. This demonstration of enhanced transport suggests that engineering of nanostructured BiVO4, with greater surface to volume ratios, in association with optical concentration to achieve enhanced fluence could result in photoanodes with all of the desirable properties of bulk BiVO4, but greatly improved carrier mobilities.
[1] Abdi, F.F.; Han, L.H.; Smets, A.H.M.; Zeman, M.; Dam, B.; van de Krol, R. Nature Communications 2013, 4, 2195.
[2] Zhou, L.; Zhao,C.; Giri, B.; Allen, P.; Xu, X.; Joshi, H.; Titova, L.V.; Rao, P.M. Nano Letters 2016, 16, 3463.
[3] Abdi, F. F.; Savenije, T. J.; May, M. M.; Dam, B.; van de Krol, R. J. Phys. Chem. Lett. 2013, 4, 2752-2757.
[4] Butler,K.T.; Dringoli, B.J.; Zhou, L.; Rao, P.M.; Walsh, A.; Titova, L.V., J. Mater. Chem A 2016, 4, 18516.
10:30 AM - ES03.07.06
Facile Fabrication of MnO2–x@Carbon Nanostructures using Structure-Guided Combustion Waves and Their High-Performance Supercapacitors Application
Dongjoon Shin 1 , Jungho Shin 1 , Hayoung Hwang 1 , Taehan Yeo 1 , Seonghyun Park 1 , Wonjoon Choi 1
1 School of Mechanical Engineering, Korea University, Seoul Korea (the Republic of)
Show AbstractThe fabrication of nanostructured metal oxides with carbon shell is crucial to advancing their electrochemical properties including electric conductivity, charge transfer resistance and capacity in the electrochemical applications such as supercapacitors and batteries. However, manufacturing the micro/nanostructured metal oxides with the desirable structure generally requires complex procedures with high costs and long processing time. Herein, we present a facile one-step fabrication of the core-shell nanostructures of manganese oxides and carbon coatings surrounding them via structure-guided combustion waves (SGCWs). When the chemical fuel is combusted along with the porous networks of nanostructures, it is realized in incomplete combustion through the chemical fuel-wrapped materials. Controlling atmosphere of combustion on MnO2 caused different phase transformation from MnO2 to Mn2O3/Mn3O4/MnO and MnO due to the changes of consumed oxygen in metal oxides. Furthermore, control of the incompletely combusted carbonaceous fuel allowed to synthesize carbon coating layers and to form Mn2O3/Mn3O4/MnO@C and MnO@C as the resulting materials. The supercapacitor electrodes, using those core–shell nanostructures of MnO2-x@C showed better performance in specific capacitance (maximum 438 F/g at 10 mV/s scan rate for Mn2O3/Mn3O4/MnO@C) and long-term stability in electrochemical cycling compared with bare MnO2 nanoparticles. The carbon coatings surrounding MnO2-x nanostructures improved the electrical conductivity of the network of nanostructures and facilitated the reversible redox reaction without degradation during cycling operations. SGCWs are attractive to facile, low-cost, and large-scale fabrication of unique nanostructures of reduced metal oxides and organic material coatings, which could greatly improve the performance of electrochemical applications.
10:45 AM - ES03.07.07
Enhanced Electrical Properties of Thermally Oxidized Cu2O—A Low Cost Light Absorber Material for Solar Cells
Garima Aggarwal 1 , K. R. Balasubramaniam 1
1 , IIT Bombay, Mumbai India
Show AbstractCuprous oxide (Cu2O) is a potential absorber material for the fabrication of low cost solar cell. Thermal oxidation is one of the simplest and cost effective methods to produce phase pure Cu2O exhibiting higher hole mobility. In this study, ultrapure (99.99%) Cu foils of 0.25 mm thickness are processed in three steps to synthesize Cu2O. Firstly, Cu foil is annealed in high vacuum for 1 h at 1000 °C followed by oxidation in dry air (P>1atm) for 2 h at 1000 °C. Finally, the samples are post-annealed in high vacuum for 2 h at 1000 °C. After post- annealing, samples are quenched from 500 °C to room temperature. During the quenching process, a thin layer of CuO forms at the surface, which is later removed through acid cleaning. The structural characterization is investigated by XRD and grain size is observed from optical micrograph. The diffraction pattern shows phase pure Cu2O in predominant (110) orientation. Hall measurement reveals the material to be p-type in nature and resistivity is found to be in the range of 2.6 × 103 to 1.09 × 103 Ω-cm. Mobility of the material is found to be highly dependent on the grain size, wherein Cu2O of ~3000 μm sized grain possesses 319 cm2V−1s−1 and ~200 μm sized grain shows 77 cm2V−1s−1. Pre-annealing and post-annealing of the samples in high vacuum eliminate CuO formation at the surface. The absence of secondary phase particles on the surface leads to the higher growth rate of grains, thereby resulting in larger grains. The higher mobility in the thermally oxidized Cu2O films is attributed to the large grains possessing lesser grain boundaries.
11:00 AM - ES03.07.08
Hybrid Organic-Inorganic Inks Flatten the Energy Landscape in Colloidal Quantum Dot Solids
Mengxia Liu 1 , Oleksandr Voznyy 1 , F. Pelayo Garcia de Arquer 1 , Edward (Ted) Sargent 1
1 , University of Toronto, Toronto, Ontario, Canada
Show AbstractBandtail states in disordered semiconductor materials result in losses in open-circuit voltage (Voc) and inhibit carrier transport in photovoltaics. For colloidal quantum dot (CQD) films that promise low-cost, large-area, air-stable photovoltaics, bandtails are determined by CQD synthetic polydispersity and inhomogeneous aggregation during the ligand-exchange process. Here we introduce a new method for the synthesis of solution-phase ligand-exchanged CQD inks that enable a flat energy landscape and an advantageously high packing density. In the solid state, these materials exhibit a sharper bandtail and reduced energy funnelling compared with the previous best CQD thin films for photovoltaics. Consequently, we demonstrate solar cells with higher Voc and more efficient charge injection into the electron acceptor, allowing the use of a closer-to-optimum bandgap to absorb more light. These enable the fabrication of CQD solar cells made via a solution-phase ligand exchange, with a certified power conversion efficiency of 11.28%. Further modifications have been made using short-chain carboxylates to tune the surface chemistry of larger-size CQDs. A quantitative ligand replacement leads to as a result CQD solar cells that, by harvesting below-silicon-bandgap infrared light, offer to augment silicon with an additional absolute power point of 0.85%.
11:15 AM - ES03.07.09
Electrochemically Generated Sulfur Vacancies in the Basal Plane of MoS2 for Hydrogen Evolution Reaction
Sangwook Park 1 , Hong Li 1 , Jens Norskov 1 , Xiaolin Zheng 1
1 , Stanford University, Stanford, California, United States
Show AbstractMolybdenum disulfide (MoS2) based catalysts for the electrochemical hydrogen evolution reaction (HER) have been widely studied as alternatives to platinum based catalysts due to the earth-abundance and great catalytic activity. Since the edge sites of 2H phase MoS2 were shown to be the active sites for HER, a great number of studies have focused on maximally exposing catalytically active edge-sites through diverse engineering process. Recently, we demonstrated that active sites could be created on the basal plane of 2H-MoS2 by generating sulfur (S)-vacancies. At the S-vacancy sites, the under coordinated Mo atoms introduce gap states that allow for favorable hydrogen binding, introducing the highest per site turnover frequency (TOF) reported for any MoS2-based catalyst for HER. However, the S-vacancies in the basal plane have so far only been generated using controlled argon (Ar) plasma exposure and H2 annealing. A more industrially viable alternative to the argon plasma desulfurization process is needed. To effectively utilize S-vacancies in MoS2 catalysts for industrial applications, a facile, general, and scalable route for generating S-vacancies in MoS2 of any morphology is needed.
Electrochemical desulfurization is one of the possible methods for generating S-vacancies by removing sulfur atoms from the basal plane of MoS2. This method removes the sulfur atoms in the basal plane of 2H-MoS2 to form hydrogen sulfide (H2S) gas through a desulfurizing activation cycle. In this work, we show an electrochemical (EC) desulfurization method for generating S-vacancies in monolayer as well as polycrystalline multilayer MoS2 supported on diverse electrodes. Density functional theory (DFT) calculations show that S-vacancies are expected to be thermodynamically favorable relative to the pristine basal plane at a sufficiently negative potential. The concentration of S-vacancies can be controlled by changing the applied desulfurization voltage. These theoretical predictions are experimentally verified with the continuously grown MoS2 monolayers on gold (Au) showing that electrochemically generated S-vacancies are comparable to the recent work about Ar-plasma treated ones. In addition, we demonstrate the generality of the electrochemical desulfurization approach by generating S-vacancies on MoS2 multilayers supported on flat carbon rods and porous carbon foams leading to a significant HER activity enhancement. Finally, we experimentally show that the HER activity is stable under extended desulfurization durations as well as operating durations and that the concentration of S-vacancies and activity can be varied using the applied potential in polycrystalline multilayer MoS2 on carbon foam electrode.
11:30 AM - ES03.07.10
Defect Engineering in Novel Transparent Conducting Oxide ZnSb2O6
Adam Jackson 1 , Benjamin Williamson 1 , Raman Kalra 1 , David Scanlon 1 2
1 , University College London, London United Kingdom, 2 , Diamond Light Source, Didcott United Kingdom
Show AbstractThe combination of transparency to visible light (optical band gaps in excess of 3.1 eV) and high electrical conductivity (conductivities > 103 S/cm) in a metal oxide material is quite unusual as these are normally mutually exclusive properties.[1] This combination has been realised, however, for a small subset of metal oxides, termed transparent conducting oxides (TCOs), such as ZnO, CdO, Ga2O3, SnO2, In2O3, BaSnO3 etc.[2-5] The cationic species in these materials are all “post transition metals” and so all possesses a (n–1)d10ns0np0 electronic structure. The hybridization between the cations s states and the O p states typically yield low lying conduction band minima (high electron affinities) with excellent conduction band dispersion (low effective masses – high electron mobility).[6] Another cation which possesses an (n–1)d10ns0np0 electronic structure is Sb(V), however, oxides featuring Sb(V) have not enjoyed a huge amount of study to date.
Recently, however, ZnSb2O6 has been identified from a high throughput computational screening to have an electronic structure that could be ideal for TCO applications.[7] There is some experimental support for this as crystalline samples of ZnSb2O6 formed from sintered powder were reported to demonstrate some n-type conductivity in 2005,[8] although not to the level necessary for TCO applications. It should be noted, however, that the best TCOs (e.g. BaSnO3) only show high performance when doped with a suitable electron donor. In this presentation, we outline a hybrid density functional theory examination of the defect chemistry of ZnSb2O6, including intrinsic defects and extrinsic donors. Our calculations have allowed us to identify the ideal dopant for ZnSb2O6, demonstrating its suitability as a next generation n-type TCO.
[1] P. D. C. King and T. D. Veal, J. Phys.: Condens. Matter, 23, 334214 (2011)
[2] M. Burbano, D. O. Scanlon, and G. W. Watson, J. Am. Chem. Soc. 133, 15065 (2011).
[3] D. O. Scanlon and G.W. Watson, J. Mater. Chem. 22, 25236 (2012)
[4] A. Walsh et al., Phys. Rev. Lett. 100, 167402 (2008)
[5] Z. Leben-Higgins et al., Phys. Rev. Lett., 116, 027602 (2016)
[6] H. Mizoguchi and P. M. Woodward, Chem. Mater, 16, 5233 (2004)
[7] G. Hautier et al., Chem, Mater, 26, 5447 (2014)
[8] N. Kikuchi et al. J. Am. Ceram. Soc., 88, 2793 (2005)
11:45 AM - ES03.07.11
Hybrid Energy Harvesters Scavenging Solar and Mechanical Energy Based on ZnO Nanorods
Xuan Li 1 , Steve Dunn 1 , Joe Briscoe 1
1 , Material Research Institute, Queen Mary University of London, London United Kingdom
Show AbstractHybrid energy harvesters have been drawing increasing interest in recent years. While large-scale photovoltaic power plants are capable of providing energy for domestic usage, research has also been focused on mechanical energy harvester with less power output, which can be integrated into self-powered electronics such as implantable device, remote wireless sensor, wearables, etc. Since the majority of these devices would work under the conditions of exposure to both incoming light and mechanical vibration, it would be beneficial to design a hybrid energy harvester scavenging solar and mechanical energy simultaneously. A small number of successful designs have been demonstrated, however their structures remain complicated; the majority of the designs involve multiple layers of the different types of energy harvesters connected in series.
Here, a simple structure based on a p-n junction-based ZnO nanorod piezoelectric energy harvester was designed. The utilization of piezoelectric n-type ZnO nanorods opens up the possibility to design a structure using p-type hole transport layer/light absorber layer/n-type piezoelectric charge transport layer, where the ZnO nanorods act as both an electron transport material and piezoelectric energy harvester. This was adapted to form either a ZnO nanorod-based dye-sensitised solar cell (DSSC), or ZnO nanorod-perovskite solar cell (PSC). The two photovoltaic systems required different adaptations, with long nanorods, CuSCN and traditional water-based PEDOT:PSS being used in the DSSC and short nanorods and a non-aqueous PEDOT:PSS used in the PSC. To allow high processing temperatures while maintaining mechanical flexibility, ‘Corning Willow glass’ was used as a substrate, which can be annealed up to 800 °C, and was compared to the more common PET/ITO. This resulted in 56% lower charge transfer resistance as shown by impedance analysis, and a related 4-fold increase in PCE efficiency for the photovoltaic system.
Mechanical bending and solar testing indicated that the devices operated both as mechanical and solar energy harvesters separately, with the current generated by the photovoltaic around two times greater than from mechanical excitation. In addition, AM1.5 illumination improved the peak power output of the device from 0.29 to 54.36 μW/cm2 while the device was oscillating at resonance frequency by a permanent magnetic shaker. This indicates that the device can perform as a hybrid nanogenerator and photovoltaic simultaneously with enhanced output.
ES03.08: Session VI
Session Chairs
Wednesday PM, November 29, 2017
Hynes, Level 3, Room 304
1:30 PM - *ES03.08.01
Nanocrystal Photovoltaic Devices on Paper
Vikas Reddy 1 , James Sham 2 , Brian Korgel 1
1 , University of Texas at Austin, Austin, Texas, United States, 2 , George Washington University, Washington, District of Columbia, United States
Show AbstractSolar cells on paper have the potential to be inexpensive and portable due to several unique features of the substrate: paper is cheap, flexible, lightweight, biodegradable and manufactured by roll-to-roll processing. Here we report the first nanocrystal photovoltaic devices (PVs) made on paper. Using spray-deposited CuInSe2 nanocrystals as the absorber material on substrates composed of bacterial cellulose nanofibers synthesized by the microorganism Gluconacetobacter hansenii, these devices demonstrate exceptional electrical and mechanical integrity. There is no significant loss in PV device performance after more than 100 flexes to 5 mm radius, and the devices continue to perform when folded into a crease. The practical use of these paper PVs is demonstrated with a prototype device powering liquid crystal displays (LCDs) mounted to various kinds of surfaces.
2:00 PM - ES03.08.02
Structured Ni Electrodes with FeNi Nanoparticles for Enhancing the Oxygen Evolution Reaction
Irene Andreu 1 2 , Audrey Taylor 1 , Mikayla Louie 1 , Michael Paul 1 , Byron Gates 1
1 , Simon Fraser University, Burnaby, British Columbia, Canada, 2 , BC Cancer Agency, Vancouver, British Columbia, Canada
Show AbstractThis report demonstrates the performance of structured earth abundant materials toward the oxygen evolution reaction (OER). Water electrolysis to form H2 and O2 gas is a promising technology that can enable the storage of energy from intermittent renewable sources. The OER occurs at the anode of the electrolizer and it is kinetically hindered, reducing the efficiency of water electrolizers. Improved catalysts are being actively pursued to drive the OER and improve its efficiency.
A series of Ni-based electrodes for alkaline water electrolysis have been the object of intensive research for improving their utilization in industrial applications, as they show good performance with reduced cost in comparison to other efficient anode materials, such as RuO2 and IrO2. The inclusion of up to 25%wt of Fe in NiOOH/Ni(OH)2 electrocatalysts improves the OER performance by reducing the overpotential needed to start the OER and increasing O2 generation as compared to pure NiOOH/Ni(OH)2.1 The surface structure of electrodes for the OER is of foremost importance, particularly at high current densities where the generation of O2 gas bubbles on the surfaces of the electrodes is the greatest, which often reduces the active surface area and, therefore, the performance of the electrodes. Surface structuring can assist in fast bubble release during operation. For example, Paul et al.2 compared hexagonal arrays of cylindrical pillars or recesses in Ni electrodes and found that both the pillars and recesses exhibited enhanced performance when compared to planar electrodes.
The present work extends the field to tuning the composition of Ni electrodes with the inclusion of FeNi nanoparticles, together with the effect of tuning the surface morphology of these electrodes to improve the OER efficiency in an alkaline electrolyte. The conditioning of these electrodes to form the NiOOH/Ni(OH)2 active phase and the presence of the FeNi nanoparticles were carefully monitored by a variety of spectroscopic and microscopic techniques. The OER performance of the structured electrodes with FeNi nanoparticles is better than the performance of the structured or planar Ni electrodes without this Fe inclusion. The combination of compositional and morphological variations is a promising method to further improve the efficiency of water electrolizers while reducing costs by using non-precious metals, such as nickel and iron.
1. Trotochaud et al. Nickel–Iron Oxyhydroxide Oxygen-Evolution Electrocatalysts: The Role of Intentional and Incidental Iron Incorporation; J Am Chem Soc (2014) 136, 6744-6753
2. Paul et al. Hexagonal Arrays of Cylindrical Nickel Microstructures for Improved Oxygen Evolution Reaction; ACS App Mat & Int (2017) 9, 7036-7043
2:15 PM - ES03.08.03
NMC Cathode Materials Synthesized by Co-Precipitation Method for Li-Ion Batteries
Lixin Wang 1
1 , A123 Systems, LLC, Detroit, Michigan, United States
Show Abstract
High nickel NMC material has been widely used in Li ion batteries as cathode materials due to the balanced high energy density, cycle life and safety performance. With the application of the Li ion batteries in electric vehicles in the past decade, the requirements on the energy density and safety performance of the NMC material are much higher than before.
In this presentation, the effects of reaction parameters, such as metal ion to ammonium ratio, resident time and pH value, on the morphology and tap density of the precursor were investigated. The lattice parameters of the NMC powder show direct relation to the material morphology and electrochemical properties.
3:30 PM - ES03.08.04
Retaining and Measuring Conductivity δ-Bi2O3 Phase at Room Temperature without Atomic Substitution by Rapid Quenching
Robert Bell 1
1 , Cornell University, Ithaca, New York, United States
Show AbstractIn equilibrium, δ-Bi2O3 is has the highest measured oxygen ion conductivity of any oxide electrolyte, but is stable only above 730°C. This δ-phase cannot be maintained to room temperature during conventional processing due to transformation to metastable β- or γ-Bi2O3, or formation of the equilibrium α-Bi2O3. Cationic substitution of Bi2O3 allows quenching of a δ phase at conventional rates but also negatively impacts the ionic conductivity. In this work, we show that the pure (unsubstituted) δ-Bi2O3 phase can be retained at room temperature following a rapid quench from high temperature. The kinetics and phase boundaries of metastable phases in this Bi2O3 system were explored using temperature gradient annealing over a wide range of temperatures and quench rates. Metastable phases were identified using spatially refined X-ray diffraction. Additionally, δ-Bi2O3 was observed in solid-solid crystallization of the as-deposited amorphous Bi2O3. Formation of metastable phase formation as a function of temperature and quench rate was mapped. Measurements of room temperature ionic conductivity of pure δ-Bi2O3 will be presented.
3:45 PM - ES03.08.05
Quasi-Amorphous Molybdenum Sulfide Nanosheets Based Hollow Porous Plate and Tube for Efficient Hydrogen Evolution
Liao Chen 1 , Hongli Zhu 1
1 , Northeastern University, Boston, Massachusetts, United States
Show AbstractSynthesis of non-precious, effective catalysts for hydrogen evolution reaction (HER) is crucial to make hydrogen as a practical chemical fuel for energy storage. Recently, the intriguing (quasi-)amorphous molybdenum sulfide (MoSx) materials with active terminal disulfide S22- units have been recognized as prominent catalysts for HER. However, possibly because of the (quasi-)amorphous statuses, the morphologies and structures of those reported MoSx materials are rather simple which may impede the extensive utilization of the merits of MoSx catalysts. Here, we diversify the MoSx morphologies and structures by a new water/ethanol-thermal method to prepare fascinating hollow porous MoSx flat boxes and nanotubes consist of nanosheets. The presences of sufficient ethanol help produce highly dispersive MoSx materials and freeze the materials at quasi-amorphous statuses and further regulate the assembly of quasi-amorphous nanosheets to form hollow porous flat boxes and nanotubes. Catalytic measurements demonstrate that the hollow porous MoSx flat boxes and nanotubes have similar outstanding HER performances and can both reach 10 mA.cm-2 current at overpotential 200-205 mV. Therefore, we have synthesized MoSx nanosheets based hollow porous flat boxes and nanotubes as effective HER catalysts and the hollow porous MoSx flat boxes and naotubes may be used as beneficial templates to prepare other catalysts.
4:00 PM - *ES03.08.06
Manipulating Earth-Abundant Interfaces for Energy Catalysis
Bing Yan 1 , Christopher Hendon 1 , Yogesh Surendranath 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractThe widespread utilization of renewable energy will require energy dense and cost-effective methods for storage. This challenge could be met by coupling renewable electricity to the reduction of carbon dioxide and/or protons to fuels and the oxidation of water to O2, providing, in net, a viable scheme for artificial photosynthesis. Likewise, the resulting fuels could be recombined in a fuel cell to comprise a net carbon-neutral cycle for energy storage and recovery. Realizing this goal requires the development of new lost-cost, earth-abundant electrocatalysis with enhanced selectivity, efficiency, and durability.
Unlike precious metals, first row transition metals are inherently substitutionally labile. As a result, the surfaces of first row transition metal oxides and chalcogenides are subject to dynamic restructuring under the conditions of catalysis. While this phenomenon has been well-characterize for many transition metal oxides, the surface dynamics of heavier chalcogenides are poorly understood. Recently, we identified Ni3S2 as a potent, selective catalyst for the oxygen reduction reaction, the efficiency limiting reaction in low temperature fuel cells. Using a combination of electrochemical methods and high resolution imaging and spectroscopies, we found that the surfaces of Ni3S2 undergo dynamic restructuring under the conditions of catalysis to expose the active sites necessary for catalysis. Our latest findings and the implications of surface dynamics for catalysis by earth-abundant materials will be discussed.
4:30 PM - ES03.08.07
Cations Controlled Growth of β-MnO2 Crystals with Tunable {100}/{111} Facets as the Catalysts for Oxygen Reduction/Evolution
Wentao Yao 1 , Gregory Odegard 1 , Yifei Yuan 2 , Zhennan Huang 3 , Meng Cheng 3 , Hasti Asayesh-Ardakani 1 , Fei Long 1 , Craig Friedrich 1 , Jun Lu 2 , Reza Shahbazian-Yassar 3 1
1 Mechanical Engineering-Engineering Mechanics, Michigan Technological University, Houghton, Michigan, United States, 2 Chemical Science and Engineering Division, Argonne National Laboratory, Chicago, Illinois, United States, 3 Mechanical and Industrial Engineering, University of Illinois at Chicago, Chicago, Illinois, United States
Show AbstractManganese dioxide has wide application in the field of energy storage, such as cathode material for lithium ion batteries, catalysts for lithium-air batteries and fuel cells, electrode for supercapacitors, etc. Exposed crystal facets of MnO2 crystals directly impact their electrochemical performance through affecting the intercalation of lithium or sodium ions as well as the active sites for catalytic reactions and charge storage. However, controlled growth of MnO2 crystals still face great challenges, because MnO2 crystals with tunnel structures (α-MnO2, β-MnO2, todorokite-MnO2, etc.) generally prefer to grow along their tunnel directions under the typical hydrothermal synthesis process. Critical engineering of MnO2 crystal facets needs effective methods to control the growth direction of the crystals during the synthesis.
In this work, β-MnO2 crystals with tunable {111} and {100} facets were synthesized using K+ cations as the surfactant. Obtained β-MnO2 crystals showed a bipyramid prism structure. Increasing the concentration of K+ cations in the precursor gradually reduced the length of β-MnO2 prism with {100} facets and increased the occupancy of {111} pyramid facets. Further ex-situ scanning electron microscopy (SEM) and X-ray powder diffraction pattern showed a formation of α-KxMnO2 intermediate phase during the growth of β-MnO2 bipyramid prism. Cross-sectional analysis using aberration-corrected scanning transmission electron microscopy (STEM) revealed a direct tunnel transition process from α-KxMnO2 to β-MnO2. The role of K+ surfactant was proposed as to impede the extraction of K+ stabilizing ions in the [2×2] tunnels of α-KxMnO2, which subsequently reduced the length of obtained [1×1] tunnels. The catalytic performance of β-MnO2 crystals with different occupancy of {111}/{100} facets were further evaluated as the cathode catalyst for Li-air batteries. The {100} facets of β-MnO2 crystals showed better performance in reducing the charging overpotential. SEM analysis of the catalysts after battery cycling showed that the {100} facets of β-MnO2 are more reactive than the {111} lateral facets. The method provided here can be further adopted to control the growth other layered or tunneled polymorphs with stabilizing ions. The facet-dependent catalytic performance of β-MnO2 crystals also offers the guidance for a better design of this important metal oxide to further improve its performance in metal-air batteries, fuel cells, water treatment, etc.
4:45 PM - ES03.08.08
Disordered Mixed Metal Oxide Nanocatalysts for the Oxygen Evolution Reaction Using Bio-Enabled Synthetic Routes
Nicholas Bedford 1
1 , Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States
Show AbstractThe oxygen evolution reaction (OER) is a critically important reaction governing the overall performance solar/electricity driven water splitting for H2 production and charging processes in metal-air batteries. As such, a tremendous amount of research effort is directed in the creation of new catalytic materials to lower the overpotential of OER, along with understanding fundamental atomic-scale structure/function relationships associated with reaction mechanisms and catalyst structure. In particular, current developments in non-precious metal oxyhydroxide catalysts using less expensive metals (Fe, Ni, Co etc.) are promising, often outperforming benchmark catalysts consisting of Ru and Ir based oxides under alkaline conditions. The exciting development of earth-abundant metal oxide catalyst is encouraging, yet the development of synthesis-dependent structure/properties arrangements are comparatively lacking, and could provide the needed fundamental insights for improving the catalytic performance of these materials. In this presentation, bio-enabled routes have been employed as means to create highly disordered bimetallic metal oxides with varying compositions with promising OER performance. Synchrotron radiation characterization efforts, both in-situ and ex-situ, have been utilized to better understand the relationships between synthetic conditions, atomic-scale properties and catalytic performance, which may provide insights into further catalyst development.