Robert L. Opila, University of Delaware
Federico Rosei, INRS
Peter Sheldon, National Renewable Energy Laboratory
Symposium Support Elsevier
RBD Instruments, Inc.
GG2: Water Splitting
Monday PM, December 02, 2013
Hynes, Level 3, Room 312
2:30 AM - *GG2.01
Design of Catalysts and Electrocatalysts for Energy Applications
Jingguang G. Chen 1
1Columbia University New York USAShow Abstract
In the current talk we will use two examples to demonstrate the importance of using surface science studies to identify catalysts and electrocatalysts. Our research approaches involve parallel efforts in density functional theory (DFT) calculations, surface science experiments on model systems, and synthesis and evaluation of supported catalysts under thermochemical or electrochemical conditions. We will first use water electrolysis to demonstrate the feasibility of using monolayer Pt on tungsten carbide (WC) to achieve the same activity as bulk Pt. We will present DFT calculations of similar electronic and chemical properties between monolayer Pt/WC and Pt, synthesis and characterization of monolayer Pt/WC films, and electrochemical evaluation of the activity and stability of Pt/WC for water electrolysis. Comparing to the leading Pt electrocatalyst, the monolayer Pt/WC represents a reduction by a factor of ten in Pt loading [1,2].
We will then use the conversion of biomass-derived oxygenates to illustrate the advantages of using bimetallic catalysts. Bimetallic catalysts often show unique activity and selectivity over their parent metals due to the electronic modification and strain effect [3,4]. We will present our results on the characterization of Ni/Pt bimetallic surfaces and catalysts under in-situ reaction conditions, further highlighting the importance of using the combined approaches of DFT calculations, surface science experiments, and reactor evaluations [5,6].
 D.V. Esposito, S.T. Hunt, K.D. Dobson, B.E. McCandless, R.W. Birkmire and J.G. Chen, “Low-Cost
Hydrogen Evolution Catalysts Based on Monolayer Platinum on Tungsten Monocarbide Substrates”, AngewandteChemie International Edition, 49 (2010) 9859-9862
 D.V. Esposito, S.T. Hunt, Y.C. Kimmel and J.G. Chen, “A New Class of Electrocatalysts for Hydrogen Production from Water Electrolysis: Metal Monolayers Supported on Low-Cost Transition Metal Carbides”, Journal of the American Chemical Society, 134 (2012) 3025-3033.  W. Yu, M.D. Porosoff and J.G. Chen, “Pt-based Bimetallic Catalysis: From Model Surfaces to
Supported Catalysts”, Chemical Reviews, (2012) DOI: 10.1021/cr300096b.
 D.A. Hansgen, D.G. Vlachos and J.G. Chen, “Using First Principles to Predict Bimetallic Catalysts
for the Ammonia Decomposition Reaction”, Nature Chemistry, 2 (2010) 484-489.
 M. Salciccioli, W. Yu, M.A. Barteau, J.G. Chen, D.G. Vlachos, “Differentiation of O-H and C-H
Bond Scission Mechanisms of Ethylene Glycol on Pt and Ni/Pt Using Theory and Isotopic Labeling Experiments”, Journal of the American Chemical Society, 133 (2011) 7996-8004.
 W. Yu, M.A. Barteau and J.G. Chen, “Glycolaldehyde as a Probe Molecule for Biomass-derivatives:
Reaction of C-OH and C=O Functional Groups on Monolayer Ni Surfaces”, Journal of the American Chemical Society, 133 (2011) 20528-20535.
3:00 AM - GG2.02
In situ Transient Optical Spectroscopy of Photo-Excited Charge Carriers at the SrTiO3/Electrolyte Interface
Matthias M Waegele 1 Xihan Chen 1 David Herlihy 1 Tanja Cuk 1 2
1University of California Berkeley USA2Lawrence Berkeley National Laboratory Berkeley USAShow Abstract
While recent efforts to enhance photon-to-O2 conversion of photoanodes for water splitting have attracted much attention, linking the resulting apparent catalytic activities to the microscopic processes of electron-hole dynamics and interfacial hole transfer remains difficult. Herein, we investigate the kinetics of photo-excited carriers within the space charge layer of Nb-doped SrTiO3 anodes under working conditions by means of time-resolved optical spectroscopy. By probing the dependence of the dynamics on various variables, including electrochemical potential, electrolyte composition, and doping concentration, we are able to quantify the kinetics of electron-hole separation in the space charge layer, and monitor hole transfer across the SrTiO3/electrolyte interface. We discuss the relevance of our results in regards to the early steps in water oxidation at the SrTiO3 interface, as well as to the design of novel photoanodes.
3:15 AM - *GG2.03
Engineered Photoanodes for High Efficiency Dye- and Quantum Dot-Sensitized Solar Cells
Gurpreet Singh Selopal 3 1 K. Therese Dembele 2 Riccardo Milan 3 1 Isabella Concina 1 3 Giorgio Sberveglieri 3 1 Alberto Vomiero 1 2 3
1CNR SENSOR Lab Brescia Italy2INRS EMT Varennes Canada3University of Brescia Brescia ItalyShow Abstract
The typical photoanode in dye- and quantum dot- sensitized solar cells is composed of a wide band gap semiconductor, which acts as electron transporter for the photoelectrochemical system. Anatase TiO2 nanoparticles are one of the most used oxides and are able to deliver the highest photoconversion efficiency in this kind of solar cells, but intense research in the last years was also addressed to ZnO and other composite systems. Modulation of the composition and shape of nanostructured photoanodes is key element to tailor the physical chemical processes regulating charge dynamics and, ultimately, to boost the efficiency of the end user device, by favoring charge transport and collection, while reducing charge recombination.
We investigated several systems: (i) TiO2 nanoparticles / ZnO nanowires ; (ii) Multiwall carbon nanotubes (MWCNTs) / TiO2 nanoparticles ; (iii) TiO2 nanotubes [3-4]; (iv) Hierarchically self-assembled ZnO sub-microstructures . Both dye molecules and semiconducting quantum dots were applied as light harvesters. Possible tailoring of structure and morphology of the photoanodes, and their implication in improving the functional properties of these kinds of excitonic solar cells will be discussed.
 A. Vomiero, I. Concina, M.M. Natile, E. Comini, G. Faglia, M. Ferroni, I. Kholmanov, G. Sberveglieri, Applied Physics Letters 95 (2009) 193104.
 K.T. Dembele, R. Nechache, L. Nikolova, A. Vomiero, C. Santato, S. Licoccia, F. Rosei J. Power Sources 233 (2013) 93-97.
 A. Vomiero, V. Galstyan, A. Braga, I. Concina, M. Brisotto, E. Bontempi, G. Sberveglieri, Energy and Environmental Science 4 (2011) 3408-3413.
 V. Galstyan, A. Vomiero, I. Concina, A. Braga, M. Brisotto, E. Bontempi, G. Faglia, G. Sberveglieri, Small 7 (2011) 2437-2442.
 N. Memarian, I. Concina, A. Braga, S. M. Rozati, A. Vomiero, G. Sberveglieri, Angewandte Chemie In Ed 50 (2011) 12321-12325.
4:00 AM - *GG2.04
Hydrogen Production from Formic Acid: An Important Catalytic Reaction for Biomass Conversion
Manos Mavrikakis 1 James Dumesic 1 Jessica Scaranto 1 Suyash Singh 1 Ronald Carrasquillo 1 Brandon O'Neill 1 Sha Li 1 Luke Roling 1 Jeff Herron 1 Guowen Peng 1
1University of Wisconsin - Madison Madison USAShow Abstract
Formic acid (HCOOH) is a simple molecule that is an abundant product of biomass processing and can serve as an internal source of hydrogen for oxygen removal and upgrading of biomass to chemicals and fuels. In addition, HCOOH can be used as a fuel for low temperature direct fuel cells. We present a systematic study of the HCOOH decomposition reaction mechanism starting from first-principles and including reactivity experiments and microkinetic modeling. In particular, periodic self-consistent Density Functional Theory (DFT) calculations are performed to determine the stability of reactive intermediates and activation energy barriers of elementary steps. In addition, pre-exponential factors are determined from vibrational frequency calculations. Mean-field microkinetic models are developed and calculated reaction rates, orders, etc are then compared with experimentally measured ones. These comparisons provide useful insights on the nature of the active site, most-abundant surface intermediates as a function of reaction conditions and feed composition. Trends across metals on the fundamental atomic-scale level up to selectivity trends will be discussed. Finally, we identify from first-principles alloy surfaces, which may possess better catalytic properties for selective dehydrogenation of HCOOH than monometallic surfaces, thereby guiding synthesis towards promising novel catalytic materials.
4:30 AM - GG2.05
Study of Hydrogen Evolving Catalyst at the Light Absorber/Electrolyte Interface Using X-Ray Absorption Spectroscopy and Micro-Focused X-Ray Fluorescence
Eitan Anzenberg 1 Alexandra Krawicz 1 Gary F Moore 1 Junko Yano 1
1Lawrence Berkeley National Lab Berkeley USAShow Abstract
Studying and improving activity and stability of earth-abundant catalysts at the light absorber/electrolyte interface to drive hydrogen production reaction is an important challenge for solar fuel generation in artificial photosynthesis. We have used X-ray Absorption Spectroscopy (XAS) and micro-focused X-ray Fluorescence (MXRF) mapping at the Advanced Light Source (ALS) to characterize molecular surface-linked catalysts at the interface. The electronic and structural properties of the metal core or ligand were probed before, during, and after electro- and photoelectro-chemical (PEC) operation with ex- and in-situ detection techniques. Using Co K-edge XAS, we have shown that a Co(dmgH)2PrCl molecular catalyst remains electronically and structurally intact after attachment through the pyridine ligand to a polymer chain linked to a light absorbing surface . Using the Co fluorescence signal, we have also studied the stability of a cobaloxime-modified photocathode after rigorous PEC operation.
 Krawicz, Yang, Anzenberg, Yano, Sharp, Moore, Photofunctional Construct that Interfaces Molecular Cobalt-based Catalysts for H2 Production to a Visible-light Absorbing Semiconductor, Journal of the American Chemical Society, (submitted)
4:45 AM - GG2.06
Surface Structure-Activity Relationship in Ceria-Based Catalysts Studied by Surface X-Ray Diffraction on Atomically Flat Thin Films
Yezhou Shi 1 2 Chuntian Cao 1 Zhuoluo A. Feng 1 Michael F. Toney 2 William C. Chueh 1 2
1Stanford University Stanford USA2SLAC National Accelerator Laboratory Menlo Park USAShow Abstract
Ceria (CeO2) is one of the most active oxide electro-catalysts for hydrogen oxidation and water-splitting reactions at elevated temperatures. The surface concentration of oxygen vacancies and Ce3+ species were found to be significantly greater than the bulk, and can plausibly explain ceria&’s high electro-catalytic activity. Furthermore, the activities of ceria are expected to depend strongly on the surface termination, as already observed in nanostructured ceria with different facets. To better understand electrochemical reaction mechanisms and the structure-property relationship on the ceria surface, we investigated how the surface crystal structure of doped ceria differed from its bulk crystal. Specifically, we employed in-situ surface X-ray diffraction (SXRD) to study the atomic arrangements of (100)-and (111)-terminated ceria surfaces. We successfully fabricated atomically flat ceria films on yttria-stabilized zirconia substrates by pulsed laser deposition and confirmed that these films had well-defined step terraces using atomic force microscopy. We correlated the surface structure under both reducing and oxidizing atmosphere to the different catalytic activities of the (100)- and (111)-terminated films.
5:00 AM - GG2.07
Synthesis of Core-Shell Ferrite Nanoparticles for Thermochemical H2 Generation from Water-Splitting
Vinod Amar 1 Jan Puszynski 1 Rajesh V Shende 1
1South Dakota School of Mines amp; Technology Rapid City USAShow Abstract
Thermochemical water-splitting is a two-step process where in step-1, redox material is heated at higher temperature creating oxygen vacancies, whereas in step-2, this partially reduced material is exposed to steam leading to H2 generation by scavenging the oxygen. As these steps are performed at very high temperatures, materials experience grain growth. As a result, surface area and porosity decrease, which translate into lower H2 volume generation with increase in thermochemical water-splitting cycles. Therefore, there is a need to thermally stabilize the redox materials with the viewpoint of mitigating the grain growth and achieving steady H2 production. In this study, Ni-ferrite nanoparticles were synthesized using the sol-gel method and later these nanopartices were utilized to prepare porous core-shell nanoparticles with Y2O3 stablized ZrO2 (YSZ). The H2 generation ability of core-shell Ni-ferrite/YSZ nanoparticles was investigated by performing five consecutive thermochemical cycles in the Inconel packed-bed reactor where water-splitting and regeneration steps were carried out at 650o-1100oC. Specific surface area (SSA) and porosity of these materials were analyzed before and after the thermochemical water-splitting reaction using BET surface area analyzer. Additionally scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the grain growth. The results suggest grain growth mitigation in core-shell Ni-ferrite/YSZ nanoparticles that resulted in relatively steady H2 volume in multiple thermochemical water-splitting cycles. The H2 volume observed with core-shell ferrite nanoparticles was higher than ferrite nanoparticles. Characterization of core-shell nanoparticles and the results obtained on H2 volume generation with ferrite and core-shell ferrite nanoparticles will be presented.
5:15 AM - GG2.08
Hydrogen Storage in Orthorhombic Mg Hydride at Ultra-Low Temperature
Byoungsoo Ham 1 Anchalee Junkaew 1 Raymundo Arroyave 1 Haiyan Wang 2 Peng Wang 3 Jerek Majewski 3 Jinhee Park 4 Hongcai Zhou 4 Yang Ren 5 Xinghang Zhang 1
1Texas Aamp;M College Station USA2Texas Aamp;M College Station USA3Los Alamos National Laboratory Los Alamos USA4Texas Aamp;M College Station USA5Argonne National Laboratory Argonne USAShow Abstract
Mg can store up to ~7 wt.% hydrogen and is an appealing candidate as light weight and low cost hydrogen storage material. However hydrogen desorption in Mg hydride typically requires unfavorably high temperature of ~ 573 K due to its high thermodynamic stability, whereas the target operation temperature of fuel cells in automobiles is ~ 373 K or less. Furthermore the kinetics of H sorption in Mg is typically slow. Here we investigate hydrogen sorption behavior of Mg/Nb multilayers. Stress-induced orthorhombic Mg hydride (O-MgH2) is thermodynamically destabilized at ~ 373 K or lower. Such drastic destabilization arises from large tensile stress in single layer O-MgH2 bonded to rigid substrate, or compressive stress due to large volume change incompatibility in Mg/Nb multilayers. Ab inito calculations were performed to analyze the influence of interfaces on H sorption in Mg films. These studies provide insight on the mechanisms that may expedite the kinetics of H sorption in Mg.
5:30 AM - *GG2.09
Conjugated Porous Organic Polymers Possessing High Hydrogen Sorption Capacity
Baohang Han 1
1National Center for Nanoscience and Technology Beijing ChinaShow Abstract
Conjugated organic polymers, possessing intrinsic properties of large surface areas, high thermal and chemical stabilities, and low skeleton density, exhibit potential applications in gas storage and separation. Based on special spirocyclic or propeller-like monomers, various organic microporous polymers were prepared through a wide variety of C-C coupling reactions and further characterized at the molecular level by 13C CP/MAS NMR spectrum, as well as other techniques. All the obtained polymers are chemically stable. Thermal analysis shows that the materials are stable up to 350 °C under nitrogen. The fluorescent emission of the obtained conjugated polymers is tunable, ranging from 440 to 600 nm depending on the molecular structure of the monomer and coupling strategy. According to the obtained nitrogen physisorption isotherms, the Brunauer-Emmett-Teller (BET) specific surface area for these polymers varies between 700 and 2200 m<2> g<-1>. Adsorption isotherms show the polymers possess nice adsorption capacity to hydrogen and carbon dioxide, showing a good gas separation of carbon dioxide over methane.
GG3: Poster Session I
Robert L. Opila
Monday PM, December 02, 2013
Hynes, Level 1, Hall B
9:00 AM - GG3.01
High Efficiency and Enhanced Fill Factor of Solution Processed Small-Molecule Solar Cells with p-DTS(FBTTh2)2:PC71BM Bulk Heterojunction
Dong Hwan Wang 1 2 Aung Ko Ko Kyaw 1 Jong Hyeok Park 2 Alan J. Heeger 1
1University of California Santa Barbara Santa Barbara USA2Sungkyunkwan University Suwon Republic of KoreaShow Abstract
Bulk-heterojunction (BHJ) solar cells based on phase-separated blends of organic materials of donor and acceptor (fullerene derivative) have been in continuous development over the past two decades.(1)-(3) Recently, solution-processable small molecule-based BHJ solar cells exhibiting comparable power conversion efficiency (PCE) of near 7% to the polymers with high potential under simple and optimized processing conditions.(4)-(6) The small-molecule donors have attractive features, including relatively simple synthesis and purification steps, mono-dispersity, and improved batch-to-batch reproducibility.
Here, we demonstrated solution-processed small-molecule p-DTS(FBTTh2)2:PC71BM BHJ solar cells with a PCE over 8 %. The fill factor (FF) is sensitive to the thickness of a calcium buffer layer between the BHJ active film and the Al cathode; for 20 nm Ca thickness, the FF is 73%, the highest value reported for an organic solar cell. The maximum external quantum efficiency exceeds 80%. After correcting for the total absorption in the cell through the normal incidence reflectance measurements, the internal quantum efficiency approach 100% in the spectral range of 600 to 650 nm and well over 80% across the entire spectral range from 400 to 700 nm. Analysis of the current-voltage (J-V) characteristics at various light intensities provides information on the different recombination mechanisms in the BHJ solar cells with various thicknesses of the Ca layer. Also, we can fabricate improved efficiency of small-molecule solar cells with PCE of 8.24% with enhanced JSC and FF using a low sheet resistance of ITO (5 Omega;/square) substrate (ITO thickness of 450 nm) which exhibits transmittance of 90% at 550 nm. The increased JSC and FF originate from the reduced series resistance (Rs). In summary, the PCE and FF of small molecule based bulk-heterojunction solar cells can be increased by optimized thickness of Ca interlayer and low sheet resistance of ITO substrate.
(1) G. Yu, J. Gao, J.C. Hummelen, F. Wudl, and A.J. Heeger, Science 270 (1995) 1789.
(2) S.H. Park, A. Roy, S. Beaupre, S. Cho, N. Coates, J.S. Moon, D. Moses, M. Leclerc, K. Lee, A.J. Heeger, Nat. Photonics 3 (2009) 297.
(3) G. Li, V. Shrotriya, J. Huang, Y. Yao, T. Moriarty, K. Emery, Y. Yang, Nat. Mater. 4 (2005) 864.
(4) Y. Sun, G. C. Welch, W. L. Leong, C. J. Takacs, G. C. Bazan, A. J. Heeger, Nat. Mater. 11 (2012) 44.
(5) C. J. Takacs, Y. Sun, G. C. Welch, L. A. Perez, X. Liu, W. Wen, G. C. Bazan, A. J. Heeger, J. Am. Chem. Soc. 134 (2012) 16597.
(6) A. K. K. Kyaw, D. H. Wang, V. Gupta, J. Zhang, S. Chand, G. C. Bazan, A. J. Heeger, Adv. Mater. DOI: 10.1002/adma.201300295.
9:00 AM - GG3.02
Exfoliated Graphene-Supported Pt and Pt-Based Alloys as Electrocatalysts for Direct Methanol Fuel Cells
Wen Qian 1
1Portland State University Portland USAShow Abstract
To greatly improve the electrocatalytic activity for methanol oxidation, high-quality exfoliated graphene decorated with uniform Pt nanocrystals (NCs) (3 nm) have been prepared by a very simple, low-cost and environmentally benign process. During the entire process, no surfactant and no halide ions were involved, which not only enabled very clean surface of Pt/graphene leading to excellent conductivity, but also greatly improved the electrocatalyst tolerance to carbon monoxide poisoning (Pt/graphene, If/Ib= 1.197), compared to commercial Pt/C (If/Ib= 0.893) catalysts. To maximize the electrocatalytic performance and minimize the amount of precious Pt, Pt-M/graphene (M=Pd, Co) hybrids have also been prepared, and these hybrids have much larger electrochemically active surface areas (ECSA), which are 4 (PtPd/graphene) and 3.3 (PtCo/graphene) times as those of commercial Pt/C. The PtPd/graphene and PtCo/graphene hybrids also have remarkably increased activity toward methanol oxidation (If/Ib= 1.218 and 1.558). Furthermore, density functional theory (DFT) simulations demonstrate that an electronic interaction occurred between Pt atoms and graphene, indicating that graphene substrate plays a crucial role in regulating the electron structure of attached Pt atom, which confirmed that the increased efficiency of methanol oxidation was due to the synergetic effects of the hybrid structure.
9:00 AM - GG3.03
Large Impact of Molecular Orientation on Ionization Energy: Picene Film
Rintaro Makino 1 Keiichirou Yonezawa 1 Kengo Kato 1 Alexander Hinderhofer 1 Takuya Hosokai 2 Koji Okudaira 1 Nobuo Ueno 1 Satoshi Kera 1
1Chiba University Chiba Japan2Iwate University Morioka JapanShow Abstract
To improve the performance of organic photovoltaic cells, mechanisms of charge transfer/transport and charge separation have been widely investigated. These studies need acculate information on the electronic structure responsible to the processes. In general, however, it is not easy to reveal the electronic structure not only at metal-molecule interfaces but also of the molecular film itself due to large structural anisotropy of the molecule and their orientation in the film. Ionization energy (Ei) of the film depends on the molecular orientation, crystal structure and packing density . In this study, we investigated the electronic structure and the molecular orientation of picene (C22H14) films prepared on SiO2 and graphite (HOPG) substrates by using ultraviolet photomission spectroscopy (UPS) and metastable atom electron spectroscopy (MAES) .
Picene molecules were vacuum deposited step-by-step (upto ~10nm) on clean SiO2 and HOPG under UHV. The deposition rate was ~1.7 Å/min on the SiO2 and ~1.1 Å/min on the HOPG. All experiments were conducted at RT (293K).
We clarified using MAES from monolayer to multilayer that the molecules stand upright on the SiO2 (long axis of the molecule is normal to the surface), while they lie flat on the HOPG (short axis of the molecule is slightly tilted w.r.t. the surface). Normal-emission UPS spectra of the standing and lying films are largely different due to the orientation dependent photoelectron angular distribution and intermolecular interaction. The valence band features of the lying film correspond well to the density-of-states from DFT of an isolated molecule, while those of the standing film represent similarlity with the result of the single crystal .
We determined Ei for the HOMO onset and peak after peak fitting analyses of the HOMO features. The Ei of the standing film at the peak position (EiPEAK= 6.06eV) is smaller by 0.74eV than that of the lying film (EiPEAK = 6.80eV), giving the energy difference ΔEiPEAK = 0.74 eV (ΔEiONSET = 0.66 eV). These ΔEi are much greater than that of pentacene (ΔEiPEAK= 0.43eV ) as well as other pi-conjugated molecules (ΔEiPEAK = 0.40eV for DIP and 0.40eV for CuPc). Effects of electronic coupling at the picene/substrate interfaces on the UPS features can be neglected because of weak molecule-substrate interaction. We also suggest that for picene the molecular dipole and energy-band dispersion do not contribute much on ΔEi. Hence we can evaluate main origin of orientation dependent Ei by considering surface electrostatic potential produced by local dipoles (>C-H+) in picene. At the conference, we will report results of the electrostatic potential culculation and gas phase spectra of picene to discuss the orientation dependence of Ei.
 S. Duhm et al, Nature Mater. 7, 326 (2008).
 Y. Harada et al, Chem. Rev. 97, 1897 (1997).
 Q. Xin et al, Phys. Rev. Lett. 108, 226401 (2012).
 H. Fukagawa et al, Phys. Rev. B 73, 245310 (2006).
9:00 AM - GG3.04
Activation of the CO2 Molecule, A Theoretical Study
Shin Nakamura 1 Katsushi Fujii 2 Koji Ogata 1 Makoto Hatakeyama 1 Yuanqing Wang 1 Xu Zeng 3 Fangming Jin 3
1RIKEN Wako Japan2The Univ Tokyo Tokyo Japan3Jiao Tong University Shanghai ChinaShow Abstract
On the CO2 activation a theoretical study is presented. On the basis of the quantum chemical calculations, the order of magnitude in the activation is described. Taking as a reference of the CO2 molecule in dilute gas phase or in vacuum, the activated states in electronic structure (wave functions) as well as in geometrical changes are described by the degree of modifications relative to the reference state.
The DFT calculations are performed to visualize this degree of activation as a function of the environmental effect on CO2; gas phase, liquid phase (especially as a function of pH), and coordination on transition metals. Special attention is paid on the activation by abundant metals such as Zn. The experimental and theoretical examples of reactions of the activated CO2 are presented in hydrothermal condition with transition metal atoms.
9:00 AM - GG3.06
Engineering ZnO@SnO2 Multilayer Structures as Photoanodes for High Efficiency Photovoltaic Devices
Riccardo Milan 1 Gurpreet Singh Selopal 1 Mauro Epifani 2 Alberto Vomiero 1 Giorgio Sberveglieri 1 Guido Faglia 1 Isabella Concina 1
1University of Brescia amp; SENSOR Lab Brescia Italy2Consiglio Nazionale delle Ricerche Istituto per la Microelettronica ed i Microsistemi Lecce ItalyShow Abstract
Excitonic solar cells (XSCs) are appealing candidates as alternative devices for solar energy conversion, being in principle low cost, rather environmental friendly and suitable for exploiting also the near infrared (NIR) region of solar spectrum. 1
Nanoparticulate TiO2 is currently the most known and exploited semiconductor metal oxide (SMO) applied as photoanode in both dye- and quantum dot-sensitized solar cells (DSCs and QDSCs), but other SMOs, such as ZnO and SnO2, are attracting a broad interest, due to higher electron mobility and band structure suitable for NIR-absorbing light harvesters, respectively. 2,3,4
Strategies devoted to either completely inhibit or at least reduce recombination of photogenerated free charges, which is still one open issue in photoconverison efficiency, are still requested.
In this work, nano-SnO2, with different particles sizes (4 to 20 nm) and tunable amount of oxygen vacancies, was applied as main active layer in photoanodes for XSCs together with ZnO (as polidisperse nano- and micro-structures or hierarchical structures) in order to engineer the global band structures involved in charge injection.
A careful optimization of different parameters, such as relative layered composition of ZnO@SnO2 interfaces and dye loading time, allows demonstrating the highly beneficial role of ZnO as blocking layer towards the exciton recombination at SnO2-light harvester-electrolyte interfaces, thus reaching high functional performances in terms of injected photocurrent and photo conversion efficiency (JSC=14.78 mA/cm2 PCE=4.96%).
Strategies successful in optimizing the functional performances of XCSs (both DSCs and QDSCs) through material interface engineering will be presented and discussed.
1 B. O&’Regan, M. Gratzel, Nature 1991, 353, 737
2 E. Guillén, L. M. Peter, J. A. Anta J. Phys. Chem. C, 2011, 115, 2262
3 N. Memarian, I. Concina, A. Braga, SM Rozati, A Vomiero, G Sberveglieri, Angew Chem 2011, 51, 12321
4 A. Hossain, JR Jenning, Z.Y. Koh,Q. Wang, ACS Nano, 2011, 5, 3172
9:00 AM - GG3.08
The Effect of Molecular Adsorption-Geometry on the Binding Energy of Interface States
K. Kato 1 K. Sato 1 K. Yonezawa 1 Y. Liu 1 T. Hosokai 2 S. Yanagisawa 3 K. R Koswattage 1 N. Ueno 1 S. Kera 1
1Graduate School of Advanced Integration Science Chiba 263-8522 Japan2Department of Materials Science and Technology, Iwate University Morioka 020-8551 Japan3Depertment of Physics and Earth Sciences, Ryukyu University Okinawa 903-0213 JapanShow Abstract
Energy level alignment at organic/metal interfaces determines the performance of organic devices. To clarify the energy level alignment it is desired to obtain precise information of electronic states, in particular the highest occupied molecular orbital (HOMO) related states, at a complicated interface that consists of functional molecules. We studied the electronic structure and geometric structure of diindenoperylene (DIP: C32H16) monolayer (ML) on a Cu (111) surface by using angle-resolved ultraviolet photoelectron spectroscopy (ARUPS). It is known that DIP molecules form two different 2-dimensional lattice structures on Cu (111) .
A Cu (111) single crystal was cleaned by repeated Ar-ion sputtering and annealing cycles. The DIP ML film was prepared on the Cu (111) substrate by vacuum evaporation. ARUPS spectra were then measured at photon incidence angle α=45°, hv=28 eV and T=295 K at UVSOR facility (BL8B) at the Institute for Molecular Science. To study geometric structure as well as HOMO derived interface states we measured azimuthal angle (phi;) dependence by rotating the sample around the surface normal and photoelectron emission angle (theta;) dependence of the spectra of the ML.
ARUPS spectra of the DIP (ML)/Cu (111) show two prominent bands in the sp-band region of Cu (111). The first band is broad and located at binding energy (EB: from the Fermi level) of ~0.7eV, which is ascribed to the former LUMO with electrons transferred from the substrate as in the case of PTCDA . The second band consists of two features that are located at EB=1.5 and 1.8 eV. We observed these two features show different phi; dependences at theta;=37°. Assuming that these two features come from DIP HOMO and using the two molecular adsorption geometries observed with STM (the short-range and the long-range ordered structures) , we computed phi; dependences of the photoelectron intensity from the two features for the two geometries, and compared with the observed phi; dependences. The agreement between the observed and computed phi; dependences is obtained when the 1.5-eV feature is originated from the long-range ordered structure and the 1.8-eV feature is from the short-range ordered structure. We can thus ascribe both of these two features at 1.5 and 1.8 eV to HOMO-derived states.
 D. G. de Oteyza et al, Phys.Chem.Chem.Phys. 11, 8741 (2009)
 S. Duhm et al, Org. Electro. 9, 111 (2008)
9:00 AM - GG3.09
Transmission Electron Backscatter Diffraction (t-EBSD) for Characterizing Ultrathin Films in the SEM
Katherine Rice 1 Roy Geiss 1 Robert Keller 1
1NIST Boulder USAShow Abstract
Transmission electron backscatter diffraction (t-EBSD) is a new technique of materials characterization using a standard scanning electron microscope (SEM). By changing the sample-detector geometry so that electrons pass through a thin specimen prior to entering a commercial EBSD detector, an interaction volume significantly smaller than that typically associated with conventional EBSD can be achieved. As a result, electron diffraction data in the form of Kikuchi patterns can be collected from extremely fine-scale films and particles, down to the sub-10 nm dimensional scale. In conventional EBSD, incident electrons are thought to undergo Kikuchi scattering in the top 10 to 40 nanometers of a film, thereby requiring a film at least that thick to produce a diffraction pattern, while achieving a lateral spatial resolution in the typical range of 20 nm to 35 nm parallel to the tilt axis and 80 nm to 90 nm perpendicular to the tilt axis. Here we present recent results and electron scattering simulations associated with probing the sampling limits of the t-EBSD technique for semiconductor industry-relevant films as thin as 5 nm, while maintaining single-nanometer lateral spatial resolution.
Transmission EBSD, performed at ~ 20 keV, provides information from large areas of ultrathin films, while requiring only little material volume, by capturing forward-scattered electrons in transmission with standard EBSD equipment. Monte Carlo simulations support experimental results on the maximum thicknesses that can be reliably characterized with this method, by giving estimates of the energy losses of the electrons as they pass through increasing film thicknesses, and practical limits of the technique are investigated in terms of the mass-thickness of the sample, regardless of composition.