Thomas A. Zawodzinski, University of Tennessee, Knoxville, and Oak Ridge National Laboratory
Nigel Brandon, Imperial College London
Vito Di Noto, University of Padova
Steven Hamrock, 3M Fuel Cell Components Program
M1: Electrodes and Catalysis
Tuesday PM, April 22, 2014
Marriott Marquis, Yerba Buena Level, Salons 5-6
2:30 AM - *M1.01
Microscopy of Fuel Cell Catalyst and Catalyst-Support Degradation
Karren More 1 Raymond Unocic 1 David Cullen 1
1Oak Ridge National Laboratory Oak Ridge USAShow Abstract
High-resolution imaging of the structural changes to Pt-based catalyst nanoparticles supported on carbon blacks using in-situ electrochemical liquid cell transmission electron microscopy (TEM) are being correlated with the behavior of similar materials incorporated in membrane electrode assemblies (MEAs) subjected to accelerated stress tests (ASTs), to elucidate catalyst and catalyst-support degradation phenomena contributing to fuel cell performance loss. Specialized in-situ holders for the TEM have been developed that enable the interactions between catalyst particles and their supports to be imaged during potential cycling in relevant liquid electrolytes, such that the critical stages of materials corrosion during fuel cell operation can be imaged in real time at nm-scale resolution. The direct TEM observations of the changes to the catalyst (Pt dissolution and particle growth/coalescence) and carbon supports (mechanisms of progressive support corrosion) during in-situ electrochemistry, combined with the post-mortem evaluation of cathode layers comprised of similar Pt/C materials after AST of MEAs, provide an unprecedented means by which to “capture” catalyst and catalyst-support degradation mechanisms such that materials optimization strategies can be implemented to enhance fuel cell durability.
Research sponsored by (1) the Office of Fuel Cells Technologies, Office of Energy Efficiency and Renewable Energy, the U.S. Department of Energy and (2) ORNL&’s Center for Nanophase Materials Sciences, Scientific User Facilities Division, Office of Basic Energy Sciences, the U.S. Department of Energy.
3:00 AM - *M1.02
Effect of Confinement on Structure, Water Solubility, Water Transport and Mechanical Properties in Nafion Thin Films
Kirt Page 1 Scott Eastman 1 Sangcheol Kim 1 Brandon Rowe 1 Joseph Dura 2 Kevin Yager 4 Ahmet Kusoglu 3 Christopher Soles 1
1National Institute of Standards and Technology Gaithersburg USA2National Institute of Standards of Technology Gaithersburg USA3Lawrence Berkeley National Laboratory Berkeley USA4Brookhaven National Laboratory Upton USAShow Abstract
Fuel cells based on polymer electrolyte membranes (PEM) show promise as a means of energy conversion for a wide range of applications both in the transportation sector and for stationary power production due to their high charge density and low operating temperatures. Devices are assembled with multiple heterogeneous materials and failure, or performance losses, can largely occur at the interfaces between these materials. While the structure and transport of bulk PEMs for fuel cell applications have been studied extensively, there has been little effort focused on these materials at interfaces and under confinement as they exist within the membrane electrode assembly (MEA) of a working PEM fuel cell. Using a combination of neutron and x-ray reflectivity, grazing-incidence small-angle x-ray scattering (GISAXS), quartz crystal microbalance (QCM), as well as polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS) we have studied the polymer-substrate interfacial structure, thin film nano-scale structure, the swelling, and water transport behavior as a function of humidity, surface chemistry, and initial film thickness (< 220 nm). We have found the interfacial structure to be highly dependent upon the substrate surface chemistry. Moreover, when the polyelectrolyte is confined to thin films there is suppression in both swelling and water diffusivity. Specifically, we observe that the relative humidity-dependent, equilibrium swelling ratio and volumetric water fraction is constant for films above 100 nm. A clear transition in the swelling response, absorbed water content, and the diffusivity (as determined from the time-dependent PM-IRRAS signal) is observed for films thinner than 60 nm. More recently, we have used a technique developed at NIST to measure the mechanical properties of these systems. Preliminary results reveal that confinement also plays a significant role in the mechanical response of Nafion and may help in elucidating the molecular origins for the observed changes in water uptake and transport. It is speculated that these confinement affects should also have an impact on the proton conductivity and overall fuel cell performance. Our studies clearly show that the behavior of the materials under confinement can be quite different than in the bulk. Current fuel cell modeling efforts rely on bulk property values, when considering the catalyst layers and interfaces, to predict structure, transport and fuel cell performance. With this new information, researchers will be able to more accurately model the performance of the MEA within a working fuel cell which could lead to improvements in MEA design and more efficient operating conditions.
3:30 AM - *M1.03
Non-Carbon Nanostructured Supports and Their Effect on Stability of Pt Nanoparticles During Voltage Cycling
Deborah Jones 1 Jacques Roziere 1 Sara Cavaliere 1
1CNRS Montpellier FranceShow Abstract
One of the major issues affecting the durability of PEMFC (Proton Exchange Membrane Fuel Cells) is electrode degradation over time. Indeed, in fuel cell conditions conventional electrocatalyst supports based on carbon suffer from corrosion leading to detachment and migration, or aggregation of electrocatalyst nanoparticles, and loss of performance. One strategy to overcome this issue is the replacement of carbon with (electro)chemically more stable supports. We are currently developing novel nanofibre and nanospherical based PEMFC support materials using alternative materials, including doped oxides and semi-conducting carbides. The challenges to be addressed are related to the development of non-carbon support materials having sufficient surface area to well disperse the electrocatalyst nanoparticles, while ensuring adequate electronic conductivity. We will review current progress in this area, and focus on morphology and physical-chemical properties of non-carbon supports prepared by electrospinning and hydrothermal methods, and the challenges of electrode development from them. Electrocatalytic activity of these systems will be addressed, in particular towards the oxygen reduction reaction, and the results of testing under accelerated ageing protocols will be described in order to compare their resistance to corrosion to that exhibited by conventional carbon based supports and assess their greater stability, and to underline the importance of a strong catalyst support interaction.
4:30 AM - *M1.04
Strategies in Structure-to-Property Correlations of Electrocatalysts
Kateryna Artyushkova 1 Plamen Atanassov 1
1University of New Mexico Albuquerque USAShow Abstract
Development and optimization of electrocatalysts, supports and components for fuel cells are hindered by the complex nature of the materials, a partial understanding of the reaction mechanisms and precise chemistry of the active site or sites and relationship between performance and morphological properties such as size of particles, surface area, roughness, porosity, etc.
XPS is one of the most widely utilized surface spectroscopic techniques for the analysis of catalyst structure. XPS is widely applied to supported nanostructured catalysts because it allows discriminating between oxidation states of the metal, including unusual ones which may play a key role in catalyst behavior.
Surface morphology is one of the most important factors affecting functional performance of components. Digital image processing (DIP) of SEM images is able to convert the 2-D intensity distribution into 1-D image descriptors that are utilized for quantitative morphology analysis. Different phenomena and processes related to the material performance correspond to different diffusion regimes at different lengthscales. A vitally important for functional characterization must be an appropriate separation of the different components of surfaces, which is not only to extract roughness, waviness and form, but also should be extended to concern all multi-scalar topographical events over surface.
Predicting macroscopic properties of interest, such as catalytic activity and stability, from materials chemistry and structure is challenging yet feasible using a multianalytical approach combined with multivariate analysis. Correlation of structure, morphology and performance of different families of materials relevant for energy applications is achieved through the application of principal component analysis (PCA).
This talk will discuss structure-to-property correlations for two different systems. The first material set are a non-platinum Group Metal (Non-PGM) ORR electrocatalysts. Due to the heterogeneous nature of the materials the basic understanding of the interplay between chemistry and morphology of the active sites is missing. The correlation between chemical composition and environment and pore size is critical in understanding catalytic performance.
In the second problem we will address durability of the catalyst layer (CL) which is linked to catalyst dissolution and agglomeration, ionomer degradation, carbon support degradation, and the degradation of pore morphology and surface properties. It is essential to determine parameters representing composition, structure and properties of cathode components and catalysts layer for the optimization of performance and durability.
5:00 AM - *M1.05
Poor Man's CVD, Rich Man's Materials: Versatile Vapor Deposition Synthesis of Precious Metal Catalysts
Alexander B Papandrew 1
1University of Tennessee Knoxville USAShow Abstract
Despite efforts to eliminate platinum-group metals (PGM) from fuel cell electrodes, the noble metals remain the most active and durable materials currently available. The current frontiers of PGM catalyst research include the synthesis of nanostructured alloys and extended metallic surfaces with extremely high activity for the oxygen reduction reaction (ORR).
While electrochemical and physical vapor deposition routes have demonstrated unique capabilities in the synthesis of supported and unsupported advanced PGM catalysts, chemical vapor deposition (CVD) methods have comparatively been overlooked. Conventional CVD is routinely applied to the fabrication of complex, functional planar nanostructures, but it is often unsuited for film deposition on powders and fibers, or within high aspect-ratio microstructures. Increasing interest in these substrates for electrocatalysis and energy conversion applications has provided considerable impetus to devise new deposition routes.
We have developed a simple, inexpensive, CVD-like fixed-bed approach to the deposition of PGM nanoparticle dispersions on finely divided substrates using metalorganic precursors. This process requires no specialized apparatus, and is conducted at mild temperatures (150 C - 270 C). During the deposition process, substrate surface chemistry initiates precursor decomposition and deposition of nanoparticle networks composed of constituent particles as small as 2 nm.
Conformal coatings with extremely high aspect ratios can also be produced within porous monolithic substrates. Subsequent thermal treatments induce morphological evolution of the deposited networks, including alloying and the development of nanoscale porosity. Sacrificial porous templates can be dissolved, liberating unsupported nanostructured catalysts. Porous Pt nanotubes produced via this method showed a specific activity for the ORR of 2400 uA cm-2 at 0.9 V. Additional case studies from low- and intermediate temperature technologies will be shown to illustrate the power and versatility of the technique for PGM catalyst synthesis.
5:30 AM - *M1.06
Graphene-Metal Composite Nanocatalysts for Oxygen Reduction and Methanol Oxidation Reactions
Shaojun Guo 1
1Los Alamos National Lab Los Alamos USAShow Abstract
Developing new synthetic methods for the controlled synthesis of Pt-based or non-Pt nanocatalysts with low or no Pt loading to facilitate sluggish cathodic oxygen reduction reaction (ORR) and organics oxidation reactions is a key issue in the development of fuel cell technology. Various nanoparticles (NPs), ranging from the size to shape, composition and structure, have shown the good potential to catalyze the sluggish cathodic and anodic reactions. In this presentation, I will talk about my recent advances on synthesis of graphene-FePt, graphene-Co/CoO and graphene-PtPd nanoparticles for effectively enhancing ORR and methanol oxidation reaction.
Thomas A. Zawodzinski, University of Tennessee, Knoxville, and Oak Ridge National Laboratory
Nigel Brandon, Imperial College London
Vito Di Noto, University of Padova
Steven Hamrock, 3M Fuel Cell Components Program
M3: Flow Batteries PEM Membranes
Wednesday PM, April 23, 2014
Marriott Marquis, Yerba Buena Level, Salons 5-6
2:30 AM - *M3.01
Engineering Transport in Electrochemical Power Conversion and Storage Systems
Matthew M. Mench 1 3 Thomas A. Zawodzinski 2 3
1University of Tennessee Knoxville USA2University of Tennessee Knoxville USA3Oak Ridge National Laboratory Oak Ridge USAShow Abstract
The ability to engineer transport of mass, heat, and charge in electrochemical power conversion and storage systems such as fuel cells and batteries is critical to ensure optimal operational stability, durability, and performance. I this talk, I will discuss two types of systems, a low temperature polymer electrolyte fuel cell and a vanadium redox flow battery. A combination of computational and experimental approaches will be shown which help us to understand and optimize system performance and durability through enhanced transport. Both systems have complex transport issues which, when engineered through materials, cell architecture or other methodologies, can be optimized.
I the first part of the talk, I will discuss the redox flow battery system as a potential disruptive technology for grid-level energy storage. Work at the University of Tennessee and Oak Ridge National Lab has recently shown an increase in the operating current density of over an order of magnitude compared to conventional systems, while maintaining high efficiency. This achievement enables a tremendous reduction in cost of the power plant. In the second part of the talk, I will discuss our efforts to maximize performance and durability in polymer electrolyte fuel cells. With a non-conventional architecture, we have shown a tremendous reduction in mass transport losses that allow us to push beyond 2 A/cm2 at high voltage. In this high performance system, dry out of the anode is the limiting behavior. Thus, there is a desire to control the direction and magnitude of the net water flux across the fuel cell. This part of the talk will explore the limits of what can be accomplished through engineering of materials within a realistic range of achievable transport parameters. The engineering of thermal and mass transport across the fuel cell will be shown to be capable of reversing the net flux of water as needed for the particular system, without resulting in a trade-off in performance.
3:00 AM - M3.02
Performance and Durability of the HBr/Br2 - H2 Redox Flow Cell
Michael C. Tucker 1 Kyu Taek Cho 1 Venkat Srinivasan 1 Vincent S. Battaglia 1 Adam Z. Weber 1
1Lawrence Berkeley National Laboratory Berkeley USAShow Abstract
The aqueous hydrogen bromide/bromine - hydrogen flow cell under development at Berkeley Lab provides high power density and stable long-term cycling. Peak power of 1.4W/cm2 and >90% efficiency while cycling at 0.4W/cm2 were reported previously. The present work describes efforts to optimize the cell materials and understand degradation mechanisms.
During discharge, a solution of Br2 in HBr (aq) is fed to the cathode compartment where bromine reacts with protons supplied from the anode side and is reduced to bromide, generating the theoretical open circuit potential of 1.098 V at 25°C. On charge, H2 and Br2 are generated from HBr at the (-) and (+) electrodes, respectively. The challenges of this system include: high vapor pressure of bromine gas; migration of water and bromine species to the hydrogen anode, especially during charging; poisoning of the anode Pt catalyst by bromine species; and, formation of mixed aqueous and liquid bromine phases at high states of charge.
Cell materials selection has a large impact on cell performance. We present results for various carbon cathode electrode morphologies, membrane types, and anode catalyst compositions. The relevant materials properties for the carbon cathode are: porosity, tortuosity, effective conductivity, and carbon type. The relevant materials properties for membranes are: proton conductivity, hydrogen permeability, bromine uptake, and electro-osmotic drag coefficient. Long-term cycling results will be discussed in terms of various classes of degradation mechanisms related to: cell materials; crossover of water and electro-active species; and, changes in solution chemistry.
3:15 AM - M3.03
Resolving In-Situ Losses in All-Vanadium Redox Flow Batteries
Che-Nan Sun 1 Frank Delnick 2 Doug Aaron 3 Emma Hollmann 3 Tom Zawodzinski 1 3
1Oak Ridge National Laboratory Oak Ridge USA2Sandia National Laboratory Albuquerque USA3University of Tennessee-Knoxville Knoxville USAShow Abstract
Redox flow batteries (RFB) are considered potential candidates for grid-integrated storage of energy generated by wind, solar and other sustainable resource. However, adoption of RFBs for this application is contingent upon reducing overall system cost. In the well-known case of the aqueous all-vanadium RFB (VRFB), both the energy storage medium and the energy conversion cells contribute significantly to the system cost. One key route to cost reduction of the cells is an increase of cell current density at the desired operating voltage, permitting decreased cell and/or stack size.
To further improve the performance, one must identify and quantify the rate-limiting processes which control the losses in the cell. In previous work, we demonstrated that the voltage losses originating from charge transfer and ohmic processes at various discharge currents can be quantified using electrochemical impedance spectroscopy (EIS) under an idealized condition; and these losses were dominant at the negative electrode.
In this work, we again apply EIS to probe the voltage losses at the VRFB negative electrode. The overvoltages resulting from ohmic, charge transfer and diffusion process are quantified individually at various operating current densities during charge and discharge. More specifically, we will demonstrate and discuss the influences of flow rate and electrode thickness on each overvoltage. The obtained results will be presented to identify and quantify the rate limiting processes at various charge/discharge currents and cell configurations leading to a pathway for performance optimization.
3:30 AM - M3.04
Metallic Micro-Lattice Cathodes for Application in Li-Air Batteries
Chen Xu 1 Betar Gallant 1 Wendy Gu 1 Timm Lohmann 2 Paul Albertus 2 Julia R. Greer 1
1California Institute of Technology Pasadena USA2Robert Bosch LLC Palo Alto USAShow Abstract
Li-O2 batteries have received considerable attention due to their high specific energy. Several challenges need to be overcome to enable practical applications of Li-O2 batteries, including low round-trip efficiency associated with high overpotentials on charge, electrode and electrolyte instability, and low rate capability at the cathode. Concerted efforts have been directed towards finding successful combinations of electrolyte solvent and cathode material. Recent work showed a 95% capacity retention after 100 cycles by nanoporous gold cathode in dimethyl sulfoxide (DMSO) .
We describe the fabrication and implementation of 3-dimensional Au micro-lattices with a relative density of 0.2% into Li-O2 batteries . The lattices were fabricated by first sputtering 500 nm of Au at room temperature onto polymer templates that were formed by self-propagating photopolymer waveguide prototyping at Hughes Research Labs, followed by fully removing the sacrificial polymer scaffold. The relatively non-smooth surface of nanocrystalline Au film in concert with a periodic, hierarchical micro-truss geometry that spans three orders of magnitude in length scale - nm, um, and mm - offers adjustable specific surface area, pore size, and mechanical stability. Surfaces of discharged cathodes are analyzed using SEM, XRD and FTIR, and deterioration is described in the framework of lithium peroxide-forming reactions under different discharge conditions.
 Peng et al, Science 2012
4:15 AM - *M3.05
Hybrid Inorganic-Organic Nanocomposite Membranes Based on PBI and HfO2 for HT-PEMFCs
Vito Di Noto 1 2 Jonas Rivetti 1 Enrico Negro 1 2 Federico Bertasi 1 2 Keti Vezzu 3
1University of Padova Padova Italy2Consorzio Interuniversitario Nazionale per la Scienza e la Tecnologia dei Materiali, INSTM Padova Italy3Veneto Nanotech S.C.p.a. Padova ItalyShow Abstract
High-temperature proton exchange membrane fuel cells (HT-PEMFCs) are an innovative family of highly efficient and environmentally-friendly energy conversion devices typically operating in the range 150HT-PEMFCs use as the electrolyte a polymeric membrane characterized by a high thermal and chemical stability (e.g., polybenzimidazole, PBI). The latter is swollen with a suitable proton-conducting medium, usually H3PO4. The resulting system is capable of efficient proton transport in the typical operating conditions of HT-PEMFCs. In this work, innovative hybrid inorganic-organic membranes for application in HT-PEMFCs are developed. The membranes consist of PBI including between 0 and 35 wt% of nanometric HfO2 and are obtained by solvent-casting processes. HfO2, which is an interesting nanofiller for its remarkable chemical and electrochemical stability and for the basic character of its surface, plays a crucial role in the development of interactions with the other components of the hybrid membranes (i.e., PBI and H3PO4), thus leading to an improved thermal stability and proton conductivity.
The essay of Hf in the hybrid membranes is determined by ICP-AES. The thermal stability and transitions of materials are investigated by HR-TG and DSC measurements, respectively. FT-MIR ATR vibrational spectroscopy measurements carried out on both sides of the membranes allows us to study the structure and interactions in nanocomposite membranes. Finally, the electric response of membranes is measured by broadband electrical spectroscopy (BES) in the 5-190°C and 1-107 Hz temperature and frequency range, respectively. Materials are investigated in completely dry and H3PO4-doped state.
In summary, the insertion of HfO2 nanofiller in bulk hybrid PBI-based materials: a) improves the thermal stability of hybrid membranes: b) inhibits the condensation at high temperature of H3PO4 to form H4P2O7; and c) increases the electrical conductivity by a factor of ca. 1.5-2, (a value of 6.6x10-2 S/cm for the membrane with 11 wt% of the nanofiller is obtained). These features make the proposed hybrid membranes very promising candidates for application in HT-PEMFCs.
4:45 AM - M3.06
Phosphoric Acid Distribution in High-Temperature Polymer Electrolyte Fuel Cell Membranes
Florian Mack 1 Stefan Heissler 2 Tasleem Ahmad Muzaffar 1 Roswitha Zeis 1
1Karlsruhe Institute of Technology (KIT) Ulm Germany2Karlsruhe Institute of Technology (KIT) Karlsruhe GermanyShow Abstract
Phosphoric acid doped polybenzimidazole (PBI) is the most common membrane material for high-temperature polymer electrolyte fuel cells (HT-PEMFC). The PBI membrane was doped by immersion in hot phosphoric acid. The sojourn time in the acid defines the doping level of the membrane. Despite the fact that this is a standard method to prepare HT-PEMFC membranes, in-depth studies of the morphology of such acid doped PBI membranes are still lacking. In particular, the impact of the doping level on the morphology and its influence on the proton conductivity is not yet well understood. Therefore, we measured the proton conductivity in a full cell setup and employed confocal Raman microscopy to spatially resolve the acid distribution within poly (2, 5-benzimidazole) (AB-PBI) membranes. To our knowledge, this is the first time such experiments are carried out on PBI type membranes.
The proton conductivity improved significantly for membranes with 6 hours of doping time compared with those doped for only 3 hours. However, a merely slight acid up-take occurred. This result shows that the doping level is not the only parameter that defines the conductivity of the membrane. The conductivity is also influenced by the micro acid distribution within the membrane, which can be determined by confocal Raman microscopy. The interactions between the basic N-sites of the AB-PBI polymer and the phosphoric acid were investigated with this method. With increasing doping time a more homogenous distribution of phosphoric acid in the AB-PBI host was observed, indicating stronger interactions between the dopant and the host. Confocal Raman microscopy allows us to study the correlation between the morphology and conductivity of phosphoric acid doped AB-PBI membranes.
5:00 AM - M3.07
Nature of Electro-Osmosis in Polymer Electrolyte Membranes for Fuel Cells Applications
Yoong-Kee Choe 1
1National Institute of Advanced Industrial Science amp; Technology Tsukuba, Ibaraki JapanShow Abstract
Polymer electrolyte membranes (PEMs) are one of the key components in polymer electrolyte membrane fuel cells (PEFCs). It is well known that proton conduction in PEMs causes co-transport of water molecules, whose phenomenon is called by the term “electro-osmosis”. Electro-osmosis leads to the localization of water molecules in the vicinity of the cathode, which reduces the performance of fuel cells. To minimize electro-osmotic drag coefficients (the number of water molecules cotransported with proton conduction), atomistic level understanding on electro-osmosis is necessary. In this presentation, we report results of first-principles molecular dynamics simulations carried out to investigate proton transport and its couplled water transport in PEMs.
5:15 AM - M3.08
A Novel Approach to X-Ray Tomography on Operating Fuel Cells
Samuel J. Cooper 1 Tao Li 2 Farid Tariq 3 Vladimir Yufit 3 Robert S. Bradley 4 Paul R. Shearing 5 Nigel P. Brandon 3 John Kilner 1
1Imperial College London London United Kingdom2Imperial College London London United Kingdom3Imperial College London London United Kingdom4University of Manchester Manchester United Kingdom5University College London London United KingdomShow Abstract
The electrochemical performance of solid oxide fuel cells (SOFC) electrodes is strongly influenced by their microstructure . Non-destructive X-ray tomography is a key technique for studying fuel cell electrodes as two dimensional imaging does not capture the full complexity of the microstructures involved . Previously, these SOFCs have been difficult to study in-operando due to the geometry of the devices, as well as the temperature and gas sealing requirements. In this work we present a novel experimental design that allows both X-ray tomography and diffraction to be performed on an operating fuel cell. When coupled with electrochemical techniques, this approach allows for the relationship between operating conditions and microstructural evolution to be better understood.
The fuel cells were found to have an engineered hierarchical pore structure on the anode side. The tortuosity factors of this material were quantified using a simulated diffusion approach , which had to be modified for the specific cell geometry considered. This parameter, along with several others, including the specific surface area, could potentially be used in an Adler, Lane and Steele  type model, enabling the electrochemical performance of the cell to be predicted and compared with the experimental data obtained.
 P.R. Shearing, D.J.L. Brett, N.P. Brandon, Int Mater Rev, 55 (2010) 347-363.
 P.R. Shearing, J. Gelb, N.P. Brandon, J Eur Ceram Soc, 30 (2010) 1809-1814.
 S.J. Cooper, D.S. Eastwood, J. Gelb, G. Damblanc, D.J.L. Brett, R.S. Bradley, P.J. Withers, P.D. Lee, A.J. Marquis, N.P. Brandon, P.R. Shearing, J Power Sources, (2013).
 S.B. Adler, J.A. Lane, B.C.H. Steele, J Electrochem Soc, 143 (1996) 3554.
Wednesday AM, April 23, 2014
Marriott Marquis, Yerba Buena Level, Salons 5-6
9:30 AM - M2.01
Multimetallic FePt-Based Nanowires as Highly Efficent Catalysts for Oxygen Reduction Reaction and Methanol Oxidation Reaction
Shaojun Guo 1
1Los Alamos National Lab Los Alamos USAShow Abstract
Various Pt-based metal nanoparticles (NPs) have shown the great potential to catalyze the fuel cell reactions. However, the main problem of these NPs for fuel cells is their limited durability. In this presentation, we focus on our recent advances in rational design and controlled synthesis of FePt-based nanowire (NW) electrocatalysts towards oxygen reduction and methanol oxidation reactions. FePt NWs have been synthesized in high yield via a simple organic phase decomposition of Fe(CO)5 and reduction of Pt(acac)2 in the 1-octadecene and oleylamine solution containing sodium oleate. Treated with acetic acid, these FePt NWs become active and stable for ORR. Through coating FePtPd NWs with 0.8 nm FePt shell, we further found that FePtPd/FePt core/shell NWs are more active and stable for ORR than FePt NWs. Furthermore, we will also show that FePtPd trimetallic NWs are active and durable for MOR.
9:45 AM - M2.02
Facile Fabrication of Electrospun Supportless Porous Intermetallic FePt Nanotubes for Highly Stable Cathode Catalysts in PEMFCs
Jaehyuk Lee 1 Youngjin Ye 1 Yeongdong Mun 1 Hee-Woo Rhee 2 Hyung Ik Lee 3 Jinwoo Lee 1
1POSTECH Pohang. Gyeongbuk Republic of Korea2Sogang University Seoul Republic of Korea3Agency for Defense Development, Daejeon Dae-jeon Republic of KoreaShow Abstract
Supportless one-dimensional (1-D) intermetallic Pt-based nanotubes are considered as promising candidates for the active and durable cathode catalyst in proton exchange membrane fuel cells (PEMFCs). However, one-dimensional Pt-based nanotubes are difficult to produce at large scale because they have generally been synthesized using a template method that requires a multistep synthetic routes. Herein, we report the simple and scalable method to produce intermetallic FePt nanotubes by electrospinning. Collapse of the tubular nanostructure was prevented by in-situ generated silica template during the high temperature heat treatment required for the conversion to fct-FePt intermetallic phase. When tested as cathode catalysts, the resulting material showed 2.2 times higher specific ORR activity than Pt/C. Moreover, a single cell test of the resulting material showed comparable initial performance and superior durability compared to Pt/C. After accelerated durability test by operating at a potential of 1.4 V for 3 h, the maximum power density of membrane-electrode-assembly (MEA) with intermetallic FePt nanotubes decreased only by 8 % whereas that of MEA with Pt/C decreased by 79 %. This approach can be applied to produce a wide range of 1-D tubular intermetallic catalysts with good scalability, tailored composition, and durability at inexpensive cost.
10:00 AM - M2.03
Adsorption of O2 on Orthorhombic LaMnO3: A Hybrid Exchange Density Functional Theory Study of an Alkaline Fuel Cell Catalyst
Ehsan A Ahmad 1 2 Giuseppe Mallia 1 2 Denis Kramer 3 Anthony R Kucernak 1 Nicholas M Harrison 1 2 4
1Imperial College London London United Kingdom2Imperial College London London United Kingdom3University of Southampton Southampton United Kingdom4Daresbury Laboratory Daresbury United KingdomShow Abstract
LaMnO3 is an inexpensive alternative to precious metals (e.g. platinum) as a catalyst for the oxygen reduction reaction in alkaline fuel cells. In fact, recent studies have shown that among a range of non-noble metal catalysts, LaMnO3 provides the highest catalytic activity. Despite this, very little is known about LaMnO3 in the alkaline fuel cells environment, where the orthorhombic structure is most stable. In order to understand the reactivity of orthorhombic LaMnO3 we must first understand the nature of the adsorbate-substrate interactions at the surface. Hence, we have carried out calculations of O2 adsorption on its electrostatically stable low index surfaces using hybrid-exchange density functional theory, as implemented in CRYSTAL09. The adsorption modes of O2 on the (100), (001), (101) and (110) surfaces are presented and discussed in terms of their structure and energetics. The reactivity of the adsorption sites that exist on these surfaces towards the oxygen reduction reaction is predicted according to the binding energy and charge transfer to O2.
10:15 AM - M2.04
A Simple Microwave Preparation of Se-Rich CoSe2/C Cathode Catalyst for PEM Fuel Cells
Xuan Cheng 1 Hengyi Li 1 Dong Gao 1
1Xiamen University Xiamen ChinaShow Abstract
Carbon supported cobalt selenides (CoSe2/C) were prepared by a simple microwave method using cobalt acetate and selenium dioxide as precursors with different Se/Co molar ratios. The electrocatalytic activities of CoSe2/C toward oxygen reduction reaction (ORR) were examined by rotating disk electrode (RDE) technique. The effects of Se/Co ratios on surface morphology, crystal structure, chemical composition and ORR activity of catalyst nanoparticles were systematically studied. The experimental compositions of CoSe1.8-CoSe2.7/C with average particle sized 12.4-15.9 nm, major orthorhombic CoSe2 and minor cubic CoSe2 phases could be obtained with the Se/Co ratios of 2.0-4.0. The potentials corresponding to ORR (EORR) reached 0.6-0.7 V, while the electron transfer numbers (n) 3.1-4.0. The Se-rich CoSe2/C prepared with the optimized Se/Co=3.0 exhibited the best ORR activity with the EORR=0.705 V and n=4. It was demonstrated that excess selenium oxide would prevent CoSe2 nanoparticles from growing and result in smaller particle sizes, which is benefited to ORR activity. However, too much selenium oxide would cause severe aggregation of CoSe2 nanoparticles, leading to poor ORR activity.
10:30 AM - M2.05
Pyridine-Based Polybenzimidazole-Functionalized Multi-Walled Carbon Nanotubes Supported Platinum Catalysts for High Temperature Polymer Electrolyte Membrane Fuel Cells
Duanghathai Kaewsai 1 Hsiu-Li Lin 1 2 T. Leon Yu 1 2
1Yuan Ze University Chung-Li Taiwan2Fuel Cell Center Chung-li TaiwanShow Abstract
This research prepared synthesized Pyridine-based polybenzimidazole (PyPBI) with a 4 to 6 molar ratio of 2,6-pyridinedicarboxylic acid (PyDA) and isophthalic acid )IPA). The PyPBI was used as a wrapping polymer of MWCNT and for depositing Pt nanoparticles on the MWCNT (Pt-PyPBI/CNT). The catalysts were physicochemically characterized by transmission electron microscopy (TEM), thermo-gravimetric analysis (TGA), X-Ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The Pt-PyPBI/CNT with Pt loading of ~46 wt.% and Pt particle sizes of about 3-4 nm is used to prepare a PBI/H3PO4 based membrane electrode assembly (MEA) and perform fuel cell test at 160°C. The We demonstrate that the MEA prepared using thePt-PyPBI/CNT catalyst has a higher fuel cell performance than that prepared using a commercial Pt-C.
11:15 AM - M2.06
Nanostructured Carbon-Based Non-Precious Metal Electrocatalysts for the Oxygen Reduction Reaction
Sang Hoon Joo 1
1Ulsan National Institute of Science and Technology (UNIST) Ulsan Republic of KoreaShow Abstract
Two classes of new electrocatalysts for the oxygen reduction reaction (ORR) based on nanoporous/nanostructured carbons are presented. Transition metal-doped ordered mesoporous porphyrinic carbons (M-OMPC) with high surface areas and tunable pore structures have been developed by nanocasting mesoporous silica templates. Among the M-OMPC catalysts, the FeCo-OMPC catalyst exhibited an excellent ORR activity in an acidic medium, higher than other non-precious metal catalysts. It showed higher kinetic current at 0.9 V than Pt/C catalysts, as well as superior long-term durability and MeOH-tolerance. A weakened interaction between oxygen atom and FeCo-OMPC compared to Pt/C as well as high surface area of FeCo-OMPC appear responsible for its significantly high ORR activity. Second example is based on the carbon nanocomposites comprising pure carbon nanotube cores and heteroatom-doped carbon sheath layers (CNT/HDC). The CNT/HDC nanostructures showed excellent ORR activity in an alkaline solution, which is one of the best performances among the heteroatom-doped nanocarbon catalysts in terms of the half-wave potential and kinetic current density. The kinetic parameters of the CNT/HDC nanostructures compared favorably with those of a Pt/C catalyst. In addition, the CNT/HDC also showed high current and power densities when employed as cathode catalysts in alkaline fuel cell.
11:30 AM - M2.07
An Investigation of Platinum Metal Monolayer Catalysts by X-Ray Photoelectron Spectroscopy and Cyclic Voltammetry
Adam James Vitale 1 Faisal Alamgir 1 Robert Rettew 1
1Georgia Tech Atlanta USAShow Abstract
Platinum group metals (PGM) are the catalyst of choice in a wide variety of catalytic reactions, including the oxygen reduction reaction (ORR). One of the main goals of catalyst development currently is to modify near-surface PGMs, namely platinum, iridium and gold, through size-, strain- and ligand-effects with the support, in order to increase robustness and efficiency while decreasing the cost. We present here our research on tailoring the near-surface electronic structure of the overlayer/support catalytic systems under low-loading limits of PGM overlayers on a wide variety of catalysts for electrochemistry. Surface-limited redox replacement (SLRR) is used for layer-by-layer PGM growth.
Synchrotron-based XPS allowed us to profile the transitions in the electronic structure from the surface down to the adlayer/support interface and beyond. Varying the source photon energy allows us to analyze the electronic structure of the layered system at several penetration depths. Catalyst durability is also a significant aspect for further consideration, with instability oftentimes caused by metal dissolution or corrosion. It is has been shown that Au can have a stabilizing effect on Pt even under high oxidizing conditions and thus can suppress Pt dissolution, resulting in improved durability of the Pt catalysts. This study looks at the durability of Pt monolayer catalysts firstly by subjecting them to aggressive cyclic voltammetry cycling and by examining the activity of the surfaces towards the ORR during potential cycling in an oxygen environment. These two aspects of experiments, spectroscopy and electrochemical tests, are the primary basis for our study.
By analyzing the XPS peak area ratios of the Pt4f and Au4f photoemissions, a relative quantification of the PMG deposit can be achieved. An increase in the ratio of the PMG 4f peaks area to the Au 4f peaks area can be seen as the number of SLRR iterations increases, showing a continuing growth of the adlayer through the SLRR process. Additionally, a negative shift of ~1.5eV in binding energy is measured for the Pt adlayer photoemission between 3 and 6 iterations of the SLRR process at room temperature, showing that Pt is not fully reduced and exhibits cationic intermediaries at low iteration numbers of the SLRR process. With regard to electrochemical durability, samples with an overlayer thickness of 2 monolayers or less show a more dramatic decay in electrochemically active surface area under aggressive cycling, indicating poor durability. However, Pt surface retention is significantly improved once it is at least 3 ML, indicating increased durability due to chemical state and thickness of the surface. The cycling in oxygen-rich media show markedly enhanced currents for the ORR once a 2 monolayer Pt overlayer thickness is achieved, showing the highest activity towards the ORR relative to the amount of platinum present.
11:45 AM - M2.08
Composites of Graphene and Conjugated Polymelectrolytes as Metal-Free Electrocatalysts for Oxygen Reduction Reaction
Jianyong Ouyang 1
1National University of Singapore Singapore SingaporeShow Abstract
Fuel cells and metal oxygen batteries are important electrochemical energy devices. A big problem for the commercialization of these devices lies in the electrocatalysts, particularly for the sluggish oxygen reduction reaction. Platinum is traditionally used as the electrocatalysts for oxygen reduction reaction. But platinum is a rare element and is very expensive. Thus, it is significant to develop platinum-free high-performance electrocatalysts for oxygen reduction reaction. In this paper, I will present the preparation of composites of graphene and conjugated polyelectrolytes and their application as high-performance electrocatalysts for oxygen reaction reaction. The performance is almost the same as that of platinum, and it is significantly better than graphene or composites of graphene and non-conjugated polyelectrolytes.
12:00 PM - M2.09
Printable Catalyst System of Metal Nanoring and Nanodot Arrays for Electrocatalytic Reaction
Sung Mook Choi 1 Sang Ho Lee 2 Joo Yul Lee 1 Doyon Chang 1 Won Bae Kim 2
1Korea Institute of Materials Science (KIMS) Changwon Republic of Korea2Gwangju Institute of Science and Technology (GIST) Gwangju Republic of KoreaShow Abstract
This research demonstrates a direct printing process of catalyst system fashioned of sub-100 nm metal ring and metal dot catalyst arrays. The stamping platforms used for this printing process are based on the vertically aligned carbon nanoarchitectures with the ring- and dot-shaped tips that are the keystone to determine the printed results (e.g., rings and dots). As a result of the printing process using the ring- and dot-featured stamps, nanoscale metal ring and dot catalysts, made of platinum and gold, are correspondently printed over a large substrate area. An advanced demonstration to understand the fundamental natures of the metal ring and metal dot catalysts as well as to incorporate them into the printable catalytic system is successfully accomplished by applying these printed metal ring and dot arrays into diverse catalyst reactions in acidic and alkaline environment.
The printable nano-sized catalyst systems, made of metal rings and metal dots, were developed for the first time. The vertically aligned carbon-based nanostructures of the ring-shaped tips and the dot-featured tips were employed as the stamps to create the nanoscale ring and dot catalyst arrays. Importantly, the printed nanorings and nanodots were employed into the electrochemical oxidation reactions, which demonstrates catalytic properties caused from the morphology difference of the metal rings and metal dots. It is straightforward that our printing methodology can be highly versatile for fabricating diverse ring and dot arrays made of not only metals but also various organic and inorganic materials, indicating that the printable sub-100-nm ring and dot arrays could play an important role in comprehending the fundamental nature of dot and ring nanomaterials and thus incorporating them into suitable device applications.
12:15 PM - M2.10
Development of Nitrogen-Coordinated Transition Metal Catalysts on Carbon Nanofibers for ORR
Jose Fernando Flores 1 Jason Komadina 1 Jennifer Q Lu 1
1UC Merced Merced USAShow Abstract
Fuel cell current density and voltage are primarily limited by the slow kinetics of the oxygen reduction reaction (ORR) on the cathode. Pt-based catalysts offer high activity for ORR at the low temperatures used in polymer electrolyte membrane fuel cells (PEMFCs), but with prohibitively high cost and poor stability. We engineer carbon nanofiber-supported nitrogen-complexed first-row transition metal (M-Nx-C) catalysts for ORR. Carbon nanofibers (CNFs) are directly grown on stainless steel current collectors. A N-doped carbon overcoat on CNFs is accomplished by electro-initiated polymerization of acrylamide and acrylonitrile. We investigated the effects of presence of metal species during pyrolysis and found the metals to play a key role in the electrocatalysis of ORR. Co yielded the highest onset potential, followed by Cu, Fe, and Zn. The CNF structure shifted the ORR onset potentials by upwards of 100 mV compared to samples without CNFs, and is comparable to Pt activity; the Co-Nx-CNF structure shows a reductive E1/2 about 70 mV more negative than that for Pt catalyst. Our findings highlight the benefits of binder-free direct electron transport, high surface area, and chemical stability of CNFs coupled with M-Nx-C catalyst sites for ORR. We will discuss the effect of metal on nitrogen heteroatom properties, which in turn affect ORR performance. This research provides new insight in the discovery and optimization of non-precious metal catalysts for low cost, high efficiency fuel cells.
12:30 PM - M2.11
Organic Transition-Metal Complex Functionalized Nanocarbons for Electrochemical Applications
Zhongtao Zhang 1 Haining Liu 1 C. Heath Turner 1
1University of Alabama Tuscaloosa USAShow Abstract
Our previous computational work on the cyclopentene-transition metal (CpTM) functionalized pristine and B-doped nanocarbons (carbon nanotubes and graphenes) demonstrated promising redox properties as an electron donor-recptor in electrochemical system (and great stability). In this work, we report a theoretical study on novel porphyrin-transition metal-nanocarbon complexes (PORTM with TM = Fe, Zn, and Mn) for electrochemical and catalytic applications. The geometries of PORTM/ pristine and B-doped CNTs and graphenes are discussed from potential energy surface scans using density functional theory (DFT) and semi-empirical PM6 methods. The energetic and electronic structural properties are also investigated from the DFT calculations by band structure analyses, natural bond order partial charges, and deformation charge density analyses to explore the stability and application of PORTM-nanocarbon complexes for nanoelectronics. For the electrochemical properties, we calculate the redox potentials and the charge transfer mechanism of PORTM-nanocarbon complexes in different solvents using DFT combined with the conductor-like polarizable continuum model (CPCM) solvation model, and compare them to the CpTM-nanocarbon complexes.
Thomas A. Zawodzinski, University of Tennessee, Knoxville, and Oak Ridge National Laboratory
Nigel Brandon, Imperial College London
Vito Di Noto, University of Padova
Steven Hamrock, 3M Fuel Cell Components Program
M5: Li Batteries and High T Electrochemistry
Thursday PM, April 24, 2014
Marriott Marquis, Yerba Buena Level, Salons 5-6
2:30 AM - *M5.01
Solid Oxide Fe-Air Battery Using LaGaO3 Based Oxide
Tatsumi Ishihara 2 1 Atsushi Inoishi 1 Shintaro Ida 1
1Kyushu University Fukuoka Japan2Kyushu University Fukuoka JapanShow Abstract
At present, there are strong demand for new battery with large capacity and metal-air battery is attracting much interest. In this study, solid state Fe-air rechargeable battery using LaGaO3-high oxide ion conducting electrolyte was studied and H2/H2O redox mediator shows high performance, including discharge potential, and high capacity. Reaction of this battery proceeds with the following equations at 773 K as we reported.
Air electrode; 1/2 O2 + 2e- → O2- (1)
Fuel electrode; H2 + O2- → H2O + 2e- (2)
Fe set chamber; 3Fe + 4H2O → Fe3O4 + 4H2 (3)
Among the various materials, Ni-Fe-base cermet is highly active anode and stable against charge and discharge for Fe-air battery using LaGaO3-based oxide ion conducting electrolyte. In particular, La0.6Sr0.4Fe0.9Mn0.1O3 (LSFM) and Ce0.6Mn0.3Fe0.1O0.2 (CMF) were highly effective as oxide used in cermet anode. Stable cycle performance was observed over 30 cycles and energy density of ca. 600 mAh/g-Fe was exhibited with 85 % round trip energy efficiency.
3:00 AM - M5.02
Synthesis, Structure and Li- Electrochemical Reactivity of Li4NiTeO6
Sathiya Mariyappan 1 2 4 Kannadka Ramesha 3 Gwenaelle Rousse 5 Dominique Foix 7 4 8 Danielle Gonbeau 7 4 8 K. GuruPrakash 3 Marie-Liesse Doublet 6 4 8 Jean-Marie Tarascon 2 4 8
1LRCS Amiens France2Collamp;#232;ge de France Paris France3CSIR-Madras Complex Chennai India4ALISTORE-EuropeanResearch Institute Amiens France5Universitamp;#233; Pierre et Marie Curie Paris France6Universitamp;#233; Montpellier 2 Montpellier France7University of Pau Pau France8FR CNRS 3459 France FranceShow Abstract
Layered Li4NiTeO6 have been synthesized and studied for its possible application in Li-ion batteries with the hope of achieving high capacity through i) the 2e- redox process associated with Ni+4/Ni+2 and ii) oxide ion participation in the redox process as observed with similar Li4MM&’O6 oxides.1-3 The material reversibly reacts with 1.5 Li+ at a potential of 4.2 V through a classical insertion mechanism enlisting the Ni+4/Ni+2 redox couple. The higher Ni+2/Ni+4 redox voltage observed for Li4NiTeO6 (4.2V) as compared to other Ni+2-based layered oxides (< 4V) was found to be associated with inductive effect from Te+6 in Li4NiTeO6 as a TeO66- moiety to lower the electron density around Ni+2 ion. However, the participation of oxide ion in the redox process have not been observed with Li4NiTeO6, presumably due to the large separation between Ni+4 d levels and O2p levels hence limiting the reversible capacity to 110 mAh/g. Though, Li4NiTeO6 has limited practical application due to toxic Te, this study open up a way to design better electrode materials with proper tuning of cell voltage and feasibility for anion- cation redox chemistry.
1. M. Sathiya, G. Rousse, K. Ramesha, C. P. Laisa, H. Vezin, M. T. Sougrati, M-L. Doublet, D. Foix, D. Gonbeau, W.Walker, A. S. Prakash, M. Ben Hassine, L. Dupont, J-M. Tarascon, Nat. Mater, 2013, 12, 827.
2. V. Kumar, N. Bhardwaj, N. Tomar, V. Thakral, S. Uma, Inorg. Chem. 2012, 51, 10471.
3. M. Sathiya, K. Ramesha, G. Rousse, D. Foix, D. Gonbeau, A. S. Prakash, M-L. Doublet, K. Hemalatha, J.-M. Tarascon, Chem. Mater. 2013, 25 (7), 1121.
3:15 AM - M5.03
TiSnSb - A Promising Anode Material for Li-Ion Batteries? The Role of the Electrode/Electrolyte Interphase
Wanjie Zhang 1 2 Herve Martinez 1 Remi Dedryvere 1 Fouad Ghamouss 2 Daniel Lemordant 2 Ali Darwiche 3 Laure Monconduit 3
1IPREM-ECP UMR CNRS 5254 Pau Cedex 9 France2PCM2E E.A. 6299 Tours France3ICGM-AIME UMR CNRS 5253 Montpellier FranceShow Abstract
Conversion materials for Li-ion batteries, such as Sb and Sn-based compounds, have attracted much intense scientific attention for their high storage capacities. Among conversion materials, TiSnSb has been developed as a negative electrode for Li-ion batteries. This material can reversibly take up 6.5 Li per formula unit that corresponds to a specific capacity of 580 mAh/g with noteworthy high rate capabilities. As the working potential of TiSnSb is out of the electrochemical window of classical electrolytes like alkylcarbonates mixtures, the formation of a protective and stable passivation film (the solid electrolyte interphase or SEI) is required.
At this time, little information can be found about the formation and composition of the SEI layer on conversion electrodes. With the aim to study the electrode/electrolyte interphase, X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS) were performed on TiSnSb electrodes associated to electrochemical studies. In order to improve the performances of TiSnSb, SEI builder additives (vinylene carbonate VC and fluoroethylene carbonate FEC) were added to the standard electrolyte (1M LiPF6 in EC/PC/3DMC) to modify the SEI composition and morphology.
XPS analysis and EIS results, lead first to the conclusion that the thickness and the resistance of the SEI layer was lower at high cycling rate (4C) than low cycling rate (C/2). Adding additives has also a strong impact on the SEI formation: FEC/VC-containing electrolyte formed a thinner SEI layer and EIS studies supported the same conclusion. In addition to the partial dissolution of the SEI layer occurs during de-lithiation, the continuously growing in thickness of the SEI layer upon cycling confirms the dynamic and unstable behavior of the SEI layer already reported for other conversion materials.
In order to overcome the drawback of an unstable SEI, a pyrrolidinium based ionic liquid (IL) was used as electrolyte instead of the alkylcarbonates. It was found not only to improve the cycling performances of TiSnSb electrode but also to decrease the cumulative capacity losses. XPS studies reveal that the nature of the SEI species is responsible to the enhanced cycleability.
In conclusion, an efficient way to improve the cycling performances of TiSnSb, and possibly other conversion electrodes, is to modify the electrolyte formulation. The use of a more stable IL as solvent or co-solvent and adding efficient additives are the best means to stabilize the SEI layer which is strongly related to the specific capacity and cycleability of this type of active material.
1. L. Monconduit et al., J. Power Sources, 107 (2002) 74.
2. J. Wolfenstine et al., J. Power Sources, 109 (2002) 230.
3. H. A. Wilhelm et al., Electrochem Commun 24 (2012) 89.
4. Peled, E. J. Electrochem. Soc. 126 (1979) 2047.
5. C. Marino et al., J. Phys. Chem. C 117 (2013) 19302.
6. M. Stjerndahl et al., Electrochim. Acta 52 (2007) 4947.
3:30 AM - M5.04
Carbon Nanotubes as Electronic Interconnects in Solid Acid Fuel Cell Electrodes
Aron Varga 1 Moritz Pfohl 2 Nicholas A Brunelli 3 Marcel Schreier 2 Konstantinos P Giapis 2 Sossina M Haile 1 2
1California Institute of Technology Pasadena USA2California Institute of Technology Pasadena USA3Georgia Institute of Technology Atlanta USAShow Abstract
Carbon nanotubes have been explored as interconnects in solid acid fuel cells to improve the link between nanoscale Pt catalyst particles and macroscale current collectors. The nanotubes were grown by chemical vapor deposition on carbon paper substrates, using nickel nanoparticles as the catalyst, and were characterized by scanning electron microscopy and Raman spectroscopy. The composite electrode material, consisting of CsH2PO4, platinum nanoparticles, and platinum on carbon-black nanoparticles was deposited onto the nanotube-overgrown carbon paper by electrospraying, forming a highly porous, fractal structure. AC impedance spectroscopy in a symmetric cell configuration revealed a significant reduction of the electrode impedance as compared to similarly prepared electrodes without carbon nanotubes.
3:45 AM - M5.05
Tuning the Electrocatalytic Activity of Cathodes for SOFCs by Control of the Oxygen Ion Conducting Oxide Support
Daehee Lee 1 Dongha Kim 1 Joosun Kim 2 Jooho Moon 1
1Yonsei University Seoul Republic of Korea2Korea Institute of Science and Technology Seoul Republic of KoreaShow Abstract
Oxide supported catalysts are ubiquitous in industrial, environmental and fuel cells applications. In particular, the oxide supports are of immense importance in solid oxide fuel cells (SOFCs) which utilize the oxygen ion conducting oxides as an electrolyte and a catalyst support in composite electrodes to provide the oxygen ion channel. In this regard, the oxide supports in electrodes of SOFCs have been only studied with respect to the ionic conductivity. However, the interaction between catalysts and oxide supports can give rise to the enhancement of the catalytic activity due to the variation of electronic structure of catalysts due to the orbital hybridization between catalysts and supports. Here, we demonstrate a novel approach to improve the catalytic activity of SOFCs cathode by controlling the oxygen ion conducting oxide supports. The catalytic activity of La0.8Sr0.2MnO3 (LSM) perovskite catalysts is characterized when contacted with different electrolyte supports including yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (ScSZ), and samaria-doped ceria (SDC). LSM thin films are deposited on the different oxide supports via pulsed laser deposition (PLD) for removal of geometrical uncommonness in terms of porosity and tortuosity and their polarization resistances are measured by the electrochemical impedance spectroscopy (EIS). With these analyses, the contributions of ionic conductivity and catalytic activity enhancement by oxide supports are determined. The optimized composite cathode has been fabricated so that the generic design rule for enhanced composite cathode has been proposed.
4:30 AM - M5.07
Additive Laser Manufacturing for Solid Oxide Cells Electrodes Fabrication
Marina Lomberg 1 Chris Bocking 2 Greg J Offer 3 Nigel P Brandon 1
1Imperial College London United Kingdom2CRDM, Ltd Bucks United Kingdom3Imperial College London United KingdomShow Abstract
The microstructure of porous electrodes has a critical impact on the performance and life-time of solid oxide cells (SOCs). Selective laser sintering (SLS) is a fast, reliable and reproducible process that allows control of the microstructure through sintering together successive layers of metal powder. In this work the use of SLS for an SOC electrode fabrication is presented for the first time by sintering a patterned Ni structure on an YSZ electrolyte. The experiments were carried out using pulsed YAG fiber laser. An optimal set of conditions for electrode fabrication was evaluated by varying the laser power (in the range of 20-200W) and laser speed (in the range of 160-4000mm/s). The electrode microstructure was studied using scanning electron microscope (SEM). The electrical conductivity was measured by the Van der Pauw method. Initial results from these feasibility studies will be reported.
4:45 AM - M5.08
Stability of Perovskite-Fluorite Composites for High-Temperature Electrochemical Systems
Sapna Gupta 1 Manoj K Mahapatra 1 Jonathan Lane 2 Jamie Wilson 2 Pawel Plonczak 2 Prabhakar Singh 1
1University of Connecticut Storrs USA2Praxair Inc. Tonawanda USAShow Abstract
Lanthanum chromite-based perovskite and aliovalent doped zirconia composites offer the potential as active components for high temperature solid state electrochemical devices. The composites can be used as membrane in oxygen transport membrane (OTM) as well as electrodes for solid oxide fuel cells (SOFC) and solid oxide electrolysis cells (SOEC). Intercationic diffusion and formation of secondary compounds due to the interaction between the perovskite and fluorite modifies the thermo-physical and electrochemical properties leading to performance degradation. This study documents our observations on the morphological, chemical and structural changes in the (La0.75Sr0.25)0.95Cr0.7Mn0.3O3 (LSCM) perovskite with yttrium stabilized zirconia (8YSZ) and scandium stabilized zirconia (10ScSZ) during sintering in oxidizing and reducing atmospheres. Significant microstructural changes in the bulk, surface, and interfaces have been observed with respect to partial pressure of oxygen. Inter-cationic diffusion and secondary phase formation are more prevalent in the reducing atmosphere and the interaction is more intense for LSCM and 10ScSZ composite. Possible reaction mechanisms and the role of oxygen pressure responsible for the above changes will be presented.
5:00 AM - M5.09
Raman Spectroscopic Study of Carbon Deposition Mechanism on Ni/CGO and Ni/YSZ Electrodes Under CO/CO2 Electrolysis
Vlad Duboviks 1 Robert C. Maher 2 Greg J. Offer 3 Gabriel R. Castillo Vega 4 Javier R. Vazquez de Aldana 4 Enrique Ruiz-Trejo 1 Masashi Kishimoto 1 Lesley F. Cohen 2 Nigel P. Brandon 1
1Imperial College London London United Kingdom2Imperial College London London United Kingdom3Imperial College London London United Kingdom4University of Salamanca Salamanca SpainShow Abstract
Durable reversible Solid Oxide Cells (SOCs) capable of operating both as a fuel cell and as an electrolyser may provide the advantage of biogas (CH4 and CO2 mix) upgrade and CO2 reduction in co-electrolysis conditions. However, SOC degradation due to carbon deposition has to be significantly reduced in order to allow for the long term utilization of carbonaceous fuels in SOCs. Currently there is a considerable gap in the understanding of the formation mechanisms and characteristics of carbon formed under negative bias on Ni-based electrodes.
In the present work we have used Raman mapping to investigate the characteristics of carbon formation in SOCs operating in electrolysis mode. These measurements have shown that majority of the carbon forms in close proximity to the electrode-electrolyte interface in porous electrodes. To investigate this process further, laser ablation coupled with electrochemical deposition of Ni was used to prepare patterned electrodes with well-defined triple phase boundaries (TPB). These structures present smooth interfaces that are particularly well suited for analysis with Raman spectroscopy. Analysis of the Raman spectra collected from patterned Ni/YSZ and Ni/CGO electrodes confirm previous observations of superior Ni/CGO resistance to coking and suggests that carbon is dissolving through Ni in both cases. Carbon agglomeration under the Ni is likely to cause electrode delamination leading to irreversible electrode degradation. Maps of the integrated peak area of CGO oxygen vacancies across the electrode surface suggest that oxygen diffusion to the TPB extends up to 100µm in lateral directions. A mechanism of carbon suppression in Ni/CGO system based on CGO electrochemical activity is proposed. We will also provide evidence that suggests that providing a CGO interlayer is effective for carbon deposition mitigation in porous electrodes in CO-CO2 electrolysis conditions.
5:15 AM - M5.10
Ce1-xSrxNbO4: A New Fast Ion Conductor for SOFC and Related Applications
Cassandra Harris 1
1Imperial College London London United KingdomShow Abstract
In the search for SOFC materials which exhibit improved oxide ion conductivity at lower temperatures, attention has recently been focussed towards materials with atypical structural chemistry and diffusion pathways. Oxygen excess materials (such as the Ruddlesden-Popper & Apatite structures) have the potential for interstitial oxide ion conduction with activation barriers to oxygen transport that are typically lower compared to the more common vacancy mechanism found in traditional SOFC materials1,2. An alternative strategy to reduce migration barriers and enhance conductivity in the intermediate temperature regime (4-600°C) is to change the charge carrier from oxide ions to protons, and develop electrolytes that conduct protons from the anode to the cathode3.
Fergusonite structured rare earth niobates (RENbO4) can exhibit both high protonic and oxygen diffusivity depending on the dopant strategy. For example the alkaline earth doped members (RE1-xAxNbO4-δ RE=La, Nd, Gd, Tb, Er A=Ba, Sr, Ca) retain protons as the dominant charge carriers upto 1000°C, with oxygen vacancy diffusion resuming >1000°C 4. The cerium analogue CeNbO4+δ, can incorporate a range of oxygen excess stoichiometries (δ=0, 0.08, 0.25, 0.33) by oxidation of Ce3+ to Ce4+ and exhibits fast oxide ion and electronic conduction5. Unlike other rare earth niobates, CeNbO4+δ conducts via an interstitial type mechanism and adopts either commensurate or incommensurate modulated superstructures showing that symmetry is not necessarily a pre-requisite for fast ion transport.
Here we report the transport properties of Sr2+ doped CeNbO4+δ under oxygen and proton containing atmospheres and show that this new material exhibits total electrical conductivity that is over one order of magnitude greater than the parent material. Full structural and redox characterisation by TOF neutron diffraction and x-ray absorption spectroscopy will be presented. Sr2+ charge compensation occurs largely via cerium oxidation from Ce3+ to Ce4+ as opposed to oxygen vacancy formation. The electrical properties of several compositions of Ce1-xSrxNbO4±δ (x=0.01 to x=0.4) under oxygen and proton containing atmospheres have been investigated; the results show significant enhancement when x>1. Currently variable pO2 and EMF measurements are underway to determine transport numbers for Ce1-xSrxNbO4±δ. It is proposed that the compensation mechanism leads to an enhancement in the electronic domain and potential application as a mixed ionic electronic conductor in SOFC&’s and related applications.
 SSI, 117, (13-14), 1205-1210, 2006
 Chem. Rec, 4, (6), 373-384, 2004
 Nat. Mater, 9, (10) 846-852, 2010
 Nat. Mater, 5, 193-196, 2006
 SSI, 177, (11-12), 1015-1020, 2006
5:30 AM - M5.11
Operando and In-Situ Studies on SOFC Anodes and Electrolytes with X-Ray and Neutron Scattering and Impedance Spectroscopy
Artur Braun 1
1Empa. Swiss Federal Laboratories for Materials Science and Technology Dubendorf SwitzerlandShow Abstract
The functionality on SOFC components depends on the structure and dynamics of their materials under operation conditions. Recent progress in instrumentation at neutron and synchrotron radiation sources has made it possible to study SOFC and SOEC systems under realistic operation conditions and understand numerous questions on the physical chemistry of the compounds in interaction with temperature and gases, and the dynamics of charge carriers. I will present a suite of very recent studies where we investigated the sulfur chemistry in SOFC anodes first ex-situ and later under control of the electrochemical potential in-situ with x-ray absorption spectroscopy at the sulfur K-edge. This study is complemented by microstructure investigations with ultra small angle x-ray scattering. The dyamics of protons in ABO3 type rare earth transition metal oxide electrolytes were done under exposure to high water vapor pressure and control of the electrochemical potential by using inelastic and quasi-elastic neutron scattering combined with impedance spectroscopy. The change of the valence band during filling of oxygen defects in these materials was investigated in-situ with high pressure XPS spectroscopy. This allows us to sketch the density of states during materials processing and component operation under realistic conditions.
1. G. Nurk, T. Huthwelker, A. Braun, Chr. Ludwig, E. Lust, R. P. W. J. Struis, Redox dynamics of sulphur with Ni/GDC anode during SOFC operation at mid- and low-range temperatures: An operando S K-edge XANES study, J. Power Sources 2013, 240, 448-457.
2. A.J. Allen, J. Ilavsky, A. Braun, Multi-Scale Microstructure Characterization of Solid Oxide Fuel Cell Assemblies with Ultra Small-Angle X-Ray Scattering, Advanced Engineering Materials 2009, 11 (6), 495-501.
3. Q. Chen, J. Banyte, X. Zhang, J. P. Embs, A. Braun; Proton Diffusivity in Spark Plasma Sintered BaCe0.8Y0.2O3-δ: in-situ combination of quasi-elastic neutron scattering and impedance spectroscopy; Solid State Ionics; in press, http://dx.doi.org/10.1016/j.ssi.2013.05.009
5:45 AM - M5.12
3D FIB-TOF Tomography of Sr- and Pr-Based Solid Oxide Fuel Cells
Gregory L Fisher 1 Scott R Bryan 1 John S Hammond 1
1Physical Electronics Chanhassen USAShow Abstract
TOF-SIMS has become an important tool for 2D and 3D imaging mass spectrometry of complex materials due to its unique capability to detect elements at a spatial resolution of < 100 nm and at a mass resolution of > 10,000 m/Δm. Among the advantages of TOF-SIMS are a 2 nm sampling depth, parallel detection and collection of the entire mass spectrum at every image pixel, and sensitivities in the ppm to ppb range. The ability to image surfaces having a large degree of topography while maintaining artifact-free chemical imaging is also highly desired; the resulting elemental images provide important information regarding the composition and structure of SOFC, PV and OLED materials. Characterization of specimens to a depth of several microns below the sample surface has become somewhat routine with the use of a sputter ion beam to remove multiple layers of atoms between analysis (chemical imaging) cycles. Nevertheless, there are practical limitations which include preferential or differential sputtering, void spaces and topography that result in a distortion or complete loss of the true 3D chemical distributions. An alternative approach to achieve 3D chemical imaging of chemically complex specimens is to utilize in situ FIB milling and sectioning in conjunction with TOF-SIMS chemical imaginghellip; what we have called FIB-TOF tomography. The advantage of the FIB-TOF approach is that artifacts caused by surface topography, void spaces, and differential sputtering are avoided.
We have used 3D FIB-TOF tomography to characterize 50 mu;m x 50 mu;m x 10 mu;m volumes of as-grown and aged SOFC specimens. The union of successive FIB sectioning and TOF-SIMS analysis cycles for 3D imaging, along with details of the observed chemistry, will be discussed for the analysis of Sr- and Pr-based SOFC samples.
M6: Poster Session
Thursday PM, April 24, 2014
Marriott Marquis, Yerba Buena Level, Salons 8-9
9:00 AM - M6.01
Fabrication of Graphene-Nanoneedle MnO2 Composites as High Performance Electrodes for Supercapacitors Reliance on Reduction Time
Myeongjin Kim 1 Myeongyeol Yoo 1 Kiho Kim 1 Jooheon Kim 1
1Chung-Ang University Seoul Republic of KoreaShow Abstract
Graphene/MnO2 composites were prepared by hydrazine hydrate-mediated reduction of graphene oxide (GO)/MnO2 at various reduction times to determine the optimal conditions to obtain materials with excellent electrochemical performance. Variations in the oxygen-containing surface functional groups were observed as the reduction time was varied. These changes were found to affect the electrical conductivity and density of nanoneedle MnO2, which impact the surface area and can significantly affect the supercapacitive performance of the composites. Morphological and microstructural characterizations of the as-prepared composites demonstrated that MnO2 was successfully formed on the GO surface and indicated the efficacy of hydrazine hydrate as a reducing agent for GO. The capacitive properties of the graphene/MnO2 electrodes prepared at a reduction time of 28 h (rGO(28)/MnO2) exhibited a low sheet-resistance value as well as a high surface area, resulting in a GO/MnO2 composite with excellent electrochemical performance (371.74 F gminus;1 at a scan rate of 10 mV sminus;1). It is anticipated that the formation of MnO2-based nanoneedles on GO surfaces utilizing the demonstrated 28-h hydrazine-reduction protocol is a promising fabrication method for supercapacitor electrodes.
9:00 AM - M6.02
High Temperature Proton Exchange Membranes Based on Polybenzi