Karen Swider-Lyons Naval Research Laboratory
Byungwoo Park Seoul National University
Ting He Honda Research Institute USA, Inc.
T3: Fuel Cell Overview I
Tuesday AM, December 01, 2009
Room 301 (Hynes)
9:30 AM - **T3.1
Nano Materials and Structures for the 4th Innovation of PEFC.
Hyuk Chang 1 Show Abstract
1 Energy Lab, SAIT, Samsung Electronics Co., Ltd., Suwon Korea (the Republic of)
Material development of sulfonated polymer based proton conducting membrane (1960’s) initiated worldwide research efforts on Polymer Electrolyte Fuel Cell (PEFC), which is regarded as the 1st innovation in this promising technology of energy conversion device having potential of high efficiency, environmentally benign and mobility. Since then, technology kept evolution and followed by the 2nd and 3rd innovations of highly efficient catalyst electrode structure (ionomer in the catalyst layer, early 1990’s) and low resistance membrane structure (ionomer in microporous membrane substrate, late 1990’s), respectively. These three subsequent innovations, which were based on bulk properties of materials and structures, led PEFC technology to near commercialization. However, it is still not enough to replace competing technologies in the view of efficiency, cost and life time, which are critical to energy conversion device. It is anticipated that the technical challenges heading for the next inflection point will be based on the nano technologies. Among them, nano scaled catalyst, nanocomposite membrane and nano structured membrane electrode assembly (MEA) are the major approaches.More specifically, SAIT conducts following activities : i) nano structured catalyst having platinum nanoparticles of 3nm can enhance the catalyst activity. Also, the nanoporous carbon can be utilized as support material for controlling the catalyst particle size and distribution. Especially when oxygen reduction co-catalyst such as Ru-N complex and highly metal-interactive element such as S are embedded in the nanoporous carbon, the catalyst is functionalized for enhancing activity and stability. ii) nanocomposite hydrocarbon membrane with exfoliated clays, especially in direct methanol fuel cell, provides high ionic conductivity and low methanol permeability because of its high enough sulfonation degree and low resistance in 50um thin but mechanically durable membrane. iii) in addition, nanostrucrued MEA with high surface density can reduce both ohmic and activation losses during polarization and enhance fuel efficiency, so that overall efficiency of fuel cell can be increased by more than 40%.In this presentation, the author would like to introduce the above three nano-based approaches and discuss that nano technologies in materials and structures will bring along the 4th innovation, so that the PEFC technology will be fulfilled for entering the commercial stationary, mobile and massive vehicle markets in the near future.
T4: Catalyst Degradation
Tuesday PM, December 01, 2009
Room 301 (Hynes)
10:00 AM - **T4.1
Platinum-Cobalt Cathode Catalyst Degradation in Proton Exchange Membrane Fuel Cells: Nano-Scale Transformations Observed by High-Resolution Microscopy.
Shuo Chen 2 3 , Hubert Gasteiger 2 3 , Katsuichiro Hayakawa 4 , Tomoyuki Tada 4 , Yang Shao-Horn 1 2 3 Show Abstract
2 Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Electrochemical Energy Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 4 , Tanaka Kikinzoku Kogyo K. K., Hiratsuka, Kanagawa, Japan, 1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Compared to platinum, platinum-cobalt alloy catalysts show enhanced activity for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs) and are commonly considered to be more stable toward platinum dissolution under automotive load-cycling (i.e., voltage cycling) conditions. For pure platinum catalysts, the platinum surface area loss produced by voltage-cycling is well understood, consisting both of Ostwald ripening of platinum nanoparticles on the carbon support in the cathode electrode and of the loss of platinum into the membrane/ionomer phase where large and electrically isolated platinum crystallites are formed. On the other hand, the microscopic degradation mechanisms of PtCo cathode catalysts are still unclear and more insight is required in order to develop strategies for cathode catalysts with improved durability.Using (scanning) transmission electron microscopy, (S)TEM, and spot-resolved X-ray energy dispersive spectroscopy, EDS, we have examined the microscopic processes leading to the aging of PtCo catalysts during voltage-cycling. While the formation of pure platinum crystallites in the membrane/ionomer phase is the same as what had been observed with conventional platinum catalysts, the morphological changes of nanoparticles in the cathode electrode are very different. We found that the majority of Pt-Co nanoparticles transformed into Pt-shell/PtCo-core nanoparticles. At the same time, we observed the formation of highly percolated nanoparticles, which consisted of nearly pure platinum and exhibited a bi-continuous porous structure which resembles that of dealloyed AuAg films. To our knowledge, this is the first time that this phenomenon was reported for the degradation of Pt-based alloy nanoparticles in PEMFC cathode, and we propose that these percolated, nearly pure platinum nanoparticles were derived from PtCo alloy nanoparticles with cobalt compositions beyond the dealloying threshold of ca. 55 atomic% Co. The mechanisms of surface area and activity loss will be discussed.
10:30 AM - T4.2
Size and Composition Dynamics of Nanoparticle Electrocatalysts Probed by in situ X-ray Scattering.
Michael Toney 1 , Chengfei Yu 2 , Shirlaine Koh 2 , Peter Strasser 2 Show Abstract
1 , Stanford Synchrotron Radiation Lightsource, Menlo Park, California, United States, 2 Department of Chemical and Biomolecular Engineering, University of Houston, , Houston, Texas, United States
The durability of the electrocatalysts in polymer electrolyte membrane fuel cells (PEMFCs) is one of the factors limiting use of this technology. To improve durability, the macroscopic durability (e.g., loss of catalyst surface area) must be understood in microscopic terms: we need to better understand the nanoparticle electrocatalyst structural dynamics at an atomic scale and in real time during electrochemical stressing. Such experiments require an in-situ approach. We are using in-situ synchrotron X-ray scattering, both small angle X-ray scattering (SAXS) and X-ray diffraction (XRD), to probe the structural dynamics of electrocatalyst nanoparticles. We use a three electrode arrangement in spectroelectrochemical flow cell to follow the SAXS and XRD patterns as function of time, voltage, and potential protocol. This enables us to monitor, in real time, the atomic scale structure of the electrocatalysts such as particle size, lattice constant and extent of crystallinity (diffracted intensity).In this talk, I describe in-situ scattering experiments of Pt and CuPt alloy nanoparticle electrocatalysts under conditions that mimic the degradation environment in operating fuel cells (electrode potential cycles and holds). For pure Pt, the goal is to explain the observed change in catalyst surface area. We observe nanoparticle growth with potential cycling with smaller particles growing faster than larger ones. This is related to change in catalyst surface area and a comparison with this suggests that cycling can improve Pt utilization. Our results further suggest that below a critical diameter (that is anodic turning potential dependent) the Pt particles are unstable and hence not useful in PEMFCs. These experiments will be compared with models of corrosion and particle size growth. For CuPt alloy nanoparticle electrocatalysts, the situation is more complex as both size and composition can change. We observe an initial shrinkage of particle size (due to loss of the active Cu) followed by coarsening, which are both more severe at higher turning potential. For a larger initial particle size, there is only the initial decrease in size. XRD data show a fast, enormous loss of diffracted intensity which we interpret as due to the formation of a poorly ordered Pt-rich region at the nanoparticle shell. This region slowly recrystallizes with time.
10:45 AM - T4.3
Transmission Electron Microscopy Observation of the Corrosion Behaviors of Platinized Carbon Blacks under Thermal and Electrochemical Conditions.
Vic Liu 1 , Junliang Zhang 1 , Paul Yu 1 , Jingxin Zhang 1 , Rohit Makharia 1 , Karren More 2 , Eric Stach 3 Show Abstract
1 Fuel Cell Research Lab, General Motors, Honeoye Falls, New York, United States, 2 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Department of Materials Engineering, Purdue University, West Lafayette, Indiana, United States
Carbon blacks such as Vulcan® XC-72 (Cabot Corp., USA) are widely used to support platinum (Pt) or Pt-alloy catalysts in proton-exchange membrane (PEM) fuel cells. Despite their widespread use, carbon blacks are susceptible to corrosion during fuel cell operations. In this work, the corrosion behaviors of Pt nanoparticles/Vulcan under thermal and electrochemical conditions were monitored by transmission electron microscopy (TEM) via in-situ (gas phase) and ex-situ electrochemical methods. The in-situ experiment was carried out in a 2% oxygen/helium environment at 500°C in an FEI Titan 80-300 environmental TEM which allows a direct observation of the thermal oxidation behavior of the Pt/Vulcan nanoparticles. The ex-situ electrochemical experiment was done by first loading the Pt/Vulcan nanoparticles bound by trace Nafion® DE2020 (DuPont, USA) on a TEM gold grid, and then electrochemically corroding the nanoparticles at 25°C and 1.5 V vs. reversible hydrogen electrode step by step for 10, 100, 1000 and 4000 minutes followed by taking TEM images from exactly the same nanoparticles after each step. This work revealed that the corrosion of the Pt/Vulcan nanoparticles proceeds via at least three modes: 1) total removal of structurally weak carbon nanoparticles; 2) breakdown of high-aspect-ratio carbon nanoparticles; and 3) inside-out corrosion of carbon nanoparticles with a well-defined amorphous core and graphitic shell. The above corrosion modes lead to a non-uniform corrosion of the carbon catalyst support and may cause a premature collapse of the fuel cell electrode structure. The results obtained from this work will provide new insight on carbon corrosion and its effects on fuel cell long-term performance and durability.
11:00 AM - T4: degradation
11:30 AM - **T4.4
New Modeling Approaches for Investigating Long-Term Platinum Nanoparticle Stability in PEM Fuel Cells.
Dane Morgan 1 , Edward Holby 1 , Wenchao Sheng 2 , Yang Shao-Horn 3 Show Abstract
1 Materials Science and Engineering, University of Wisconsin - Madison, Madison, Wisconsin, United States, 2 Mechanical Engineering and Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
One of the major barriers to implementation of practical PEMFCs is the degradation of the cathode catalyst under operating conditions. Present cathode catalysts are usually made from carbon supported Pt or Pt alloy nanoparticles, which have large surface area and high catalytic activity. However, fuel cell efficiency is reduced as electrochemically active surface area is lost over time, limiting the lifetime of the fuel cell. In this talk I will focus on understanding the mechanisms of surface area loss in Pt nanoparticle cathodes. In particular, I will discuss how we have constructed an electrochemical rate model for Pt degradation and what it can tell us about mitigation strategies. I will focus on the effects of particle size distribution, and demonstrate that surface energy driven instability changes dramatically in the commercially relevant region of 2-5nm diameter particles. I will also show a surprising role for hydrogen crossing over from the anode, demonstrating that it can dramatically alter the mechanisms and extent of surface area loss.
12:00 PM - **T4.5
In-Situ Microscopy of Fuel Cell Nanoparticle Catalyst and Catalyst-Support Degradation.
Karren More 1 , Lawrence Allard 1 , K. Shawn Reeves 1 Show Abstract
1 , Oak Ridge National Laboratory, Oak Ridge , Tennessee, United States
Atomic-scale imaging of the structural changes to individual Pt-based catalyst nanoparticles supported on carbon black (such as Vulcan XC-72 or Ketjen Black) using in-situ Z-contrast Scanning Transmission Electron Microscopy (STEM) is being used to directly understand the mechanism(s) of catalyst particle growth/coalescence under simulated fuel cell operating conditions. Specialized in-situ holders for the STEM are being developed to image catalyst particles and their support structures during exposure at temperatures <120°C, with and without ionomer films. These in-situ microscopy studies include heating the catalyst and support materials in air and in water vapor environments. Near-live-time observations of the changes to the catalyst nanoparticles and supports in-situ will help elucidate the primary corrosion mechanisms contributing to catalyst and catalyst-support degradation during the operation of PEM fuel cells.Results will be presented that focus primarily on (1) nanoparticle microstructural features related to the stability of several Pt-based alloy cathode catalysts and (2) observed catalyst-support interactions and their effect on nanoparticle stability. Mechanisms of nanoparticle coalescence in air and water-vapor, as well as in the presence of Nafion ionomer films, will be compared._________________________________________Research sponsored by (1) the Office of Hydrogen, Fuel Cells, and Infrastructure Technologies, Office of Energy Efficiency and Renewable Energy, the U.S. Department of Energy and (2) ORNL’s SHaRE User Facility, Scientific User Facilities Division, Office of Basic Energy Sciences, the U.S. Department of Energy.
12:30 PM - T4.6
Mechanisms of Pt Degradation in PEM Fuel Cells.
Qingmin Xu 1 , Eric Kreidler 1 , Ting He 1 Show Abstract
1 , Honda Research Institute USA, Columbus, Ohio, United States
The direct conversion of chemical energy to electricity via fuel cells has attracted significant attention for many decades. However, due to the sluggish kinetics of oxygen electroreduction and particularly the poor durability of fuel cell system in service, the mass utilization of fuel cells has been inhibited. To overcome the technical barriers associated with fuel cell durability, it is necessary to understand the degradation mechanisms of oxygen reduction electrode and propose countermeasures.In this presentation, we will report our new findings on the mechanisms of coarsening and dissolution of Pt catalysts at fuel cell cathodes. It has been found that the coarsening is a result of double-layer-potential-induced Ostwald ripening whereas the dissolution results from direct-oxidation of Pt nanoparticles. Details of these new findings will be discussed and countermeasures will be proposed.
12:45 PM - T4.7
Degradation of Pt Catalysts in Polymer Electrolyte Fuel Cells.
Eric Kreidler 1 , Ting He 1 Show Abstract
1 , Honda Research Institute, Inc., Columbus, Ohio, United States
The mass commercialization of polymer electrolyte fuel cells for transportation applications is significantly inhibited by high materials costs and poor service life which can be largely attributed to the Pt catalysts used at the cathodes. Previously, we reported in-situ electrochemical scanning tunneling microscopy studies on the coarsening behavior of Pt nano crystals under potentiostatic holding and potential cycling as well as the direct dissolution of Pt nanoparticles as a function of electrochemical potential [1,2]. It was found that Pt nano crystal coarsening is a result of double-layer-potential-induced Ostwald ripening and Pt particle dissolution results from direct electro-oxidation of Pt nanoparticles. To verify these findings, fuel cell tests utilizing Pt black and carbon-supported Pt cathode electrocatalysts were conducted. Individual fuel cells were operated under high potential (850 mV), double-layer potential (600 mV), and potential cycling (open circuit to 300 mV and back)conditions for extended periods of time. Electrochemical active surface area (ECSA) was measured as a function of time and the catalyst layers were analyzed after operation using x-ray diffraction (XRD), electron microprobe analysis (EPMA), and transmission electron microscopy (TEM). Details of the experiments and results will be presented and discussed. Q. Xu, E. Kreidler, D.O. Wipf, and T. He, J.Electrochem. Soc. 2008, 155, B228. L. Tang et al., to be published.
T5: Fuel Cell Overview - II
Tuesday PM, December 01, 2009
Room 301 (Hynes)
2:30 PM - **T5.1
PEM Fuel Cells.
Yu-Min Tsou 1 Show Abstract
1 , BASF Fuel Cells, Somerset, New Jersey, United States
This presentation will address two important topics in PEM fuel cells. The first one is approaches to eliminate/reduce the most commonly observed durability problems: carbon corrosion. The second one is the fundamental understanding of nano-sized Pt particles in the context of characterization with electrochemical and spectroscopic methods. Carbon support corrosion problem is one of the most important barriers in hampering the commercialization of fuel cells. Support corrosion results in the loss of electrochemical activity through agglomeration of catalyst particles and loss of conductivity of catalyst layer. Even a loss of 10-15% of carbon support can lead to severe performance drop due to electrode conductivity loss from the support contact loss. Most severe support loss occurs during shutdown/re-start-up periods when gas mixing occurs. Feeding H2 into air filled anode chamber can easily set up local battery effect that drives carbon support to corrosion potentials. While mitigation processes have been proposed to reduce corrosion but they are hard to practice and also very costly. Therefore, development of materials solution to overcome carbon corrosion becomes the focus of BFC’s work.The first approach is using corrosion resistant carbon. Electrochemical carbon screening methodology will be presented and successful examples are demonstrated. Unsupported catalyst is another attractive approach. BFC has extended the high performance supported Pt catalysts technology to synthesize high surface area unsupported Pt catalysts. 3-5 nm is the typical size, affording high surface area. Cell stack testing indicates the much better durability of gas diffusion electrode (GDEs) with unsupported catalysts (USC) in 3000-4000 hour experiments. GDEs with UNC also showed advantage in low humidity operation and fast break-in. Technology in optimizing the performance durability, related to water management, of GDEs with UNC will be illustrated. Ion beam deposition (IBD) is demonstrated to afford anode GDEs with similar performance to conventional one with complete dry process and without incorporating ionomer for proton conductivity. Cathode IBAD GDEs exhibit mass transport problem. Roll-to-roll IBAD manufacture is demonstrated.BFC is capable of manufacturing Pt particles with very small crystallite sizes even at very high loadings on supports. With a series of Pt catalysts we are able to use cyclic voltammograms as useful characterization tools. The main findings include (i) intensity of weak hydrogen adsorption peak is associated to low coordination defect sites in addition to edge/corner sites, thus indicative of “extent of disorder” of a Pt particle; (ii) size effect for oxygen reduction reaction is proposed to be composed of primary effect associated with large activity difference between Pt atoms on crystalline planes and those on defect sites, and secondary effect associated with size of crystalline plane. Primary particle size effect becomes important only when the percentage of corner/edge/ becomes so high that they dominate the activity, i.e., as particle size falls below 18-20 A. Experimental results are supplied to support the two-effect hypothesis; (iii) voltammetric peaks for reduction of OH on corner/edge/defects are identified at 180-280 mv more negative of that on crystalline planes. The corresponding OH formation peak is at very positive potential and can be attributed to be responsible for CO stripping from all sites. The origin of multiple CO voltammetric peaks will be discussed in detail.
T6: Computational Modeling
Tuesday PM, December 01, 2009
Room 301 (Hynes)
3:00 PM - **T6.1
Effects of Core Composition on the Activity and Stability of Pt-skin Surfaces in Fuel Cell Cathodes.
Perla Balbuena 1 Show Abstract
1 Chemical Engineering, Texas A&M University, College Station, Texas, United States
Pt-skin surfaces have been shown to offer good activity and stability properties for the reduction of molecular oxygen in acid medium. Such behavior is attributed to favorable interactions with subsurface atoms that play a significant role in modifying the electronic structure and geometric properties of the surface. Here we report systematic density functional theory studies of the effect of changes in the electronic structure of the core on the performance of Pt-skin (111) surfaces towards oxygen reduction reaction activity and stability of the Pt surface atoms against dissolution in acid medium. We first investigate trends of pure cores to segregate to the surface and show how this trend is related to the core electronic structure and what the influence of such electronic distribution on the stability of the Pt surface atoms is. By examination of the oxygen reduction reaction activity of the group of stable pure metal cores it is concluded that a rational alloy core design may be obtained by combining elements of the stable (M) and stable or unstable cores (Y) of MxY1-x composition. The results will be illustrated for Pt/Pd3Y alloys. Interesting trends are found for the stability and activity of the surface Pt atoms as a function of the differences in electronic structure between the surface and the subsurface. We also discuss the effect of the increase of the shell thickness on the stability and activity properties, and we demonstrate that the beneficial effect of the surface/subsurface interaction is lost when the shell thickness grows beyond one monolayer.
3:30 PM - T6.2
A First-Principles Study of the Electropotential Dependent Shape Stability of Metal Nanoparticles.
Nicephore Bonnet 1 , Ismaila Dabo 2 , Nicola Marzari 1 Show Abstract
1 , MIT, Cambridge, Massachusetts, United States, 2 , CERMICS-ENPC, Marne la Vallée France
Understanding the catalytic activity of transition metal nanoparticles is a central issue in the development of novel fuel cell materials. Observed trends are often interpreted in terms of the size dependent morphology of nanoparticles, in particular the relative density of low coordination sites. However, no consensus exists regarding the direction or the mechanism of such an effect.In this context, ab-initio methods can be useful to extract relevant parameters. Here, we calculate surface energies under realistic electrochemical conditions and use the Wulff construction to infer stable nanoparticle contours. The electropotential is adjusted through its conjugate variable, the charge, and density countercharge periodic-image corrections are applied . The surrounding solvent is treated as a combination of a continuum dielectric and a classical ionic distribution at equilibrium.Two quantities are studied. One is the metal surface capacitance with no specific adsorption. It is shown that unspecific electrostatics have no effect on the nanoparticle shape. The other one is the Pourbaix diagram of interfacial water including O and OH as oxidized species. An effect on the nanoparticle shape is predicted from the surface orientation and potential dependent coverages of those species.References I. Dabo, B. Kozinsky, N.E. Singh-Miller, N. Marzari, Electrostatics in periodic boundary conditions and real-space corrections, PRB 77, 115139 (2008)
3:45 PM - T6.3
Computational Design of Nanosegregated Catalysts for Polymer Electrolyte Membrane Fuel Cells.
Guofeng Wang 1 2 Show Abstract
1 Department of Mechanical Engineering, Indiana University Purdue University Indianapolis, Indianapolis, Indiana, United States, 2 Richard G. Lugar Center for Renewable Energy, Indiana University Purdue University Indianapolis, Indianapolis, Indiana, United States
Knowledge on the arrangement of different elements in surface region is critical in the design and synthesis processes of Pt alloy electro-catalysts for their applications in PEM fuel cells. Particularly, there is a useful material process which we can take advantage of during catalyst design. It is called surface segregation, which refers to the phenomenon that chemical composition at the surface of multi-component materials differs from the corresponding value in the bulk. In this work, I employed an atomistic Monte Carlo simulation method to predict the equilibrium structure and surface composition of nanosegregated Pt alloy nanoparticles considering surface segregation process. The approach consists of two integrated parts: (1) developing interatomic potentials for Pt alloys within the modified embedded atom method based on first-principles computation data, and (2) applying these potentials to determine the chemical composition of extended and nanoparticle surfaces of Pt alloys using the Monte Carlo method. I have examined the reliability of the developed computational approach for three Pt bimetallic alloys that represent different fashions of Pt segregation to surfaces: Pt-Ni (strong and oscillatory surface segregation), Pt-Re (strong and monotonic surface segregation), and Pt-Mo (weak and monotonic surface segregation). Moreover, I have extended this multi-scale computational approach to study the equilibrium structure of Au/PtFe core-shell ternary alloy nanoparticles.
4:00 PM - T6.4
Multiscale Modeling of Electrocatalysis in PEM Fuel Cell.
Liang Qi 1 , Joshua Fujiwara 1 2 , Ju Li 1 Show Abstract
1 Dept. of Materials Science & Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 , Honda Research Institute, Columbus, Ohio, United States
In proton-exchange membrane (PEM) fuel cells, oxygen reduction reaction (ORR) on cathode is a complex multi-electron transfer process and its reaction mechanism is still unclear, partially because of the difficulties in direct investigation of its reaction intermediates, such as O2*, OOH*, O* and OH*(* means adsorbed state), and corresponding electron transfer dynamics. We analyzed the charge states of all ORR intermediates adsorbed on catalyst surfaces based on first-principles calculations and found that all of them are in near-neutral states, which indicate that the electron transfer in ORR should occur through proton-coupled mechanism (PCET). Then first-principle methods were used to study PCET near different metallic surfaces, which show that there are negligible activation barriers for PCET near the surfaces except the energy differences between the initial and final states. However, there are still potential-dependent activation barriers for proton transfer from bulk electrolyte to catalyst surface. Based on these reaction mechanisms illustrated by first-principles analysis, a kinetic model of total ORR rate is build by considering coverage-dependent reaction rate and energies for each elementary step, which can semi-quantitatively explain the activity differences between different catalyst surfaces.
4:15 PM - T6.5
Theoretical Study of Au-modified Pt as ORR Catalysts.
Joshua Fujiwara 1 2 , Liang Qi 1 , Ju Li 1 Show Abstract
1 Dept. of Materials Science & Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 , Honda Research Institute, Columbus, Ohio, United States
Pt and its alloys are used as catalysts for oxygen reduction reaction (ORR) in proton-exchange membrane (PEM) fuel cells. However, these catalysts would lose electrochemical active surface area (ECSA) during long-time operation due to the dissolution of Pt atoms and coarsening of Pt nanocrystals on electrodes. Recently Pt-Au alloys are reported to have considerable catalytic activity and better stability than pure Pt. To confirm and explain this result, we study different types of Au clusters on Pt (111) surface. The results show that although stable Au clusters have too weak adsorption ability for ORR intermediates, such as O* and OH*, for good catalytic activity, the adsorption properties of Pt surface close to Au clusters are modified, so that it may have better ORR activity to compensate the loss of active surface area covered by Au clusters. For the stability issue, Pt surface oxide formation during cathodic polarization is one of the key steps to induce the dissolution of Pt atoms in the anodic polarization. Au clusters would change the oxidation process on Pt surfaces, which results the increase of anti-corrosion stability.
4:30 PM - T6.6
Ab-initio Analysis of CO Adsorption in Pd70Co20X10, (X=Au, Mo, Ni) Compounds for PEM Fuel Cell Catalysts.
Mauricio Garza-Castanon 1 , Marco Jimenez 1 , Jorge Acevedo-Davila 1 , Luis Garza 4 , Oxana Kharissova 2 , Velumani Subramaniam 3 Show Abstract
1 Postgraduate Studies and Research, COMIMSA, Saltillo Mexico, 4 Mecatronica, ITESM - Monterrey, Monterrey Mexico, 2 Facultad de Ciencias Fisico-Matematicas, Universidad Autonoma de Nuevo Leon, San Nicolas de los Garza Mexico, 3 Fisica, Instituto Tecnologico y de Estudios Superiores de Monterrey, Monterrey Mexico
Application of trimetallic nanoparticles is becoming more important, the local atomisticstructure of such alloyed particles, which is critical for tailoring their properties, is not yet very clearlyunderstood. In this work we present detailed theoretical analysis on the atomistic structure and COadsorption in Pd70Co20X10 (X=Mo,Au,Ni) trimetallic composite alloys for their application in theproton exchange membrane (PEM) fuel cells as oxygen reduction reaction (ORR) catalysts. The basicstructure and their most stable configuration for all the three composites are determined. Quantummechanical approaches and classic molecular dynamics methods are applied to model the structureand to determine the lowest energy configurations. Our theoretical results almost coincide with theexperimental results of XRD. Taking those structures as base, simulations were performed todetermine the magnitude of CO poisoning. The results obtained by ab-initio techniques allow us toestimate the CO-tolerance that these catalysts might have and compare with Pt (1 1 0) used as acommercial catalyst. From these results, a comparison has been made to show different CO adsorptionstrengths. This is the first step to make an efficient engineering that allows us to obtain highperformance,low-cost nanostructured catalysts.
4:45 PM - T6.7
The Influence of Morphology on the Mechanical Properties of Proton Exchange Membranes.
Yue Qi 1 , Yeh-Hung Lai 2 Show Abstract
1 Materials and Processes Lab, GM R&D Center, Warren, Michigan, United States, 2 Fuel Cell Research Lab, GM R&D Center, Honeoye Falls, New York, United States
The nano-scale morphology of proton exchange membrane (PEM) determines the network connectivity of hydrophilic domains and strongly influences its proton conductivity and mechanical performance. In this study a multi-scale modeling approach has been developed to first obtain the morphologies of hydrated Perfluorosulfonic Acid (PFSA) membranes and then to predict their mechanical properties based on the simulated morphology. Two representative morphologies were compared, namely spherical and cylindrical ionic domains to represent cast and extruded membranes. The overall elastic moduli are very close for both morphologies and agree well with experiments. The nano-scale phase segregation in hydrated PFSA induces non-uniform distribution of local stress. The cylindrical morphology develops much lower peak stress than the isotropic spherical morphology under the same level of strain. The peak stress is localized at the smeared water/PFSA interface. These results may be able to explain the difference of recast and extruded PEM samples, which show similar modulus but the extruded membrane shows 10 times longer life time.
T7: Electrodes and MEAs
Tuesday PM, December 01, 2009
Room 301 (Hynes)
5:00 PM - T7.1
Integrated Pt/CNT Based Electrodes for High Efficiency Proton Exchange Membrane Fuel Cells.
Zhe Tang 1 , Daniel Chua 1 , How Ng 2 Show Abstract
1 Department of Materials Science & Engineering, National University of Singapore, Singapore Singapore, 2 Division of Environmental Science and Engineering, National University of Singapore, Singapore Singapore
Carbon nanotubes (CNT) have shown promising characteristics as alternative catalyst support material for proton exchange membrane (PEM) fuel cells. Previous studies on CNT based electrode have suggested that CNT support with high surface area and chemical stability could enhance the electrocatalyst's activity and stability of platinum (Pt) particles by their active interaction. However, typically the coating of Pt catalyst on CNT requires a series of complicated wet-chemical processes such as surface oxidation and purification of CNT, as well as reduction of Pt precursor solution. In addition, an additional carbon black based gas diffusion layer is still necessary for CNT supported catalyst thus limiting its overall effectiveness. In this work, an integrated Pt/CNT based electrode has been fabricated by an efficient two-step process, including in-situ growth of a dense CNT layer on plain carbon paper using chemical vapor deposition (CVD) technique followed by direct sputter-deposition of Pt nanoparticles onto the CNT layer. The in-situ grown CNT layer on carbon paper showed tunable diameter and density under different growth processes. Brunauer-Emmett-Teller (BET) and scanning electron microscopy (SEM) characterization demonstrated that with optimum morphology and coverage the CNT layer is able to provide extremely high surface area and porosity which can serve as both gas diffusion layer and catalyst layer simultaneously. Microstructure of the sputter-deposited Pt catalyst on carbon nanotubes was characterized by transmission electron microscopy (TEM), which illustrated well-dispersed Pt nanodots with nanoscaled grain size and small size distribution. In polarization test, the Pt/CNT based electrode showed notable improvement compared to conventional ink-process prepared electrodes with different commercial carbon black supported Pt catalysts. A higher maximum power density of 650 mW cm-2 has been obtained with 0.04 mg cm-2 Pt loading on both anode and cathode. In-situ characterization techniques such as cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and accelerated degradation test (ADT) have been carried out to fully evaluate the Pt/CNT based electrode. Results confirmed that the Pt/CNT catalyst can yield higher Pt utilization as well as superior electrochemical stability compared with commercial catalysts. Moreover, the reduced charge transfer and mass transport resistance of the Pt/CNT electrode suggested that the integrated CNT gas diffusion layer and catalyst layer sputtered with highly localized Pt catalysts has an intrinsic structural merit for high Pt utilization. Therefore, this combined fabrication method shows a great potential for the ease of scale-up and mass production of PEMFC electrodes.
5:15 PM - T7.2
Improvement of the Pt/Graphene Interface Adhesion by Metallic Adatoms for Fuel Cell Applications.
Fatih Sen 1 , Yue Qi 2 , Ahmet Alpas 1 Show Abstract
1 Department of Mechanical, Automotive and Materials Engineering, University of Windsor , Windsor, Ontario, Canada, 2 Materials and Processes Laboratory, General Motors R&D Center, Warren, Michigan, United States
The degradation of carbon supported Pt catalyst limits the lifetime of polymer electrolyte membrane (PEM) fuel cells. In order to understand and prevent Pt particle loss, first principles calculations were carried out for searching metallic adatoms that can enhance the Pt and carbon interface adhesion. Graphene was used to represent carbon surface, since it has negative bonding energy with Pt, and thus mimics the weak bond formed between Pt and carbon support in fuel cells. Various metallic adatoms were systematically adsorbed on the graphene surface and the favourable adsorption sites were determined. The interface was modeled by a slab by six layers of Pt(111) planes and a graphene plane with one metal atom adsorbed on its favourable site. In this way the adhesion strength between the Pt atoms and the modified graphene surface was evaluated. Accordingly, Pt/graphene interface strength increased with modification of the graphene surface by metal adatoms. The work of adhesion values decreased with increasing the atomic number within the elements at the same row of the periodic table. Early transition metals belonging to the IIIB-VB group, such as Ti, V, Zr and Nb, were found to be the most promising candidates for bridging the Pt to graphene. Especially, Zr and Nb were found to enhance the adhesion of Pt to carbon at most, correlated with an increase in the rumpling of the Pt surface. These atoms formed strong bonds with both carbon and Pt due to their particular electronic structure with unfilled d orbitals, which enhance their bonding affinity to both carbon and Pt. Electronic structure investigations revealed that considerable amount of charge transfer occurred at the interface from the adatoms to Pt and graphene surface and the work of adhesion values were shown to be proportional to the amount of charge transfer.
5:30 PM - T7.3
Integration and Performance of Supportless Nanoporous Metal Membrane Electrodes into PEM Fuel Cells.
Joshua Snyder 2 1 , Jonah Erlebacher 1 2 Show Abstract
2 Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 1 Materials Science, Johns Hopkins University, Baltimore, Maryland, United States
Similar surface area/volume, specific surface area, and precious metal loading as nanoparticle-based PEM fuel cell catalysts can instead be made by using ultrathin (~100 nm) nanoporous metal membranes. We discuss here how ultrathin porous membranes can be made using electrochemical dealloying, and how to integrate such membranes into functional fuel cells. Dealloying is the selective dissolution of one or more components from a non-porous precursor alloy. Under the right electrochemical conditions, the remaining alloy component(s) are driven to diffuse along the alloy/electrolyte interface to form a porous metal with pores even smaller than 5 nm. Nanoporous metals can be intrinsically catalytic toward oxygen reduction, or can be coated with thin catalyst layers to form low Pt core-shell catalysts. Using nanoporous metal electrodes for fuel cell catalysis may remove stability issues associated with carbon supports, and opens new avenues for catalyst design.
5:45 PM - T7.4
AFM Imaging of PFSA Polymer Adsorption on Model Graphite, Mica and Platinum Surfaces.
Roland Koestner 1 , Sergiy Minko 2 , Yuri Roiter 2 Show Abstract
1 Fuel Cell Research Laboratory, General Motors, Honeoye Falls, New York, United States, 2 School of Arts & Sciences, Clarkson University, Potsdam, New York, United States
The interaction of perfluorosulfonic acid polymer (PFSA, EW ~ 900 g/mol) with atomically flat graphite, mica and Pt surfaces is visualized at the single molecule level using in situ liquid atomic force microscopy (AFM) experiments. The adsorbed PFSA chains are characterized quantitatively within a controlled liquid environment that includes substrate surface charge, solvent composition, pH(e) and polymer aggregation in the liquid phase.The polymer structure in the liquid phase is imaged by rapid deposition on mica via spin coating (aggregation level) and by weak adsorption on highly oriented pyrolytic (HOPG) graphite (globular vs micellar conformation). This adsorption is driven by electrostatic interaction of the pendant sulfonate groups which is then correlated with the HOPG surface charge by zeta potential (net) and AFM force-distance curves (local) at varying solvent composition and pH(e). In contrast, the polar mica surface shows much stronger adsorption, while the bare Pt surface is much weaker than graphite. In summary, molecular-level mapping of the PFSA polymer interaction with these model surfaces should provide a quantitative basis to improve its distribution and morphology in Proton Exchange Membrane Fuel Cell (PEMFC) electrode layers.
T8: Poster Session: Fuel Cell
Karen Swider Lyons
Wednesday AM, December 02, 2009
Exhibit Hall D (Hynes)
9:00 PM - T8.1
A New Membrane Electrode Assembly for Low-Temperature PEM Fuel Cells having a Nanocomposite Catalyst Layer.
David Dvorak 1 , Mohsen Shahinpoor 2 Show Abstract
1 School of Engineering Technology, University of Maine, Orono, Maine, United States, 2 Mechanical Engineering, University of Maine, Orono, Maine, United States
Studies are currently underway to manufacture a novel membrane electrode assembly (MEA) for polymer electrolyte fuel cells. Specifically, innovative processes are being developed for applying a nanocomposite form of catalysts to the ion exchange polymer membrane. This MEA will be designed to incorporate a nanocomposite catalyst layer comprising a functionally graded distribution of Platinum nano particles chemically embedded near boundaries and surfaces of the polyelectrolytic membrane. The nanochemistry involved is called REDOX operation in which first the ionic polymer PSM is oxidized with a catalyst metal salt and then reduced in a reduction solution. This manufacturing technique incorporates two distinct processes. Initial process of oxidizing the PSN ionic polymer with an organometallic salt of a catalyzing metal salt such as Pt(NH3)4HCl in the context of chemical reduction processes. After oxidation, the ionic polymer is reduced to create functionally-graded conductor composite and near boundary porous electrodes. This membrane-catalyst layer nanocomposite is then sandwiched between two porous carbon gas diffusion layers. The catalyst layers of the membrane also function as electrodes, eliminating the need for a separate porous layer applied to the GDL. The whole assembly is then sandwiched between two flow-field or bi-polar plates in a standard fashion, thus giving rise to a 5-layer fuel cell rather than the currently standard 7-layer fuel cells. Note that precious metal catalysts can be combined with not-precious metal species to improve conductivity and lower cost. The penetration of the catalyst layer into the membrane can be controlled, as can the composition of the metallic species. Thus, deeper layers of metallic nanocomposites can be constituted of low-cost non-precious metals to allow electronic conduction (reducing the effective ionic conduction thickness of the membrane) while concentrating catalytic precious metals closer to the surface of the membrane. Initial performance tests of fuel cells incorporating these membranes show promising results which will serve as a baseline for further process optimization.
9:00 PM - T8.10
High Methanol-tolerant DMFC Cathode Catalyst based on Palladium.
Man-Yin Lo 1 , Ying-Chieh Chen 1 , Yen-Ze Chen 1 Show Abstract
1 , ITRI, Hsin-Chu Taiwan
Platinum is by far the best catalyst for the cathodic oxygen reduction reaction (ORR) in DMFC without the presence of methanol. However, the performance of Pt catalyst has not reached a status set forth for the commercialization of DMFC. The most serious problem to the cathode catalyst is mainly caused by the methanol crossover from the anode through the membrane. Methanol undergoes oxidation reaction at the cathode because Pt is one of the most active methanol oxidation catalysts. Mixed-potential due to cathodic methanol oxidation is detrimental to the performance of the cathode catalyst. Furthermore, incomplete oxidation of methanol also resulted in the accumulation of CO on the Pt surface. This CO poisoning effect greatly reduces the availability of Pt active site needed for the cathodic ORR. In order to alleviate the poisoning effect of methanol at the cathode, palladium based catalyst with both high ORR activity and methanol tolerance was explored as a replacement of Pt catalyst. Details concerning the preparation of Pd and PdM (M=Fe, Cu, Co and, etc.) catalysts and their ORR performance in the presence of methanol will be reported in this paper.
9:00 PM - T8.11
Amorphous Carbon Film Coating on Stainless Steel Bipolar Plate for Fuel Cell.
K. Kohara 1 , K. Takahashi 1 , Y. Nishimura 1 , Y. Fukami 1 , H. Murata 1 , Yoshiyuki Show 1 Show Abstract
1 Dept. of Electrical and Electronic Engineering, Tokai University, Hiratsuka Japan
Stainless steel bipolar plate for the polymer electrolyte membrane and the direct methanol fuel cells(FCs) has advantages of high manufacturability and mechanical strength. Passive film (Chrome oxidized) exists on its surface and plays role of anticorrosion layer. However, this oxidized layer increases contact resistance between bipolar plate and membrane electrode assembly (MEA) in fuel cell (FC) and decreases output power of the FC. In this study, amorphous carbon (a-C) film was coated on bipolar plate made of the stainless steel to prevent the formation of the oxidized layerStainless steel electrode was used as metal bipolar plate. The a-C film was grown on the bipolar plates by using plasma CVD equipment. Acetylene gas was used as source gas. Growth temperature was varied from room temperature to 600oC. Growth time was fixed at 30 min. The polymer electrolyte membrane and direct methanol fuels cell assembled with the a-C film coated bipolar platesFuel cell assembled with bare (no a-C coated) stainless steel showed maximum output power of 2.5W. The a-C film coating on the bipolar plate increased the maximum output power of the FC to 3W which was 1.2 times higher than that of the bare bipolar plate. The contact resistance measurement revealed the electrical resistance between the bipolar plate and the MEA surface was reduced from 17 to 12 mOhm by the a-C coating. These results indicates that the coating of the a-C film on the bipolar plate the increases output power of the fuel cell resulting in the decrease in the contact resistance.
9:00 PM - T8.12
Block Terpolymer Derived Nanocomposites Towards Designer Electrode Materials.
Morgan Stefik 1 , Francis DiSalvo 1 , Ulrich Wiesner 1 Show Abstract
1 , Cornell University, Ithaca, New York, United States
Fuel cell electrode operation requires three interconnecting and continuous pathways for the transport of electrons, ions, and fuel/oxidant. Toward this end, we report on the synthesis of three-component nanocomposites derived from the microphase separation of pentablock terpolymers. These polymers were designed to have three chemically distinct polymer blocks in order to facilitate the transport of the three chemical species of interest. The block terpolymer contained a block with a high yield of carbon upon pyrolysis, a block which was swellable with oxide sol, and a block that was thermally removable to result in porosity. The resulting nanocomposites contained electrically conductive carbon, surface proton conductive oxide, and fuel/oxidant pathways. The average mesopore size, wall thickness, and weight fraction of carbon in these materials were all controlled by the block terpolymer chemistry.
9:00 PM - T8.13
Nanoparticle Enhancement of Polymer Electrolyte Membrane Fuel Cell Power Output.
Cheng Pan 1 , Kenny Kao 2 , Sijia Zhao 1 , Miriam Rafailovich 1 Show Abstract
1 Materials Science and Engineering, State University of New York at Stony Brook, Stony Brook, New York, United States, 2 , George School, Newtown, Pennsylvania, United States
PEM fuel cell technology is one of the most promising future alternative energy sources because it has relatively low operating temperature, high power density, quick response, pollution-free operation. However, its relatively low power output compared to that of its price has prevented it from many practical applications. Nanoparticles have been widely known to possess catalytic capabilities. Marvrikakis et al have predicted that gold nanoparticles that are platelet shaped and have direct contact to the substrate to be the “perfect” catalysts. We have shown that such particles can be synthesized by first starting with the standard two phase method, which produces spherical gold (Au) and palladium (Pd) nanoparticles. When a solution containing these particles is spread at the air water interface, X-ray reflectivity and EXAFS spectroscopy indicate that some of the Au or Pd atoms are removed, as the water displaces the hydrophobic thiol chains from the particle surface, resulting in platelet shaped particles with a 2:1 aspect ratio. Furthermore, if the particles are spread on a Langmuir trough where surface pressure can be applied to compress them, they form films consisting of one or more monolayers. These particle films can then be lifted onto a solid surface, such as the PEM membrane where the particle surface can make direct electronic contact with the fuel cell membrane, greatly increasing the efficiency of the catalysis process and increasing the ion current through the membrane.A series of parallel experiments were done to explore the various factors that may affect the performance of PEM fuel cell, such as hydrogen flow rate, metal-thiol ratio of nanoparticles, type of nanoparticles, surface pressure of the LB trough etc. We found that under the optimal hydrogen flow rate of 20 CCM (cubic centimeter per minute), the addition of 1:1 metal-thiol gold nanoparticles resulted in more than 80% increase in the power output of the fuel cell.
9:00 PM - T8.14
Micro Polymer Electrolyte Membrane Fuel Cell Based on Fully Conventional Semiconductor Processing.
Jin Tae Kim 1 , Chan Hyeok Yeo 1 , Won Suk Chang 1 , Kyu Hyung Cho 1 , Yeon Ho Im 1 2 Show Abstract
1 School of Semiconductor and Chemical Engineering, Chonbuk National University, Jeonju Korea (the Republic of), 2 Department of Hydrogen and Fuel Cells Engineering, Specialized Graduate School, Chonbuk National University, Jeonju Korea (the Republic of)
Currently, there has been increasing research interest in micro power sources for portable and autonomous micro systems drives research on micro fuel cell systems as a key component of micro power generation system. The goal of this work is to develop novel monolithic type microfuel cell based on conventional semiconductor processing. In order to form monolithic type fuel cell, thin film type proton exchange membrane which consists of micro-structure arrays and sulfonated fluorocarbon films, was developed in this work. The Si based micro-structures were used to increase the surface area of the effective proton exchange membrane. The proton conductivities of the synthesized polymer electrolyte membrane were evaluated as functions of temperature and humidity. Finally, Pt catalytic could be formed by thermal evaporator system, and fuels were supplied through micro-channels formed by polydimethylsiloxane (PDMS). Therefore, the developed micro fuel cell is fully compatible with the conventional semiconductor technology. The performance of novel micro fuel cell was evaluated under CH3OH and KMnO4 flow using Potentiostat.
9:00 PM - T8.15
Variable Pressure and Temperature Study of Water Self-Diffusion in Composite Polymer Fuel Cell Membranes.
Jaime Farrington 1 , Bruno Pinto 1 , Alessandra D'Epifanio 2 , Nicola Boaretto 3 , Phillip Stallworth 1 , Steve Greenbaum 1 Show Abstract
1 Physics and Astronomy Dept., Hunter College of CUNY, New York, New York, United States, 2 Chemistry Dept., University of Rome Tor Vergata, Rome Italy, 3 Chemistry Dept., University of Padova, Padova Italy
Proton exchange membrane fuel cells (PEMFCs) operating in the normal 60-80°C temperature range, face problems including poor carbon monoxide tolerance and heat rejection. These drawbacks can be overcome by increasing the operation temperature range up to 110-150°C. However, this causes rapid water loss from Nafion electrolyte membranes. Since the proton conductivity of Nafion is critically dependent on water content, PEM fuel cell performance degrades severely. On the other hand, composite membranes prepared by the addition of metal oxide particles to Nafion demonstrate enhanced fuel cell performance at elevated temperatures under reduced humidity conditions. Interactions between the polymer and the particle surface can have a significant effect on the membrane microstructure. There are powerful Nuclear Magnetic Resonance (NMR) techniques that can be applied to these materials that yield important dynamic and structural information. In particular, activation parameters for ionic and molecular transport can be obtained by self diffusion NMR measurements. Activation energies are obtained from variable temperature studies while activation volumes are collected from variable pressure data. By independently controlling two thermodynamic variables, a broader characterization of the transport properties of ionic conduction membranes can be achieved. An experimental setup has been engineered to perform water self diffusion NMR measurements while independently controlling pressure and temperature. Measurements where performed on Nafion doped with mixed oxides such as ZrO2/SiO2 and ZrO2/HfO2, Nafion doped with SnO2 nH2O and pure Nafion, which was used as a reference. Preliminary results suggest a decrease in activation volume for water diffusion in fully hydrated Nafion. Results for the composite membranes with variable water content will be presented.
9:00 PM - T8.16
Pd-Pt Bimetallic Nanodendrites with High Activity for Oxygen Reduction.
Byungkwon Lim 1 , Majiong Jiang 2 , Pedro Camargo 1 , Eun Chul Cho 1 , Jing Tao 3 , Yimei Zhu 3 , Younan Xia 1 Show Abstract
1 Department of Biomedical Engineering, Washington University, St Louis, Missouri, United States, 2 Department of Chemistry, Washington University, St Louis, Missouri, United States, 3 Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York, United States
Platinum (Pt) is the most effective catalyst to facilitate both hydrogen oxidation and oxygen reduction in a proton-exchange membrane fuel cell, but several critical issues still need to be addressed before such cells can be commercialized for automotive applications: For example, the oxygen reduction reaction (ORR) is kinetically limited at the cathode, and the scale of the Pt crystallites leads to high costs for Pt-based electrocatalysts with sufficient surface area and activity. In order to overcome these barriers, it is necessary to maximize the activity of a Pt-based catalyst by engineering its morphology and/or composition. Here we present a facile, aqueous-phase route to synthesize bimetallic nanodendrites consisting of a dense array of Pt branches on a core of palladium (Pd) nanocrystal. In this approach, truncated octahedral nanocrystals of Pd with an average size of 9 nm were used as seeds so as to direct the dendritic growth of Pt upon the reduction of K2PtCl4 by L-ascorbic acid in an aqueous solution. Using this simple approach, we routinely produced Pd-Pt bimetallic nanodendrites with high surface areas and the particularly active facets for the ORR in high yields. These Pd-Pt nanodendrites were two and a half times more active on the basis of equivalent Pt mass for the ORR than the state-of-the-art Pt/C catalyst and five times more active than the first-generation supportless Pt-black catalyst. This synthesis also provides a convenient and environmentally benign route to large-scale production because it does not require high temperature, organic solvent, or electrochemical deposition.
9:00 PM - T8.17
Synthesis and Characterization of Different Carbon Nanotube Supported Catalysts and Their Effects on Methanol and Ethanol Electro-oxidation.
Raghavendar Reddy Sanganna Gari 1 , Zhou Li 2 , Lifeng Dong 1 Show Abstract
1 Department of Physics, Astronomy, and Materials Science, Missouri State University, Springfield, Missouri, United States, 2 Greenwood Laboratory School, Missouri State University, Springfield, Missouri, United States
Both direct methanol fuel cells (DMFCs) and direct ethanol fuel cells (DEFCs) are extensively studied as potential power sources for portable electronic devices and automobiles. However, their performances are limited by low electrochemical activity of methanol and ethanol electro-oxidation. Recently, carbon nanotubes (CNTs) were demonstrated as a desirable catalyst support for improving catalytic activity. A primary goal of this work is to systematically study the electrochemistry of both methanol and ethanol oxidation on different carbon nanotube supported catalysts. In this work, both single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) supported Pt and Pt-Ru catalysts were synthesized by an ethylene glycol (EG) reduction method. The morphology and catalyst distributions of both Pt/CNTs and Pt-Ru/CNTs were characterized by field emission scanning electron microscope (FESEM) equipped with X-ray energy dispersive spectrometer (EDS). Comparative electrochemical measurements of Pt/SWCNTs, Pt-Ru/SWCNTs, Pt/MWCNTs, and Pt-Ru/MWCNTs catalysts were conducted using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry techniques. Experimental results show that, SWCNTs supported Pt and Pt-Ru catalysts have higher catalytic activity and lower charge transfer resistance towards methanol and ethanol oxidation in comparison to MWCNTs supported catalysts. Acknowledgement: This work was partially supported by a Faculty Research Grant from Missouri State University, the American Chemical Society Petroleum Research Fund (47532-GB10), and the National Science Foundation (DMR-0821159).
9:00 PM - T8.18
Characterization of Polymer Blends for Proton Exchange Membranes.
B. Seyhan Gunduz 1 , Jingjing Pan 3 , Christopher Sloan 2 , Ashley Speranza 4 , Joshua Wilson 4 , Thomas Smith 3 , Peggy Cebe 1 Show Abstract
1 Physics and Astronomy, Tufts University, Medford, Massachusetts, United States, 3 Chemistry, Rochester Institute of Technoloy, Rochester, New York, United States, 2 Chemistry and Physics, Gallaudet University, Washington, District of Columbia, United States, 4 , Rochester Institute of Technoloy, Rochester, New York, United States
We report the phase structure, morphology, and properties of a binary polymer blend for use as a proton exchange membrane. The blend comprises a semicrystalline polymer, poly(vinylidene fluoride), PVF2, with an amorphous polymer, poly[4(5)-vinylimidazole], PVIm, doped with trifluoro-methylsufonylimide, TFSI. Blends of PVF2//PVIm/VIm+TFSI- were prepared in dimethylformamide with 15, 25, 35, and 50 mol% of TFSI. Real-time simultaneous wide and small angle X-ray diffraction showed that films cast from solution contained polar beta phase PVF2 crystals. Heat treatment, by cooling from the melt, resulted in formation of the non-polar alpha crystallographic phase and altered both the thermal properties and the crystal morphology of the blends. Impact of TFSI content on conductivity using dielectric relaxation spectroscopy will be reported.Research supported by the National Science Foundation, Division of Materials Research, Polymers Program, through DMR-0906455.
9:00 PM - T8.2
Synthesis and Characterization of Polythiophene-composited Pd Catalysts for Hydrogen Electrooxidation.
EunJa Lim 1 , Min Ho Seo 1 , Sung Mook Choi 1 , Hyung Ju Kim 1 , Won Bae Kim 1 Show Abstract
1 Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of)
Although there have been many attempts to develop a new platinum-free catalyst for proton exchange membrane fuel cell (PEMFC), Pt is still the only metal showing the high and stable performance on hydrogen oxidation in the acid-based PEMFCs. Development of Pt-free catalysts is necessary for reducing fuel cell stack cost, but unfortunately pure and composited catalysts based on common transition metals is not stable in acid condition because of its thermodynamically and electrochemically unstable property at low pH and high potential region. In our previous work, composited Pd with a conducting polymer of polypyrrole (Pd-PPy) demonstrated high activity levels with practical implications for the hydrogen fuel oxidation electrodes of PEMFCs. As further work, here, we also propose that polythiophene(PTh) as other conjugated polymer could stabilize the Pd metal. The Pd-PTh composite shows an improved stability and activity for hydrogen oxidation compared to electrodeposited bare Pd. Such catalytic stability and activity of Pd-PTh are demonstrated by half-cell test and cyclic voltammetry test together with physico-chemical characterization. While the bare Pd shows a poor stability on the hydrogen oxidation performance, the Pd-PTh composite catalyst maintains the activity up to 500 cycles. It seems that the conducting polymer of the polythiophene layer effectively prevents the active Pd catalyst from undergoing oxidative dissolution, allowing the high electrocatalytic activity of Pd to be maintained under acidic conditions. This should enable a new strategy for electrocatalyst development through the stabilization of highly reactive but otherwise unstable non-noble metal catalysts.  M. H .Seo. et.al, submitted for the publication.
9:00 PM - T8.3
Synthesis of Carbon Nanofiber-Supported Pt by Polyol Processing Technique for Use as Electrodes in DMFCs.
Zhan Lin 1 , Mariah Woodroof 1 , Liwen Ji 1 , Yingfang Yao 1 , Xiangwu Zhang 1 Show Abstract
1 Department of Textile Engineering, Chemistry and Science, North Carolina State University, Raleigh, North Carolina, United States
Direct methanol fuel cells (DMFCs) have been considered as one of the promising energy systems since they produce electric power by the direct conversion of the methanol fuel at the anode of fuel cells. In this study, Pt/carbon nanofiber composites (Pt/CNFs) were prepared by depositing Pt nanoparticles onto electrospun carbon nanofibers (CNFs) using polyol processing technique, and their electrocatalytic properties were characterized towards the oxidation of methanol. Transmission electron microscopy images show that CNFs exhibit smooth and straight fibrous morphology with diameters ranging from 200 to 300 nm, and Pt nanoparticles are observed on the surface of CNFs after chemical deposition. However, there are just a few relatively large Pt nanoparticles and their diameters are around 20.0 nm on CNFs without any surface treatment. After treatment, Pt nanoparticles are evenly distributed on the surface of CNFs, and their diameters are much smaller, which are between 3.0 - 5.0 nm. Cyclic voltammetry was used to study the electrocatalytic activity of Pt/CNF composite electrodes toward the oxidation of methanol. A small methanol oxidation peak of Pt/CNFs without any surface treatment is found around 0.80 V (vs. Ag/AgCl/4.0 M KCl), however, there is no peak found when scanning back. In comparison, Pt/CNF electrodes present the electro-oxidation of methanol, which starts at + 0.42 V and then the current density increases to a maximum at + 0.63 V. Moreover, another current peak is found at +0.55 V when scanning back, which signifies the desorption of CO generated through the methanol oxidation. It is also seen that the current density peaks of Pt/CNFs with 1-aminopyrene functionalization are much larger than that of Pt/CNFs with HNO3 + H2SO4 acid oxidation, which means that the 1-aminopyrene functionalization leads to better catalytic activity toward the oxidation of methanol. In summary, Pt nanoparticles deposited on CNFs by the polyol processing technique exhibit good electrocatalytic activity toward the methanol oxidation, and can be potentially used as electrodes in DMFCs.
9:00 PM - T8.4
Synthesis of Cobalt/Polypyrrole/Carbon Nanotube and Catalytic Activity for Oxygen-reduction Reaction.
Hye-mi Bok 1 , Hyun-Jong Kim 1 , Kyoungjun An 1 , Mk Han 1 , Hansung Kim 2 Show Abstract
1 Nano surface technology team, Korea Institute of Industrial Technology, Inchen Korea (the Republic of), 2 Department of Chemical Engineering, Yonsei university, Seoul Korea (the Republic of)
Fuel cells have been recognized as clean energy-converting devices due to their high efficiency and low/zero emissions. Especially, study of non-platinum catalysts is important and attractive issue in the energy conversion efficiency of polymer electrolyte membrane fuel cells (FEMFC) because it is a new class of low cost nano-composite catalysts compared to platinum catalysts. Herein, we described a cobalt/polypyrrole/carbon nanotube (Co/PPy/CNT) as non-platinum catalysts for FEMFC. PPy-CNT composite was first prepared by using chemical oxidation polymerization of pyrrole in the presence of ferric chloride (FeCl3) and the obtained material was mixed with a solution containing cobalt(Co) ion. The PPy/CNT was characterized by fourier transform-infrared (FT-IR) spectroscopy and X-ray diffraction (XRD). FT-IR spectra indicated that each individual CNT could be well coated by PPy. XRD patterns showed the presence of characteristic broad peak of PPy and the strong peaks of CNT. The tubular morphology of Co/PPy/CNT was observed with scanning electron microscopy (SEM). Also, Extended X-ray absorption fine structure (EXAFS) spectroscopy revealed that the Co ion is successfully coordinated by nitrogens(N) atoms. Elecrocatalytic oxygen-reduction reaction was measured by using the rotating disk electrode. An onset potential of catalyst was approximately 0.69 V (NHE) and the PEMFC performance was 50 mA cm-2 at 0.6 V in both H2-O2 condition. The electrocatalytic activity was dependant on Co/N ratio and thermal treatment conditions. Therefore, the interaction between Co ion and N atom should play as active site. Also, the heat treatment is a necessary step to enhance activity and stability of this catalyst.
9:00 PM - T8.5
Electrochemical Characterization of Air-breathing Direct Methanol Fuel Cells Cathodes Under Flooding Conditions.
Ana Tavares 1 , Francesca Capitanio 1 Show Abstract
1 Energie, Materiaux et Telecommunications, Intitut National de la Recherche Scientifique, Varennes, Quebec, Canada
Small fuel cells that run on methanol have intrinsically higher energy density than batteries, improved autonomy and instant re-charge. However, in air breathing DMFC the cathode performance is strongly limited by the flooding due to water and methanol accumulation. To quantify the factors governing the cathode deactivation under flooding, a series of DMFCs electrodes with catalyst layers of different structure and hydrophilic degree were electrochemically characterized in 0.5 moldm-3 H2SO4. This condition was chosen to simulate severe flooding. Nafion and Teflon were used as binders in the fabrication of the catalyst layers, and their content was varied between 15/0 and 0/15 wt% Nafion/Teflon with respect to Pt. The Pt loading was 3 mgcm-2 and the electrodes were prepared by spray deposition on non teflonized carbon cloth. Cyclic voltammetry in N2 saturated solution revealed that the Pt electrochemical surface area is 19 m2g-1 for the Nafion bonded electrodes and 15 m2g-1 for all other compositions. Since the Pt utilization is almost the same, differences in the cathodes’ performance can be ascribed to variations into their hydrophilic character and/or in their morphology.AC electrochemical impedance spectroscopy was carried out in N2 saturated solution and a DC voltage in the double layer charging region was applied as bias potential. The Nyquist plot of the 15 wt% Nafion electrode include a 45° region at high frequencies due to the ion diffusion through the electrode porous structure. The extent of this region decreases when Nafion is partially replaced by Teflon and the capacitance feature dominates the EIS spectra of Teflon bonded electrodes. The cathodes were also investigated for oxygen reduction in the O2 saturated solution. Steady state polarization curves reveal the strong influence of the binder nature: the overpotential for the ORR is lower for the more hydrophilic electrode, but the Tafel slope is lower for the Teflon bonded electrode (81 mV) and the limiting current increases by one order of magnitude by replacing Nafion with the Teflon. The higher limiting current for the ORR reaction on the Teflon bonded electrodes was expected, but this study clearly shows that an hydrophobic polymer has to be used as the main binder in the catalyst layer of an air-breathing DMFC cathode in order to keep it operating under flooding. An hydrophilic component is necessary for the ORR reaction but its content in the catalyst layer has to be minimized, or other alternatives Nafion have to be used.The morphology of the electrodes will be analysed by SEM, and water absorption capacity of the cathodes will be quantified by Dynamic Vapor Sorption. The cathodes performance in DMFC operation will be also investigated.
9:00 PM - T8.7
Synthesis and Characterization of Gold-Platinum Nanoparticles as Electrocatalysts for Fuel Cells.
Bridgid Wanjala 1 , Derrick Mott 1 , Rameshwori Loukrakpam 1 , Jin Luo 1 , Peter Njoki 1 , Bin Fang 1 , Chuan-Jian Zhong 1 Show Abstract
1 Department of Chemistry , State University of New York at Binghamton, Binghamton, New York, United States
Bimetallic nanoparticles exhibit interesting electronic, optical, and chemical or biological properties due to bifunctional or synergistic effects. Several types of gold-based bimetallic nanoparticles for catalytic reactions have recently been studied. One example involves use of AuPt nanoparticles as electrocatalysts for fuel cell reactions. The ability to synthesizing and processing the bimetallic nanoparticles with controllable composition in a wide range is an important focus of the exploration. This presentation discusses recent results of our investigation of the synthesis and processing of AuPt bimetallic nanoparticles in organic solvents. By controlling the feed ratios of Au and Pt precursors, the relative concentrations, the reducing and capping agents, AuPt nanoparticles with bimetallic compositions ranging from 0-100 Au% and particle sizes ranging from 2 to 4 nm were synthesized. The composition was determined by direct current plasma - atomic emission spectroscopy. A 1:1 linear correlation between the precursor feed ratio and the nanoparticle compositions was established. The size and morphological properties were characterized using transmission electron microscopy and X-ray diffraction. A focus of the discussion will be the correlation between the bimetallic composition and the electrocatalytic activity of the catalysts for oxygen reduction reaction (including fuel cell performance). Selected examples of the bimetallic nanoparticles for the design of fuel cell catalysts will also be discussed with emphasis on electrocatalytic characterization.
9:00 PM - T8.8
Rotating Disk Electrode Study of the Electrocatalytic Activity and Stability of Bimetallic/Trimetallic Nanoparticle Catalysts for Oxygen Reduction Reaction.
Peter Njoki 1 , Bridgid Wanjala 1 , Rameshwori Loukrakpam 1 , Bin Fang 1 , Jin Luo 1 , Chuan-Jian Zhong 1 Show Abstract
1 Department of Chemistry , State University of New York at Binghamton, Binghamton, New York, United States
Fuel cells represent a promising front of research and development in exploring alternative future energies, which are highly efficient and environmentally clean. A key challenge for the commercialization of fuel cells is availability of active, robust, and low-cost catalyst. The development of effective strategies for the synthesis of alloy nanoparticles with controllable size and composition is an important approach to the catalyst preparation. This poster will discuss recent results of an investigation of the electrocatalytic activity and stability of bimetallic/trimetallic nanoparticle catalysts for oxygen reduction reaction. A focus of the discussion is the correlation of the nanoscale size and composition with the electrocatalytic activity and stability. In addition to synthesis of multimetallic alloy nanoparticles with controlled size and composition, the electrocatalytic activity and stability of the catalysts for oxygen reduction reaction are investigated using cyclic voltammetry and rotating disk electrode techniques. The electrocatalytic activity and stability of selected catalysts will be discussed, along with their correlation with preliminary performance evaluation in fuel cells.
9:00 PM - T8.9
High Surface Area Catalyst Support Structures for Oxygen Reduction.
Ryan Tucker 1 3 , Michael Fleischauer 1 , Arman Bonakdarpour 2 , Hillary Cheng 2 , David Wilkinson 2 , Michael Brett 1 3 Show Abstract
1 , NRC-National Institute for Nanotechnology, Edmonton, Alberta, Canada, 3 Electrical & Computer Engineering, University of Alberta, Edmonton, Alberta, Canada, 2 Chemical & Biological Engineering, University of British Columbia, Vancouver, British Columbia, Canada
Nanostructured thin film oxygen reduction catalysts consisting of Pt nanocrystals on crystalline organic whisker supports offer considerable stability and performance enhancements over standard carbon-supported dispersed Pt.1 Whisker-like support structures consist of aligned crystals of a perylene derivative on the order of 50 nm in width and upwards of one micron in length numbering ~50 per square micron.2 Magnetron sputtered Pt nanocrystals nucleate uniformly every 6-8 nm over this high surface area support,3 leading to large electrochemical surface areas. The electrochemical surface area is stable with potential cycling, indicating a high stability of Pt catalysts against corrosion.4The nanostructured thin film (NSTF) supports used with a Pt-based catalyst have demonstrated significant enhancements in both specific activity and durability.3 However, non-noble metal catalysts such as Fe-C-N are not compatible with the organic whisker supports since a high temperature “activation” step is required.5 Metal oxides such as Ti4O7 and Ti0.9Nb0.1O2 have demonstrated better temperature stability and are thus being considered as alternate catalyst support materials.6We have recently demonstrated that the Glancing Angle Deposition (GLAD)7,8 thin film fabrication technique can be used to produce columnar Ti supports for Pt oxygen reduction catalysts.9 Here we report on expanding this work to the Ti-O system - chosen for stability, variable conductivity, and ease of fabrication - as a model for high surface area metal oxide supports.The GLAD technique offers a high degree of control over the architecture of porous nanostructured thin films. Arrays of micron-long vertically aligned posts ~30 nm to ~200 nm in diameter can be produced with this method. Control of the deposition angle alters film porosity between 20% and 100% of bulk material. We will report on the oxygen reduction performance (determined by rotating disk electrode measurements and cyclic voltammetry) of Pt on Ti-O supports as a function of Pt loading, support porosity, and support conductivity, and outline the potential of columnar high surface area metal oxide supports. References:1 M.K. Debe et al., ECS Trans., 1, 51 (2006).2 M.K. Debe and R.J. Poirier, J. Vac. Sci. & Tech. A, 12, 2017 (1994).3 L. Gancs et al., Chem. Mater., 20, 2444 (2008).4 M.K. Debe et al., J. Power Sources, 161, 1002 (2006).5 E.B Easton et al., Electrochem. Solid-State Lett., 9, A463 (2006).6 G. Chen et al., J. Electrochem. Soc., 149, A1092 (2002).7 U.S. Patents 5,866,204, 6,206,065, 6,248,422, 6,549,253.8 K. Robbie and M.J. Brett, J Vac. Sci. & Tech. A, 3, 1460 (1997).9 A. Bonakdarpour et al., Appl. Catal. A, 349, 110 (2008).