Symposium Organizers
Karen Swider-Lyons Naval Research Laboratory
Byungwoo Park Seoul National University
Ting He Honda Research Institute USA, Inc.
T3: Fuel Cell Overview I
Session Chairs
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
1 Energy Lab, SAIT, Samsung Electronics Co., Ltd., Suwon Korea (the Republic of)
Show AbstractMaterial 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
Session Chairs
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
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
Show AbstractCompared 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
1 , Stanford Synchrotron Radiation Lightsource, Menlo Park, California, United States, 2 Department of Chemical and Biomolecular Engineering, University of Houston, , Houston, Texas, United States
Show AbstractThe 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
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
Show AbstractCarbon 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
BREAK
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
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
Show AbstractOne 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
1 , Oak Ridge National Laboratory, Oak Ridge , Tennessee, United States
Show AbstractAtomic-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
1 , Honda Research Institute USA, Columbus, Ohio, United States
Show AbstractThe 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
1 , Honda Research Institute, Inc., Columbus, Ohio, United States
Show AbstractThe 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.[1] Q. Xu, E. Kreidler, D.O. Wipf, and T. He, J.Electrochem. Soc. 2008, 155, B228.[2] L. Tang et al., to be published.
T5: Fuel Cell Overview - II
Session Chairs
Tuesday PM, December 01, 2009
Room 301 (Hynes)
2:30 PM - **T5.1
PEM Fuel Cells.
Yu-Min Tsou 1
1 , BASF Fuel Cells, Somerset, New Jersey, United States
Show AbstractThis 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
Session Chairs
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
1 Chemical Engineering, Texas A&M University, College Station, Texas, United States
Show AbstractPt-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
1 , MIT, Cambridge, Massachusetts, United States, 2 , CERMICS-ENPC, Marne la Vallée France
Show AbstractUnderstanding 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 [1]. 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[1] 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
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
Show AbstractKnowledge 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
1 Dept. of Materials Science & Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 , Honda Research Institute, Columbus, Ohio, United States
Show AbstractIn 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
1 Dept. of Materials Science & Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 , Honda Research Institute, Columbus, Ohio, United States
Show AbstractPt 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
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
Show AbstractApplication 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
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
Show AbstractThe 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
Session Chairs
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
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
Show AbstractCarbon 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
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
Show AbstractThe 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
2 Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 1 Materials Science, Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractSimilar 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
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
Show AbstractThe 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
Session Chairs
Ting He
Byungwoo Park
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
1 School of Engineering Technology, University of Maine, Orono, Maine, United States, 2 Mechanical Engineering, University of Maine, Orono, Maine, United States
Show AbstractStudies 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
1 , ITRI, Hsin-Chu Taiwan
Show AbstractPlatinum 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
1 Dept. of Electrical and Electronic Engineering, Tokai University, Hiratsuka Japan
Show AbstractStainless 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
1 , Cornell University, Ithaca, New York, United States
Show AbstractFuel 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
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
Show AbstractPEM 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
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)
Show AbstractCurrently, 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
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
Show AbstractProton 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
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
Show AbstractPlatinum (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
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
Show AbstractBoth 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
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
Show AbstractWe 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
1 Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of)
Show AbstractAlthough 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[1], 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. [1] 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
1 Department of Textile Engineering, Chemistry and Science, North Carolina State University, Raleigh, North Carolina, United States
Show Abstract 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
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)
Show Abstract 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
1 Energie, Materiaux et Telecommunications, Intitut National de la Recherche Scientifique, Varennes, Quebec, Canada
Show AbstractSmall 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
1 Department of Chemistry , State University of New York at Binghamton, Binghamton, New York, United States
Show AbstractBimetallic 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
1 Department of Chemistry , State University of New York at Binghamton, Binghamton, New York, United States
Show AbstractFuel 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
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
Show AbstractNanostructured 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).
Symposium Organizers
Karen Swider-Lyons Naval Research Laboratory
Byungwoo Park Seoul National University
Ting He Honda Research Institute USA, Inc.
T9: ORR Catalysts I
Session Chairs
Wednesday AM, December 02, 2009
Room 301 (Hynes)
9:30 AM - **T9.1
Pd Alloy-supported Pt Monolayer O2 Reduction Electrocatalysts: From Single Crystal to Nanoparticle Scale-up Synthesis Studies.
Weiping Zhou 1 , D. Su 2 , J. Wang 1 , K. Sasaki 1 , M. Vukmirovic 1 , W. Chen 1 , Y. Zhu 2 , R. Adzic 2
1 Chemistry Department, Brookhaven National Laboratory, Upton, New York, United States, 2 Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York, United States
Show AbstractThe polymer electrolyte membrane fuel cell (PEMFC) is considered a potential power source for automotive and residential applications. However, high content of Pt as the cathode catalysts and the slow kinetics of oxygen reduction reaction (ORR) on conventional Pt catalysts is still one major obstacle for its wide-spread commercialization. The PtML acting as the ORR catalyst when deposited on suitable metal [1] or oxide surfaces [2] is a very attractive approach for solving these problems encountered in conventional Pt electrocatalysts. This study of ORR on a PtML covered Pd alloy surfaces, Pd3Fe(111) and Pd2Co/C nanoparticles, is a continuation of efforts to achieve a fundamental understanding of the substrate effect on chemical and electrocatalytic properties of Pt monolayers and to manipulate this effect on nano-scale materials.We studied the ORR on a well-ordered Pd3Fe(111) with and without Pt monolayer in 0.1 M HClO4 at room temperature. By comparing the specific activity at 0.9 V, we observed that a Pt monolayer supported on Pd3Fe(111) shows higher ORR kinetics compared with Pt(111), increased by a factor of at least 2, and also demonstrates significantly increased ORR activity in comparison with PtML/Pd(111), while the bare Pd3Fe(111) surface has comparable ORR activity to a Pt(111).We synthesized a small quantity of well-defined Pd3Fe (core) – and Pd2Co (core) – Pt(shell) nanoparticles (on a R.D.E) and also a several hundred milligram-batch using the Cu upd and Pt replacement method. High Pt mass activities are achieved for those core shell materials under RDE test conditions. EELS and HAADF-TEM techniques provided insights on the structure property of these core-shell catalysts. This will be discussed in detail at the meeting.This work is supported by U.S. Department of Energy, Divisions of Chemical and Material Sciences, under the Contract No. DE-AC02-98CH10886.1. J. Zhang, M. B. Vukmirovic, Y. Xu, M. Mavrikakis, and R. R. Adzic, Angew. Chem. Int. Ed 44 (2005) 2132.2. K. Sasaki, L. Zhang, and R. R. Adzic, Phys. Chem. Chem. Phys. 10 (2008) 159.
10:00 AM - T9.2
Organically Capped Platinum Nanoparticles as Electrocatalyst for Oxygen Reduction.
Henri Perez 1 , Bertrand Baret 1 , Laurent Akrour 1 , Christelle Cremona 1 , Arnaud Morin 2 , Arnaud Etcheberry 3
1 DSM/IRAMIS/SPAM-LFP, cea, Gif sur Yvette France, 2 DRT/Liten/DTH/LCPEM, CEA, Grenoble France, 3 Institut Lavoisier UMR 8180 , CNRS/Université de Versailles Saint Quentin, Versaille France
Show AbstractPlatinum is still the reference material as electrocatalyst for oxygen reduction and hydrogen oxidation in Proton Exchange Membrane Polymer Fuel Cells (PEMFC). The efficiency and optimization of the electrocatalyst incorporated in the electrodes of fuel cells depend on the features of the catalyst itself (size and/or shape of the nanoparticules) and those of the active layer in which it is incorporated. With these respects the bottom-up approach which consists in pre-synthesizing nanoparticles followed by their controlled organisation in an active layer is of particular interest. Indeed, using organic capping which strongly interacts with the nanoparticle surface, wet chemistry routes allows the nanoparticles to be isolated as powder, which can be further re-dissolved and handled in adapted solvents. However, regarding electrocatalyts related to PEMFC, they are still quite few reports dealing with the use or study of such capped electrocatalyst [1-3]. In this paper we present our results recorded in this field, which are based on the synthesis of crown derivatized platinum nanoparticles [4]. These nanoparticles can be organized in mixte Langmuir- Blodgett thin films and their electrochemical behaviour studied as a function of platinum amount deposited or as a function of the features of the organic crown [5]. The interesting results recorded recently led us to contemplate the controlled combination of the capped electrocatalysts with carbon nanotubes and the formation of porous active layers on carbon felts. These electrodes were studied over a wide range of platinum loading, down to few µg/cm2 [6]. Electrochemical characterizations were performed by cyclic voltametry in such conditions that the integrity of the capped electrocatalyst was preserved. We believe that this research is both, of fundamental and practical interest. Indeed, our latest results show that these electrodes formed with capped platinum electrocatalyst exhibit high performances with quite low platinum loading when used in real fuel cell devices.
10:15 AM - T9.3
Platinum Nanorod Arrays for PEM Fuel Cell Electrodes.
Wisam Khudhayer 1 , Ali Shaikh 2 , Tansel Karabacak 1
1 Applied Science, UALR, Little Rock, Arkansas, United States, 2 chemistry department, university of arkansas t little rock, little rock, Arkansas, United States
Show AbstractVertically aligned platinum (Pt) nanorod arrays produced by glancing angle deposition technique (GLAD) have been investigated for their electrochemical properties as a cathode in polymer electrolyte membrane (PEM) fuel cells. These single-layer catalyst nanorods without any carbon support have been produced at lengths varying between 50-600 nm, which correspond to Pt loadings as low as 0.04-0.50 mg/cm2. Pt nanorods were deposited on flat Pt film coated silicon substrates at a glancing angle of θ = 85o with respect to substrate normal. Substrates were also rotated azimuthally along their substrate normal axis at a speed of 1 rpm. Prior to Pt film deposition, a thin layer of chromium was deposited as an adhesion layer to the silicon substrate in order to avoid delamination during electrochemical tests. Conventional polycrystalline Pt thin film were also produced at a normal incidence (θ = 0o) flux to be compared to Pt nanorods for their material and electrochemical properties. Cyclic voltammetry (CV) and rotating ring disk electrode (RRDE) voltammetry were performed to characterize the electrochemical activity and kinetics of the Pt nanorods. The well-defined peaks in the CV profile of the nanorods represent various crystal plane orientations and indicate that Pt nanorods are electrochemically more active than Pt thin films. In addition, RRDE results show that the oxygen reduction occurs through direct four-electron process. Morphology and crystallographic structure of Pt nanorods have been studied using scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. SEM results reveal that Pt nanorods are well-isolated, vertically aligned, and single-crystal with atomically sharp tips. The single-crystal property allows enhanced electrochemical activity and reduced surface oxidation, while the isolated nature of the rods in lateral directions can provide a channeled porosity for effective transportation of gases in a PEM fuel cell. In addition, the XRD results illustrate that Pt nanorods are mainly oriented in the (220) direction unlike the typical (111) texture of the polycrystalline Pt film. Pt (111) is the energetically favorable growth plane of Pt films and has a poorer electrochemical activity than that of Pt (110) and Pt (100) planes due to the relatively strong adsorption of bi-sulfate ions as confirmed in the previous studies. It has been observed that as the length/loading of Pt nanorods increases, Pt (110) planes become more dominant and this enhancement is less pronounced for Pt (100). Our results demonstrate that GLAD technique is a promising approach to control the crystal orientation by promoting the crystal orientation of Pt (110) growth which is the most active surface for oxygen reduction reaction in PEM fuel cells.
10:30 AM - T9.4
Nanoscale Control of Pt-Based Electrodes.
Changwoo Nahm 1 , Chunjoong Kim 1 , Yejun Park 1 , Byungwoo Park 1
1 Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of)
Show AbstractProton exchange membrane fuel cell (PEMFC) and direct-methanol fuel cell (DMFC) are promising power sources for the environmental-friendly low/zero emission devices. However, prohibitive issues remain, such as the inefficient utilization of Pt, low efficiency of cathode for oxygen-reduction reaction (ORR), the loss of Pt activity by a long-term operation, etc. To resolve these, highly efficient Pt-based electrodes have been synthesized by optimizing the nanostructures, and the physical/chemical origins of the improved properties are examined. Iron-phosphate/Pt/C nanocomposites showed the enhanced stabilities during long-term operation of PEMFCs. The well-dispersed FePO
4 nanoparticles prevented both the dissolution and agglomeration of Pt nanoparticles, and thereby preserving the Pt surface activities during long-term cycles. Also, for porous Pt, Pt
xAl
1-x alloyed thin films were examined by repeated electrochemical cycles. Nanoporous Pt thin films were straightforwardly synthesized by complete dissolution of Al. Higher methanol-oxidation activities were also observed in the nanoporous thin films. [1] C. Kim, B. Lee, Y. Park, B. Park, J. Lee, and H. Kim,
Appl. Phys. Lett. 91, 113101 (2007). [2] Y. Park, B. Lee, C. Kim, Y. Oh, S. Nam, and B. Park,
J. Mater. Res. (in press). Corresponding Author: Byungwoo Park:
[email protected]10:45 AM - T9.5
Synthesis of Monodispersed Platinum Nanoparticles Supported on Functionalized Multi-walled Carbon Nanotubes and their Electrochemical Activity.
Wenchao Sheng 1 , Shuo Chen 2 , Ethan Crumlin 2 , Seung Woo Lee 3 , Yang Shao Horn 2 4
1 Department of Chemistry, MIT, Cambridge, Massachusetts, United States, 2 Department of Mechanical Engineering, MIT, Cambridge, Massachusetts, United States, 3 Department of Chemical Engineering , MIT, Cambridge, Massachusetts, United States, 4 Department of Material Science and Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractHybrid nanomaterials such as carbon nanotube supported metal nanoparticles (NPs) have seen wide potential application in heterogeneous catalysis. Ultra fine, surfactant-free and highly monodispersed platinum NPs supported on functionalized multi-walled carbon nanotubes (MWCNTs) were synthesized through 1) immobilization of anionic platinum precursor onto positively charged MWCNTs by electrostatic interaction; and 2) pyrolysis of platinum precursor/MWCNTs composite at elevated temperatures. The loading of platinum species on MWCNTs was found to be related to the pH level of the suspension of anionic platinum precursor and MWCNTs, as well as the concentration of the platinum precursor. Pyrolysis of platinum precursor/MWCNTs composite at high temperature generated platinum nanoparticles smaller than 2 nm with a narrow size distribution. Electrochemical characterization in acidic environment exhibited a two-fold enhancement towards oxygen reduction reaction (ORR) and comparable methanol oxidation reaction activity on Pt NPs/MWCNTs over commercial Pt NPs supported on high surface area carbon. The mechanisms for enhanced ORR activity will be presented. The catalytic stability is under investigation. This method can be potentially extended to produce other metal NP/MWNTs hybrid systems.
11:30 AM - **T9.6
Design and Nano-Engineering of Multimetallic Catalysts for PEM Fuel Cells.
Chuan-Jian Zhong 1 , Jin Luo 1 , Bin Fang 1 , Peter Njoki 1 , Bridgid Wanjala 1 , Rameshwori Loukrakpam 1 , Jun Yin 1 , Derrick Mott 1 , Ting He 2
1 Department of Chemistry , State University of New York at Binghamton, Binghamton, New York, United States, 2 , Honda Research Institute USA, Inc., Columbus, Ohio, United States
Show AbstractProton exchange membrane fuel cells (PEMFCs) are attractive because of the high conversion efficiency, low pollution, lightweight, and high power density. A major area of challenge is the design and engineering of active, robust, and low-cost electrocatalysts. We have been exploring nano-engineered multimetallic nanoparticles as active, robust, and low-cost electrocatalysts to address some of the challenges. This presentation discusses recent findings of our investigations of the design and nano-engineering of platinum- and gold-based multimetallic nanoparticles and catalysts in terms of nanoscale size, shape and composition parameters. Examples of transition metals in our Pt- and Au-based multimetallic nanoparticles include Fe, V, Ni, Cu, Co, W, Pd, Cr, Zr, Ti, Ag, Ir, Rh, etc. The nano-engineering work focuses on developing novel synthetic methods to produce the desired mutlimetallic nanoparticles, probing the synergistic electrocatalytic properties for oxygen reduction reaction, and establishing the correlation among size, shape, phase, and composition of the multimetallic nanostructures. PEMFC performance evaluation and theoretical modeling of the nanostructured catalysts are also part of our overall efforts. Current challenges and opportunities in the development of advanced fuel cell catalysts will also be discussed.
12:00 PM - T9.7
Electrodeposition of Pt-(Ni,Co,Cu,Pb) Alloys and Intermetallics for Fuel Cell Applications.
Thomas Moffat 1 , Liang-Yeuh Ou Yang 1 , Jon Mallett 1 , Sun-Mi Hwang 1 2 , Ugo Bertocci 1 , John Bonevich 1 , Jae Jeong Kim 2
1 , NIST, Gaithersburg, Maryland, United States, 2 , Seoul National University, Seoul Korea (the Republic of)
Show AbstractRecently the ability to electrochemically co-deposit Pt100-xTMx alloys (where TM=Fe, Co, Ni, Cu) at potentials above that required to deposit the pure TM has been demonstrated. The growth process is sustained by the strong bonding enthalpy between Pt and TM that in the first approximation can be envisioned as underpotential TM deposition coupled with on going overpotential deposition of Pt. In order to gain better insight into the co-deposition process a study of underpotential deposition of Co and Ni on Pt single crystal surfaces has been initiated. At the same time the study has been expanded to examine the formation of Pt alloys and intermetallics using alloying elements whose upd behavior is reasonably well known, such as Cu and Pb.All of the above alloy systems are known to have interesting catalytic activity towards either oxygen reduction or organic fuel oxidation reactions. Experiments detailing the relationship between the co-deposition process and the relevant electrocatalytic activity will be described.
12:15 PM - T9.8
Preparation and Property of Platinum-on-Metal Heterogeneous Electrocatalysts.
Zhenmeng Peng 1 , Jianbo Wu 1 , Hong Yang 1
1 Department of Chemical Engineering, University of Rochester, Rochester, New York, United States
Show AbstractHeterogeneous nanostructures that contain discrete domains of platinum and other metals are attractive candidates as advanced fuel cell catalysts. In this talk we present the preparation of various platinum-on-metal (Pt-on-M) bimetallic nanostructures in non-hydrolytic systems. We show fine controls over the heterogeneous nucleation and growth of secondary nanoparticles are possible.[1] Platinum can be deposited on different metal nanoparticles through the reduction of platinum salt precursors at elevated temperatures. Using these Pt-on-M nanoparticles as starting material, platinum nanostructures can be obtained via post-synthesis treatments. The electrochemical properties of both Pt-on-M and their derived nanostructures have been characterized in detail. The Pt-on-Pd electrocatalyst exhibits a high area-specific current density of 307 mA/cm2 metal at 0.9 V, a value almost doubles that for a commercial Pt catalyst (166 mA/cm2 Pt) towards the oxygen reduction reaction (ORR). [2] This catalyst also has an impressive stability, with 12% loss of its electrochemical active surface area (ECSA) and a degradation of 9 mV in the half-wave potential over 30,000 cycles in the accelerated stability test. On the contrary, 39% in ECSA and 35 mV in half-wave potential are observed for a size-comparable pure Pt electrocatalyst.[2] The Pt-Au bimetallic heterogonous electrocatalysts made from the Pt-on-Au nanoparticles are much more active than pure Pt in formic acid oxidation reaction (FAOR) and show large negative shifts in on-set potentials and over eight times of enhancement in its peak current density.[3]References:(1)Peng, Z. M.; Yang, H. Designer platinum nanoparticles:Control of shape, composition in alloy, nanostructure and electrocatalytic property. Nano Today 2009, 4, 143-164.(2)Peng, Z. M.; Yang, H. Synthesis and oxygen reduction electrocatalytic property of Pt-on-Pd bimetallic heteronanostructures. J. Am. Chem. Soc. 2009, 131, 7542-7543.(3)Peng, Z. M.; Yang, H. Structures and electrocatalytic properties of PtAu bimetallic heteronanostructures made from Pt-on-Au nanoparticles. Nano Res. 2009, 2, 406-415.
12:30 PM - T9.9
Platinum Nanoparticles Supported on Tantalum and Niobium Oxyphosphates and Oxides for High Activity Oxygen Reduction Electrocatalysts.
Yannick Garsany 1 , Albert Epshteyn 1 , Andrew Purdy 1 , Karen Swider-Lyons 1
1 Chemistry Division, Naval Research Laboratory, Washington, District of Columbia, United States
Show AbstractLower-cost, more durable oxygen-reduction electrocatalysts are needed for oxygen reduction at the cathodes of proton exchange membrane fuel cells (PEMFCs). We are researching platinum on tantalum oxy-phosphate, niobium oxy-phosphate, tantalum oxide and niobium oxide, all which are impregnated on Vulcan carbon [1]. They key to high activity catalysts is synthetic routes which facilitate high contact between the Pt nanoparticles and oxide or oxy-phosphate support. We use both reverse micelle and solution deposition techniques directly onto the carbon support to make high surface area active nanoparticles. The catalysts are characterized using both rotating disk electrode methodology and in 10 cm2 fuel cells. The mass activity of the platinum-tantalum oxyphosphate/carbon catalyst is 2x that of a 50% Pt/C standard from TKK. The platinum/niobium oxyphosphate/carbon catalysts also show high mass activity. The oxyphosphates appear to be better supports than the oxides. We conclude that the tantalum and niobium-based supports impart metal-support interactions on platinum that improve its activity for oxygen reduction.[1] K. Swider-Lyons, et al., in “Catalysts for Oxygen Electroreduction - Recent Developments and New Directions,” 2009: 169-193 ISBN: 978-81-7895-313-7 Editor: Ting He.
12:45 PM - T9.10
Mechanism for Increased ORR Reactivity with Pt Nanoparticles on Niobium Oxide and Oxyphosphate Supports as Revealed by in situ XAS Analysis.
Anna Korovina 1 2 , Yannick Garsany 1 , Albert Epshteyn 1 , Karen Swider-Lyons 1 , David Ramaker 2 1
1 Chemistry, Naval Research Laboratory, Washington, District of Columbia, United States, 2 Chemistry, George Washington Univ, Washington, District of Columbia, United States
Show AbstractPromotion effects for the oxygen reduction reaction (ORR) and other fuel cell reactions [1,2,3] have been reported recently for Pt/Nb2O5. However, the exact nature of this promotion effect has not been clarified. We have found that the electrochemical activity for 2-3 nm Pt particles is also enhanced when supported on Nb2O5 or niobium oxyphosphate (NbOPO4) with Vulcan carbon (VC), the Vulcan carbon providing good electrical conductivity in an electrochemical cell. We correlate the ORR activity of these materials, either Pt-Nb2O5/VC or Pt-NbOPO4/VC (about 20% Pt, 5% oxide, and 75% VC) to their physical and chemical properties as determined by in situ X-ray absorption spectroscopy (XAS) at the Pt L3 and Nb K edges. The ORR activity of the electrocatalysts follows the order: Pt-NbOPO4/VC > Pt-Nb2O5/VC > the Pt/VC standard. The XAS data, taken in situ with the electrocatalysts as cathode in 1M HClO4, are analyzed utilizing the Δµ XANES adsorbate isolation technique [4]. The Pt L3 Δμ reflects the OH and O adsorbate coverage on Pt with potential, the Nb K edge Δμ reflects the oxidation state of the oxide, and the EXAFS analysis provides the particle morphology and cluster size. The Pt L3 edge Δμ shows the OH adsorption onset is shifted up and the H adsorption onset shifted down in potential compared to Pt/VC indicating that both the Pt-OH and Pt-H bond strength is increased relative to that for Pt/VC. This indicates that the NbX supports are more ionic and exert a ligand effect on the Pt. However the onset for O adsorption on Pt shows a delayed onset, with adsorption on the support occurring concurrently. This strongly suggests O spill-over from the Pt to the support occurs, a common occurrence with oxide supports. The delayed onset for O on the Pt leaves more sites free for the ORR, leading to higher activity. Similar studies on Pt/Ta2O5/VC and Pt/TaOPO4/VC, show these supports to be more covalent (delaying the OH onset potential), with only a very small spillover effect. Since the Pt/TaOPO4 shows the highest reactivity, this suggests that the electronic ligand mechanism and its strong effect on the coverage of OH/Pt is the most critical to determining the ORR reactivity. [1] K. Sasaki et al, Phys. Chem. Chem. Phys., 10, 159 (2008) [2] J.-S. Huang et al, J. Solid State Electrochem. 12,113 (2008) [3] S. Guerrero et al, J. Cat. 262, 102 (2009) [4] M. Teliska; W. E. O'Grady; D. E. Ramaker, J.Phys. Chem. B, 109, 8076, (2005).
T10: ORR Catalysts II
Session Chairs
Wednesday PM, December 02, 2009
Room 301 (Hynes)
2:30 PM - T10.1
Nanostructural Formation of Pd-Co Nanoparticles on HOPG Surfaces and High Surface Area Carbon Support.
Carlos Cabrera 1 , Lisandra Arroyo 1 , Raphael Raptis 1
1 Department of Chemistry, University of Puerto Rico, San Juna, Puerto Rico, United States
Show AbstractA new single source approach was developed to synthesize Pd-Co nanoparticles using a bimetallic compound, [Et3NH]2[CoPd2(μ-4-I-3,5-Me2pz)4Cl4] (CoPd2), as a precursor to obtain dispersed catalyst on highly ordered pyrolytic graphite (HOPG) surfaces and high surface area carbon support, in view of preparing oxygen reduction catalysts for direct methanol fuel cells. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) techniques were employed to characterize the nanostructure formations and to determine the composition and morphology of the complex on the HOPG. Results of high resolution XPS analysis (HR-XPS) revealed the binding energies corresponding to the atomic constituents of the precursor. When the precursor solution was placed on the surface of the HOPG, the bimetallic complex assumes a tubular structure and it appears that the surface of the HOPG offers a ground for the self-organization of nanostructural formations. Nanoaprticles were also formed on high surface area carbon support (e.g. Vulcan) and tested for the oxygen reduction reaction with and without methanol.
2:45 PM - T10.2
A Facile Tuning of Bimetallic AuPd Nanoparticle Core Size onto Thiol Functionalized Carbon Nanotubes: Ectrocatalytic Property.
Junhyung Kim 1 , Seung Woo Lee 2 , Shuo Chen 1 , Yang Shao-Horn 1
1 Department of Mechanical Engineering and Material Science and Engineering, MIT, Cambridge, Massachusetts, United States, 2 Department of Chemical Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractThe deposition of metal nanoparticles onto carbon nanotubes is one of the methods to obtain new hybrid materials with useful properties for materials science, catalysis, sensors, and energy conversion applications. Monometallic Au, Pd nanoparticles and bimetallic AuPd nanoparticles with a few atoms in the cores without ligands were prepared from Au(III), Pd(II) precursor ions on thiol functionalized multiwalled carbon nanotubes (MWNTs) by NaBH4 reduction at room temperature. XPS and XRD techniques evidenced the presence of Au, Pd, and bimetallic AuPd nanoparticles on the supported MWNTs. A stable few tens and hundred atoms of metal nanoparticle core sizes were tuned on the MWNT with high monodispersity, achieved by controlled temperatures from room temperature to 400 °C leading to core sizes in the range from 0.5 to 5.0 nm in diameter as indicated by transmission electron microscopy. The electrocatalytic activity of Au/MWNT and bimetallic AuPd/MWNT towards oxygen reduction was examined in alkaline solution. The synthesis and characterization of Au based bimetallic AuPd nanoparticles on the thiol functionalized multiwalled carbon nanotubes for electrocatalytic oxygen reduction in alkaline media will be presented.
3:00 PM - T10.3
Modification of Gold Catalysis with Aluminum Phosphate for Oxygen-Reduction Reaction.
Yejun Park 1 , Byungjoo Lee 1 , Chunjoong Kim 1 , Jongmin Kim 1 , Seunghoon Nam 1 , Yuhong Oh 1 , Byungwoo Park 1
1 Material Science and Engineering, Seoul National University, Seoul Korea (the Republic of)
Show AbstractGold is an unusual catalyst in terms of its inertness in the bulk state and its catalytic activity with specific nanostructures. The catalytic nature of gold has been found to be tunable through the control of nanoparticle size, the selection of matrix materials, and the nanostructures of metal-matrix composites. There are number of concerns associated with the oxygen-reduction reaction under various conditions including acid or alkaline solutions. To resolve these, catalytic activities of the prepared Au/AlPO
4 nanocomposites were examined for oxygen-reduction reaction in the acidic or alkaline media. In the acidic media, the Au/AlPO
4 nanocomposites presented higher onset potential and the steeper reduction slope than that of the Au catalyst. In the alkaline media, more feasible reaction paths existed within the region of approximately 0.8 – 1.0 V (vs. reversible hydrogen electrode). It is believed that the transfer of electron density between Au and AlPO
4 plays an important role in controlling the Au catalytic activities with the modification of electronic structure. [1] C. Kim, B. Lee, Y. Park, B. Park, J. Lee, and H. Kim,
Appl. Phys. Lett. 91, 113101 (2007). [2] Y. Park, B. Lee, C. Kim, J. Kim, and B. Park,
J. Mater. Res. 24, 140 (2009). Corresponding Author: Byungwoo Park:
[email protected]3:15 PM - T10.4
Metallo-Macrocycle Functionalized Multiwall Carbon Nanotubes for Catalytic Oxygen Reduction.
Robert McGuire 1 2 , Seung-Woo Lee 2 , Daniel Nocera 1 , Yang Shao-Horn 2 3 4
1 Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Electrochemical Energy Lab, Massachusetts Institute of Technology, Cambridge , Massachusetts, United States, 3 Mechanical Engineering, Massachusetts Institute of Technology, Cambridge , Massachusetts, United States, 4 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge , Massachusetts, United States
Show AbstractThe electrochemical reduction of oxygen imparts the largest current density losses in polymer electrolyte membrane fuel cells (PEMFCs). Consequently, lowering the operational overpotential requires the use of high surface area catalysts. Currently carbon supported platinum and platinum alloys are the most stable and efficient catalyst materials in use. However, platinum presents a large economic challenge to commercialization of PEMFCs. Replacement by less expensive and earth abundant materials is critical to the development of cost effective PEMFCs. One promising approach is the combination of macrocyclic cobalt and iron complexes with high surface area carbon supports. It has been well established through molecular models that a cofacial arrangement of electro-active metal centers with a spacing of ~ 4 Å offers an ideal geometry for O-O bond breaking and the direct 4e- reduction of oxygen. In this study, we use multiwall carbon nanotubes (MWCNTs) to support these molecular catalysts, and undertake a study of MWCNTs functionalized with a series of mono- and dimeric molecular catalysts for oxygen reduction. MWCNTs covalently modified with carboxylic acid groups were further functionalized noncovalently with monomeric iron and cobalt phthalocyanine (pc), 5,10,15,20-tetraphenyl porphyrin (tpp), and tetramethyl-dibenzotetraaza[14]annulene (taa) catalysts. These materials allow the effect of different macrocycle properties including cavity size and redox potential to be tuned in conjunction with MWCNTs for the first time. Metallo-macrocycle functionalized MWCNTs were characterized by a range of techniques such as XPS, FTIR, and UV-vis spectroscopy. The electrocatalytic activity and mechanism of the series toward oxygen reduction determined by rotating ring disk electrode measurements will be discussed in the context of the various macrocycle properties.
3:30 PM - T10.5
Study of Carbon Nanofiber as Support Materials for RuSe Based Oxygen Reduction Reaction Catalyst for Polymer Electrolyte Fuel Cells.
Sauradip Malkhandi 1 , Petra Bele 1 , Odysseas Paschos 1 , Siegfried Schreier 1 , Ulrich Stimming 1 2 3
1 Department of Physics E19, Technische Universität München TUM, Garching Germany, 2 NANOTUM, Center for Nanotechnology and Nanomaterials, Technische Universität München, Garching Germany, 3 , ZAE Bayern, Garching Germany
Show AbstractThe advances of various novel carbon based nano-structures open up further possibilities of a new ‘class’ of catalyst support materials aiming at an improved performance for polymer electrolyte fuel cells. This presentation covers the study of carbon nanofiber platelets (CNF-PL) supported RuSe catalyst for oxygen reduction reaction (ORR) for polymer electrolyte methanol fuel cell system. One main obstacle is the proper synthesis of RuSe nano-particle catalysts on CNF-PL support. Further, the influences of the CNF-PL support on the ORR by RuSe catalysts are still partly unknown and therefore, requires more detailed investigations. In this work, for the first time CNF-PL supported RuSe nano-particle catalysts are synthesized. The properties of this synthesized new catalysts are investigated by electrochemical methods and Transmission Electron Microscopy (TEM). In initial measurements, it is found that the synthesized catalysts have 10 ~ 5 nm particle size and the mass specific ORR current is about 10.8 mA/mg at 0.7 V (RHE) on 177 μg/cm2 loading. Electrochemical results indicate that the synthesized CNF-PL supported RuSe catalysts have similar performance to carbon black supported RuSe catalysts.
3:45 PM - T10.6
Electronic Structure Versus Electrocatalytic Activity of Perovskite-class Oxides as Studied by X-ray Absorption Spectroscopy (XAS) and Rotating Disk Electrode.
Jin Suntivich 1 , Naoaki Yabuuchi 1 , Hubert Gasteiger 1 , Yang Shao-horn 1
1 Materials Science and Engineering, and Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractEfficient, inexpensive electrocatalysts for the Oxygen Reduction Reaction (ORR) in hydrogen fuel cells is indispensable for enabling hydrogen-based energy storage. The lack of better ORR electrocatalysts is attributed to the lack of fundamental understanding of the electronic structure parameters that govern the ORR activity. To develop an understanding of the governing electronic structure needed to design a better electrocatalyst, we have synthesized a series of perovskite oxide (ABO3 formula, where A is La, and B is a 3d transition metal) model compounds to study the relationship between electronic structure and the ORR activity. We examined the correlation between the perovskites with different B-site metals (B = Cr, Mn, Fe, Co, Ni) and found that the ORR activity increases with decreasing O K-edge XAS energy position, which we believe reflects the positive effect of decreasing O adsorption strength on ORR activity. Furthermore, we will discuss the effect of partial substitution of B-site metals on ORR activity and catalyst stability.
4:30 PM - T10.7
Combinatorial Investigation of Pb-Ru Pyrochlores for Oxygen Reduction.
Jonathan Petrie 1 , John Gregoire 2 , Michele Tague 2 , Hector Abruna 2 , Frank DiSalvo 2 , R. van Dover 1
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 2 Chemistry and Chemical Biology, Cornell University, Ithaca, New York, United States
Show AbstractWith a relatively high oxygen reduction (ORR) activity in acidic mediums, Pb-Ru pyrochlores present an intriguing alternative to Pt cathodes in PEM fuel cells. This study employed a combinatorial co-sputtering process to explore nanometer-scale thin films exhibiting a spread of Pb:Ru composition ratios. We have developed a high-throughput fluorescence technique that allowed identification of binary regions with high catalytic activity towards oxygen reduction. These regions were tested by voltammetry in a miniaturized electrochemical cell. In addition, data on the effects of adding a third cation to the Pb-Ru pyrochlore phase to further increase the ORR activity will be presented.
4:45 PM - T10.8
Underpotential Deposition of Ni, Co, Cu and Pb on Flame Annealed 1x2 and 1x1 Pt(110).
Liang Yueh Ou Yang 1 , Tomas Moffat 1
1 Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractIn the last decade significant attention has been given to exploring the effect of alloying on electrocatalysis. Pt alloys with Ni, Co, Cu and Pb are known to exhibit enhanced performance towards oxygen reduction as well as organic fuel oxidation reactions, respectively. These alloys and intermetallics may be produced by a variety of means as well as different morphologies. Co-deposition by means of underpotential processes is a particularly easy and inexpensive means to generate such bimetallic materials. However, much remains to be understood about the role of crystalline anisotropy in the deposition and performance of these systems. In this talk, Ni, Co, Cu and Pb underpotential deposition on single crystal Pt surfaces will be discussed. Particular attention will be given to the Pt(110) surface. Careful control of the flame annealing process allows one to generate either the 1x1 and 1x2 surface. Voltammetric and STM experiments of underpotential deposition reactions on these surfaces will be detailed.
5:00 PM - T10.9
Fuel Cell Performance of Platinum-Based Multimetallic Nanoparticle Catalysts in PEMFC.
Bin Fang 1 , Jin Luo 1 , Peter Njoki 1 , Rameshwori Loukrakpam 1 , Derrick Mott 1 , Bridgid Wanjala 1 , Xiang Hu 1 , Chuan-Jian Zhong 1
1 Department of Chemistry , State University of New York at Binghamton, Binghamton, New York, United States
Show AbstractProton exchange membrane fuel cells are becoming increasingly attractive power sources because of the high conversion efficiencies and low pollution. The high cost and poor activity of many existing Pt-based cathode catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFC) has been a long-standing problem. The ability to engineer multimetallic nanoparticles in terms of size and composition represents an important approach to the ultimate development of active, robust and low-cost fuel cell catalysts. This presentation reports our recent findings of the electrocatalytic performance of the nanostructured bimetallic and trimetallic nanoparticle catalysts in PEMFCs. One example involves membrane electrode assembly (MEA) using nano-engineered PtmVnFe100-m-n nanoparticles (~3 nm) supported on carbon as the cathode electrocatalysts. The fuel cell performance and stability data for the PtVFe/C catalysts were compared with those obtained using MEAs prepared with commercial Pt/C catalysts. The results reveal that the PtVFe/C catalysts exhibited much better fuel cell performance and better durability than that using the commercial Pt/C catalyst. The results have demonstrated potential applications of the nano-engineered multimetallic catalysts in PEMFCs.
5:15 PM - T10.10
Metal Nanoparticle/Block Copolymer Self-assembly as a Potential Synthetic Method for Fuel Cell Electrodes.
Zihui Li 1 2 , Hiroaki Sai 2 , Scott Warren 1 2 , Marleen Kamperman 2 , Sol Gruner 3 , Ulrich Wiesner 2
1 Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York, United States, 2 Department of Material Science and Engineering, Cornell University, Ithaca, New York, United States, 3 Department of Physics, Cornell University, Ithaca, New York, United States
Show AbstractNanostructured metal materials are of potential interest for fuel cell electrode applications as they combine the catalytic activities of metals as well as the high specific surface area of nanostructured materials. By utilizing ligand-stabilized platinum nanoparticles (Pt NPs) in the self-assembly with poly (isoprene-block-dimethylaminoethyl methacrylate) (PI-b-PDMAEMA) or poly (syrene-block-dimethylaminoethyl methacrylate) (PS-b-PDMAEMA) block copolymers, organic-inorganic hybrid materials with high metal loadings were synthesized and four different morphologies were generated. Further processing such as disassembly or heat treatment can convert the hybrids into isolated nano-objects or mesoporous Pt materials, respectively. Results of Pt NP ligand head group density estimation based on HAADF-STEM images and thermo gravimetric analysis (TGA) data will be compared to results for alkanethiol self-assembled monolayers (SAMs) on Pt {111} surface.
5:30 PM - T10.11
In situ Real-time X-ray Diffraction Study of Phase Transformations in Au-Pt Nanocatalysts.
Oana Malis 1 , M. Radu 2 , D. Mott 3 , B. Wanjala 3 , J. Luo 3 , Chuan-Jian Zhong 3
1 Physics Dept., Purdue University, West Lafayette, Indiana, United States, 2 Physics Dept., Binghamton University, Binghamton, New York, United States, 3 Chemistry Dept., Binghamton University, Binghamton, New York, United States
Show AbstractPlatinum has long been established as the catalyst of choice in a series of important chemical reactions. In particular the catalytic role of Pt in the oxygen reduction reaction (ORR) is of considerable importance for applications in fuel cells. However, Pt is expensive and in short supply world-wide. Moreover, it has limited catalytic efficiency and is dissolved in the ORR reaction [1]. Therefore, efforts to identify materials with reduced Pt content and improved activity and stability have been stepped up in recent years. Most interestingly, Au clusters have been shown to improve the stability of Pt electrocatalysts without loss of activity [2]. Furthermore, Au nanoparticles have been proven to exhibit unprecedented catalytic activity of their own for CO and methanol oxidation [3], two other reactions of considerable importance for fuel cells. It is therefore believed that Au-Pt nanoparticles could exhibit synergistic catalytic properties that make them ideal for fuel cell applications [4]. In spite of the active research in the field, the exact structure of Au-Pt nanoparticles is not completely understood. The bulk Au-Pt phase diagram exhibits a miscibility gap, and therefore Au-Pt nanoparticles are expected to phase segregate into Pt-rich and Au-rich phases. However, alloyed Au-Pt nanoparticles have been synthesized over almost the entire composition range [4]. The effect of phase segregation on the catalytic properties of nanoparticles is of considerable practical interest, but not completely understood at this time. We have performed a detailed in-situ time-resolved x-ray diffraction study of phase segregation and coarsening of 2-15 nm Au-Pt nanoparticles synthesized from solution on various substrates (Si, silica, carbon-black, and alumina membranes) during annealing at high temperatures. Contrary to the expectations from the bulk phase diagram, silica-supported Au-Pt nanoparticles have an alloyed structure that is preserved even after extensive annealing at temperatures as high at 700 C. In stark contrast, alumina-supported Au-Pt nanoparticles exhibit a rich phase behaviour that is sensitive to alloy composition and the details of the synthesis process. In particular, low-density as-prepared Au41Pt59 nanoparticles exhibit the signature of incipient phase-segregation that develops into full phase separation during annealing at high temperature. We will also discuss the results of an ongoing study of the early stage of catalyst synthesis, i.e. while the nanoparticles are annealed at low temperatures (at or below 300 C).[1]Ferreira P J, la O' G J, Shao-Horn Y, Morgan D, Makharia R, Kocha S and Gasteiger H A 2005 J. Electrochem. Soc. 152 A2256-71.[2]Zhang J, Sasaki K, Sutter E and Adzic R R 2007 Science 315 220-222.[3]Haruta M 2004 J. New Mat. Electrochem. Sys. 7 163-172.[4]Mott D, Luo J, Njoki P N, Lin Y, Wang L and Zhong C-J 2007 Catalysis Today 122 378-385.
5:45 PM - T10.12
Green Synthesis of Platinum-encapsulated Nickel Nanocatalyst and Its Microstructure Evaluation.
Jingbo Liu 1 , Iliana Medina-Ramirez 2 , Sajid Bashir 3
1 Chemistry, Texas A&M University-Kingsville, Kingsville, Texas, United States, 2 Chemsitry, Universidad Autonoma de Aguascalientes, Aguascalientes Mexico, 3 Chemistry, Texas A&M University-Kingsville, Kingsville, Texas, United States
Show AbstractFuel cells are green energy resources in that they can spontaneously convert chemical energy into electricity, releasing heat and water when electrochemical reaction occurs. Proton exchange membrane fuel cells (PEMFCs) are devices, which consist of a solid Nafion polymer as the electrolyte, are drawing significant attention. It is commonly agreed that platinum (Pt) is the most efficient electrocatalyst. However, due to its high cost, it is unfeasible to use a stand-alone Pt catalyst for PEMFC commercialization. To remedy this problem, a platinum-encapsulated nickel (PEN) nanocatalyst was fabricated using the cost-effective green colloidal chemistry to obtain higher catalytic activity. The green colloidal method allows for precise formulations at low temperature with controlled monodispersity and the elemental composition to be tailored at the molecular level. The state-of-the-art instruments have been employed to characterize the crystalline and atomic structure, elemental composition, and stability of the colloids. The morphology and crystallinity was determined using a Tecnai F20-G2 transmission electron microscopy (TEM). In this study, the high resolution TEM equipped with post-collumn Gatan Image Filter was applied. It can be seen that PEN-nanocatalysts were mono-dispersed and highly crystalline. In order to identify the elemental compoistion, X-ray energy dispersive (equiped with the TEM) and X-ray photoelectron spectroscopy were used as complementary techniques to ensure the quality of the quatitative analysis. The elemental composition is determined to be aligned well with the experimental design.The monodispersity and electrophoretic mobility was evaluated using ZetaPALS facility, which is significantly sensitive to the analyts compared with other techniques. The application of low fields to eliminate thermal problems allows for the excellent results. The measured value (-39.44 to -40.27 mV) under various fabrication parameters of the PEN indicates that the colloid is highly stable and agglomeration is successfully prevented using a surfactant. The ultrafine particles provide large specific surface area, which favors the redox reaction on the catalyst to improve the PEMFCs performance. Cyclic voltammetry (CV) experiments were carried out using a Vanostat HA-301 potentiostat equipped with PowerLab Chart V4.0 for data acquisition. Aqueous solutions of 0.1 M NaOH were used as electrolyte and were deaerated by purging with nitrogen gas for 15 min before recording the CVs to remove the oxygen from the solution and prevent masking of the catalyst. The catalyst performance was determined using exchange current density with an average value of 310 mA/cm2. It was noticed that the current density was independent on the sweep rates in the region of 2 mV/min and 100 mV/min, which indicates that the limiting reaction rate was resulting from the electron transfer instead of mass diffusion.