bluuebunny/crossref_metadata_2025 huggingface dataset:
A Proton Conducting Electrolyte Based on Novel Polyparabanic Acid Doped by H3PO4 for Medium Temperature PEMFC.
Authors: Aihara Yuichi , Sonai Atsuo
Published: November 2006

A novel polyparabanic acid, PPAPyMD was synthesized from the intermolecular cyclocondensation of polyurea and characterized to use as a phosphoric acid doped proton conducting membrane. After doping of H3PO4, the ionic conductivity was measured by using the AC impedance method. The temperature dependence of the ionic conductivity showed low activation energy and high ionic conductivity. The ionic conductivity of the membrane was 3.64 mScm-1 at 423K. For the medium temperature fuel cell operation, the cell made of the H3PO4 doped PPAPyMD exhibited typical polarization curves without humidifier. The cyclic voltammetry and the linear sweep voltammetry were performed for investigating the electrochemical reaction at 423K. The test cell was evaluated by 0.1Acm-2 constant current operations until 800 h at 423K without humidifier.
In-situ Synchrotron X-ray Spectroscopy of Ruthenium Nanoparticles Modified with Selenium for Oxygen Reduction Reaction
Authors: You Hoydoo , Inukai Junji , Wieckowski A. , Chang Kee-Chul , Komanicky Vlado
Published: November 2006

In-situ Se K edge X-ray spectroscopy measurements were carried out for selenium modified ruthenium nanoparticles during oxygen reduction. X-ray powder diffraction verified that the samples had pure Ru cores. In-situ XANES showed that there were significant amounts of oxidized Se in the Ru/Se samples that could be reduced by negative potentials. Selenium in the sample was found to oxidize at electrode potentials of 900 mV and higher (vs. RHE). Analysis of extended x-ray absorption fine structure shows an enhancement of the Se-Ru bonds during oxygen reduction reaction.
Oxygen Reduction Reaction and PEM Fuel Cell Performance of a Chalcogenide Platinum Material
Authors: Alonso Gabriel , Gochi Yadira , Barbosa Romeli , Arriaga Luis G. , Alonso Nicolas
Published: November 2006

This work focuses on the development of electrocatalysts through a synthesis procedure with sulphur-platinum in combination with tungsten. We report a novel and simple synthetic method by chemical reaction using a thio-salt and metallic salts at room temperature. This chemical reaction produces a chemical electrocatalytic precursor which is thereafter supported in carbon Vulcan. After a thermal treatment at 400{degree sign}C the electrocatalyst in the nanoscale length is obtained. In addition, commercial 20 wt % Pt/C (Electrochem) was used for comparison. The novel material was characterized electrochemically and by XRD and TEM before and after the thermal treatment. We investigated the effects of methanol toward the oxygen reduction reaction (ORR) on PtxWySz/C in 0.5M H2SO4 + 0.5M CH3OH. We measured a tolerance of 80% in comparison to Pt/C. Fuel Cell measurements using two different assemblies (MEAs) were done by the hot-spray technique, the electrocatalytic inks were prepared and airbrush-deposited onto membrane.
Influence of the Molecular and Mesoscopic Structure on the Electrocatalytic Activity of Pyrolysed CoTMPP in the Oxygen Reduction
Authors: Bogdanoff Peter , Herrmann Iris , Schmithals Gerrit , Fiechter Sebastian
Published: November 2006

Novel oxygen reduction electrocatalysts are obtained by thermolysis of chelates such as cobalt- tetramethoxyphenylporphyrin (CoTMPP) in presence of the foaming agent FeC2O4. EXAFS spectra point to the presence of molecular Fe-N4 and Co N4 centres embedded in a graphite-like matrix. The foaming agent provokes the generation of a porous material (800 m2/g) exhibiting a high fraction of mesopores (5 to 30 nm). Adding elemental sulphur to the precursors CoTMPP and FeC2O4, the catalytic activity in ORR of the final catalyst significantly improves due to an increase of mesopores and the formation of extended graphene layers in a glassy carbon-type material. The added sulphur not only facilitates the removal of inorganic by-products formed in the process of pyrolysis, but also provides an appropriate environment for catalytic centres so that the formation of undesired H2O2 is significantly decreased. In RDE measurements a catalytic activity in ORR equal to commercial platinum catalysts has been achieved.
Co-C-N Oxygen Reduction Catalysts Prepared by Combinatorial Magnetron Sputter Deposition
Authors: Yang Ruizhi , Dahn Jeff R. , Bonakdarpour Arman , Easton E. Bradley
Published: November 2006

Thin film libraries of CoxC1-x-yNy (0 < x < 0.106, 0.003 < y < 0.190) have been prepared by combinatorial magnetron sputter deposition and subsequent heat-treatment at 700, 800 and 1000{degree sign}C in N2. Libraries with 0 < x < 0.105 and 0.026 < y < 0.096 heat-treated at 800{degree sign}C show good catalytic activity towards the oxygen reduction reaction (ORR) in 0.1M HClO4 solution at room temperature. The catalytic activity of the CoxC1-x-yNy libraries is strongly dependent on the heat-treatment temperature. Heat-treated CoxC1-x-yNy libraries show good stability against Co dissolution in 0.5M H2SO4 at room temperature, suggesting that catalysts stable in the PEM fuel cell environment can be found.
Thermally Treated Fe-C-N Oxygen Reduction Catalysts Prepared by Vacuum Deposition
Authors: Easton E. Bradley , Bonakdarpour Arman , Yang Ruizhi , Stevens David , O'Neill David , Vernstrom George , O'Brien Denny , Schmoeckel Alison , Wood Tom , Atanasoski Radoslav , Dahn Jeff R.
Published: November 2006

Vacuum deposition techniques were used to prepare composition spread samples of thin film Fe-C-N catalysts. After deposition, catalyst films were thermally treated to induce structural and composition changes. Catalytic activity was found to be at its largest when the films were annealed at ca. 800{degree sign}C. At this temperature, partial graphitization of the film occurred but it still contained a significant amount of nitrogen, which is required to have an active site. Above 800{degree sign}C, a significant quantity of Fe3C, which is inactive and not stable in acid, was formed. Single composition thin films were also prepared, thermally treated, and tested in a 50-cm2 fuel cell. After thermal treatment of the catalyst, the fuel cell performance was significantly improved.
PEFC Electrodes Based on Vertically Oriented Carbon Nanotubes
Authors: Hatanaka Tatsuya , Nakanishi Haruyuki , Matsumoto Shin-Ichi , Morimoto Yu
Published: November 2006

Well-aligned multi-wall carbon nano tubes (CNTs) grown on a silicon substrate were applied to a catalyst support of PEFC electrodes and single cells using the electrode were assembled. Their cell voltages at high current densities were remarkably higher than that using a conventional carbon black. The protonic and electronic conductivities of the electrode were also higher. These advantages were likely to be derived from their continuous and direct path structure formed by the vertically oriented CNTs.
Characterization of Carbon Nanofiber-Based Fuel Cell Electrodes
Authors: Hacker Viktor , Baumgartner Wolfgang R. R. , Wallnöfer Eva , Schaffer Thomas , Besenhard Jürgen
Published: November 2006

Fuel cell electrodes with silver and platinum as catalyst material supported on carbon nanofibers (CNFs) were investigated with an alkaline electrolyte. The advantageous chemical properties, the large surface area and the high electric conductivity of the nanostructured material make them an interesting candidate for an application in fuel cell electrodes. The electrodes prepared by a sedimentation process consist of CNFs in the active layer as well as in the gas diffusion layer. PTFE was used as binder material and hydrophobic agent to prevent the electrode from being flooded by the electrolyte. The electrodes were electrochemically investigated by measuring polarization curves and impedance spectroscopy in half cell tests to show the performance for the cathode with Pt and Ag supported CNF. Furthermore, the electrodes were investigated with SEM to correlate the electrochemical behavior to the structure of the active layer and the gas diffusion layer.
Hexaboride Ceramics as PEMFC Electrode Catalysts Supports
Authors: Brosha Eric L. , Wilson Mahlon , Garzon Fernando , Johnston Christina , Uribe Francisco A.
Published: November 2006

Metal hexaborides demonstrate the unusual ability to spontaneously deposit noble metals from solution without the need for separate reducing agents or pretreatments. A range of deposition thicknesses are possible and uniform and strongly adherent 30 nm thick metal films on lanthanum hexaboride sputter- coated glass are easily and quickly achieved. Full and uniform coverages of hexaboride powders are obtained even with deposits only ca. 1 nm thick. Cyclic voltammetry for 4 wt% Pt on a roughly 1 m2/g EuB6 powder show electrochemically active Pt surface area, derived from the area under the hydrogen absorption curve, to be 39 m2/g Pt and is exceptional considering the low hexaboride support surface area. This result suggests that the entire support area is covered with Pt (approximately 1 nm thick) and that the entire Pt surface is electrochemically active.
Preparation of Nano-Structured Catalyst Layers on Nafion® Membrane by Electrophoretic Deposition
Authors: Munakata Hirokazu , Ishida Tomohiko , Kanamura K.
Published: November 2006

A membrane electrode assembly (MEA) was successfully prepared by electrophoretic deposition (EPD) process onto Nafion® 117 membrane. An ethanol suspension containing carbon powder with Pt catalyst and Nafion® ionomer was utilized to the EPD process. The catalyst layers fabricated by the EPD process were well-attached to both sides of the membrane and those thicknesses were easily controlled in a sub-micrometer scale by the EPD duration and applied electric field intensity. The obtained catalyst layer had uniform and porous structure compared to that prepared by a decal transfer process. This structure was favorable for fuel gas diffusion, resulting in improvement of Pt utilization up to 76%. Accordingly, the MEA prepared by the EPD process exhibited higher cell performance with half amount of Pt loading compared to the ordinary one.
Improvement of PEM Fuel Cell Performance Using Low Equivalent Weight PFSA Ionomers
Authors: Xu Hui , Kunz Harold R. , Fenton James M. , Bonville Lenonard J.
Published: November 2006

The effects of lower equivalent weight (EW) PFSA ionomers on the cathode performance of PEM fuel cells were investigated at two atmospheric pressure operating conditions: low temperature/high relative humidity (RH), 80 oC/100% RH, and high temperature/low RH, 120 oC/35% RH. The optimized content in the electrode changed with the ionomer EW, from 32% for 1100EW Nafion®, 28% for 920 EW Nafion® to 25% for a developmental PFSA 800 EW ionomer. Compared to 1100 EW Nafion®, 800 EW ionomer significantly improved the cell performance by 39 mV at 120 oC/35% RH; however, at 80 oC/100% RH, its effect was not apparent.
Nafion Quantity Variation on Electrodes used in SPE Electrolyzer
Authors: Morales Lizbeth , Arriaga Luis G. , Cano Ulises , Acosta Roberto
Published: November 2006

The production of hydrogen using renewable sources by for example electrolysis and photoelectrolysis, avoids the emission of pollutants to the environment, especially if the electrical power for the electrolyzer is supplied by renewable energy. At the moment two types of commercial hydrogen generators exist by means of an electrolysis process: the alkaline electrolyzer (EA) and the solid polymer electrolyte electrolyzer, called SPE. SPE electrolyzer technology has brought the possibility of having a cleaner hydrogen generator. Essential part of an SPE electrolyzer, is the membrane- electrode assembly (MEA), where hydrogen generation (cathode electrode) and oxygen evolution (anode electrode) reactions take place. In the present work IrO2 and Pt/Vu were used as anode and cathode respectively for an ESP electrolyzer. Electrochemical measurements were realized using 5 different MEÁs, prepared by a hot-spray technique, where electrocatalytic inks were prepared and airbrushdeposited onto the membrane at 20 cm. After several deposited layers the obtained dried catalytic surfaces were rather homogeneous. After deposition, a thermomechanical process was used. All assemblies were prepared using Nafion® 117 and loads of 2 mg-cm-2 of IrO2 (Electrochem)as anode and 1 mg-cm-2 of 20% Pt/Vu (Electrochem) as cathode, nafion solution, ethylic alcohol to the catalyzer and then ultrasound stirred. The Nafion solution quantity was varied for the cathode and anode. Data were collected obtaining the polarization, power density and EIS (Electrochemical Impedance Spectroscopy)curves at 25{degree sign}C using a hardware manufactured in the laboratory, containing titanium mesh as current collector
Distribution of Nafion Ionomer in PEFC Electrodes with High Catalyst Utilization
Authors: Uchida Hiroyuki , Song Jung Min , Watanabe Masahiro
Published: November 2006

To clarify the superiority of newly developed electrocatalyst layer (ECL) for PEFCs, the microstructure of the new ECL was analyzed by using mercury porosimetry and TEM observations. It was clearly observed by 2D and 3D-TEM that Nafion ionomer was distributed more uniformly inside Pt/CB agglomerates, compared with those simply mixed with ball-mil in a conventional manner.
Analysis of Gas Diffusion Layer and Flow Field Design using Neutron Radiography
Authors: Yoshizawa Koudai , Ikezoe Keigo , Tasaki Yutaka , Kramer Denis , Lehmann Eberhard , Scherer Günther G.
Published: November 2006

A carbon cloth gas diffusion layer (GDL) displays better performance than a carbon paper GDL under humidified conditions. A straight flow field displays better performance than a serpentine flow field. To investigate these phenomena, neutron radiography was used to compare the amount of liquid water that accumulated in test fuel cells. It was found that a larger amount of water accumulated in a carbon cloth GDL than in a carbon paper GDL. From the standpoint of cell performance, the carbon cloth GDL was less influenced by the accumulated water than the carbon paper GDL. It is assumed that the broader pore distribution of a carbon cloth GDL creates oxygen diffusion paths even if water accumulates in the GDL. With a serpentine flow field, water accumulated in the corner and the gas bypassed the flow field. These phenomena are the main causes of performance deterioration with a serpentine flow field.
Two-phase Transport Properties and Transport Simulation of the Gas Diffusion Layer of a PEFC
Authors: Koido Tetsuya , Furusawa Toru , Moriyama Koji , Takato Keiichiro
Published: November 2006

A series of analysis methods is proposed to simulate the liquid gas two-phase and multi-component transport phenomena in the gas diffusion layer (GDL) of a polymer electrolyte fuel cell (PEFC). These methods involve measuring and predicting the two- phase flow properties of a GDL, the capillary pressure and relative permeability, and simulating the two-phase multi- component transport in the GDL. The methods are described and applied to a carbon-fiber paper GDL. The predicted capillary pressure and relative permeability correctly captured the shape of the curve of the measured results and showed the similar magnitude to those. Transport simulation is carried out with the properties to identify in detail the two-phase multi- component transport. Since the fibrous structure and wettability of the GDL are considered, advanced analysis can be conducted with the methods.
Diffusion Media and Interfacial Effects on Fluid Storage and Transport in Fuel Cell Porous Media and Flow Channels
Authors: Mench Matthew , Turhan Ahmet , Kowal J. J. , Heller Kevin , Brenizer Jack
Published: November 2006

The residual water content stored in fuel cell media under steady or time-varying operation is of great interest, because it can play a critical role in the operating performance, pressure loss, degradation via ionic contaminants or mechanical damage, and time to start and degradation from a frozen condition. Liquid water storage and distribution in the diffusion media of polymer electrolyte fuel cells (PEFCs) is not solely a function of the diffusion media properties, however, and although the diffusion media plays a strong role in water removal, the interface between the land and diffusion media also has an important influence on the water storage and removal rate under steady and transient operation. In this study, our current understanding of the relationship between the diffusion media, channel geometry, land area, and interfacial forces on the water storage in the fuel cell will be discussed, based on extensive imaging and analysis compiled at the FCDDL.
Fabrication and Properties of High Temperature Proton Conducting Perovskites
Authors: Martinez Julian , López-Robledo Manuel-Jesús , Ramírez-de-Arellano-López Antonio , Real-Pérez Concepción , Peña-Torre José-Ignacio , Sayir Ali
Published: November 2006

High temperature protonic conductors (HTPC) were fabricated by solid-state sintering and by melt processing by laser-heated floating zone method. Several families of compositions were selected: SrCe1-xMxO3-δ (with M: Zr and Y; x = 0.1, 0.2), BaCe1-xMxO3-δ (with Yb, Ca and Y; x = 0.05, 0.2), Sr3Ca1.18Nb1.82O9-δ, SrZr0.8Y0.2O3-δ and SrTi0.95Sc0.05O3-δ. Their mechanical properties have been studied by compression test at constant load and constant compression rate. As produced directionally solidified materials presented a unique microstructure consisting of strongly textured cells with an intercellular phase. The cells have a crystalline Pnma structure. The relation between the processing, dopants, microstructure and mechanical properties is discussed. Understanding of plasticity is important to determine the ultimate component performance, and because its direct relationship to processing and transport. The high temperature mechanical properties of melt grown crystals are superior to the mechanical properties of polycrystals.
Impact of Gas Partial Pressure on PEMFC Chemical Degradation
Authors: Liu Han , Zhang Jingxin , Coms Frank , Gu Wenbin , Litteer Brian , Gasteiger H. A.
Published: November 2006

Impact of reactant gas partial pressure on membrane chemical degradation is presented in this paper. The relationship between degradation rate and pH2 / pO2 is elucidated using fluoride release rate (FRR) as the assessment criterion. The effect of pH2 / pO2 on the location of the Pt redeposition band is clarified. Experimental results and model predictions are compared. The mechanism of FRR dependency on relative humidity (i.e., relative water partial pressure) is also examined by H2O2 flow cell study.
Membrane Degradation Mechanisms in PEMFCs
Authors: Mittal Vishal , Kunz Harold R. , Fenton James M.
Published: November 2006

Based on experimental findings it is suggested that formation of active oxygen species from H2O2 decomposition or the direct formation of active oxygen species in the oxygen reduction reaction are not the dominating membrane degradation mechanisms in PEMFCs, instead it is the molecular H2 and O2 that react on the surface of the Pt catalyst to form the membrane degrading species. The source of H2 or O2 is from reactant crossover through the membrane. The reaction mechanism is chemical in nature and depends upon the catalyst surface properties and the relative concentrations of H2 and O2 at the catalyst. The membrane degradation rate also depends on the residence time of the species in the membrane and the volume of the membrane. The sulfonic acid groups in the Nafion® side chain are key to the mechanism by which the radical species attack the polymer.
Effective Testing Matrix for Studying Membrane Durability in PEM Fuel Cells: Part 2. Mechanical Durability and Combined Mechanical and Chemical Durability
Authors: Crum Matt , Liu Wen
Published: November 2006

Accelerated testing that targets specific mechanisms of chemical and mechanical durability, and tests that target both failure mechanisms at the same time can be an effective tools to advance membrane technologies for PEM fuel cells. Such tests should be accelerated to reduce development times, with conditions relevant to the given application. In studies of membrane mechanical durability, uniform membrane degradation was obtained by using careful test design. When conducting a combined mechanism accelerated test, the relative balance of the two mechanisms should be considered. Too much mechanical stress in the test can overwhelm improvements in the chemical durability of the materials and vise versa. Customer screening and more realistic testing conditions are used to verify accelerated test conclusions. Test results indicate that combinations of these test protocols enable the dependable selection of more mechanically and chemically durable membranes and also provide quantitative data to assist understanding of degradation mechanisms in fuel cells under various operation conditions.
Aging Tests of Radiation Grafted Fuel Cell Membranes
Authors: Gubler Lorenz , Slaski Michal , Wokaun Alexander , Scherer Günther G.
Published: November 2006

Radiation grafted membranes developed at PSI have shown lifetimes in the single cell of several thousand hours. With the objective of establishing accelerated testing, we have taken first steps at identifying suitable conditions to study the chemical stability of membrane materials. On the other hand, recent work using alpha-methylstyrene instead of styrene as grafting monomer indicate that membranes with higher durability can be obtained using advanced monomer combinations.
Dissolution of Platinum in Acidic Media
Authors: Ota Kenichiro , Koizumi Yuuki , Mitsushima Shigenori , Kamiya Nobuyuki
Published: November 2006

Platinum dissolves chemically after the formation of oxide in oxygen atmosphere, such as the cathode of polymer electrolyte fuel cells(PEFCs). Considering the platinum depositions in the membrane electrolyte of PEFCs, the solubility of platinum (oxide) in the electrolyte might be one of key issues, in order to improve the durability of PEFCs. In this study, platinum solubility has been determined in acidic medium as a function of temperature, pH, and potential which was controlled with oxygen partial pressure. The solubility was 2.9x10-6mol dm-3 at 23oC in 1mol dm-3 H2SO4 under air, and increased with temperature and with the decrease of pH. The platinum solubility significantly increased with the presence of oxygen. From these results, the dissolution of a platinum oxide in acidic medium would follow an acidic dissolution mechanism.
Deterioration of Pt Catalyst Under Potential Cycling
Authors: Kawahara Shuya , Mitsushima Shigenori , Ota Kenichiro , Kamiya Nobuyuki
Published: November 2006

Using the rotating ring-disk electrode, Pt consumption has been investigated to clarify the dissolution mechanisms under potential cycling which was the symmetric and asymmetric potential wave. The charge of Pt oxidation was always larger than that of reduction. The difference of the oxidation and reduction charges should be caused by Pt dissolution. Pt dissolved during the oxide formation at anodic sweep for Symmetric rectangular wave , Symmetric triangular wave and Slow anodic triangular wave . The charge transfer number of the anodic dissolution reaction was ca. 4, based on the relationship between the difference of anodic/cathodic charges and the consumption. Therefore, the dissolution reaction would be Pt → Pt4+ + 4e- or chemical dissolution of PtO2 that was electrochemically 4-electron oxidized. For Slow cathodic triangular wave , Pt dissolution during cathodic sweep was also observed. The charge transfer number of the cathodic dissolution reaction was ca. 2. This reaction would be PtO2 + 4H+ + 2e- → Pt2+ + 2H2O.
Study of Accelerated Test Protocol for PEFC Focusing on Carbon Corrosion
Authors: Chizawa Hiroshi , Ogami Yasuji , Naka Hiroshi , Matsunaga Atsushi , Aoki Nobuo , Aoki Tsutomu
Published: November 2006

Carbon corrosion caused by rapid potential changes is presented. Test results with full-scale single cells suggest rapid voltage changes during start-up and shutdown can accelerate carbon corrosion significantly, without local or global fuel starvation. Impacts of carbon corrosion on material degradation and cell performance decay with various operation modes (e.g. voltage cycles, OCP hold and constant load) are also evaluated. The results indicate voltage cycles by start-up and shutdown, which advances carbon corrosion on cathode, accelerates cell performance decay with electrochemical surface area reduction and mass transport loss on cathode. The voltage cycle testing focusing on carbon corrosion is expected to be one of the promising test protocols for accelerated durability testing.
Degradation of Carbon Supported Pt Anode and Cathode Catalysts in PEM Fuel Cells
Authors: Okada Tatsuhiro , Sugiura Mikio , Xie Gang
Published: November 2006

Various types of carbon supported platinum catalysts for the anode and the cathode of polymer electrolyte fuel cells are tested with the electrochemical rotating ring disk electrode and the short stack fuel cell configurations. Good correlations were found between the Pt specific surface area and the evolution of H2O2 at the anode potential conditions when O2 existed on the Pt surface. For the cathode potential condition, CO2 emerging from the Pt/C cathode catalyst layer as a result of the carbon corrosion increased with the increase in the specific surface area of the carbon substrate. Graphitized carbon substrate made the cathode catalyst layer most durable during repeated cycle tests between OCV and 0.7 V vs. RHE potential scanning.
Durability Investigation of Cup-Stacked Carbon Nanotubes Supported Pt as PEMFC Catalyst
Authors: Waje Mahesh M. , Li Wenzhen , Chen Zhongwei , Yan Yushan
Published: November 2006

The durability of Pt supported on cup stacked carbon nanotubes (CSCNTs) was investigated with an accelerated test using cyclic voltammetry as a tool. The loss in electrochemically active surface area is compared with that of an E-TEK Pt/Vulcan XC-72 carbon catalyst. The relatively lesser surface area loss in case of Pt/CSCNT catalyst is attributed to better corrosion resistance of CSCNTs. A preliminary data on the durability of cup stacked carbon nanotubes based membrane electrode assembly is presented.
The Impact of Hydrogen Fuel Contaminates on Long-Term PMFC Performance
Authors: Garzon Fernando , Uribe Francisco A. , Rockward Tommy , Urdampilleta Idoia G. , Brosha Eric L.
Published: November 2006

We have studied the effects of H2S and fuel impurity mixtures on hydrogen polymer fuel cell performance. The tests included a range of H2S concentrations, exposure times, and multiple impurity mixtures at various operating conditions such as cell voltage and times of exposure. Analytical methods included fuel cell polarization experiments, cyclic voltammetry, and effluent water and gas analysis using specific ion sensor probes. H2S concentrations as low as 10 ppb, produced negative effects on fuel cell performance. The extent of sulfur poisoning of the anodes was also shown to be a strong function of fuel cell operating voltage during H2S exposure.
Identifying Contributing Degradation Phenomena in PEM Fuel Cell Membrane Electride Assemblies Via Electron Microscopy
Authors: More Karren , Borup Rod , Reeves Kimberly
Published: November 2006

Advanced electron microscopy and ultramicrotomy specimen preparation techniques have been used to characterize the microstructural changes within PEM fuel cell membrane electrode assemblies (MEAs) that contribute to performance loss. Atomic- level structural and compositional analyses have been conducted on intact 3-layer MEAs before and after life-testing to identify the microstructural degradation of individual constituents comprising the MEA, i.e., carbon support, electrocatalyst, polymer membrane, and recast ionomer. Analyses conducted in this way are required to correlate observed microstructural changes with durability and fuel cell performance.
Characterization of Catalyst Layer Structural Changes in PEMFC as a Function of Durability Testing
Authors: Li Jing , He Ping , Wang Keping , Davis Mike , Ye Siyu
Published: November 2006

Structural (morphology) changes of the catalyst layer in a proton exchange membrane fuel cell (PEMFC) during durability tests were characterized using transmission electron microscope (TEM) and scanning electron microscope (SEM). Observations were that platinum was redistributed in the catalyst layer and membrane depending on the fuel cell operating conditions. Pt particle agglomeration, dissolution and migration into the membrane resulted in a reduction in Pt surface area. A Pt depletion layer was also observed in the catalyst layer using an accelerated aging test. Following carbon corrosion, a well known failure mechanism, the original porous structure in the catalyst layer collapsed, resulting in high mass transport loss. It has been found that cathode corrosion is more severe underneath the plate landing, and especially on the anode landing area where local fuel starvation may occur.
PEMFC Component Characterization and Its Relationship to Mass-Transport Overpotentials during Long-Term Testing
Authors: Wood David , Davey John , Atanassov Plamen , Borup Rod
Published: November 2006

Individual overpotential contributions to PEM Fuel Cell performance are examined to determine how these change during long operating times. The cathode mass-transport overpotential and its relationship to O2 diffusion mechanisms and liquid- water transport is examined in detail. A method, governing equation, and durability case study is presented here for estimating both overpotential contributions as a function of testing time, as well as the breakdown of mass-transport overpotential for the cathode Gas Diffusion Layer (GDL) and catalyst layer. The importance of correlating component characterization with this durability data is also shown using high-resolution scanning electron microscopy (HRSEM) and pore- size distribution (PSD) measurements obtained with Hg and H2O porosimetry.
Evaluation of High Temperature Degradation of Pt/C Catalysts in PEM Fuel Cells
Authors: Arico Antonino S. , Stassi Alessandro , Modica Ester , Ornelas Ruben , Gatto Irene , Passalacqua Enza , Antonucci Vincenzo
Published: November 2006

An investigation of carbon supported Pt/C catalysts was carried out with the aim to evaluate their stability under high temperature PEM operation. Nanosized platinum particles supported on carbon were prepared by using a low temperature colloidal route allowing to achieve a mean particle size between 1.5 and 2.3 nm. A pre-evaluation of the various catalysts was carried out in a gas-fed sulfuric acid electrolyte half cell. The catalysts that showed the most proper compromise in terms of activity and stability under accelerated corrosion conditions were selected for further analysis under PEM configuration at 130 {degree sign}C. Electrochemical active surface area and catalyst performance were measured at 80 {degree sign}C before and after operation at 130 {degree sign}C. The variation of electrochemical active surface area after high temperature operation was analysed.
Degradation Rates of PEM Fuel Cells Running at Open Circuit Voltage
Authors: Aarhaug Thor A. , Svensson Ann Mari
Published: November 2006

Degradation experiments of PEM fuel cells running at open circuit voltage have been performed. Two levels of gas flow rates were applied. No other condition expected to give source to accelerated degradation was chosen. The change of gas flow rates was compared to drop in open circuit voltage and loss of peak effect, i.e. maximum effect obtained from the polarization curve. Further, these losses were compared to the fluoride release rates measured throughout the experiment. The results indicate that fluoride release rates contain contributions from both drop in open circuit voltage as well as loss of peak effect performance.
Systems Strategies to Mitigate Carbon Corrosion in Fuel Cells
Authors: Perry Mike L. , Patterson Timothy , Reiser Carl
Published: November 2006

The oxidation of carbon used as catalyst support in state-of- the art fuel cells is a serious decay mechanism that must be mitigated in order to achieve acceptable performance stability. Although the corrosion of carbon is certainly not a new concern for fuel-cell developers, a number of fairly recent developments have brought this issue to the forefront. These concerns include the unique operating conditions of transportation applications, the discovery of a mechanism that results in higher-than-expected potentials (i.e., the reverse- current mechanism), and the use of certain materials (e.g., high surface area carbon supported catalysts with high Pt mass fractions). Since improvements in catalyst-support stability typically comes at the expense of performance (and/or cost), and these improvements alone will be insufficient for many applications, system-mitigation strategies are required. A number of system strategies that have been developed and demonstrated at UTC Power will be described.
Electrocatalytic Corrosion of Carbon Support in PEMFC at Fuel Starvation
Authors: Baumgartner Wolfgang R. R. , Baumgartner Wolfgang R. R. , Wallnöfer Eva , Schaffer Thomas , Hacker Viktor , Peinecke Volker , Prenninger Peter
Published: November 2006

PEMFC degradation effects under critical operating conditions like low fuel stoichiometry or cell reversal can be detected at both electrodes. The cell was characterized with electrochemical impedance spectroscopy to show changes of the conductivities and cyclic voltammetry to measure the reduction of the active platinum surface areas. The analyzing of the electrode corrosion at fuel starvation with online gas analysis shows small amounts of carbon dioxide at both gas outlets and carbon monoxide at the anode side. To analyze the carbon corrosion effects at the cathode side, potential effects were investigated and current distribution measurements were realized.
Effect of Anode Catalyst Support on MEA Degradation Caused by Hydrogen-Starved Operation of a PEFC
Authors: Takagi Yasuo , Sato Yuichi , Wang Zhen
Published: November 2006

The effect of different anode catalysts on mitigating the performance degradation caused by hydrogen-starved operation of a polymer electrolyte fuel cell was made clear. The tested catalysts included ones fabricated on highly anti-corrosive supports such as graphitized carbon and carbon-free catalysts like platinum black, which were used in place of conventional carbon black-supported platinum catalysts. The diagnostic techniques used in this study such as AC impedance spectroscopy, cyclic voltammetry and gas chromatography measurement revealed that performance degradation induced by carbon corrosion mainly occurred only at the anode catalyst.
Stop-Start and High-Current Durability Testing of Nanostructured Thin Film Catalysts for PEM Fuel Cells
Authors: Debe Mark K. , Steinbach Andrew J. , Noda Kazuki
Published: November 2006

This paper reports two new PEM fuel cell catalyst durability test results using 3M's nanostructured thin film (NSTF) catalysts, which do not use carbon-supports or additional ionomer in the electrode layer. One test uses an automotive start/stop (S/S) testing protocol provided through communication with Nissan, and compares the NSTF catalyst durability with that of a conventional carbon supported dispersed Pt catalyst. Fuel cell performance, cyclic voltammograms, surface area changes, specific activity and XRD crystallite sizes were measured before and after S/S testing. The NSTF catalyst show much less loss of performance under the S/S cycling and most of the loss is recoverable. The second test involves high current density operation under totally dry H2/O2 conditions. Operating with an average current density of 1 A/cm2, with over 1600 scans between 0.1 and 2 A/cm2, the NSTF MEA lasted 1000 hours, consistent with extremely low measured fluoride ion emission rates.
Durability and Reliability in High-Temperature Reformed Hydrogen PEFCs
Authors: Schmidt Thomas J. , Baurmeister Jochen
Published: November 2006

This work summarizes the effect of carbon monoxide and hydrogen sulfide on the cell potential of a high temperature Celtec® P1000 MEA. We could demonstrate a H2S tolerance of at least 10 ppm, a value significantly higher than state-of-the-art fuel processor and shift catalysts can tolerate. More than 3000 hours operation in reformate with 5ppm H2S and 2% CO is proven. Under certain conditions poisoning from both CO and H2S are just additive, which represent valuable conditions for sustained and stable cell voltage. On the other hand, in a region where effects from H2S and CO contaminants are not additive, the anode typically becomes rapidly poisoned
Computational Model of Physical Damage during Freeze/Thaw of PEFCs
Authors: Mench Matthew , He Suhao
Published: November 2006

The modes of degradation that can occur during freeze/thaw of a PEFC have become a recent topic of interest. Direct evidence of physical damage to fuel cell components have been observed by some groups, but is not yet fully understood. A computational model based on a frost heave mechanism has been developed to simulate the physical damage process and help achieve design solutions. In a previous study by the authors, two modes of physical damage have been proposed: 1) diffusion media punch through caused by ice lens formation under the channel at the interface of diffusion media and catalyst layer; 2) catalyst delamination caused by sub-zero unfrozen water diffusion from the electrolyte to the interface of catalyst layer and electrolyte, where it is rapidly frozen. The results of an ongoing computational parametric study are detailed in this paper. Controlling parameters in the physical damage process have been determined to be 1) drainage rate of diffusion media and catalyst layer, 2) drainage rate of the electrolyte, 3) heat transfer rate within the MEA, and 4) the irreducible water content of PEFC components.
Dynamics of PFSA Polymer Hydration Measured in Situ by SAXS
Authors: Herring Andrew M. , Yandrasits Michael A. , Aieta Niccolo V. , Stanis Ronald J. , Hamrock Steven J. , Cookson David J.
Published: November 2006

Proton exchange membranes were cast from three perfluorosulfonic acid (PFSA) ionomers, Nafion®, the 3M PFSA polymer, and the Dow membrane, with side chains -O-(CF2CF(CF3)- O-(CF2)2SO3H, -O-(CF2)4-SO3H, and -O-(CF2)2-SO3H respectively. The materials were heated above the Tg and the reorganization of the polymer morphology was studied in situ on the nanoscale by SAXS using synchrotron radiation. It was shown that both the 3M and the Dow membranes are much more crystalline and featured than the Nafion® membrane. The membranes were then hydrated at 80, 100, and 120ºC, with a humidified gas stream (80ºC dew point), and the kinetics of the morphological changes studied. In general the SAXS features increased in intensity as the ionomer peak grew in and swelled. Various heteropoly acid additives were also added to the membrane which was found to suppress the ionomer peak.
Parameter Changes During Gradual Flooding of a PEM Fuel Cell through EIS Studies
Authors: Cano-Castillo Ulises , Ortiz Alondra , Manzo Samuel , Arriaga Luis G. , Orozco Germán
Published: November 2006

The gradual flooding of a single PEM fuel cell was produced and Electrochemical Impedance Spectroscoy (EIS) measurements were realized in order to follow changes of the fuel cell impedance parameters. These changes were followed by using two equivalent circuit models: one simple model of the Randles type accounting for cathode and anode interfaces and a more complex model based on distributed elements, more suitable for porous electrodes in order to include protonic resistance of the catalyst layers
Design and Characterization of an On-line Electrochemical Mass Spectrometry System for Measurement of Multi-Step Reaction Kinetics
Authors: Roen Laura M. , Stuve E. M.
Published: November 2006

A micoreactor system for variable temperature measurements of electrochemical reaction kinetics is described. The reactor was made from a silicon wafer, in which fluid channels were etched, mated to a glass wafer that contained vapor-deposited Pt and Pd electrodes. A Teflon membrane, placed over an opening in the silicon wafer allowed volatile reaction products to diffuse into an attached vacuum system for detection by mass spectrometry. System response was characterized with computational fluid dynamics and conductance measurements in the vacuum system. Performance of the reactor is demonstrated by measurements of electrooxidation of methanol on a thin-film Pt electrode at 0.6 V vs. Pd/H and room temperature followed by post-reaction stripping of adsorbed CO remaining from the methanol reaction. The results show that the reactor is capable quantitative measurement of CO2 produced during methanol reaction and CO oxidation and illustrate the steps needed to improve system response.
The Use of Limiting Current to Determine Transport Resistance in PEM Fuel Cells
Authors: Baker Daniel R. , Wieser Christian , Neyerlin Kenneth C. , Murphy Michael W.
Published: November 2006

Limiting current measurements are used to derive estimates of oxygen transport resistance through the cathode diffusion medium/micro-porous layer (DM/MPL) of a fuel cell. For the case of unteflonated Toray 060 (without an MPL), the estimates are compared to ex situ measurements of the effective diffusion coefficient for water vapor. For dry operating conditions at low currents, the comparison shows that the large majority of transport resistance detected by limiting current occurs in the Toray 060 and not through ionomer or water layers in the electrode. Effective diffusion coefficients at wetter conditions, derived from limiting currents, show a clear dependence on current density and thus on water production. An example of this behavior is given for SGL 25 BC (a DM with MPL).
Oscillations in the Gas Channels - The Forgotten Player in Impedance Spectroscopy in Polymer Electrolyte Fuel Cells A. Exploring the Wave
Authors: Schneider Ingo A. , Kramer Denis , Wokaun Alexander , Scherer Günther G.
Published: November 2006

Our experimental results shown here disprove that finite diffusion can generally be assumed in impedance models for H2/air-PEFCs to account for the diffusive transport of oxygen through the gas diffusion layer (GDL) towards the air electrode. It is shown that the amplitude of the oxygen concentration oscillation created as a consequence of superimposed ac current at the air electrode, is not zero at the channel/GDL interface, but extends into the gas channels, at least below modulation frequencies of fmod=10Hz. By this, sinusoidal oxygen concentration oscillations within the cathode gas channels are excited locally along the flow field. Due to the forced air convection in the flow field channels a coupling via the gas phase occurs downstream the flow field. The coupling strongly affects the local and by this the overall impedance response of the cell and evokes the formation of a low frequency arc in H2/air-PEFC impedance spectra.
Elucidation of PEMFC Electrocatalyst-Layer Surface and Interfacial Phenomena via Neutron Reflectivity
Authors: Wood David , Chlistunoff Jerzy , Watkins Erik , Atanassov Plamen , Borup Rod
Published: November 2006

Neutron reflectivity (NR) is being used to measure simulated long-term behavior of idealized electrode interfacial structures in varying humidity environments. Nafion® ionomer dispersions were examined after deposition onto glassy carbon (GC) substrates before and after accelerated testing, and significant changes in the oxide content of GC and scattering length density of Nafion® were observed. Single layers of Nafion® and Nafion®/Pt bilayers on GC have also been investigated. Data was obtained for these samples with Nafion® 1100-EW films equilibrated in three different water vapor relative humidity (RH) environments - ambient ~10% H2O, 10% D2O, and 100% D2O. This data shows that a multilayer, in-situ NR model is needed to describe thin Nafion films when equilibrated with water vapor and is discussed in context of its implications on the oxygen reduction reaction and Pt-Nafion microelectrode studies.
Deterministic Impedance Models for Interpretation of Low-Frequency Inductive Loops in PEM Fuel Cells
Authors: Orazem Mark E. , Roy Sunil K.
Published: November 2006

A mechanistic approach is presented for interpreting the inductive loops often observed at low-frequencies in the impedance spectra of PEMFCs. Four possible electrochemical reaction mechanisms were considered. The side reactions and intermediates involved in both hydrogen peroxide formation and platinum dissolution could account for the low frequency inductive loops in the impedance spectra. The interpretation of the inductive features could be important for predicting the life-time of fuel cells since peroxide degrades the materials used for the fuel cell components and the platinum dissolution adversely affects electrochemical activity and lifetime of the catalyst used.
Plate In-Plane Electrical Resistance Impact to Stack Performance
Authors: Wang Guoqing , Ramani Manikandan , Eldrid Chev
Published: November 2006

In a cell consisting of composite bipolar plates and a polymer electrolyte membrane a significant cell voltage difference has been measured between the reactant inlet end and the reactant outlet end when the cell is aged or defective. In order to gain further understanding, modeling and experimental studies were conducted simulating the effects of local defects in the MEA. The studies indicate that in the presence of a high local resistance in the MEA or GDL, current bypasses the region creating voltage differences due to high in-plane current. The studies also included incorporating metal plates into the cell with a region of the MEA blocked. In this case, both experimental and modeling results show uniform cell voltage from inlet to outlet. It was concluded that both bipolar plate through-plane electrical resistance and in-plane electrical resistance are important metrics for plate selection and design.
Numerical Evaluation of Effective Gas Diffusivity - Saturation Dependence of Uncompressed and Compressed Gas Diffusion Media in PEFCs
Authors: Schulz Volker P. , Mukherjee Partha P. , Becker Jürgen , Wiegmann Andreas , Wang Chao-Yang
Published: November 2006

In the current work, we present a comprehensive modeling framework to predict the effective gas diffusivity, as a function of liquid water saturation, based on realistic 3-D microstructures of the uncompressed as well as compressed gas diffusion layer (GDL). The presented approach combines the generation of a virtual microscopic GDL and different physical modeling. We develop a reduced model in order to simulate the compression of the GDL layer since its compression has a strong impact on the material properties such as the water transport or its gas diffusion. Then, we determine the two-phase distribution of a non-wetting fluid, i.e. water, and a wetting fluid, i.e. air, within the GDL for different saturations. This is done using a full morphology (FM) model. Finally, solving the Laplace equation for the partly saturated medium we determine the relative gas diffusion, i.e. the gas diffusion depending on the saturation. In the present work, our approach is applied to a typical GDL medium, a SGL10BA carbon paper.
Modeling of Catalyst Layer Surface Coverage and Volume Blockage Owing to Liquid Water in a PEFC
Authors: Wang Chao-Yang , Mukherjee Partha P.
Published: November 2006

A comprehensive pore-scale modeling framework has been developed for the catalyst layer of a polymer electrolyte fuel cell in order to study the effects of site coverage and volume blockage owing to liquid water. The catalyst layer microstructure is reconstructed using a stochastic generation method. The liquid water distribution is obtained from a two- phase lattice Boltzmann simulation and the catalytic surface coverage leading to reduced electrochemical activity is estimated from the saturation maps. The pore blockage effect due to liquid water is evaluated using a direct numerical simulation model from the reduced oxygen diffusivity owing to the resistance offered by the blocked pores.