bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation of Pt-Ru-Co Ternary Catalyst on Carbon Paper for PEMFC with Electrodeposition and Galvanic Displacement
Authors: Ahn Sang Hyun , Kim Soo-Kil , Kwon Oh Joong , Hwang Sun-Mi , Kim Jae Jeong
Published: October 2008

The Pt-Ru-Co ternary catalyst was prepared on the carbon paper with electrodeposition and galvanic displacement. The carbon paper without PTFE (polytetrafluoroethylene) was used as the substrate for catalyst deposition. The catalyst was prepared with Co electrodeposition on carbon paper through the change of deposition potential and time. The Co nucleation on carbon paper was investigated by using the electrochemical techniques of linear sweep voltammetry (LSV), cyclic voltammetry (CV), chronoamperometry (CA) and field emission scanning electron microscopy (FESEM). Then Pt and Ru galvanic displacement were carried out by control of displacement time. Consequently, the Pt-Ru-Co ternary catalyst was successfully formed using electrodeposition and galvanic displacement, and it showed competitive catalytic activity compared to other reported results in electrochemical analysis.
Electrochemical Studies of Unsupported PtIr Electrocatalyst as Bi-Functional Oxygen Electrode in Unitized Regenerative Fuel Cells (URFCs)
Authors: Jung Ho-Young , Park Sehkyu , Ganesan Prabhu , Popov Branko N.
Published: October 2008

The electrochemical characteristics of unsupported PtIr black catalysts with various compositions were investigated by CV, LSV, and polarization techniques. The catalyst composition of 85 wt. % Pt and 15 wt. % Ir shows higher oxygen evolution reactivity and comparable electrochemical activity to the unsupported Pt black catalyst. Based on the electrochemical characteristics, URFC using the 85Pt:15Ir catalyst shows higher round-trip efficiency than that of unsupported Pt black catalyst at different current densities.
ORR Adsorbate Dynamics on Pt Single Crystal PEM Fuel Cells
Authors: Dhanda Abhishek , O'Hayre Ryan , Pitsch Heinz
Published: October 2008

This paper presents a novel experimental setup for studying the ORR on well-defined single crystal Pt/Nafion interfaces. Low frequency inductive loops are observed in the impedance spectra that correspond to the dynamics of the adsorbed intermediates. An appropriate reaction mechanism is proposed and the kinetic parameters are derived using a combination of mathematical modeling and impedance analysis.
Fine Tuning of Activity for Nanoscale Catalysts
Authors: Strmcnik Dusan , Van der Vliet Dennis , Lucas Chris , Karapetrov Goran , Markovic Nenad M. , Stamenkovic Vojislav
Published: October 2008

The ability to tune the electronic and structural properties of nanocatalysts can potentially lead towards their superior catalytic activity. This can be achieved by numerous ways such as controlling the size and shape of nanoparticles, the introduction of another metal into the bulk of the catalyst and tuning of the nanoscale surface morphology. The later has been in focus of this report and can be controlled by either preparation procedure or by in-situ electrochemical treatment.
Correlations between Microstructures and Properties of Pd-modified Nafion® Membranes
Authors: Zhang Lu , Cheng Xuan , Zhang Ying , Fan Qinbai
Published: October 2008

The Nafion membrane was modified using chemical deposited Pd in an effort to reduce methanol crossover in DMFC. The surface morphology, crystal structure and chemical composition of the Pd-deposited membranes were characterized. The glass transition temperature (Tg), proton conductivity and methanol-inhibiting performance of the Pd deposited membranes were studied and compared with those of non-modified membranes. It was shown that Pd-modified membrane exhibited better performance in methanol inhibition and proton conductivity than the Nafion®112 membrane.
Dielectric Relaxations and Conductivity Mechanism of Nafion: Studies Based on Broadband Dielectric Spectroscopy
Authors: Di Noto Vito , Piga Matteo , Pace Giuseppe , Negro Enrico , Lavina Sandra
Published: October 2008

The electrical performance of Nafion was investigated from -155 to 155 C in the frequency range from 10 mHz to 10 MHz and for two different hydration conditions. The electrical responses are mainly due to conductivity, electrode polarization and relaxation phenomena. These features were correlated to the molecular and nano-scale structure of the material and to the transition/relaxation phenomena observed in both DSC and DMA studies.
PEM Fuel Cell Properties of Pre-Stretched Recast Nafion®
Authors: Lin Jun , Wu Pin-Han , Wycisk Ryszard , Pintauro Peter
Published: October 2008

Pre-stretched recast Nafion is a new membrane material with many desirable properties for PEM fuel cells. It was previously shown that the proton conductivity of this membrane in room temperature water was identical to that of commercial Nafion but its permeability to methanol was significantly reduced. Consequently, the power output from a direct methanol fuel cell with pre-stretched recast Nafion (draw ratio of 4) was 50% higher than that with Nafion 117. In an effort to better characterize pre-stretched recast Nafion, additional property measurements were made and compared to those for commercial Nafion. There was a substantial increase in the polymer crystallinity with increasing draw ratio which translated into improved membrane mechanical properties (a higher storage modulus and ultimate tensile strength). There was also a modest increase in the α-transition temperature when the membrane was elongated, as determined from dynamic mechanical analysis. Preliminary results indicated that the proton conductivity of pre-stretched membranes at a sub-zero temperature (-20oC) was about 35% greater than that for Nafion 212 or Nafion 117. On the other hand, the proton conductivity of a water vapor equilibrated pre-stretched Nafion film (draw ratio 4) at 95% relative humidity was identical to that of Nafion 212 for temperatures in the 15-60oC range.
Development of Highly Durable PFSA Membrane and MEA for PEMFC Under High Temperature and Low Humidity Conditions
Authors: Endoh Eiji
Published: October 2008

The world's first highly durable PFSA membrane and MEA for PEMFC have been developed, which can operate for more than 6,000 hours at 120ºC and 50% relative humidity (RH). The MEA is comprised of a newly invented composite polymer (NPC polymer), which has exceptional chemical stability against degradation caused by the hydroxyl radical even at 120ºC. This achievement has opened up a new era of operating PEMFC in the temperature range of near freezing to120ºC under low humidity as well as under high humidity conditions for an extended period of time.
DEMS Analysis of Small Organic Molecule Electrooxidation: A High-Temperature High-Pressure DEMS study
Authors: Jusys Zenonas , Behm R. Juergen
Published: October 2008

The electrooxidation of methanol, ethanol and ethylene glycol on a Pt/Vulcan catalyst was investigated over a wide temperature range [20 to 100oC] at 3 bar overpressure and under continuous electrolyte flow by differential electrochemical mass spectrometry [DEMS]. Oxidation of methanol, ethanol and ethylene glycol at 0.6 V at ambient temperatures yields CO2 current efficiencies of ~40, 5 and 4%, which increase to 100, 24 and 33% at 100oC, respectively. The apparent activation energies for the overall reaction and for oxidation to CO2 were found to be 58 and 64 kJ mol-1 for methanol oxidation, for ethanol / ethylene glycol they were 41 / 32 kJ mol-1 and 73 / 53 kJ mol-1, respectively. The mechanistic and kinetic implications of these data and the importance of model studies under realistic reaction conditions will be discussed.
Efficiency of CO2 Generation during the Electrooxidation of Ethanol on Platinum with Various Roughness Factors
Authors: Mitsushima Shigenori , Takahashi Tomoaki , Ariffin Azreena , Matsuzawa Koichi , Ishihara Akimitsu , Ota Ken-ichiro
Published: October 2008

In order to clarify the electrooxidation reaction of ethanol, the current efficiency of CO2, CH3CHO, and CH3COOH generation has been determined on platinum of various roughness factors at 70oC in 0.1 mol dm-3 H2SO4 with 1 mol dm-3 C2H5OH. The oxidation current density based on geometrical surface area increased with the roughness factor. On the other hand, the oxidation current density based on a real platinum surface area decreased, and the CO2 generation current efficiency increased. The crystal structure of the platinum surface did not change with roughness factor, because the shape of hydrogen adsorption and desorption in cyclic voltammogram was independent of the roughness factor. Therefore, this behavior would be caused by the difference in the pore structure of Pt plated Pt with the potential distribution. The current efficiency of CO2 generation increased with the decrease of the potential, and became more than 50% at 0.4 V vs. RHE.
Oxidation of Alcohols in Acidic and Alkaline Environments
Authors: Cremers Carsten , Bayer Domnik , Kintzel Birgit , Joos Martin , Jung Florina , Krausa Michael , Tübke Jens
Published: October 2008

The electro-oxidation reactions of methanol and ethanol were studied in sulfuric acid and potassium hydroxide solution. Different electrode materials were tested for this reaction including base metal electrodes in the alkaline case. Tests were performed using standard electrochemical techniques such as cyclic voltammetry, chronoamperometry and differential electrochemical mass spectrometry. Comparing both reactions it was found that in the acidic environment the methanol oxidation proceeds faster and is more complete than the ethanol oxidation. However, the situation changes in alkaline solution. Here, the kinetic enhancement of the ethanol oxidation reaction is in many cases so strong that the ethanol oxidation kinetics become faster than the methanol oxidation kinetics at the same metal and under the same conditions.
Electrocatalyst Design for an Elevated Temperature Proton Exchange Membrane Direct Ethanol Fuel Cell
Authors: Bocarsly Andrew B. , Niangar Ellazar
Published: October 2008

Ethanol presents several advantages over other alternative fuels. Its volumetric energy density (23.4 MJ/L) is slightly lower than gasoline (33.4 MJ/L), but much better than available with either methanol or hydrogen. If an ethanol is used in a proton exchange membrane (PEM) fuel cell the lowered energy density compared to gasoline in an internal combustion engine can in theory be overcome. This assumes that an electrochemical system can be developed that carries out the complete 12-electron oxidation of ethanol. To reach this goal, new catalyst systems must be developed. It is found that multicomponent catalysts such as platinum tin oxide (Pt/SnO2) and platinum tin oxide titanium dioxide (Pt/SnO2/TiO2) improve the conversion of ethanol to its 12-electron oxidation products. Catalysts of this type can be quickly prepared usingamicrowave-assisted polyol procedure. Elevation of the operating temperature of a PEM fuel cell using the indicated catalysts to 130åC facilities production of CO2 and provides an improved current-voltage response.
Effects of Oxygen Concentration in the Cathode Gas on the Oxidation of Acetaldehyde to Carbon Dioxide in a Direct Ethanol Fuel Cell
Authors: Katayanagi Yuta , Yamazaki Yohtaro
Published: October 2008

The effect of oxygen crossover in a direct ethanol fuel cell with acetaldehyde fuel was investigated. The cell was operated at a constant voltage of 0.2 V, and the fuel flow rate of the anode and the oxygen concentration in the cathode gas were varied. The reaction products in the anode were analyzed using gas chromatography. When the O2 concentration in the cathode gas increased and the fuel flow rate decreased, the amounts of the evolved CO2 gas increased.
Carbon Corrosion of a PEMFC During Shut-down/Start-up when Using an Air Purge Procedure
Authors: Ofstad Axel , Davey John , Sunde Svein , Borup Rodney L.
Published: October 2008

Carbon corrosion rates were measured for four types of polymer-electrolyte membrane (PEM) electrode assemblies (MEAs) during shut-down air purging and start-up. The corrosion rates were measured at different purge rates, temperatures, and relative humidities. The highest amount of carbon corrosion occurs when gases are humidified and when using low flow rates for the air purging during shut-down and low hydrogen flow during start-up. Dry conditions give the highest rates of corrosion during shut-down when comparing the same flow rates of hydrogen and air, while humid conditions gives the highest rate of corrosion during start-up when comparing the same flow rates of hydrogen and air.
CFD Study of Carbon Corrosion in PEM Fuel Cells
Authors: Jain Kunal , Gidwani Ashok , Kumar Sanjiv , Cole James Vernon
Published: October 2008

This paper addresses the durability and degradation of Proton Exchange Membrane (PEM) fuel cells with a focus on carbon corrosion at electrodes. To address this, detailed Butler-Volmer kinetics are implemented in a general purpose finite volume CFD code CFD-ACE+. The code was validated against experimental and model data from the literature showing excellent match with polarization data and partial current densities for individual reactions. Numerical calculations of fuel cell operation under different corrosion conditions were performed in two-dimensional and three-dimensional geometries. Results are presented in terms of distribution of fuel, potential and the current densities. The simulations and results indicate that advanced CFD with detailed Butler-Volmer kinetics can be used to identify the conditions leading to corrosion and guide development of operating conditions and materials to mitigate the electrode degradation and improve the fuel cell system durability.
High Resolution Neutron Radiography Imaging of Operating PEM Fuel Cells: Effect of Flow Configuration and Gravity on Water Distribution
Authors: Spendelow Jacob , Mukundan R. , Davey John , Rockward Tommy , Hussey Daniel S. , Jacobson David , Arif Muhammad , Borup Rodney L.
Published: October 2008

High resolution neutron radiography was used to image polymer electrolyte membrane fuel cells (PEMFCs) during operation under a variety of conditions. The effect of specific operating conditions, including flow direction (co-flow or counter-flow), orientation of the PEMFC with respect to gravity, and simulated anode recycle loop, were examined. Counter-flow operation was found to result in higher water content than co-flow operation, with more uniformly distributed water. Orientation with respect to gravity was also significant, with net water transport observed from the higher side of the cell to the lower side. The higher anode flow rate resulting from the simulated recycle loop facilitated convective removal of liquid water from the anode flow field, leading to lower overall levels of water in the PEMFC.
Enhanced Diffusion in Polymer Electrolyte Membrane Fuel Cell using Pulsating Flow
Authors: Hwang Yong-Sheen , Cha Suk Won , Kim Seo-Young , Ji Sang-Hoon , Lee Daeheung , Choi Hoon , Choi Jong Won , Seo Jeong-Hoon , Kim Min Soo , Lee Dae-Young
Published: October 2008

This study considers the feasibility of the concentration control of the fuel and vapor by oscillating flow in the channel of Polymer Electrolyte Membrane Fuel Cells(PEMFCs). PEMFC Stack performance is largely influenced by the fuel and vapor concentration. If the fuel concentration is lower than stoichiometry 1.25 of the hydrogen and 2.5 of the air or the flooding is happened by excess water, its performance deteriorates seriously because of the fuel and air starvation. In this respect the optimization of the fuel and vapor concentration is crucially important to maximize fuel cell stack performance. The objective of the current study is to apply the principle of the mass transfer being enhanced by the oscillating flow to the cathode channel.
Double Role of Water in the Fuel Cell Oxygen Reduction Reaction
Authors: Ogasawara H. , Naslund L. A. , McNaughton J. , Anniyev T. , Nilsson Anders
Published: October 2008

Water is present during the normal operating condition of polymer electrolyte membrane fuel cells (PEMFCs) and we have, through model experiments on a platinum surface using x-ray photoelectron spectroscopy, investigated its role in two different stages in the oxygen reduction reaction (ORR). We found that the activation of oxygen to the adsorbed atomic phase occurs readily in the dry region, but not in the humid region process. In this case, water is acting to inhibit the active sites on the catalyst. On the contrary, water is found to promote the reduction of adsorbed atomic oxygen in the formation of a water-hydroxyl surface complex.
Probing the Structure of Operating Fuel Cell Cathode Catalysts using XAS
Authors: Hudson Sarah L. , Ball Sarah C. , Blaney Katie B. , Chouchelamane Gael H. , Fiddy Steven G. , Harvey Ian , Sivasubramaniamb Prabalini , Tessier Béatrice C. , Theobald Brian R. , Thompsett David , Russell Andrea E.
Published: October 2008

A proton exchange membrane fuel cell has been designed to enable correlation of cathode catalytic activity with structural parameters determined by in situ XAS investigations in transmission mode. The cell design is described and validated for oxygen reduction activity measurement using both Pt and PtCo alloy catalysts. Findings from in situ XAS investigations at the Pt LIII edge are presented for a 60% Pt/C cathode catalyst operating at OCV, under load with oxygen feed, and during time resolved potential step experiments with oxygen and nitrogen feeds. In nitrogen XANES and EXAFS analysis show increasing oxide formation and particle disruption with increasing potential up to 1.0 V. In oxygen the catalyst structure remained unchanged irrespective of the applied potential and therefore load drawn from the cell. Differences in coordination number at the same applied potential in oxygen compared to nitrogen indicate that a particle morphology change occurs during the ORR.
Functionalized Polybenzimidazoles for PEMFC
Authors: Peron Jennifer , Ng Feifei , Ruiz Elodie , Jones Deborah , Roziere Jacques
Published: October 2008

A novel sulfonated polybenzimidazole has been prepared by solution copolycondensation of diaminobenzidine, 5-sulfobenzene-1,3-dicarboxylic acid and 4,4'-(hexafluoropropylidene) bis(benzoic acid) in various stoichiometric ratios using polyphosphoric acid as solvent. The resulting polymers, characterized by 1H NMR spectroscopy, are soluble in polar aprotic solvents and show excellent film-forming characteristics. Mechanically tough and flexible films are prepared by solution casting. The properties of the polymer and membranes have been characterized as a function of the degree of sulfonation, and compared with those of sulfonated poly-[(1-(4,4'-diphenylether)-5-oxybenzimidazole)-benzimidazole] prepared by direct sulfonation. The hexafluoropropyl group imparts flexibility and favours clustering of sulfonic acid rich domains that are favourable for proton transport.
Low EW poly [perfluorosulfonic acids] /Phosphotungstic acid /Teflon® Supported Membrane Electrode Assemblies
Authors: Li Bo , Choi Pyoungho , Pearman Benjamin P. , Rodgers Marianne , Agarwal Rohit , Mohajeri Nahid , Linkous Clovis A. , Yoon Wonseok , Huang Xinyu , Slattery Darlene , Bonville Leonard , Kunz H. R. , Fenton James M.
Published: October 2008

Two different fabrication procedures of catalyst coated membranes (CCMs) using 750 EW poly [perfluorosulfonic acid] ionomer composite membranes that contain phosphotungstic acid are discussed in this study. Cell polarization was obtained at three operating conditions: 80/100/75, 100/70/70, and 120/35/35 (cell temperature {degree sign}C/anode %RH/cathode %RH), and ambient pressure. Hydrogen/air cell performances at 120/35/35 and 400 mA/cm2 varied with the procedure from 0.39V to 0.64 V. Utilization of different fabrication procedures has a significant effect on electrode structure and thus relative overpotential, but little influence on membrane resistance and related ohmic loss. Although much higher performance occurred with the non-heat treatment process, durability issues require heat treatment for stabilization. Further study on the physical and chemical properties of the fabrication process of 750EW poly [perfluorosulfonic acid] ionomers/phosphotungstic acid CCMs is necessary to optimize both the performance and durability of elevated temperature and low relative humidity CCMs.
Water Uptake and Interfacial Structural Changes of Thin Film Nafion® Membranes Measured by Neutron Reflectivity for PEM Fuel Cells
Authors: Murthi Vivek S. , Dura Joseph , Satija Sushil , Majkrzak Charles
Published: October 2008

Nafion thin films (~500 Aå) spin coated onto the Pt and Au layers on Si are investigated for water uptake and swelling. Neutron Reflectometry data demonstrate that these structures are composed of nafion layers which differ from their bulk properties in terms of their scattering length density and water uptake. However, as the relative humidity is increased, the amount of water in the layers increases for a Nafion on Au and is comparable to that observed on bulk nafion membranes only up to 80 % RH. However, the Nafion on Pt reaches complete hydration at 96% RH. Although, a single layer model was able to fit the NR data obtained on nafion under vapor conditions, only a bilayer model, with an outer less hydrated nafion and an inner more hydrated nafion layer, was able to fit the data in liquid water.
Water Uptake Characteristics and Backbone Flexibility of Novel Polymers for Proton Exchange Membranes
Authors: Mangiagli Patrick , Ewing Chrostopher , Xu Kui , Wang Qing , Hickner Michael A.
Published: October 2008

Gravimetric analysis was performed during a step change in relative humidity for a series of sulfonated polymers to determine their dynamic water uptake characteristics. The mass change was recorded as a function of time for both stiff-backboned and flexible-backboned polymers when the humidity was instantaneously increased from 40 to 50 %. The observed water uptake profiles were distinctly different based on the inferred stiffness of the sulfonated polymer backbone. A sulfonated poly(sulfone)-based membrane had a slower mass uptake than more flexible Nafion with time constants of 307 s and 150 s for the sulfonated poly(sulfone) and NRE212, respectively. The dynamic water absorption properties were measured for a series of sulfonated poly(styrene)-b-poly(vinylidene fluoride)-b-sulfonated poly(styrene) membranes. The backbone flexibility of these polymers was intermediate to that of the poly(sulfone) and Nafion membranes and could be tuned based on the molecular weight of the poly(styrene) blocks and sulfonation level.
Development of Micro Direct Methanol Fuel Cell Systems and Their Possible Applications
Authors: Cao Jianyu , Yuan Ting , Huang Qinghong , Zou Zhiqing , Xia Baojia , Yang Hui , Feng Songlin
Published: October 2008

To meet the demands for high power microelectronic devices, research efforts at SIMIT have involved the optimization of Si based flow fields using the MEMS technology, the development of key components for the air-breathing micro direct methanol fuel cells (µDMFCs), the assembly of µDMFC stacks and the integration of micro energy systems. We found that the microstructure of both the anodic and cathodic flow fields has a significant influence on the performance of the µDMFCs. By adjusting the microstructure of the flow field plates, it is possible to obtain the better performance of a µDMFC with Si based flow field plates than that using traditional flow field plates. Recent research results including the fabrication of the membrane electrode assembly with improved performance and the water management under the air-breathing mode will be presented. Integrated µDMFC systems and their possible applications will be discussed.
Anode-Controlled Water Management in Direct Methanol Fuel Cells
Authors: Shaffer Christian E. , Wang Chao-Yang
Published: October 2008

A low water crossover from anode to cathode in a direct methanol fuel cell (DMFC) must be realized if highly concentrated methanol fuel is to be used. The use of a low-α membrane electrode assembly (MEA) is vitally important in achieving this goal. The low rate of water crossover for a low-α MEA has traditionally been attributed to the hydrophobic cathode micro-porous layer (MPL), thin membrane combination, but it has recently been discovered that a hydrophobic anode MPL is also effective in reducing water crossover. In this paper we demonstrate that a hydrophobic anode MPL may play an even more significant role than cathode MPL in reducing water crossover, and we embark on developing anode-controlled water management strategies for DMFCs. As a first step in this process, we show that a thicker, more hydrophobic anode MPL with lower permeability is more effective in reducing water crossover.
Analysis of the Transient Behavior of a Passive Air Breathing Direct Methanol Fuel Cell using 1-D Model Simulation
Authors: Ha Seungbum , Chang Ikwhang , Cha Suk Won
Published: October 2008

The transient behavior of a passive air breathing direct methanol fuel cell (DMFC) operated on vapor-feeding mode is studied in this paper. As a result of experiment, the output performance is sometimes unstable and there are some overshoots. A mathematical dynamic one-dimensional model for simulating transient response of the DMFC is presented. In this model a DMFC is decomposed into its subsystems using lumped model. A one-dimensional, non-isothermal, combined heat and mass transport model is developed that captures the coupling among water generation and transport, oxygen consumption, self-heating and natural convection. For validation, similar experiments were carried out. As a result of simulation and experiments, strong effects of feeding methanol concentration and water transport were found out. The model and experiment analysis provides several conclusions. The performance drop after peak point is caused by insufficiency of water at the anode. The excess water at the cathode makes performance recovery impossible.
High Fuel Concentration Direct Liquid Fuel Cell with Redox Couple Cathode
Authors: Ilicic Alan B. , Wilkinson David P. , Fatih Khalid , Girard Francois
Published: October 2008

A unique approach which facilitates the use of high fuel concentrations in Direct Liquid Fuel Cells (DLFCs) is reported. By substituting the air cathode of a conventional DLFC with a redox couple cathode, a 3D carbon-based electrode can be employed to achieve cathode selectivity. This configuration not only eliminates cathode depolarization, but also enhances the cell design flexibility, allows for a Pt-free cathode and precludes cathode flooding as it is an all-liquid system. Methanol and formic acid are used as model fuels with the Fe2+/Fe3+ redox couple in cyclic voltammetry and fuel cell performance tests to demonstrate the positive attributes of this system. Fuel cell tests include the use of Nafion® 112 or Nafion® 117 as the membrane and fuel concentrations approaching that of pure fuel.
Pulse Voltammetry [of Alloy Metal Catalysts] at Fuel Cell Electrodes
Authors: Pietrasz Patrick , Sankaran R. M. , Zawodzinski Thomas
Published: October 2008

Pulse voltammetry as a technique was used to explore the conditions under which platinum oxides form in an operating fuel cell. The technique is shown to have much slower reaction times due to the high surface area of the fuel cell electrodes.
Best Combination of Gas Diffusion Layers for Polymer Electrolyte Fuel Cell under Cathode Condition of Very Low Humidity
Authors: Kitahara Tatsumi , Konomi Toshiaki , Nakajima Hironori , Tateishi Yoshinobu , Murata Makoto , Haak Nico , Wilde Peter
Published: October 2008

The present study was carried out to find out the best combination of gas diffusion layers (GDLs) for a polymer electrolyte fuel cell (PEFC) operated under very low-humidity conditions at the cathode and high-humidity conditions at the anode using a test apparatus in which the clamp pressure on the cell could be accurately controlled. For cathode GDLs, it is important to maintain humidity and prevent dehydration of the MEA. A microporous layer (MPL) coating on the low-porosity carbon paper substrate is effective for enhancing PEFC performance. For anode GDLs, however, it is important to increase water transport from the humidified hydrogen gas to the MEA. An anode GDL with the MPL reduces PEFC performance. Hydrophobic treatment by PTFE (polytetrafluoroethylene) loading in the anode GDL is effective for performance enhancement. However, when the PTFE content becomes too high, the water transport properties are reduced, thereby lowering PEFC performance.
Highly-Efficient Buckypaper-Based Electrodes for PEMFC
Authors: Zhu Wei , Zheng Jim P. , Liang R. , Wang Ben , Zhang Chun , Walsh Shawn , Au George , Plichta Edward J.
Published: October 2008

The Pt catalytic electrode was developed using carbon nanotube film (buckypaper) as a supporting medium through use of the electrodeposition method. Buckypapers are free-standing thin films consisting of single-walled carbon nanotubes (SWNT), multi-walled carbon nanotubes (MWNT) or carbon nanofibers (CNF) held together by van der Waals forces without any chemical binders. Mixed buckypapers may be developed by layered microstructures with a dense and high-conducting SWNT networks at the surface, as well as large porous structures of MWNT or CNF networks as supports. This unique microstructure may improve Pt catalyst accessibility and the mass exchange properties. Pt particles were uniformly deposited in porous buckypaper and had an average particle size of about 6 nm. A promising electrochemical surface area of about 40 m2 g-1 was obtained from these electrodes. A Pt utilization of as low as 0.5 g kW-1 was achieved for the cathode electrode at 80 oC. Pt utilization efficiency may be further improved by optimization of the electrodeposition condition in order to reduce the Pt particle size.
Effect of Hydrophobic and Structural Properties of GDL on PEM Fuel Cell Performance
Authors: Park Sehkyu , Popov Branko N.
Published: October 2008

The effect of hydrophobic and structural properties of the cathode gas diffusion layer on mass transport in PEM fuel cells was examined experimentally and theoretically. The results indicated that liquid water transport at the cathode is controlled by the interplay between fraction of hydrophilic surface and average pore diameter in the cathode gas diffusion layer.
Relationship Between Structure and Surface Properties on Capillary Behavior in PEMFC Gas Diffusion Layers
Authors: Cheung Perry , Fairweather Joseph D. , Schwartz Daniel T.
Published: October 2008

The relationship between capillary pressure (PC) and liquid saturation (SL) in gas diffusion layers (GDLs) is an important feature of water management in polymer electrolyte membrane fuel cells (PEMFCs) (1). Experimentally measured PC vs. SL data (3-7) have emerged as an important way to characterize this key water management-related property, but a theoretical framework for analyzing PC vs. SL data to understand fundamental structure/property relationships is lacking. We present here a bundle of capillaries model capable of analyzing experimental PC vs. SL data that deconvolute the effect of pore structure and surface properties on GDLs in PEMFCs.
In-Situ Characterization of GRAFCELL® Flexible Graphite Film as Gas Diffusion Layers for PEMFCs
Authors: Gurau Vladimir , Zawodzinski Thomas , Wayne Ryan
Published: October 2008

Single cell testing is carried out using a sensitivity testing approach to evaluate the performance of GRAFCELL® materials used as macro-porous substrate for cathode GDLs under a range of flow, pressure, temperature and humidity conditions. Polarization curves and electrochemical impedance spectroscopy data are used to establish a correlation between the processing factors and the in-situ fuel cell performance, to identify the key characteristics required to optimize the fuel cell performance and to downselect the specimens with the best combination of properties.
Evaluation of Liquid and Mass Transfer in GDL by Direct Network Simulation
Authors: Inoue Gen , Matsukuma Yosuke , Minemoto Masaki
Published: October 2008

It is important to investigate the two-phase condition in PEFC gas diffusion layer (GDL) to improve mass transfer rate. The structure of simulated GDL made of layered carbon fibers was produced by the numerical analysis in this study, and the structural properties of various simulated GDL were investigated, for example pore distribution, permeability and tortuosity. With these structures, the two-phase analysis model in GDL was developed with a 3-dimensional network model converted from simulated GDL directly, and the two-phase condition in GDL was calculated on various conditions of GDL structure and hydrophilicity. And the influences of multi-layer GDL structure were evaluated. As a result, it was confirmed that the liquid water distribution was affected by multi-layer structure and that optimizing the connection of pore-pore and changing the contact angle along the direction of water flowing out lead to decrease the amount of water and increase O2 diffusivity.
Effect of Water Management Schemes on the Membrane Durability in PEMFCs
Authors: Huang Xinyu , Wang Xiaofeng , Preston Joshua , Bonville Leonard , Kunz H. R. , Perry Michael , Condit David
Published: October 2008

The authors report the degradation behavior of polymer-electrolyte membrane fuel cells tested under two types of water-management schemes: the solid plate (SP) cells that mange water via flow and dew point control of the reactant gases, and water transport plate (WTP) cells that actively remove liquid through micro-porous bipolar plates. Comparative experiments were conducted. Cell performance degradation was tracked by periodic diagnostic testing. After cell testing, the residual mechanical strength of the membrane electrode assemblies was characterized. It was found that both water management schemes led to cell performance reduction via the loss of the electrochemical active area. However, the SP cell led to rapid reduction of membrane toughness. The WTP cell tended to preserve the membrane mechanical toughness better. Post-analysis found localized membrane failure in SP cell test during which a step change in performance occurred. Abrupt performance degradation was not observed for either of the WTP cell tests.
Characterization and Modeling of Gas Crossover and its Impact on the Membrane Degradation of PEMFCs
Authors: Shim Jae Young , Tsushima Shohji , Hirai Shuichiro
Published: October 2008

Membrane degradation was investigated by accelerated membrane degradation tests in various gas-supply conditions. Results show that the anode side of the membrane was more deteriorated under H2-O2 supply conditions. However, the cathode side of the membrane was more deteriorated under H2-air supply conditions. Quantitative examination of the oxygen crossover by direct gas mass spectroscopy (DGMS) elucidated that the oxygen crossover depends on the oxygen partial pressure and relative humidity of the supplying gas. Based on membrane degradation and oxygen crossover, we modeled membrane thinning with a simple rate equation with the effect of partial pressure. Calculated values of membrane thinning were consistent with the experimental values.
Degradation of Perfluorinated Membranes Having Intentionally Formed Pt-Band
Authors: Hasegawa Naoki , Asano Takashi , Hatanaka Tatsuya , Kawasumi Masaya , Morimoto Yu
Published: October 2008

Open-circuit durability tests are carried out for intentionally Pt-precipitated membranes with and without electrodes to clarify the roles of Pt-band and the electrodes. The Pt-precipitated membrane without electrodes gives a small but non-zero fluoride emission rate (FER). The Pt-precipitated membrane with electrodes gives the highest FER, which is much higher than that of membrane with electrodes (conventional MEA). Chemically aggressive species are produced on both Pt-band and electrodes. Pt band, without electrodes, is only slightly detrimental for the membrane but, with electrodes, it significantly accelerates membrane degradation.
Mitigation of Perfluorosulfonic Acid Membrane Chemical Degradation Using Cerium and Manganese Ions
Authors: Coms Frank D. , Liu Han , Owejan Jeanette E.
Published: October 2008

Cerium and manganese ions are very effective reversible scavengers of •OH in an operating PFSA-based PEM fuel cell. The use of these ions in very small quantities can reduce the fluoride release rate by up to three orders of magnitude relative to an unmitigated sample and thereby afford extremely durable membranes. A chemically rational mechanism that accounts for the remarkable effectiveness of these chemical mitigants is presented.
Analysis of Proton Transport in Pseudo Catalyst Layers
Authors: Iden Hiroshi , Ohma Atsushi , Shinohara Kazuhiko
Published: October 2008

Analytical techniques were investigated for examining the influence of the ionomer network structure on proton transport in the catalyst layers of a polymer electrolyte fuel cell. It was verified that the proton transport resistance of a pseudo catalyst layer consisting of a carbon black support and ionomer between two membranes as an intermediate layer (IL) was estimated by a hydrogen pump technique. Using the technique, the effective proton conductivity of ILs with different carbon supports was investigated. It was found that the effective proton conductivities differed. An analysis of the difference revealed the following two possible causes. One is that the Bruggeman factor of the samples might have been affected by the state of ionomer coverage. Another is that the proton conductivities of the ionomer as bulk differed, which might have been due to a difference in water content attributable to the carbon supports.
Dependence of Electrode Proton Resistivity on Electrode Thickness and Ionomer Equivalent Weight in Cathode Catalyst Layer in PEM Fuel Cell
Authors: Liu Yuxiu , Ji Chunxin , Baker Daniel , Gu Wenbin , Jorne Jacob , Gasteiger H. A.
Published: October 2008

Dependence of electrode proton resistivity on electrode thickness, Pt-loading, and ionomer equivalent weight (EW) was investigated using Pt/Vulcan catalyst. The proton resistivity, an intrinsic electrode property, is independent of the electrode thickness and Pt-loading, but depends on the ionomer EW.
Surfactant Assisted Catalyst Layer Deposition for PEM Fuel Cells
Authors: Bauer Alex , Wilkinson David P. , Gyenge Elod , Bizzotto Dan , Ye Siyu
Published: October 2008

The potentiostatic electrodeposition of platinum onto gold coated Si wafers and a gold rotating disk electrode (RDE) was carried out with non-ionic surfactants that functioned as templating agents to obtain mesoporous deposits with size features in the nanometer range. The particle size and morphology were studied by surface analysis (SEM and AFM). The electrochemically active surface area of Pt electrodeposited onto the RDE by using a mixture of Brij 56 and n-heptane was increased by a factor of ~2 compared to Pt deposited without structure directing additives. Corresponding oxygen reduction tests at 2500 rpm revealed an improvement of about 14 % (from 5.9 to 7.2 x 10-4 A cm-2) for the cathodic current density at 0.9 V vs. RHE while the mass transfer limited current density was increased by ~25 % from 4.4 to 5.5 x 10-3 A cm-2.
Enhanced PEMFC Cathode Kinetics at 120{degree sign}C and Low Relative Humidity Using Heteropolyacid Additives
Authors: Baker Phillip , Brooker Robert P. , Kunz H. R. , Bonville Leonard , Parnas Richard
Published: October 2008

Silicotungstic acid (STA), a heteropolyacid, was added to the electrode of polymer electrolyte membrane fuel cells (PEMFCs) and evaluated for increased performance at high temperature and low relative humidity (RHs). Activity was shown to increase for cells containing STA by as much as 35% at 118{degree sign}C/40%RH compared to the cells at 78{degree sign}C/100%RH. Additionally, STA was shown to decrease the fluoride emission rate (FER) by an order of magnitude compared to cells with no additive.
Using Heteropolyacids in the Anode Catalyst Layer of Dimethyl Ether PEM Fuel Cells
Authors: Ferrell Jack R. , Turner John A. , Herring Andrew M.
Published: October 2008

In this study, polarization experiments were performed on a direct dimethyl ether fuel cell (DMEFC). The experimental setup allowed for independent control of water and DME flow rates. Thus the DME flow rate, backpressure, and water flow rate were optimized. Three heteropoly acids, phosphomolybdic acid (PMA), phosphotungstic acid (PTA), and silicotungstic acid (STA) were incorporated into the anode catalyst layer in combination with Pt/C. Both PTA-Pt and STA-Pt showed higher performance than the Pt control at 30 psig of backpressure. Anodic polarizations were also performed, and Tafel slopes were extracted from the data. The trends in the Tafel slope values are in agreement with the polarization data. The addition of phosphotungstic acid more than doubled the power density of the fuel cell, compared to the Pt control.
Nafion Ionomer Aggregation and its Influence on Proton Conduction and Mass Transport in Fuel Cell Catalyst Layers
Authors: Xie Zhong , Navessin Titichai , Zhao Xinsheng , Adachi Makoto , Holdcroft Steven , Mashio Tetsuya , Ohma Atsushi , Shinohara Kazuhiko
Published: October 2008

Aggregation of Nafion in water and in n-propyl alcohol (NPA)/water and its influence on the size of Pt/C agglomerates in catalyst inks has been studied by Dynamic Light Scattering (DLS). DLS shows that Nafion more strongly aggregates in water than in NPA/water. This is believed to be responsible for differences found in FC performance for catalyst layers prepared from these two different dispersion media.
Direct-Glycerin Fuel Cell for Mobile Applications
Authors: Ragsdale Steven R. , Ashfield Chris B.
Published: October 2008

The oxidation of caustic, crude glycerin in a passive direct-fuel cell using an alkaline anion-exchange membrane (AAEM) at ambient temperature is reported. Glycerin is a byproduct of the biodiesel production process and the recent surge in biodiesel production has resulted in increased and underutilized glycerin supplies. The described AAEM fuel cell uses crude glycerin directly and eliminates the need for costly neutralization, distillation and purification procedures. The AAEM fuel cell using crude glycerin demonstrated five times greater energy density than a comparable direct-methanol fuel cell. The enhanced energy density is attributed to the AAEM and glycerin fuel combination, which allows for significantly higher fuel concentrations to be used, a consequence of the AAEM reducing fuel-crossover and preventing water-management problems at the cathode. The described fuel cell performance and demonstrated energy densities could facilitate the use of fuel cells in portable power applications, particularly for low-watt, hand-held mobile electronic devices.
A First Principles Study of Direct Oxidation of Aqueous Borohydride on Au and Pt Surfaces
Authors: Rostamikia Gholamreza , Janik Michael J.
Published: October 2008

Direct Borohydride Fuel Cells (DBFCs) have the potential to generate high power densities for use in portable power applications. Despite the potential of DBFC's, current applications are limited in part, by the lack of an effective anode electrocatalyst. Though a number of pure metals and alloys have been tested as anodes, gold and silver electrodes are uniquely capable of completing direct oxidation at near 100% coulombic efficiency. Overpotentials on Au anodes, however, limit the overall cell efficiency and little is known of the elementary electrocatalytic mechanisms, reaction intermediates, or limiting elementary steps . In this study, we apply density functional theory (DFT) calculations to examine borohydride electro-oxidation over the Au(111), and compare with Pt(111) surfaces for which non-selective hydrolysis paths compete with direct oxidation. Possible stable surface intermediates and limiting elementary steps are identified and results are discussed in comparison with experimental data from the literature.
SnO2:F Coated Duplex Stainless Steel for PEM Fuel Cell Bipolar Plates
Authors: Wang Heli , Turner John A.
Published: October 2008

Duplex 2205 stainless steel was deposited with ˜0.6 µm thick SnO2:F coating; coated steel was characterized for PEMFC bipolar plate application. Compared with bare alloy, interfacial contact resistance (ICR) values of the coated 2205 steel are higher. SnO2:F coating adds its own resistance to the air-formed film on the steel. In a PEMFC anode environment, a current peak of ca. 25 µA/cm2 registered at ca. 30 min for coated 2205 steel. It stabilized at ca. 2.0~-1.0 µA/cm2. This peak is related to the complicated process of coating dissolution and oxide-layer formation. Anodic-cathodic current transfer occurred at ca. 200 min polarization. In a PEMFC cathode environment, current was stable immediately after polari¬zation. The stable current was ca. 0.5~2.0 µA/cm2 during the entire polarization period. AES depth profiles with tested samples and ICP analysis with the tested solutions confirmed the excellent corrosion resistance of the SnO2:F coated 2205 alloy in simulated PEMFC environments.
Advanced Bipolar Plate for a Unitized Regenerative Fuel Cell
Authors: Mittelsteadt Cortney K. , Braff William
Published: October 2008

An advanced composite bipolar plate is described for a unitized regenerative fuel cell and electrolyzer system that operates on pure feed streams (H2/O2 and water, respectively). The composite bipolar plate can greatly simplify "closed-loop" unitized fuel cell/electrolyzer power systems, as it eliminates the need for saturators, a second stack, and water/gas phase separation equipment. It provides a substantial system improvement over presently used alkaline systems in that it allows for simple high pressure electrolyzer operation with a high differential pressure. Additionally, it allows for dead-ended H2 and O2 feed during fuel cell operation, eliminating parasitic pumping losses required for water removal in a conventional fuel cell. Results from a 50 cm2 bench design are presented. Additionally, the composite bipolar plate has been used to deliver methanol vapor to a direct methanol fuel cell, resulting in a lower methanol concentration at the catalyst/membrane interface and reduced methanol cross-over.
Measurement of the Potential of Bipolar Plates Inside a PEFC During Operation
Authors: Kikuchi Katsuhide , Kato Ikuyasu , Yoshida Makoto , Wada Mikio , Mizuno Seiji
Published: October 2008

The commercialization of metal bipolar plates for polymer electrolyte fuel cells (PEFCs) requires excellent corrosion resistance, and low costs are also demanded. It is thus important to have an accurate grasp of the corrosive environment. In this study, we developed equipment that measures potential and pH around the surface of a bipolar plate during power generation in real time. The corrosive environment revealed that the cathode side at the time of Open Circuit (OC) is the severest. Moreover, it became clear that due to differences in pH the potential on the surface of a bipolar plate is relatively low compared with that of a catalyst layer.
New Reference Electrode Approach for Fuel Cell Performance Evaluation
Authors: Herrera Omar E. , Merida Walter , Wilkinson David P.
Published: October 2008

We report on the separation of anodic and cathodic potentials in a working fuel cell via reference electrodes at constant conditions. The reference electrodes consisted of four platinized platinum electrode wires and two patches of the same catalyst layer used in the anode. All the reference electrodes were unaffected by the operating conditions of the fuel cell and those with patches provided the most stable potentials. Additional sensing electrodes were placed at the fuel and oxidant inlet and outlet to provide localized information on the operating conditions and the state of the membrane electrode assembly (MEA). Our results show that this type of sensing electrode system can be used to detect flooding, dehydration, and low stoichiometry events, while the reference electrodes provide detailed behavior of the anode and cathode potentials.