bluuebunny/crossref_metadata_2025 huggingface dataset:
Ballmilling of Carbon Supports to Enhance the Performance of Fe-based Electrocatalysts for Oxygen Reduction in PEM Fuel Cells
Authors: Proietti Eric , Dodelet Jean-Pol
Published: October 2008

The effect of ballmilling three carbon black supports on the ORR activity of Fe-based electrocatalysts was investigated. Catalysts were prepared by acid-washing these ballmilled carbon supports, then impregnating them with iron(II) acetate and pyrolyzing in NH3 at 950{degree sign}C. It was found that ballmilling the carbon support improved the ORR activity for catalysts made with Black Pearls 2000 (Cabot), but decreased it for those made with N650 and left it relatively unchanged for those made with N234 (both low surface area commercial furnace carbon blacks from Sid Richardson Carbon Corporation). For catalysts made with ballmilled Black Pearls 2000, it was found that ORR activity increases as i) degree of disorder increases, ii) the change in micropore surface area due to pyrolysis increases, iii) nitrogen content increases and iv) crystallite size (La) approaches 24 Aå. No compelling trends were found for catalysts made with ballmilled N234 and N650.
Development of Nitrogen-Modified Carbon-Based Catalysts for Oxygen Reduction in PEM Fuel Cells
Authors: Nallathambi Vijayadurga , Li Xuguang , Lee Jong Won , Popov Branko N.
Published: October 2008

Carbon-based catalysts for oxygen reduction reaction (ORR) were synthesized by modifying the carbon surface with nitrogen-containing precursors. The electrocatalytic properties were studied as a function of surface treatment, nitrogen and oxygen concentrations, and heattreatment temperature. The catalysts showed an onset potential for ORR close to 0.83 V and the amount of H2O2 generated was about 1 % at 0.5 V under our experimental conditions. The current transient in fuel cell at 0.4 V exhibited an initial increase of current density to approximately 0.12 A cm-2 and then a steady-state current profile for up to 200 h. The characterizations indicated that pyridinic and graphitic nitrogen acts as catalytic sites for ORR.
Fe-N-C Oxygen Reduction Catalysts Supported on Burned-off Activated Carbon
Authors: Yang Ruizhi , Dahn Tara , Dahn Jeff
Published: October 2008

Fe-N-C catalysts were prepared by impregnating FeCl3 within two kinds of activated carbon (Kuraray GC and Nuchar) that had been previously burned-off at 500oC in air to vary their pore sizes in a controlled way. The impregnated samples were subsequently heated at 850oC in NH3. The average pore size of the samples was determined by small-angle X-Ray scattering (SAXS) measurements and quantified by the radius of gyration (Rg) of the pores. The catalytic activities of the samples vary with the pore size of the activated carbon, which depends on the burn-off time. The results support suggestions from the Dodelet group about the importance of the pore size in determining catalytic activity.
Group 4 and 5 Oxide-based Compounds as New Cathodes without Platinum Group Metals for PEFC
Authors: Ishihara Akimitsu , Tamura Motoko , Maekawa Youta , Ohgi Yoshiro , Matsuzawa Koichi , Mitsushima Shigenori , Ota Ken-ichiro
Published: October 2008

A partially oxidized TaC0.58N0.42 has been investigated as a new cathode for polymer electrolyte fuel cells. The catalytic activity for oxygen reduction reaction (ORR) significantly depended on an oxidation state of the TaC0.58N0.42. TaC0.58N0.42 and Ta2O5 had a poor catalytic activity for the ORR. The onset potential on the partially oxidized TaC0.58N0.42 for the ORR had a maximum value of 0.9 V vs. RHE in 0.1 mol dm-3 H2SO4 at 30oC. Hard X-ray PhotoElectron Spectroscopy and XRD analyses indicated that the surfaces of the partially oxidized TaC0.58N0.42 were oxidized, although the inner parts of the partially oxidized TaC0.58N0.42 remained tantalum carbonitride. This result indicated that an appropriate oxidation of the TaC0.58N0.42 was essential to enhance the catalytic activity for the ORR.
Development of PtRu Electrocatalysts on 1-Aminopyrene Functionalized MWCNTs for Direct Methanol Fuel Cells
Authors: Jiang Sanping , Wang Shuangyin , Wang Xin
Published: October 2008

A new synthesis method for the preparation of high performance PtRu electrocatalysts on multi-walled carbon nanotubes (MWCNTs) is reported. In this method, bimetallic Pt-Ru electrocatalysts are deposited onto 1-aminopyrene (1-AP)-functionalized MWCNTs by a microwave-assisted polyol process. The non-covalent functionalization of MWCNTs by 1-AP is simple and can be carried out at room temperature without the use of expensive chemicals or corrosive acids, thus preserving the integrity and the electronic structure of MWCNTs. PtRu electrocatalysts on 1-AP functionalized MWCNTs show much better distribution with no formation of aggregates, higher electrochemically active surface area and higher electrocatalytic activity for the electrooxidation of methanol in direct methanol fuel cells as compared to that on conventional acid treated MWCNTs and carbon black supported PtRu electrocatalysts.
Impact of PtRu Anode Catalyst Degradation on DMFC MEA Performance
Authors: Cabello-Moreno Noelia , Crabb Eleanor , Fisher Janet , Russell Andrea E. , Thompsett David
Published: October 2008

This paper reports an 'MEA based' accelerated ageing test designed primarily to investigate stability of anode catalysts for DMFCs. The effect of potential cycling on the anode with increasing number of cycles is investigated. Methanol stripping voltammetry is used to characterize changes at both the anode and cathode catalysts and the changes observed are related to quantitative changes in performance of the MEA polarization data. Changes in catalyst morphology and surface composition are characterized by TEM. In particular, comparisons between unsupported PtRu ('black') and carbon supported PtRu catalysts are made.
Fabrication and Characterization of Nano Electrocatalyst (Pt) for Methanol Electro Oxidation
Authors: Chatterjee Moitrayee , Ghosh Susanta , Basumallick Indra N.
Published: October 2008

Nanosized platinum catalysts were deposited onto graphite and carbon felt surface by both chemical and electrochemical techniques. The controlled potentiostatic condition was used for electrodeposition using cationic surfactant, CTAB, at pre-CMC concentration in electrolytic bath. Electrocatalytic activity of such electrodes for methanol oxidation were studied and compared. The parameters like peak potential (Ep), peak current (ip), apparent diffusion coefficient for methanol (Dapp), Tafel slope and apparent rate constant (k) were obtained from cyclic voltammograms of methanol oxidation in acid medium. The morphology and crystal structure of these electrodes were analyzed by SEM and XRD. Electrokinetic parameters of these systems clearly indicate that methanol oxidation rates are almost comparable onto these electrodes. It is thus suggested to follow electrochemical route using surfactant as capping agent. Graphites are found to be better substrate than felt material. SEM pictures clearly indicate formation of highly dispersed catalytic particles (Pt) via electrochemical route.
Electrochemical Stability of PtCu and PtCuCo Core-Shell Oxygen Reduction Reaction Electrocatalysts in Liquid Electrolyte
Authors: Neyerlin Kenneth C. , Srivastava Ratndeep , Strasser Peter
Published: October 2008

Pt25Cu75 and Pt20Cu20Co60 electrochemically dealloyed electrocatalysts were shown to possess improved resistance to electrochemical surface area (ECSA) loss relative to commercially available Pt/HSC and Pt/Vu catalysts. The difference in ECSA loss was shown to be directly related to the temperature at which the alloy catalysts were prepared (i.e. reduced/annealed), with higher temperatures resulting in greater resistance to ECSA loss. To normalize for preparation conditions, commercially available catalysts were exposed to a heat treatment process mimicking the annealing/reducing procedure for the Pt alloys.
Aging Studies of Voltammetrically Dealloyed Pt-Cu Nanoparticle ORR Electrocatalysts
Authors: Strasser Peter , Liu Zengcai , Koh Shirlaine
Published: October 2008

Voltammetrically dealloyed Pt-Cu alloy nanoparticles show significantly improved Pt-mass and specific activities for the oxygen reduction reaction in acidic media in both RDE and MEA configurations. The active phase of the catalyst is prepared from very Cu-rich precursor materials which are formulated into catalyst inks and electrode layers. The high Cu content of the precursor materials raises fundamental and practical questions as to the molecular stability / oxidation state of the Cu rich catalyst surface and the shelf-life of precursor powders, inks and electrode layers. Here we present aging studies of a carbon-supported Pt25Cu75 nanoparticle catalyst precursor. We monitored how the surface area (ECSA) and the oxygen electroreduction (ORR) reactivity of dealloyed precursors (active form of catalyst) change as a function of the exposure time to air of the Pt25Cu75 precursor at room temperature. Similarly, we aimed to investigate how ECSA and ORR of the active catalyst changed with the time the liquid catalyst ink was exposed to air. We find little detrimental effect of air aging of the precursor on ORR activity over the time scales investigated. The effect of air aging of the catalyst inks is more complex, however. Initially, aged inks show increased ORR reactivity, that is, aged inks result in more active catalyst layers. After about 4-5 days of aging of the inks in air, however, we observed a drop in ORR activity of the resulting catalyst layers. This complex aging behavior of the inks seems independent of prior air aging of the dry powder precursor.
Effect of Operating Conditions on the Acidity of H2/Air PEM Fuel Cells' Water
Authors: Abdullah Aboubakr M. , Okajima Takeyoshi , Kitamura F. , Ohsaka Takeo
Published: October 2008

The pH of the water drained out from the cathode and the anode sides was measured using a flow pH meter connected to the exits of the anode and cathode compartments and was found to depend mainly on the cell's operating conditions and the MEA's aging condition. Aged MEA operating at low temperature - low RH condition led to a significant increase in the acidity of the water drained out from the cathode side (pH 1.8). On the other hand, the water drained out from the anode side has a pH value of 4.8 on average. Reactions that might affect the pH of the water drained out from the PEM fuel cell were studied. Membrane degradation via hydroxyl radicals (⋅OH) was found to be the most influencing reaction that lowers the pH of water within PEM fuel cells.
Phase Change Driven Water Transport in Polymer Electrolyte Fuel Cells
Authors: Kim Soowhan , Mench Matthew
Published: October 2008

The objective of this work is to investigate water transport of polymer electrolyte fuel cell (PEFC) materials subjected to a temperature gradient. Experiments on different fuel cell materials (Nafion®, reinforced membrane, reinforced membrane electrode assembly (MEA), non-reinforced MEA, hydrophilic and hydrophobic diffusion media) were performed using an in-house fuel cell fixture with an imposed temperature gradient between the anode and cathode. Contrary to thermo-osmotic flow in fuel cell membranes (17, 18), a net flux of water was found to flow from the hot to cold side of the fuel cell. The key to this is the existence of some gas phase in the catalyst layer or other porous media. This mode of transport can be explained by a phase-change driven flow, also known as a heat pipe effect. The measured water transport through the membrane electrode assembly is the net effect of mass diffusion as well as thermo-osmosis in the membrane, which moves counter to the direction of the phase-change driven flow. The net flux of water was fit by Arrhenius functions that are dependent on material set, temperature gradient, and average temperature across the materials. In addition to direct quantification, the phase-change driven flow was visualized and confirmed using high resolution neutron radiography.
Determination of Liquid Water Distribution in Porous Transport Layers
Authors: Buechi Felix N. , Flückiger Reto , Tehlar Denis , Marone Federica , Stampanoni Marco
Published: October 2008

The local saturation in porous transport layers (PTL) has been determined using synchrotron-based x-ray micro-tomography. The water distribution inside the porous structure could be resolved on the scale of the pores. After phase segmentation of the image data, the measurement of the liquid saturation as function of the through plane coordinate of the PTL and the capillary pressure was possible. For verification, first experiments with complete cells are also shown.
Use of Anomalous X-ray Scattering for Probing the Structure, Composition and Size of Binary Alloy Nanoparticle Electrocatalysts
Authors: Toney Mike , Koh Shirlaine , Yu Chengfei , Strasser Peter
Published: October 2008

X-ray diffraction (XRD) and small angle X-ray scattering (SAXS) are methods that are used to characterize the atomic structure and particle size of nanoparticle electrocatalysts. These methods do not inherently provide element specific information on structure and particle size. However, with the use of an anomalous scattering approach, one can obtain element specificity. This contribution describes these methods and applies these to fuel cell nanoparticle catalysts.
Pt-Ru Alloys Deposited by Sputtering as Catalysts for Methanol Oxidation
Authors: Jiang Xirong , Prinz Friedrich , Bent Stacey
Published: October 2008

Using rf co-sputtering, we have successfully deposited Pt-Ru catalysts of well controlled Ru content over a wide range of compositions. The surface morphology of the films, acquired from scanning electron microscopy studies, is very rough and nanoporous. The structure of the films has been verified as polycrystalline by x-ray diffraction analysis. The electrochemical behavior of the electrodes has been characterized using chronoamperometry with methanol oxidation as the probe reaction in a H2SO4/MeOH electrolyte at room temperature. The results indicate that the optimal stoichiometry of the alloys measured in 1 M MeOH and 16.6 M MeOH is Ru0.24Pt0.76 and Ru0.46Pt0.54, respectively. These alloys have an onset potential 0.2 volt lower than pure Pt.
The Effect of Co-adsorbed Water on the Stability and Configuration of Formyl (HCO) and Hydroxymethylidyne (COH) Intermediates on Pt(111): A Density Functional Theory Study
Authors: Arnadottir Liney , Jo´nsson Hannes , Stuve Eric M.
Published: October 2008

Two forms of the reaction intermediate with H:C:O stoichiometry were studied on Pt(111) using density functional theory. Three cases were studied: the intermediate on a clean surface, the intermediate and one water molecule on the surface and the intermediate with a water bilayer. Both the H-C=O (formyl) and C-OH (hydroxmethylidyne) configurations were found to be stable on clean Pt(111) and when coadsorbed with a water molecule. Interconversion between the two configurations was studied using the nudged elastic band method. On the clean surface interconversion between the two forms goes through COads and Hads intermediates, meaning that, although both HCO and COH are stable on the clean surface, they will not interconvert. In the presence of a single coadsorbed water molecule the activation barrier for interconversion from HCO to COH was found to be 0.62 eV. The HCO configuration is stable in the presence of a water bilayer, but the COH configuration dissociates to COads and Hads. These results suggest that, in the presence of water, the HCO form will be the only stable form of the reaction intermediate of H:C:O stoichiometry.
Recent Progress in Improving the Oxidation of Formic Acid on High Surface Area Platinum and Palladium Catalysts: Surface Alloying and pH Effects
Authors: Haan John L. , Masel Richard I.
Published: October 2008

Recent progress in studies on the direct formic acid fuel cell reported here includes improvements to the anode catalyst and analysis of the impact of pH on reaction rate. We demonstrate that several adatoms can be underpotentially deposited to the surface of the palladium anode catalyst to improve the oxidation of formic acid. Antimony and lead adatoms show strong improvement to operation of the fuel cell. We also demonstrate that the solution pH has a strong effect on the reaction rate in a nearly irreversible reaction (formic acid oxidation). We eliminate the effects of adsorbed surface species and conclude that the change in pH results in a change in thermodynamic driving force that is evidenced by a remarkable increase in reaction rate with increase in pH.
Effect of the Anode Structure on the Performance of Direct Formic Acid Fuel Cells
Authors: Chenitz Régis , Dodelet Jean-Pol
Published: October 2008

Single MEA direct formic acid fuel cells were assembled using various anode diffusion electrodes and various Nafion/Pd black ratios for the catalyst layers. Power densities above 100 mW cm-2 were obtained at room temperature with 10 M formic acid fed to the anode and O2 at atmospheric pressure fed to the cathode. The best results were obtained when untreated carbon cloth was used as the anode diffusion layer and with a catalyst layer composed of equal volumes of Nafion and Pd black electrocatalyst. We have also observed increased performance of the MEA when the flow of formic acid is drastically reduced, probably due to a better evacuation of CO2; the gas produced at the anode due to the oxidation of formic acid.
The Impacts of Repetitive Carbon Monoxide Poisoning on Performance and Durability of a Proton Exchange Membrane Fuel Cell
Authors: Angelo Michael , Bender Guido , Dorn Susanne , Bethune Keith , Hossain Tim , Posey Dan , Gazda Jerzy , Ghatak-roy Amiya , Rocheleau Rick
Published: October 2008

In this paper, we report the effects on cell performance and durability of repeatedly poisoning the anode catalyst of a proton exchange membrane fuel cell (PEMFC) to 2 ppm carbon monoxide (CO) in the hydrogen fuel. The experiments were designed to simulate repeated exposure to low level impurities as may be experienced in a dynamically operated PEMFC. Experiments were conducted over a period of 1000 hours and accompanied by weekly diagnostics to characterize detailed changes in performance. Results for the repeatedly poisoned cell were compared to those of a control cell which was operated identically but without CO in the anode feed stream. Two effects were observed: the electro-chemically active area (ECA) of the test cell anode decreased significantly during the initial 300 hours of the experiment and the hydrogen crossover rates increased by a factor of 67 by the end of the experiment. Both effects contributed to performance losses, while the latter also indicated the end of life for the membrane electrode assembly (MEA). The results of the experiments emphasize the impact low level CO contaminant may have on MEA lifetime and cell performance under dynamic conditions.
PEMFC Contamination Model: Competitive Adsorption Followed by an Electrochemical Reaction
Authors: St-Pierre Jean
Published: October 2008

A mathematical model is derived describing the effect of an electroactive contaminant on the catalyst surface. Two cases are considered and characterized by different rate determining steps: contaminant reaction and contaminant product desorption. Each case leads to a closed form solution for the transient and scaled current density either during the contamination or recovery process. The model was partially validated using proton exchange membrane fuel cell (PEMFC) data obtained by operating with hydrogen contaminated with small amounts of CO. Results suggest the use of well designed experiments to minimize artifacts and additional model validation using a wider range of operating conditions.
Proton Exchange Membrane Based on Sulfonated Polyethersulfone for H2/Air and Direct Methanol Fuel Cells
Authors: Ghassemi Hossein , Subbaraman Ram , Brockman Christopher , Pyle Brandon , Zawodzinski Thomas
Published: October 2008

Sulfonated poly(ether sulfone) (SPES) copolymers with a degree of sulfonation higher than 30% show high proton conductivity (> 60 mS/cm) as well as a high extent of swelling. Two methods were considered to decrease the swelling and improve dimensional stability. First, composite membranes were prepared by blending SPES and polyacrylonitrile (PAN) and annealing under nitrogen at 280 oC. In a second approach, SPES was blended with polysulfone (PSU) and heated at 260-280 oC to form sulfone crosslinks in the membrane. The membranes prepared by these methods showed significantly lower swelling in water and methanol with minor decreases in conductivity.
The Effect of Modification of PtRu Anode Catalyst with SnO2 on CO Tolerance
Authors: Takeguchi Tatsuya , Wang Guoxiong , Muhamad Ernee , Ueda Wataru
Published: October 2008

PtRuSnO2/C catalyst was prepared by the ethylene glycol method to improve the CO tolerance for polymer electrolyte membrane fuel cell. The prepared catalysts were characterized by X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), CO stripping voltammetry and single cell performance measurements. Based on XRD and STEM results, PtRuSnO2/C catalyst exhibited a slightly smaller particle size than PtRu/C catalyst due to the addition of SnO2. CO stripping voltammetry showed that SnO2 promoted CO electro-oxidation on PtRuSnO2/C catalyst at low potential. And PtRuSnO2/C catalyst gave a better single cell performance under 500 ppm CO-contaminated H2. These results suggested that the performance improvement was due to the combined promotional effect of SnO2 and Ru species on Pt for CO tolerance.
Inorganic Electrolyte Membrane for High-temperature PEM fuel cell: Conception, Preparation and Performance
Authors: Tang Haolin , Jiang Sanping
Published: October 2008

A novel conception of inorganic proton exchange membrane for elevated temperature PEM fuel cell was proposed in this research. The inorganic electrolyte was approached by trapping heteropolyacid (HPA) molecules inside mesoporous silica structure via a self-assembly route assisted with a structure-directing surfactant, and then construct an inorganic membrane based on mesoporous silica matrix and HPA proton conducting sites. Such mesoporous HPA/silica significantly enhance the stability of HPA molecules, and provided continuous proton transfer channels with diameter of 3~4 nm, resulting high proton conductivity of about 0.05 S/cm at 300oC. A PEMFC based on the mesoporous HPA/silica inorganic PEM and a non-platinum cathode catalyst achieved a power density of 102 mW/cm2 at 300oC, closing to the performance of the cell with Pt catalyst at temperature of 80 oC.
Performance Assessment of Proton Exchange Membrane Fuel Cell on Toy Design
Authors: Pa P.S.
Published: October 2008

The purpose of this research is to apply proton membrane fuel cells to toys, and assess its feasibility. The study uses Taguchi Methods to analyze the "Proton Exchange Membrane Fuel Cell Power Supply and Work Module for Toys". The study assembled the proton exchange membrane fuel cell power supply module in the "Toy of Hydrogen-based Energy Module-Ship of Hydrogen-based Energy" and observes its operation state. It finds that the ship moved forward smoothly, and indicates that hydrogen can be used for this toy. This study uses renewable "Solar Energy" matching "the Proton Exchange Membrane" to design the "Hydrogen and Oxygen Fuel Module", which creates the hydrogen and oxygen fuel supply for the "Proton Exchange Membrane Fuel Cell Power Supply and Work Module" for toys using hydrogen-based energy. "Hydrogen-based Energy" will become applied extensive to the toy field in the future by way of this study.
Surface Oxide Film and its Influence on the Oxygen Reduction on Pd-Co and Pt-Co PEFC Cathodes
Authors: Tamura Yuichi , Taneda Kento , Ueda Mikito , Ohtsuka Toshiaki
Published: October 2008

PtCo and PdCo alloy electrodes were investigated in a 0.5 M sulfuric acid solution by electrochemistry, ellipsometry, laser Raman scattering spectroscopy, XPS, and GD-OES. The corrosion resistibility of Pt-Co and Pd-Co alloys decreased with increase of Co addition. The increase of Co addition, however, enhanced the catalytic efficiency on the ORR. The alloy surfaces may be covered by CoOOH and Pt or Pd oxide 2-3nm thick. At the potential of 1.2V vs. Ag/ AgCl/ sat. KCl, the thickness of oxide film increased with the Co addition. The presence of the oxide film on the alloy electrodes increases the overvoltage for the ORR. The effect of the oxide thickness on the ORR was discussed.
Degradation of Carbon Supports in PEFC Cathode Electrode Investigated by Electrochemical STM: Effects of Platinum and Oxygen on Enhanced Carbon Corrosion
Authors: Matsumoto Masashi , Manako Takashi , Imai Hideto
Published: October 2008

The corrosion of highly oriented pyrolytic graphite (HOPG) model electrodes' surfaces with platinum nanoparticles and oxygen molecules in an aqueous solution was investigated using electrochemical scanning tunneling microscopy in order to understand the degradation of carbon supports found in polymer electrolyte fuel cells (PEFCs) cathode electrode. Structural changes of HOPG surfaces with platinum nanoparticles and oxygen due to the corrosion were observed directly at atomic levels under the real conditions at which PEFCs operate. The STM observations revealed that the graphite surface oxide formation due to corrosion of the HOPG surfaces with platinum nanoparticles occurred initially at step edge sites, i.e., at defect sites and then grew toward terraces. This indicates that platinum particles and oxygen on the HOPG surface accelerated the corrosion. Surface oxygen species formed through the partial oxidation of water and the dissociative adsorption of oxygen molecules likely enhance the oxidation rate of graphitic oxide species.
Performance of Pd/C Cathode Electro-Catalysts for the ORR in Sulfuric Acid Containing Small Organic Molecules
Authors: Fraire Luna S. , Rodriguez Varela F.J. , Dabek R. , Savadogo O.
Published: October 2008

We studied the performance of carbon-supported Pd cathode electrocatalysts in O2-saturated acid solution containing ethanol. The Pd/C electrocatalysts showed an important selectivity toward the Oxygen Reduction Reaction (ORR), and a very high degree of tolerance to poisoning due to the presence of the alcohol. A negative shift in onset potential for the ORR of only 10 mV for a 20% Pd/C electrocatalyst in 0.5M H2SO4 + 0.125M C2H5OH electrolyte was measured, whereas the shift for a 20% Pt/C electrocatalyst was of 398 mV in the same solution. Similar high tolerances were established at increasing C2H5OH concentrations for Pd/C.
Numerical Analysis of Liquid and Heat Transfer in Heterogeneous GDL
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. In order to calculate liquid and heat transfer in heterogeneous GDL, the multi-calculation network model which consists of pore section and fiber section was developed on the basis of the structure of simulated GDL. And the influence of the temperature distribution on the condition of staying liquid water was examined by this model for internal condensation. As a result, it was found that the nonisothermal calculation was indispensable to examine the condition of liquid water in detail. In addition, the conditions of staying liquid water and the cell voltage were differed by each contact angle, and it was found that the performance of mass transfer was affected by not only the value of saturation but also the effective pore structure formed by staying liquid water.
Fabrication and Performance of MEA for DMFC by Bar-Coating Method
Authors: Lee Jae-Hyuk , Peck DongHyun , Kim Sang-Kyung , Lim Seong-Yop , Jung Doo-Hwan , Baeck Sung-Hyeon , Jang Jae-Hyuk
Published: October 2008

Membrane electrode assemblies (MEA) for direct methanol fuel cell (DMFC) were prepared using PtRu/C (70 % Pt alloy base) and Pt/C (75 % Pt alloy base) as their anode and cathode catalysts, respectively. The anode and cathode catalyst layer were coated by using semi-automatic bar-coating method, which can prepare the catalyst layer with uniform thickness. To study the effect of Nafion contents on performance, MEA in which Nafion ionomer contents were used (20 wt.%, 35 wt.%, 40 wt.%) was fabricated. And surface and cross-section morphologies of the catalyst layers were observed by SEM. The performances and resistance of the MEAs were investigated through a single cell evaluation.
A Link Between Design of the Fuel Cell Stack and Properties of MEAs - Experimental Evidence and its Influence on a Stack Performance Aspect (Cool-Start)
Authors: Lewinski Krzysztof A. , Steinbach Andrew J. , Hendricks Susan M. , Miller Darren R.
Published: October 2008

The fuel cell community has by now wholeheartedly accepted the notion of matched MEA components as necessary ingredients of fuel cell performance and durability equation. Considerable research has been conducted on optimizing the combined properties of the gas diffusion layer backing and microporous layer, catalyst and ionomer. The same logic seems to be quite universally applied to interplay between stack components and MEAs, but direct evidence as to why this would be so has not been researched or publicized widely. In this work we attempt to show such link does indeed exist, and to back up our claims with experimental data.
Induction of In-plane Current at Start-and-Stop Operations on a PEFC
Authors: Fukumoto Hisatoshi , Yoshioka Shoji , Matsumoto Shuichi
Published: October 2008

In-plane induction currents in electrodes and bipolar plates by reactant fed into a PEFC were evaluated using a 20-segmented cell. When hydrogen was fed into anode in the condition of anode (negative electrode) and cathode (positive electrode) exposed air, in-plane currents were detected in both electrodes in spite of the open-circuit condition. In-plane currents of anode and cathode in each segment had each other opposite direction and nearly equal quantity. Simultaneously, carbon dioxide and oxygen were also detected in the cathode exhaust.
Effects of Temperature and Relative Humidity on Oxygen Permeation in Nafion® and Sulfonated Poly(Arylene Ether Sulfone)
Authors: Takamura Yuichi , Nakashima Eiji , Yamada Hirohisa , Tasaka Akimasa , Inaba Minoru
Published: October 2008

Oxygen permeation in Nafion®117 and sulfonated poly(arylene ether sulfone) (BPSH-50) were investigated at different temperatures and relative humidities by a potential step method using a Pt microelectrode. The diffusion coefficient increased, while the solubility decreased with an increased in temperature and relative humidity for both samples. Consequently, the permeability increased with an increased in temperature and relative humidity for both samples. The permeability in BPSH-50 was approximately four times lower than that in Nafion®117, due to a smaller diffusion coefficient and a lower solubility in BPSH-50 than those in Nafion®117. Mass transport of oxygen in these membranes was correlated with microstructural changes of the membranes.
Electrocatalytic O2 Reduction Properties of Pyrochlore-Type Oxides for Alkaline DAFCs
Authors: Saito Morihiro , Saito Yoshinobu , Konishi Takayuki , Kawai Hideki , Kuwano Jun , Shiroishi Hidenobu , Uchimoto Yoshiharu
Published: October 2008

To explore new electrocatalysts for alkaline DAFCs, oxygen reduction reaction (ORR) activity of the pyrochlores Ln2Ru2O7-d(LnR, Ln=Pr,Nd,Sm,Gd,Dy,Yb) and Ln2Ru2-xMnxO7-d(LnRMnx, Ln=Pr,Nd) were examined in 0.1 M KOH at 70oC. The onset potential (Eon) of the ORR current and the efficiency (Eff4) of 4-electron ORR were evaluated by semi-steady state voltammetry with rotating ring-disk electrodes. In the LnR series, PrR with the highest ORR activity showed Eon = 0.85 V vs. RHE and Eff4 above 90 %. Their Eon and Eff4 values revealed that LnR with a smaller atomic number had a higher ORR activity. In addition, effects of Mn substitution for the Ru-site were confirmed in both PrRMnx and NdRMnx series. The NdRMn0.25 exhibited the highest ORR activity (Eon = 0.95 V and Eff4 above 90%) in the pyrochlore single phase. The Eon value kept unchanged even in 0.1 KOH containing 1 M methanol, ethanol, ethylene glycol and 2-propernol.
Influence of Anisotropic Transport Properties of the GDL on the Performance of PEMFCs
Authors: Zhang Xu , Song Datong , Wang Qianpu , Huang Cheng , Liu Zhong-Sheng
Published: October 2008

A two-dimensional, non-isothermal two-phase model, which includes the full anisotropy of GDL, was developed to investigate the effect of anisotropic ratios on cell performance. Among the four anisotropic ratios, the anisotropic ratio of diffusivity,γD, is the most sensitive parameter to cell performance. The present study demonstrated the possibility of improving cell performance by using innovated GDL porous materials with higher anisotropic ratios, especially higher γD
Effects of Atmospheric Trace Species on the Oxygen Reduction Reaction and the Production of Hydrogen Peroxide
Authors: Imabayashi Shin-ichiro , Kondo Yoko , Komori Ryotaro , Kawano Akihiko , Ohsaka Takashi
Published: October 2008

The effects of the atmospheric trace species (SO2, Cl-, NH3) on the formation of H2O2 accompanying the O2 reduction reaction (ORR) have been elucidated in 0.1 M HClO4 using rotating ring-disk Pt electrode methodology. The potential at which the ORR starts shifts to the negative direction and the amount of formed H2O2 increases concomitantly as the amount of added SO2 or Cl- increases, although Cl- less affects. The extent of the H2O2 formation is correlated to the coverage of SO2 or Cl- which was estimated from the decrease in the area of a hydrogen desorption peaks. This suggests that the adsorption of SO2 or Cl- on Pt reduces the number of the adjacent adsorption sites necessary for breaking of the O-O bond and then enhances the production of. No effect on the ORR activity and the H2O2 formation was observed for NH3.
Investigation of Migrated Platinum Distributions in PEMFC Under Excess H2/O2
Authors: Kim L. , Chung Chul Goo , Sung Young Wook , Chung Jong Shik
Published: October 2008

In order to verify the dissolution mechanism of Pt in the electrode of proton-exchange membrane fuel cell (PEMFC), the distributions of migrated platinum particles in the electrolyte membrane were investigated. The migrated platinum was observed by transmission electron microscope (TEM) after long-term operations under various conditions. Experimental results show that a large amount of Pt can be dissolved from cathode by chemical oxidation under excess O2. The distribution and particle size of migrated Pt are strongly dependant on H2 and O2 partial pressures. Possibility of Pt dissolution from anode is also appeared from observation of the MEA operated under lean H2 condition.
Direct Relationship between Carbon Corrosion and Cathode Potential during Fuel Starvation in PEMFC
Authors: Kim Jutae , Lee Junhee , Lee Gibaek , Tak Yongsug
Published: October 2008

Fuel starvation during start-up and shut-down processes affected the performance of proton exchange membrane fuel cell significantly. Fuel starvation was intentionally made by supplying hydrogen and air into anode side alternatively and the individual electrode potential was in-situ measured with dynamic hydrogen electrode (DHE). Cathode potential was raised up to 1.6 V when air / hydrogen boundary developed on anode side. The development of high cathode potential caused the oxidation of carbon support and the amount of CO2 evolution is proportional to the cathode potential above 1.0 V. Above ~1.2 V, CO was electrochemically generated and a small amount of SO2 was formed above ~1.3 V. Although higher cathode potential was induced irrespective of cell temperature, the oxidation of carbon support is remarkably retarded at low temperature.
Three Mechanisms for Protecting the Fuel Cell Membrane, Plates and Catalysts
Authors: Halalay Ion C. , Merzougui Belabbes , Mance Andrew
Published: October 2008

The performance of the perfluorinated sulfonic acid polymer electrolyte membrane in PEM fuel cells degrades through a multi-step process: (i) hydroxyl radicals attack on the fluorinated polymer with the release of fluoride ions; (ii) corrosion of the plates and alloy catalysts by the fluoride anions, with the release of base metal cations; (iii) generation of more hydroxyl radicals through Fenton's reaction catalyzed by the metal ions. While fluoride ion release can be greatly reduced through the inclusion of cerium, manganese or sodium ions into the PFSA polymer membrane, we present here an alternative approach for mitigating the membrane degradation. We propose three chemical methods for increasing the overall durability of the fuel cell by interfering with each step of this degradation cycle: the uses of (i) hydroquinones, to neutralize hydroxyl radicals, (ii) aza-crowns for sequestering fluoride anions, and (iii) crown ethers to sequester base metal cations.
Current Mapping of a Diagnostic Modeling Cell
Authors: Yuan Xiao Zi , Gu Elton , Sun Colin , Wang Haijiang , Wu Jinfeng , Martin Jonathan
Published: October 2008

In this work, local current distribution was investigated by temperature mapping without disturbing the operation of a diagnostic modeling cell. A temperature mapping ramp was measured using micro-thermocouples embedded into the anode plate of the modeling cell. Then, the current distribution was calculated based on the relation between current and heat generated from the reaction, and the assumption of the adiabatic condition. The effects of different operation conditions on current distribution were also investigated. The results show that the temperature derivative tends to increase along the flow field from the inlet to close to the outlet and then decrease under various conditions. This trend is exactly opposite to that of the local voltage distribution. We conclude that local current distribution depends on not only the flow field design but also the local voltage distribution.
MicroCT X-ray Imaging of Water Movement in a PEM Fuel Cell
Authors: Zhu Wei , Dunbar Zachary W. , Masel Richard I.
Published: October 2008

Micro CT was used to look through the graphite flow channels to provide accurate pictures of water inside of an operating PEM fuel cell. Water was observed emerging as water droplets on the surface of gas diffusion layer. Drops in both hydrophobic and hydrophilic flow channels were found to distort from the expected spherical shape before they started to move. However, drops in hydrophobic flow fields did not detach from the diffusion layer before moving, whereas water in the hydrophilic channel formed a thin water layer at the bottom of the channel. This is believed to be due to the role of the channel side walls, as well as possible non-uniformities in the flow channel surface.
Advanced In-situ Analysis of Reactant Gas Partial Pressure at Catalyst Layer/PEM Interfaces
Authors: Mashio Tetsuya , Ohma Atsushi , Shinohara Kazuhiko
Published: October 2008

An advanced in-situ analysis technique for evaluating the reactant gas partial pressure at the catalyst layer/polymer electrolyte membrane (CL/PEM) interfaces has been developed using a Pt probe inserted into the PEM. The results showed that the H2 partial pressure drop through the anode diffusion electrodes was significant and was affected by the relative humidity of the reactant gases. The O2 partial pressure drop through the cathode diffusion electrodes was affected by both the relative humidity of the reactant gases and the O2 partial pressure in the gas flow channels. The effect of the O2 partial pressure at the cathode CL/PEM interfaces on performance was also investigated. The results suggest that IR loss due to proton transport in the cathode might dominate performance under high O2 concentration conditions. On the other hand, the O2 partial pressure might dominate performance under low O2 partial pressure.
Effect of Relative Humidity on Contamination of Cathode and Anode Electrodes by Sulfur Dioxide in Air Stream in PEMFC
Authors: Tsushima Shohji , Morioka Hiroyuki , Kaneko Keisuke , Hirai Shuichiro
Published: October 2008

Catalyst poisoning by the SO2 supply to the PEMFC under OCV and load operational conditions was examined using simultaneous monitoring of cell voltage and SO2 emissions from the cathode exhaust. Results show that all supplied SO2 was readily absorbed in the cell during the initial period, thereby degrading cell voltage while poisoning of the catalyst proceeded more slowly in later periods. The relative humidity (RH) difference between the anode and the cathode brought considerable difference of the catalyst poisoning behaviors. Deteriorative poisoning was observed in the higher cathode RH with the lower anode RH because water transport from the cathode to the anode enhanced transport of contamination to the anode catalyst.
Sulfur Dioxide and Hydrogen Adsorption on Pt3Co(111) Surfaces: A First Principles Study
Authors: Pillay Devina , Johannes Michelle D.
Published: October 2008

Interactions between sulfur dioxide, SO2, and hydrogen on two different surfaces of Pt3Co(111) were investigated using density functional theory. The two surfaces considered were a Pt-skin and Ll2 Pt3Co(111) surface. SO2 adsorption was found to be more favorable on the Ll2 surface owing to its d-band center being closer to the Fermi energy. However, both surfaces adsorbed SO2 more weakly in comparison to Pt(111). The adsorption energies of H follow the same adsorption energy trends as SO2 on the different surfaces and show a preference for the three fold-hollow sites similar to other fcc metal (111) surfaces. The weaker adsorption of SO2 on the alloy Pt3Co(111) surfaces agree well with experimental observations that removal of sulfur to attain the initial mass of activity of the catalysts prior to sulfur adsorption requires less cleaning cycles for the alloy. Additionally, our results indicate that less hydrogen adsorbs to alloy surfaces than to pure Pt(111), also in agreement with experiment. SO2 adsorption trends across the three surfaces closely mirror those of atomic sulfur, indicating that surface sulfur tolerance does not depend on the specific oxidation species.
Durability of PEMFC Cathodes Exposed to Toluene-contaminated Air
Authors: Li Hui , Zhang Jianlu , Fatih Khalid , Shi Zheng , Wu Shaohong , Song Datong , Zhang Jiujun J. , Jia Nengyou , Wessel Silvia , Abouatallah Rami , Joos Nathan
Published: October 2008

The effects of toluene contamination on the performance of polymer electrolyte membrane fuel cells (PEMFCs) were studied. The severity of the contamination effect increased with increases in the current density, the toluene concentration and air stoichiometry, but decreased with an increase in the back pressure. The effect of toluene contamination on current dynamic operation was also studied by cycling the current density from 0.0 to 0.2, and then to 1.0 A cm-2 at the presence of toluene. The degradation of the fuel cell performance during the current dynamic operation was accelerated by the presence of toluene.
Determining the Mechanisms of Cationic Contamination on PEMFCs using a Strip Cell Configuration
Authors: Kienitz Brian , Zawodzinski Thomas , Pivovar Bryan , Garzon Fernando H.
Published: October 2008

Cationic contamination of polymer electrolyte fuel cells has been shown to cause serious performance degradation but the exact mechanisms of this degradation are not fully understood. A strip cell configuration was devised to study the mechanisms of performance degradation due to cationic contamination by changing the time and length scales of traditional fuel cells while providing a suitable reference electrode. This "strip cell" configuration utilizes traditional Nafion® membranes in an in-plane configuration with electrodes painted on each end. Using this cell it was determined that cationic contaminants collect near the cathode of the fuel cell under load and that this profile leads to increased losses primarily in the cathode region. These results can be directly related to performance losses in a typical PEMFC contaminated by foreign cations.
Research Strategies for Development of an Efficient and Effective Electrocatalyst for Polymer Electrolyte Membrane Fuel Cells and Progress Summary
Authors: Payne Terry L. , Benjamin Thomas , Garland Nancy , Kopasz John
Published: October 2008

The current electrocatalyst formulation for the polymer electrolyte membrane fuel cell (PEMFC), platinum supported on carbon (Pt/C), is known to be an effective promoter of redox reactions in fuel cells. However, the cost of Pt (currently ~$2,000/troy ounce) hinders its use as a practical catalyst in commercial fuel cell-powered vehicles at current platinum loading. Another issue with respect to adoption of any electrocatalyst for vehicle applications is durability, especially in light of transportation drive cycle operation with start/stop, start-up/shut-down, and transient requirements. Thus, a robust alternative to current Pt/C technology is needed as the PEMFC electrocatalyst for the oxygen reduction reaction (ORR) on the cathode. The U.S. Department of Energy is funding cathode catalyst research on low-platinum group metal (PGM) catalysts, including alloys and core-shell systems, and on non-PGM catalysts. This paper provides an overview of the issues, approaches, and status of the research.
Effects of Annealing Conditions on Catalytic Activities of Pt-Cu Nanoparticle Electrocatalysts for PEM Fuel Cells
Authors: Koh Shirlaine , Hahn Nathan , Yu Chengfei , Strasser Peter
Published: October 2008

Dealloyed Pt25Cu75 bimetallic nanoparticle electrocatalysts exhibit up to 6 times higher oxygen reduction reaction activities than Pt-C catalysts. The effects of annealing temperature and duration on the catalyst activity are studied, with annealing temperature varied from 600 {degree sign}C to 950 {degree sign}C and for 7h and 14 h. XRD and electrochemical analyses is used to obtain insight to the structural details of the catalyst samples. Information regarding extend of alloying, Pt and Cu compositions and distributions on the nanoparticles and particle (crystallite) sizes is correlated with the trends observed from mass and specific activities of the catalysts. It is found that annealing duration of 14 h offers little or no benefit to catalytic activities compared to 7 h. Pt25Cu75 annealed for 7 h, at 800 {degree sign}C was found as an optimal compromise between the extend of alloying and particle size growth to give the highest catalytic activity.
Preparation of Ptshell-Pdcore Catalysts and Its Application for Polymer Electrolyte Membrane Fuel Cell
Authors: Choi Insoo , Kwon Oh Joong , Kim Jae Jeong
Published: October 2008

Oxygen reduction reaction is one of two main reactions occurring when the fuel cell operates. Unfortunately, high over-potential induced by the irreversibility of such a reaction causes low performance of the fuel cell. In order to overcome the obstacle, researches on utilizing Pt have been extensively studied. Because of low economic efficiency of Pt it is difficult to commercialize synthesized catalysts or practice to them into other applications In this regards, the objectives of this study are to reduce the amount of Pt and promote the reduction reaction by synthesizing Ptshell-Pdcore electrocatalyst. The Pd/C nanoparticle was surrounded by Cu using electroless deposition then, Cu was displaced by Pt using galvanic displacement method. XPS, XRD were applied to identify metallic composition and its existence. And TEM was adopted to image the catalysts. The catalytic properties were investigated using rotating disk electrode.