bluuebunny/crossref_metadata_2025 huggingface dataset:
The Influence of Surfaces and Deposition Processes on Pt Structure and Properties
Authors: Coombs Sidney , Dameron Arrelaine , Engtrakul Chaiwat , Pylypenko Svitlana , Lee Jinsuk , Olson Tim S. , Bochert Christopher , Gennett Thomas , Simpson Lin , Pivovar Bryan , Dinh Huyen N.
Published: October 2010

Transparent conductive oxides (TCOs), In-Zn-O (IZO) and Ga-Zn-O (GZO), on glass are used as model substrates to study the effect of surface treatments and deposition processes on Pt growth and nanostructure. The TCO type and surface treatments appear to affect Pt nucleation and growth. Ar and O2 plasma surface treatments significantly lowered the contact angle of water measured on TCOs compared to trimethylaluminum surface treatment and samples without surface treatment. Annealing TCO samples in oxygen resulted in lower IZO conductivity and higher contact angle; while annealing in vacuum or hydrogen resulted in increased carbon on the surface, which appears to be related to higher water contact angles and higher conductivity. Higher amounts of zinc and carbon (probably due to contamination from the annealing chamber) on the IZO surface seem to correlate with lower water contact angles and lower conductivity.
Enhanced Oxygen Reduction Kinetics in PEMFCs at 120°C and Low Relative Humidity Using Silicotungstic Acid
Authors: Baker Phillip , Kunz H. Russell , Bonville Leonard J.
Published: October 2010

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 by as much as 30% for cells dipped in STA compared to cells dipped in deionized water at 120°C/35%RH.
A New Fabrication Technique to Manufacture an MEA Using Direct Coating of Nafion® onto Catalyzed GDL
Authors: Ding Xiaoyu , Didari Sima , Fuller Thomas F. , Harris Tequila A.
Published: October 2010

A new fabrication technique to manufacture an MEA using extrusion slot coating of ionomer onto the catalyzed GDL was presented. Preliminary coating tests were conducted to study the feasibility and effectiveness to directly coat Nafion® D2021 onto the catalyzed Toray 060 carbon paper. The uniformity of the coated membrane and the penetration of the Nafion® dispersion into the catalyst layer were analyzed. After that, pressing and blowing operations were introduced to increase the membrane uniformity and decrease the penetration of Nafion® dispersion and effects of these operations were analyzed.
The Role of Nitrogen Doping on Durability in the Pt-Ru/HOPG System
Authors: Pylypenko Svitlana , Queen Aimee , Neyerlin Kenneth C. , Olson Tim , Dameron Arrelaine , O'Neill Kevin , Ginley Dave , Gorman Bryan , Kocha Shyam , Dinh Huyen N. , Gennett Thomas , O'Hayre Ryan
Published: October 2010

This study investigates the role of the nitrogen doping on the durability of Pt-Ru metal nanophase catalysts supported on highly-oriented pyrolytic graphite (HOPG) substrates. The effect of the ion dose during N2 low ion energy implantation on the degree of the HOPG modification and levels of nitrogen doping are evaluated using X-ray photoelectron and Raman spectroscopy. Pt-Ru catalyst metal was deposited onto unmodified and N-implanted HOPG substrates using microwave and magnetron sputtering deposition routes, resulting in deposition either with or without preferential nucleation in the defect-sites. The role of the nitrogen on improved bonding between catalyst and support is evident from the microscopic evaluation of substrates after potential cycling.
Durability of Pt3Co/C Cathodes in a 16 Cells PEMFC Stack: Degradation Mechanisms and Modification of the ORR Electrocatalytic Activity
Authors: Dubau Laetitia , Maillard Frédéric , Chatenet Marian , André Johan , Rossinot Elisabeth
Published: October 2010

In this work, we operated a 16-cells stack based on Pt/C anode and Pt3Co/C cathode under H2/air at constant current (j = 0.6 A cm-2) for 1124 h. The MEA were characterized with special emphasis on the cathode electrocatalyst, using physical, chemical and electrochemical techniques after different life stages: as received (fresh: 0 h), conditioned (17 h) and aged for 504 or 1124 h. The fresh Pt3Co/C cathode catalyst is not stable during PEMFC operation and suffers compositional changes. In particular, the dissolution of Co atoms at the surface yields to the formation of a Pt-shell/Pt-Co alloy core structure. The high electrochemical potential of the cathode induces formation of surface oxides and drives continuous Co surface segregation. The dissolution of Co atoms at the surface increases the affinity of the surface to oxygenated and hydrogenated species and renders it less active towards the ORR.
In Situ and Ex Situ Characterization of Carbon Corrosion in PEMFCs
Authors: Fairweather Joseph D. , Li Bo , Mukundan Rangachary , Fenton J. , Borup Rodney L.
Published: October 2010

Carbon corrosion is an important degradation mechanism that impairs PEMFC performance through destruction of catalyst connectivity, collapse of pore structure, and loss of hydrophobic character. In this study, carbon corrosion was quantified in situ by measurement of carbon dioxide in fuel cell exhaust gases through non-dispersive infrared spectroscopy (NDIR). Performance degradation was also studied by a DOE protocol for catalyst support accelerated stress testing. Finally, changes in gas diffusion layer and microporous layer carbon surfaces were observed through an ex situ aging procedure.
Elaboration and Characterizations of Platinum Nanoparticles Supported on Cellulose-Based Carbon Aerogel
Authors: Rooke Joanna , Matos Camila , Chatenet Marian , Sescousse Romain , Budtova Tatiana , Berthon-Fabry Sandrine , Mosdale Renaut , Maillard Frédéric
Published: October 2010

This work investigates the deposition of Pt nanoparticles onto carbonized aerocellulose (CAC), via impregnation of the CAC with H2PtCl6 followed by reduction either under H2 at 300-400{degree sign}C or in a basic NaBH4 solution. H2 reduction yields uniform Pt nanoparticles (average diameter < 2 nm) dispersed over the CAC surface, as revealed by transmission electron microscopy (TEM). Larger agglomerates can be seen in TEM images for NaBH4 reduced samples, which is confirmed by powder X-ray diffraction (XRD). A rotating disk electrode was employed to analyze the electrochemical properties of the Pt/CAC materials. The active area of the platinum nanoparticles was evaluated using hydrogen adsorption/desorption cyclic voltammetry and CO-stripping measurements. The oxygen reduction reaction kinetic parameters of the Pt/CAC materials compare well with those of commercial Pt/Carbon Black (CB). Finally, PEMFC unit cell testing demonstrates that a Pt/CAC electrocatalyst synthesized using 3 successive impregnation/reduction steps can compete with state-of-the-art Pt/CB electrocatalysts.
MWNTs-Poly(3,4-ethylenedioxy Thiophene) and Polystyrene Sulphonic Acid Nanocomposite as a Catalyst Support for PEFCs
Authors: Mohanapriya Subramanian , Tintula Kottakat , Sridhar P. , Pitchumani S. , Shukla Ashok
Published: October 2010

A nanocomposite of MWNTs and poly(3,4-ethylenedioxythiophene)-poly(styrenesulphonate) is synthesized and characterized using Fourier-Transform Infra-Red spectroscopy (FTIR),Thermogravimetric analysis (TGA) and Scanning electron microscopy (SEM) in conjunction with Atomic force microscopy (AFM). X-ray diffraction (XRD) and electrochemical characterization performed on Pt/nanocomposite and Pt/MWNT reveal superior catalytic activity for Pt/nanocomposite under reduced platinum and Nafion loadings. It is found that mixed conducting nanoporous and inter-connected network of MWNTs and poly (3, 4-ethelendioxythiophene)-poly (styrenesulfonate) promotes the catalytic efficiency of platinum. The study suggests improved dispersion and consequent better catalyst utilization on nanocomposite support comprising MWNT and mixed (electronic and ionic) polymeric conductive components.
Effect of Electrolyte Polymer Acidity on Platinum Degradation in MEAs
Authors: Hirayama Tetsuaki , Kondo Jun-ichi , Taomoto Akira , Gyoten Hisaaki
Published: October 2010

We fabricated MEAs having the EW200 or EW1000 electrolyte in the catalyst layer. The potential cycle test (square-wave potential cycling between 0.6-1.0 V with a pulse width of 3 s) was performed for these MEAs to evaluate the ECA change from CVs. It was revealed that the ECA decrease of the EW200 MEA was 1.6 times faster than that of the EW1000 MEA. It was revealed that the onset shift of the platinum oxidation potential, caused by the sulfonic acid group adsorption [6], depended on the electrolyte EW. The shifts were 0.7 V and 0.8 V for the EW1000 MEA and the EW200 MEA, respectively. These differences would presumably affecte on the ECA change rate.
A Simple Synthesis Method of Sulfur-Free Fe-N/C Catalyst with High ORR Activity
Authors: Ding Zhongfen , Johnston Christina M. , Zelenay Piotr
Published: October 2010

To try to deconvolute factors affecting the activity and durability of nitrogen-metal-carbon (N-M-C) type non-precious catalysts for oxygen reduction reaction (ORR), N-M-C catalysts based on iron chloride, polyaniline (PANI) and Ketjen-black carbon were synthesized under different conditions. The catalysts were characterized electrochemically and tested as cathodes for hydrogen fuel cells. PANI is usually oxidatively polymerized using ammonium persulfate (APS). To eliminate sulfur in the synthesized catalysts, a simple synthesis method using iron(III) chloride as oxidant for aniline polymerization was developed. The catalyst synthesized using this simple method has ORR activity comparable to the state-of-the-art PANI-derived catalyst synthesized in a much more complicated procedure. The fact that sulfur sources are completely eliminated in the synthesis suggests that sulfur is not necessary for the ORR catalysis activity.
Catalytic Activity of Zirconium Based Cathode without Platinum for Oxygen Reduction Reaction
Authors: Ohgi Yoshiro , Ishihara Akimitsu , Matsuzawa Koichi , Mitsushima Shigenori , Ota Ken-ichiro , Matsumoto Masashi , Imai Hideto
Published: October 2010

Partially oxidized zirconium carbonitrides (Zr-CNO) powders were evaluated as a non-precious cathode for polymer electrolyte fuel cells. Zr-CNO powders were prepared from zirconium carbonitrides (ZrC0.5N0.5) with heat-treatment under controlled oxygen partial pressure from 10-3 to 10-22 atm at 1000oC. The voltammetry was performed to evaluate the catalytic activity for the oxygen reduction reaction (ORR) under nitrogen and oxygen in 0.1 mol dm-3 H2SO4 at 30oC. The catalytic activity for the ORR significantly improved with partial oxidation. In particular, the onset potential increased drastically with slight increase of ratio of cubic ZrO2 phase, and became constant over 0.90 V vs. RHE. XRD spectrum and the color of specimen indicated that the growing oxide phase had oxygen vacancies by substituting some of the oxygen atoms with nitrogen and carbon atoms. It is predicted that carbon and nitrogen atoms in starting material, ZrC0.5N0.5, may affect the production of oxygen vacancies according to TOF-SIMS measurements. Therefore, the defects such as oxygen vacancies in the Zr-CNO might affect the catalytic activity for the ORR.
New Multi Acid Side-Chain Ionomers for Proton Exchange Membrane Fuel Cells
Authors: Schaberg Mark S. , Abulu John E. , Haugen Gregory M. , Emery Michael A. , O'Conner Sara J. , Xiong Pa N. , Hamrock Steven
Published: October 2010

This work describes the modification of the sulfonyl fluoride precursor of perfluorinated sulfonic acids (PFSAs) by the conversion of the sulfonyl fluoride group to a bis sulfonylimide group. The usefulness of these new polymers for fuel cell applications includes novel proton exchange membranes, catalyst additives or tie layers designed to be thermally and chemically robust while operating within a fuel cell's harsh environment at higher temperatures.
Morphological Control of Electrospun Nafion Nanofiber Mats
Authors: Ballengee Jason , Pintauro Peter
Published: October 2010

There are a number of applications where Nafion must be electrospun into a nanofiber mat, including composite fuel cell membranes. Unfortunately, Nafion perfluorosulfonic acid polymer is notoriously difficult to electrospin and requires the presence of a high molecular weight carrier polymer in the electrospinning solution. In this paper, we report on the morphology of electrospun Nafion mats that were created using a low concentration (1-2 wt%) of poly(ethylene oxide) (PEO) as a carrier polymer. The average diameter of well-formed Nafion/PEO nanofiber mats ranged from 300 nm to 900 nm. The effects of electrospinning conditions, i.e., air humidity, polymer solution solvent, carrier polymer molecular weight, electrospinning voltage, and electrospinning flow rate, on the quality of the electrospun mat (the presence/absence of unwanted bead-on-fiber morphologies) and the mat-averaged nanofiber diameter are presented and discussed.
Rigid Rod Poly(p-Phenylene Sulfonic Acid) PEMs: High Conductivity at Low Relative Humidity Due to "Frozen-In-Free Volume"
Authors: Litt Morton , Granados-Focil Sergio , Kang Junwon , Si Kun , Wycisk Ryszard
Published: October 2010

Rigid-rod poly(p-phenylene sulfonic acids) were shown to have "frozen-in" free volume that enabled them to retain water at low relative humidity, generating very high conductivity; the best was 0.1 S/cm at 15% RH and 75C. Efforts to generate dimensional stability by grafting alkyl benzenes on the polymers worked well for poly(biphenylene disulfonic acid). Poly(phenylene disulfonic acid) grafting has not yet produced water stable PEMs.
Molecular Design Aspect of Sulfonated Polymers for Direct Methanol Fuel Cells
Authors: Kim Dae Sik , Guiver Michael , McGrath James , Pivovar Bryan , Kim Yu Seung
Published: October 2010

Molecular structural effects of sulfonated polymers for direct methanol fuel cells (DMFCs) are investigated using a length scale parameter, Percent Conducting Volume (PCV). Sulfonated polymers were categorized based on molecular composition (nanometer length scale) and polymer architecture (sub micrometer length scale) and plotted methanol permeability as a function of PCV and molecular structure. Polymers having functional group showed the least methanol permeability while fluorinated polymers showed the highest methanol permeability at a given PCV. DMFC performance of selected sulfonated polymers is presented in order to support the analysis.
Preparation and Characterization of New Sulfonated Partially Fluorinated Polyarylenesulfones and Their Blends with Polybenzimidazole
Authors: Katzfuß Anika , Krajinovic Katica , Chromik Andreas , Kerres Jochen A.
Published: October 2010

A novel partially fluorinated and sulfonated poly(arylene sulfone) was successfully synthesized via nucleophilic polycondensation of 2,2-Bis(4-fluorophenyl)hexafluoropropane with 4,4'-Thiobisbenzenethiol (TBBT). In a second step the prepared poly(arylene sulfide) was oxidized to poly(arylene sulfone). The polymer was blended with the polybenzimidazole PBIOO to obtain a mechanically stable membrane. This film was compared with other polymer blends, which were synthesized in our groups in the last years. All membranes were analyzed in terms of water uptake, thermal and oxidative stability. Additional the blend membranes were characterized by gel permeation chromatography (GPC). The novel poly(arylene)sulfone SPSO blend shows a high molecular weight and an excellent TSO3H, onset of 334°C. The proton conductivity is 0,11 S/cm and the water uptake reaches 30%.
Acidity Effect on Proton Conductivity of Hydrocarbon-Based Ionomers
Authors: Chang Ying , Bae Chulsung
Published: October 2010

A novel efficient sulfonation of aromatic polymer, which involves the iridium catalyzed C-H activation/borylation followed by the Suzuki coupling, was developed. Using this method three sulfonated moieties with different acidities (fluoroalkyl sulfonic, aryl sulfonic, and alkyl sulfonic acids) could be conveniently incorporated to the aromatic rings of polystyrene. The effect of structure of sulfonic acid group acidity on the proton conductivity was studied, and the results showed that ionomers with superacidic fluoroalkyl sulfonic acid outperformed the less acidic ionomers at low relative humidity.
Polymer Electrolyte Membranes Based on Sulfoethylcellulose and Poly(vinyl Alcohol) for Direct Methanol Fuel Cells
Authors: Kasai Yutaka , Okayama Toru , Abudula Abuliti
Published: October 2010

We have investigated the solvent uptake, thermal stability, tensile strength, proton conductivity, and the methanol permeability coefficient (PM) in aqueous methanol solutions for cross-linked sulfoethylcellulose/poly(vinyl alcohol) blend membrane (CL-SEC/PVA) and have investigated its applicability to direct methanol fuel cells (DMFC). CL-SEC/PVA membrane exhibits a proton conductivity of 0.017 S cm-1 at 25 ºC. CL-SEC/PVA membrane also shows low methanol permeability in methanol aqueous solutions. The membrane electrode assembly has been prepared by applying Nafion® as a binder in the catalyst layer. Performance of DMFC was estimated with different methanol concentrations. The open-circuit voltage is decreased with increasing the methanol concentration. CL-SEC/PVA membrane achieves the highest power density of 13mW cm-2 with 5M methanol solution at 25 ºC. The results suggest that CL-SEC/PVA membrane is potentially applicable to polymer electrolyte membranes for DMFC utilizing a high concentration methanol solution as a fuel.
Sulfonated Low-Cost Ionomers as Acidic Cross-Linkers for High-Temperature PBIOO Membranes
Authors: Kerres Jochen A. , Katzfuß Anika , Chromik Andreas
Published: October 2010

The low-cost polymers poly(styrene) and poly(α-methylstyrene) have been sulfonated in a first step. Then both sulfonated ionomers have been blended with PBIOO® (30 wt% sulfonated ionomer, 70 wt% PBIOO), the sulfonated ionomer serving as acidic cross-linker which enhances the PBIOO stability. Both membrane types were treated with Fentons Reagent to investigate their oxidative stability. Of particular interest was whether the poly(α-methylstyrene) ionomer was more stable against radical attack. It was indeed found that the PBIOO-sulfonated poly(α-methylstyrene) blend membrane showed less weight loss during and after Fenton Test than the respective poly(styrene sulfonic acid) PBIOO-containing membrane. The macromolecules are partially degrading by radical attack to the main chain of the sulfonated poly(α-methylstyrene) polymers but still remain in the blend membrane matrix due to acid-base interactions. Since the PBIOO/sulfonated poly(α-methylstyrene) blend membranes conserved their integrity even after Fentons Test they can be regarded as interesting low-cost high-T fuel cell membranes.
Novel Hybrid Heteropoly Acid/Polymer Ionomers with Very High Proton Conductivity
Authors: Horan James L. , Kuo Mei-Chen , Ziegler Zachary , Zhang Fan , Perdue Andrew S. , Jessop Jeri D. , Herring Andrew M.
Published: October 2010

We have fabricated proton conducting films using monomers based on vinyl substituted silicotungstic acid heteropoly acids (HPAs) and acrylate co-monomers. In this work we probe the morphology of this system based on increasing the weight loading of the HPA to 85 wt%. Although impressive proton conductivities can be achieved with these films under hotter and drier operating conditions than in conventional proton exchange membranes, the materials have mechanical limitations. We have begun to develop more practical systems in which ester and methylene groups are eliminated from the polymer backbone.
Polyimide-Based Electrolyte Modified with Siloxane Segments for Proton Transportation
Authors: Tseng Ji-Yong , Ye Yun Sheng , Hwang Bing-Joe
Published: October 2010

A series of copolymer electrolytes containing ODA-based sulfonated polyimide and siloxane segments in various ratios were prepared and characterized for direct methanol fuel cell applications. The prepared copolymer electrolyte membranes were flexible and showed good thermal stability as well as proton conductivity. A maximum proton conductivity of 5.78×10-2 S/cm was obtained for the SPI_DSX75 membrane at 90 åC. The transport properties of the membranes were found to be strongly influenced by water uptake and the number and nature of the ionic clusters in the hydrophilic domains. TEM analysis showed evidences for the phase segregation in the membranes and revealed the influence of flexible siloxane segments in ionic clustering.
Properties of Melt-Extruded vs. Solution-Cast Proton Exchange Membranes Based on PFSA Nanocomposites
Authors: Mokrini Asmae , Raymond Nathalie , Theberge Karine , Robitaille Lucie , Del Rio Carmen , Ojeda M.C. , Escribano Pilar Garcia , Acosta José Luis
Published: October 2010

This study examined the relationships between structure/morphology and properties of series of composite proton exchange membranes prepared using two processing techniques; solution-casting and melt-extrusion. Three families of inorganic fillers with different aspect ratios and specific areas have been used; spherical 60nm SiO2 nanoparticles, fiber-like sepiolite clay, and non-structured mesoporous silica. The results show that composite PEMs present in general higher water uptake than reference membranes; water uptake increases with the specific area of the filler, and translate to lower volume change and higher dimensional stability for the fillers with low specific area. Solution cast membranes show in general higher water uptake than extruded ones that translates to lower volume change and higher dimensional stability of extruded PEMs. Finally conductivity results show that at high levels of hydration, solution-cast membranes have in general higher conductivities than extruded samples, while at high temperature and reduced relative humidity conditions, melt extruded samples show higher conductivities.
Sulfonated Titanium Nanotubes Based Nanocomposite Blend Membranes for Fuel Cell Applications
Authors: Nancoo Kandice , Stewart Kerrilee , Missan Harinder Pal S.
Published: October 2010

New nano-composite electrolyte membranes with good electrical and mechanical properties have been developed using various blend compositions of poly(1-vinylimidazole) (PVIm), poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP) and trifluoromethansulfonic acid (TA) with sulfonated nano-tubular titania (sTNT). Sulfonated nano-tubular titania and nanocomposite membranes have been successfully synthesized using in house acid-functionalised nano-tubular titania which was synthesized using hydrothermal method. Investigations of the synthesized membranes yield results of elevated conductivity and stability at temperatures in excess of 120°C. Conductivity values of 10-3 S/cm have been noted within these membranes and the morphology has also been found to improve with the addition of sulfonated nano-tubular titania. The nano-composite membranes also shows decrease in the water uptake with the addition of nano-tubular titania.
Detection of OH Radicals Generated in Polymer Membranes of PEFC
Authors: Nosaka Yoshio , Ohtaka Kenji , Ohguri Nobuaki , Nosaka Atsuko Y.
Published: October 2010

OH radicals formed during the PEFC operation of a single cell were detected by means of a fluorescence probe method with coumarin. In polymer electrolyte, coumarin molecules were impregnated to react with OH radicals to form a highly fluorescent product, umbelliferone. By measuring the fluorescence intensity of the cross section of the membrane with a fluorescence microscope, the distribution of the OH radical density in the membrane could be evaluated for various operational conditions.
Development of a PEFC with Serpentine-Interdigitated Hybrid Pattern Gas Channels
Authors: Takazono Yasutaka , Tsuda Kazuto , Kitahara Tatsumi , Nakajima Hironori , Konomi Toshiaki
Published: October 2010

Serpentine-interdigitated hybrid pattern gas channels were developed for polymer electrolyte fuel cells (PEFCs). The performance of conventional (triple-serpentine channel), interdigitated and serpentine-interdigitated hybrid pattern gas channels were compared. The performance of the interdigitated channel is significantly higher than that of the conventional channel. However, the interdigitated channel causes flooding under high air utilization. The hybrid pattern channels have the highest performance of the three patterns. A through-pore ratio (A/A0) was also developed. This ratio indicates the level of flooding in the gas diffusion layer (GDL) under the rib. According to calculated values of this ratio, flooding is suppressed when using the hybrid pattern channels.
Effect of Flow Field Pattern and Microporous Layer on Gas Purge of a Polymer Electrolyte Fuel Cell
Authors: Nakajima Hironori , Kitahara Tatsumi , Konomi Toshiaki
Published: October 2010

The effect of flow field pattern and microporous layer (MPL) on the exhaust of the residual water at the flow channel, gas diffusion layer (GDL), and catalyst layer (CL) in the cathode of a polymer electrolyte fuel cell during gas purge after shutdown is separately studied for preventing freeze damage and efficient cold start below freezing point. The time variations of the high frequency and charge transfer resistances are obtained from electrochemical impedance spectroscopy to detect the drying of each component separately. This can be used to stop the purging appropriately to minimize energy consumption. An interdigitated type flow field drys the GDL substrate faster than a serpentine flow field. In addition, MPL drying process and its moisture retention effect on the drying of the CL and electrolyte membrane are observed. The serpentine flow field is shown to dry the MPL faster than the interdigitated type flow field.
Development of Low Cost PEMFC Metal Bipolar Plate
Authors: Zhang Lin , Finch Joshua , Gontarz Gerald , Wang Conghua
Published: October 2010

TreadStone has developed a proprietary design and processing technologies that have been applied on the commercially available 304SS and 316SS stainless steel foils. The treated SS foil has been used as the bipolar separate plate material to replace graphite in PEMFC, which will lead to 40~50% stack weight and volume reduction. We have demonstrated over 8500 hours stable operation of a small single cell using the SS bipolar plates. The cost analysis indicates that TreadStone's technology could reduce the cost to $3.53/kW for automobile applications.
Understanding Differences in the Performance of Laboratory Scale PEMFCs: I. The Effect of Active-Area
Authors: Opu Md. S. , Choi DongWoong , Ohashi Masato , Shimpalee Sirivatch , Van Zee John W.
Published: October 2010

The ability to compare, analyze, and interpret laboratory-scale experimental data for polymer electrolyte membrane fuel cells (PEMFCs) is often limited by differences in the performance between 25 cm2 and 50 cm2 active area cells. The present study includes the material of gas diffusion layers (GDL), their compression pressure, and the operating conditions to quantify and understand the effect of these factors on the performance of PEMFCs with different active area of electrodes. The experimental data show that under the same compression the internal compression pressure is higher for smaller cells compared to larger cells. Typically one assumes by increasing the compression pressure that the contact resistance is decreased and better performance is obtained. However, further increase of compression may cause mass transfer resistance inside of GDL due to the change of physical properties including pore size distribution.
Characterization of Proton Conduction in Nafion Membranes Using Current Sensing Atomic Force Microscopy
Authors: Kwon Osung , Wu Shijie , Zhu Da-Ming
Published: October 2010

We show that the local proton conductance distribution in Nafion membranes can be mapped using current sensing atomic force microscopy (CSAFM) to reveal the characteristic heterogeneity of proton channel structures of the membranes. From the current sensing images obtained using CSAFM, the averaged conductance of an individual proton channel and averaged density of the channels can be derived, and are found to be consistent with that obtained using other experimental methods. The method can be used to study microscopic changes in proton conducting properties of Nafion and other proton exchange membranes in aging and temperature cycling processes.
Influence of Hydrophilic and Hydrophobic Double MPL Coated GDL on PEFC Performance without Cathode Humidification
Authors: Kitahara Tatsumi , Nakajima Hironori , Konomi Toshiaki
Published: October 2010

Gas diffusion layers (GDLs) coated with a hydrophobic microporous layer (MPL) have been commonly used to improve the water management properties of polymer electrolyte fuel cells (PEFCs). In the present study, a new hydrophilic and hydrophobic double MPL coated GDL was developed to achieve further enhancement of PEFC performance without cathode humidification. A hydrophobic binder of polytetrafluoroethylene (PTFE) and a hydrophilic binder of polyvinyl alcohol (PVA) were used to coat the MPL on the carbon paper substrate. The hydrophilic layer is effective for conserving humidity at the catalyst layer, while the hydrophobic intermediate layer between the hydrophilic layer and the substrate prevents the removal of water in the hydrophilic layer via dry air in the substrate. Reducing the hydrophilic layer thickness to 5 μm was effective for enhancing PEFC performance. Appropriate enhancement of hydrophilicity by increasing the PVA content to 5 mass% was also effective for enhancing PEFC performance.
Innovative Hydrophilic MPL for Cathode Gas Diffusion Media (GDM)
Authors: Tanuma Toshihiro
Published: October 2010

In a departure from the conventional design of hydrophobic MPLs, the author conceived the idea of hydrophilic double MPLs. The hydrophilic layers are composed of carbon fibers and a hydrophilic polymer. The ratio of hydrophilic polymer to carbon fiber is designed to be low in the first layer (catalyst side) and high in the second layer (GDM side), in order that the two layers should function differently. The first layer removes liquid water from the cathode catalyst layer and the second layer retains water, thus preventing the membrane from drying-out. The MEA, which uses a cathode GDM with hydrophilic double MPLs, exhibits excellent performance under both high and low humidity conditions. This work clearly indicates that applying hydrophobic MPLs to the cathode GDM is not a golden rule in the design of MEAs.
Advanced Gas Diffusion Layers for PEM Fuel Cells
Authors: Stanic Vesna , Tatalovich Jason
Published: October 2010

One of the most critical components for proper water management and catalyst functioning in the proton exchange membrane fuel cell (PEMFC) is the Gas diffusion layer (GDL). This paper presents a preliminary study on advanced GDL performance characteristics in fuel cell environment. Off-shelf-carbon fiber based materials with promising microstructure typically used for applications other than PEM FC were employed for this study. The material electrochemical functionalities were evaluated in-situ and compared with standard Sigracet SGL 35 BC. The 5cm2 fuel cells were assembled with a 3-layer standard MEA and the GDLs and tested at 80{degree sign}C with 100% humidified gases at ambient pressure. The results show that the advanced GDL enhanced catalyst ECSA, and decreased fuel cell ohmic losses. Finally, the current status of the advanced GDL functionalization properties are discussed and future materials optimization is proposed.
A New Paradigm for PEMFC Ultra-Thin Electrode Water Management at Low Temperatures
Authors: Steinbach Andrew J. , Debe Mark K. , Wong Jimmy , Kurkowski Michael J. , Haug Andrew T. , Peppin Daniel M. , Deppe Sandy K. , Hendricks Susan M. , Fischer Edward M.
Published: October 2010

In this paper, we provide initial results of a novel method which dramatically improved the performance of ultra-thin electrode polymer electrolyte membrane fuel cells under highly water-condensing operating conditions, realized via modification of the anode gas diffusion layer and utilization of reduced anode reactant pressures, including sub-atmospheric pressure down to 20kPa. Measurements indicated that the sub-atmospheric anode reactant acted to greatly reduce the water flux exiting out the cathode, likely reducing cathode water flooding and oxygen transport limitations.
Investigation of Transport Properties, Microstructure, and Thermal Behavior of PEFC Catalyst Layers
Authors: Sun Che-Nan , More Karren L. , Zawodzinski T. A.
Published: October 2010

Several experimental techniques have been used to characterize the properties of ionomer in PFEC catalyst layers (CLs). NMR methods have been applied to determine the water motions at long-range (diffusion) and short-range (relaxation) in CLs. Our preliminary results suggest that the water diffusion in the ionomer phase is affected by the amount of catalyst particles (Pt/C) present in CLs. To further assess the factor(s) that might influence water diffusion in CLs, Transmission Electron Microscopy (TEM) has been conducted to investigate the dispersion of ionomer and catalyst particles in CLs. The composition effect on the CL structure will be discussed. In addition, thermal properties of CLs have been studied by modulated differential scanning calorimetry (MDSC) in an attempt to reveal polymer-Pt/C interactions. When compared with the thermal behavior of bulk Nafion (Nafion-112), additional features are observed in the MDSC 'kinetic' component during heating process. The nature of this feature is currently under investigation.
Pt Utilization Analysis at Low RH Condition
Authors: Shinozaki Kazuma , Yamada Haruhiko , Morimoto Yu
Published: October 2010

Pt utilization, i.e. the ratio of the electrochemically active Pt surface area of a MEA to the Pt surface area of the catalyst, was analyzed at 20-100%RH, 40-80°C. Pt utilization significantly decreased with decreasing RH for Pt/C catalysts in which Pt particles are supported not only on the carbon surface but also inside the carbon, while kept high even at low RH in the samples with Pt particles supported only on the carbon surface. We presume that this is because the Pt particles inside are not covered with ionomers and protons cannot access any longer at low RH.
In Situ, Through-Plane Measurements of Ionic Potential in a PEMFC Catalyst Layer
Authors: Hess Katherine C. , Epting William , Yu Ssu-Chieh , Litster Shawn
Published: October 2010

A novel apparatus for measuring in situ, through-plane, ionic potential distribution within the cathode catalyst layer of a polymer electrolyte membrane (PEM) fuel cell is presented here. This new diagnostic method makes use of a micro-structured electrode scaffold (MES), which is a stack of alternating insulating and sensing layers that surround a 100 µm diameter cylinder of catalyst layer material. Here we present measurements of ionic potential at four points through the thickness of a PEM fuel cell cathode. These preliminary results show significant variations of the ionic potential within the electrode at high currents. In addition, the local ionic potential provides an accurate measure of the local IR-free potential in the catalyst layer. Possible applications of the ionic potential data gathered from the MES include investigating mass and charge transport limitations, spatially characterizing electrode kinetics, and validating porous electrode models.
In Situ Measurement of Oxygen Partial Pressure in a Cathode Catalyst Layer
Authors: Epting William , Hess Katherine C. , Litster Shawn
Published: October 2010

A micro-structured electrode scaffold (MES) was developed for performing in-situ measurements of through-plane oxygen partial pressure (OPP) distributions in the cathode of a polymer electrolyte membrane fuel cell (PEMFC). Alternating layers of insulating material and platinum are stacked and bonded, and surround a 100 micron diameter hole filled with catalyst layer material. The platinum layers serve as ultra-microelectrodes, allowing the measurement of local OPP at discrete intervals through the catalyst layer thickness. Following an investigation of ultra-microelectrode sensitivity and repeatability, pulsed amperometric detection was selected over potentiostatic operation as the most effective method for performing OPP measurements. Using calibration points at the full air and zero OPPs, the OPP distribution at a fuel cell current density of 450 mA cm-2 was measured.
Relative Humidity Effect on Anode Durability in PEMFC Startup/Shutdown Processes
Authors: He Ping , Cheng Tommy , Bashyam Rajesh , Young Alan P. , Knights Shanna
Published: October 2010

Ru dissolution and crossover to the cathode from PtRu anode catalysts, which are commonly used in polymer electrolyte membrane fuel cells (PEMFCs) to provide CO tolerance for reformate-based fuel cell applications, have been previously identified as critical durability issues. In this investigation, the effect of relative humidity (RH) on Ru dissolution and crossover was studied using an anode accelerated stress test (AST) to mimic anode potential variation that occur during fuel cell start-ups and shut-downs. Stress testing at lower RH resulted in less Ru degradation, which was indicated by changes in cyclic voltammetry (CV), namely CO stripping peak shifts. The relative degree of Ru crossover was also reflected by the decreases in cell performance and CO tolerance. The results highlight the critical role of water in the Ru degradation mechanism and indicate that controlling the RH could be an effective strategy to mitigate Ru crossover.
AC Impedance and Transient Technique Based PEFC Diagnostics: Insights from Submillimeter Resolved Local Measurements in Channel and Land Areas
Authors: Schneider Ingo A. , Von Dahlen Steffen , Bayer Michael H. , Scherer Günther G. , Wokaun Alexander
Published: October 2010

An experimental approach for submillimeter resolved current distribution measurements in Polymer electrolyte fuel cells (PEFCs) is presented. The approach is employed for locally resolved in situ diagnostics in channel and land areas. Thereby, we focus on laterally resolved transient techniques. The results of ac impedance, voltage step, and cyclic voltammetry experiments demonstrate that phenomena, which occur as a result of inhomogeneous operation of PEFCs in the down the channel direction typically on a length scale of tens of centimeters, have their counterpart on the millimeter scale of channels and ribs in the direction perpendicular to the flow channels. Both must be treated with same attention.
Investigation of Catalyst Ink Dispersion Using Small Angle X-ray and Small Angle Neutron Scattering
Authors: Xu Fan , Zhang HangYu , Ho Derek , Ilavsky Jan , Justics Matt , Petrache Horia , Stanciu Lia , Xie Jian
Published: October 2010

One of the major aims of this investigation is to fill the gap of the micro-structural organization of ionomer particles and Pt/C aggregates dispersed in a catalyst ink. The dispersion of Nafion® ionomer particles and Pt/C catalyst aggregates in liquid media was studied using ultra small angle x-ray scattering (USAXS) and cryogenic TEM technologies. A systematic approach was taken to study the dispersion of each component (i.e. ionomer particles and Pt/C aggregates) first, then the combination, last the catalyst ink. A multiple curve fitting was used to extract the particle size, size distribution and geometry from scattering data. The results suggest that the particle size, size distribution and geometry of each system are not uniform, rather, vary significantly. The results also indicate that interaction among components (i.e. ionomer particles and Pt/C aggregates) exists. The cryogenic TEM, by which the size and geometry of particles in a liquid can be directly observed, was used to validate the scattering results, which shows the excellent agreement. Based on this study, a methodology of analyzing dispersion of Pt/C particles, Nafion particles in a catalyst ink has been developed and it can serve as a powerful tool for making a desired catalyst ink which is the crtical step for making rational designed MEA.
Start-Stop Phenomena in Channel and Land Areas of a Polymer Electrolyte Fuel Cell (PEFC)
Authors: Von Dahlen Steffen , Scherer Günther G. , Wokaun Alexander , Schneider Ingo A.
Published: October 2010

In this work, we focus on effects of the flow field design and the operation conditions on local current transients, which are induced by start-up and shutdown processes in a polymer electrolyte fuel cell (PEFC). Submillimeter resolved in situ diagnostics are employed for the measurement of local current transients in the areas of channel and land. Local current transients have been proposed to play a significant role in the degradation of the catalyst layer. Therefore, start-stop processes are evaluated as a source for degradation by using local CO stripping voltammetry. In addition, local effects of proposed mitigation strategies are presented. First results of local degradation in channel and land areas indicate a higher degradation in the land areas after a series of start-stop cycles.
Tomographic Imaging of Water Injection and Withdrawal in PEMFC Gas Diffusion Layers
Authors: Gostick Jeff T. , Gunterman Haluna , Kienitz Brian , Newman John , MacDowell Alastair , Weber A.
Published: October 2010

X-ray computed tomography was used to visualize the water configurations inside gas diffusion layers for various applied capillary pressures, corresponding to both water invasion and withdrawal. A specialized sample holder was developed to allow capillary pressure control on the small-scale samples required. Tests were performed on GDL specimens with and without hydrophobic treatments.
In Situ Imaging of Water Distribution in a Gas Diffusion Layer by Neutron Radiography
Authors: Gao Yan , Nguyen Trung V. , Hussey Daniel S. , Jacobson David
Published: October 2010

In this study, neutron imaging was used to study water transport in a gas diffusion layer (GDL) during liquid water imbibition and drainage. It was shown that the liquid water saturation level in the GDL above the ribs was less than that above the channels, illustrating the role of the flow field elements on the local water distribution in the GDL. The difference in the liquid saturation level was attributed to the higher compression level of the GDL above the ribs leading to different morphological properties and, consequently, transport properties. Once liquid water breakthrough was reached, water was observed to flow through a single pathway. These results demonstrate that the assumption of isotropic transport properties of the GDLs in PEM fuel cell models needs to be reconsidered.
Characterization of the PEMFC Catalyst Layer by Cross-Sectional Visualization and Performance Evaluation
Authors: Suzuki Takahiro , Tsushima Shohji , Hirai Shuichiro
Published: October 2010

Cross-sectional visualization and performance evaluation of catalyst coated membranes (CCMs) having different Nafion® and carbon content ratio (N/C) in catalyst layers (CLs) of a proton exchange membrane fuel cell (PEMFC) were performed by using cross-sectional polishing (CP) method and scanning electron microscopy (SEM). It was revealed that the cell performance was clearly related with the CL structures. In N/C=1.0, sufficient proton, electron, and oxygen paths are likely established and thus the relatively higher cell performance per Pt loading was obtained. On the other hand, in N/C=3.0, insufficient transport paths were synthesized due to plugging nano-scale pores by the Nafion® ionomer. In addition, there is a possibility that effective gas diffusivity is higher in N/C=0.3 because of increasing porosity.
Digital Volume Imaging of the PEFC Gas Diffusion Layer
Authors: Mukherjee Partha P. , Shim Eunkyoung , Mukundan Rangachary , Borup Rodney L.
Published: October 2010

The gas diffusion layer (GDL) plays a key role in the overall performance/durability of a polymer electrolyte fuel cell (PEFC). Of profound importance, especially in the context of water management and flooding phenomena, is the influence of the underlying pore morphology and wetting characteristics of the GDL microstructure. In this article, we present the digital volumetric imaging (DVI) technique in order to generate the 3-D carbon paper GDL microstructure. The internal pore structure and the local microstructural variations in terms of fiber alignment and fiber/binder distributions are investigated using the several 3-D thin sections of the sample obtained from DVI.
Water Balance Simulations of a PEM Fuel Cell Using a Two-Fluid Model
Authors: Berning Torsten , Odgaard Madeleine , Kær So̸ren
Published: October 2010

A previously published computational multi-phase model of a polymer-electrolyte membrane fuel cell has been extended in order to account for the anode side and the electrolyte membrane. The model has been applied to study the water balance of a fuel cell during operation under various humidification conditions. It was found that the specific surface area of the electrolyte in the catalyst layers close to the membrane is of critical importance for the overall water balance. Applying a high specific electrolyte surface area close to the membrane (a water-uptake layer) always leads to a lower net water transport coefficient. Thus we can reduce flooding at the cathode and may obtain improved cell performance due to a better humidified membrane. The results also suggest that membrane dehydration may occur at either anode or cathode depending on the net water transport.
Modeling the Dynamic Behavior of Proton-Exchange Membrane Fuel Cell
Authors: Olapade Peter O. , Mukundan Rangachary , Davey John , Borup Rodney L. , Meyers Jeremy P.
Published: October 2010

A two-phase transient model that incorporates the permanent hysteresis observed in the experimentally measured capillary pressure of GDL has been developed. The model provides an explanation for the difference in time constants between membrane hydration and dehydration observed in the HFR experiments. When there is liquid water at the cathode catalyst layer, the time constant of the water content in the membrane is closely tied to that of liquid water saturation in the cathode catalyst layer, as the vapor is already saturated. The water content in the membrane will not reach steady state as long as the liquid water flow in the cathode catalyst layer is not at steady state. Also, increased resistance to proton transport in the membrane is observed when the cell voltage is stepped down to a low value, with a corresponding large increase in current.
Numerical Simulation of Transport Phenomena in Proton Exchange Membrane Fuel Cell with Multichannel Serpentine Flow Fields
Authors: Hu Guilin , Fan Jianren
Published: October 2010

The flow field structure has important effect on the flow characteristics and cell efficiency. So the flow field design and optimization becomes an important method to improve fuel cell's performance. A steady three-dimensional mathematical CFD based model presented in the author's previous paper is applied to investigate spatial distribution of local gas flow field, species concentration and local current density in the PEMFC with multi-channel serpentine flow field in this paper. Numerical study was conducted on a small-scaled single proton exchange membrane fuel cell (the electrode active area 5.9*6.1 cm2). Based on the model, spatial distribution of characteristic parameters as species concentration, fluid flow, local current density and pressure are computed. The flow characteristics and transport mechanism inside the fuel cell are discussed and analyzed. Results indicate that current density is relatively uniform with this design, and cell can offer promise good performance.