bluuebunny/crossref_metadata_2025 huggingface dataset:
Titania Supported Platinum Catalyst with High Electrocatalytic Activity and Stability for Polymer Electrolyte Membrane Fuel Cell
Authors: Huang Sheng-Yang , Ganesan Prabhu , Jung Won Suk , Cadirov Nicholas , Popov Branko N.
Published: October 2010

Titania supported Pt electrocatalysts (Pt/TiO2) were synthesized and investigated as alternative cathode catalysts for polymer electrolyte membrane fuel cells (PEMFCs). Transmission electron microscope (TEM) images revealed uniform distribution of Pt nanoparticles (dPt = 3-5 nm) on the TiO2 support. In-house developed accelerated durability test (ADT, continuous potential cycling between 0.6 and 1.4 V) in half-cell condition indicated nearly ten-fold higher ORR activity (1.20 mA cm-2) when compared to the Pt/C catalyst (0.13 mA cm-2). The Pt/C catalyst showed no activity in fuel cell testing after 2000 potential cycles due to severe carbon corrosion, Pt dissolution, and catalyst particle sintering. Conversely, the Pt/TiO2 electrocatalyst showed only a small voltage loss (0.09 V at 0.8 A cm-2) even after 4000 cycles. The ADT results showed excellent stability for the Pt/TiO2 electrocatalysts at high potentials in terms of minimum loss in the Pt electrochemical surface area (ECSA).
RuxTi1-xO2 as Catalyst Support for PEM Fuel Cell
Authors: Lo Chih-Ping , Kumar Amod , Ramani V.
Published: October 2010

Electrochemical stability and electrocatalytic activity of Pt supported on RuxTi1-xO2 were examined. The binary metal oxides were found to possess high stability during potential cycling between 0 and 1.8 V. The ECA of Pt/ RuxTi1-xO2 changes slightly after up to 1000 cycles, which suggests a strong interaction between Pt particles and the metal oxides. The synthesized RuO2 showed low BET surface areas, which may cause the low ECA and performance of Pt/ RuO2. Thus, RuxTi1-xO2 may be a promising material as a stable support for PEM fuel cells with increased specific surface area.
Enhancing the Catalytic Performance of Pt/C Catalysts Using Steam-Etched Carbon Blacks as a Catalyst Support
Authors: Wang MeiXian , Xu Fan , Liu Qi , Sun HongFang , Cheng Ruihua , He Hao , Stach Eric , Xie Jian
Published: October 2010

XC-72 carbon blacks were etched using steam for different times and used as a catalysts support for oxygen reduction reactions. Transmission electron microscopy (TEM) results show that the center parts of the XC-72 were more easily etched away. X-ray diffraction shows that the 002 and 10 peaks of the XC-72-based samples are initially sharp, but then broaden during the corrosion process. TEM shows that the steam etching can improve the Pt dispersion uniformity on the surface of the support and decrease the Pt particle size. Electrochemical characterization shows that the mass activity of a sample etched for 1h was better than that of the unetched samples and a commercial catalyst. The electrochemically active surface area of the samples was also significantly increased after etching. Steam etching is a simple and efficient method to increase the performance of the fuel cells catalysts.
Preparation and Characterization of Graphitic Particles as Alternative Support for Oxygen Reduction Reaction Catalysts in Fuel Cells
Authors: Wang MeiXian , Xu Fan , Sun HongFang , Liu Qi , Artyushkova Kateryna , Stach Eric , Xie Jian
Published: October 2010

The suitability of a nanoscale graphite as polymer electrolyte membrane fuel cells (PEMFCs) catalyst support were evaluated and compared with that of most popular commercial catalysts on Vulcan XC72 carbon black. It is observed that the distribution and structure of Pt nanopartcles for the synthesized catalyst and commercial catalysts is similar. The synthesized Pt catalysts show a better electrochemical surface area (ECSA). The accelerate degradation tests were performed by a glassy carbon rotating disk electrode, the results show that ECSA loss after 1500th cycling was 46.92% and 62.2% while mass activity loss was 59.2% and 97.9% for the synthesized catalyst and commercial catalyst, respectively. The temperature programmed oxidation results also show that the synthesized catalysts have better resistance against the corrosion. The obtained results show that the nanoscale graphite can be a promising alternative to the traditional used Vulcan XC72 carbon black as electrocatalyst support.
Defects on Graphene with and without Nitrogen
Authors: Kattel Shyam P. , Kiefer Boris , Atanassov Plamen
Published: October 2010

We have used density functional theory calculations to study the stability of high density bulk defects in carbon with and without nitrogen. It was found that all the structures are energetically unstable, and the stability of the defects decreases with increasing number of nitrogen atoms independent of synthesis route and the carbon reference state. The results also highlight the significance of stabilizing factors for these defects, such as transition metals which are often used during synthesis of the carbon supports.
Morphological Origins of the Enhanced Durability of a Pt/C Electrocatalyst Derived from Nafion®-Stabilized Colloidal Pt Nanoparticles
Authors: Curnick Oliver J. , Mendes Paula , Pollet Bruno
Published: October 2010

The degradation behavior of Pt/C electrocatalysts derived from Nafion®-stabilized colloidal Pt was found to be dependent on their morphology. Catalysts having agglomerated Pt particles showed significantly enhanced durability compared with those having well-dispersed Pt, and compared with a commercial (E-Tek) Pt/C catalyst. It is proposed that the preparation route starting from Nafion®-stabilized colloidal Pt results in a highly-effective distribution of Nafion® within the catalyst layer, which enhances durability via inhibition of particle growth mechanisms.
New Approaches to Non-PGM Electrocatalysts Using Porous Framework Materials
Authors: Goenaga Gabriel , Ma Shengqian , Yuan Shengwen , Liu Di-Jia
Published: October 2010

The catalytic oxygen reduction reaction (ORR) at the cathode is a critical process to proton exchange membrane fuel cell (PEMFC) operation. The current catalyst materials of choice are platinum group metals (PGMs) with high costs and limited reserves. Reported herein are our recent efforts in developing non-PGM electrocatalyst materials using rational design and synthesis. A variety of porous organic materials were developed as the catalyst precursors for preparing of ORR catalysts with high surface area and active site density free of carbon support. Electrocatalytic activities and physical properties of the new catalysts were investigated by various techniques in the process of understanding of the active site formation.
Multistep Pyrolysis of Fe Phthalocyanine and Phenolic Resin for Nonprecious Metal Cathode Catalysts
Authors: Nabae Yuta , Wu Libin , Moriya Shogo , Matsubayashi Katsuyuki , Kuroki Shigeki , Kakimoto Masa-aki , Ozaki Jun-ichi , Miyata Seizo
Published: October 2010

Pyrolysis protocol of a mixture of Fe phthalocyanine and phenolic resin was studied to develop non-precious metal cathode catalysts for PEMFCs. Multi-step pyrolysis of the precursor improves both catalytic activity and durability of the resulting carbon materials. The maximum output with these catalysts is 0.42 W cm-2, at 0.2 MPa and 80ºC.
Novel System of Electrocatalysts for Oxygen Reduction Based on Organic Metal Complexes in Acidic Media for PEMFCs
Authors: Qiao Jinli , Lin Rui , Liu Jianshe , Ma Jianxin
Published: October 2010

This work reports the preparation and characterization of novel organic metal complexes with N2O2 coordination structure for oxygen reduction reaction (ORR) in acidic media, bis[(N-2,6-diisopropylphenyl)salicylaldimine], bis[3-methyl-(N-2,6-diisopropylphenyl)salicylaldimine] and bis[3-isopropyl-(N-2,6-diisopropylphenyl)salicylaldimine] coordinating to Ni(II) (deﬁned as [Ni(diph)], [Ni(bmdiph)] and [Ni(bidiph)], respectively). The catalytic activity was found to depend strongly on the heat-treated temperature and the structural property. The resulting Ni(bmdiph)/C of 40/60 ratio with no heat treatment shows much better catalytic performance in terms of ORR than that at 100oC and 200oC but lower than that at 400oC. Also, Ni(bmdiph) shows better catalytic performance in terms of ORR than Ni(diph) and Ni(bidiph) do. Results of electrochemical characterization, which was performed using a rotating disc nelectrode (RDE) by cyclic voltammetry (CV) and liner sweep voltammetry (LSV), with emphasis on the activity of the catalyst are presented.
Non-Noble Metal Catalysts Prepared from Fe in Acid Solution
Authors: Hatchard Tim , Dahn Jeff
Published: October 2010

Non-noble metal catalysts (NNMC) have been prepared from iron in acidic solution by imbibing the solution into a porous activated carbon. Rotating ring disk electrode (RRDE) measurements have been performed along with 24 hour electrolysis at 600 mV. These catalysts are found to be very active for oxygen reduction and have good stability over time.
Morphology and Performance of Stretched PFSA for Direct Methanol Fuel Cells
Authors: Zhang Wenjing , Kish Daniel Lee , Pintauro Peter
Published: October 2010

Uniaxial stretching was used to promote desirable morphological changes to membranes composed of 3M Corporation's 825 equivalent weight (EW) perfluorosulfonic acid (PFSA) polymer. Stretching of solution cast PFSA films to a draw ratio of 4 was carried out prior to a high temperature annealing step. Film stretching increased the polymer crystallinity by 22% with an improvement in the membrane's mechanical properties. There was a small increase in proton conductivity after stretching, with a substantial decrease in methanol permeability. In direct methanol fuel cell tests at 60 degC and 1.0 M methanol, the power density at 0.4 V with a stretched 3M 825 EW membrane was 72 mW/cm2, which was considerably greater that that obtained with a solution cast unstretched membrane (28 mW/cm2) or with a commercial Nafion 117 membrane (55 mW/cm2).
Synthesis of Benzimidazole Tethered Perfluoropolymer/Perfluoromacromolecules for High Temperature Fuel Cell Applications
Authors: Ding Zhongfen , Kim Dae Sik , Labouriau Andrea , Kim Yu Seung
Published: October 2010

Fuel cells running at high temperatures have the advantage of higher energy efficiency, simpler water management and enhanced CO tolerance etc. However, Nafion® loses proton conductivity at high temperatures (ca. >100oC) due to water evaporation. Heterocyclic structures such as imidazole (Im) and benzimidazole (BIm) groups can replace water as proton carriers at high temperatures. Polybenzimidazole and Im, or BIm tethered hydrocarbon polymer are promising candidates for high temperature membranes. However, most of these polymers have very rigid backbone structure, which limits the application of these materials as ionomers in the electrodes as it is very hard for the rigid polymer chains to reorganize into efficient H+/e/gas conducting active sites. In this study, we synthesized benzimidazole (BIm) tethered perfluoropolymers (PF) or perfluoromacromolecules to be used as ionomers for electrode binder. The synthesized BIm-PF and Im-PF have PF flexible chain structure of both the backbones and side chains. The solubility of these BIm-tethered perfluoromaterials is very limited.
Membrane Performance and Durability under Automotive Fuel Cell Operation Conditions
Authors: Li Jing , Wang Keping , Yang Yunsong
Published: October 2010

In the present research, long side chain (LSC) and short side chain (SSC) PFSA are evaluated for automotive fuel cell applications. Performance of the MEAs under low inert gas RH and hot condition was improved by replacing the LSC membranes with SSC membranes due to increase of the ion exchange capacity (IEC) (decrease of ionomer equivalent weight (EW)). There was no significant performance gain by further increasing the IEC of ionomers. One of the trade offs was gas crossover increasing with on increase of the IEC, which impacts on the fuel efficiency and driving range. A compromise with durability was also observed in the cyclic OCV lifetime test (an accelerated stress test (AST)).
Ionomers with Highly Fluorinated Side Chains for Use in Battery and Fuel Cell Applications
Authors: Gervais Matthieu , Miller Adam D. , Kerr John B.
Published: October 2010

Polymers with pendant double bonds were synthesized by functionalization of a ready backbone with polysulfone or through polymerization of monomers that contain a relatively unreactive double bond under the polymerization reaction conditions. Styrene-based monomer and epoxides were polymerized through an anionic mechanism leading to polymers with polydispersity indexes of 1.23 and 1.21 respectively. Fluorinated lithium salts were linked to the polymers through platinum-catalyzed hydrosilylation of the pendant double bonds prior to an ion-exchange with an acid. The conductivities of the resulting ionomers were measured giving a maximum conductivity of 3 mS/cm for a polysulfone functionalized with a fluorinated sulfonimide
Effect of Pore Size Distribution on Cathode Performance of Membrane-Electrode Assembly with a Hydrocarbon-Based Binder
Authors: Kawaji Jun , Suzuki Shuichi , Takamori Yoshiyuki , Mizukami Takaaki , Morishima Makoto
Published: October 2010

The relationship between pore size distribution and cathode performance was investigated for membrane-electrode-assemblies (MEAs) with a hydrocarbon-based (HC) binder and a poly (perfluorosulfonic acids) (PFSA) binder. The MEA with an HC binder exhibited a higher gas diffusion resistance than that with the PFSA binder. The pore size distribution measurement revealed that the HC binder was likely to cover a larger area of the carbon support surface compared with a PFSA binder, and that a large amount of the HC binder easily penetrated the primary pores inside Pt/C agglomerates, which decreased the volume of the pores. Conceivably, the HC binder in primary pores blocked the oxygen diffusion to the cathode catalyst. Based on the above consideration, we focused on increasing the primary pore volume. Consequently, the volume was doubled, and therefore, the gas diffusion resistance at 0.25 A cm-2 was successfully reduced from 1600 to 410 mΩ cm2.
Highly Sulfonated and Highly Cross-Linked Poly(ether Ether Ketone) Proton Exchange Membranes
Authors: Zhou Shuhua , Kim Jieun , Kim Dukjoon
Published: October 2010

Sulfonated poly(ether ether ketone) with pendant carboxylic acid groups was synthesized and used to prepare polymer electrolyte membranes for fuel cell applications. The cross-linking was employed to limit the extreme water uptake and improve the dimensional stability of the membrane. compared with Nafion 117, this cross-linked membranes were likely far more robust. The proton conductivity, water uptake, methanol permeability, thermal stability and cell performance were investigated in order to evaluate its fuel cell applications. The CSPEEK-20% membrane exhibited a high proton conductivity of 0.05 S cm-1, a methanol permeability of 4.3×10-7 cm2 s-1, and a water uptake of 21%. This especially good cell performance, and high oxidative and hydrolytic stability operation suggested that this cross-linked membrane is a promising candidate in fuel cell applications.
Phosphonic Acid Based Proton Exchange Membrane
Authors: Schlichting Gregory J. , Horan James L. , Herring Andrew M.
Published: October 2010

Phosphonic acid based fuel cell membranes show promise for making polymer electrolyte membranes that can operate at higher temperatures, >100C and low relative humidity. A copolymer of vinyl phosphonic acid with vinyl zirconium phosphonate has been synthesized into a clear, flexible, amorphous membrane. Chemical characterization has been accomplished using EDX, FTIR and CPMAS NMR. XRD and SAXS have been used to confirm an amorphous nature. EIS and PFGSE NMR have been used to characterize the ionic transport through the membrane on different length scales.
Proton Conduction Mechanism in H3PO4 Imbibed PEMs: The Effect of Chemical Structure and Steam
Authors: Daletou Maria , Kallitsis Jannis , Neophytides Stylianos G.
Published: October 2010

The proton conduction mechanism was studied in H3PO4 acid imbibed electrolytes by means of AC impedance spectroscopy for conductivity and polarization resistance measurements and thermogravimetric analysis to determine the hydration level of the membrane. It was found that the enthalpy of hydration varies between -73 and -119kJ/mol for 0mol H2O/mol H3PO4 hydration level, higher than that of H2O and H3PO4 alone, which demotes strong interaction of the water molecules with the polymer matrix. Proton conductivity is enhanced even by an order of magnitude by exposing the polymer electrolyte to water partial pressure up to 12kPa, while the activation energy of the process varies between 11 and 22kJ/mol. The significant increase in activation energy can be attributed to the strengthening of the H bonds of the H2O/H3PO4/membrane network. This increases the barrier of hydroniun/water molecules reorientation for the accomplishment of the structural diffusion/transport of proton.
Influence of the Molecular Structure on the Properties and Fuel Cell Performance of High Temperature Polymer Electrolyte Membranes
Authors: Kallitsis Joannis K. , Geormezi Maria , Gourdoupi Nora , Paloukis Fotis , Andreopoulou Aikaterini K. , Morfopoulou Christina , Neophytides Stylianos G.
Published: October 2010

Aromatic polysulfones containing 2,5-bis(4-hydroxyphenyl) pyridine, or tetramethyl-biphenyl-diol units or 2,5-bis(4-methyl phenyl)-hydroquinone have been synthesised employing various comonomers' ratios. The resulting soluble high molecular weight copolymers were thoroughly investigated as potential electrolytes for high temperature PEM fuel cells. Excellent film forming properties, mechanical integrity, as well as high thermal and oxidative stability were confirmed for all the polymeric materials. The above characteristics, in combination with the high phosphoric acid doping level which results in conductivities in the range of 10-2 S cm-1, enabled the use of these poylelctrolytes as the proton conducting membranes in fuel cells operating at temperatures up to 200°C. A discussion on the effect of the chemical structure on the membranes' properties and fuel cell performance is herein presented.
Investigation of Advanced Hybrid PEM Based on Sulfonyl Fluoride PFSA and Grafted Inorganic Nanoparticles
Authors: Mokrini Asmae , Siu Ana , Robitaille Lucie , Gonzalez Leandro , Sanchez Felix
Published: October 2010

Nano-composite polymer electrolyte membranes were prepared by melt processing of sulfonyl fluoride form of perfluorosulfonic acid (PFSA) ionomer and two families of inorganic nanofillers, spherical nanoparticles of silicon dioxide prepared by sol-gel, and clay sepiolite ungrafted and grafted with alkyl-sulfonic acid moieties. This approach produces hybrid electrolyte membranes with substantially better properties when compared to reference (neat polymer) and commercial Nafion. The melt-extruded nano-composite electrolytes showed very efficient dispersion of the inorganic fillers, an overall improvement in thermal and dimensional stability, and improved conductivities between 10-2 to 10-3 S.cm-1 at 80{degree sign}C over the entire humidity range from 100 to 30%.
Chemical Degradation of Membrane Polymer Model Compounds under Simulated Fuel Cell Conditions
Authors: Schiraldi David A. , Savant Deepa , Zhou Chun
Published: October 2010

Peroxide radical degradation is widely accepted as one of the key mechanisms by which PEM fuel cell membranes are eroded and ultimately fail. Testing of the mechanism of such failures is difficult, given the intractable nature of typical PEM polymers, and the low levels of degradation necessary to bring about failure. By use of low molecular weight model compounds, the mechanism of chemical degradation of both perfluorinated and hydrocarbon-based membranes can be simulated. These tests tell a clear story that common organic chemical reactivity patterns are followed, both polymer backbone carboxylic acid groups and side chain ether linkages are weak in perfluoro PEM materials, and that aromatic groups can be hydroxylated, and ether groups cleaved in hydrocarbon systems.
Investigation of Molecular Probes Sensitivity to the Fenton Reaction Using Fluorescence Spectroscopy
Authors: Prabhakaran Venkateshkumar , Arges Christopher G. , Ramani V.
Published: October 2010

A fluorescence spectroscopy system has been set up for studying the interaction of molecular probes (fluorescent dyes) with hydroxy and hydroperoxy radicals. From this work, a method will be developed for in-directly monitoring the chemical degradation of the Nafion® membrane in-situ during fuel cell operation. Different molecular probes (Fluorescein and 6-carboxy Fluorescein) have had their fluorescence signal assessed in solvent environments of varying pH. Stern-Volmer relationships have been observed and fitted to correlate hydrogen peroxide concentration to fluorescent signal quenching. Additionally, free radical scavengers were added to formulations and have shown to mitigate the free radical attack on the molecular probe.
Acceleration of Chemical Degradation of Perfluorosulfonic Acid Ionomer Membrane by Mechanical Stress: Experimental Evidence
Authors: Yoon Wonseok , Huang Xinyu
Published: October 2010

The authors report experimental evidence of interactions between chemical degradation rate and mechanical stress for perfluorosulfonic acid membrane. A modified gas phase Fenton's test was used for this study. Mechanical stress was applied to iron impregnated NRE211 membranes while chemical degradation was occurring via Fenton's reaction. After the aging test, the fluoride ion released from the sample membrane was measured. The membrane samples were also analyzed by FTIR. The test results suggest that mechanical stress accelerates the rate of chemical decomposition of perfluorosulfonic acid membranes, identified by the increase in fluoride emission from the membrane and the increase in concentration of carboxylic (COOH) end groups in the membrane when mechanical stress was applied to the sample under gas phase Fenton tests.
Mixed Hydrocarbon/Fluoropolymer Membrane/Ionomer MEAs for Durablity Studies
Authors: Li Bo , Kim Yu Seung , Mukundan Rangachary , Wilson Mahlon S. , Welch Cynthia , Fenton J. , Borup Rodney L.
Published: October 2010

The durability of polymer electrolyte membrane (PEM) fuel cells is a major barrier to the commercialization of these systems for stationary and transportation power applications. Commercial viability depends on improving the durability of the fuel cell components to increase the system reliability. The aim of this work is to separate ionomer degradation from membrane degradation via mixed membrane / ionomer MEA experiments. The challenges of mixed MEA fabrication due to the incompatibility of the membrane and the electrode are addressed. OCV accelerated testing experiments (AST) were performed. Development of in situ diagnostics and unique experiments to characterize the performance and properties of the ionomer in the electrode as a function of time are reported. These measurements, along with extensive ex situ and post-mortem characterization, can delineate the degradation mechanisms in order to develop more durable fuel cells and fuel cell components.
Influence of Different Gas Diffusion Layers on the Water Management of Polymer Electrolyte Unitized Reversible Fuel Cell
Authors: Ito Hiroshi , Maeda Tetsuhiko , Nakano Akihiro , Hwang Chul Min , Ishida Masayoshi , Yokoi Naoto , Hasegawa Yasuo , Kato Atsushi , Yoshida Tetsuya
Published: October 2010

Unitized reversible fuel cells (URFC) combine the functionality of a fuel cell and electrolyzer in one unitized device. For a URFC with proton exchange membrane, the Ti-felt is applied to the GDL substrate at the oxygen electrode, and responsible for an optimum humidification state and liquid water distribution in the catalyst layer during both operations of a fuel cell and an electrolysis. The experimental result indicates that the loading PTFE on the Ti-felt substrate brings a negative effect on the mass transport of liquid and gas during the fuel cell operation and no effect on the electrolysis performance. The larger fiber diameter of Ti-felt brings better performance of the fuel cell, whereas the electrolysis performance is degraded.
Investigation of Two-Phase Transport in Polymer Electrolyte Fuel Cell Channels Using the Volume of Fraction Method
Authors: Cho Sung Chan , Wang Yun
Published: October 2010

Two-phase flow in the gas channel of a polymer electrolyte fuel cell (PEFC, also called PEM fuel cells) is investigated using the volume of fraction (VOF) method. We examine two-phase flow patterns, pressure drop and water droplet formation at various hydrophobic surfaces. Evolution of pressure drop is also presented to indicate its dependence on the two-phase transport status. The results also show that in the regime of high water flow rate and low gas velocity the slug annular flow emerges. When the gas flow increases, the annular type flow occurs. Experimental test is also conducted to compare with the numerical result. The developed numerical tool can be employed to investigate the fundamentals of channel two-phase flow in fuel cell.
Fundamental Analyses, Observations, and Predictions of Liquid Droplet Movement on Etched-Metal Surfaces for PEMFC
Authors: Lilavivat Visarn , Shimpalee Sirivatch , Van Zee John W. , McCrabb Heather , Lozano-Morales Alonso
Published: October 2010

This project aims to address the fundamental problem of the behavior of water droplet in the channel for fuel cells. The pressure drop and channel characteristics become more interesting when liquid water presents in the gas channels of PEMFCs. Characteristics of water droplet motion in the flow channels of PEMFCs are important. There have an influence to cell performance, but the moving mechanism is not clear. Considering for metal bipolar plate manufactured by electrochemical etching technology, which form the wall of the gas channel, the experiments of water droplet on difference surface roughness were set up.
An Experimental Study of the Saturation Level in the Cathode Gas Diffusion Layer of a PEM Fuel Cell
Authors: Wang Xuhai , Nguyen Trung V.
Published: October 2010

A Proton Exchange Membrane (PEM) fuel cell with a flow field that can be switched between the serpentine flow mode and the interdigitated flow mode was used to measure the liquid water saturation level in the gas diffusion layer (GDL) of the cathode. The gas pressure drop across the GDL was used along with the correlations between the saturation level and gas relative permeability obtained by neutron imaging to determine the liquid water saturation level in the GDL during operation. The results showed that the saturation levels in the cathode GDL during the interdigitated mode was much lower than that during the serpentine mode leading to better oxygen gas access to the cathode catalyst layer and consequently better fuel cell performance, especially at high current densities and low oxygen stoichiometric flow rate.
Through-Mask Electroetching for Fabrication of Metal Bipolar Plate Gas Flow Field Channels
Authors: McCrabb Heather , Taylor E. Jennings , Lozano-Morales Alonso , Shimpalee Sirivatch , Inman Maria , Van Zee John W.
Published: October 2010

Transition of PEM fuel cells to the commercial market requires low-cost components, materials and manufacturing processes. Considering that bipolar plate manufacturing currently contributes to a significant percentage of the total fuel cell manufacturing cost, an inexpensive bipolar plate manufacturing process must be realized for fuel cells to achieve prominence in the commercial energy sector. A through-mask electro-etching process for high volume manufacturing of stainless steel bipolar plate gas flow field channels is being developed using pulse and pulse reverse electric fields. It has been demonstrated that the process can achieve a uniform channel depth, exhibits good repeatability for multiple experiments performed under the same conditions and the undercut beneath the photoresist mask varies linearly with channel depth indicating that pattern design compensation prior to photoresist patterning of the substrate to achieve the dimensional accuracy of the gas flow field channels and ribs is possible.
The Effect of Water on the Stress Relaxation and Life Estimation of Seals in Polymer Electrolyte Membrane Fuel Cells
Authors: Cui Tong , Chao Yuh , Lin Chih-wei , Van Zee John W.
Published: October 2010

Polymer Electrolyte Membrane fuel cell (PEMFC) is a promising power source for automobiles in the near future. Polymers are usually used as the sealing or gasket materials in PEM fuel cells and they are viscoelastic materials. The stress relaxation behavior of a polymer, liquid silicone rubber, is studied in different media The result shows that the relaxation mechanism remains the same with the specimen in ambient air from 25°C to 120°C, however, it is changed by the introduction of water, and the changed mechanism cause the failure of Arrhenius equation for life estimation, but time temperature superposition still works well.
Water Transport in Proton Exchange Membranes: Insights from Time-Resolved Infrared Spectroscopy
Authors: Hallinan Daniel , Grazia De Angelis Maria , Giacinti Baschetti Marco , Sarti Giulio , Elabd Yossef A.
Published: October 2010

Water transport in proton exchange membranes (PEMs) is relevant to several advanced technologies, especially fuel cells. The dynamics of changing water conditions can significantly impact the PEM conductivity and fuel cell performance. Accurate water diffusion coefficients in Nafion, the industry standard PEM, have been determined, non-Fickian regimes identified and modeled, and infrared data used to confirm the validity of these models.
Analysis of State of Water in Polymer Electrolyte Membrane by Raman Spectroscopy and DFT
Authors: Tabuchi Yuichiro , Ito Rei , Tsushima Shohji , Hirai Shuichiro , Horai Atushi , Aotani Koichiro , Kubo Norio , Shinohara Kazuhiko
Published: October 2010

Proton and water transport in polymer electrolyte membrane (PEM) are key transport properties for the improvement in PEMFCs performance under high current density operation which is desired in PEMFCs for automobiles. In this study, state of water in PEM is investigated by using confocal micro-Raman spectroscopy and density functional theory (DFT). The results showed that OH vibration peak shape indicated the state of water in the membrane. In particular, OH vibration peak around 3500cm-1 was strongly related to water transport through the membrane, while a peak around 3200cm-1 was assigned by formation of hydrogen-bonded water molecule network around sulfonic acid by DFT. DFT calculation also indicated that a hydronium ion around sulfonic acid contributes to the formation of water network.
Molecular Dynamics Study of Proton Transfer Including Grotthus Mechanism in Polymer Electrolyte Membrane
Authors: Yoshida Taiki , Tokumasu Takashi
Published: October 2010

This study describes the property of proton transfer in Nafion membrane analyzed by molecular dynamics (MD) simulation including both Vehicle and Grotthus mechanism. To treat Grotthus mechanism, Empirical Valence Bond (EVB) method was introduced to MD simulation. The potential energy barrier of proton hopping obtained by EVB method was adjusted to the computational result of Density Functional Theory (DFT). After adjusting EVB potential, it is confirmed that protons hop along the hydrogen bond network consecutively. The parameter for the simulation of Nafion membrane was water contents λ, which is defined as the ratio of water molecules and hydronium ions to sulfo groups, SO3-, obtained byλ=NH2O,H3O+/NSO3-. The changes of transferring properties and structure of molecules with the changes of λ were analyzed by Mean Square Displacement and Radial Distribution Function, respectively.
Water Transport in Polymer Electrolyte Membranes Investigated by Dissipative Particle Dynamics Simulation
Authors: Sawada Shin-ichi , Yamaki Tetsuya , Ozawa Taku , Suzuki Akihiro , Terai Takayuki , Maekawa Yasunari
Published: October 2010

In order to deepen the insight into water transport in polymer electrolyte membranes (PEMs), we calculated the self-diffusion coefficient of water, DW, by dissipative particle dynamics (DPD) simulation. The simulation target materials are a Nafion membrane and radiation-grafted PEMs in the fully-hydrated states. DW was obtained by the following procedures: (i) molecular modeling with the coarse-grained particles representing groups of several atoms; (ii) calculation of the diffusivity of water particles, DWParticle, in the PEM systems in the equilibrium states; (iii) determination of the unit of time in the DPD simulation by comparing DWParticle with DW in bulk water; (iv) conversion of DWParticle of the PEM systems in the DPD unit into DW in the standard SI unit. Interestingly, DW was found to decrease with the diffusion time period, Δt, probably owing to the geometrical confinement effect by water-transport hydrophilic regions. Quantitative analysis of this relationship provided us with the size of hydrophilic regions.
GDL Degradation in PEFC
Authors: Perry Mike L. , Patterson Tim , Madden Tom
Published: October 2010

Performance decay in a polymer-electrolyte fuel cell can result from changes in the gas-diffusion layer, particularly in the micro-porous layer. Examples and characteristics of this decay will be presented here. Performance decay is greater with exposure to potential cycles than with exposure to constant high potential holds. Presumably, electrochemical oxidation of the carbon within the micro-porous layer is primarily responsible for this performance decay; it is known that transient potentials can accelerate the electrochemical oxidation of carbon. The implication that these results have on the development of advanced gas-diffusion layer materials is also considered. Finally, a recommendation for a standardized accelerated stress test protocol focused on the gas-diffusion layer is proposed.
Effect of Hydrophilic Treatment of Microporous Layer on Fuel Cell Performance
Authors: Mukundan Rangachary , Davey John , Fairweather Joseph D. , Spernjak Dusan , Spendelow Jacob S. , Hussey Daniel S. , Jacobson David , Wilde Peter , Schweiss Ruediger , Borup Rodney L.
Published: October 2010

The gas diffusion layer in a polymer electrolyte fuel cell is the component primarily responsible for effective water management under a wide variety of conditions. The incorporation of hydrophilic alumosilicate fibers in the microporous layer leads to an improvement in the fuel cell performance associated with a decrease in the mass transport resistance especially under high RH operation. This improvement in performance is obtained without sacrificing performance under low RH conditions. The alumosilicate fibers create domains that wick liquid water away from the catalyst layer. The improved mass transport performance is corroborated by AC impedance and neutron radiography analysis and is consistent with an increase in the average pore diameter inside the microporous layer.
Effect of Microporous Layer (MPL) on Water Management Investigated by Electrochemical Impedance Spectroscopy (EIS) on a Running PEM-FC
Authors: Dotelli Giovanni , Omati Luca , Gallo Stampino Paola , Brivio Davide , Grassini Paolo
Published: October 2010

Gas diffusion media (GDM) based on carbon cloth material (SAATI S.p.A.) and coated with Micro Porous Layers (MPL) containing 12% or 40% PTFE were investigated. The GDMs were tested in a cell using a catalyst coated membrane (CCM) made from Nafion® 212 and with a Pt load of 0.3/0.6 mg cm-2. The test conditions were: 60 °C, flow rates of 0.2 Nl min-1 at the anode and 1.0 Nl min-1 at the cathode; relative humidity (RH) equal to 60 % or 100 % at cathode side and fixed at 80 % at the anode; the GDMs were compressed to 50 % of their initial thickness. The cell performances were assessed by analysis of the polarization curves, and the influence of PTFE loading of the MPLs on water management ability was investigated at different air RH conditions by AC impedance spectroscopy.
Characterization of Microporous Layer in Carbon Paper GDL for PEM Fuel Cell
Authors: Martínez-Rodríguez Michael J. , Tong Cui , Shimpalee Sirivatch , Van Zee John W.
Published: October 2010

Characterization of a custom series of Toray TGP-H-060 carbon paper gas diffusion layer (GDL) was performed by using scanning electron microscopy (SEM) images, pore size distribution (PSD), MacMullin number, and fuel cell performance. The GDLs were customized by the addition of a microporous layer (MPL) and the treatment of, either or both, the substrate and MPL with 10% and 40% hydrophobic agent. SEM images correlated very well with the data shown for PSD. Distinction between the substrate layer and the MPL were clearly shown as two different slopes in the integral distribution and two different peaks in the differential distribution. The MacMullin number increased with increase in wet proofing but decreased with the addition of the MPL. Results showed that the cell performance with the different GDLs is affected by a competitive effect of pore volume in the substrate region, wet proofing treatment, and the MacMullin number.
Ice Formation in Gas-Diffusion Layers
Authors: Dursch Thomas J. , Radke Clayton , Weber A.
Published: October 2010

Under sub-freezing conditions, ice forms in the gas-diffusion layer (GDL) of a proton exchange membrane fuel cell (PEMFC) drastically reducing cell performance. Although a number of strategies exist to prevent ice formation, there is little fundamental understanding of the mechanisms of freezing within PEMFC components. Differential scanning calorimetry (DSC) is used to elucidate the effects of hydrophobicity (Teflon® loading) and water saturation on the rate of ice formation within three commercial GDLs. We find that as the Teflon® loading increases, the crystallization temperature decreases due to a change in internal ice/substrate contact angle, as well as the attainable level of water saturation. Classical nucleation theory predicts the correct trend in freezing temperature with Teflon® loading.
Experimental Study of Relative Permeability of Porous Media Used in PEM Fuel Cells
Authors: Wang Xuhai , Nguyen Trung V. , Hussey Daniel S. , Jacobson David
Published: October 2010

This study investigated gas and liquid relative permeability, one of the important two-phase transport properties of the porous media used in proton exchange membrane (PEM) fuel cells. The experiment showed that the gas relative permeability obtained by the gravimetric analysis and neutron imaging agreed at low saturation levels, but differs at high saturation levels. The liquid relative permeability in the saturation level range of 0.3 to 0.8 was measured by neutron imaging. Because of dead air pockets in the porous materials and certain saturation levels are required to establish continuous flow of liquid water through gas diffusion media, liquid permeability at both high and low saturation levels could not be obtained. It was shown that the 3rd-order power correlation of gas permeability generally used in numerical simulation only fitted the porous media of A1 and A3 at low saturation levels.
Effective Thermal Conductivity of Gas Diffusion Layers Used in PEMFC: Measured with Guarded-Hot-Plate Method and Predicted by a Fractal Model
Authors: Radhakrishnan Arjun , Lu Zijie , Kandlikar Satish G.
Published: October 2010

An experimental setup to determine thermal conductivity and thickness of a gas diffusion layer (GDL) as a function of compression was developed and calibrated. The actual thermal conductivities, based on compressed thickness, of plain Toray TGP-H gas diffusion layer (GDL) at compression pressures of 0.04 to 1.5 MPa and over temperature range of 25 °C to 75 °C are reported in this paper. The thermal conductivity of TGP-H GDL was found to decrease with temperature and to increase with compression. An effort was made to numerically account for the effective thermal conductivity by using theoretical models. Krischer model was found to be able to match with the experimental data, but this model relied on a priori knowledge of the thermal properties of the solid matrix. A new analytical model based on fractal analysis of GDL microstructure is proposed to account for GDL thermal conductivity as well as its variation with compression without using any empirical parameter.
Analysis of the Ionomer Coverage of Pt Surface in PEMFC
Authors: Ikeda Kotaro , Nonoyama Nobuaki , Ikogi Yoshihiro
Published: October 2010

We have developed a new cyclic voltammetry (CV) technique to analyze the ionomer coverage of Pt/C surfaces. The ionomer coverage ratio was estimated by comparing the capacitance current under perfluorohydrocarbon solvent and under nitrogen. When the cathode electrode was immersed in perfluorohydrocarbon solvent, the proton supply from adsorbed water is inhibited by blocking water adsorption. Accordingly, proton supplies from the ionomer can be differentiated from that of adsorbed water. Using this technique, the effect of carbon species on the ionomer coverage ratio was investigated. Using Ketjen carbon in the catalyst layer resulted a low ionomer coverage ratio, which also influenced V-I performance.
Analysis of Major Parameters in Catalyst Layer Structure Affecting on PEFC Performance
Authors: Nishino Masayoshi , Tabe Yutaka , Chikahisa Takemi
Published: October 2010

Because electron, proton, and oxygen are necessary for the cathode reaction in polymer electrolyte fuel cell, achieving the optimum structure of electrode catalyst layer and the efficient transport of the reactants is significantly effective to reduce the usage of Pt catalyst. In this study, we presented evaluation equations to investigate the relationship between the structure of cathode catalyst layer and the cell performance. The evaluation equations are based on the analysis using the three-phase boundary model by the authors, and can estimate the effects of cathode catalyst layer structures on the cell performance easily. This paper discusses optimum structure of the catalyst layer using these evaluation equations. Furthermore, the dominant parameter of the catalyst layer structure such as the amount of polymer electrolyte and the oxygen solubility in the polymer was confirmed experimentally.
Electrode Structure Effects on Current Up-Transient Operation in Polymer Electrolyte Fuel Cells
Authors: Kongkanand Anusorn , Sinha Puneet
Published: October 2010

Transient responses of conventional carbon-supported Pt nanoparticle (Pt/C) and 3M's nanostructured thin film (NSTF) oxygen reduction electrodes are reported. The ultrathin 0.3 μm thick NSTF electrode exhibits less-than-zero voltage, i.e. a failed up-transient, when current is increased instantaneously from 0.02 A/cm2 to 1.0 A/cm2 at 80°C and the channel RH is greater than 80%. In contrast, under the same conditions, a 10 μm thick Pt/C electrode exhibits robust transient response. A transient model, coupled with experiments, is deployed to delineate the water transport dynamics and ensuing voltage response. It is found that thin electrodes, due to their low water buffer capacities, flood with liquid water rendering negative cell voltages during transients. Effects of operating conditions and electrode thickness on the transient response are investigated.
Accelerated Degradation and High Potential Treatment of E-TEK Anodic GDE by an Improved Half Cell
Authors: Liu Lian , Zhang Lu , Cheng Xuan , Zhang Ying , Weng Fang-Bor , Su Ay
Published: October 2010

In this work, an improved three-electrode half cell and corresponding working electrode was designed and implemented to establish an environment as close as possible to that of an actual direct methanol fuel cells, and especially, to meet the requirements for long-time degradation analysis. A series of accelerated degradation tests and the high potential activation treatments of E-TEK anode gas diffusion electrodes (GDEs) were carried out to confirm the stability and applicability of the electrochemical devices. The data were acquired by combinations of electrochemical analyses (EIS, CO-Stripping and CV) and ICP-MS analyses in the accelerated degradation tests of E-TEK anode GDEs and high potential treatments. Special attention has been paid to analyzing the amount of Ru dissolved in supporting electrolyte by ICP-MS, which provides quantitative information of Ru dissolution non-destructively.
Investigation of the Carbon Corrosion Process for Polymer Electrolyte Fuel Cells Using a Rotating Disk Electrode Technique
Authors: Xu Fan , Wang MeiXian , Liu Qi , Sun HongFang , Simonson Seth , Ogbeifun Noma , Stach Eric , Xie Jian
Published: October 2010

The carbon corrosion process of low-surface-area Pt/XC72 and high-surface-area Pt/BP2000 was investigated using an developed accelerated durability testing (ADT) method under simulated fuel cell conditions (a Rotating Disk Electrode (RDE) approach). Compared with the complex MEA system, this innovated approach using RDE can simply focus on carbon corrosion process and avoid the use of MEA in which many degradation/corrosion processes simultaneously occur. A steam etching experiment was also carried out for further understanding of the carbon corrosion process for XC72 and BP2000. It was observed that different carbon corrosion processes resulted in different performance (electrochemical active surface area, mass activity and double layer capacity) decay of catalysts. The corrosion process was studied using TEM. It was found that in the case of Pt/XC72, major corrosion occurred at the center of the Pt/XC72 particle, with some minor corrosion on the surface of the carbon particle removing some amorphous carbon black filaments, while in the case of Pt/BP2000, the corrosion started on the surface. The understanding of carbon corrosion process provides the guidance for making high corrosion resistance catalysts to increase the durability performance of PEFC.
Development of a Rapid Beginning-of-Life MEA Robustness Test
Authors: Edmundson Mark D. , Tomiie Takehiko , Busby F. C.
Published: October 2010

A small-scale, 19-hour, beginning-of-life robustness test has been developed for Proton Exchange Membrane (PEM) fuel cells which is suitable for Statistical Process Control (SPC). The test covers a wide range of cell temperatures (Tcell = 60oC-110oC), relative humidities (RH = 11%-152% at the inlet) and anode/cathode stoichiometric ratios (SRa = 1.1-2.0, SRc = 1.3-2.5). The test begins with an accelerated break-in protocol and then utilizes newly developed polarization curve protocols that combine increased definition with shorter measurement times. A rigorous qualification was performed that demonstrated an excellent signal-to-noise ratio for many conditions. The test has also been applied to the research and development of new materials for PEM fuel cells.
Normal Pulse Voltammetry: In Situ Kinetic Analysis of Proton Exchange Membrane Fuel Cells
Authors: Stuckey Philip A. , Pietrasz Patrick , Zawodzinski T. A.
Published: October 2010

Normal pulse voltammetry (NPV) is applied to operating proton exchange membrane fuel cells (PEMFCs) using a high current potentiostat. Kinetic information including the Tafel slope and exchange current density for the oxygen reduction reaction (ORR) is directly extracted from the steady state voltammetric response obtained from the NPV experiment. Temperature, relative humidity, and conditioning potential are varied independently to observe their effect on the PEMFC through the Tafel slope calculation. This NPV technique provides kinetic information previously collected through ex situ techniques such as rotating disc electrodes. The ability to probe in situ the kinetic effects of catalysts within operational PEMFCs has never been proposed in this detail. NPV measurements take less than 30 seconds to conduct thus making the process simple and efficient. The observed Tafel slope is about 60mV/decade for oxide covered platinum and 120mV/decade for oxide free platinum.