bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic SIMS Analysis of PEMFC Catalyst Layer/Solid Electrolyte Interfaces
Authors: Ebihara Takayoshi , Nojima Masashi , Kondo Takeshi , Yuasa Makoto
Published: March 2013

Cobalt polypyrrole-supported carbon (CoPPy/C) has been expected to be a low-cost alternative to platinum catalysts for proton exchange membrane fuel cell (PEMFC) cathode. Although the catalytic activity of the CoPPy/C is relatively high, improvement of the durability to long-term use is still challenging problem. In order to know the deterioration mechanism of PEMFC cathode, dynamic-secondary ion mass spectrometry (D-SIMS) was used in this study for analysis of cathode catalyst layer/solid electrolyte membrane interfaces before and after an aging test. The depth profile of cobalt species across the interface of a CoPPy/C cathode was significantly changed after the aging test. From the depth profile of cobalt in the CoPPy/C catalyst, it is suggested that the cobalt species may transfer in the membrane along with the flow of the back diffusion water.
STXM Characterization of PEM Fuel Cell Catalyst Layers
Authors: Susac Darija , Berejnov Viatcheslav , Hitchcock Adam P. , Stumper Jürgen
Published: March 2013

The synchrotron based scanning transmission soft X-ray microscopy (STXM) utilizing near edge X-ray absorption fine structure (NEXAFS) is a novel technique for characterization of membrane electrode assembly (MEA) components in proton exchange membrane fuel cells (PEMFC). Component maps for carbon support, Pt and ionomer in the cathode catalyst layer and perfluorosulphonic acid (PFSA) membrane including the reinforced layer have been obtained from full C 1s multi-energy image sequences and maps from images at four energies in the C 1s and F 1s regions. The ability of this technique to distinguish both structural and chemical differences in cathode catalyst layers from two significantly different designs has been demonstrated. The ionomer distribution in the cathode catalyst layer of an advanced catalyst coated membrane (CCM) structure is compared to that of the cathode in a gas diffusion electrode (GDE).
Analysis and Experiments of Major Parameters in Catalyst Layer Structure Affecting on PEFC Performance
Authors: Kobayashi Masaya , Tabe Yutaka , Chikahisa Takemi
Published: March 2013

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 polymer electrolyte membrane fuel cells. In this paper, we fabricated the catalyst coated membrane (CCM) and estimated structural parameters of the catalyst layer from observation of the CCM by a SEM. The characteristics of the cell performance were calculated using an agglomerate model with the estimated parameters, and the simulation model was validated by comparing the simulated and experimental results. Then, we evaluated the effects of the major parameters such as the polymer electrolyte film thickness covering carbon agglomerates on the cell performance by the simulation, and present a new concept effective for reducing the identified major resistances of oxygen supply by controlling the film structure of polymer electrolyte.
Performance Characteristics of PEFCs with Patterned Electrodes Prepared by Piezo-Electric Printing
Authors: Malevich Dzmitry , Saha Madhu S. , Halliop Ela , Peppley Brant A. , Pharoah Jon G. , Karan Kunal
Published: March 2013

The potential for the fabrication of patterned electrodes using a piezo-electric printer was examined. Challenges in generating sharp features were identified. The polarization behavior and electrochemically active surface area of patterned catalyst layers were found to be influenced by the geometry of the patterns.
Influence of Hydrohilic and Hydrophobic Double MPL Coated GDL on PEFC Performance
Authors: Kitahara Tatsumi , Nakajima Hironori , Mori Kyohei , Inamoto Masaoki
Published: March 2013

Gas diffusion layers (GDLs) coated with a hydrophobic microporous layer (MPL) have been commonly used to improve water management properties of polymer electrolyte fuel cells (PEFCs). In the present study, a novel hydrophilic and hydrophobic double MPL coated GDL was developed to further enhance the PEFC performance under both low and high humidity conditions. Under low humidity conditions, a thin hydrophilic layer using titanium dioxide coated on the hydrophobic MPL is effective to conserve the humidity of the MEA, while a hydrophobic intermediate MPL between the hydrophilic layer and the GDL substrate prevents the removal of water in the hydrophilic layer. Under high humidity conditions, a double MPL coated GDL is also effective to reduce flooding on the cathode catalyst layer, which results in a higher PEFC performance compared with that for a conventional hydrophobic MPL coated GDL.
Observation of Water Transfer Phenomena in Micro-Porous Layer of PEFC
Authors: Aoyama Yusuke , Kadowaki Kazumasa , Tabe Yutaka , Chikahisa Takemi
Published: March 2013

MPLs play an important role in the water management of PEFCs, but details of the mechanism to suppress water flooding has not been fully understood. In this study, we observed distributions of condensed water at the cross-section surface of the MPL using freezing method and a CRYO-SEM to clarify the effect of the MPL on discharge of produced water. By comparing two observations under normal operational condition and water flooded condition, we discuss water transfer phenomena in the MPL. The observation result shows that condensed water accumulates not in the MPL under normal operational condition but in the MPL under water flooded condition such as lower cell temperature operation. This indicates that water transfer phenomena in the MPL depend on cell temperature; under low temperature conditions such as 10 ℃, produced water condenses in the MPL because of small vapor transport capacity through the MPL due to low temperature.
Measurement of Capillary Pressure Curves in GDLs at Elevated Temperatures
Authors: Shrestha Kiran Prasad , Gostick Jeff. T
Published: March 2013

An experimental setup has been designed to measure air-water capillary pressure curves for gas diffusion layers (GDLs) used in polymer electrolyte membrane fuel cells at elevated temperatures. Experiments were conducted at various temperatures from 25 to 85{degree sign}C for Toray 120 with 0% and 10% PTFE by weight. In untreated samples the results suggest that GDL wettability actually changes with temperature once the temperature dependence of the surface tension has been accounted. In treated samples, however, the wettability remains constant with temperature. This behavior is in agreement with the temperature dependent values of water contact angle on PTFE and graphite.
Water Distribution in GDL near Optimal Humidification
Authors: Eller Jens , Roth Jörg , Gaudenzi Rocco , Irvine Sally , Marone Federica , Stampanoni Marco , Wokaun Alexander , Büchi Felix N.
Published: March 2013

In order to better understand the two phase properties of the porous GDL, the liquid water pattern and local saturation in the Toray 060 gas diffusion layer (GDL) is visualized in-situ in cells close to the optimal performance point at 80 {degree sign}C by X-ray tomographic microscopy. A recording time of about 10 s is achieved. At the optimal performance point (dew point of reactant gases 74 {degree sign}C) the water volume fraction observed depends on the rib width. A variation of {plus minus} 8 {degree sign}C of the feed gas dew point leads to significant saturation and performance changes. For different current densities the water volume fraction and permeability of the liquid phase of the cathode are determined and analyzed.
PEMFC Gas Diffusion Media Degradation Determined by Acid-Base Titrations
Authors: Chlistunoff Jerzy , Davey John R. , Rau Karen C. , Mukundan Rangachary , Borup Rodney L.
Published: March 2013

Numerous interlinked processes are responsible for limited durability of polymer electrolyte membrane fuel cells. One of the major phenomena that contribute to accelerated degradation of PEMFCs is loss of hydrophobicity of diffusion media caused by oxidation of carbon in the gas diffusion layer.1 The process is accompanied by formation of oxygen containing surface functional groups. While the vast majority of these groups produce characteristic signals in XPS, DRIFTS, FTIR ATR, etc., frequently an unfavorable signal to noise ratio in such measurements prevents accurate determination of the surface concentration of those functionalities. In this paper, we demonstrate successful application of Boehm type acid base titrations to determine concentrations of acidic functionalities in gas diffusion layer samples that underwent in situ and ex situ oxidation under different conditions and demonstrate correlations between those conditions and carbon oxidation.
Employing Dew Point Diagrams to Optimize PEMFC Operating Conditions
Authors: Berning Torsten
Published: March 2013

Dew point diagrams show the dew point temperature of the anode and cathode outlet gas streams as function of the cell pressure, stoichiometric flow ratios and the effective drag coefficient of water across the membrane in a PEM fuel cell. They are a useful tool for specifying the operating temperature for a given pressure and stoichiometric flow ratio to avoid cell flooding or membrane dehydration. In this work a sequence of logical steps is presented that help determining the optimum cell operating conditions in a natural way rather than employing a trial-and-error method. Furthermore, modeling results are presented for the specified case. The results indicate that fuel cell operation on completely dry inlet gases at anode and cathode stoichiometric flow ratios of ξa = 1.03 and ξc = 1.1 is possible. However, the predicted membrane hydration level of λ ≈ 9 for this case is below expectation.
Role of the Cathode Microporous Layer in a PEMFC
Authors: Nishiyama Enju , Hara Masaya , Murahashi Toshiaki
Published: March 2013

The role of the cathode microporous layer (MPL) of the gas diffusion layer in a polymer electrolyte exchange membrane fuel cell was investigated by comparing the performance of several cells containing different MPLs. MPLs were prepared with different hydrophobic agent contents to impart different water capillary pressures and hydrophobic properties. Experimental data were evaluated according to the water vapor activity of the cathode, which was modified with the capillary pressure of the MPL. As a result, the modified activity was determined to be a key factor to explain the occurrence of cathode flooding. Liquid water saturation in the diffusion media and the cathode catalyst layer (CCL) are determined by the balance of capillary pressures of the pores of each layer. Increase of the diffusion resistance of oxygen in the CCL is significant, while that in the diffusion media is moderate, which indicates that the CCL is susceptible to flooding.
Performance and Durability of HT-PEFCs with Customized Flow Field
Authors: Liu Fang , Kvesić Mirko , Wippermann Klaus , Reimer Uwe , Lehnert Werner
Published: March 2013

Geometries of flow fields have a strong impact on the gas distribution in fuel cells. In this work, two different flow field geometries are compared for high temperature polymer electrolyte fuel cells, a serpentine like flow field and a spiral one. Computational fluid dynamics analysis yielded a mixed flow distribution over the active area of the spiral flow field. This cell exhibited a significantly higher voltage than the cell with the serpentine flow field. Additionally, the degradation rate of the cell with the spiral flow field was five times lower after an operation of 1000 h. Moreover, electrochemical impedance spectroscopy and cyclic voltammetry presented lower resistances and 50% larger specific electrochemical surface area after long term tests for the cell with the spiral flow field compared to the one with the serpentine flow field.
Impact of Polymer Electrolyte Membrane Degradation Products on the Activity of the Oxygen Reduction Reaction for Platinum Catalysts
Authors: Christ Jason M. , Neyerlin K.C. , Wang Heli , Richards Ryan M. , Dinh Huyen N.
Published: March 2013

Cyclic voltammetry (CV) utilizing a rotating disk electrode was used in order to investigate the potential impact on electrochemical performance of platinum catalysts in the presence of perfluorinated model compounds representing polymer electrolyte membrane degradation products. Under the experimental conditions tested, it was found that the carboxylic acid functional group caused an impact on catalyst electrochemical surface area whereas the sulfonic acid functional group did not. However, neither produced a direct impact on the oxygen reduction reaction (ORR). Performance effects on the ORR were observed for two model compounds each containing both sulfonic and carboxylic acid functionalities indicating that processes other than direct adsorption due to either chemical functionality are occurring at the electrode/solution interface.
Verification of Durability Test Methods of an MEA for Automotive Application
Authors: Hashimasa Yoshiyuki , Shimizu Takahiro , Matsuda Yoshiyuki , Imamura Daichi , Akai Motoaki
Published: March 2013

Potential cycle tests that simulate the operation of a fuel cell vehicle are widely adopted as a durability testing method of membrane-electrode assemblies (MEAs). The Fuel Cell Commercialization Conference of Japan (FCCJ) has proposed methodologies for testing MEAs and their materials in 2007, focusing on the evaluation of the durability of electrode materials. The two protocols, start/stop durability test and load cycle durability test, were revised in 2011 based on the up-to-date knowledge concerning fuel cell durability. In this study, we applied the revised protocols to a standard electrocatalyst, and the effect of the revision was verified. We have demonstrated that the revision of the protocols accelerates the evaluation of fuel cell materials and verified that the revised protocols effectively separate the degradation of Pt electrocatalyst from that of carbon support.
Investigation on Effect of PTFE Treatment on GDL Micro-structure by High-resolution X-ray CT
Authors: Sasabe Takashi , Inoue Gen , Tsushima Shohji , Hirai Shuichiro , Tokumasu Takashi , Pasaogullari Ugur
Published: March 2013

To remove liquid water from a gas diffusion layer (GDL) effectively and minimize an increase of transport resistance, hydrophobic treatment with a polytetrafluoroethylene (PTFE) is widely used. Because the GDL micro-structure has strong impact on transport properties, detailed understanding of fiber and porous network and PTFE distribution is strongly requested. To investigate correlation between the GDL micro-structure, PTFE treatment, and transport properties, micro-structure of the GDL was visualized by high-resolution X-ray computed tomography (X-ray CT). Newly designed sample holder allowed to regulate compression pressure. Visualization results with spatial resolution of 1.0 um made it possible to distinguish carbon fibers, binder material, PTFE, and voids (air), and non-uniform distribution of PTFE was observed. Because non-uniform porosity and contact angle distribution in the direction of thickness change the liquid water morphology within the GDL, understanding and controlling the GDL micro-structure is important and manufacturing process of GDL should be scientifically developed.
Fabrication and Optimization of Membrane Electrode Assembly with Support-Less Platinum Catalysts for Space Applications
Authors: Huang Xinyu , Rigdon William A , Billings Keith J. , Valdez Thomas I.
Published: March 2013

Hydrogen-oxygen fuel cell technology is a critical component for crewed space exploration mission beyond low earth orbit. While lowering platinum loading is of paramount importance for automotive fuel cells, it is not a significant constraint for MEAs used for space applications. As such, support-less platinum black catalysts is a viable choice. Historically, surfactant-stabilized polytetrafluoroethylene (PTFE) emulsion is used as the binder for platinum black electrode. High temperature treatment steps needed for the PTFE emulsion prevents the direct deposition of the electrocatalysts onto the Nafion® membrane. In this study, two alternative materials have been used to replace PTFE emulsion. These include surfactant-free PTFE fine particles and functionalized carbon nanotube with Nafion®. An ultrasonic spray deposition technique was applied to directly deposit support-less Pt black catalyst ink onto the Nafion® membrane. The fabrication process was optimized to produce high performance membrane electrode assemblies that approaching NASA performance target.
Investigating the Performance of Catalyst Layer Micro-Structures with Different Platinum Loadings
Authors: Khakbaz Baboli M. , Harvey David A. , Pharoah J. G.
Published: March 2013

In this study a four-phase micro-structure of a PEFC catalyst layer was reconstructed by randomly placing overlapping spheres for each solid catalyst phase. The micro-structure was mirrored to make a micro-structure. A body-fit computational mesh was produced for the reconstructed micro-structure in OpenFOAM. Associated conservation equations were solved within all the phases with electrochemical reaction as the boundary condition at the interface between ionomer and platinum phases. The study is focused on the platinum loading of CL. The polarization curves of the micro-structure performance have been compared for different platinum loadings. This paper gives increased insight into the relatively greater losses at decreased platinum loadings.
Development of Ultra-Low Pt Alloy Cathode Catalyst for PEM Fuel Cells
Authors: Popov Branko N. , Xie Tianyuan , Kim Taekeun , Jung Won Suk , Kriston Akos , Murphy Brian , Gamliel David , Ganesan Prabhu
Published: March 2013

Hybrid cathode catalysts containing Pt (Pt/CCC, HCC-1) and Pt-alloy (Pt-alloy/CCC, HCC-2) with ultra-low Pt loading were synthesized as cathode catalysts for polymer electrolyte membrane fuel cells (PEMFC). The approach combines a non-platinum carbon based composite catalyst (CCC) containing active catalytic sites for the oxygen reduction reaction (ORR) as a support and highly active Pt/Pt-alloy catalysts. Rotating ring disc electrode (RRDE) and fuel cell studies confirmed the synergistic effect of combining CCC and Pt/Pt-alloy. The HCC catalysts exhibited 2-3 times higher mass activities (0.35 - 0.45 A mgPt-1) than the conventional Pt/C catalyst (0.18-0.24 A mgPt-1). The HCC-2 catalyst exhibited H2-air fuel cell performance of 1.4 A cm-2 at 0.58 ViR-free at a cathode stoic of 2.0.
In Situ and Ex Situ Contact Resistance Measurements of Stainless Steel Bipolar Plates for PEM Fuel Cells
Authors: Laedre Sigrid , Kongstein Ole Edvard , Oedegaard Anders , Seland Frode , Karoliussen Håvard
Published: March 2013

Passivation of stainless steel caused by the formation of an oxide layer on the surface is one of the main concerns when it comes to using stainless steel as bipolar plate material. Interfacial Contact Resistance (ICR) between the bipolar plate and the gas diffusion layer was measured both in situ and ex situ. A method for measuring ICR in situ was developed, and initial results showed that the ICR measured in situ is close to the ICR measured ex situ, for both non-coated and gold coated stainless steel bipolar plates. At a compaction pressure of 205.79 N cm-2, the in situ ICR was found to be close to 50 mΩ cm2 and the ex situ measurement performed on the same plate ex situ was found to be approximately 40 mΩ cm2. The in situ method for ICR measurements enables direct studies of the passivation processes at the bipolar plate interface, while the cell is in operation, under the actual fuel cell conditions.
A Direct DME High Temperature PEM Fuel Cell
Authors: Vassiliev Anton , Jensen Jens Oluf , Li Qingfeng , Pan Chao , Cleemann Lars N. , Steenberg Thomas , Hjuler Hans Aage , Bjerrum Niels J.
Published: March 2013

Dimethyl ether (DME) has been identified as an alternative to methanol for use in direct fuel cells. It combines the advantages of hydrogen in terms of pumpless fuel delivery and high energy density like methanol, but without the toxicity of the latter. The performance of a direct dimethyl ether fuel cell suffers greatly from the very low DME-water miscibility. To cope with the problem polybenzimidazole (PBI) based membrane electrode assemblies (MEAs) have been made and tested in a vapor fed system. PtRu on carbon has been used as anode catalyst and air at ambient pressure was used as oxidant. A power density of 79 mW/cm² has been achieved at 200 {degree sign}C.
Percolation in a Proton Exchange Membrane Fuel Cell Catalyst Layer
Authors: Stacy Stephen Andrew , Allen Jeffrey S.
Published: March 2013

Water management in the catalyst layers of proton exchange membrane fuel cells (PEMFC) is confronted by two issues, flooding and dry out, both of which result in improper functioning of the fuel cell and lead to poor performance and degradation. At the present time, the data that has been reported about water percolation and wettability within a fuel cell catalyst layer is limited. A method and apparatus for measuring the percolation pressure in the catalyst layer has been developed based upon an experimental apparatus used to test water percolation in porous transport layers (PTL). The experimental setup uses a pseudo Hele-Shaw type testing where samples are compressed and a fluid is injected into the sample. Testing the samples gives percolation pressure plots which show trends in increasing percolation pressure with an increase in flow rate. A decrease in pressure was seen as percolation occurred in one sample, however the pressure only had a rising effect in the other sample.
Fuel Cell Performance of Electrospun Membranes with 660 Equivalent Weight Perfluorosulfonic Acid
Authors: Ballengee Jason B. , Pintauro Peter N.
Published: March 2013

Composite membranes with polyphenylsulfone (PPSU) nanofibers reinforcing a perfluorosulfonic acid (PFSA) film of 3M Company's 660 equivalent weight (EW) polymer were fabricated and tested in a hydrogen/air fuel cell. The membranes exhibited very high conductivity, i.e. 93 mS/cm at 120oC and 50% relative humidity (RH) for a membrane composed of 72 vol% 3M660 and 28 vol% PPSU. This compares to 37 mS/cm for a commercial Nafion® film at the same temperature and humidity condition. Hydrogen/air fuel cell performance of membrane-electrode-assemblies with 3M660/PPSU membranes (58 vol% ionomer) was very good, with a high power output that was insensitive to feed gas humidity at 100oC and ambient pressure for 50%< RH< 93%.
Mechanism of Perfluorsulfonic Acid Membrane Chemical Degradation Under Low RH Conditions
Authors: Coms Frank D. , Xu Hui , McCallum Tom , Mittelsteadt Cortney
Published: March 2013

A highly versatile and robust hydrogen peroxide vapor test has been employed to probe the chemical degradation of NRE212CS and N112 membranes under a wide variety of RH environments. Under very low RH conditions, sulfonic acid pKa value increases and chain scission processes become operative leading to an increase in the carboxylic acid content and subsequent decreased high humidity chemical stability of the membranes.
Polymer Electrolyte Membrane Durability -Local Degradation at Pinholes
Authors: Kreitmeier Stefan , Wokaun Alexander , Büchi Felix N.
Published: March 2013

Membrane defects are a frequent failure mode of polymer electrolyte fuel cells. To understand the degradation mechanisms at defects, small pinholes are implemented artificially in membranes and their evolution is monitored during accelerated stress tests by online gas permeation analysis, ex-situ X-ray tomographic microscopy and local temperature analysis. Membrane degradation at defects is controlled primarily by the synergetic effect of chemical and mechanical degradation processes. The elimination of the synergism mitigates degradation significantly. Further, local temperatures of up to 140 degree celsius induce catalyst agglomeration and carbon oxidation of the MPL in the vicinity of the membrane defects.
Role of Chemical-Mechanical Energies in Understanding Structure and Properties of Aged and Degraded Membranes
Authors: Kusoglu Ahmet , Weber Adam Z.
Published: March 2013

Polymer fuel-cell membranes are the core component of fuel-cells having multiple functionalities including water absorption, ionic conductivity, and mechanical support. All these functionalities are correlated via the membrane nanostructure and chemical properties. This study aims at investigating the changes in the structure-uptake relationship due to membrane degradation and ageing. We show that, after in-situ chemical degradation (i.e., OCV holds), the membrane's water uptake and water-domain spacing both decrease compared to a fresh membrane. In addition, the MEA manufacturing process is also found to alter the membrane's nanostructure and uptake behavior, which suggests that changes in the properties of bare membranes during processing and cell operation must be accounted for when analyzing and modeling cell performance. The experimental data is evaluated using an energy-balance approach to examine the correlations among domain spacing, water content, and mechanical properties for degraded membranes.
On the Diffusion Coefficient of Water in Polymer Electrolyte Membranes
Authors: Olesen Anders C. , Berning Torsten , Kær Søren Knudsen
Published: March 2013

The Fickian diffusivity of water in Nafion has been shown to exhibit a local maximum. In the present research effort it is shown that this spike vanishes if the equilibrium water content and chemical diffusivity are modeled carefully. Further, it is shown that permeation experiments falsely can generate a local maximum, if a wrong equilibrium water content relation is used. Finally, in order to study the obtained diffusivity model a parameter variation is carried out using a one-dimensional steady-state model. The effect of diffusivity model, surface roughness and water content driving force is studied.
A Study on Structural Property of Ionomer as a Model for Catalyst Layer: Relationship between Thickness and Proton Conduction for Ionomer Thin Film on Different Substrate
Authors: Ohira Akihiro , Kuroda Seiiti , Mohamed Hamdy F. M.
Published: March 2013

To study the property of proton conduction for electrolyte thin film inside catalyst layer, model ionomer thin films were prepared on different surfaces such as carbon and platinum substrates. An atomic force microscopy coupled with electrochemical technique (e-AFM) demonstrated that proton conduction reduced with film thickness, and abruptly decreased when film thickness was less than 10 nm for both carbon and platinum substrate. This indicates that number of active proton conductive pathway and/or connectivity of proton path network change with film thickness, and is though that the morphology of thin film is essentially different from that of a bulk membrane.
Degradation of Perfluorosulfonic Acid Membrane Water Permeance via Formation of Sulfonic Acid Anhydrides
Authors: Clapham Shawn M. , Coms Frank D. , Fuller Timothy J. , Zou Lijun
Published: March 2013

Six perfluorosulfonic acid (PFSA) membranes were subjected to hygrothermal aging at 95 {degree sign}C and monitored by FTIR to assess the rates and extent of ionomer cross linking to the sulfonic anhydride form. Anhydride formation was observed to occur for all PFSA membrane structures studied. The rates of transformation were found to be strong functions of relative humidity, air flow and membrane thickness. Several membrane properties including water permeance, conductivity, and IEC were correlated with the extent of the cross linking reaction.
Cross-linked Aromatic Polymers for High Durability PEM Membranes: Materials and Methods
Authors: Di Vona Maria Luisa , Sgreccia Emanuela , Knauth Philippe
Published: March 2013

Sulfonated aromatic polymers (SAP) are promising ionomer materials, however for applications as fuel cell membranes these polymers must be improved in terms of durability. The goal is to achieve a locally high density of functional groups such as sulfonic acid groups, but to keep the swelling low by appropriate cross-linking. Thermal cross-linking in presence of residual solvent dimethylsulfoxide without any addition of cross-linker molecules increases spectacularly the mechanical and hydrolytic stability of SAP, making them suitable for use up to 130 {degree sign}C. The developed method is also inexpensive, being incorporated in the normal membrane casting procedure.
Proton Mobility in Hydrated Acidic Polymers: Consequences for Optimization of Proton Conductivity
Authors: Knauth Philippe , Di Vona Maria Luisa
Published: March 2013

Proton conductivity and water uptake of hydrated acidic polymers can be combined to calculate the effective proton mobility u(H+) in the acidic solutions inside ionomers. The quantitative analysis shows common features for various ionomers, which can be related to percolation and tortuosity. The decrease of the proton mobility with increasing proton concentration c(H+) can be described by a power law above the percolation threshold of hydrated nanometric channels.
PFG-NMR and SANS Studies in Cation Exchange Membranes Based on Sulfonated Polyphenylene Multiblock Copolymers
Authors: Yoshida Miru , Zhao Yue , Yoshizawa-Fujita Masahiro , Ohira Akihiro , Takeoka Yuko , Koizumi Satoshi , Rikukawa Masahiro
Published: March 2013

We employed the pulsed field gradient nuclear magnetic resonance (PFG-NMR) technique to investigate the self-diffusion coefficient of water, D-NMR, in newly designed cation exchange membranes, made of sulfonated poly(p-phenylene)-poly(ether ketone) multiblock copolymers, which are denoted by S-6H (n) x:y. The D-NMR value was measured as a function of the gradient strength, g, from 0.1 to 11.0 T m-1. S-6H (14) 1:1 showed the D-NMR value of 2.35 x 10-10 m2 s-1 at 30 ºC and 90% RH, which are about 10 times lower than the value in bulk liquid water. Small angle neutron scattering (SANS) measurements showed two peaks in S-6H (14) 1:1. The low q peak is attributed to the formation of microdomains and the high q peak is due to the formation of ionic clusters in the swollen microdomains.
Synthesis and Characterization of Polyethylene-g-Sulfonated Polysulfone Copolymers for Proton Exchange Membranes
Authors: Kim Hyung Kyu , Zhang Min , Yuan Xuepei , Lvov Serguei N. , Chung T. C. Mike
Published: March 2013

This paper discusses a new class of PEMs that are based on a PE-g-s-PAES graft copolymer containing several sulfonated poly(arylene ethersulfone) side chains. The unique combination of hydrophobicity, semi-crystallinity, and high molecular weight of PE backbone offers PEM with a strong and stable (non-swellable) matrix, and the embedded hydrophilic s-PAES proton-conductive domains show only moderate water swelling (λ <15) even with high IEC >3 mmol/g in the s-PAES domains. All PE-g-s-PAES PEMs show higher through-plane conductivity (up to 160 mS/cm) than in-plane conductivity, as well as good fuel selectivity. Evidently, the low surface energy of PE backbone forms a thin hydrophobic layer on the PEM surfaces that not only result in anisotropic conductivity but also create a methanol diffusion barrier to prevent fuel loss. Overall, the newly developed PE-g-s-PAES membranes offer a desirable set of PEM properties, including conductivity, selectivity, mechanical strength, stability, and cost-effective, for fuel cell applications.
Synthesis of Hydrocarbon Ionomer Materials and Evaluations of MEA
Authors: Miura Satoshi , Oshima Tatsuya , Umezawa Kensuke , Yoshizawa-Fujita Masahiro , Ohira Akihiro , Takeoka Yuko , Rikukawa Masahiro
Published: March 2013

We synthesized a new sulfonated phenylene block copolymer (S-PPBP-PES) by a Ni(0) coupling reaction. Membrane electrode assemblies (MEAs) were fabricated with the S-PPBP-PES ionomer and a Nafion 112 membrane. Five alcohols (methanol, ethanol, 1-propanol, 2-propanol, or mixed propanol) were used as the dispersion solvent for catalyst ink, and the effect of solvents on the fuel cell performance was investigated. These MEAs prepared with mixed propanol exhibited the highest power density among them due to the larger electrochemically active area and smooth surfaces of the catalytic layer compared with others.
Performance of the HT-PEM Membrane Electrode Assembly
Authors: Hjuler Hans Aage , Steenberg Thomas , Terkelsen Carina , Holst Thorsten , Garcia Hector R. , Cooper Kevin
Published: March 2013

High Temperature Polymer Electrolyte Membrane (HT-PEM) Fuel Cells provide an attractive alternative to Low Temperature (LT) PEM fuel cells with respect to fuel flexibility, simplified cooling system and balance of plant, higher value waste heat and no need for humidification of reactants. Polybenzimidazole (PBI) membranes doped with phosphoric acid have been demonstrated to be the most successful system to achieve high temperature operation of HT-PEM fuel cells. HT-PEM fuel cells face a number of challenges related to the performance that needs to be addressed. In this work we present the recent PBI membrane and single-cell fuel cell testing results with respect to performance and durability. In addition, we present results on the in-plane and through-plane ionic conductivity of phosphoric acid-doped PBI membrane. Lastly, we show preliminary results on post-mortem cell characterizations which are the key for understanding the breakdown mechanisms and maximizing cell performance and lifetime.
Performance Analysis of a High-Temperature Polymer Electrolyte Membrane Fuel Cell under Mechanical Compression Control
Authors: Diedrichs Anja , Wagner Peter
Published: March 2013

This work explores how the performance of a high-temperature polymer electrolyte membrane fuel cell is affected by the degree of compression. Contact pressure measurements in the range of 2 to 25 bars have been conducted on commercial membrane-electrode-assemblies (MEAs). When increasing the contact pressure, the MEA performance continuously decreases for lower current densities and increases or goes through a small maximum for higher current densities. The electrochemical characterization reveals a decrease in membrane as well as contact resistance and shows an increase in mass transport restriction, hydrogen crossover as well as electrical short circuits. The electrochemical active surface area is not affected by contact pressure rising. A comparison of two flow field types illustrates that the MEA performance not only depends on the geometry of the analyzed flow fields, but it is also influenced by the real contact area between flow field and MEA surface.
Thermogravimetric and Spectroscopic Investigation of the Interaction between Polybenzimidazole and Phosphoric Acid
Authors: Majerus Anne , Conti Fosca , Korte Carsten , Lehnert Werner , Stolten Detlef
Published: March 2013

Poly(2,5-benzimidazole) (ABPBI) doped with different acid concentrations were analyzed by means of conductivity and thermogravimetric measurements as well as Raman spectroscopy. The conductivity is measured as a function of temperature and relative humidity. The condensation of the phosphoric acid can be observed in the signal of the proton conductivity under dry conditions. Raman spectroscopic measurements of variously doped membranes are performed to investigate the ABPBI - phosphoric acid interactions. The results are correlated to those obtained from the conductivity measurements. The dehydration of the acid is confirmed by thermogravimetric analysis of pure phosphoric acid and doped ABPBI.
Novel Polybenzimidazole-Phosphoric Acid Membranes for Fuel Cell Applications
Authors: Yeager Gary William , Krishnan Lakshmi , Early Thomas A. , Zhang Tracy Chunxin , LaTorre Maria R.
Published: March 2013

Polybenzimidazole-phosphoric acid membranes have been used extensively in high temperature fuel cell applications. They are generally prepared either by copolymerization of tetramines and dicarboxylic acids (AA/BB copolymers) or by homopolymerization of diaminoacids (AB homopolymers). We describe the preparation of 4-(3,4-diaminophenylsulfonyl) benzoic acid, a diamino acid useful for the synthesis of novel AB polybenzimidazoles having excellent thermal and thermal-oxidative stability. The polymer, readily cast from polar aprotic solvents, when imbibed with phosphoric acid produces polymer electrolyte membranes exhibiting proton conductivities ranging from 0.06-0.12 S/cm at 80-160 {degree sign}C (20% RH) at a phosphoric acid doping level of 6.1.
Advanced Hybrid Super Acidic Inorganic-Organic PEMs for Hotter and Drier Operation
Authors: Herring Andrew M. , Horan James L. , Kuo Mei-Chen , Jessop Jeri D. , Schlichting Gregory J. , Yang Yuan
Published: March 2013

Copolymers of vinyl phosphonic acid with zirconium vinyl phosphonate have been synthesized via free radical polymerization from immiscible mixtures into amorphous, transparent, water stable, flexible membranes. Ion exchange capacities range from 6 to 10 meq/g corresponding to equivalent weights well below 200 g/mol. A 20wt% loading of the vinyl zirconium phosphonate co-monomer is XRD amorphous. It is shown that 1.5 of the 2 protons in the beginning acidic groups are dissociated in the 20wt% VZP loaded ionomer allowing these materials to have high proton conductivities, up to and exceeding 0.1 S cm-1 at 80{degree sign}C and 80%RH. Water uptake measurements show very little swelling of the material below 70%RH and ca. 1 water per proton at low RH. Proton conductivity under dry conditions, roughly 0.05 S cm-1 with a lambda < 1, indicates that the material conducts protons under limiting hydration conditions and strongly implicates transport by a pure Grotthuss mechanism.
Anhydrous Novel Acid-Base Binary and Ternary Systems for Fuel Cell Applications
Authors: Singh Marisa , Missan Harinder Pal Singh
Published: March 2013

A new series of anhydrous binary and ternary acid-base systems composed of trifluoroacetic acid (TFAA), imidazole (IM) and Poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-HFP) has been developed. The acid and base was added to the polymer in various compositions to improve the properties of polymer electrolyte such proton conductivity and thermal stability. However, it was found that some of the acid and base combinations outperformed the ternary system in proton conductivity testing obtaining conductivity in the 10-2 S/cm range. Further testing was then carried out on the binary systems to determine their suitability for use as high temperature performance materials. Analysis of their thermal stabilities found that these materials were not only good proton conductors but also had high thermal stabilities, where some of them resulted in high thermal stability of up to 200oC.
Membranes for a Regenerative H2/Br2 Fuel Cell
Authors: Park Jun Woo , Wycisk Ryszard , Pintauro Peter N.
Published: March 2013

Regenerative hydrogen bromine (H2/Br2) fuel cells, which utilize a membrane-electrode-assembly (MEA) with a polymeric cation exchange membrane, are an attractive energy storage system. In this paper, dual nanofiber electrospun composite proton exchange membranes were created by electrospinning two polymers: perfluorosulfonic acid (Nafion®) and polyphenylsulfone (PPSU). The dual nanofiber mat was processed into Nafion nanofibers embedded in PPSU. For this regenerative H2/Br2 fuel cell system, proton conductivity, the Br2/Br3- diffusion coefficient and permeability in composite membranes with different Nafion volume fractions are presented and discussed.
Composite Sulfonated Polyether Ether Ketone (SPEEK) Membranes with 3-(Trihydroxysilyl)-1-Propanesulfonic Acid for a Direct Methanol Fuel Cell (DMFC)
Authors: Yun Sukhwan , Parrondo Javier , Ramani Vijay K.
Published: March 2013

3-(trihydroxysilyl)-1-propanesulfonic acid (TPS) was used as a precursor to prepare SPEEK composite membranes (with added sulfonated silica). The ionic conductivity of SPEEK composite membranes (at 60oC in DI water) increased ~15 mS/cm after incorporation of 15wt% TPS, and the methanol permeability was slightly reduced (5-10%). Two batches of SPEEK with different ion exchange capacity (IEC) were prepared. SPEEK11 and SPEEK13 have IEC of 1.06{plus minus}0.02 mmolg-1 and 1.34{plus minus}0.05 mmolg-1, respectively. SPEEK11 +5wt% TPS and SPEEK13 +5wt% TPS composite membranes were tested in a DMFC at 60oC using air and 3M methanol, and the current density obtained at 0.4V was 187 mA/cm2 and 240mA/cm2 respectively.
Polyelectrolytes Functionalized Graphene as Metal-Free Electrocatalysts for Oxygen Reduction
Authors: Dai Xianfeng , Shi Penghui , Ding Lei , Tian Binglun , Liu Shiyao , Qiao Jinli
Published: March 2013

This work reports PDDA and QHECE-functionalized graphene nanosheets (N-GNSs) as metal-free catalyst for the oxygen reduction reaction in alkaline media. Although GNSs, PDDA or QHECE alone has little catalytic activity, their hybrid exhibits an unexpected high ORR activity. The structure, morphology, composition, and surface properties of the N-GNSs catalysts were characterized by transmission electron microscopy (TEM), and linear sweep voltammetry (LSV) as well as rotating disk electrode (RDE) techniques. An enhancement in the ORR electrocatalytic activity on N-GNSs was observed with increasing the mass ratio of N:GNSs, where QHECE:GNSs = 1:4 exhibits the highest activity for the ORR with onset potential and the half-wave potential of 0.06V and -0.1V, respectively.
Catalyst Coated PBI Membrane High Temperature Assemblies
Authors: Donzel Nicolas , Séphane Nicolas , Kreisz Aurélien , Bernard d'Arbigny Julien , Jones Deborah J , Rozière Jacques
Published: March 2013

A route has been developed to stabilise a polybenzimidazole gel membrane formed in polyphosphoric acid by simultaneous cross-linking. With increasing degrees of cross-linking the mechanical properties of the high acid content PBI membranes are significantly improved, while the phosphoric acid content and the membrane conductivity are not greatly affected. PBI/H3PO4 membranes are generally integrated into an assembly using gas diffusion electrodes. In the present work, cross-linked PBI membranes have been used as substrates for catalyst coated membrane preparation using a Pt/C catalyst transferred by decal to the membrane surfaces. The final membrane electrode assemblies have been characterized for their high temperature performance and durability.
Evaluation of the Pt/C Catalyst for Fuel Cells Prepared by a NanoparticleFormation Pulsed Arc Plasma Source
Authors: Agawa Yoshiaki , Endo Satoshi , Matsuura Masamichi , Ishii Yoshikazu
Published: March 2013

We have proposed a new platinum catalyst supporting method using a nano particles formation pulse arc plasma source.This supporting method has the following features.1) Distribution of nano particle diameter is small. 2) Nano particle diameter can be easily controlled by changing discharge parameter. 3) Nano particle diameter can be kept constant while its deposition rate is changed.4) Since nano particles are adhered to surface of the supporting material strongly, aggregation of the catalysts can be suppressed even at high temperature..5) Platinum catalyst on the carbon powder for polymer electrolyte fuel cell electrodes was prepared using this method, and current / voltage characteristic of its MEA was evaluated. Although its performance is a little inferior compared with the conventional catalyst market prepared by a wet process , it may be concluded that a good characteristic is acquired taking account of platinum quantity of 1/10 of the conventional one.
Influence of Pore Structure of N-Doped Mesoporous Carbon in PEM Fuel Cells
Authors: Shrestha Sujan , Ashegi Sasha , Timbro Jeffrey , Mustain William E
Published: March 2013

SBA-15 was treated with different concentrations of tetraethyl orthosilicate (TEOS) in the presence of HCl, which catalyzed the hydrolysis and condensation of TEOS, resulting in additional silica to be deposited onto SBA-15, modifying its structure. Although the pore size distribution (PSD) plot showed that wall thickness of SBA-15 changed upon treatment with TEOS, the pore size of the resulting nitrogen doped mesoporous carbon (NMC) did not change significantly. The NMCs were increasingly structurally disordered with the additional TEOS treatment. When platinum nanoparticles (Pt NPs) were deposited on them, uniform particle size and distribution was obtained. Among the NMCs, the most disordered sample showed the lowest activation and mass-transfer overpotentials in a laboratory scale proton exchange membrane fuel cell.
Pt Nanoparticles Dispersion Influence on Fuel Cell Performance
Authors: Darab Mahdi , Gómez de la Fuente Jose Luis , Skinlo Thomassen Magnus , Sunde Svein
Published: March 2013

Distinct membrane electrode assemblies (MEAs) fabricated of three electrocatalysts with different nano-structural orientation of Pt particles were studied in terms of ex-situ and in-situ electrochemical activity by a liquid electrolyte cell and a single-cell PEMFC respectively. The results exhibited that the electrochemical performance and durability are highly influenced by the dispersion of platinum nanoparticles over the matrix of the support. The variations of the electrochemical performances with respect to pure isolated Pt particles, a film of networked nanoparticles and a mixture of individual particles and aggregated ones were presented with addresses to fuel cell performances.
Theoretical Study of the Structure, Stability and Oxygen Reduction Activity of Ultrathin Platinum Nanowires
Authors: Matanović Ivana , Kent Paul R.C. , Garzon Fernando H. , Henson Neil J.
Published: March 2013

We use density functional theory to study the difference in the structure, stability and catalytic reactivity between ultrathin, 0.5-1.0 nm diameter, platinum nanotubes and nanowires. Model nanowires were formed by inserting an inner chain of platinum atoms in small diameter nanotubes. In this way more stable, non-hollow structures were formed. The difference in the electronic structure of platinum nanotubes and nanowires was examined by inspecting the density of surface states and band structure. Furthermore, reactivity towards the oxygen reduction reaction of platinum nanowires was addressed by studying the change in the chemisorption energies of oxygen and hydroxyl groups, induced by inserting the inner chain of platinum atoms into the hollow nanotubes. Both ultrathin platinum nanotubes and nanowires show distinct properties compared to bulk platinum. Nanotubes with diameters larger than 1 nm show promise for use as oxygen reduction catalysts.
Oxygen Reduction Activity of Vapor-Grown Platinum Nanotubes
Authors: Papandrew Alexander B. , Atkinson Rob W. , Goenaga Gabriel A. , Wilson David L. , Kocha Shyam S. , Neyerlin K.C. , Zack Jason W , Pivovar Bryan S. , Zawodzinski Thomas A.
Published: March 2013

Supportless platinum nanotubes are synthesized by the decomposition of a platinum acetylacetonate vapor within anodic alumina templates at 210 {degree sign}C. As synthesized, the nanotubes are nanoparticulate aggregates composed of Pt crystallites approximately 3 nm in diameter and with a range of lengths from 1 μm to 20 μm. Annealing treatments result in crystallite growth and morphological evolution of the tubular nanostructures. The oxygen reduction activity of the PtNTs was investigated using the rotating disc electrode method at room temperature. PtNTs annealed at 500 {degree sign}C exhibited a specific activity of 2084 μA/cm2Pt at 0.9 V, a value approaching that of polycrystalline Pt. The electrochemical surface area of the annealed structures was found to be quite low, from 5-10 m2/g, resulting in moderate overall mass activity of up to 177 mA/mgPt.