bluuebunny/crossref_metadata_2025 huggingface dataset:
Active Area Determination for Porous Pt-Electrodes used in PEM Fuel Cells - Temperature And Humidity Effects
Authors: Wreland Lindström Rakel , Korstdottir Katrin , Lindbergh Göran
Published: September 2009

This paper aim to discuss a proper measure of the electrochemical active area of carbon supported Pt nanoparticle catalyst used in polymer electrolyte membrane (PEM) fuel cells. The cyclic voltammetric determination of hydrogen under potential deposition (Hupd) and carbon monoxide monolayer oxidation (CO stripping) performed in a fuel cell at fuel cell relevant conditions are compared and the influences of operation temperature (25-80 {degree sign}C) and relative humidity (RH) (40-90% RH) are discussed. The results show that both the shape and the charge of the Hupd are strongly dependent on operating conditions. However, for the CO stripping experiments only a negative shift in potential with increasing temperature or humidity was observed in accordance with results from aqueous electrolytes, whereas the charges for CO monolayer oxidation were almost constant for the temperatures investigated.
Properties of Catalyst Layers Prepared by Electrospray Deposition
Authors: Chaparro Antonio M. , Folgado M. Antonia , Gallardo Blanca , Martín Antonio J. , Daza Loreto
Published: September 2009

Catalyst layers composed of Pt/C catalyst with ionomer (NafionR), for proton exchange membrane fuel cell (PEMFC) electrodes, have been prepared by electrospray deposition. Relevant properties for electrochemical fuel cell reactions are studied, related with total surface area (BET), platinum electroactive area, and single cell testing. Studies of surface area show lower values on electrospray deposited layers, compared with layers prepared by other methods (airbrush). It appears that a higher proportion of mesopores is filled with the ionomer, which reflects closer interaction between the ionomer and the catalyst aggregates. On the other hand, the electrochemical active area of Pt/C electrosprayed films shows values above those of films deposited by other common techniques or commercial electrodes. Electrode testing as cathodes in single cells shows better performance of electrosprayed layers due to lower electrode resistance, as a consequence of the improved distribution and interaction of the ionomer film among Pt/C catalyst aggregates.
Degradation Studies of PEMFC Cathodes Based on Different Types of Carbon
Authors: Wesselmark Maria , Lagegren Carina , Lindbergh Göran
Published: September 2009

In this study different accelerated degradation tests were used evaluating three different carbon supports as well as a thin model electrode. Cyclic ADTs, by 1000 cycles beween 0.6 and 1.2 V in nitrogen, did not degrade the porous electrodes to any larger extent in terms of oxygen reduction activity, whereas a significant loss of electrochemical surface area was seen, often more than 50%. Potentiostatic hold at 1.4 V during 3 h, did not permanently degrade the electrodes but instead an improved activity was obtained after rest during night. A correlation of increase in double layer capacitance and improved performance was seen and believed to be caused by the good proton conductivity of carbon surface oxides. CO-stripping peaks revealed that the humidity and wetting of NafionTM may have caused the observed temporary changes during the potentiostatic hold.
Development of High Durability Bi-functional Oxygen Electrode for Unitized Regenerative Fuel Cell (URFC)
Authors: Jung Ho-Young , Ganesan Prabhu , Popov Branko
Published: September 2009

The performance of different PtIr catalysts with varying Ir contents was optimized under fuel cell and in electrolyzer mode in unitized regenerative fuel cell (URFC). Overall conversion efficiency of 49% was obtained with 85Pt:15Ir catalyst composition. The long term stability of the URFC was improved using gold coated Ti bipolar plates. The characteristics of gold coated Ti bipolar plates were studied using x-ray diffraction (XRD), cyclic voltammetry (CV), and linear sweep voltammetry (LSV). An attempt was made to prepare high stability microporous layer (MPL) using corrosion resistant graphitized carbon. In addition, the hydrophobic characteristics of the bifunctional oxygen electrode (BOE) catalyst were modified by the incorporation of 5 wt.% PTFE binder in the catalyst layer.
Durability Investigation of a PEM-type Unitized Reversible Cell
Authors: Kato Atsushi , Masuda Masao , Takahashi Atsushi , Ioroi Tsutomu , Yamaki Masahiro , Ito Hiroshi
Published: September 2009

A PEM-type unitized reversible cell (URC) is combined the functionality of a fuel cell (FC) and water electrolyzer (WE) in one unitized device. In past researches, it was confirmed that URC had enough conversion efficiency and output compared with individual function of FC and WE. In this study, durability for each mode (single mode and switching mode between WE and FC) were verified by using single cell with electrode area of 250cm2 for practical use. As results, a few thousand level of durability was confirmed at each single operation mode. And the same level of durability was confirmed even in the switching mode that is the most practical mode in URC.
Effect of SO2 Concentration and Relative Humidity on Contamination of Cathode and Anode in PEMFC
Authors: Kaneko Keisuke , Tsushima Shohji , Hirai Shuichiro
Published: September 2009

Catalyst poisoning by the SO2 supply to proton exchange membrane fuel cells (PEMFCs) under open circuit voltage (OCV) and load operational conditions was examined using simultaneous monitoring of cell voltage and SO2 emissions from the cathode exhaust. Results show that cell voltage reduction is inversely proportional to the concentration of supplied SO2. Experiments with different relative humidity conditions and measurement of the electro-chemical surface area (ECSA) by cyclic voltammetry investigated considerable RH effects on contamination of anode electrodes. At OCV condition, anode contamination was observed with a decrease of RH condition; little poisoning existed in fully dried conditions. On the other hand, little poisoning occurred at load operational conditions.
Structures and CO Tolerance of Anode PtRu Catalyst for Polymer Electrolyte Fuel Cells
Authors: Takeguchi Tatsuya , Yamanaka Toshiro , Wang Guo-Xiong , Muhamad Ernee N. , Ueda Wataru
Published: September 2009

An anode catalyst for a polymer electrolyte fuel cell should be CO-tolerant, i.e., it should have the function of hydrogen oxidation in the presence of CO, since hydrogen fuel gas generated by the steam reforming process of natural gas contains CO. PtRu/C catalysts with the same degree of Pt-Ru alloying and with various sizes of PtRu particles were prepared, and the dependence of CO tolerance on particle size was investigated. Polarization curves were obtained with pure H2 and CO/H2 (CO concentrations of 500-2040 ppm). It was found that highly dispersed PtRu/C (HD) with small metal particles has much higher CO tolerance than that of poorly dispersed PtRu/C (LD) with large metal particles. The CO tolerance of PtRu/C (HD) was higher than that of a commercial PtRu/C catalyst. The high CO tolerance of PtRu/C (HD) is probably due to efficient concerted functions of Pt, Ru, and their alloy.
Theoretical Study of the Effect of Ni Doping on Catalytic Activity of Nano-clusters for Fuel Cell Applications
Authors: Shirvanian P.
Published: September 2009

Using density functional theory (DFT) calculations, we systematically study dissociation/adsorption and stability of oxygen/hydrogen on Pt3Ni cluster to find insight into the enhanced ORR mechanism on this alloy cluster. The adsorption studies show that both hydrogen and oxygen undergo dissociative adsorption in the side-on approached to the nano-clusters with higher adsorption energy associated with oxygen on Ni-doped nano-cluster. This is explained in terms of the d-band upshift of the Pt3Ni cluster and the charge transfer from Ni to Pt leading to an increased d-orbital density of states near the Fermi level.
Key Parameters for the Preparation of High Performance PtRu/C Anode Catalyst for DMFC
Authors: Lo Man-Yin , Chen Yen-Ze , Chen Ying-Chieh , Chen Yu-Wen
Published: September 2009

Catalyst accounts for more than half the cost of MEA in Direct methanol Fuel Cell (DMFC). PtRu/C is currently the state-of-the-art catalyst for the anodic methanol oxidation reaction (MOR). However, the inferior performance of the current state-of-the-art PtRu/C catalyst remains one of the major obstacles towards the realization of DMFC. Development of low cost and high performance anode catalyst is therefore desperately needed in order to bring DMFC to the consumers market. In this study, carbon support with high surface area, in conjunction with its surface modification, was employed in order to enhance the dispersion of Pt and Ru active sites. Enhancement in PtRu dispersion resulted in the decreases in particle size and increases in PtRu utilization. Furthermore, better dispersion of PtRu was obtained when NaH2PO2 was used as the reduction agents in the deposition-precipitation procedure. The conductivity of the carbon support also contributes to the performance of the catalyst towards MOR. Details on the key parameters for the preparation of high performance PtRu/C catalyst for the anodic MOR will be revealed in this paper.
Comparing Proton Conductivity of Polymer Electrolytes by Percent Conducting Volume
Authors: Kim Yu Seung , Pivovar Bryan
Published: September 2009

Proton conductivity is a critical property for polymer electrolytes used in fuel cells. Mass based water uptake and ion exchange capacity are typical characteristics used to make comparisons between polymer electrolytes, but have significant limitations when correlated to proton conductivity of different polymer electrolytes. In this paper, we report a length scale parameter, percent conducting volume, which is rather simply obtained from the chemical structure of polymer to compare proton conductivity of different polymer electrolytes. Morphological effects on proton conductivity at low relative humidity are also discussed using the percent conducting volume parameter.
Surface Structure Analysis of Polymer Electrolyte Membrane under Water Permeation Process by Tapping-Mode Atomic Force Microscopy
Authors: Tsushima Shohji , Tsubota Akihiro , Tabuchi Yuichiro , Hirai Shuichiro
Published: September 2009

Through-plane water permeation across the membrane is one of the fundamental processes involved in operational PEMFCs. In recent years, water transport resistance at the membrane-gas interface has been reported and is related to relative humidity applied to the membrane. In this study, we investigated variation of surface structure of the membrane under water permeation process by using tapping-mode atomic force microscopy (AFM). AFM results revealed that surface structure of the membrane depends on relative humidity at the both side of the membrane and also suggested that local equilibrium was not necessarily established at the membrane-gas interface under water permeation associated in the membrane.
Nafion Nanofiber Membranes
Authors: Lee Kyung Min , Choi Jonghyun , Wycisk Ryszard , Pintauro Peter N. , Mather Patrick
Published: September 2009

A new type of proton conducting fuel cell membrane has been fabricated and evaluated via preliminary physical property determinations. The membrane is composed of a 3-D interconnected network of Nafion (perfluorosulfonic acid) nanofibers that have been embedded in an uncharged and inert polymer matrix. Nafion was successfully electrospun into fibers by adding to the spinning solution a low concentration (1 wt% relative to Nafion) of high molecular weight poly(ethylene oxide). Membranes were made with an average fiber diameter in the range of 161-730 nm, where the nanofiber mat occupied 60-80% of the membrane volume. The inert matrix polymer was UV-crosslinked Norland Optical Adhesive 63. The resulting membranes exhibited a high proton conductivity (0.06-0.08 S/cm at 25oC in water), low water swelling (12-23 wt% at 25oC), and improved mechanical properties, as compared to a recast homogeneous Nafion film.
Novel PVdF-graft-VIm Based Nano-composite Polymer Electrolyte Membranes for Fuel Cell Applications
Authors: Stewart Kerrilee A. , Singh Marisa , Missan Harinder Pal Singh
Published: September 2009

Nano-composite polymer electrolyte membranes were synthesized by the grafting of a vinyl based base molecule unto a fluorinated polymer backbone, namely poly(vinylidene fluoride). Polymer acid-base blends were synthesized using dicarboxylic acid based acid polymer with the grafted polymer. The properties of the membranes have been found to improve with the addition of acid polymer into the blend and could be due to the acid base interactions taking place between the polymers. Ternary system membranes has also been developed containing the graft polymer, triflic acid and poly(ethylene-co-acrylic acid) using in-situ approach. Ionic conductivity of 10-3 S/cm and higher has been observed for these systems. Nano-composite blend and ternary system membranes have also been developed by addition of nano-tubular titanium dioxide. The synthesized membranes have been studied for their morphological, electrical, thermal and mechanical properties. High conductivities, good morphological structure and thermal stabilities were observed for blend membranes as well as for nanocomposite ternary system membranes.
Development of Covalently Cross-linked and Composite Perfluorosulfonic Acid Membranes
Authors: Zhang Yong Ming , Li Lei , Tang Junke , Bauer Bernd , Zhang Wei , Gao Hong Rong , Taillades-Jacquin Melanie , Jones Deborah J. , Rozière Jacques , Lebedeva Natalia , Mallant Ronald
Published: September 2009

A straight forward approach to increase proton conductivity at relatively dry conditions is to increase the number of sulfonic acid groups in the polymer. Although various PFSAs of significantly lower EW can be prepared, the limitation of this approach is that the polymer and membrane properties are also affected, with membranes showing increased water uptake and dimensional swelling. Our approach has been to develop a series of approaches for the cross-linking of PFSAs in order to improve membrane mechanical properties and reduce membrane swelling in the presence of water. Novel side-chain component multifunctional monomers have been developed that are cross-linkable after membrane fabrication. The result of this approach is that a suite of polymers have been synthesized that, after membrane casting and cross linking show excellent proton conductivity, even under conditions of elevated temperature and <50% RH.
Proton Exchange Membranes for High Temperature Fuel Cells: Equivalent Weight and End Group Effects on Conductivity
Authors: Maalouf Manale , Pyle Brandon , Sun Che-Nan , Wu Dongsheng , Paddison Stephen J. , Schaberg Mark , Emery Michael , Lochhaas Kai H. , Hamrock Steven J. , Ghassemi Hossein , Zawodzinski Thomas A.
Published: September 2009

The proton conductivity and water uptake were measured for a series of 3M ionomer membranes with various equivalent weights (EWs) and different acid groups. For the EW variation, the conductivity of PFSA samples with EW as low as 580 g/eq were studied. Results show that conductivity increases with decreasing EW. In particular, at lower EW conductivity dramatically increases at low RH. For 580 EW at 120oC, the conductivity exceeds the target set by DOE for automotive fuel cells (100 mS/cm). The effect of water content is investigated through water uptake measurements that showed the clear dependence of conductivity on lambda (λ). Moreover, the nature and effects of changes in the morphology are studied with simulations and NMR relaxation and diffusion measurements probing the effect of water content on long vs. short range motions. For the different acid groups, conductivity and water uptake of polymers with sulfonic acid, sulfonyl amide and asymmetric sulfonyl imide end groups were compared.
Engineered Gas Diffusion Layers for Proton Exchange Membrane Fuel Cells
Authors: Blanco Mauricio , Wilkinson David P. , Wang Haijiang , Liu Simon Z.S.
Published: September 2009

The present study was carried out to determine how perforated metal sheets used as cathode gas diffusion layers affect fuel cell performance at different operating conditions. Analysis indicated that in-plane gas diffusion of these engineered materials had to be taken into account with through-plane gas diffusion in order to achieve enhanced fuel cell performance. Although these structured gas diffusion layers are in an early stage of development they have great potential to reduce cost and they can be tailored to improve the overall performance of the fuel cell under any operating condition. This may allow a reduction in the system requirements for the fuel cell (e.g., lower humidification, lower flow rates, etc.) which would reduce overall parasitic losses. The design and modeling process and predictive capability for these components is also improved due to their simplified nature.
Evaluation of Gas Diffusion Performance in Wet GDL with 3D Pore Network Model
Authors: Inoue Gen , Matsukuma Yosuke , Minemoto Masaki
Published: September 2009

Various GDL structures were developed by numerical analysis, for example, carbon paper, paper with binders and cloth. Next, our past two-phase network model was improved and we evaluated the gas diffusion performance in wet various GDL with this model.
Study of the effects of transport porous layer wettability and morphological properties on the water percolation in PEMFC
Authors: Medici Ezequiel F. , Allen Jeffrey S.
Published: September 2009

A two dimensional network model is implemented to simulate the capillary-driven two-phase flow regime taking place inside a fuel cell. The fuel cell model is of the cathode and includes a catalyst layer, a gas diffusion media, and a single gas channel. Water generation is modeled as a source term proportional to the fuel cell current intensity. The pore size distribution is generated using a Weibull distribution functions. Six different porous transport layers models are considered. These models correspond to six different pore size distributions generated by varying the scale and shape parameters in the Weibull probability distribution function. A parametric study of the wetting properties of the gas diffusion media is also carried out considering five typical contact angle values for non-wetting surfaces. The average pressure at the water injection place, the non-dimensional water-air interface length and the non-dimensional wetted area are discussed for each simulation.
Contamination of Membrane-Electrode Assemblies by Ammonia in Polymer Electrolyte Fuel Cells
Authors: Zhang Xiaoyu , Serincan Mustafa F. , Pasaogullari Ugur , Molter Trent
Published: September 2009

Experimental and computational investigation of contamination of polymer electrolyte fuel cell (PEFC) membranes and catalyst layers with ammonia (NH3) is reported. Cyclic voltammetry (CV) scans and electrochemical impedance spectroscopy (EIS) analyses show that trace amounts of ammonia can significantly contaminate both the polymer electrolyte membrane (PEM) and the catalyst layers. The results show that the catalyst layer contamination can be reversed under certain conditions, while the membrane recovery tends to be much slower, and permanent effects of ammonia contamination is observed. A model is also developed to predict the degradation of the cell performance due to the decrease in membrane conductivity. The model incorporates Nernst-Planck equations to represent the multi-component cationic transport across the membrane, which helps differentiate between the degradation due to internal resistance and contamination of the catalyst layers. Mechanisms of contamination of the polymer electrolyte and catalyst layers, and performance degradation of the PEFC are also postulated.
Using a Reference Electrode to Understand the Effect of Trace Fuel Contaminants on PEMFC Behavior
Authors: Jung Myunghee , Van Zee John W.
Published: September 2009

With commercialized GORE{trade mark, serif} PRIMEA® 57 Series MEAs, a reference electrode was implemented by using NAFION® strips and tested without any modification in the normal fuel cell set up. Registration measurements showed that even acceptable manufacturing tolerances can affect the potential measured with this reference electrode. The data show the NAFION® strip should be attached to the side with an oversized cathode to measure the change of anode potential relative to reference electrode. The reference electrode was used to obtain the change of the anode overpotential during CO poisoning.
In-situ Diagnostics for Cell Performance and Degradation
Authors: Stumper Juergen , Rahmani Reza , Fuss Felix
Published: September 2009

A 10-cell Mk 9 stack was characterized using current/voltage mapping during automotive drive cycle testing. Using performance, voltage loss breakdown and CO-stripping data so called degradation "fingerprints" were constructed that provide deeper insights into the underlying degradation modes. Three degradation phases could be distinguished and characterized by the dominant loss type. Localized OCV measurements are shown to provide useful information about crossover leak formation and location.
Impact of Solvent on Ionomer Structure and Fuel Cell Durability
Authors: Johnston Christina M. , Lee Kwan-Soo , Rockward Tommy , Labouriau Andrea , Mack Nathan , Kim Yu Seung
Published: September 2009

Electrode structure within PEFCs, including the Pt-ionomer interface, is created while making electrodes from catalyst inks based on ionomer dispersed in solvent. The relationship between final electrode structure and processing conditions is poorly understood. We have varied the solvent used in cathode catalyst inks, and then subjected the resulting MEAs to hydrogen-air performance and durability testing. Specifically, cathodes cast from inks based on inonomer dispersions in water-propanol-isopropanol (W/P cathode) initially perform better than cathodes cast from glycerol-based dispersions (Gly cathode), but are far less durable. After 10,000 potential cycles from 0.60 V to 1.0 V in N2, the performance on air of the W/P cathode falls significantly below that of the Gly cathode. NMR and neutron scattering measurements of ionomer dispersions, as well as AFM and TEM data from cast ionomer films, offer insight into how the effect of solvent choice on the ionomer structure may impact durability.
Proton Conducting Ionic Liquid Electrolyte for High Temperature PEMFC
Authors: Martinez Mathieu , Iojoiu Cristina , Judeinstein Patrick , Cointeaux L. , Lepretre Jean-Claude , Sanchez Jean-Yves
Published: September 2009

The paper deals with the synthesis and characterisation of proton conducting ionic liquids (PCIL) and their polymer electrolytes obtained by blending modified Nafion membranes with different concentrations of PCIL. We studied the impact of the acid nature on the PCILs thermal and electrochemical performances. It has been shown that the membranes conductivities depend more on the PCIL structure than on its intrinsic conductivity. Conductivities approaching at 130{degree sign}C those of current Nafion membranes at 80{degree sign}C and 98% relative humidity were obtained with the best blends.
Regression Analysis of High Temperature PBI Based PEMFC Performance
Authors: Ubong Etim , Dimitrov Boyan , Domadia Aadil
Published: September 2009

Four factors are used to investigate the effect of temperature, pressure (of air and hydrogen) and current (load) on the output voltage (response variable) of a 45 cm2 high temperature polybenzimidazole (PBI) based proton exchange membrane fuel cell. A statistical approach is introduced to obtain a good regression model to unravel the impact of these factor variables on the response variable. The validation of the model is achieved by using various comparison statistical tests applied upon the experimentally observed data. In most cases the results show a good agreement between hypotheses based on the early obtained experimental observations and this massive data approach. We conclude that there are a sufficiently large number of regression models which accurately predict the behavior of the cell within the range of variables tested and modeled.
Development of Direct Ethanol Fuel Cell Membrane Electrode Assemblies Using Sulfonated Polyetheretherketone Mixed-Matrix Membranes
Authors: Cremers Carsten , Jung Florina , Kintzel Birgit , Roelofs Kimball , Schiestel Thomas , Tübke Jens
Published: September 2009

In the framework of a project funded by the Fraunhofer Gesellschaft, a direct ethanol fuel cell has been developed. As part of the development, a new catalyst concept for the anodic oxidation of ethanol at an increased CO2 efficiency by using two different catalysts for two steps in the reaction process has recently been presented. Furthermore, new membranes based on an organic-inorganic mixed-matrix which exhibit reduced ethanol cross-over at an increased selectivity for water diffusion, have been developed. In this paper we will describe the developments which were made to integrate these two approaches into membrane electrode assemblies. The obtained membrane electrode assemblies showed better performance in a DEFC compared to membrane electrode assemblies using Nafion® 115, in particular at low temperature and low cathode airflow conditions which are typical for portable applications.
Simultaneous Measurement of Proton Conductivity and Methanol Permeability for the Development of Direct Methanol Fuel Cell Membranes
Authors: Beer Leanne , Olmeijer David L. , Lefebvre Mark C.
Published: September 2009

DMFC membrane development is complicated by the fact that the two most important transport properties, methanol crossover and proton conductivity, are coupled, thus strategies that improve one property will almost invariably have an undesirable effect upon the other. Each measurement is usually done in separate experiments, even under different conditions. These measurements can be carried out in fuel cells and are indeed simultaneous, however, many complicating factors can interfere with the derived properties. This paper presents a methodology for the simultaneous measurement of membrane conductivity and methanol permeability. The equipment and method will be presented, and examples discussed including a comparison to analogous in-fuel cell results as well as examination of a series of experimental DMFC membranes. Further, a graphical means of viewing transport results as well as the derived benefits in rapid analysis and comparison of candidate membranes will be presented.
Fabrication of Metal Matrix Composites Based on Stainless Steel Having Low Electrical Contact Resistance by Powder Metallurgy
Authors: Choi Joon-Hwan , Choi Jong-Jin , Ryu Jungho , Hahn Byung-Dong , Yoon Woon-Ha , Lee Byoung-Kuk , Park Dong-Soo
Published: September 2009

Metal matrix composite materials having low electrical contact resistance based on 316L stainless steel (STS) matrix alloy with ZrB2 or TiB2 particles were fabricated for PEMFC separator by powder metallurgy (PM). The addition of the boride particles remarkably enhanced electrical conductivity on the surface compared to commercial STS alloys. SEM observation on the surface of the samples revealed that the boride particles were protruded out of the matrix surface and the particle density existing on the surface increased with increasing the boride content, causing increase of the total contact area between the conductive particles and gas diffusion layer. The ICR of the samples also decreased with increasing the boride content resulted from the increased contact area. The enhanced electrical property is possibly attributed to the conductive particles protruded out of the matrix surface acting as electrically conductive channels through the passive film formed on the stainless steel matrix.
Root-Cause of Hysteresis in Capillary Pressure Curves of Porous Media Used in PEM Fuel Cells
Authors: Gao Yan , Wang Xuhai , Nguyen Trung V.
Published: September 2009

In this study, experimental results of the micro-pump and volume displacement methods were compared to elucidate the root-cause of hysteresis in capillary pressure measurements. It was shown that hysteresis between the imbibition curve and drainage curve was apparent in the capillary curve of the micro-pump system. The measured capillary pressure curves by the micro-pump technique were observed to be highly dependent on the pump rate. Results of the volume displacement method showed that the hydrophobic layer affected both imbibition and drainage processes. Results showed higher pressure was needed to introduce water into the sample and hysteresis was observed only when the hydrophobic layer was used.
PEMFC Metallic Bipolar Plates: Effect of Manufacturing Method on Corrosion Resistance
Authors: Koc Muammer , Mahabunphachai Sasawat , Dundar Furkan
Published: September 2009

Estimated high production volumes of bipolar plate manufacturing, strict dimensional and surface quality requirements and nature of their designs with thousands of meters of micro-channels demand engineers and scientists from production, design, and fuel cell operations sides look into alternative manufacturing processes, and compare their outcomes in terms of certain metrics such as productivity (plate/second), dimensional tolerances (um/mm), surface quality (Ra),cost ($), corrosion and contact resistance, and durability. In this study, the effect of manufacturing processes, stamping and hydroforming, on the corrosion resistance of thin metallic plates was investigated. The effects of process speed (stamping speed, hydroforming pressure rate) were also considered in this study. The results showed that in general SS316L possesses better corrosion resistance than SS304, as expected and reported in many literatures. In addition, while the effect of manufacturing processes was expected to degrade the corrosion resistance of the formed plates when compared the a non-deformed plate, this hypothesis only held true in the case of stamping as the hydroformed plates revealed better corrosion resistance than a non-deformed plate.
Effect of Micro Porous Layer on Membrane Hydration Path under Low Humidity Operation of PEMFC
Authors: Fujii Yoshinobu , Tsushima Shohji , Hirai Shuichiro
Published: September 2009

Micro porous layer (MPL) effects on membrane hydration under a low-humidity condition were examined in a polymer electrolyte membrane fuel cell (PEMFC) using nuclei-labeling magnetic resonance imaging (NL-MRI). This technique enables investigation of the effects of three water sources--humidification water at the cathode, humidification water at the anode, and water generated through electrochemical reactions--on membrane hydration. Results show that MPL increases the membrane water contents at the cathode side. Furthermore, the MPL at the cathode side enhances membrane hydration by water generated by the electrochemical reaction and interferes with membrane hydration of humidification water at the anode.
In-situ Measurements of Contact Resistance and In-situ Durability studies of Steels and Coatings to be used as Bipolar Plates in PEMFCs
Authors: Oyarce Alejandro , Holmström Nicklas , Bodén Andreas , Randström Sara , Lindbergh Göran
Published: September 2009

In this study, a fast, low cost and reliable methodology for bipolar plate material screening and testing is presented. Ex-situ measurements of contact resistance are used as a screening tool, while in-situ measurements such as: fuel cell performance, in-situ contact resistance, high frequency impedance spectroscopy, together with post analysis of stainless steel surfaces, MEAs and fuel cell effluent water evaluates the real performance of the most promising stainless steels and coatings, providing reliable data for future fuel cell stack test.
Effect of Tungsten Addition on Electrochemical Property of Austenitic Stainless Steel in a Simulated PEMFC Environment
Authors: Kim Kwang Min , Kim Jong Hee , Kim Kyoo Young
Published: September 2009

Austenitic stainless steel is considered as a candidate material for metallic bipolar plate in PEMFC due to its good mechanical property and reasonably good corrosion resistance. Austenitic stainless steel with addition of various amounts of W was evaluated in terms of corrosion and contact resistance in a simulated PEMFC environment. Results from electrochemical test and contact resistance test showed that addition of W content below 4wt% in the austenitic stainless steel not only improved the corrosion resistance but also reduced the contact resistance. However, W addition above 4wt% increased the amount of precipitates and reduced the corrosion resistance. From XPS analysis, it was confirmed that improvement of the corrosion resistance was due to the formation of stable WO3 as well as to the enhanced amount of MoO42- which acted as an inhibitor.
Electrode Degradation in PEMFCs as Studied in Model Systems and PEMFC Testing
Authors: De Bruijn Frank A. , Dam Van-Anh T. , Janssen Gaby J. , Makkus Robert C.
Published: September 2009

In order to meet the durability criteria for PEM Fuel Cells, needed for their successful application in transport, more insight is needed into which conditions have a detrimental effect on the long term performance, and which materials improvements are needed to make PEMFC better suited to withstand some of these conditions that are unavoidable in practice. To obtain such insights ex situ model studies under well-defined conditions as well as in situ accelerated stress tests under more realistic conditions have been combined. MEAs using state of the art materials have been subjected to 57 freeze/thaw cycles or 30,000 voltage cycles. Both conditions lead to a decrease in electrochemical surface area; in addition, voltage cycling leads to significant oxygen transport losses. Model studies in perchloric acid revealed that both platinum and carbon corrode when exposed to high potentials at high temperatures. Decreasing temperature leads to a significant decrease in the corrosion rates.
Accelerated Durability Testing of Perfluorosulfonic Acid MEAs for PEMFCs Using Different Relative Humidities
Authors: Rodgers Marianne P. , Agarwal Rohit , Pearman Benjamin P. , Li Bo , Slattery Darlene K. , Bonville Leonard J. , Kunz Harold R. , Fenton James M.
Published: September 2009

Durability studies were carried out on membrane electrode assemblies (MEA)s containing commercial Nafion® membranes. Fuel cells were run under hydrogen/air for 100 hours at 10 to 100% relative humidity, 90 and 100 oC, and open circuit voltage. The voltage was monitored during the durability test, as was the condensate water for presence of fluoride ions. Crossover current (CO), electrochemically active surface areas (ECA), and polarization curves were evaluated pre- and post- test. High and low %RH (10 and 80-100% RH) resulted in the least degradation while medium-low %RH (20-30% RH) resulted in the highest level of degradation. By examining the various parameters that were used to measure the level of degradation more closely, it may be possible to gain a deeper understanding of how the humidity of an operating fuel cell effects degradation.
Catalyst Structure - Performance Trends for Sibunit Carbon Based Cathodes for Proton Exchange Membrane Fuel Cells
Authors: Lebedeva Natalia , Booij Arend , Voropaev Ivan , Simonov Pavel , Romanenko Anatoly , Bukhtiyarov Valerii
Published: September 2009

Synthetic mesoporous carbon - Sibunit - offers a unique possibility to tune porous structure of the catalyst support without changing other textural parameters, enabling fundamental studies of the support structure - catalyst performance relationship. Three different Sibunit carbons with similar surface area of ca. 450-500 m2/g but widely varying pore size distribution were used for the preparation of the 40 wt% Pt/C catalysts for the cathode in H2/O2 PEMFC. Porous structure of the catalyst support was shown to affect both Pt utilization and the transport properties of the catalyst. Presence of the small - 3-4 nm in diameter - pores was shown to increase the utilization of Pt, while impairing the transport properties of the catalyst. For Sibunit supports, featuring large meso- and macropores, a lower degree of Pt utilization was found. Electrodes prepared using the latter catalysts exhibit excellent transport properties, comparable to those of the commercial benchmark Vulcan XC72 material.
HPW/MCM-41 Mesoporous Silica Composites as Novel Proton Exchange Membranes for Elevated Temperature Fuel Cells
Authors: Lu Shanfu , Wang Deli , Lu Jinlin , Zeng Jie , Jiang San Ping
Published: September 2009

A novel inorganic proton exchange electrolyte based on highly ordered mesoporous MCM-41 silica with assembled phosphotungstic acid is synthesized through vacuum-assisted impregnation method. The structure and physical properties of the electrolytes before and after impregnation were characterized and compared with conventional impregnated method by using TEM, SAXS, FT-IR and BET method. The proton conductivity of the electrolytes obtained by vacuum-assisted impregnation is 0.018 S cm-1 and 0.045 S cm-1 at 25 ° and 150 °, respectively. The cell based on the inorganic proton exchange membrane achieved a power density of 95 mW cm-2 in a H2/O2 at 100 ° and 100% RH, and 90 mW cm-2 in methanol/O2 at 150 ° and 0.67% RH.
Nafion/Tin Oxide Composite Membranes for Direct Methanol Fuel Cells
Authors: Chen Fang , D'Epifanio Alessandra , Mecheri Barbara , Traversa Enrico , Licoccia Silvia
Published: September 2009

Composite Nafion-based membranes were prepared and characterized, using hydrated tin oxide as a filler. Water Uptake and proton conductivity were measured as a function of temperature. Methanol crossover through reference Nafion and composite membranes was evaluated by a voltametric method and the electrochemical performance of the membranes was assessed by tests in a single direct methanol fuel cell (DMFC). The formation of the composite improved the properties of Nafion matrix in terms of methanol crossover and DMFC performance, allowing to identify Nafion membrane with 10wt% tin oxide as a suitable electrolyte to be used in a DMFC device operating at T {greater than or equal to} 90 degree C.
Low Potential Electrolysis of Aqueous Glycerin Using Polymer Electrolyte Membrane
Authors: Yahiro Hidenori , Matsunaga Yamato , Asamoto Makiko , Yamaji Tsuyoshi
Published: September 2009

Electrolysis of aqueous glycerin using polymer electrolyte membrane (PEM) was investigated. Electrolysis of aqueous glycerin was achieved with lower applied cell voltage (0.4 V) than that of water and simultaneously hydrogen was produced from the cathode side. Electrolysis efficiency of aqueous glycerin was increased with an increase in operating temperature.
Fabrication of On-Chip Fuel Cells on Polymer Substrates
Authors: Tominaka Satoshi , Nishizeko Hiroshi , Shinohara Hidetoshi , Mizuno Jun , Osaka Tetsuya
Published: September 2009

Here we report fabrication of tiny on-chip fuel cells on polymer films. Since on-chip cells which we have so far fabricated on silicon substrates through a series of microfabrication procedures are of a simple microchannel-based design, their fabrication on a polymer substrate by molding is attractive in terms of the rapid fabrication and of the inexpensive fabrication procedures and materials. To do so, a nickel mold was first prepared by electroplating from the conventional silicon-based cell, i.e., a master, and then the cell was replicated on cycloolefin polymer films by hot embossing. The microchannel thus replicated on the polymer film was confirmed to be almost identical to the silicon master by observation with a confocal microscope. Finally, Au current collectors sufficiently adhesive to the polymer were successfully deposited after the surface modification by an oxygen plasma treatment.
Gas Purge for Switching of Polymer Electrolyte Unitized Reversible Fuel Cell
Authors: Ito Hiroshi , Maeda Tetsuhiko , Kato Atsushi , Yoshida Tetsuya , Ulleberg Øystein
Published: September 2009

Unitized reversible fuel cells combine the functionality of a fuel cell and electrolyzer in one unitized device. Gas purge operation is essential for switching from electrolyzer to fuel cell operation at a polymer electrolyte unitized reversible fuel cell. In order to examine the relationships between the spending time and the gas flow rate, a gas purge model is presented. The model considers physical phenomena such as evaporation and diffusion from liquid water in the GDL and the membrane. Experimental data obtained with two cells with different size are also presented. The simulated curves of high frequency resistance versus time are in good agreement with the experimental data.
Fuel Cell Stack Operation with Low Cathode Stoichiometry with Cells or Sections Fed in Series
Authors: Bezmalinović Dario , Barbir Frano
Published: September 2009

Reducing the air flow rate at the stack inlet could lower parasitic power and improve the system efficiency. However, this gain should not be offset by the loss of stack performance due to lower cathode stoichiometry. A configuration in which the sections of a stack are fed in series enabling operation at low stoichiometry while each section operates with significantly higher stoichiometry is analyzed. A drawback is that the second and each subsequent section would operate with reduced oxygen concentration at the inlet. The results of experimental and numerical analysis show that for the high pressure systems a stack with cathode sections fed with air in series could be considered as an alternative to the conventional parallel-fed stack design. However, this advantage diminishes for the systems with reduced parasitic losses such as the systems operating at lower pressures and the high pressure systems with an expander at the cathode exhaust.
Investigation into PEFC Characteristics Using Four-Layer Electrode Catalyst
Authors: Ide Masahiro , Umeda Minoru , Ikeda Hironosuke
Published: September 2009

Water management of the catalyst layer in a polymer electrolyte membrane fuel cell was improved by focusing on the three-phase boundary. To fabricate the cathode catalyst layer, carbon-support with catalyst and fluorocarbon resin were mixed and heat-treated at the melting temperature of fluorocarbon resin. The transmission electron microscopy images of this electrode catalyst showed that the surfaces of the catalyst particle and of the carbon-support were partly coated by thin film of melted fluorocarbon resin. Ionomer electrolyte material was added to this electrode catalyst, and an electrode catalyst with a four-layer structure was fabricated. The durability at 50{degree sign}C of a single cell using the four-layer electrode catalyst as the cathode was examined. The deterioration rate was lower than that using the conventional three-layer electrode catalyst. In addition, a load change test at 50{degree sign}C, and a durability test at room temperature gave good results.
Pt-Co Electrodeposited Electrodes: Surface Distribution and Depth Profile
Authors: Martín Antonio J. , Chaparro Antonio M. , Guillén Cecilia , Folgado M. Antonia , Daza Loreto
Published: September 2009

Electrodeposition is used for the preparation of Pt-Co electrodes for proton exchange membrane fuel cells. Lateral and in-depth inhomogeneities in the composition of the electrodes are followed with different techniques. Cross sectional analysis shows a profile of catalyst concentration decreasing towards the interior of the carbon black substrates. Sputtering assisted XPS analysis shows that the top surface has higher proportion in Pt, increasing the amount of alloyed Co in layers below. Lateral inhomogeneities in composition can be checked on 4x4 cm2 electrodes with X-ray fluorescence mapping. The electrodes have been tested as cathode in single cell, showing enhanced mass specific activities when compared with standard electrodes.
High Pressure Study of Localized States Related to Lanthanide Ions in Solids
Authors: Grinberg Marek
Published: September 2009

The latest results on high pressure investigations of luminescence related to Pr3+and Eu2+ in different lattices are presented in this contribution. In the latter case the influence of pressure on anomalous luminescence in BaxSr1-xF2 for x=0, 0.3 and 0.5 and 1, and the LiBaF3:Eu2+ system as a function of pressure are presented and discussed. A theoretical model describing an impurity trapped exciton as a system where the first carrier is localized at the impurity and the second one is captured by the Coulomb potential at Rydberg-like states is developed. The model is used to analyze the anomalous luminescence in Eu2+ doped fluorides and pressure quenching of Pr3+ luminescence in oxides. The model explains the differences in the formation of an impurity trapped exciton in dependence, if the first excited impurity state belongs to 4fn or 4fn-15d1 electronic configurations.
Modeling of Optical Properties of 3d and 4f Ions
Authors: Brik Mikhail G.
Published: September 2009

Examples of application of three different models (exchange charge model of crystal field, modified Judd-Ofelt theory and DFT-based ab initio calculations of the band structure and optical properties of pure and doped crystals) are described in the present paper. The considered hosts are as follows: CsCdCl3, CsCdBr3, and MgBr2 doped with Ni2+; 50GeO2-43PbO-5PbF2-2PrF3 glass; pure and Nd3+-doped YAlO3. Results of calculations are discussed and compared with available experimental data.
On the Luminescence of Octahedrally Coordinated Eu2+ in CsCaF3
Authors: Happek Uwe , Aycibin Murat , Srivastava A. M. , Comanzol Holly , Camardello Sam
Published: September 2009

The luminescence of divalent europium in CsCaF3 is characterized by an extreme blue shift with increasing temperature. First reported by Sommerdijk and Bril in 1976, more recently this shift has been attributed to an excitonic emission by Dorenbos. Considering that CsCaF3 is a textbook example for the Jahn Teller effect (Eu2+ is octahedrally coordinated), a splitting of the degenerated d-levels due to the Jahn-Teller effect is an alternative model to explain both the large Stokes shift at low temperature and the blue shift of the emission at elevated temperatures.
Electron Transfer between RE3+ Ions in Oxide Hosts: Experiments and Initial Quantitative Analysis
Authors: Setlur Anant , Shiang Joseph
Published: September 2009

We discuss the electron transfer (ET) reactions between the excited Ce3+(5d1) level and Yb3+/Eu3+ in oxide hosts. The exothermic free energy of this ET reaction is estimated using spectroscopic parameters, while the re-organizational energy is estimated using the Marcus theory for ET in molecular systems and solvents. Using these parameters and a semi-classical model for the ET rate, we quantitatively analyze these ET processes.
Light Emission in Three-dimensional Si/SiGe Nanostructures: Physics and Applications
Authors: Tsybeskov Leonid
Published: September 2009

In this paper we discuss physics and applications of light emission in SiGe nanostructures. In order to be commercially valuable, these light emitters should be efficient, fast, and operational at room temperature. Another important requirement is in the emission wavelength, which should match the optical waveguide low-loss spectral region, i.e., 1.3-1.6 μm. Among other approaches, epitaxially-grown Si/SiGe quantum wells and quantum dot/quantum well complexes produce efficient photoluminescence (PL) and electroluminescence (EL) in the required spectral range. Until recently, the major roadblocks for practical applications of these devices were strong thermal quenching of the luminescence quantum efficiency and a long carrier radiative lifetime. The latest progress in the understanding of physics of carrier recombination in Si/SiGe nanostructures is reviewed, and a new route toward CMOS compatible light emitters for on-chip optical interconnects is proposed.