bluuebunny/crossref_metadata_2025 huggingface dataset:
Pt Coating on Flame-Generated Carbon Particles and Their Application for a Catalytic Electrode of Proton Exchange Membrane Fuel Cell (PEMFC)
Authors: Choi In Dae , Lee Donggeun
Published: October 2008

Carbon black, activated carbon and carbon nanotube have been used as supporting materials for precious metal catalysts used in fuel cell electrodes. One-step flame synthesis method is used to coat 2-5nm Pt dots on flame-generated carbon particles. By adjusting flame temperature, gas flow rates and resident time of particles in flame, we can obtain Pt/C nano catalyst-support composite particles. Additional injection of hydrogen gas facilitates pyrolysis of Pt precursor in flame. The size of as-incepted Pt dots increases along the flame due to longer resident time and sintering in high temperature flame. Surface coverage and dispersion of the Pt dots is varied at different sampling heights and confirmed by Transmission electron microscopy (TEM), Energy-dispersive spectra (EDS) and X-ray diffraction (XRD). Crystalline and surface bonding groups of carbon are investigated through X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The electro-catalytic property of Pt/C composites for the application to catalytic electrode PEMFC are also investigated by Cyclic voltammetry (CV).
Behavior of Water Molecules in PEFCs as Studied by 1H NMR Spectroscopy
Authors: Nosaka Atsuko Y. , Nosaka Yoshio
Published: October 2008

Water molecules confined in perfluorinated ionomer membranes which are extensively used for polymer electrolyte fuel cells, presented characteristic 1H NMR spectra reflecting the difference in the morphology. For the hydrated membrane the water molecules at the distinct segments of the polymer undergo rapid exchange to give an apparent single signal. The signal shifts to the higher field with increasing the water content due to the increase of the fraction of the bulk water molecules. On shortage of bulk water the morphological conversion takes place. The membrane of such morphology exhibits a spectrum with separated regions at room temperature regardless of the water content, since the morphology prohibit the rapid exchange among the water molecules localized at the distinct segments. The characteristic spectral changes of water molecules associated with the chemical exchange among the water molecules in the different water domains and the change of the polymer morphology were demonstrated
Electrocatalytic Properties of Pyrochlore-Type Oxide for PEFC
Authors: Iwanaga Takuro , Takase Satoko , Shimizu Youichi
Published: October 2008

Electrocatalytic properties of various pyrochlore-type oxides (A2-xA'xB2O7−Z: A = Pb, A' = Pb, Bi, Sb, In; B = Ru) synthesized by a co-precipitation method were systematically investigated for oxygen reduction, hydrogen oxidation and tolerance of CO poisoning for the electrocatalyst of the polymer electrolyte fuel cell. Most of the pyrochlore-type oxides could be synthesized by the co-precipitation method at 380 - 600oC in aqueous solutions. The electrode containing Pb1.9In0.1Ru2O7-Z prepared at 380oC indicated high oxygen reduction activity, 181mA/cm2 at +0.4 V vs. RHE in 2N H2SO4. In addition, hydrogen oxidation current density of Pb2Ru2O7-Z was 117mA/cm2 at 0.2V vs. RHE in same solution. Pb1.9M0.1Ru2O7-z (M = In, Sb, Bi, Pb) oxides indicated rather high oxygen reduction activity in the order of M= In > Sb > Bi > Pb.
Magnetic Resonance Imaging as an In-Situ Diagnostic Method to Characterize Water Flooding
Authors: Dunbar Zachary W. , Masel Richard I.
Published: October 2008

Water management remains a significant challenge for the commercialization of PEM fuel cells. Many mathematical models have been created to gain insight into the effects of water distribution on cell performance. However, model verification remains difficult due to the challenging nature of acquiring relevant experimental data about water generation and movement inside an operating fuel cell. In this work, magnetic resonance imaging (MRI) is demonstrated as a strong diagnostic tool to gather information about water generation and transport inside an operating PEM fuel cell. The MRI technique is used to gather quantitative water distribution data in three dimensions. Acquisition times are as fast as 8 seconds, allowing observation of dynamic processes within the flow channels. Flow channel depth, geometry and hydrophobicity are varied, and the effect on water distribution and overall cell performance measured.
Measurement of Oxygen Distribution underneath Ribs with Pressure Sensitive Paint
Authors: Okamiya Minoru , Yamamoto Takashi , Sano Seiji , Kajiwara Takashi
Published: October 2008

Pressure Sensitive Paint (PSP) is useful measuring method to analyze oxygen distribution underneath a rib in a fuel cell. High spatial resolution of the PSP measurement is made by creating the uniformly thin PSP film. By using spin coating, which is effective implement to make a thin film, the spatial resolution is improved to 150 µm. PSP phosphorescence intensity depends on oxygen partial pressure. An accurate image of oxygen partial pressure is obtained from calibration curve of each pixel of a PSP image, which is captured by a CCD camera. By calculating each oxygen partial pressure from each calibration curve of its pixels, the error of oxygen partial pressure is decreased to 10%.
Probing Liquid Water Profile in the Polymer Electrolyte Fuel Cell Membrane
Authors: Mukherjee Partha P. , Springer Thomas , Mukundan R. , Hussey Daniel S. , Jacobson David , Arif Muhammad , Borup Rodney L.
Published: October 2008

Water transport in the ionomeric membrane, typically Nafion®, has profound influence on the performance of the polymer electrolyte fuel cell, in terms of internal resistance and overall water balance. In this work, the response of Nafion® membrane water content and the resulting water gradient to fuel cell operational variability are investigated and the results from a theoretical modeling study are furnished along with reference to neutron imaging observations.
MRI Investigation of Water Transport Mechanism in a Membrane under Elevated Temperature Condition with Relative Humidity and Current Density Variation
Authors: Ikeda Tomofumi , Koido Tetsuya , Tsushima Shohji , Hirai Shuichiro
Published: October 2008

An environmentally controlled MRI technique was used to investigate the effect of relative humidity and current density on the transverse water content profile in a membrane under fuel cell operation at elevated temperature. MRI visualization revealed that, in the dry condition (40% RH), the water content in the membrane was around 3 and the water content profile was flat. In the wet condition (92% RH), a higher water content of around λ=15 was observed than that at 80% RH, suggesting that the generated water in the cathode catalyst layer was transported to the membrane at 92% RH. A larger water concentration gradient was observed at 0.1A/cm2 with 92% RH than that at 80% RH, suggesting that the larger water content in the membrane induced greater electro-osmotic drag, since the electro-osmosis coefficient was positively correlated with the water content.
Performance Improvement in PEMFC using Aligned Carbon Nanotubes as Electrode Catalyst Support
Authors: Liu Di-Jia , Yang Junbing , Kariuki Nancy , Goenaga Gabriel , Call Ann , Myers Deborah J.
Published: October 2008

A novel membrane electrode assembly (MEA) using aligned carbon nanotubes (ACNT) as the electrocatalyst support was developed for proton exchange membrane fuel cell (PEMFC) application. A multiple-step process of preparing ACNT-PEMFC including ACNT layer growth and catalyzing, MEA fabrication, and single cell packaging is reported. Single cell polarization studies demonstrated improved fuel utilization and higher power density in comparison with the conventional, ink based MEA.
Preparation and Characterization of Pt/NbTiO2 Cathode Catalysts for Unitized Regenerative Fuel Cells (URFCs).
Authors: Ganesan Prabhu , Huang Shenyang , Popov Branko N.
Published: October 2008

Nb-doped TiO2 support in pure rutile phase with high electrical conductivity (0.83 S cm-1) was synthesized by a simple hydrolysis method. The synthesized support showed disordered mesoporous structure with a surface area of 35 m2g-1. The support showed better stability than Vulcan carbon at more anodic potentials. Nanosized Pt particles were deposited by a borohydride reduction method. Pt/Nb-TiO2 catalyst showed comparable oxygen reduction reaction (ORR) activity and selectivity (> 95%) that of a conventional Pt/C catalyst when tested in rotating ring disk electrode (RRDE).
750 EW Perfluorosulfonic Acid Composite Membranes With Stabilized Phosphotungstic Acid for High Temperature/Low Relative Humidity PEM Fuel Cells
Authors: Mohajeri Nahid , Pearman Benjamin P. , Rodgers Marianne , Agarwal Rohit , Slattery Darlene , Bonville Leonard , Kunz H. R. , Fenton James M.
Published: October 2008

750 EW perfluorosulfonic acid composite membranes with 15% phosphotungstic acid (FSEC3) were prepared and characterized for high temperature/low relative humidity PEM fuel cell. The membranes at different stages of fabrication, i.e., as cast, Cs treated, and protonated were evaluated with FTIR, XRD, TGA, water uptake, TEM and SEM. By using a low relative humidity atmosphere during the fabrication process, particle sizes of ~20 nm for Cs-PTA within the membrane were achieved. At 30{degree sign}C and 80% relative humidity a conductivity of 80 mS/cm for FSEC3 membrane was measured, which is 2.5 times higher than Nafiona^ 112 conductivity at the same conditions and exceeds the current DOE milestone of 70mS/cm.
Qualitative Determination of H2S Crossover Rates in Nafion{trade mark, serif} Membranes using Ion-probe Techniques
Authors: Brosha Eric L. , Rockward Tommy , Uribe Francisco A. , Garzon Fernando H.
Published: October 2008

The H2S permeability through dry and humidified Nafion{trade mark, serif} PEMFC membranes was studied using ion probe techniques. A sulfide anti-oxidant buffer solution was used to trap and concentrate trace quantities of H2S that permeated through 50 cm2 samples of Nafion{trade mark, serif} 117 and 212 membranes using a partial pressure difference up to 1030ppm at room temperature. Experiments were conducted for up to 24 hours in order to achieve sulfide ion concentrations high enough to be precisely determined by subsequent titration with Pb(NO3)2. The rate of H2S crossover for dry 117 and 212 were identical at 1.2e-7 g/min. Humidification increased the crossover rate to 5.9e-7 g/min and 1.8e-6 g/min for 117 and 212 respectively. An accurate determination of permeation constants from this work was not possible because the H2S partial pressure was found to be not constant throughout the experiment.
R&D of Asahi Kasei Aciplex Membrane for PEM Fuel Cell Applications
Authors: Miyake Naoto , Kita Kohei , Honda Masatoshi , Tanabe Tsuneaki
Published: October 2008

Asahi Kasei Chemicals Co. (AKC) has been developing and producing perfluorinated ionomer membrane for PEFC (PEM) to become new business as the core of membrane and energy business in the future. Recently we focus on R&D of PEM for both stationary and automotive application. In this paper, our latest achievement is summarized and elucidation of membrane degradation mechanism is also conducted.
Direct Alcohol Electro-oxidation in an Intermediate Temperature Fuel Cell
Authors: Otomo Junichiro , Nishida Satoru , Kato Hiroyuki , Nagamoto Hidetoshi , Oshima Yoshito
Published: October 2008

Anodic reactions in a direct alcohol fuel cell (DAFC) at intermediate temperature (250 oC) were investigated from the standpoint of achieving high performance. In order to evaluate the temperature effect on the electro-oxidation of small alcohols in the intermediate temperature region, a kinetic study on the electro-oxidation of methanol and ethanol on Pt/C was conducted using a single cell fabricated with CsH2PO4 proton conducting solid electrolyte. At 250 oC, the current density of ethanol electro-oxidation is comparable to that of methanol electro-oxidation in a low potential region (< 400 mV vs. RHE). In addition, the analysis of reaction products suggests that C-C bond cleavage in ethanol electro-oxidation can proceed at the intermediate temperature. Through the electrochemical measurements, characteristic features in the alcohol electro-oxidation at the intermediate temperature were discussed.
Modelling and Simulations on Mitigation Techniques for Carbon Oxidation Reaction Caused by Local Fuel Starvation in a PEMFC
Authors: Hu Jingwei , Sui Pang-Chieh , Djilali Ned , Kumar Sanjiv
Published: October 2008

A two dimensional model is developed to simulate carbon corrosion reaction caused by local fuel starvation during the operation of a PEMFC. This work focuses on the evaluation of different mitigation techniques for carbon corrosion reactions, namely use of catalyst with high oxygen evolution reaction (OER) activity, membrane of low O2 diffusivity, corrosion-resistant carbon support and high proton conductivity in the catalyst layer. It is found that using the OER-favorable catalyst and low O2-diffusivity membrane are two effective techniques for mitigation of carbon corrosion reaction for local starvation.
Water Transport and Degradation Analysis in PEMFC by in-situ MRI Visualization
Authors: Hirai Shuichiro , Tsushima Shohji
Published: October 2008

Recent developments in MRI visualization for water transport and degradation analyses in PEMFC are presented. High-resolution MRI experiments were performed for a 117-μm-thick membrane. Partial dehydration of the membrane's anode side was visualized with the increase of current density. Nuclei-labeling MRI was also presented. Results demonstrated its unique potential for direct visualization of the water source on membrane hydration using D2 and D2O. Spatially-resolved NMR was also applied to a degraded membrane. The membrane's cathode side, as measured using 1H-NMR spectra, showed a greater chemical shift.
Direct Imaging of Hydrated Polymer Electrolyte Membranes for Fuel Cell Application
Authors: Park Moon Jeong , Balsara Nitash P.
Published: October 2008

Ion conducting polymers containing sulfonic acid are of interest for the fuel cell applications. This study is based on sulfonated poly(styrene-b-methylbutylene) block copolymers. In dry state, these materials show remarkably rich sequence of phase transitions, i.e., lamellae, gyroid, hexagonally perforated lamellae, hexagonal cylinder, and disorder, depending on temperature, molecular weight, and fraction of sulfonated monomers. The effect of hydration on the dry morphologies is determined by a combination of in-situ neutron scattering and cryogenic electron microscopy.
PEM Fuel Cell with Dead-ended Operation
Authors: Pien Michael , Warshay Marvin , Lis Stephen , Jalan Radha
Published: October 2008

ElectroChem, Inc. has demonstrated a dead-ended fuel cell operating at very low excess oxygen requirement and maintaining very stable performance. The fuel cell not only showed significantly higher voltages at high current density but also demonstrated the gravity-independent operation. The dead-ended operation significantly enhances the fuel cell power density by creating self-humidification and obtaining high efficiency of gas utilization.
The Effect of Pt Cluster Size on Micro-Morphology of PEMFC Catalyst Layers- A Molecular Dynamics Simulation
Authors: Cheng Chin-Hsien , Malek Kourosh , Djilali Ned
Published: October 2008

An equilibrium molecular dynamics simulation is employed to investigate the morphology changes inside the catalyst layer (CL) due to different sizes of Pt particles. The microstructure formed during the fabrication stage determines majority of the CL performance. Different sizes of the nano Pt particles are formed during the fabrication process. It is important to investigate the relation between the microstructure and the Pt cluster sizes. Different sizes (about 1, 2 and 3 nm) of Pt particles are considered in the present work. It was found that the small Pt particles (case of 1 nm) tend to merge to form a larger Pt cluster. This was not so in the case of lager Pt particles (2nm and 3nm). The microstructure formed at various Pt cluster sizes is shown to be quite different. Detailed information about the structure was obtained by carrying out structural analysis in view of radial distribution function (RDF)
Composite Nanofiber Network Membranes for PEM Fuel Cells
Authors: Choi Jonghyun , Lee Kyung Min , Wycisk Ryszard , Pintauro Peter , Mather Patrick
Published: October 2008

A new class of proton-exchange membranes has been developed and characterized, where an interconnected network of proton conducting polymer nanofibers is embedded in an inert (non-conducting) polymer matrix. In the present study the nanofiber network membrane contained electrospun fibers from sulfonated poly(arylene ether sulfone) solutions (with/without sulfonated polyhedral oligomeric silsesquioxane, sPOSS). The membranes were characterized in terms of morphology, proton conductivity, and water uptake. In-plane proton conductivity was measured using a BekkTech cell that was placed in a controlled temperature/humidity chamber. The data show: (1) There was a modest increase in nanofiber > 50%.membrane conductivity when the IEC of the fibers was increased from 2.1 to 2.6 mmol/g (in the absence of sPOSS), (2) There was a substantial increase in membrane conductivity when sPOSS was added to the fibers, and (3) The proton conductivity of the sPOSS-loaded membranes was significantly higher than that for a commercial Nafion 212 sample at 30oC for a relative humidity
Design of Filling Polymer Electrolytes for 3DOM Composite Membrane
Authors: Sasajima Keiji , Munakata Hirokazu , Kanamura Kiyoshi
Published: October 2008

Three-dimensionally ordered macroporous (3DOM) silica composite membrane including a binary polymer consisting of sulfonated poly (ether ether sulfone and poly styrene (SPEES-PS) was fabricated by stepwise filling method. In the SPEES-PS composite, SPEES coated 3DOM-silica surface and PS occupied a vacancy of remaining pore of SPEES composite. Therefore, the structure of SPEES-PS composite were core-shell like structure. Water uptake and methanol permeability of SPEES-PS composite was greatly suppressed. However SPEES-PS composite exhibited relatively high proton conductivity.
Proton Conductive Inorganics for Composite Membranes in PEM Fuel Cells
Authors: Wang Chunmei , Chalkova Elena , Lute Christopher , Fedkin Mark , Komarneni Sridhar , Chung T.C. Mike , Lvov Serguei
Published: October 2008

The main objective of this study is to synthesize new membrane materials in which inorganic proton conductors are deposited within a functionalized and cross-linkable Teflon-type polymer. These new composite membranes are aimed to efficiently conduct protons at temperatures above 100 oC and relative humidity (RH) down to 25% in proton exchange membrane (PEM) fuel cells. To effectively choose inorganic proton conductors, the conductivity studies of different materials are performed in our lab. An experimental system was developed and Gamry Electrochemical Impedance Spectroscopy (EIS) was applied to measure the proton conductivity of inorganic materials. Alpha zirconium phosphate was used as a standard to check the accuracy of the present experimental approach. The conductivity of the solid acid sulfated zirconia (S-ZrO2) was studied. The proton transport mechanisms in inorganic proton conductors were discussed.
The Optimization SPEEK Membranes using Phosphotungstic Acid as a Dopant
Authors: Rhoden Stephen L. , Linkous Clovis A.
Published: October 2008

As pollution and climate change continues to affect the world renewable, non-polluting sources of fuel are vital. Hydrogen fuel cells have been shown to be very effective in converting fuel to usable energy, with water being the only product. Sulfonated poly aryl compounds such as sulfonated poly(etheretherketone) (SPEEK) are oxygen-containing organic polymers, which when hydrated exhibit proton-conducting properties. The use of solid inorganic fillers such as phosphotungstic acid (PTA) to increase proton conductivities at high temperatures is of much interest to MEA fabricators. Previously we showed that SPEEK membranes doped with 15 wt% PTA that had been treated with a 0.1 M cesium carbonate solution to render the it insoluble, increased the conductivity by over one order of magnitude over a range of relative humidities. The optimal loading of PTA into the membrane, plus conditions for PTA and SPEEK membrane co-precipitation are both of much interest.
Design and Control Method for Compact BOP of Direct Methanol Fuel Cell
Authors: Chang Young-Soo , Cho Changhwan , Kim Youngchan
Published: October 2008

We have developed an electro-chemical model of a stack to analyze its performance. The model includes methanol solution at the anode to "cross over" to the cathode through, which reduces the system efficiency and increases fuel consumption. BOP (Balance of plants) system - condenser, cooler, and methanol solution tank - was modeled. Dynamic simulation was performed to evaluate and develop a control algorithm of the fuel cell system for an efficient operation of DMFC. We simulated the effects of the varying total UA (overall heat transfer coefficient), and proposed minimum UA of the condenser and cooler. When the volume of the methanol solution tank decreases below a certain level, ON/OFF based control algorithm leads to an unstable fuel cell operation. By adopting PID based control algorithm, the system has better controllability of methanol concentration and power generation in response to load change under the same methanol solution tank volume.
Model and Experimental Study of Hydrodynamic Coupling between a Fuel Pump and a Direct Methanol Fuel Cell
Authors: Buie Cullen , Santiago Juan
Published: October 2008

Controlled experiments on a direct methanol fuel cell (DMFC) elucidate the effects of methanol flow rate and current density on pressure drop across the DMFC anode. A novel experimental technique is developed to measure void fraction, liquid slug length, and velocity of the slug/annular two phase flow exiting a DMFC anode. For the explored channel geometry, hydraulic diameter (Dh) of 600 microns, pressure drop scales with the number of slug/bubble interfaces, surface tension, and Dh. We present an empirical correlation of more than 160 measurements to aid in predicting pressure drop for DMFCs of similar scale. This work will aid in the design of fuel pumps for miniature DMFC systems.
Investigation of Carbon Loss on the Cathode during PEMFC Operation
Authors: Takeuchi Norimitsu , Fuller Thomas F.
Published: October 2008

Carbon loss phenomena, such as partial hydrogen starvation and startup, have been investigated in previous works. Even for short times, these situations can be fatal and some mitigation were suggested to improve PEMFC durability. Small carbon loss occurs under ordinary PEMFC operation. Although this impact is less than for hydrogen starvation and startup, it is still large enough to cause the degradation of PEMFC cell performance after long-term operation. Carbon loss under PEMFC operation is investigated in this work with a physical model. These results suggest that high cell potential, high humidity, and imbalance of water vapor pressure in the cell affect carbon loss. Oxygen reduction promoted carbon loss due to a reduced solution potential at the fuel-cell cathode-membrane interface.
Mechanical Degradation Behavior of Recast Composite PFSA Membrane and Nafion® N-112 Membrane under OCV Condition
Authors: Huang Xinyu , Rodgers Marianne , Yoon Wonseok , Li Bo , Mohajeri Nahid
Published: October 2008

The authors report the mechanical degradation behavior of perfluorosulfonic acid (PFSA) membranes under open circuit voltage hold condition. The degradation behavior of an ePTFE reinforced PFSA membrane impregnated with phosphotungstic acid (PTA) in cesium form was compared with that of an extruded Nafion® N-112 membrane. Membrane electrode assemblies were fabricated by spraying carbon supported platinum catalysts on either side of the membrane. Diagnostic tests were conducted before and after 100 hours of OCV hold period. Mechanical tests were performed on as-fabricated MEAs and MEAs after OCV hold test. The PTA additive was found to be very effective in reducing fluoride emission rates. However, the mechanical strength decay for both type of membranes remains significant. The composite membrane retained a comparatively higher level of residual toughness than the N112 membrane. SEM analysis revealed localized cracks form inside the membranes as a result of OCV hold.
The Displacement Fields of Atoms in Nanoparticles of Platinum and its Alloys Adsorbed onto a Carbon Substrate: Effect on Fuel Cell Catalysis
Authors: Subbaraman Ram , Zawodzinski Thomas , Mann Jay A.
Published: October 2008

The structure of supported nanocatalysts plays a significant role in the kinetics of fuel cell reactions. A molecular dynamics (MD) approach to understanding the structure based on the interaction energy between atoms in the nanoparticle and support is presented. The effect of particle size on the "strain," as represented by the displacement field, is determined for nanoparticles of platinum and various alloys. Effects of alloying elements and the nature of the support are discussed.
Effect of the Micro Porous Layer on Water Transport under Low Humidity Condition
Authors: Fujii Yoshinobu , Tsushima Shohji , Fukuzato Katsuhiko , Hirai Shuichiro
Published: October 2008

An effect of a micro porous layer (MPL) on water transport under a low-humidity condition was examined in a PEMFC with a single straight channel using a tunable diode laser absorption spectroscopy (TDLAS) measurement system, which can measure local through-plane water transport based on measurement of the distribution of water vapor concentration along the channel. The TDLAS results showed that the MPL imparts mass transport resistance at the cathode side under low-humidity conditions with co-flow and counter-flow modes and enhanced back-diffusion of the generated water to the anode side. The MPL at the cathode side strongly affected through-plane water transport and is therefore effective for membrane hydration under low-humidity conditions.
Influence of Ionomer Equivalent Weight on Kinetic and Transport Properties in PEFC MEAs
Authors: Sambandam Satheesh , Ramani V.
Published: October 2008

The ionomer/binder type and composition can influence both ionic and mass transport in a PEFC electrode. For an electrode to have minimum resistance to O2, proton and electron transport, the ionomer composition has to be optimized for its EW and volume fraction. An optimum ionomer composition in the electrode results in higher Pt utilization and hence better MEA performance. Ion and species transport characteristics of electrode layers containing PFSA ionomers with different EWs are examined in this study by analysis of MEA polarization data at different relative humidities. Steady state polarization curves were obtained with air and oxygen. The polarization data for MEAs was analyzed to determine the relative contributions of the different sources of polarization, namely activation losses, membrane resistance losses, ohmic losses in the electrode, and mass transport losses in the GDL and electrode.
PEMFC Degradation Assessed by Effluent Analysis from Designed Experiments
Authors: Aarhaug Thor Anders , Svensson Ann Mari , Baumann Ofstad Axel , Ho̸ydahl So̸rli Jan Gregor , Couvert Héloi¨se
Published: October 2008

Experimental design has been applied to study PEMFC performance and durability as a function of operating conditions. Two levels of relative humidity, clamping pressure and back pressure have been systematically applied to an ON/OFF load cycle. Effluent analysis of fluoride and sulfate has been performed to correlate the emission rates to the durability observed. Background effluent levels for fuel cell test rigs were also assessed. Fluoride emission rates increases with time. The rates are higher for the experiments with back pressure, but they do not correlate well with voltage losses. High initial emission rates of sulfur are observed. After flushing with humidified inert gas, the emission rates decline but are sustained at high rates compared to fluoride. Sulfate emission rates are higher for experiments with high humidification levels. The total mass of sulfur released is higher than expected from the ionomer equivalent weight.
H2O2 Formation Depending on Ru Content of Pt-Ru/C Catalyst
Authors: Nakamori Yoji , Suzuki Naotoshi , Tanaka Kazuhisa , Aoki Tsutomu
Published: October 2008

H2O2 formation on Pt/C catalyst and Pt1Run/C (n = 1/3, 1/2, 1, 3/2, 2) catalysts was studied with rotating ring-disk electrode (RRDE) in 0.5 M H2SO4. H2O2 formation on Pt/C catalyst and Pt1Run/C catalysts with smaller Ru content increased sharply below 0.1 V vs. RHE. On the other hand, for larger Ru content catalysts, Pt1Run/C (n = 1, 3/2, 2), their H2O2 formation was lower than that of smaller Ru content catalysts below 0.1 V vs. RHE. Pt1Run/C catalysts with larger Ru content prevented H2O2 formation in anode catalyst layer and mitigated membrane degradation in PEFC. Potential cycles between 0.1 V and 1.0 V and between 0.1 V and 1.2 V vs. RHE were applied for Pt1Ru2/C catalyst. H2O2 formation below 0.1 V vs. RHE increased after potential cycles. Ru dissolution from Pt1Ru2/C catalyst was considered to promote H2O2 formation.
Degradation Mitigation in Polymer Electrolyte Membranes using Free Radical Scavengers
Authors: Trogadas Panagiotis , Parrondo Javier , Ramani V.
Published: October 2008

The efficacy of CeO2 nanoparticles in mitigating free radical induced PEM degradation is investigated. Commercially obtained CeO2 and nanoparticles synthesized in-house were incorporated within a recast Nafion® membrane. MEAs were prepared using Nafion® and Nafion®-CeO2 composite membranes (0.5wt%, 1wt%, and 3wt% CeO2). The composite membranes exhibited very similar proton conductivities (~35mS/cm) and hydrogen crossover (~1 mA/cm2) as Nafion®. However, the fluoride emission rate (estimated from accelerated tests) was lowered by more than one order of magnitude upon addition of CeO2 into the Nafion® membrane, suggesting that CeO2 nanoparticles have potential to enhance membrane durability.
Effect of Relative Humidity on Electrochemical Active Area and Impedance Response of PEM Fuel Cell
Authors: Malevich Dzmitry , Halliop Ela , Peppley Brant , Pharoah Jon , Karan Kunal
Published: October 2008

The influence of humidity of supplied gases on on electrochemically active surface area and charge transfer resistance in cathode process of PEM fuel cell was studied. Impedance spectra for cells operated with various gas stream combinations - H2/Air, H2/O2, H2/H2 and H2/N2 - was analyzed to determine the physical/chemical origin of the spectra features. Cathode charge transfer resistance increased with a decrease in the humidity of supplied gases. As well, a reduction in the electrochemically active surface area with a decrease in relative humidity was observed.
Membrane and Electrode Materials for Alkaline Membrane Fuel Cells
Authors: Varcoe John R. , Beillard Marion , Halepoto Dost M. , Kizewski Jamie P. , Poynton Simon , Slade Robert C. T.
Published: October 2008

This paper and the associated presentation will describe the latest developments regarding alkaline anion-exchange membrane (AAEM) fuel cells at Surrey. The program of work conducted has been targeted at the materials development of both membranes and electrodes containing alkaline ionomers and as such has focused on H2/O2 fuel cell testing. Radiation-grafted AAEMs can be made with fully hydrated thicknesses between 18 - 80 μm with conductivities in water of up to 0.06 S cm-2 at 60oC. A peak power density of 230 mW cmgeo -2 and a maximum current density at full discharge of 1.3 A cmgeo -2 have been obtained in a H2/O2 fuel cell at 50oC with a 18 μm AAEM and Toray carbon paper based electrodes (Pt/C(20%mass), 0.5 mgPt cmgeo -2 loading) that were treated with Surrey's first generation alkaline ionomer. A future priority is the development of the next generation alkaline ionomer.
Pt-Free Cathode Catalyst Performance in H2/O2 Anion-Exchange Membrane Fuel Cells (AMFCs)
Authors: Filpi Antonio , Boccia Massimiliano , Gasteiger H. A.
Published: October 2008

H2/O2 AMFCs enable the use of Platinum Group Metal (PGM) free Membrane Electrode Assemblies (MEAs), especially for the Oxygen Reduction Reaction (ORR). A promising catalysts for the ORR (Acta's "K14"), has been developed and tested using Rotating Disk Electrode (RDE) analysis, showing promising performance. In this paper we characterize current Anion-Exchange Membranes (AMs), show the fuel cell activity of AM-based MEAs prepared with K14 ORR catalyst, and compare their performance with the kinetic and ohmic limits projected from the membrane and catalyst properties. The data and projections show promising results for this technology.
Determination of Kinetic and Diffusional Parameters for Sodium Borohydride Oxidation on Gold Electrodes
Authors: Santos Diogo M. , Sequeira Cesar A.
Published: October 2008

Potential step experiments were carried out with a Au disc electrode in alkaline sodium borohydride solutions of varying concentrations and temperatures. Analysis of the current transients for the full timescale enabled the delimitation of the domains where diffusion, electron transfer, and mixed control prevail. Chronoamperometric measurements in the diffusion controlled region led to current transients exhibiting Cottrellian behaviour, from which accurate diffusion coefficients, D, were estimated. Arrhenius plots of D allowed determination of the diffusion activation energies, Ed, and maximum diffusion coefficients, D0. Chronocoulometric measurements generated Anson plots from which the kinetic rate constants, k, and charge transfer activation energies, Ect, were calculated. Analysis of the current densities in conditions of infinite mass transfer led to Tafel plots from which exchange current densities, i0, transfer coefficients, α, standard rate constants, ks, and standard activation energies for charge transfer, Ect0, were determined. Purely charge transfer regimes were never observed for the studied applied potentials.
Novel Porous Bipolar Plates for Use with Acid-Doped PBI Fuel Cells at Elevated Temperatures
Authors: Zaffou Rachid , Brooker Robert P. , Kunz H. R. , Bonville Leonard , Parnas Richard
Published: October 2008

Light-weight, porous bipolar plates were developed that are ideally suited for use with phosphoric acid-doped polybenzimidazole membrane fuel cells. The porous nature of the bipolar plates allows for a reservoir of acid to remain in intimate contact with the MEA to replenish lost acid. Single-cell and 4-cell stack data show good repeatability, both in flow distribution and performance scans. Over 1000 hour endurance data show performance losses are due to MEA decay, and not bipolar plate corrosion.
Performance and Durability of PEM Fuel Cells Operated at Sub-Freezing Temperatures
Authors: Mukundan R. , Davey John , Lujan Roger , Spendelow Jacob , Kim Yu Seung , Hussey Daniel S. , Jacobson David , Arif Muhammad , Borup Rodney L.
Published: October 2008

The effect of MEA preparation on the performance of single-PEM fuel cells operated at sub-freezing temperatures is presented. The cell performance and durability are dependent on the MEA and are probably influenced by the porosity of the catalyst layers. When a cell is operated isothermally at -10 oC in constant current mode, the voltage gradually decreases over time and eventually drops to zero. AC impedance analysis indicated that the rate of voltage loss is initially due to an increase in the charge transfer resistance and is gradual. After a period, the rate of decay accelerates rapidly due to mass transport limitations at the catalyst and/or gas diffusion layers. The high frequency resistance also increases over time during the isothermal operation at sub-freezing temperatures and was a function of the initial membrane water content. LANL prepared MEAs showed very little loss in the catalyst surface area with multiple sub-freezing operations, whereas the commercial MEAs exhibited significant loss in cathode surface area with the anode being unaffected. These results indicate that catalyst layer ice formation is influenced strongly by the MEA and is responsible for the long-term degradation of fuel cells operated at sub-freezing temperatures. This ice formation was monitored using neutron radiography and was found to be concentrated near cell edges at the flow field turns. The water distribution also indicated that ice may be forming mainly in the GDLs at -10 oC and could be concentrated in the catalyst layer at -20 oC.
Establishment of Accelerated Degradation Method of PEFC Stacks (NEDO Project: Fundamental Research of Degradation of PEFC Stacks)
Authors: Yamazaki Osamu , Shintaku Hideki , Oomori Yasuharu , Tabata Takeshi
Published: October 2008

Long-term continuous operation test under the actual operation condition in the system was carried out for more than 24,000 hrs using full-size cell stack manufactured by Sanyo Electric Corp.. Degradation tendencies of CO tolerance of anode and gas diffusivity of cathode were evaluated quantitatively by measuring the voltage drop by high concentration CO poisoning and air utilization dependence on the voltage. Accelerated degradation method concerning the gas diffusivity of cathode developed by Sanyo was verified. Accelerated magnifying power of gas diffusivity was calculated as about 2,100.
The Mechanical Changes in the MEA of PEM Fuel Cells due to Load Cycling
Authors: Huang Cheng , Liu Zhong-Sheng , Mu Deqiang
Published: October 2008

The purpose of this work is to establish a theoretical framework for modeling of the interface changes between the MEA components of PEM fuel cells due to load cycles. A 2D finite element model with the cohesive zone model and the fractional contact model is proposed to simulate the interface changes due to hydrothermal cycles. The material properties as functions of temperature, humidity and strain rate are applied here. The stress-strain simulations show stress and strain distributions inside the MEA, how and where, the interface changes take place during the load cycle and the cause of membrane thinning.
Durability Investigation on Change in Material and Structure of MEA for Well-Defined PEFC under High Temperature and Low Humidified Operation Condition
Authors: Ide Masahiro , Suzuki Yutaka , Ikeda Hironosuke
Published: October 2008

The analysis and the clarification of the deterioration phenomena of MEA for the practical use of PEFC are important. For this purpose, we carried out the investigation of MEA which was made of well-defined materials throughout well-defined process of manufacturing. The long term durability test was conducted for the improvement of cell operations. Various performances were measured periodically by electrochemical measurements. The cells were disassembled periodically to observe the change of materials that composed MEA. The deterioration phenomena of the cells were revealed.
Recent Insights Obtained from Local in situ Diagnostics in Polymer Electrolyte Fuel Cells
Authors: Schneider Ingo A. , Bayer Michael , Boillat Pierre , Wokaun Alexander , Scherer Guenther G.
Published: October 2008

In this talk, we present key results obtained in our laboratory using local electrochemical impedance spectroscopy (EIS), local cyclic voltammetry (CV) and current step technique as well as through plane and in plane neutron radiography in PEFCs. It is shown that processes along the gas flow channels have a tremendous impact on the local and the overall transient response of technical PEFCs. Their identification and consideration is crucial for a meaningful interpretation of results.
Optimization of the Cathode Catalyst Layer Composition using a Novel 2-step Preparation Method
Authors: Friedmann Roland , Nguyen Trung V.
Published: October 2008

For optimal performance and high durability PEM fuel cells run at high water saturation levels. Excess liquid water can block pores in both the gas diffusion layer and the catalyst layer and reactant gasses can't access the active catalyst sites. Thus, to prevent electrode flooding the catalyst layer structure has to provide pathways for both gas and liquid water transport as well as high ionic and electronic conductivity. This study presents a 2-step preparation method for such a catalyst layer and also gives an optimal composition of the catalyst ink resulting in high fuel cell performance. Teflon® has been incorporated into the catalyst layer to provide a hydrophobic pathway without blocking active catalyst sites. In general, less Nafion® content needed more Teflon® in the catalyst ink. The optimal ratio was found to be C:Nafion®:Teflon® = 1:0.875:0.875.
Kinetics of Non-Platinum Group Metal Catalysts for the Oxygen Reduction Reaction in Alkaline Medium
Authors: Piana Michele , Catanorchi Stefano , Gasteiger H. A.
Published: October 2008

Working in the area of alkaline fuel cell and electrolyzer technology, Acta S.p.A. developed over the past two years catalysts without Platinum Group Metals (PGM), named K14 and K18, with high activity for the oxygen reduction reaction (ORR) in alkaline medium. The comparison of the ORR activity between K14, K18 and commercial 10 wt% Pt on Vulcan XC-72R at 0.9 V vs. RHE (Reversible Hydrogen Electrode) has been carried out using Rotating Disk Electrode (RDE) analysis in 0.1 M KOH, showing how K14 has an activity close to Pt/C while the ORR activity of K18 is significantly higher. An important advantage of this catalysts is the absence of any oxidation reaction with fuels like alcohols. We used the Rotating Ring-Disk Electrode (RRDE) to detect the peroxide production and to demonstrate for K14 and, most of all, for K18 the almost complete conversion of oxygen via the 4 electrons mechanism.
Development of Low Cross-over Composite Membrane Composed of Porous Polyimide and Polymer Electrolyte for Direct Methanol Fuel Cells
Authors: Yamamoto Dai , Sasajima Keiji , Munakata Hirokazu , Kanamura Kiyoshi
Published: October 2008

Three kinds of proton conducting composite electrolyte membranes with three-dimensionally ordered macroporous (3DOM) polyimide were fabricated. Their performances for direct methanol fuel cells were compared. Poly (2-acrylamido-2-methylpropane sulfonic acid) (PAMPS), sulfonated poly (1,4-phenylene ether ether sulfone) (SPEES), and sulfonated poly (1,4-phenilene ether ether ketone) (SPEEK) were employed as filling electrolytes. No swelling was observed in any composite membrane. The highest proton conductivity of 7.4 x 10-2 S cm-1 was obtained for composite membrane with PAMPS having the highest ion exchange capacity. On the other hand, the lowest methanol permeability of 1.3 x 10-6 cm2 s-1 was obtained for composite membrane with SPEEK having the lowest water uptake. The contribution of 3DOM polyimide to the methanol permeability was larger than to the proton conductivity. Thus, two orders of magnitude larger proton transfer selectivity of 1.1 x 106 S cm3 s-1 compared to Nafion membrane was obtained in the SPEEK composite membrane.
Numerical Investigation on the Transport in a PEMFC using a Microstructure Reconstruction Technique
Authors: Hu Jingwei , Sui Pang-Chieh , Djilali Ned
Published: October 2008

The relationship between predicted cell performance and the microstructures of the porous components such as the gas diffusion layer (GDL) and catalyst layer (CL) is a challenge for proton exchange membrane fuel cell (PEMFC) modelling. In this study, the GDL and CL are reconstructed based on complicated structure generated software GeoDict. The effective transport properties are then derived from reconstructed structures. By incorporating the thus obtained effective transport properties, a two-dimensional, two-phase cathode model is developed to predict the cathodic polarization curve. This study offers a way to correlate microstructures of the GDL and the CL with cell performance.
The Study of Water Adsorption and Desorption by a PBI Membrane and its Impact on H3PO4 Transport
Authors: Shimpalee S , Gu Tao , Van Zee J. W.
Published: October 2008

The objective of this study is to aid the development of an understanding of the mechanisms of H3PO4 loss and transport in PolyBenzImidazole (PBI)-type High Temperature Membranes (HTM) fuel cells. The isotherms for adsorption and desorption of water in PBI-type HTM are critical data and reported for the first time here for a commercially available membrane. Depending on their values, this adsorption/desorption could play an important role in the long-term dilution of acid and thereby affect (in the long-term) the transport of this acid and proton flux in the membrane. Inclusion of these data is necessary in the development of a mechanistic model that allows for design of new experiments and prediction of fuel cell performance.
Vitali Parkhutik: His Contributions to Porous Semiconductor Science and Technology Over 30 Years
Authors: Canham Leigh
Published: October 2008

Vitali Parkhutik conducted research into porous silicon from 1975 right up to when he died in 2006. Trained initially in semiconductor physics, he rapidly became fascinated by electrochemistry, and the etching processes via which mesoporous structures are created from metals and semiconductors. Significant contributions include quantitative modelling of formation mechanisms and the development of both advanced hardware and software techniques for detailed characterization. One key technical advance was realizing the importance of hydrogen-induced stress and point defects in the silicon lattice, as a factor in pore creation from HF-based electrolytes. His passion for education was the inspiration for many of his students to begin careers in interdisciplinary materials science. He also played a key role in developing a truly international porous semiconductor R&D community through a very popular biannual series of conferences, and was a regular attendee of Electrochemical Society meetings.
Volker Lehmann: An Unconventional Scientist
Authors: Gösele Ullrich , Föll Helmut
Published: October 2008

It is generally known that Volker Lehmann has made numerous important contributions to the science and technology of the various forms of porous silicon. Less well known is that he started his education in the world of art and that he kept this interest alive, even after a professional career in engineering, materials science, physics and electrochemistry. In addition he was an athlete, enjoying all kinds of sports and physical challenges. The paper will be based upon the personal experience of the authors who worked directly with Volker Lehmann or in related fields of research for over two decades.
A Three Pulse Electrochemical Regime as a Fabrication Platform for Nano-structured Multifunctional Silicon Based Materials and Their Primary Prototypes
Authors: Matveeva Eugenia , Makushok Yuri , Bichto Leszek , Pastor Ester
Published: October 2008

Nano-Silicon is an extremely versatile material that can be structured at the level of its porosity, multi-film thicknesses or size of particles. Science's keen interest in these new nanomaterials is motivated by new fascinating properties and their tunability. Different forms of nano-Si primary prototypes can be made using a novel cyclic three-pulse electrochemical regime presented in this work. It consists of three pulses of different intensity: a working pulse when layer with determined thickness and porosity is formed; a cut pulse that introduces an embedded pre-partition between the layers; and an etch stop pulse when electrolyte is refreshed. An easy control by electrical means of overall morphology opens the possibility for large variations of nano-structuring in the obtained material. In-situ deposition of some metals simultaneously with layers formation through variation of the electrolyte composition and some parameters of the electrical regime is attainable as well.