bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance Characteristics and Liquid Water Transport in PEFC with Porous Separator
Authors: Tabe Yutaka , Morioka Satoshi , Nasu Takuya , Chikahisa Takemi
Published: October 2010

The porous separator has recently been proposed as an alternative to cells with gas flow channels in PEFCs. In this study, basic characteristics of a PEFC with porous separator were identified using a cell for the direct observation of phenomena at the surface of porous separator and measurements of the local current density. The transport behavior of liquid water inside the porous separator was also investigated using another cell for the direct observation of the porous cross-section. Because of the higher contact resistance, the cell voltage with porous separator is lower than that with serpentine separator, but a stable operation can be maintained with the porous separator under conditions at higher current density. The cross-sectional observation showed that the porous separator is superior in the drainage performance from the surface of gas diffusion layer, and the hydrophilic property of porous separator is important for the better cell performance.
Effects of Water Vapor Proportion in Generated Water on Performance of Polymer Electrolyte Fuel Cells under Dry Operating Conditions
Authors: Zhang Xu , Hu Guilin , Wang Qianpu , Song Datong , Liu Zhong-sheng
Published: October 2010

A one-dimensional, non-isothermal, single-phase, steady-state model is developed for dry operating conditions to investigate the effects of different types of generated water as liquid or vapor in electrochemical reaction on the proton exchange membrane fuel cell (PEMFC) performance, A parameter (Γ) denoting vapor phase fraction in generated water is employed in the model. The agglomerate model with thin film was employed in catalyst layers. Water transport and its effects on cell performance were discussed under different operating conditions such as reactants relative humidity, vapor phase fraction and micro-porous layer thickness. The results indicated that the net water transport coefficients were positive under equal feed gas humidity in both anode and cathode. At high current density, the more the proportion of water vapor in generated water is, the better cell performance is. However, at low current density, the effect of vapor phase proportion on cell performance is not very obvious.
Measurement of the Resistance Ratio of PEFC during Operation
Authors: Habu Toshiya , Yamamoto Takashi , Tunokawa Masaru , Sato Hiromichi , Ikeda Kouitirou
Published: October 2010

Realization of efficient fuel cell operation under high temperature and with no-humidifying condition, must be soon achieved indeed. A humidified state of MEA under high-temperature with no humidifying condition was recently investigated by a measurement technology that has been newly developed. Minute probe lines were inserted in the center portion of MEA, then the resistance of MEA over the cross-sectional direction was effectively measured during actual operation and shown as the resistance ratio. As a result, it was apparent that when the operation performance declined, it was because of the falling of performance at the H2 outlet on the anode side, caused by drying.
Water Content Measurement of Gas Diffusion Media and Membranes by Neutron Radiography
Authors: Hussey Daniel S. , Baltic Elias , Jacobson David
Published: October 2010

Neutron radiography is an excellent tool for measuring water in metallic housings; in stable conditions measurement sensitivity down to 4 μm water thickness in a 127 μm pixel has been demonstrated (1). Recent advances in detector technology have produced neutron imaging detectors with spatial resolution approaching or less than 10 μm, enabling direct measurement of the water content in gas diffusion media (GDM) and membranes with a through-plane thickness greater than 100 μm. This improvement in spatial resolution is demonstrated in Figure 1 for a proton exchange membrane fuel cell (PEMFC) operated nominal under the same conditions. This article will focus on the performance of high resolution neutron imaging detectors and image analysis methods for fuel cell research.
Determination of Local GDL Saturation on the Pore Level by In Situ Synchrotron Based X-ray Tomographic Microscopy
Authors: Büchi F. , Eller Jens , Marone Federica , Stampanoni Marco
Published: October 2010

In-situ synchrotron-based tomographic microscopy (SRXTM) with a spatial resolution in the order of 1μm and sensitivity for carbon and liquid water, has the potential to provide fundamental information for the understanding of the wetting properties of gas diffusion layer (GDL) materials on the pore level. This is important for the understanding of the solid-water interactions in the porous structures since water transport in GDLs is considered a key transport mechanism polymer electrolyte fuel cells (PEFC). However SRXTM of PEFC is a major experimental challenge. To obtain quantitative results, a complete cell needs to be operated under realistic conditions in the constrained space of the small field of view on the beamline sample stage without disturbing the sample rotation.
High-Resolution Visualization of Water Accumulation Behavior in an Operating PEMFC by Soft X-ray Radiography
Authors: Sasabe Takashi , Tsushima Shohji , Hirai Shuichiro
Published: October 2010

A carbon-cloth gas diffusion layer (GDL) displays better performance than a carbon-paper GDL under humidified condition. To investigate the relationship between GDL micro-structure and liquid water transport phenomena, water accumulation behavior in an operating Proton Exchange Membrane Fuel Cell (PEMFC) was visualized by soft X-ray radiography. Utilization of the soft X-ray range made it possible to visualize the liquid water in a PEMFC with the spatial resolution of 0.5 um and temporal resolution of 1.0 sec/frame. The water accumulated in a carbon-cloth GDL was locally distributed, and a larger amount of water accumulated in it than in a carbon-paper GDL. These results suggested that the broader pore distribution creates oxygen transport paths even if water accumulates in the GDL, and the pore structure has great importance. Furthermore, to investigate liquid water transport in more detail, stereoscopy technique has developed to get three-dimensional information with high temporal and spatial resolution.
Through-Plane Water Transport Visualization in an Operating PEM Fuel Cell by Visible and Infrared Imaging
Authors: Daino Michael M. , Lu Zijie , LaManna Jacob , Owejan Jon , Trabold Thomas , Kandlikar Satish G.
Published: October 2010

In this study, the liquid water emergence and transport within anode and cathode gas diffusion layers in an operating fuel cell was observed from the cross-section with a digital microscope and a high resolution infrared camera. In the cathode, water droplets were found to be formed on the channel side of the GDL cross-section, while little water was detected in the vicinity of the microporous layer. This finding suggested that water was condensing inside the GDL and may imply the existence of a condensation front, which has been predicted by numerical simulation but previously has not been verified experimentally. The anode results indicate that water was transported through anode GDL dominantly in the vapor form. The temperature distributions across the anode and cathode GDL were also measured with a high resolution infrared camera. These visualizations provided critical information on the water transport across a fuel cell.
In Situ Investigation of Water Distribution in Polymer Electrolyte Fuel Cell Using Neutron Radiography
Authors: Mishler Jeffrey , Wang Yun , Mukundan Rangachary , Borup Rodney L. , Hussey Daniel S. , Jacobson David
Published: October 2010

This paper investigates the water content within operating polymer electrolyte membrane (PEM) fuel cells using neutron radiography. We consider fuel cells with various PTFE loadings in their gas diffusion layers (GDL) and microporous layers (MPL), and examine the impacts of MPL/GDL properties on the liquid water behavior and fuel cell performance. Fuel cells are tested at both dry and fully hydrated conditions with different serpentine flow fields. Water contents in the projected areas of channel and land regions are probed. We find that the fuel cell may be subject to more flooding at low current-density operation. Both MPL and GDL wetting properties have substantial impacts on the water content. Cell performance also varies on different scenarios of the MPL/GDL wetting properties. The quad-channel flow field exhibits higher water content without remarkable change in performance at low current densities. Liquid water profile along the channel is presented and on-set clearly indicated.
Measurement of Water Content in Polymer Electrolyte Membranes Using High Resolution Neutron Imaging
Authors: Spernjak Dusan , Mukherjee Partha P. , Mukundan Rangachary , Davey John , Hussey Daniel S. , Jacobson David , Borup Rodney L.
Published: October 2010

Sufficient water content within a polymer electrolyte membrane (PEM) is necessary for adequate ionic conductivity. Membrane hydration is therefore a fundamental requirement for fuel cell operation. The hydration state of the membrane affects the water transport within, as both the diffusion coefficient and electro-osmotic drag depend on the water content. Membrane's water uptake is conventionally measured ex situ by weighing free-swelling samples equilibrated at controlled water activity. In the present study, water profiles in Nafion® membranes were measured using high-resolution neutron imaging. The state-of-the-art, 13 μm resolution neutron detector is capable of resolving water distributions across N1120, N1110 and N117 membranes. It provides a means to measure the water uptake and transport properties of fuel cell membranes in situ.
A Cross-Sectional Observation of Water Behavior in the Flow Channel in PEFC
Authors: Lee Sang-Kun , Ito Kohei , Sasaki Kazunari
Published: October 2010

Liquid water growth pattern in the gas flow channel in PEFC was visualized by using an ex-situ optical cross-sectional observation system developed. We investigated the impact of surface hydrophobicity of the GDL and channel on the liquid water growth pattern. The liquid water, which was emerged at 5 mm back from the gas outlet, was observed with spatial resolution of 20 μm by optimizing the optical system including CCD camera. Pressure drop through the channel was measured to evaluate the impact of water droplet on it. As a result, it is obtained that adhesion force formed in combination of hydrophobic GDL and hydrophilic channel sucked the water from GDL to channel corner, and suppressed the water contact with the GDL surface, and accelerated the water drainage, leading to prevent the water droplet growing in the channel.
3D Imaging of Polymer Electrolyte Fuel Cell Electrodes
Authors: Schulenburg Hendrik , Schwanitz Bernhard , Krbanjevic Julijana , Linse Nicolas , Mokso Rajmund , Stampanoni Marco , Wokaun Alexander , Scherer Günther G.
Published: October 2010

The degradation of Polymer Electrolyte Fuel Cell (PEFC) electrodes was examined by electrochemical and 3D imaging methods. A potential cycling test was conducted with a commercial catalyst coated membrane (CCM) where the cathode side of the cell was subjected to a potential square wave of 0.6V and open circuit voltage. After 24000 cycles, the PEFC performance remains nearly unchanged except for minor current losses in the low current regime. According to hydrogen under potential desorption measurements the electrochemically active Pt area decreases to 25% of the initial value. Synchrotron-based X-Ray tomography of the CCMs yields thickness distributions of catalyst layers and the membrane. A bubble like structure of the cathode layer is observed. Focused Ion Beam/Scanning Electron Microscopy-serial sectioning was employed to determine the pore structure of the cathode. The porosity before and after degradation was almost unaltered by the cycling test. TEM lamellas of the pristine and degraded cathode catalyst layers show an increase of the Pt particle size from 2.2nm to 4.6nm. Under the given conditions, an increase of hydrogen permeability across the membrane and a loss of Pt surface area are the predominant degradation mechanisms.
Analysis of Oxygen Dissolution Rate from Gas Phase into Nafion Surface and Development of an Agglomerate Model
Authors: Kudo Kenji , Suzuki Takahisa , Morimoto Yu
Published: October 2010

To clarify the rate determining process for the oxygen transport in a catalyst layer of PEFCs, an oxygen dissolution resistance from gas phase into Nafion surface was measured. The oxygen dissolution resistance, which was estimated form the relationship between Nafion thickness on Pt electrode and the diffusion-limited current density on the electrode, was found to account for a large part of the total oxygen transport loss. By introducing the oxygen dissolution resistance, an agglomerate model was able to predict I-V performance of a PEFC using a reasonable size of agglomerate.
A Five Layer One-Dimensional PEMFC Model with Detailed Electrode Kinetics
Authors: Fiçicilar Berker , Eroğlu İnci , Nguyen Trung V.
Published: October 2010

In this study, a non-isothermal, two-phase, one-dimensional, and steady state proton exchange membrane (PEM) fuel cell model is developed to investigate the detailed electrode kinetics in the anode and cathode catalytic regions and the effects of these reaction mechanisms on the performance of a PEM fuel cell. Langmuir-Butler-Volmer (LBV) type reaction rate expressions are suggested for both anode and cathode electrochemical reactions. A two-phase energy balance approach is used to catch the thermal transport phenomena in cases when there is a significant temperature difference between the fuel cell temperature and the reactants inlet temperatures like during cold start-up.
The Effect of MPL Permeability on Water Fluxes in PEM Fuel Cells: A Lumped Approach
Authors: Baghalha Morteza , Eikerling Michael , Stumper Jürgen
Published: October 2010

The distribution of water fluxes in an operating polymer electrolyte fuel cell (PEFC) is strongly influenced by the properties of the cathode catalyst layer (CCL) adjacent media, viz. polymer electrolyte membrane (PEM) and microporous layer (MPL). We propose a water analysis model which treats each layer as an effective homogeneous medium. The model is applied under steady state conditions, with varying humidification of the cathode feed gas (from dry to fully saturated). We distinguish contributions to water removal due to liquid and vapor transport via anode and cathode. The model warrants definition of a critical current density up to which water removal out of the CCL to the cathode side proceeds completely via vapor diffusion. Above the critical current density, excessive water generation leads to the build-up of an excess liquid pressure in the CCL, which acts as a driving force for hydraulic fluxes to PEM and MPL sides.
Two-Dimensional Model for Cold Start in a Polymer-Electrolyte-Membrane Fuel Cell
Authors: Balliet Ryan , Newman John
Published: October 2010

A two-dimensional, nonisothermal, transient model is developed which is capable of predicting polymer-electrolyte fuel-cell performance during cold start. Transport of water in gas, liquid, and membrane phases at temperatures both above and below 0°C is included. In the porous media, the saturation levels of ice and liquid, as well as their pressures, are predicted based on the chemical potential of each phase and the physical and chemical properties of the cell materials. Simulation results show that liquid-water transport near but below 0°C plays an important role in determining the cell potential as a function of time during startup because it can allow for rapid drainage of the cathode catalyst layer once enough fine-pore ice has melted.
Reduced Complexity Models for Water Management and Anode Purge Scheduling in DEA Operation of PEMFCs
Authors: Siegel Jason B. , Yesilyurt Serhat , Stefanopoulou Anna G.
Published: October 2010

In this work, the dynamic behavior of Fuel Cell operation under Dead-Ended Anode conditions is shown. A DEA can be fed with dry hydrogen, since water crossing through the membrane is sufficient to humidify the fuel. The reduced requirements for inlet humidification yield a system with lower cost and weight compared to FCs with flow-through or recirculated anodes. The accumulation of water and nitrogen in the anode channel is first observed near the outlet. A stratified pattern develops in the channel where a hydrogen-rich area sits above a depleted region and is stabilized by the effect of gravity. A model is presented which describes the dynamic evolution of a blanketing N2 front in the anode channel and a hydrogen starved region. Understanding, modeling, and predicting the front evolution can reduce the H2 wasted during purges, avoid over drying the membrane, and mitigate degradation associated with hydrogen starved areas.
Elucidating Through-Plane Liquid Water Profile in a Polymer Electrolyte Membrane Fuel Cell
Authors: Wang Yun , Chen Ken S.
Published: October 2010

In this paper, a numerical model incorporating micro-porous layers (MPLs) is presented for simulating water transport within the gas diffusion layers (GDLs) and MPLs as well as across their interfaces in a polymer electrolyte membrane (PEM) fuel cell. One-dimensional analysis is conducted to investigate the impacts of MPL and GDL properties on the liquid-water profile across the anode GDL-MPL and cathode MPL-GDL regions. Furthermore, two-dimensional numerical simulations that take MPLs into account are also carried out to elucidate liquid water transport, particularly through-plane liquid-water profile in a PEM fuel cell. Results from case studies are presented.
Evaluating Polymeric Materials as Potential Sources of PEMFC System Contaminants
Authors: Wang Heli , Coombs Sidney , Macomber Clay , O'Neill Kevin , Bender Guido , Pivovar Bryan , Dinh Huyen N.
Published: October 2010

The cost and durability of polymer electrolyte membrane fuel cell (PEMFC) systems have limited their deployment. The relative cost of the balance of plant (BOP) has risen in importance with decreasing fuel cell stack cost. Lowering costs of PEMFC system components require the understanding of potential contaminants from these materials. System contaminants have received very limited attention publicly. We here present ex-situ leaching tests with materials that could be considered as gasket materials to quickly screen BOP component materials. Aliquots of the leachant solutions were collected periodically and analyzed (pH, conductivity, etc.) to identify and quantify contaminants. The influence of the leachant on the electrochemical performance of Pt was also investigated.
Aniline as a Cationic and Aromatic Contaminant in PEMFCs
Authors: Cho Hyun-Seok , Jung Myunghee , Navarro Jose , Ohashi Masato , Van Zee John W.
Published: October 2010

Aniline as a possible contaminant in polymer electrolyte membrane fuel cells (PEMFCs) has been studied by several ex-situ techniques. The aniline isotherm for MEA shows more affinity to ion-exchange with the PEM than other monovalent such as sodium and ammonium ions, thus indicating stronger performance loss at the same concentration. The results of cyclic voltammetry (CV) of Pt/C show the loss of electrochemical surface area (ECSA) by with the addition of aniline in the electrolyte. The appearance of unknown peaks in CV may indicate the production of polyaniline (PANI) film which appears to grow with the number of CV tests. These studies indicate that the use of balance of plant components that leach aniline should be avoided since its presence appears to decrease the electrochemical activity of the electrode for the oxygen reduction reaction. Further studies on aniline with in-situ experiment may not be warranted.
Characterizing Polymeric Leachants for Potential System Contaminants of Fuel Cells
Authors: Macomber Clay , Wang Heli , O'Neill Kevin , Coombs Sidney , Bender Guido , Pivovar Bryan , Dinh Huyen N.
Published: October 2010

The role of system contaminants in the performance degradation of Proton Exchange Membrane (PEM) fuel cells has been underappreciated to date. This work seeks to identify potential contaminants of system components with the ultimate goal of tying contaminant exposure to performance and durability After aging of select polymers in solution, leachant samples were qualitatively identified via GCMS and FTIR-ATR. Total Organic Carbon (TOC) content quantitatively provided information relative to contaminant level extracted from polymeric samples. Results will be presented focusing on SBR rubber and neoprene. Qualitative concentration vs. time charts elucidate leachant evolution, showing among other things potential chemical degradation in solution.
Two-Stage Degradation of PEMFC Performance Due to Sulfur Dioxide Contamination
Authors: Tsushima Shohji , Kaneko Keisuke , Hirai Shuichiro
Published: October 2010

Accelerated degradation tests of a PEMFC due to SO2 poisoning were performed to investigate time-evolutional process of the cell performance. It was revealed that SO2 contamination in the cathode air stream caused either one-stage or two-stage degradation of the PEMFC performance, which depends on cell operating condition. Partial recovery of the cell voltage indicated that weak (reversible) absorption and strong (irreversible) absorption of SO2 are involved in the contamination process by SO2 in the electrode. Experimental observation on two-stage degradation depending on the cell voltage suggested a formation of a sulfur monolayer followed by a multilayer formation of sulfur on the catalyst in the two-stage degradation of the PEMFC.
Effect of Alloying Pd with Oxophillic Metals on Electro-Oxidation of Alcohols in Alkaline Media
Authors: Halevi Barr , Olson Tim , Pylypenko Svitlana , Robson Michael , Datye Abhaya K. , Atanassov Plamen
Published: October 2010

The effect of alloying Pd with Zn for use in electro-oxidation of methanol and ethanol in alkaline media was studied. Pd, Zn, and PdZn supported on Vulcan XC72R were synthesized, tested for alcohol electro-oxidation and compared to unsupported PdZn. It was found that alloying Pd with Zn had a synergistic effect on the oxidation of ethanol but not of methanol.
Electrocatalytic Activity of Pt Nanoparticles on Karst-Rock Shaped Ni Thin Films toward Methanol and Ethanol Oxidation in Alkaline Solutions
Authors: Chen Chung-Shou , Pan Fu-Ming , Yu Hisn-Jung
Published: October 2010

We prepared Ni thin films with a karst-rock topography on the Si substrate and used the thin film as the electrocatalyst support for the study of methanol and ethanol oxidation in alkaline media. Well-dispersed Pt nanoparticles were pulse-electrodeposited on the rugged Ni thin film, which provided a very large surface for the Pt loading. The cyclic voltammertry (CV) showed that the Pt/Ni electrode had a high electrocatalytic activity toward methanol oxidation compared with blanket Pt. Nanosized Pt particles electrodeposited on the rugged surface of the Ni thin film provide a large amount of electrocatalytic sites for methanol oxidation. Hydroxyl surface groups bound on the Ni karst-rock nanostructures in the alkaline solution may greatly enhance CO electro-oxidation in terms of the bifunctional mechanism. The study demonstrates that the karst-rock shaped Ni thin film is a potential candidate as the Pt electrocatalyst support for direct methanol alkali fuel cells.
Methanol, Ethanol and Iso-Propanol Performance in Alkaline Direct Alcohol Fuel Cell (ADAFC)
Authors: Santasalo-Aarnio Annukka , Peljo Pekka , Aspberg Eero , Kontturi Kyösti , Kallio Tanja
Published: October 2010

The performance of an alkaline direct alcohol fuel cell (DAFC) supplied with a FAA-2 membrane as an electrolyte and utilizing methanol, ethanol and iso-propanol solutions as a fuel was studied. In addition, the permeability of these fuels through the membrane is investigated at different concentration to facilitate the interpretation of the fuel cell results. The permeability decreased with the increasing size of the alcohol molecule and it was some ten times lower through FAA-2 compared to Nafion® 115 for all the studied fuels. In the alkaline DAFC, the highest power density was obtained with 1 mol dm-3 iso-propanol (0.75 mW cm-2). However, the cell showed good performance with more concentrated fuels, even with 15 mol dm-3 methanol solution. Solution resistances of these MEA materials at different fuels and concentrations were obtained with electrochemical impedance spectroscopy.
Investigation of the Electrochemical Behavior of Potential Denaturing Agents for Ethanol Compatible with the Use in Direct Ethanol Fuel Cells
Authors: Cremers Carsten , Bayer Domnik , Kintzel Birgit , Tübke Jens
Published: October 2010

In order to be tax free, the ethanol for use in direct ethanol fuel cells (DEFC) needs to be denatured. The electrochemical behavior of a number of potential denaturing agents was therefore studied with respect to their compatibility with DEFC operation. Tests comprised the investigation of the denaturing agents' oxidation at platinum model electrodes, their influence on the ethanol oxidation at platinum model electrodes and at fuel cell catalysts as well as the analysis of the products which get formed. Cyclic voltammetry, chronoamperometry and differential electrochemical mass spectrometry were used as methods. Eventually, a mixture of ethyl-tert-butyl ether and Bitrex® was found which should qualify as denaturing agent and did not show any severe detrimental effect on electrochemical reactions important for DEFC operation.
XAFS Analysis of Unpyrolyzed CoPPyC Oxygen Reduction Catalysts for Anion-Exchange Membrane Fuel Cells (AMFC)
Authors: Asazawa Koichiro , Yamamoto Kazuya , Yamada Koji , Tanaka Hirohisa , Matsumura Daiju , Tamura Kazuhisa , Nishihata Yasuo , Atanassov Plamen
Published: October 2010

CoPPyC were analyzed with synchrotron X-ray adsorption fine structure (XAFS) measurements, and the correlations between electrochemical properties and structure of electrocatalysts are discussed. Electrochemical properties have been analyzed by using rotating-ring disk electrode in 1M KOH. Acid-treated CoPPyC (CoPPyC-AT) has higher activity than PPyC for oxygen reduction reaction. Concentration of Co in CoPPyC-AT is as low as 0.1 atomic %. From the analysis of EXAFS of Co, CoPPyC electrocatalysts as synthesized consist of two peaks. The peak around 1.6 Aå was assigned to Co-N and/or Co-O shells. The second peak around 2.6 Aå was assigned to Co-O-Co shells originated from cobalt hydroxide. CoPPyC-AT showed only one peak of assigned to Co-N and/or Co-O, and it indicates that cobalt hydroxide is removed by acid treatment. So, it is clear that a co-existence of cobalt and nitrogen in CoPPyC-AT shows specific performance, and pyrolysis is not necessary to make correlation of Co-N.
Iron-Cobalt Modified Electrospun Carbon Nanofibers as Oxygen Reduction Catalysts in Alkaline Fuel Cells
Authors: Jeong Beomgyun , Uhm Sunghyun , Lee Jaeyoung
Published: October 2010

Iron, cobalt, and carbon nanofiber (FeCo-CNF) composite electrocatalysts for the oxygen reduction reaction (ORR) in alkaline fuel cells (AFCs) have been fabricated via a simple and cost-effective process―electrospinning and the subsequent pyrolysis of a mixture of a nitrogen-containing polymer and organo-metallic compounds. From subsequent electrochemical characterizations, the resultant FeCo-CNFs catalysts demonstrated comparable electrocatalytic activity and stability to commercial carbon-supported platinum (Pt/C) for ORR, a direct 4-electron reduction pathway, and better ethanol tolerance than Pt/C in an alkaline electrolyte. According to material characterizations, metal inclusion seems to result in oxygen-related active site formations and enhancement of electrical conductivity. Therefore, with this synthesis approach, we expect that it is possible to make advanced cathode materials with high conductivity, surface area, ORR activity, and stability for AFCs without requiring noble metal catalysts.
Recent Advances in Nonprecious Metal Catalysts for Oxygen Reduction Reaction in Fuel Cells
Authors: Li Xuguang , Popov Branko N. , Kawahara Takeo , Yanagi Hiroyuki
Published: October 2010

Non-precious metal catalysts (NPMCs) are developed for oxygen reduction in alkaline fuel cell (AFC). The performance of the catalyst in alkaline electrolyte is studied by rotating disk electrode (RDE). The NPMC prepared with carbon-supported metal-nitrogen composite precursor and subjected to heat-treatment shows comparable activity for oxygen reduction when compared with Pt/C catalyst. The fuel cell performance of the catalyst was studied using anion exchange membrane (AEM) from Tokuyama Corporation. The NPMC exhibits an open circuit potential (OCP) of 0.97 V and a maximum power density of 177 mW cm -2 at 50 °C.
Electrocatalysis of Oxygen Reduction on Nonprecious Metallic Centers at High pH Environments
Authors: Ramaswamy Nagappan , Mukerjee Sanjeev
Published: October 2010

Iron(III) tetraphenyl porphyrin (FeTPP) macrocycle supported on high surface area Black Pearl Carbon prepared by ball milling and subsequent pyrolysis under inert atmosphere at 600{degree sign}C to 800{degree sign}C exhibits remarkable 4e- oxygen reduction reaction activity with minimal peroxide yield in alkaline medium. The pyrolytic evolution of the catalytic site has been systematically investigated using a combination of two powerful techniques, i) Square Wave Voltammetry (SWV) capable of isolating the Faradaic charge transfer from the non-Faradaic capacitive current and ii) in situ X-ray Absorption Near Edge Spectroscopy (XANES). Using these techniques we clearly show here clearly the two advantages obtained by pyrolysis in the case of FeTPP. i) Anodic shift in redox potential of the iron metal center and ii) the formation of a mixed-valence dimeric catalyst site capable of binding molecular oxygen and enable charge transfer in a concerted fashion.
Oxygen Reduction Catalysts for Alkaline Polymer Electrolyte Fuel Cells
Authors: Maheswari Subbiah , Selvarani Ganesan , Sridhar P. , Pitchumani S. , Shukla Ashok
Published: October 2010

Commercially available anion-exchange membranes are used in the Alkaline Polymer Electrolyte Fuel Cells (APEFCs) that are reported here. Ionic conductivity of the alkaline polymer electrolytes are measured by a c impedance. Incorporation of anion conducting ionomer in the catalyst layer of the membrane electrode assembly and its influence on the performance of APEFCs is studied. Pt/C is used as an anode catalyst while Pt/C or Pd/C or Au/C is used as the cathode catalyst for membrane electrode assemblies of APEFCs. The catalyst with maximum performance is characterized by linear sweep voltammetry, impedance in conjunction with cell polarization. APEFC comprising Pd/C delivers a peak power density of 55mW/cm2 in relation to 40 mW/cm2 and 1 mW/cm2 delivered by APEFCs with Pt/C and Au/C anodes, respectively.
Synthesis of Pd@MoOx Electrocatalysts for Oxygen Reduction Reaction in Alkaline Media
Authors: Dylla Anthony G. , Stevenson Keith J.
Published: October 2010

We describe the synthesis of carbon supported Pd@MoOx nanoparticles by a one pot reaction involving Pd(acetylacetonate)2 and MoCl3 with octadecanol, oleylamine and diphenyl ether acting as reducing agent, ligand stabilizer and solvent, respectively. Mon+ species are initially adsorbed to the XC72 surface while Pd core nanoparticles grow in solution. Later the Pd nanoparticles adsorb to the carbon support and Mo surface species alloy with the Pd nanoparticles to form ~10 nm Pd@MoOx core@shell nanoparticles. High resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray spectroscopy (EDS) and XPS suggest a phase segregated structure that comprises of a Pd core and an oxidized Mo shell (Pd@MoOx). Cyclic voltammetry (CV) and rotating disk electrode (RDE) measurements show that the core@shell structure enhances the catalytic activity for the oxygen reduction reaction (ORR) in 0.1 M KOH in comparison to Pd/C catalysts.
Development of Direct-Ethanol Anion-Conducting Solid Alkaline Inorganic Fuel Cell
Authors: Takeguchi Tatsuya , Takahashi Hiroki , Yamanaka Toshiro , Nakamura Ayaka , Ueda Wataru
Published: October 2010

Anion-conducting solid alkaline inorganic fuels cell was developed. This fuel cell could be operated at high temperature of 110ºC. NaCo2O4 showed OH- conduction and activity for oxygen reduction reaction. The Fe-Co-Ni alloy catalyst prepared in this experiment showed activity not only for hydrogen oxidation reaction but also for ethanol oxidation reaction. Completely precious metal-free fuel cell composed of NaCo2O4 and Fe-Co-Ni cell was made. The cell generated a high output power density of 64 mW/cm2 directly from ethanol at current density of 160 mA/cm2.
Bioelectrochemical Oxidation of Urea with Urease and Platinized Boron Doped Diamond Electrodes for Water Recycling in Space Applications
Authors: Nicolau Eduardo , Rodríguez-Martínez José A. , Fonseca José , Richardson Tra-My J. , Flynn Michael , Griebenow Kai , Cabrera Carlos R.
Published: October 2010

The recovery of potable water from spacecraft wastewater is critical for the life support and environmental health of crew members in long-term missions. NASA estimates that during manned space missions 60 g/person·day of urine is produced, with urea and various salts as its main components. In this research we explore the utilization of urease enzymes (EC 3.5.1.5) to convert urea to nitrogen using a two step process of urease catalyzed decomposition of urea to ammonia followed by the electrochemical decomposition of ammonia to nitrogen. Urease was immobilized on granulated activated carbon to serve as a bio-reaction platform, while platinum was electrodeposited on boron-doped diamond electrodes by cycling the potential to attain active electrodes. Samples from NASA Ames Research Center water recycling equipment, containing urine, were used to test the herein proposed system.
Ion Conduction in Layered Oxide Solid Electrolyte
Authors: Takahashi Hiroki , Takeguchi Tatsuya , Yamanaka Toshiro , Kyomen Toru , Hanaya Minoru , Ueda Wataru
Published: October 2010

In the present study, membrane potential for concentration cell of NaOH was measured to seek inorganic materials with anion conduction for high-temperature-resistant fuel cells without noble-metal catalyst. We discovered the anion conduction in layered oxide NaCo2O4 and KCo2O4. Although LiCoO2 has the similar layered structure to NaCo2O4 and KCo2O4, this oxide showed cation conduction. Moreover, we succeeded in generating electricity by using NaCo2O4 electrolyte. The anion-conductivity is considered to be caused by reduction and hydration of NaCo2O4.
Anion Conducting Polyaromatics Having Guanidine Base
Authors: Kim Dae Sik , Kim Yu Seung
Published: October 2010

A guanidine based poly(arylene ether sulfone)s (PAES-TMG) membrane was synthesized from the poly(arylene ether sulfone)s having activated fluorine group and tetramethylguanidine (TMG) without chloromethylation and/or bromination. The methylated PAES-TMG membranes do not have β-hydrogen, and TMG groups have high basicity (pKa = 13.6), which may reduce the potential of degradation due to E2 and SN2 reaction. The membrane showed the good stability in alkaline conditions (0.5M NaOH boiling temperature for 2hr, 80oC for 382hr). The OH- conductivities before and after NaOH test at 80oC for 382hr are 0.036 S/cm, and 0.023S/cm, respectively. The conductivity after exposure to ambient air is 0.019S/cm (σHCO3-) at 80oC.
Effect of Ammonium Ion Structures on Properties of Alkaline Exchange Membrane Fuel Cells
Authors: Lee Yeong-Beom , Lee Hanniel , Bae Chulsung
Published: October 2010

To investigate how quaternary ammonium ion structure affects the membrane stability and conductivity property of alkaline exchange membrane (AEM), we synthesized a series of polysulfones (PSUs) functionalized with various ammonium hydroxide groups. Ammonium ions with different steric environments were prepared by our recently developed Suzuki cross-coupling reactions of borylated polysulfone. We used two different synthetic strategies for the final polymers: In path A, like a general process for AEMs amine functional groups are first introduced to the PSU and quarternized afterward. In path B, pre-quarternized ammonium ions are directly introduced to the PSU.
Poly(vinyl Alcohol)/Poly(acrylamide-Co-Diallyldimethylammonium Chloride) (PVA/PAADDA) Composite as Novel Anion-Exchange Membranes for Potential Use in Fuel Cells
Authors: Qiao Jinli , Fu Jing , Lin Rui , Liu Jianshe , Ma Jianxin
Published: October 2010

In this work, a new type of alkaline ion-exchange membrane (AAEM) composed of poly(vinyl alcohol) and poly(acrylamide-co-diallyldimethylammonium chloride)(PVA/PAADDA) has been successfully established by blending and chemical cross-linking. The resultant membranes were characterized in detail at structural and conducting property by FTIR spectroscopy, thermal gravity analysis, swelling behavior, ion exchange capacity and alkali resistance stability. A maximum conductivity of up to 6.86×10−4 S cm-1 at room temperature was achieved for PVA/PVP in a mass ratio of 1:0.25, along with the good membrane mechanical property. The ion-exchange capacity thus measured is 0.91 with a reasonable water uptake of 56.6%. High temperature tolerance was achieved where the thermal degradation temperature in air Td, was in the range of 223-250oC. In addition, the membrane showed relatively good alkaline stability without losing its integrity and ionic conductivity after exposure to 1M KOH at 80oC and, only 12.5% decreased in ionic conductivity after conditioning in 6M KOH at 80oC.
Backing Out Diffusion Coefficients in Alkaline Anion Exchange Membranes
Authors: Myles Timothy D. , Kiss Andrew , Grew Kyle , Peracchio Aldo , Chiu Wilson
Published: October 2010

Water diffusion coefficients for electrolyte membranes are a subject of interest due to the relationship between water content and ionic conductivity. These diffusion coefficients are functionally dependent on water content. Many existing techniques for measuring the diffusion coefficient suffer from experimental complexity or a lack the diffusion coefficient's detailed behavior. This paper uses a simple technique for determining the water diffusion coefficient involving the use of experimental data coupled with a numeric model. This back out algorithm was validated through the use of Nafion®, a proton exchange membrane, with the results comparing well with NMR data from the literature. The process has also been applied to SnowPure ExcellionTM, an alkaline exchange membrane, to obtain the diffusion coefficient as a function of water content. It was found that these membranes are much less permeable to water with the diffusion coefficient being almost an order of magnitude less than that of Nafion®.
Mathematical Modeling of the Concentration Profile of Carbonate Ions in an Anion Exchange Membrane Fuel Cell
Authors: Siroma Zyun , Watanabe Shin , Yasuda Kazuaki , Fukuta Kenji , Yanagi Hiroyuki
Published: October 2010

An anion exchange membrane fuel cell (alkaline membrane fuel cell) was operated after the absorption of carbon dioxide. The release of carbon dioxide from the anode, which is known as "self-purging", was observed during cell operation. The content of carbonate ions in the electrolyte membrane after it reached a steady-state was assumed to be a function of the current density. A mathematical model was developed to explain the experimental results.
Dynamic Modeling and Simulation Based Analysis of an Ammonia Borane (AB) Reactor System for Hydrogen Storage
Authors: Devarakonda Maruthi N. , Holladay Jamie , Brooks Kriston , Rassat Scott , Herling Darrell
Published: October 2010

Research on ammonia borane (AB, NH3BH3) has shown it to be a promising material for chemical hydrogen storage in PEM fuel cell applications. AB was selected by DOE's Hydrogen Storage Engineering Center of Excellence (HSECoE) as the initial chemical hydride of study because of its high hydrogen storage capacity (up to 19.6% by weight for the release of three molar equivalents of hydrogen gas) and its stability under typical ambient conditions. A model of a bead reactor system which includes feed and product tanks, hot and cold augers, a ballast tank/reactor, a H2 burner and a radiator was developed to study AB system performance in an automotive application and estimate the energy, mass, and volume requirements for this off-board regenerable hydrogen storage material. Preliminary system simulation results for a start-up case and for a transient drive cycle indicate appropriate trends in the reactor system dynamics. A new controller was developed and validated in simulation for a couple of H2 demand cases.
Hydroquinone Fuel Cells
Authors: Sachdeva Sonny , Ferrell Jack , Haag Joanna , Yoon Ji-Ho , Koh Carolyn , Herring Andrew M.
Published: October 2010

Direct hydroquinone fuel cells have been studied where hydroquinone is oxidized to benzoquinone and the electrons released flow through the external circuit generating electricity. Different catalyst systems have been used to optimize the performance of these fuel cells. The effect of temperature, pressure and feed concentration on the fuel cell performance has been studied. At 20 psi back pressure, 80 oC cell temperature and 0.5 M feed concentration for the Pt/Ru oxidation catalyst an open circuit potential of 297 mV is obtained. The maximum current density of 15 mA/cm2 at 100 mV is observed. With the increase in pressure, temperature and concentration the fuel cell performance becomes better. However, with the increase in temperature and concentration, the open circuit potential lowers probably due to the increased crossover effects of these parameters.
On the Origin of Reactive Pd Catalyst for an Electrooxidation of Formic Acid
Authors: Jeon Hongrae , Jeong Beomgyun , Uhm Sunghyun , Lee Jaeyoung
Published: October 2010

We investigated the reactivation of Pd catalysts during the electrocatalytic oxidation of formic acid. Pd catalyst was electrochemically deposited onto carbon paper substrate that was characterized by XRD, SEM, and XPS. Pd catalysts showed fast deactivation, though their activity could be simply recovered by applying a reduction potential at which hydrogen generation can occur. XPS results revealed that the surface of Pd catalysts is significantly affected by interaction with formic acid. High coverage of formic acid and/or formate is found at active state of Pd catalyst and diminished as deactivation proceeds. We concluded that cathodic polarization may remove poisoning species on the Pd electrode and form an active site for formic acid oxidation. This reactivation method can sustain a durability of Pd catalysts.
Manufacturing of Direct Methanol Fuel Cell Electrodes by Spraying
Authors: Koraishy Babar M. , Morter Douglas , Solomon Sam , McDonald Brian , Meyers Jeremy P. , Wood Kris
Published: October 2010

Spraying is a well-established coating process used to fabricate electrodes for both PEMFC and DMFC fuel cells, and also for the fabrication of gas-diffusion media (GDM) used in fuel cells (1-7). Despite its popularity as a process there is little basic research on how spray parameters and nozzle characteristics affect the drop sizes of catalyst inks, and how those droplet sizes, affect the electrode structure, porosity, conductance and eventually the overall MEA performance. We present results from an experimental study to systematically answer these questions, characterizing the spray nozzle and measuring drop diameters, and then investigating the microstructural effects on electrode performance. For this purpose, first a spraying apparatus was developed and calibrated, and MEA's were fabricated with fixed electrode loadings but with different droplet sizes. Droplet sizes were controlled by characterizing the spray nozzle and measuring the spray by two methods, optically by utilizing high-speed photography and by the hot wire method (8-12).
Non-Flooding Hybrid Polymer Fuel Cell
Authors: Shen Weida , Zhang Fengyuan , Prasad Ajay , Hertz Joshua
Published: October 2010

One of the chief difficulties associated with low temperature (<100°C) fuel cells is water management. Specifically, nucleation of liquid water droplets in the electrodes (i.e., flooding) causes a drop in power output as reactants are prevented from arriving at the electrodes. Here, we describe first attempts at a hybrid polymer fuel cell that prevents flooding. A proton exchange membrane and an alkaline exchange membrane are placed on opposite sides of a porous, water-soaked layer. Water formed in the porous layer is shunted to the exterior of the fuel cell. Though the design is promising, preliminary attempts have shown that the electrolytic resistance is too high for practical use.
Facile Surface Functionalization of Carbon/Nafion for Enhancement of Methanol Electro-Oxidation
Authors: Hsieh Yu-Chi , Chang Li-Chung , Wu Pu-Wei , Lee Jyh-Fu , Liao Chen-Hong
Published: October 2010

We report a facile electrochemical method to produce functional groups on the carbon surface in which multiple cyclic voltammetric (CV) sweeps are imposed in 0.5 M H2SO4 electrolyte on the samples containing carbon cloth, Vulcan XC72R, and Nafion ionomer. With supply of ambient O2, the generation of radicals from the oxygen reduction and Nafion ionomer degradation enables an accelerated formation of oxygenated functional groups on the carbon surface. Raman analysis reveals structural variation for the carbon electrodes after CV modifications. X-ray photoelectron spectroscopy confirms the alteration of carbon structure in conjunction with notable increase of oxygenated groups and reduction in fluorine amount. The functionalized electrodes allow a 250% increment for PtRu electrodeposition as compared to the reference sample. We carry out electrochemical measurements on methanol electro-oxidation for the PtRu samples. The functionalized electrode demonstrates significant improvement in apparent current density and mass activity as opposed to the reference sample.
DMFCs with Enhanced Catalytic Activity and Durability Using Transition-Metal Carbides as Catalyst Support
Authors: Nishanth K.G. , Sridhar P. , Pitchumani S. , Shukla Ashok
Published: October 2010

Molybdenum carbide (MoC) and Tungsten carbide (WC) are obtained by direct carbonization method. Pt-Ru supported on MoC, WC and Vulcan XC-72R are prepared, and characterized by XRD and TEM techniques. Electrochemical activity for methanol electro-oxidation is studied by cyclic voltammetry (CV) and durability study on all the electro-catalysts is conducted by accelerated durability test (ADT). The electrochemical activity for methanol electro-oxidation of carbide-supported electro-catalysts is found to be higher than carbon-supported catalysts before and after ADT. Direct methanol fuel cells (DMFCs) employing carbide-supported Pt-Ru exhibit higher performance towards methanol oxidation in relation to carbon-supported Pt-Ru.
RRDE and EIS Study of Pt-Co/MWCNT Electrocatalysts as ORR Electrodes in Sulfuric Acid Containing Small Organic Molecules
Authors: Rodríguez-Varela Javier , López de la Fuente Dulze , Morales-Acosta Diana , Arriaga Luis Gerardo
Published: October 2010

We investigated the behavior of the Pt70-Co30/MWCNT alloy as oxygen reduction reaction (ORR) cathode under fuel-free and fuel-containing acid electrolyte conditions. In the absence of organic molecules, the ORR on the alloy seems to proceed via a 4 e- transfer mechanism, with a negligible production of H2O2, as supported by RRDE results. In the presence of the different liquid fuels (ethylene glycol, ethanol or 2-propanol), the alloy shows a high degree of tolerance. The EIS measurements suggest that at high polarization potentials, the competitive interaction of oxygen reduction and liquid fuels oxidation at the catalytic surface sites of the alloy leads to a faster reaction, as indicated by the smaller charge transfer resistances (Rct) obtained from Nyquist plots in the solutions containing the organic molecules, compared to the Rct values without organic molecules. The results of Pt-Co/MWCNT are compared to those of a commercial Pt/C cathode.