bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Investigations on a PEMFC at Sub-Freezing Temperatures
Authors: Pinton E. , Fourneron Y. , Rosini S. , Antoni L.
Published: June 2009

Ice/frost formation in a Proton Exchange Membrane Fuel Cell (PEMFC) operating under sub-zero temperatures can lead to its shutdown during start up. Isothermal potentiostatic and galvanostatic tests were performed on 220 cm2 single cells under a wide range of operating conditions in order to investigate the “cold start” behaviour. Different parameters have been investigated: the initial water contained in the membrane, the operating voltage, the cell temperature and current. An optimal wetting level of the fuel cell (FC) core for which cumulated heat generated by the electrochemical reaction is maximal, has been observed. Water management analysis from the membrane coupled with cell resistance measurement allowed to formulating a phenomenological interpretation of the overall performance evolution of the FC. FC starving is not only due to ice formation in the cathode layer pores, thus hindering oxygen transport. It is also due to ice formation in active reaction sites increasing the electrical resistance of the cell. Both factors dramatically reduce FC performance under load. The relative balance of each effect has been assessed.
Development of Performance Analysis Method on SOFC: Long Time Operation of Tubular SOFC and Comparison to Post Test Analysis
Authors: Watanabe Takao , Yamamoto Tohru , Yasumoto Kenji , Morita Hiroshi , Mugikura Yoshihiro , Yamashita Akihiro , Tomida Kazuo , Yokokawa Harumi , Sakai Natsuko , Horita Teruhisa , Yamaji Katsuhiko
Published: June 2009

Cell and stack life and reliability is one of the biggest issues to realize solid oxide fuel cell (SOFC) power generation systems. The R&D investigation on reliability has been carried out under New Energy Development Organization (NEDO) program by authors. Endurance tests were implemented for tubular type SOFCs, and performance analysis results were compared to post test analysis results. The performance was analyzed by using performance estimation equations developed by CRIEPI and longitudinal increase of cathode overpotential was observed. Comparing to the post test analyzed by AIST, Cr poisoning was also observed at the cathode. These results indicate the adequacy of performance estimation method.
Kinetic Analysis of C4 Alkane and Alkene Pyrolysis: Implications for SOFC Operation
Authors: Al Shoaibi Ahmed , Dean Anthony M.
Published: June 2009

Pyrolysis experiments of isobutane, isobutylene, and 1-butene were performed over a temperature range of 550–750 °C and a pressure of ∼ 0.8 atm. The residence time was ∼ 5 s. The fuel conversion and product selectivity were analyzed at these temperatures. The pyrolysis experiments were performed to simulate the gas phase chemistry that occurs in the anode channel of a solid-oxide fuel cell. The experimental results confirm that molecular structure has a substantial impact on pyrolysis kinetics. The experimental data show considerable amounts of C5 and higher species (∼2.8 mole % with isobutane at 750 °C, ∼7.5 mole % with isobutylene at 737.5 °C, and ∼7.4 mole % with 1-butene at 700 °C). The C5+ species are likely deposit precursors. The results confirm that hydrocarbon gas phase kinetics have substantial impact on SOFC operation.
Fuel Cell Vehicle Learning Demonstration: Study of Factors Affecting Fuel Cell Degradation
Authors: Kurtz Jennifer , Wipke Keith , Sprik Sam
Published: June 2009

The 5 year “Controlled Hydrogen Fleet and Infrastructure Demonstration and Validation Project” (or Fuel Cell Vehicle Learning Demonstration) was initiated by the U.S. Department of Energy (DOE) in 2004. The purpose of the project is to conduct an integrated field validation that simultaneously examines the performance of fuel cell vehicles and the supporting hydrogen infrastructure. Four industry teams are currently operating more than 92 vehicles and 14 refueling stations throughout the United States. More than 40 additional vehicles and several additional refueling stations will be added to the project through 2009. At the National Renewable Energy Laboratory (NREL), on-road driving and refueling data are analyzed to assess the technology status and progress, as well as to provide feedback to the hydrogen research and development community. A new/updated set of public results, in the form of composite data products (constructed to protect the intellectual property of the four teams), is released twice a year in the spring and fall. In addition to the public results, detailed analyses results are shared with each participating team. One of the analyses studies fuel cell degradation. The study includes following the fuel cell performance degradation trends, e.g. identifying fuel cell stacks that are decaying at a different rate than others of a similar design and in the same fleet, and explores connections between the real world data and fuel cell degradation. This study differs from other degradation studies in a lab setting or at the single cell level because this study uses full scale fuel cell stacks in vehicles with on-road driving and refueling. In the study, researchers investigate degradation factors by applying multivariate analyses for each individual team and for the combination of all four teams. Detailed results are reviewed with the individual teams in an effort to improve each analysis iteration and comprehension of the results. This paper will detail NREL’s study of fuel cell degradation factors by describing the process, reviewing the latest public results, and reporting on any observed dominant factor groups affecting fuel cell degradation.
Effect of Anode-Off Gas Recirculation at Solid Oxide Fuel Cell System
Authors: Baek Seugnwhan , Kim Yongmin , Bae Joongmyeon
Published: June 2009

The aim of this work is to analyze system efficiency when anode-off gases are recirculated at a diesel driven solid oxide fuel cell system. Diesel was chosen as a fuel due to advantages of its high energy density and well-established infrastructure. Three systems were mainly investigated which have different system configurations. First system does not use recirculation of anode-off gas at the system. At second model anode-off gases are recirculated to a diesel reformer in the system. Finally anode-off gases are recirculated to the anode side of a solid oxide fuel cell stack. Three different systems are compared in terms of total efficiency, performances of diesel reformer and solid oxide fuel cell. It was found that various inlet conditions and split conditions would make differences of total efficiencies and component performances at the three different systems.
Use of Glass-Fabric/Epoxy End Plates in High Temperature Proton Exchange Membrane Fuel Cell to Reduce Startup Time
Authors: Kim Ji-Seok , Park Jeong-Bin , Kim Yun-Mi , Kim Nam-Il , Sun Hee-Young , Kim Kyunghoon , Song Tae-Won , Hong Suk-Gi , Ahn Sung-Hoon
Published: June 2009

The end plates of fuel cell assemblies are used to support the inner stacks, reduce the contact pressure, and provide sealing between membrane-electrode assemblies. They therefore require sufficient mechanical strength to withstand the tightening pressure. The end plates must be stiff enough to resist large deformations, be light enough to ensure a high energy density, have stable electrochemical properties, and provide adequate electrical insulation. In the past, end plates were made from metals such as aluminum, titanium, and stainless steel alloys. However, due to large thermal losses and excessive weight, alternative materials are now being considered. This paper focuses on replacing the conventional stainless steel end plates of a high temperature proton exchange membrane fuel cell by those made of a glass-fiber/epoxy composite to decrease the startup time. To achieve this goal, following steps were performed. First, glass-fiber/epoxy composite specimens were fabricated to measure their mechanical properties. Then, a finite element analysis was performed using the measured material properties to confirm that the composite end plates could withstand the load conditions and to estimate the startup time. Finally, glass-fiber/epoxy composite end plates were fabricated, assembled, and tested to compare the startup time and generated voltage with the values obtained using stainless steel end plates.
A Numerical Investigation Into the Use of Patterned Electrodes in a Segmented-in-Series Tubular SOFC
Authors: Haberman B. A. , Bortuzzo G. , Marquis A. J.
Published: June 2009

A typical segmented-in-series tubular SOFC consists of flattened ceramic support tubes with rows of electrochemical cells fabricated on their outer surfaces and connected in series along their length. In this design, the electrical resistance of the long current flow path is minimised by using high conductivity electrodes. Therefore the resistance of the cathode, which typically has a low electrical conductivity, is reduced by fabricating an additional high conductivity current collector layer. This study is concerned with investigating the design of this additional layer using the newly developed SOHAB multi-physics computer code. Initial simulations identified the optimum thickness of a uniform current collector with respect to cell performance and component cost. However, it was found that this uniform layer causes ionic current to concentrate near the edges of the electrolyte, potentially enhancing cell degradation. Further simulations investigated whether a patterned current collector could be designed to control the current flow within the cell and reduce this detrimental effect. It was found that, for an identical thickness collector layer, a patterned design could reduce spatial variations of ionic current by a factor of over two with a negligible effect on cell performance. Therefore, patterned current collectors represent a means to control the current flow path within a segmented-in-series cell and further improve its performance.
Measurement of Liquid Water Accumulation in a Proton Exchange Membrane Fuel Cell With Dead-Ended Anode
Authors: Siegel Jason B. , McKay Denise A. , Stefanopoulou Anna G.
Published: June 2009

The operation and accumulation of liquid water within the cell structure of a polymer electrolyte membrane fuel cell (PEMFC) with a dead-ended anode is observed using neutron imaging. The measurements are performed on a single cell with 53 square centimeter active area, Nafion 111-IP membrane and carbon cloth Gas Diffusion Layer (GDL). Even though dry hydrogen is supplied to the anode via pressure regulation, accumulation of liquid water in the anode gas distribution channels was observed for all current densities up to 566 mA cm−2 and 100% cathode humidification. The accumulation of liquid water in the anode channels is followed by a significant voltage drop even if there is no buildup of water in the cathode channels. Anode purges and cathode surges are also used as a diagnostic tool for differentiating between anode and cathode water flooding. The rate of accumulation of anode liquid water, and its impact on the rate of cell voltage drop is shown for a range of temperature, current density, cathode relative humidity and air stoichiometric conditions. Neutron imaging of the water while operating the fuel cell under dead-ended anode conditions offers the opportunity to observe water dynamics and measured cell voltage during large and repreatable transients.
Porous Anode Model for Coal Syngas Fuelled SOFC: Combined Mass and Energy Transport Normal to Cell Plane
Authors: Gerdes Kirk , Gemmen Randall
Published: June 2009

Solid oxide fuel cells are being developed for integrated gasification combined cycle hybrid power systems. It is therefore necessary to evaluate the coupled temperature and concentration profiles for SOFC anodes exposed to coal syngas. In this work the SOFC anode was treated as a porous composite of 50/50 (volume) Ni / YSZ. Porous transport was modeled using the dusty gas model (DGM) and included two pore reactions, namely water gas shift and steam reforming of methane. The thermal transport model considered heat exchange by radiation between the interconnect and SOFC surface, convective transfer from bulk gas flow over the anode, heat generation terms due to pore reactions, and heat generation terms at the electrolyte boundary due to electrochemical reactions, ohmic heating, and concentration polarization. Composition profiles throughout the porous anode were considered for the DGM alone and were compared to the DGM including energy (DGME). The cases examined were for current densities ranging from 0.000–0.750 A/cm2 and for pressures from 1–19 atm absolute. Simulation results predict that the average cell operating temperature will increase 10 to 60°C relative to the furnace wall with inclusion of the energy equations. However, the thermal gradients within the anode are small due to the good thermal conductivity of the Ni-based anode. The effect of inclusion of energy transport on the hydrogen concentration profile is mixed depending on the independent parameter considered, with relative insensitivity to changes in the current density, but modest sensitivity to changes in operating pressure. Consideration of the thermal transport is important for determination of the interaction of coal syngas trace species with the anode, but is less critical for material stability.
Techno-Economic Optimal Design and Application of SOFC Systems for Residential Micro-CHP Applications in the U.S.
Authors: Braun Robert J.
Published: June 2009

A techno-economic optimization study investigating optimal design and operating strategies of solid oxide fuel cell (SOFC) micro-combined heat and power (CHP) systems for application in U.S. residential dwellings is carried out through modeling and simulation of various anode-supported planar SOFC-based system configurations. Five different SOFC system designs operating from either methane or hydrogen fuels are evaluated in terms of their energetic and economic performance and their overall suitability for meeting residential thermal-to-electric ratios. Life cycle cost models are developed and employed to generate optimization objective functions which are utilized to explore the sensitivity of the life cycle costs to various system design and economic parameters and to select optimal system configurations and operating parameters for eventual application in single-family, detached residential homes in the U.S. The study compares the results against a baseline SOFC-CHP system that employs primarily external steam reforming of methane. The results of the study indicate that system configurations and operating parameter selections that enable minimum life cycle cost while achieving maximum CHP system efficiency are possible. Life cycle cost reductions of over 30% and CHP efficiency improvements of nearly 20% from the baseline system are detailed.
Modeling and Controls of a Fuel Delivery System With Dual Recirculation Lines for a PEM Fuel Cell System
Authors: He Jinglin , Choe Song-Yul , Hong Chang-Ouk
Published: June 2009

A fuel delivery system with dual recirculation lines is investigated in this paper, which can reuse the exhausted gas from the outlet of anode flow channel. In the automotive application, the fuel delivery system regulates the hydrogen pressure and flow rate from the tank to the anode flow channel that change dynamically with load. The control objectives of fuel cell stack require that a slight pressure difference between the anode and cathode be maintained to prevent the damage of the membrane. In addition, the unconsumed hydrogen is circulated to a supply line by the recirculation lines. The fuel delivery system analyzed in this paper consists of two supply lines and two recirculation lines. The supply line with a low pressure regulator accounts for the supply of fuel at relatively low load demands. The other supply line with a flow controller starts to provide additional fuel with controllable flow rate at high load demands. The recirculation line with an ejector allows for mixing the unconsumed hydrogen with the supplied fuel. The other recirculation line with a blower is used to improve the controllability of the recirculation flow rate. Analysis of the fuel delivery system with dual recirculation lines is carried out by modeling and simulating an integrated system, where the components are modeled involving the dynamic characteristics. The major components of fuel delivery and recirculation system are an ejector, a blower, and a pressure regulator. In addition, the linearization of the integrated system is expressed in the approach of state equations to form the control problem of the system. Then the linear controllers are designed based on the decentralized proportional and integral control, and the state feed-back control. The systems with the different controllers are simulated at different operating points to evaluate their tracking performance by comparing the dynamic response curves.
Proton Exchange Membrane Fuel Cell Catalyst: Synthesis and Characterization
Authors: Franco Egberto Gomes , Dantas Filho Paulo Lucas , Ribeiro Carlos Eduardo Rollo , Burani Geraldo Francisco , Linardi Marcelo
Published: June 2009

Fuel cells are a promising technology to deal with energy sustainability, especially for mobility purposes the Proton Exchange Membrane Fuel Cell and hydrogen produced from biomass could be coupled to overcome the amount of CO2 emissions. In order to improve fuel cells performances the search for new electrocatalysts has a great importance in this technology the challenge for a fuel cell catalyst that is less poisoned by CO is one of the most important field in low temperature fuel cell developments that use alcohol and hydrocarbons as primary fuels. In this work PtSm, PtTb, PtDy, PtU, PtRuMo and PtRuDy systems have been synthesized by the colloid method, investigated by the following techniques: X-rays fluorescence analysis (XFA), X-rays powder diffraction (XRD), X-rays photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), cyclic voltammetry (CV) and polarization curves (Exi). The results obtained in this work shows that PtRuMo is the best choice for direct methanol oxidation. For direct ethanol oxidation the higher activity was found in PtRuDy system. PtU system was investigated and showed an interesting behaviour in ethanol oxidation. After two cycles of H2/O2 and ethanol/O2 the catalyst was able to reach the initial figures on hydrogen/oxygen oxidation which means that no degradation of the catalyst was indentified.
RGA Analysis of a Solid Oxide Fuel Cell Gas Turbine Hybrid Plant
Authors: Tsai Alex , Banta Larry , Tucker David , Gemmen Randall
Published: June 2009

This paper presents a Relative Gain Array (RGA) analysis of a simulated SOFC/Gas Turbine plant based on a multivariate empirical formulation of a 300kW hybrid system. The HyPer test facility at the National Energy Technology Laboratory, served as the test bed for deriving frequency response data and subsequent multivariable model of a direct fired, recuperated hybrid cycle plant. Through the modulation of various airflow bypass-valves, magnitude and phase data is used to formulate Transfer Function {TF} equations that describe input/output system interaction. A frequency dependent RGA calculation of the empirical Transfer Function matrix provides a means of quantifying the degree of coupling between system inputs and outputs for the configuration studied. Various input/output interaction time scales are obtained to identify frequencies where fully developed system coupling occur. Analysis of the RGA matrix leads to a better understanding of the inherent properties the hybrid configuration, and can serve as a validating tool to existing analytical RGA calculations of similar types of hybrids.
Multivariable Robust Control of a Simulated Hybrid Solid Oxide Fuel Cell Gas Turbine Plant
Authors: Tsai Alex , Banta Larry , Tucker David , Gemmen Randall
Published: June 2009

This paper presents a systematic approach to the multivariable robust control of a hybrid fuel cell gas turbine plant. The hybrid configuration under investigation comprises a physical simulation of a 300kW fuel cell coupled to a 120kW auxiliary power unit single spool gas turbine. The facility provides for the testing and simulation of different fuel cell models that in turn help identify the key issues encountered in the transient operation of such systems. An empirical model of the facility consisting of a simulated fuel cell cathode volume and balance of plant components is derived via frequency response data. Through the modulation of various airflow bypass valves within the hybrid configuration, Bode plots are used to derive key input/output interactions in Transfer Function format. A multivariate system is then built from individual transfer functions, creating a matrix that serves as the nominal plant in an H-Infinity robust control algorithm. The controller’s main objective is to track and maintain hybrid operational constraints in the fuel cell’s cathode airflow, and the turbo machinery states of temperature and speed, under transient disturbances. This algorithm is then tested on a Simulink/MatLab platform for various perturbations of load and fuel cell heat effluence.
A Novel Flow Design on the Planar Printed-Circuit-Board DMFC Modules
Authors: Kuan Y.-D. , Lee S.-M. , Chang J.-Y. , Sung M.-F.
Published: June 2009

A direct methanol fuel cell (DMFC) fabricated using the printed circuit board fabrication process places multiple cells in planar arrangement and forms a PCB DMFC module. Properly transporting the methanol solution into the cells and maintaining continual DMFC operation are very important. This paper presents a strategy for producing anode flow channel designs on planar DMFC modules. The flow designs are accomplished using computational fluid dynamic (CFD) simulations. The proposed strategy was successfully applied to produce flow designs on several DMFC modules.
Effects of Electrode Microstructure on Polarization Characteristics of SOFC Anodes
Authors: Sakamoto Yusuke , Shikazono Naoki , Kasagi Nobuhide
Published: June 2009

Anode microstructure parameters were quantified by SEM-EDX measurements and the dependence of polarization characteristics on the anode microstructure parameters is investigated experimentally. Nickel yttria-stabilized zirconia (Ni-YSZ) anode supported cells with a thin YSZ electrolyte, lanthanum-strontium-manganite (LSM)-YSZ composite cathode, and LSM cathode current collector layers were fabricated by dip coating method. Anode microstructure was successfully imaged and quantified by ultra low voltage SEM and by means of stereology. Cell voltage measurements and impedance spectroscopy were performed at 650 and 750°C with hydrogen diluted by nitrogen as a fuel. A quantitative relationship between measured polarization and microstructure parameters, e.g., three phase boundary length, contiguity, etc., was discussed. Finally, a cell with an anode functional layer (AFL) was fabricated to investigate the possibility of improving both activation and concentration polarization characteristics.
Development of a Rapid Simulation Tool for PEM Fuel Cell Stacks
Authors: Rasmussen Peder L. , Sui Pang-Chieh , Kær So̸ren K. , Djilali Ned
Published: June 2009

When investigating fuel cell stack design and performance detailed stack modeling is needed. By using a combination of the commercial software MATLAB and COMSOL, a stack model has been developed. The model incorporates a flow network model (FNM) and a 2D finite element method (FEM) model. The FNM model initially calculates the flow distribution in the stack, and transfers this information to the FEM model. The FEM model solves for electron transport, thermal conduction and simplified reactant and coolant transport. This stack model is validated and used to investigate the behaviour of a stack and individual cells under various operating conditions, with a special focus on cell-to-cell electrical coupling. Furthermore the effects of changing flow header dimensions are investigated. This type of modeling is well suited for initial stack performance estimates, and tests of worst case scenarios. This can contribute to faster stack design iterations.
Preparatory Tests for 1kW Diesel-Powered SOFC Systems
Authors: Kang Inyong , Yoon Sangho , Bae Gyujong , Kim Junghyun , Baek Seungwhan , Bae Joongmyeon , Yoo Yungsung
Published: June 2009

High operating temperature of SOFCs can make internal reforming effective as well as inhibit CO poison over the Ni-based anode. Therefore, SOFCs give us a wide range of fuel choice. In this study, diesel known as a very tough fuel for fuel cell applications was chosen as the SOFC fuel. Our final goal is to develop the 1kWe diesel-powered SOFC systems for residential power generation purpose. Before the system construction, we have drawn a few engineering and scientific problems from the bench tests of reformer and stack. Most of all, coke formation in the reformer and stack was very serious. Coking in the diesel reformer was greatly associated with fuel delivery process in our micro-reactor tests, which was more serious in scaled-up reformer. With several fundamental tests, the prototype construction of 1kWe SOFC system is in progress. Essentially, all heat-related components (e.g. stack, reformer, heat exchanges, after-burner) were installed inside one chamber, so called ‘hot box’. The design was mainly focused on thermal sustenance. In a 6-cell stack test using sulfur-free synthetic diesel, the system initially showed the power of ∼110We at average 0.8V of the cells. But, there was severe coke formation after a few hours operation.
Optimization of Conductive Fillers of a Composite Material for PEM Fuel Cell Bipolar Plates
Authors: Petrach Elaine , Wang Xia , Abu-Isa Ismat
Published: June 2009

Bipolar plates are necessary components in the current design of polymer electrolyte membrane (PEM) fuel cell stacks. The traditional materials used for bipolar plates are graphite and metal. In this investigation an elastomeric material with different types of conductive fillers is developed to avoid the high machining or coating costs associated with the traditional materials. The conductive fillers investigated here include Cytec thermal graphite fibers, Asbury Carbons PAN AGM 99 fiber, synthetic graphite (4012), natural flake (3763), surface enhanced flake (3775), and different grades of graphite powder (TC 301–305). Some of these conductive fillers were implemented in a two component silicone slurry matrix (RTV 627 by GE) to make a composite material. A bulk electrical resistivity of 0.0310 Ω-cm was achieved for the composite containing 28% by volume DKD fiber and 7% synthetic graphite (Asbury 4012) mixed in the elastomeric matrix.
Development of Low-Cost Anode Material for Solid Oxide Fuel Cells
Authors: Menzer Sophie , Coors Grover , Beeaff Dustin , Storjohann Dan
Published: June 2009

Manufacturing cost remains one of the major issues facing the solid oxide fuel cell (SOFC) industry. In the anode supported SOFC design, the cermet anode constitutes around 90% of the total material required to build a cell, making the technology very sensitive to anode raw material price. A new patent-pending process called “nickel yttria reaction-sintered zirconia (NiYRSZ)” has been developed for manufacturing SOFC anodes at a fraction of the cost. Typically, the solid component of the anode consists of about 50/50 volume percent nickel and 8 mole percent yttria stabilized zirconia, the latter being a rather costly material. It was discovered that zirconia and yttria powders sintered in the presence of nickel oxide readily form the cubic phase at moderate temperature. Cells manufactured using this process show excellent microstructures for anode supports: a strong bond between the electrolyte and the anode, and a high porosity without addition of pore formers. The strength of the anode was 100 MPa making the material equivalent or slightly superior to an anode fabricated with the traditional NiO/8YSZ material of similar porosity. The resistivity of the material was measured at 850°C and found to be less than 2 mΩ·cm. Cell performance was also compared to cells manufactured with traditional material. Every indication is that SOFC anodes fabricated with this new method perform as well as anodes made with the conventional material set.
Spray Coating of Electrolyte Films for Solid Oxide Fuel Cells
Authors: Persky J. , Beeaff D. , Menzer S. , Storjohann D. , Coors G.
Published: June 2009

Fabrication of defect free co-sintered electrolytes with thickness between 12 μm and 40μm has been demonstrated on planar and tubular cells produced via a spray coating process. Leak testing using a helium leak method showed low diffusional leak rates for cells using optimized spray parameters. The electrolytes were characterized using scanning electron microscopy to qualitatively assess pin holes. Average open circuit voltages (OCVs) of 1080 mV were obtained on tubular cells with spray-coated electrolytes using 3% humidified hydrogen as the fuel. This paper presents spray coating as a viable, cost effective method for electrolyte application in co-fired, anode supported SOFCs.
Uniform Distribution of Species in Fuel Cells Using a Multiple Flow Bifurcation Design
Authors: Li Peiwen , Coopamah Devasubramaniam , Ki Jeong-Pill
Published: June 2009

This paper presents the results obtained from the study about flow distribution in maintaining uniformity of flow fields in fuel cells. Three novel flow distribution designs on bipolar plates are proposed for a proton exchange membrane fuel cell (PEMFC). The flow distributors have multiple levels of bifurcations to split a flow into sub-streams of equal flow rates. There are three types of bifurcation structure proposed and studied, which are the 90° tee-type, rounded-type and slanted-type. Experiments were carried out to test the velocities of flows from the multiple channels after bifurcations, and the flow uniformity on the bipolar plate is estimated and studied. Overall evaluation of flow uniformity in the three designs was conducted. The rounded-type bifurcation structure showed the best flow uniformity. After experimental verification of the uniform flow distribution in the novel design, three PEM fuel cell was fabricated which adopted the novel flow fields. From the experimental test and comparison under dry fuel and air condition, it is found that the PEMFC with new flow field can have a better performance. Thorough experimental investigation is planned for the future study.
Mathematical Modeling of a Molten-Carbonate Fuel Cell Using MathCAD
Authors: Blekhman David , McClain Stephen T.
Published: June 2009

The topic of fuel cells remains novel in most of the engineering programs. While a good selection of textbooks has been introduced, the need for enlightening and achievable projects and homework problems remains strong. The application of MathCAD to a molten-carbonate fuel cell course project is presented. This work effectively brings together the authors’ efforts to offer students the cutting edge experiences in thermal sciences and fuel cell theory. It has been shown that the topic of fuel cells can naturally be introduced from the coverage of reacting systems and combustion in particular. Likewise, there has been a significant development of a uniform mathematical model of a variety of thermodynamic phenomena employing MathCAD, with a considerable increase in the difficulty level of problems that can be completed by the student. MathCAD functionality has been applied to problems in Thermodynamics, Energy Systems, Internal Combustion Engines, and now Fuel Cells. The principles of modeling the carbon-hydrogen-oxygen-nitrogen (CHON) systems have been extended to reflect the thermo- and electro-chemical processes in fuel cells, which includes the dynamically shifting Nernst potential as reactants flow through the fuel cells. Operational parameters, like fuel and oxidizer utilization, can also be evaluated. The intent of this paper is to demonstrate how MathCAD can be used to perform very powerful calculations for fuel cell applications while the intuitive solving structures and mathematical report-like worksheets created in MathCAD promote learning of fuel cell topics. The presented project model can be broken into progressive assignments or just individual homework problems in an undergraduate applied thermodynamics or fuel cell applications course.
Water Vapor Effects on Fuel Cell Desulfurizer Performance: A Decade of Field Experience
Authors: Israelson Gordon
Published: June 2009

Operation of Siemens solid oxide fuel cell (SOFC) units using natural gas fuel has required sulfur selective sorbents for fuel desulfurization. Experience with physical sorbents has shown varying sulfur capacity during field operation. This has been puzzling and produced great uncertainty for selection of sorbents. This mystery of changing sorbent sulfur capacity has been partially solved. Measurements of considerably variable and unexpectedly high water vapor content in pipeline natural gas supplies appears to be a major contributor to competition for sulfur adsorption sites and results in variable sorbent performance. A summary (Table 1) shows operating lifetimes of several sorbents to remove sulfur from pipeline natural gas at several field sites, spanning about one decade of experience.
Development of Logistic Fuel Desulfurizers Endowed With Nanoartifacts
Authors: Sundararajan Desikan , Azad Abdul-Majeed
Published: June 2009

Sulfur content in the logitstic fuels such as diesel, jet fuel and coal poses great challenge, as it leads to severe deactivation and poisioning of the reforming catalysts. The utilization of logistic fuel in high efficiency fuel cells as hydrogen-rich reformates, therefore, necessitates that the sulfur (mostly present as organosulfur species) be either eliminated totally, or its level be reduced below such levels as not to mitigate the long-term sustained performance of the reforming catalysts. Besides, SOFC anodes are also quickly poisoned by sulfur present even in trace amounts (1–2 ppm). Thus, desulfurization becomes an important and integral component in harnessing clean power from these abundunt fuel resources. Recently, we have developed a series of novel sulfur sorbents with agile scavengers dispersed thoroughly and uniformly on lightweight, highly periodic nanoporous biomimetic or zeolitic inert matrices. These formulations have been tested in a range of temperatures for durations ranging from 12 to 100 hours in sulfur-bearing gas streams. In this presentation, their synthesis, characterization (before and after sulfidation) by XRD, SEM/EDS, RBSE imaging, on-line real-time quantification in gas chromatography in conjunction with systematic chemical analyses to gauge their efficacy in sulfur removal will be discussed.
Modelling of Co-Planar Type Single-Chamber Solid Oxide Fuel Cells (SC-SOFCs)
Authors: Akhtar Naveed , Decent Stephen P. , Loghin Daniel , Kendall Kevin
Published: June 2009

A two dimensional, non-isothermal numerical model of a single-chamber solid oxide fuel cell (SC-SOFC) has been developed. For the sake of simplicity in developing the model, hydrogen-air mixture (80% hydrogen, 20% air by volume which is considered as safe) has been chosen instead of hydrocarbon-air mixtures (which require complex modelling strategy such as reforming via partial oxidation, modelling of two active fuels, i.e. hydrogen and carbon monoxide). The model is based on considering yttria-stabilized zirconia (YSZ) as electrolyte supported material, nickel yttria-stabilized zirconia (Ni-YSZ) as anode and lanthanum strontium manganite (LSM) as cathode material. Effect of varying distance between anode and cathode, flow rate, temperature, porosity and electrolyte thickness has been investigated in terms of electrochemical performance. It has been found that the flow rate and distance between the electrodes pair are the most sensitive parameters in such type of fuel cells. The model was coded in a commercial software package of finite element analysis, i.e. COMSOL Multiphysics, 3.3a.
Mechanical Properties of LSGM as an Electrolyte for Solid Oxide Fuel Cells
Authors: Mohammadi Alidad , Smirnova Alevtina L. , Sammes Nigel M.
Published: June 2009

Strontium- and magnesium-doped lanthanum gallate (LSGM) due to its high ionic conductivity and chemical stability over a wide range of oxygen partial pressures and temperatures has been considered as an alternative electrolyte for solid oxide fuel cell (SOFC) systems. Mechanical properties of LSGM electrolyte layer however need to be well studied. An overview of mechanical behavior of LSGM on an all-perovskite SOFC is presented in this work. Dense La0.8Sr0.2Ga0.7Mg0.3O2.8 electrolyte pellets were studied. Mechanical properties, such as hardness, elastic modulus, fracture toughness, and modulus of rupture (MOR) of the electrolyte pellets at different sintering temperatures were measured and correlated with the SEM morphological characterization. Samples sintered for 2h at 1500°C demonstrated slightly enhanced mechanical properties than those sintered at 1450°C and 1400°C.
Surface Treated SS304 Stainless Steel Bipolar Plates: Its Properties and Single Cell Performance
Authors: Lee Yu-Ming , Lee Shuo-Jen , Lee Chih-Yuan , Lai Ping-Hung
Published: June 2009

In this paper, a thin SS304 stainless steel is chosen as metallic bipolar plate. In order to improve the surface qualities such as anti-corrosion capability, surface roughness and clearness, the surface of bipolar plate is treated by a specific surface modification technology. From the results of corrosion and potentionstatic tests, the corrosion rate and corrosion current of treated plate is much improved. The corrosion rate and corrosion current are reduced to 0.037 mmpy and 3.56μ A/cm2. The cell performance tests shows the peak power of treated cell is lower than original cell. However, for the long term tests, the cell with treated plate has a more stable power output. The results show that the treated plate has a good potential for using in the fuel cell.
Comparative Evaluation of Heating Techniques for Room Temperature Startup of a PEMFC
Authors: Bapat Chaitanya J. , Thynell Stefan T.
Published: June 2009

We study the use of different external heating techniques for startup of a PEM fuel cell initially at room temperature. If a hot liquid is used to heat the fuel cell, the startup time depends on the Reynolds number of the hot liquid flow and also on the convective heat transfer coefficient at the liquid channel/bipolar plate interface. Therefore, apart from the energy required to heat the liquid, additional power is required for the external hot liquid pump. Fuel cell can also be directly heated by using electric heaters. Thin flexible heaters were found to be most suitable for the purpose as they allow the use of thin bipolar plates and reduce the thermal contact resistance at the heater/bipolar plate interface. The thermal mass of the bipolar plates was found to be an important factor affecting the startup time. Hence using materials with lower heat capacities reduces startup time. Embedding a heating element in the GDL reduces the startup time as the thermal mass of the GDLs and MEA is much smaller than the bipolar plate. GDLs with low through-plane thermal conductivities and high in-plane thermal conductivities are able to further reduce the startup time when used in conjunction with a heating element in the GDL.
Modeling the Species Transport and Reactions in an SOFC Cathode Using Smoothed Particle Hydrodynamics
Authors: Ryan Emily , Amon Cristina
Published: June 2009

A computer model for species mass transport within the cathode of a solid oxide fuel cell (SOFC) is being developed based on the smoothed particle hydrodynamics method. Smoothed particle hydrodynamics is a grid-free modeling technique which uses a Lagrangian framework to model fluid dynamics systems as a discrete system of particles using a smoothing approximation. The method is able to handle complex geometries and complex physical and chemical phenomena with relative ease compared to grid based methods. The model is being developed to investigate chromium poisoning in the cathode of solid oxide fuel cells by examining the transport and reactions of chromium species in the cathode. The model includes ordinary and Knudsen diffusion within the cathode, which have both been shown to be significant mass transport processes in solid oxide fuel cells, and the adsorption reactions on the surface of the cathode. Chromium is thought to adsorb to the surface of the cathode reducing the number of adsorption sites for oxygen. The pore scale nature of smoothed particle hydrodynamics eliminates the need for effective properties of the porous structure to be used in the diffusion model. Previous solid oxide fuel cell electrode models based on effective diffusion models such as the dusty gas model rely on the bulk properties of the porous medium such as porosity and tortuosity to describe the complex microstructure of the electrodes. Bulk properties add unwanted uncertainty and error into the model, by using the smoothed particle hydrodynamics method some of these uncertainties can be removed from the model. The paper reviews past work on chromium poisoning, discusses the applicability of smoothed particle hydrodynamics for modeling the solid oxide fuel cell cathode and describes the model in detail.
Optimization of Passive Air Breathing Fuel Cell Cathodes
Authors: Babcock Bryan , Tupper A. J. , Clark Dan , Fabian Tibor , O’Hayre Ryan
Published: June 2009

Air-breathing polymer electrolyte membrane fuel cells (ABFCs) use free convection airflow to supply oxygen to their cathodes. These cells are typically characterized by low output power densities compared to forced-convection fuel cells. Because ABFC designs rely on natural convection air delivery, cathode performance is often the bottleneck. This paper specifically examines the tradeoff between mass transport losses and ohmic electrical resistance losses for optimal ABFC cathode design. Optimization is non-trivial because the simultaneous requirements for excellent cell compression, current collection and gas access are often in contradiction. Simple scaling analysis and experimental observations suggest that the tradeoff between lateral mass transport resistance losses and cathode/gas diffusion layer (GDL) contact resistance losses determines optimal ABFC cathode design. In order to quantitatively study these effects, we have tested a series of different cathode geometries in a standardized ABFC. Using high frequency resistance measurements and fast-scan polarization measurements, we have been able to interrogate both the ohmic and mass transport losses associated with each cathode configuration. We have also used pressure sensitive foils to examine the pressure distribution for representative configurations, providing a quantitative link between pressure distribution and cell resistance. Finally, we have studied the effect of deploying a current collecting contact layer between the cathode and the GDL. Results indicate that the deployment of a sufficiently stiff yet highly porous contact layer significantly reduces contact resistance losses while imposing minimal additional mass transport losses. A stiff yet porous contact layer reduces the contact resistance losses by increasing total contact surface area and providing a more even distribution of pressure across the face of the cell. By minimizing contact resistance losses, this strategy enables the deployment of ABFC cathode structures with greater than 90% open area, thereby leading to enhanced ABFC performance, particularly at high current densities.
Improving PEM Fuel Cell Catalysts Using Nitrogen-Doped Carbon Supports
Authors: Zhou Yingke , Pasquarelli Robert , Berry Joe , Ginley David , O’Hayre Ryan
Published: June 2009

This study experimentally examines the effect of nitrogen doping on the activity of Pt/C catalyst systems. The investigation was accomplished through the development of geometrically well-defined model catalytic systems consisting of tunable assemblies of Pt catalyst nanoparticles deposited onto both N-doped and undoped highly-oriented pyrolytic graphite (HOPG) substrates. N-doping was achieved via ion beam implantation, and Pt was electrodeposited from solutions of H2PtCl6 in aqueous HClO4. Morphology from scanning electron microscopy (SEM) and catalytic activity measurement from aqueous electrochemical analysis were utilized to examine the N-doping effects. The results strongly support the theory that doping nitrogen into a graphite support significantly affects both the morphology and behavior of the overlying Pt nanoparticles. In particular, nitrogen-doping was observed to cause a significant decrease in the average Pt nanoparticle size, an increase in the Pt nanoparticle dispersion, and a significant increase in catalytic activity for both methanol oxidation and oxygen reduction.
Modeling of Material Parameters for Increased Steam-Permeation in Yttrium-Doped Barium Cerate Ceramic Membranes
Authors: Sanders Michael D. , O’Hayre Ryan P. , Coors W. Grover
Published: June 2009

Ceramic steam-permeation membranes permit high temperature transport or separation of water vapor and have the potential to significantly improve the efficiency of a variety of energy conversion technologies including solid oxide fuel cells, membrane reformers, and coal gasification. Though previously overlooked because it was believed that steam either could not be transported selectively or that transport rates would inevitably be far lower than O2 transport membrane (OTM) alternatives, recent results indicate that steam-permeation membranes may be a compelling alternative to OTMs. In addition to high protonic conduction, yttrium- and gadolinium-doped barium cerate (BCY and BCG respectively) have also exhibited impressive steam-permeation capabilities under suitable conditions. Through analytical modeling of hydration thermodynamics and ambipolar diffusion kinetics, this paper examines the materials parameters that lead to increased steam-permeation, focusing in particular on BaCe0.9Y0.1O3. The relationship between dehydration temperature and the temperature of maximum flux, as well as the effect of ionic diffusion activation energies on these quantities, are presented. Insight provided by these models provides directions for the future development as well as understanding of improved steam permeation materials and their possible deployment in fuel cell applications.