bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Simulation of Electrochemical Reaction in Reconstructed Three-Dimensional LSM/YSZ Composite Cathode
Authors: Nakagawa Tadahiro , Shikazono Naoki , Kasagi Nobuhide
Published: June 2009

In the present study, a novel computational scheme for the assessment of the activation polarization of LSM/YSZ composite cathodes is proposed. The scheme consists of modeling techniques of three-dimensional microstructures and an evaluation method of electrochemical characteristics. Two modeling techniques of microstructures are employed, i.e. the stochastic reconstruction (SR) method and the random packing model (RPM). In the SR method, the 3-D structure is reconstructed statistically from the two-point correlation function of the cross-sectional image of SEM-EDX. In RPM, on the other hand, spherical LSM and YSZ particles are randomly packed in the computational domain. This model is mainly used for the parametric survey, because control parameters used in the model have good correspondence to the parameters used in the actual cell manufacturing process. The lattice Boltzmann method coupled with the Butler-Volmer equation is employed for the detailed assessment of the electrochemical characteristics inside the constructed 3-D cathode microstructures. The oxygen diffusion and the electronic and ionic conductions are calculated simultaneously, and coupled with the charge transfer at the three-phase boundary (TPB) using the Butler-Volmer equation. As a result, potential, polarization and current density distributions are fully investigated. The results from the SR method reveal that the cathode sintered at 1150 °C shows the smaller overpotential than the cathodes sintered at 1200 and 1250 °C. The RPM results show that particle diameter and its standard deviation as well as volume fraction of species have large effects on the cathode performance.
A Modeling Study of the Effect of Cathode Delamination on SOFC Performance
Authors: DiGiuseppe Gianfranco , Licon Gladys Morin
Published: June 2009

In this paper cathode delamination is studied in order to better understand its effect on the electrochemical performance of planar solid oxide fuel cells (SOFCs). In recent published work cathode delamination has been suggested to play a significant role in voltage degradation. Voltage degradation has challenged this new technology in recent years and has prevented SOFC systems to enter the commercial market except for a few prototypes. The objective of this work is to quantify the effect of cathode delamination on the cell electrochemical performance. This study will better elucidate the delamination problem which will in turn inspire more work to improve cathode adhesion by modifying the cathode properties. Modeling results indicate that the SOFC performance is affected if the cathode cannot maintain a good attachment with the SOFC assembly. Voltage-current density curves indicate that the performance of the SOFC declines as the percentage of the separation increases. Therefore a portion of the observed voltage degradation could be attributed to the delamination of the cathode.
A Combined Finite Element-Upwind Finite Volume-Newton’s Method for Liquid-Feed Direct Methanol Fuel Cell Simulations
Authors: Sun Pengtao , Xue Guangri , Wang Chaoyang , Xu Jinchao
Published: June 2009

In this paper, a three-dimensional, two-phase transport model of liquid-feed direct methanol fuel cell (DMFC), which is based on the multiphase mixture formulation and encompasses all components in a DMFC using a single computational domain, is specifically studied and simulated by a combined finite element-upwind finite volume discretization along with Newton’s method, where flow, species, charge-transport and energy equations are simultaneously addressed. Numerical simulations in 3D are carried out to explore and design efficient and robust numerical algorithms for the sake of fast and convergent nonlinear iteration. A more reasonable source term of water transport equation, and a series of efficient numerical algorithms and discretizations are specifically designed and analyzed to assist in achieving this goal. Our numerical simulations demonstrate that the convergent and correct physical solutions can be attained within 100 more steps, against the oscillating and long-running nonlinear iterations (up to 5000 steps) operated by standard finite element/volume method without new numerical techniques.
Effects of Ambient Conditions on the Cell Performance of a Passive Air-Breathing DMFC
Authors: Zhu Xiaowei , Li Jun , Liao Qiang , Zhu Xun , Ye Dingding
Published: June 2009

In the present study, a passive air-breathing direct methanol fuel cell (DMFC) with an active area of 4.41 cm2 and a built-in methanol solution reservoir of 8 ml was used to investigate the effects of relative humidity (RH) and temperature of ambient atmosphere on cell performance and cathodic flooding. The experimental results indicate that the effects of RH on cell performance are dependent upon temperature. When the temperature is below 10 °C, RH shows no effect on the cell performance. At the temperature of 20 °C and 35 °C, the cell performance is quite similar at low to medium current densities, and the cell performance increases with the decrease of RH at high current densities. In the case of 50 °C, it seems that RH has a greater effect on the cell performance than those at lower temperature: the cell performance is improved at low to medium current densities, whereas it is depraved at high current densities with the increase of RH. Furthermore, it is found that water flooding at the cathode was strongly dependent on the competition of water evaporation and production. High RH and low temperature led to more serious water flooding at the cathode. A better long-term discharge performance can be obtained under the condition of high temperature and low RH.
Basic Fuel Cell Electrochemical Thermodynamic Studies: Utilization and Thermodynamic Performance for Various Fuels
Authors: Winkler Wolfgang , Williams Mark
Published: June 2009

This study gives information of new opportunity fuels having increasing importance is all future energy scenarios. It compares the basic thermodynamic performance of fuel cells with various fuels — ammonia, methanol, hydrogen, carbon monoxide and carbon(s). For both oxygen ion conducting and proton conducting fuel cell, where applicable, its performance as a function of utilization is considered. The fuel cell itself will be considered as a reversible electrochemical reactor, generating power and mixing substances, but without further restrictions on its design. The thermodynamic state and the excess air are further parameters of variation. The consequences of the use of air and oxygen are considered as well. The principal reversible combustion of the fuel is the base of the operation of any fuel cell. The utilisation of the fuel changes the gas concentrations on the anode and cathode side depending on the ionic transport mechanism. The reversible SOFC model was used to describe the influence of the fuel utilisation, the thermodynamic state, and the operational parameters for the fuel H2 on the local Nernst voltage in previous publications. This work has been expanded to proton conducting cells and different opportunity and hydrocarbon fuels. Ammonia is quite different and at lower utilizations appears to be a superior fuel. Methanol is superior to methane over a wide utilization range. Hydrocarbons like methane have a smaller voltage decrease during utilization than hydrogen and carbon monoxide. Excess air larger than two has a small impact on voltage loss. Direct utilization of hydrocarbon fuels without reforming is a key development path toward higher efficiency.
Characterization of PSCF3737 for Intermediate Temperature-Operating Solid Oxide Fuel Cell (IT-SOFC)
Authors: Park Kwangjin , Baek Seungwhan , Bae Joongmyeon
Published: June 2009

Pr0.3Sr0.7Co0.3Fe0.7O3−δ (PSCF3737) was prepared and characterized as a cathode material for intermediate temperature-operating solid oxide fuel cell (IT-SOFC). X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS), and electrical property measurement were performed to study cathode performance of the material. XPS and EXAFS results proved that oxygen vacancy concentration was decreased and lattice constants of the perovskite structure material was increased by doping Fe up to 70 mol% at B-site of the crystal structure, which also extended the distance between oxygen and neighbor atom. Thermal expansion coefficient (TEC) of PSCF3737 is smaller than that of Pr0.3Sr0.7CoO3−δ (PSC37) due to lower oxygen vacancy concentration. PSCF3737 showed better cathode performance than PSC37. It might be due good adhesion by a smaller difference of TEC between Gd0.1Ce0.9O2 (CGO91) and electrode. Composite material PSCF3737-CGO91 showed better compatibility of TEC than PSCF3737. However, PSCF3737-CGO91 did not represent higher electrochemical property than PSCF3737 due to a decline of reaction sites by CGO91.
A New Technology of Scrape-Applied Method for the Manufacturing of MEA of Fuel-Cell System
Authors: Wu Shinn-Dar , Lee Chi-Hung , Chou Chang-Pin , Wang Yen-Zen
Published: June 2009

The technical transfer from electrode of lithium battery to MEA of fuel cells (including PEMFC and DMFC) were discussed in this study. There are three common methods for the manufacturing of lithium battery electrode; such as roller-applied method, scrape-applied method and spurt-applied method. The first two methods are the most commonly used method. This study was focused on the development of new scrape-applied equipment for lithium battery electrode. This new method was tested by measure the weight and thickness of dry electrode. The stability and reproducibility on electrode fabrication were also conducted by systematical data analysis. The results can offer an important basis to the future research on academic and commercial field.
Control Sensitivity Study for a Hybrid Fuel Cell/Gas Turbine System
Authors: Banta Larry , Absten Jason , Tsai Alex , Gemmen Randall , Tucker David
Published: June 2009

The National Energy Technology Laboratory (NETL) has developed a hardware simulator to test the operating characteristics of Solid Oxide Fuel Cell/Gas Turbine (SOFC/GT) hybrid systems. The Hybrid Performance (HyPer) simulator has been described previously, and has contributed to the understanding of SOFC/GT system operation. HyPer contains not only the requisite elements of gas turbine/compressor/generator, recuperator, combustor, and associated piping, but also several air flow control valves that are proposed as system control mechanisms. It is necessary to know how operation of these valves affects the various entities such as cathode air flow, turbine speed, and various temperatures important to the safe and efficient operation of fuel cell/gas turbine hybrid systems. To determine the interactions among key variables, a series of experiments was performed in which the effect of modulating each of the key manipulated variables was recorded. This document outlines the test methods used and presents some of the data from those tests, along with analysis and interpretation of that data in the context of control system design.
Oxygen Reduction Mechanism at Sm0.5Sr0.5CoO3−δ/Sm0.2Ce0.8O1.9 Composite Cathode for Solid Oxide Fuel Cell
Authors: Baek Seung-Wook , Bae Joongmyeon , Kim Jung Hyun
Published: June 2009

The oxygen reduction mechanism at porous Sm0.5Sr0.5CoO3−δ/Sm0.2Ce0.8O1.9 composite cathode, in which Sm0.5Sr0.5CoO3−δ is a perovskite type mixed ionic and electronic conductor (MIEC), was studied with respect to the oxygen partial pressure and temperature. Symmetric half cells with Sm0.2Ce0.8O1.9 electrolyte were prepared, and cathode behavior was measured by using electrochemical impedance spectroscopy at frequency range of 0.1Hz∼5MHz and temperature range of 400∼900°C. Oxygen partial pressure range for the measurement was from 0.0002 to 1atm. In present research, reaction model based on the empirical equivalent circuit was established. Three elementary reaction steps were considered to describe the oxygen reduction reaction at Sm0.5Sr0.5CoO3−δ/Sm0.2Ce0.8O1.9 composite cathode. Electrode resistances corresponding to the high and low frequency seem to represent the oxygen ion transfer at the interface of electrolyte and gas phase diffusion of oxygen, respectively, from electrochemical impedance analyses as functions of oxygen partial pressure and temperature. The medium frequency process is expected to correspond to the oxygen ion conduction in the bulk cathode from this study.
Design and Fabrication of Novel Electrode-Supported SOFC Having Honeycomb Structure
Authors: Yamaguchi Toshiaki , Suzuki Toshio , Fujishiro Yoshinobu , Awano Masanobu , Shimizu Sota
Published: June 2009

We have developed a novel and highly effective electrode-supported SOFC with honeycomb structure for intermediate temperature operation. Honeycomb supported SOFC is known as one of the most compact SOFCs due to the large electrode area per unit volume, which is attractive with regard to space saving and cost reduction. In this study, we summarized the design of channel shape, size and sequence using numerical simulation and the technologies to realize the designed honeycomb SOFC fabrication. The calculation results showed that the wall thickness and the channel size of the honeycomb had to be less than 0.22 mm and more than 0.3 mm, respectively, for the sufficient net channel surface and the acceptable pressure drop. And a cathode-honeycomb supported SOFC can be the more efficient form with the lower current collection resistance, as compared with the anode-supported type. The actually fabricated honeycomb SOFC exhibited a high volumetric power density above 1 W/cm3 at 650 °C under wet H2 fuel flow.
Effect of Cathode Gasket Thickness to Performance of Direct Methanol Fuel Cells
Authors: Choi Hoon , Hwang Yong-Sheen , Lee Dae-Young , Kim Seo Young , Cha Suk-Won
Published: June 2009

This study considers the performance effect about a variation of the gasket thickness at the cathode side of the DMFC’s (Direct Methanol Fuel Cell) stack. Stack performance is largely influenced by the compressed thickness of GDL (Gas Diffusion Layer). The compressed thickness of GDL is directly controlled by gasket thickness. When GDL is not compressed enough, the ohmic loss is increased. Additionally, the differential pressure is decreased, because the channel of the separator is not blocked by GDL. On the contrary, being compressed extremely, GDL or MEA (Membrane Electrode Assembly) is physically damaged. The differential pressure is increased as well. In this respect, the optimization of the gasket thickness is one of the important factors to maximize the stack performance. In this study, the unit cell stacks with respect to changing gasket thickness at the cathode side are made in order to verify the effect about the compressed thickness of GDL. It is shown how the optimal gasket thickness may be achieved at the cathode side.
Characterization of the DMFC Stack With a BOP System
Authors: Kuan Yean-Der , Chang Yu-Pei
Published: June 2009

A direct methanol fuel cell (DMFC) with a BOP system is introduced. The DMFC stack operating with this BOP system is characterized. The DMFC stack performance gradually degrades as flooding occurs. A series of experiments under different environmental conditions were carried out to determine the ways for minimizing flooding. The results show that the water flooding more easily occurs when the DMFC stack operating in a closed system than in an open system. In a closed system, the temperature is the most important control factor to maintain the DMFC stack sustainable operation. Lower temperature differences among the airflow entrance, the exterior side DMFC module, and the DMFC sidewall temperature could reduce the possibility of water flooding occurs inside the DMFC stack. In addition, a large temperature difference between airflow entrance and exit of the DMFC stack would also lead the water flooding inside the stack.
Analysis and Design of a PEM Fuel Cell Structure
Authors: Chung Tien-Tung , Lin Chin-Te , Shiu Huan-Ruei , Jheng Yi-Ting , Chen Chi-Chang , Yan Yi-Yie
Published: June 2009

This paper studies the analysis and design of a proton exchange membrane (PEM) fuel cell stack. The aim of this study is to recognize the structural behaviour of PEM fuel cell under the steady state operation by using finite element analysis (FEA). First, the solid model of the PEM fuel cell are generated by AutoCAD software with a parametric program, and then the model is imported into the ANSYS software to establish the FEA meshes. Next, a series of FEA are executed to analyze the thermal and structural behaviour of the fuel cell stack. Structural behaviour of a single-cell fuel cell stack is analyzed at the beginning. Structural and thermal boundary conditions are applied into the meshed model, including the heat generation of chemical reaction, the force convection of cooling water, and assembly pressure on the end plate. In addition, the analyses of 7-cell fuel cell stack are executed to derive the characteristics of the multiple-cell stack. Results of analyses show that temperature distribution in the fuel cell stack is non-uniform, and high structural and thermal stresses are found in the structure, which will result in the failure of the fuel cell stack, especially on the carbon plates.
Electrical and Thermal Time Constants Fuel Cell System Identification: A Linear Versus Neural Network Approach
Authors: Outeiro M. T. , Cardoso Alberto J. L. , Chibante R. , Carvalho A. S.
Published: June 2009

The energy generated by PEM fuel cells can be used in many different applications with emphasis to commercial power generation and automotive application. It requires the integration of various subsystems such as chemical, mechanical, fluid, thermal and electrical ones. Their electrical and thermal time constants are important variables to analyze and consider in the development of control strategies of electronic converters. For this purpose, a mathematical model of the PEM fuel cell system was developed in Matlab/Simulink based on a set of equations describing cell operation. The model considers static and dynamic operating conditions of the PEM. Using experimental measurements at different load conditions made in a Nexa™ PEM fuel cell system, analysis based on linear ARX (Autoregressive with Exogenous Input) and neural network methods were made in Matlab in order to identify the electrical and thermal time constant values. Both linear ARX and neural network approaches can successfully predict the values of the time constants variables. However, the identification by the linear ARX is appropriated around the most significant operation points of the PEM system while neural network allows at obtaining a nonlinear global model. The paper intends to be a contribution for the identification of the electrical and thermal time constants of PEM fuel cells through these two methodologies. The linear approach is simple but presents some limitations while the non-linear one is widespread but more complex to be implemented.
Examination of the Effect of System Pressure Ratio and Heat Recuperation on the Efficiency of a Coal Based Gas Turbine Fuel Cell Hybrid Power Generation System With CO2 Capture
Authors: VanOsdol John G. , Gemmen Randall , Liese Eric
Published: June 2009

This paper examines two coal-based hybrid configurations that employ separated anode and cathode streams for the capture and compression of CO2. One configuration uses a standard Brayton cycle, and the other adds heat recuperation ahead of the fuel cell. Results show that peak efficiencies near 55% are possible, regardless of cycle configuration, including the cost in terms of energy production of CO2 capture and compression. The power that is required to capture and compress the CO2 is shown to be approximately 15% of the total plant power.
Comparative Study of SOFC’s Fabricated With Conventional and Reaction-Sintered 8YSZ Powders
Authors: Storjohann Daniel , Menzer Sophie , Daggett James , Sullivan Neal , Beeaff Dustin
Published: June 2009

“Reaction-sintered” powder processing is a new method for low-cost production of yttria-stabilized zirconia (YSZ). Developed by CoorsTek, Inc., reaction-sintered 8YSZ powders may prove to be a low-cost alternative to conventional ceramic powders used in solid oxide fuel cells (SOFC’s). However, the performance of fuel cells fabricated using reaction-sintered 8YSZ powders needs to be quantitatively compared to the conventional 8YSZ powders. In this study, we present results of such a comparison by evaluating both planar anode supports and tubular SOFC’s fabricated using reaction-sintered and conventional 8YSZ powders. Comparisons between material sets were conducted to compare cell morphology and composition, in addition to a number of different SOFC-performance metrics, including gas transport, fuel-conversion and power density. Experimental results show that the performance of SOFCs fabricated using reaction-sintered 8YSZ is comparable to cells fabricated with conventional 8YSZ powders.
Optimal Design of Hybrid Electric Fuel Cell Vehicles Under Uncertainty and Enterprise Considerations
Authors: Han Jeongwoo , Papalambros Panos
Published: June 2009

System research on Hybrid Electric Fuel Cell Vehicles (HEFCV) explores the tradeoffs among safety, fuel economy, acceleration, and other vehicle attributes. In addition to engineering considerations, inclusion of business aspects is important in a preliminary vehicle design optimization study. For a new technology, such as fuel cells, it is also important to include uncertainties stemming from manufacturing variability to market response to fuel price fluctuations. This paper applies a decomposition-based multidisciplinary design optimization strategy to an HEFCV. Uncertainty propagated throughout the system is accounted for in a computationally efficient manner. The latter is achieved with a new coordination strategy based on sequential linearizations. The hierarchically partitioned HEFCV design model includes enterprise, powertrain, fuel cell, and battery subsystem models. In addition to engineering uncertainties, the model takes into account uncertain behavior by consumers, and the expected maximum profit is calculated using probabilistic consumer preferences while satisfying engineering feasibility constraints.
Part I of II: Development of MERESS Model—Developing System Models of Stationary Combined Heat and Power (CHP) Fuel Cell Systems (FCS) for Reduced Costs and Greenhouse Gas (GHG) Emissions
Authors: Colella Whitney G. , Schneider Stephen H. , Kammen Daniel M. , Jhunjhunwala Aditya , Teo Nigel
Published: June 2009

Stationary combined heat and power (CHP) fuel cell systems (FCSs) can provide electricity and heat for buildings, and can reduce greenhouse gas (GHG) emissions significantly if they are configured with an appropriate installation and operating strategy. The Maximizing Emission Reductions and Economic Savings Simulator (MERESS) is an optimization tool that was developed to allow users to evaluate avant-garde strategies for installing and operating CHP FCSs in buildings. These strategies include networking, load following, and the use of variable heat-to-power ratios, all of which commercial industry has typically overlooked. A primary goal of the MERESS model is to use relatively inexpensive simulation studies to identify more financially and environmentally effective ways to design and install FCSs. It incorporates the pivotal choices that FCS manufacturers, building owners, emission regulators, competing generators, and policy makers make, and empowers them to evaluate the effect of their choices directly. MERESS directly evaluates trade-offs among three key goals: GHG reductions, energy cost savings for building owners, and high sales revenue for FCS manufacturers. MERESS allows users to evaluate these design trade-offs and to identify the optimal control strategies and building load curves for installation based on either 1) maximum GHG emission reductions or 2) maximum cost savings to building owners. Part I of II articles discusses the motivation and key assumptions behind MERESS model development. Part II of II articles discusses run results from MERESS for a California town and makes recommendations for further FCS installments (Colella 2008 (a)).
Investigating the Use of Stamped Metal Foils as Bipolar Plates in PEM Fuel Cell Stacks
Authors: Backes Rachel T. , McMillan David T. , Herring Andrew M. , Berger John R. , Turner John A. , Wang Heli
Published: June 2009

The process of stamping stainless steel bipolar plates is developed from initial plate design through manufacturing and use in a fuel cell stack. A stamped design incorporating a serpentine flow field for the cathode and an interdigitated flow field for the anode is designed. This bipolar plate consists of only one piece of thin stainless steel sheet. The process of rubber-pad stamping was chosen to reduce shearing of the thin sheet. Dies were designed and made. Stainless steel plates were stamped, but stress were higher than anticipated and die failure was observed. The plates were tested both in-situ and by doing simulated fuel cell testing. Although sealing was an issue due to lack of proper gaskets and endplates, tests determined that the stamped bipolar plates will work in a PEM fuel cell stack. Dies were redesigned to improve durability. Gaskets and endplates were designed to complete the stack construction.
1-D Computational Model of a PEM Fuel Cell Using Reaction Rate Law Kinetics to Model the Consumption of Hydrogen at the Anode
Authors: Goudy Sean , Bade Shrestha S. O. , Sahin Iskender
Published: June 2009

Computational models of Polymer Electrolyte Membrane (PEM) fuel cell have historically simulated the anode side reaction assuming the system is mass transfer limited. Specifically, the models assume that the hydrogen gas mass transfer rate is much slower than the reaction rate. Although this assumption makes computational simulations easier, the model does not accurately describe the system. This model introduces a novel method of simulating the anode side reaction. Specifically, the model uses the reaction rate law kinetics of hydrogen gas adsorption onto the platinum electrode and the subsequent ionization of the hydrogen atom to model the anode side reaction dynamics. The benefit is that the model is capable of predicting the actual behavior of the system at the electrode and polymer membrane interface. Because of the computational complexity of this system, the model assumes that a fraction of the hydrogen gas in contact with the polymer membrane dissolves into the polymer membrane and diffuses to the cathode side. The fraction of hydrogen, which is dissolved into the polymer membrane, is proportional to the Damko¨hler number (Da). Specifically, the model assumes that if the reactant is not completely consumed when it comes into contact with the polymer membrane that some fraction of the hydrogen gas will dissolve into the polymer membrane and will be diffused to the cathode side. In addition, because of the slight negative charge of the polymer membrane, the model assumes that no oxygen diffuses into the polymer membrane.
Increased Cathodic Kinetics in IT-SOFCs by Inserting Highly-Conductive Nanocrystalline Materials
Authors: Huang Hong , Holme Tim , Prinz Fritz B.
Published: June 2009

One of the crucial factors for improving intermediate-temperature SOFC performance relies on reduction of the activation loss originating from limited electrode reaction kinetics. We investigated the properties and functions of nanocrystalline interlayer via quantum simulation (QS) and electrochemical impedance analyses. Electrode impedances were found to decrease several-fold as a result of introducing a nanocrystalline interlayer and this positive impact was the most significant when the interlayer was a highly ionic-conductive nanocrystalline material. Both exchange current density and maximum power density were highest in the ultra-thin SOFCs (fabricated with MEMS compatible technologies) consisting of a 50nm thick nano-GDC interlayer. Oxygen vacancy formation energies both at the surface and in the bulk of pure zirconia, ceria, yttria-stabilized zirconia (YSZ), and gadolinia doped ceria (GDC) were computed from density functional theory, which provided insight on surface oxygen vacancy densities.
Power Generation Properties of a Micro Tubular SOFC Bundle Under Pressurized Conditions
Authors: Hashimoto S. , Liu Y. , Asano K. , Mori M. , Funahashi Y. , Fujishiro Y.
Published: June 2009

A micro tubular solid oxide fuel cell (SOFC) bundle was developed based on new concept. The anode-supported micro tubular SOFCs with the cell configuration, La0.6Sr0.4Co0.2Fe0.8 O3−δ (LSCF) – Ce0.9Gd0.1O2−δ (CGO) cathode / CGO electrolyte / Ni – CGO anode were fabricated and were bundled by a porous LSCF current collecting cube 1 cm on a side. The power generation test of the fabricated SOFC bundle was carried out under pressurized conditions. Using wet 30%H2 / N2 mixture gas and air, the cubic power density of the bundle at 500°C was 0.47 Wcm−3 at 0.4Acm−2, atmospheric pressure (0.1MPa). With increasing operating pressure, the performance has been improved, and the cubic power density finally reached to 0.66 Wcm−3 at 0.6MPa. Pressurization effect for the power improvement was brought about by the open circuit voltage enhancement and reduction of the polarization resistance.
Exergy Analysis a 5kW Polymer Electrolyte Fuel Cell (PEFC) With Cogeneration
Authors: Ahmadi A. , Ehyaei M. A.
Published: June 2009

In this paper, design and exergy method optimization of a 5kW power output PEFC fuel cell with cogeneration application has been investigated. It is assumed that cooling water is passed through fuel cell cooling channel, warmed up and supplied for space heating application. The performance of the proposed system has been optimized by the second law based exergy analysis. Results show for the maximum system efficiency and minimum entropy generation, fuel cell temperature and voltage should be as high as possible in the range of application. Also, the fuel cell pressure and stoichiometric air fuel ratio should be as low as possible in the range of application. The results of this investigation are valid for full load of condition of 5 KW. So, the results are not applicable for any other power level.
A High-Performance No-Chamber Fuel Cell Operated on Flame
Authors: Wang Kang , Ahn Jeongmin , Shao Zongping
Published: June 2009

A no-chamber solid-oxide fuel cell that operated on a fuel-rich ethanol flame was reported. Heat produced from the combustion of ethanol thermally sustained the fuel cell at a temperature range of 500 ∼ 830 °C. Considerable amounts of hydrogen and carbon monoxide were also produced during the fuel-rich combustion directly providing the fuels for the fuel cell. The location of the fuel cell with respect to the flame was found to have a significant effect on the fuel cell temperature and performance. The highest power density was achieved when the anode was exposed to the inner flame. By modifying the Ni+Sm0.2Ce0.8O1.9 (SDC) anode with a thin Ru/SDC catalytic layer, the fuel cell envisaged not only an increase of the peak power density to ∼ 200 mW/cm2 but also in a significant improvement of the anodic coking resistance.
Liquid Water Effects on the Performance of a PEMFC With Serpentine-Parallel Channels
Authors: Zhou Biao , Le Anh Dinh
Published: June 2009

Water management is one of the most important issues for the performance of Proton Exchange Membrane Fuel Cell (PEMFC). Understanding of water liquid behaviors in the gas-liquid flow of PEMFC is necessary for the optimization of PEMFC. In this study, a three-dimensional and unsteady PEMFC model with serpentine-parallel channels has been incorporated to investigate not only the fluid flow, heat transfer, species transport, electrochemical reaction, and current density distribution but also the behaviors of water liquid in the gas–liquid flow of the channels and porous media. The results show that tracking the interface of water liquid in a reacting gas-liquid flow in PEMFC can be fulfilled by using Volume-of-Fluid (VOF) algorithm combined with solving the conservation equations of continuity, momentum, energy, species transport and electrochemistry. Consequently, the behaviors of liquid water were fully understood by presenting the motion and deformation of water droplets inside the channels and the penetration of liquid through the porous media at different time instants. Additionally, the presence of liquid water in the channels significantly influences the flow fields. Due to the blockage of water liquid, the gas flow became unevenly distributed, the high pressure regions took place around the locations where water liquid appears, and the reactant transport in the channels and porous media was hindered by water liquid occupation.
Modeling Water-Droplet Detachment From GDL/Channel Interface in PEM Fuel Cells
Authors: Chen Ken S.
Published: June 2009

The onset of water-droplet detachment from the cathode GDL (gas diffusion layer)/channel interface in PEM (proton exchange membrane or polymer electrolyte membrane) fuel cells was studied numerically and analytically in the inertia-dominating flow regime. This is the flow regime of interest in real-world PEM fuel-cell applications. Our three-dimensional (3-D) numerical model employs the VOF (volume of fluid) method to track the dynamic liquid/gas interface as water droplet is being deformed and eventually detached by flowing-air drag. Our simplified, analytical model is based on the force balance between pressure drag tending to detach the droplet and surface tension tending to hold the droplet in place. Using our numerical model and for a given initial droplet size, we compute the 3-D droplet shape as a function of air-flow velocity — this enables us to determine the critical velocity above which the droplet is detached. Analytically, we develop an explicit expression that relates the critical air-flow velocity to droplet diameter, channel height, and static contact angle. We compare computed critical velocities at various droplet diameters with experimental data available from the literature and reasonably good agreements are obtained.
Geometry Optimization for Self-Breathing PEMFC With Sequential Quadratic Programming Method
Authors: Xing Xiu Qing , Lum Kah Wai , Wu Yan Ling , Poh Hee Joo
Published: June 2009

The strong links between COMSOL and MATLAB offers a useful option for the self-automated geometrical optimization process in PEMFC, which overcomes the difficulties on geometry optimization in Computational Fuel Cell Dynamics based design. Geometry optimization of self-breathing PEMFC, including the channel-rib ratio at anode and the open ratio at the cathode side are investigated in order to improve the fuel cell performance. A sequential quadratic programming method is selected to deal with the constrained design problem, while the objective function is calculated by running the 3D simulation script of COMSOL in the MATLAB environment. Simulation results show that for the self-breathing PEMFC operating at 353K and 1 atm with a voltage of 0.7V, when the channel-rib ratio at anode side is fixed at 10%, the optimal open ratio of the self-breathing cathode is found to be 49.8%. While, when the open ratio at the cathode is set at 80%, the optimal channel-rib ratio is located at 34.7%. However, the differences in the current density are not significant when the channel-rib ratio at the anode is varied while maintaining the open ratio at 80% for the cathode side.
A Novel Reactant Delivery System for PEM Fuel Cells
Authors: Greska Brenton , DeRoche Peter , Krothapalli Anjaneyulu
Published: June 2009

This paper deals with the use of microjets as a reactant delivery method for a PEM fuel cell. The flow physics of this technique have been adapted such that an even distribution of reactants over the membrane is achieved. A single cell based on this microjet delivery method has been built and tested using the fuel cell test station at SESEC. Polarization curves were obtained for a number of different operating conditions in which the relative humidity and supply pressure of the air supply were varied. Similar operating conditions were used to obtain polarization curves for a similarly sized commercially available fuel cell that utilizes commonly used serpentine flow channels for reactant delivery. Comparison of the polarization curves at similar operating conditions revealed that the microjet-based fuel cell was relatively unaffected by the changes in relative humidity and and positively affected by an increase in supply pressure, which was in stark contrast to what was observed for the commercial fuel cell.
Sensitivity Analysis of a SOFC-GT Based Power Cycle
Authors: Zabihian Farshid , Fung Alan S. , Koksal Murat , Malek Shakil , Elhebshi Moftah
Published: June 2009

This paper presents the sensitivity analysis of tubular Solid Oxide Fuel Cell (SOFC) stacks. The macro level modelling implemented in AspenPlus™ for the simulation of hybrid SOFC-gas turbine systems. The macro level thermodynamic first law analysis was previously performed on the same model. This sensitivity analysis is the continuation towards investigating the effects of different fuel compositions and turbine and compressor efficiencies on cycle efficiency and other parameters. The model is 0-dimensional, can accept hydrocarbon fuels with user inputs of current density, fuel and air composition, flow rates, temperature, pressure and fuel utilization factor. The model outputs the composition of the exhaust, work produced, heat available for reformer, etc. The model was developed considering the activation, concentration and ohmic losses within SOFC and mathematical expressions for these were chosen based on available studies in recent literatures. In this paper different fuels such as reformed natural gas, biogas with different compositions are considered to investigate the effect of fuel composition on the performance of the hybrid SOFC-gas turbine systems. In order to monitor the performance of the system parameters such as thermal efficiency, cycle specific work, SOFC specific work, gas turbine specific work, and work ratio (SOFC work / gas turbine work) are investigated. Furthermore, for specific fuel the effect of turbine and compressor efficiencies on system’s overall performance are studied for entire range from 50% to 100%, keeping gas turbine efficiency constant and increasing compressor efficiency by 5% and vice versa. For instance, if the fuel is switched from natural gas (with 100% CH4) to biogas (with the composition of 70% CH4, 25% CO2 and 5% H2) and the other parameters are kept constant (isentropic efficiency 85% for both turbine and compressor) the overall thermal efficiency will decrease by 1.4%, whereas the cycle specific work will increase by 36.7%. In addition, the work ratio will increase by 25.1% showing that more power is generated in SOFC in comparison to gas turbine. In addition, if the efficiency of turbine and compressor increase from 85% to 90%, the efficiency and cycle specific work of the system will increase by 3.1% and 3%, respectively whereas, the work ratio will decrease by 5.6%, due to the more power generated in gas turbine.
An Investigation of Doped Perovskites Based on La, Pr, and Sm Ferrites as Cathode Materials for Solid Oxide Fuel Cells
Authors: Lassman Alexander , Smirnova Alevtina , Sammes Nigel
Published: June 2009

Perovskites with the composition ABO3 have been studied as cathode candidate materials for solid oxide fuel cells. Both the A and B sites can be doped. This paper investigates ABO3 perovskites in which the A site ion is lanthanum (La), praseodymium (Pr), or samarium (Sm), doped with strontium (Sr). The B site ion is iron (Fe) doped with cobalt (Co) or nickel (Ni). Powders were prepared by the glycine-nitrate process, and were calcined at temperatures between 700°C and 900°C. XRD analysis was performed to determine the effect of calcination temperature on structure. Cathode pellets were made and sintered at 1200°C for 4 hours. The electrical conductivity of these pellets was measured, in ambient air, at temperatures ranging from 200°C to 800°C. The measured conductivity was generally higher for the ferrite-nickelates than the ferrite-cobaltites. Additionally, the samples with lanthanum as the A site cation demonstrated higher electrical conductivity than those with samarium or praseodymium.
Effect of Bridging Groups on Sulfonated Poly(Imide-Siloxane) for Application in Proton Exchange Membrane of Fuel Cells
Authors: Lee Chi-Hung , Chen Jia-Ru , Shiu Hung-Wei , Ho Ko-Shan , Wu Shinn-Dar , Hsieh Kuo-Huang , Wang Yen-Zen
Published: June 2009

A series of six-membered sulfonated poly(imide-siloxane)s were synthesized using 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), aminopropyl-terminated polydimethylsiloxane (PDMS) 2,2-benzidinedisulfonic acid (BDSA), as the sulfonation target diamine groups, and various non-sulfonated diamine monomers behaving as bridging groups. The structure-property relationship of SPI-SXx membranes is discussed in details according to the chemical structure of the nvarious non-sulfonated diamines of SPI-SXx membranes from the viewpoints of proton conductivity, ion exchange capacity (IEC) and membranes properties (water uptake, membrane swelling) at equal PDMS content SPI-SXx. They showed good solubility and high thermal stability up to 300 °C. The PDMS was introduced to enhance the proton conductivity and water uptake attributed from the highly flexibility of the siloxane segments. They showed a comparable or even higher proton conductivity than that of Nafion 117 in water at 60 °C. The conductivity and water uptake of angled, SPI-SXm and ODA-based SPI-SX membranes (SPI-SXO) are greater than those prepared from DDM-based SPI-SX membranes (SPI-SXD) at a given IEC. These differences resulted from the increased numbers of entanglements of the flexibility membrane. The SPI-SXD showed alomost isotropically dimensional changes with the increases of water uptake and the volume were slightly smaller than those estimated from the additivity rule. Microscopic analyses revealed that these smaller (<10 nm) and well-dispersed hydrophilic domains contribute to the better proton conducting properties. The new sulfonated poly(imide-siloxane)s have proved to be a possible candidate as the polymer electrolyte membrane for PEFCs and DMFCs.
A EMM Fabrication Method of Metallic Bipolar Plates for PEM Fuel Cell
Authors: Lee Yu-Ming , Lee Shuo-Jen , Shih Cheng-Hong
Published: June 2009

A prototype of metallic PEM fuel cell with thin stainless steel bipolar plates is tested for their potential applications in portable electronic products. The bipolar plate is produced by UV-LIGA and electrochemical micro-machining (EMM) technologies. The cathode electrode, the tool, is the mirror image of flow channels. It is produced by the UV-LIGA technology and the dimension is 200μm in width and 500μm in height for the intension to fabricate a serpentine flow channel of 500μm width and 200μm depth. The flow channels on 0.6mm thick SS 316L plates are fabricated by EMM process within 30 seconds with effective area of 625mm2. From the results of cell performance tests, the peak power densities are 0.67 W/cm2 at 0.45 V. During the 5 hours of cell life test, the cell was operated with a constant load of 0.4 V. The peak power density is stable. It just dropped slightly from 0.7 W/cm2 to 0.65 W/cm2. The results demonstrate the UV-LIGA and EMM technologies is an efficient method to fabricate flow channel for stainless steel bipolar plates.
Effect of Bolts Locking Sequence on Flow-Channel Plate in Micro-PEMFC
Authors: Chien Chi-Hui , Li Shih-Chun , Hsu Wei-Tsung , Lin Chih-Wei
Published: June 2009

The design and method of cell assembly play important roles in assessing the performance of PEM fuel cell. The cell assembly will affect the contact behavior between the bipolar plates, flow-channel plates, gas diffusion layers (GDLs) and membrane electrode assembly (MEA). From the past studies, it is noted that the flow-channel plates in the cell will be deformed while the cell was assembled by locking with bolts. This phenomenon may lead to leakage of fuels, high contact resistance and malfunctioning of the cells. The main aim of this research is to study the variation of the deformation mode of the flow-channel plat in a micro-PEM fuel cell assembly subjected to different bolts locking sequences. The commercial FEM package, ANSYS, was adopted to model the three-dimensional single micro-PEMFC FEM model and the numerical simulation analyses were performed. The effect of the bolts locking sequence on the deformations of flow-channel plate in the micro-PEMFC was presented.
Numerical Simulation of an Innovative PEM Fuel Cell Stack
Authors: Bhamidipati Kanthi L. , Amani Hoda , Strauss Sylvia , Harris Tequila A. L.
Published: June 2009

This paper describes a novel design approach for a fuel cell stack to address the uniformity of reactant streams and eliminate the bipolar plate to reduce cost, size, volume, and weight. Computational analysis for a novel PEM fuel cell stack and two conventional stacks is conducted. Preliminary results based on a comparison study have shown that eliminating bipolar plates from the fuel cell drastically increases power density, while maintaining uniformity in reactant distribution. Specifically, preliminary case studies suggest that the power density using the novel design is four times that of conventional approaches.
Comparison of Feeding Gas Strategies (Co- and Counter-Flow) in a PEM Fuel Cell Through a Pseudo 2D Diphasic Water Model
Authors: Chupin Sylvain , Ramousse Julien , Agbossou Kodjo , Dube´ Yves , Didierjean Sophie , Maranzanna Gael
Published: June 2009

The purpose of this study is to establish a simple model representing diphasic water flows in a single cell PEM fuel cell in order to improve fuel cell control. The pseudo-2D model describes the water transfers from one electrode to the other, all along the feeding gas channels. Both vapor and liquid water are considered. The location of first appearance of liquid water can be noticed. The influence of the feeding gas strategies (co- and counter-flow) on the water distribution in the cell are investigated. As a consequence, with the counter-flow feeding gas strategy, water is better distributed in the whole cell, but flooding of the electrode may occur. With a co-flow feeding gas strategy flooding risks are lower, but water distribution in the cell is less homogeneous and could result in a early deterioration of the membrane by drying.
Ethanol Logistics for Fuel Cells Applications in Brazil
Authors: Franco Egberto Gomes , Dantas Filho Paulo Lucas , Taioli Flavio , Ribeiro Carlos Eduardo Rollo , Burani Geraldo Francisco
Published: June 2009

One important element to reduce the impact of the present economic development model in nature is the energy generation. The need for more efficient sources of energy is evident, as the world relies on fossil fuel sources that become scarcer and expensive. Furthermore, imposes the use of clean fuels, like hydrogen and renewable primary fuels in large scale. The fuel cells technology have shown to be an interesting and very promising alternative, among others, to solve the problem of generating clean energy with high efficiency, using hydrogen, natural gas and ethanol. Hydrogen production from ethanol is an attractive technique, due to it renewable source, allowing clean energy generation. To permit that, the logistics of ethanol plays an essential role, allowing easy and full access to this fuel also in remote areas. In this article, we identify the necessary infra-structure to lead Brazil as a global player in the Hydrogen Economy. The costs of natural gas and ethanol as “carriers” were identified, pointing out weaknesses and strongest points of these primary fuels. The combination of these two technologies could drive Brazil to a clean and renewable energy source, mainly in remote areas.