bluuebunny/crossref_metadata_2025 huggingface dataset:
Degradation of Gasket Materials in a Simulated Fuel Cell Environment
Authors: Tan Jinzhu , Chao Y. J. , Lee Woo-Kum , Smith C. S. , Van Zee J. W. , Williams C. T.
Published: September 2008

A Polymer Electrolyte Membrane (PEM) fuel cell stack requires elastomeric gaskets in each cell to keep the reactant gases within their respective regions. If any gasket degrades or fails, the reactant gases (O2 and H2) can leak overboard or mix with each other directly during operation or during standby, and affect the overall operation and performance of the fuel cell. The degradation of four commercial gasket materials was investigated in a simulated fuel cell environment in this study. In an effort towards predicting lifetime of fuel cells, two solutions and two temperatures were used in the short-term, accelerated aging tests. Bend-strip environment crack resistance tests were performed on samples with various bend angles. Weight loss was monitored and surface structure changes were examined using optical microscopy on the samples exposed to the simulated fuel cell environment for selected periods of time. Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) spectroscopy was employed to study surface chemistry of the gasket materials before and after exposure to the simulated fuel cell environment over time. Stress and strain analysis was conducted using finite element method (FEM) to quantify the stress/state in test samples. The test results reveal that two silicone materials were degraded significantly while the other two did not show much degradation up to 42 weeks exposure to the simulated fuel cell environment. Optical microscopy and ATR-FTIR spectroscopy analysis indicate that the surface chemistry altered gradually via mechanisms involving de-cross linking and chain scission in the backbone. From experimental and numerical results, it is concluded that there is an interaction between chemistry and stress that appears to accelerate the degradation of the gasket materials in fuel cell environment.
An Impedance Spectroscopy Study of a Micro PEMFC With Different Flow Fields
Authors: Yang Sheng-Huang , Hsieh Shou-Shing , Feng Chih-Lun
Published: September 2008

The H2/air micro PEMFCs with three different flow fields were designed and fabricated in-house through a deep UV lithography technique. SU-8 photoresist was used as microstructure material for fuel cell flow-field plates. Different operational parameters were examined by electrochemical impedance spectroscopy (EIS). The operational parameters include cell operating temperature (25°C, 35°C, and 50°C), back pressures (1atm, 1.5atm, and 2atm) of reactant gases on anode site, and three different flow fields configurations (mesh, interdigitated, and serpentine). The effect of the above parameters on high frequency, medium frequency, and low frequency arc were found. The influence in terms of impedance on dynamic response of the present H2/air micro fuel cell under different operating conditions and flow geometry can be quantitatively measured. Results are presented in the form of the polarization VI curves, PI curves, and impedance spectra under different operating conditions. The possible transport mechanisms associated with the parametric effects were discussed. In addition, it was found that, among the three flow patterns considered, significant improvements can be reached with a specified flow geometry.
Two-Dimensional Dynamic Simulation of Hydrogen Storage in Metal Hydride Tanks
Authors: Brown Tim M. , Brouwer Jacob , Samuelsen G. Scott , Holcomb Franklin H. , King Joel
Published: September 2008

As proton exchange membrane fuel cell technology advances, the need for hydrogen storage intensifies. Metal hydride alloys offer one potential solution. However, for metal hydride tanks to become a viable hydrogen storage option, the dynamic performance of different tank geometries and configurations must be evaluated. In an effort to relate tank performance to geometry and operating conditions, a dynamic, two-dimensional, multi-nodal metal hydride tank model has been created in Matlab-Simulink®. Following the original work of Mayer, Groll, and Supper and the more recent paper from Aldas, Mat, and Kaplan, this model employs first principle heat transfer and fluid flow mechanisms together with empirically derived reaction kinetics. Energy and mass balances are solved in cylindrical polar coordinates for a cylindrically shaped tank. The model tank temperature, heat release, and storage volume have been correlated to an actual metal hydride tank for static and transient adsorption and desorption processes. The dynamic model is found to accurately predict observed hardware performance characteristics portending a capability to well simulate the dynamic performance of more complex tank geometries and configurations. As an example, a cylindrical tank filled via an internal concentric axial tube is considered.
NiO/YSZ Composites for SOFC: Synthesis and Characterization
Authors: Martins R. F. , Brant M. C. , Domingues R. Z. , Matencio T.
Published: September 2008

Solid oxide fuel cell (SOFC) works at high temperature and is normally used in stationary devices which are of wide interest in the world market. The most currently SOFC developers utilize yttria-stabilized zirconia (YSZ) as electrolyte, strontium-doped lanthanum manganite (LSM) as cathode and a Ni/YSZ cermet obtained from NiO/YSZ in situ reduction as anode. The electrode performance is directly influenced by powder grain sizes, homogeneity, purity, and amount of Ni. Although physical mixture is a simpler procedure it hardly gives homogeneous materials as suitable to SOFC applications. Alternative chemical methods are sol-gel, impregnation and those derived from Pechini route. The present work compares thermal stability and hydrogen reducibility of NiO/YSZ composites prepared by impregnation (I), Pechini (P) and physical mixture (PM) procedures.
Inorganic Proton Exchange Membranes
Authors: Reissman Timothy , Fang Austin , Garcia Ephrahim , Kirby Brian J. , Viard Romain , Fauchet Philippe M.
Published: September 2008

Direct Methanol Fuel Cells (DMFCs) offer advantages from quick refills to the elimination of recharge times. They show the most potential in efficient chemical to electrical energy conversion, but currently one major source of inefficiency within the DMFC system is the electrolyte allowing fuel to cross over from the anode to cathode. Proprietary DuPont™ Nafion® 117 has been the standard polymer electrolyte thus far for all meso-scale direct methanol power conversion systems, and its shortcomings consist primarily of slow anodic reaction rates and fuel crossover resulting in lower voltage generation or mixed potential. Porous Silicon (P-Si) is traditionally used in photovoltaic and photoluminescence applications but rarely used as a mechanical filter or membrane. This research deals with investigations into using P-Si as a functioning electrolyte to transfer ions from the anode to cathode of a DMFC and the consequences of stacking multiple layers of anodes. Porous silicon was fabricated in a standard Teflon cylindrical cell by an anodization process which varied the current density to etch and electro-polish the silicon membrane. The result was a porous silicon membrane with approximately 1.5 μm pore sizes when optically characterized by a scanning electron microscope. The porous membranes were then coated in approximately 0.2 mg/cm2 Pt-Ru catalyst with a 10% Nafion® solution binding agent onto the anode. Voltage versus current data shows an open circuit voltage (OCV) of 0.25V was achieved with one layer when operating at 20°C. When adding a second porous silicon layer, the OCV was raised to approximately 0.32V under the same conditions. The experimental data suggested that the current collected also increased with an additional identical layer of anode prepared the same way. The single difference was that the air cathode side was surface treated with 0.1 mg of Pt black catalyst combined with a 10% Nafion® binding agent to aid in the recombination of hydrogen atoms to form the water byproduct. Porous silicon endurance runs with 2ml of 3% by volume methanol (0.7425M) fuel dissolved in water showed an operating voltage was generated for approximately 3 hours before the level dropped to approximately 65% of the 0.25V maximum voltage. Endurance runs with a second layer added extended the useful cell life to approximately 5 hours under the same conditions. In an effort to quantify these layering results, Fourier Transform Infrared Spectrometry was conducted on a number of samples to verify decreased methanol concentration present in the second layer.
Modelling and Testing a PEM Fuel Cell Fuelled by a Steam Reforming System
Authors: Minutillo Mariagiovanna , Jannelli Elio
Published: September 2008

In this paper the performance of a natural gas power system has been discussed. The power generation unit is composed by a fuel cell and a fuel processor integrated in a compact system. The hydrogen generator uses the steam reforming technology. A CO shift converter and a preferential oxidation reactor are used to minimize the CO concentration in the reformate gas. The hydrogen dilution in the reformate gas calls for a modification of the fuel cell feeding system. The dead-end mode is not practicable for the fuel cell operation, but it is necessary to open the anode flow channels. In order to increase the efficiency of the integrated system, the anode off gas mass flow is burned to supply heat for the reforming reaction. The fuel cell performance has been evaluated using the test bed of the University of Cassino. The experimental activity has been focused to evaluate the performance in different operating conditions. A semi-empirical model of the fuel cell has been employed to forecast the fuel cell behaviour with pure hydrogen and reformate gas feeding. The semi-empirical coefficients of the model have been fitted by using the experimental data. The target of the fuel cell modelling has been to develop a tool capable of predicting the performance in different operating conditions. The same tool can be used to identify the areas for design improvements.
Numerical Thermal and Mass Analyses of Autothermal Reformer
Authors: Lee Shinku , Bae Joongmyeon , Lim Sungkwang
Published: September 2008

This paper discusses numerical analysis of heat and mass transfer characteristics in autothermal fuel reformer. Assuming local thermal equilibrium between bulk gas and surface of catalyst, one medium approach for energy equation is incorporated. Also, mass transfer between concentrations of bulk gas and near the surface of catalyst is neglected due to relatively low gas mixture velocity. For surface chemical reaction Langmuir-Hinshelwood reaction is incorporated when methane (CH4) is reformed to hydrogen-rich gases by autothermal reforming (ATR) reaction. Complete combustion, steam reforming, water gas shift and direct methane steam reforming reactions are included in the chemical reaction model. Under two operating conditions (O/C and S/C), ATR reactions are estimated from the numerical calculations. Mass, momentum, and energy equations are simultaneously calculated with chemical reactions. From the predicted results, we can estimate optimum operating conditions for high hydrogen yield.
Structural and Electrochemical Properties of Pr1−xSrxCoO3−δ as a Cathode Material for Intermediate Temperature-Operating Solid Oxide Fuel Cell
Authors: Kim Jung Hyun , Bae Joongmyeon
Published: September 2008

Reducing operation temperature of Solid Oxide Fuel Cell (SOFC) may provide many advantages for material selections of sealing, interconnects and Balance-Of-Plant (BOP). This study focus on the advanced performance of another cathode material and the performance according to structure change about Pr1−xSrxCoO3−δ compositions (PSCs, x = 0, 0.3, 0.5 and 0.7). High temperature XRD measurement and electrochemical impedance methods were used to study the characteristics of the material as a cathode material for Intermediate Temperature-operating Solid Oxide Fuel Cell (IT-SOFC) application. Lattice parameters and crystal structures of PSCs as well as Area Specific Resistance (ASR) of PSCs on solid oxide electrolytes are discussed at various x values (x = 0, 0.3, 0.5 and 0.7) and temperatures. One of various compositions of PSC showed 0.17 Ωcm2 of ASR on 10% Gd-doped cerium oxide at 700°C.
Optimal Design of Hybrid Fuel Cell Vehicles
Authors: Han Jeongwoo , Kokkolaras Michael , Papalambros Panos
Published: September 2008

Fuel cells are being considered increasingly as a viable alternative energy source for automobiles because of their clean and efficient power generation. Numerous technological concepts have been developed and compared in terms of safety, robust operation, fuel economy, and vehicle performance. However, several issues still exist and must be addressed to improve the viability of this emerging technology. Despite the relatively large number of models and prototypes, a model-based vehicle design capability with sufficient fidelity and efficiency is not yet available in the literature. In this article we present an analysis and design optimization model for fuel cell vehicles that can be applied to both hybrid and non-hybrid vehicles by integrating a fuel cell vehicle simulator with a physics-based fuel cell model. The integration is achieved via quasi-steady fuel cell performance maps, and provides the ability to modify the characteristics of fuel cell systems with sufficient accuracy (less than 5% error) and efficiency (98% computational time reduction on average). Thus, a vehicle can be optimized subject to constraints that include various performance metrics and design specifications so that the overall efficiency of the hybrid fuel cell vehicle can be improved by 14% without violating any constraints. The obtained optimal fuel cell system is also compared to other, not vehicle-related, fuel cell systems optimized for maximum power density or maximum efficiency. A tradeoff between power density and efficiency can be observed depending on the size of compressors. Typically, a larger compressor results in higher fuel cell power density at the cost of fuel cell efficiency because it operates in a wider current region. When optimizing the fuel cell system for maximum power density, we observe that the optimal compressor operates efficiently. When optimizing the fuel cell system to be used as a power source in a vehicle, the optimal compressor is smaller and less efficient than the one of the fuel cell system optimized for maximum power density. In spite of this compressor inefficiency, the fuel cell system is 9% more efficient on average. In addition, vehicle performance can be improved significantly because the fuel cell system is designed both for maximum power density and efficiency. For a more comprehensive understanding of the overall design tradeoffs, several constraints dealing with cost, weight, and packaging issues must be considered.
Location and Magnitude of Heat Sources in Solid Oxide Fuel Cells
Authors: Fischer Katharina , Seume Joerg R.
Published: September 2008

The correct prediction of the temperature distribution is a prerequisite for the reliable determination of species and current distributions in any solid oxide fuel cell (SOFC) model. It is even more crucial if the model is intended for the analysis of thermo-mechanical stresses. This paper addresses the different mechanisms of heat generation and absorption in the fuel cell. Particular attention is paid to the heating associated with the oxidation of hydrogen, which is commonly assigned to the interface between electrolyte and anode in SOFC modeling. But for a detailed determination of the temperature profile in the fuel cell solid components the separate consideration of the cathodic and anodic half-reactions is required. A method for determining the specific entropy change of the half-reactions based on Seebeck-coefficient data is adopted from the literature and applied to the SOFC. In order to exemplarily demonstrate the contribution of the various heat sources to the overall heat generation as well as the influence of their location, a spatially discretized model of a tubular SOFC is used. Temperature profiles obtained with and without separate consideration of the electrode reactions are compared. The comparison shows that the spatially descretized reaction model is indeed necessary for the reliable assessment of temperature gradients in the ceramic SOFC components.
Methanol Reforming Over PT Catalysts for Polymer Electrolyte Membrane Fuel Cells
Authors: Lee Taehee , Bae Joongmyeon , Kim Ju-Yong
Published: September 2008

An experimental investigation on hydrogen generation from methanol using Pt catalysts is presented in this paper. Methanol has the advantages of high energy density, high reforming activity and low CO selectivity at low temperatures. At present Cu-based catalysts are widely used for methanol reforming. But they are pyrophoric and thermally unstable, which causes issues in operating a real system. Pt catalysts dispersed on cerium oxides were tested for methanol reforming to resolve the problems. Steam reforming over Pt/cerium oxides showed the low conversion ratio less than 90% and the high CO concentration of about 15% at 400 °C. Autothermal reforming by adding O2 rapidly promoted the conversion of methanol and reduced the concentration of CO at lower temperature. Increasing the amount of dispersed Pt, the range of 0.5–3.0 wt%, shifted the reforming trends towards lower temperature and decreased the concentration of CO. To achieve more production rate within a given catalyst bed, catalysts coated monolithic honeycomb is prepared. It showed very high conversion at space velocities of up to 60,000/h.
Performance of Direct Formic Acid Fuel Cell With Self-Assembled PEMs
Authors: Tang Haolin , Pan Mu , Mu Shichun , Wan Zhaohui , Yuan Runzhang
Published: September 2008

Direct liquid fuel cells have attracted intensive research because of the promised application in Portable Fuel Cell Systems. Liquid fuel crossover through the proton exchange membranes (PEMs, e.g. Nafion™ membrane) is one of the major obstacles that currently prevent the widespread commercial applications of direct liquid fuel cell. In this paper, PEMs constructed by self-assembling metal nanoparticles on Nafion™ membranes were prepared to probe the crossover behaviors. The results show that the fuel crossover has a remarkable decrease comparing with the original PEMs. This satisfactory performance gives the self-assembled PEMs a promised prospect in direct liquid fuel cells.
A Feasibility Study on the Application of Fuel Cells in Oil and Gas Surface Production Facilities
Authors: Schols Victor , Klaver Theo , Pettitt Mark , Ubuan Chris , Miedema Sape , Hemmes Kas , Vlasblom W. J.
Published: September 2008

This paper presents the results of a study to evaluate the feasibility of deploying fuel cells in hydrocarbon producing facilities. For the majority of hydrocarbon production facilities, electric power is generated on-site, most often, by the combustion of some of the produced hydrocarbons. To optimize its performance, Shell is continuously looking at applying new technologies, which can increase the availability of her production facilities and/or reduced lifecycle costs and/or improve safety and environmental performance. Shell has identified fuel cell technology as being capable of delivering some of these benefits because of its potential to achieve high availability, reliability and fuel efficiency when compared to conventional technologies. An inventory has been made of the specific design specifications and the state-of-the-art of commercially available fuel cell systems. Most of the required capacities fall in the range of 1kW to 1 MW, which is compatible with state of the art fuel cell developments or it can be achieved in the near future. A software-screening tool has been constructed to evaluate the various options with respect to conventional technologies. The specific design specifications can vary from production site to site, but in general availability and low maintenance are two of the main criteria to be considered and most favorable for fuel cells. Depending on the specific requirements for a particular hydrocarbon production facility a polymer fuel cell, MCFC or SOFC system are considered suitable alternatives to conventional technology. The screening tool has been applied and evaluated in a case study of one of the unmanned production facilities of Shell. A 20 kW SOFC system was found to score higher than a commercially available gas engine of 25 kW on eight of the most important of several criteria. However, SOFC system lifecycle costs are still 15 to 20% higher due to the development costs needed for this ‘prototype’ SOFC system to make it suitable for use in hydrocarbon producing facility. When applied in more surface production facilities the SOFC system also becomes costs competitive with conventional technologies.
Single Cell Performance of Catalyst Coated Membrane Based on Superthin Proton Exchange Membrane
Authors: Mu Shichun , Cheng Niancai , Zhao Pei , Cheng Lei , Pan Mu , Yuan Runzhang
Published: September 2008

The superthin PEM (≤ 30 μm in thickness) can be used in CCMs (Catalyst coated membranes) and helpful to lower the cost of fuel cells. In this paper, the CCM based on Nafion NRE® 211 membrane (thickness ∼25 μm) was prepared and assembled into a single fuel cell. The activation time, the V-I curves and the voltage vs time plot were used to characterize the performance of CCMs under variuos hydrogen/air humidifying conditions at ambient pressure. The experimental results showed that the fuel cell with CCMs based on NRE® 211 membrane had a shorter activation time and higher performance under humidifying conditions compared to that based on nafion NRE® 212 membrane (thickness ∼50 μm). However, it’s important to remove water from anode in order to maintain a stable performance of fuel cell. Moreover, the performance of the single fuel cell using superthin membranes could be improved at a high current density under non-humidifying conditions.
The Performance of Large-Scale PEM Fuel Cell With Interdigitated Flow Channels
Authors: Shiu H. R. , Chang C. T. , Yan Y. Y. , Chen Falin
Published: September 2008

A large-scale polymer electrolyte membrane fuel cell (PEMFC) with novel interdigitated (or discontinuous) flow channel has been investigated experimentally. Interdigitated channel geometry has the advantages of effective water removal and higher reaction efficiency through forcing gas transport in the diffusion layer. In this study, multiple-Z type flow pattern has been adopted on the interdigitated channels. The active area of flow channel plate is 256 cm2 (16 cm × 16 cm). The channel width and depth are 1 mm and 0.8 mm respectively. The rib width is 1 mm. The performance of single PEM fuel cell with an interdigitated flow field is studied with appropriated operating conditions. The results demonstrated that the multiple-Z interdigitated flow channel has better performance compared with the conventional Z type by presented in the form of Current-Voltage (I-V) polarization curves. The pressure drop loss of multiple-Z interdigitated flow field increases about one time with the conventional one. The experimental results under the effects of gas humidification temperature and reactant gas flow rate, etc. have been comprehensively discussed in this work.
Direct Water Removal in Gas Diffusion Layer of Proton Exchange Membrane Fuel Cells by a Flexible Electroosmotic Pump
Authors: Cha S. W. , Fabian T. , Posner J. , Buie C. , Kim D. J. , Prinz F. B. , Eaton J. K. , Santiago J.
Published: September 2008

An electroosmotic pump is a non-mechanical pump that can remove water by applied electric field. A flexible electroosmotic (EO) pump was directly attached to a gas diffusion layer (GDL) on the cathode side of a miniature proton exchange membrane fuel cell (PEMFC). The operation of EO pump improved the voltage-current response of a PEMFC. Especially, the increase of limiting current was observed. We assume the reduced flooding in GDL was achieved by the operation of EO pump. Further investigation with AC impedance spectroscopy support the assumption as the reduced mass transport resistance was observed.
Numerical Modeling of SOFC Based on Mixed Conductive Electrolyte
Authors: Iwai Hiroshi , Ishikawa Tatsuo , Yoshida Hideo
Published: September 2008

As one of the possible electrolyte materials for intermediate temperature SOFCs that works around 500 to 800°C, we focus on Gadolinia Doped Ceria (GDC). This ceramic material shows reasonable ion conductivity even at 600°C. It, however, is a mixed conductive material having non-negligible electronic conductivity. In this study, the fundamental performance of a simple planar SOFC with GDC electrolyte is numerically investigated. The effects of electrical leakage on the cell performance are the main focus of discussion. The electrolyte thickness is varied in a range from 50 to 200μm. Both air and fuel flows are assumed to be steady and laminar. Governing equations are the continuity, momentum, energy and mass transfer equations. They are solved numerically by the control volume method. It is found that the leakage of electricity becomes larger for the smaller electrolyte thickness cases, and is more prominent for an electrolyte thickness of less than 80μm. Under such conditions, output power and energy conversion efficiency decrease dramatically. On the other hand, energy conversion efficiency also decreases for an electrolyte thickness that is too large because of the increase of ohmic overpotential of the electrolyte. Consequently, there seems to be an adequate thickness for the electrolyte that gives preferable output power and energy conversion efficiency.
Two-Phase Modeling of a PEMFC With CO Poisoning Effect Using Dilute Hydrogen Feed
Authors: Wang Chien-Ping , Chu Hsin-Sen
Published: September 2008

A one-dimensional, two-phase mathematical model was developed to analyze the poisoning effect of anode CO kinetics on the performance of a PEM fuel cell. Both vapor and liquid water transport are examined inside the cell. The theoretical results indicate that a higher CO concentration results in large CO coverage across the anode catalyst layer. The slowing of the chemical reactions at both the anode and the cathode reduce the liquid water saturation level in the catalytic layers. At high CO concentration and dilute hydrogen feed, the effect of the electro-osmotic drag is small and less liquid water is generated at the cathode catalyst layer, causing the liquid water distribution to have a small slope across the membrane. The distribution of liquid water depends more strongly on the CO concentration than on dilution of hydrogen in the MEA of the fuel cell. A large dropping rate of the current density is observed in the range between 10–50 ppm CO. Increasing the amount of pure hydrogen drastically increases the current density for a wide range of CO contents, promoting the tolerance for CO of the fuel cell.
Modeling of CO Influence in PBI Electrolyte PEM Fuel Cells
Authors: Korsgaard Anders Risum , Nielsen Mads Pagh , Bang Mads , Kær So̸ren Knudsen
Published: September 2008

In most PEM fuel cell MEA’s Nafion is used as electrolyte material due to its excellent proton conductivity at low temperatures. However, Nafion needs to be fully hydrated in order to conduct protons. This means that the cell temperature cannot surpass the boiling temperature of water and further this poses great challenges regarding water management in the cells. When operating fuel cell stacks on reformate gas, carbon monoxide (CO) content in the gas is unavoidable. The highest tolerable amount of CO is between 50–100 ppm with CO-tolerant catalysts. To achieve such low CO-concentration, extensive gas purification is necessary; typically shift reactors and preferential oxidation. The surface adsorption and desorption is strongly dependent upon the cell temperature. Higher temperature operation favors the CO-desorption and increases cell performance due to faster kinetics. High temperature polymer electrolyte fuel cells with PBI polymer electrolytes rather than Nafion can be operated at temperatures between 120–200°C. At such conditions, several percent CO in the gas is tolerable depending on the cell temperature. System complexity in the case of reformate operation is greatly reduced increasing the overall system performance since shift reactors and preferential oxidation can be left out. PBI-based MEA’s have proven long durability. The manufacturer PEMEAS have verified lifetimes above 25,000 hours. They are thus serious contenders to Nafion based fuel cell MEA’s. This paper provides a novel experimentally verified model of the CO sorption processes in PEM fuel cells with PBI membranes. The model uses a mechanistic approach to characterize the CO adsorption and desorption kinetics. A simplified model, describing cathode overpotential, was included to model the overall cell potential. Experimental tests were performed with CO-levels ranging from 0.1% to 10% and temperatures from 160–200°C. Both pure hydrogen as well as a reformate gas models were derived and the modeling results are in excellent agreement with the experiments.
Numerical Simulation of Two-Phase Flow and Transient Response in Polymer Electrolyte Fuel Cell
Authors: Masuda Hiromitsu , Ito Kohei , Kakimoto Yasuyuki , Miyazaki Tomohiko , Ashikaga Kensuke , Sasaki Kazunari
Published: September 2008

It is important to elucidate the transient characteristics of polymer electrolyte fuel cells (PEFC), especially when PEFC is applied to relatively small-scale power applications where it will be subjected to a wide range of loads, and may have frequent starts and stops. In addition, the water management problem, which is represented by flooding in cell and drying in proton exchange membrane (PEM), is another issue to address. The flooding is caused by liquid water accumulated in GDL and/or flow channel; the liquid water hinders mass transfer of gases to and from active layers; it can lead to rapid deterioration of cell performance. And the water management relates to the transient response of PEFC frequently. Based on these issues we wrote a numerical simulation program for unit-PEFC, which can simulate the successive events of vapor condensation, liquid saturation growth, corresponding to the dynamic change of cell voltage. We formulated mass, momentum and energy conservation equation with equivalent electric circuit; we discretized and numerically solved them. As for the gas/liquid two-phase flow formulation in GDL, we utilized multi-phase mixture (M2) model. As for the multi-component diffusion formulation, we utilized Stefan-Maxwell equation. Using the program, we simulated the transient response to rapid increase of load current. When the current density changed from 0.5 A/cm2 to 1.0 A/cm2 instantaneously, cell voltage (Vcell) changed in the following manner. Just after the change of current, Vcell decreased instantaneously corresponding to IR resistance and decreased again in 10−1s time-scale with the re-distribution of oxygen and with the charge of electric double layer capacitor. Then Vcell increased slightly in 101s time-scale with PEM wetting. Finally, Vcell decreased in 102 ∼ 103 s time-scale with the development of liquid saturation in GDL.
Comparison of a Multi-Dimensional Model With a Reduced Order Pseudo Three-Dimensional Model for Simulation of Solid Oxide Fuel Cells
Authors: Pakalapati Suryanarayana , Yavuz Ibrahim , Elizalde-Blancas Francisco , Celik Ismail , Shahnam Mehrdad
Published: September 2008

Numerical modeling has helped the SOFC research for over a decade in which period the models grew in complexity and detail. Multi-dimensional detailed models such as FLUENT’s SOFC module calculate three dimensional distributions of velocity, temperature, concentration and electric potential inside all components of the fuel cell. Such models while being very helpful in understanding the processes inside the fuel cell may prove to be very expensive for transient simulations and simulations of multi-cell stacks. Hence reduced order modeling is still used for such applications. However, reduced order modeling entails reduction of detail and consequent loss in accuracy. In this paper a multi-dimensional SOFC code, FLUENT’s SOFC module, is compared with a reduced order pseudo three-dimensional model, DREAM SOFC. FLUENT’s SOFC module is a commercial solver built on the popular CFD solver FLUENT. DREAM SOFC is an in house code developed at Computational Fluid Dynamics and Applied Multi Physics (CFD&) Center at West Virginia University. It is a combination of a one dimensional model for channels and three-dimensional models for the rest of the components in a SOFC. This approach avoids having to solve Navier-Stokes equations inside channels but still retains the three-dimensionality inside important components. Same test cases with similar conditions are simulated with these codes and results are compared with each other.
Steady-State Analysis and Energetic Comparison of Air Compressors for PEM Fuel Cell Systems
Authors: Arsie Ivan , Di Domenico Alfonso , Pappalardo Luca , Pianese Cesare , Sorrentino Marco
Published: September 2008

The aim of the work is to perform a comparative study of the compression system for a polymer electrolyte membrane (PEM) fuel cell. This study wishes also to address some key-features on the suitability of different compressors with respect to the main system design issues (e.g. energy balance, system performance and control). According to the technologies currently considered as being able to meet fuel cell system requirements, sliding vane, twin-screw and centrifugal compressors have been studied. The analysis has been performed making use of a modeling approach based on both thermodynamic description of the plant and synthesis of experimental efficiency data. Altogether, the results indicate that the centrifugal compressor should be preferred due to its higher efficiency as compared to the other compressors analyzed. Nevertheless, specific applications (e.g automotive field) may redirect the selection of the optimal compression device towards the other typologies, because of the highly fluctuating power demands and the issues associated with the narrow centrifugal compressor operation range.
An Hourly Building Simulation Model Aimed at Fuel Cell Applications
Authors: Henderson Hugh I. , Karambakkam Bharathkrishna , Boyer Jeffrey , Staudt Rhonda
Published: September 2008

The successful widespread adoption of fuel cell systems is highly dependent upon the economics of the installation. This entails closely matching system capabilities with customer requirements. System sizing requires accurate predictions of building thermal and electrical loads. The TRNSYS-based building simulation model presented in this paper was developed to accurately integrate a fuel cell into the space heating, water heating, and cooling equipment in a building. The simulation tool determines water heating, space heating, and cooling loads for a single zone building on an hour-by-hour basis throughout the year using TMY2 weather data. It integrates empirical and theoretical state point models of the components of a fuel cell-based cogeneration and tri-generation system as well as baseline HVAC technologies. The key components include: hot water loops, stratified water tanks, boilers, furnaces, air conditioners, absorption chillers, space conditioning coils, heat rejection equipment, and ventilation controls. Various control options are incorporated to maintain setpoints, stage equipment, and limit power export. Renewable power systems such as PV and wind are also integrated into the model. The TRNSYS calculation engine iterates to find the state of the system for each hour. The simulation tool also includes post-processing capabilities to apply complex electric tariffs, organize annual simulation results, and manage multiple parametric runs. The tool has been developed to optimize the configuration of a fuel cell in a given building application and to complete numerous parametric runs to evaluate the economics of a system in different locations and building applications. This work was funded in part by the New York State Energy Research and Development Authority.
In Situ Calorimetric Measurements in a Polymer Electrolyte Fuel Cell
Authors: Mo̸ller-Holst Steffen , Kjelstrup Signe , Vie Preben J. S.
Published: September 2008

We present calorimetric measurements on a single isothermal polymer electrolyte fuel cell, operated on dry hydrogen and oxygen at 50 °C. The measured heat production of the complete cell was decomposed into ohmic and non-ohmic heat effects. The results predicted the thermo-neutral potential of the cell within 7% error. The part of the heat production that originated mainly from the cathode overpotential, was analyzed in terms of standard overpotential theory, giving an exchange current density of the bulk cathode overpotential of 6×10−4 A/cm2 and a transfer factor of 0.27. (The cathode catalyst surface area was not determined.) This is the first time an overpotential of an electrode has been determined from its heat production.
Design and Optimization of the Gas Channels of a PEMFC Using CFD-Based Simulation
Authors: Sui P. C. , Kumar S. , Djilali N.
Published: September 2008

The flow field plate of a proton exchange membrane fuel cell (PEMFC) functions as electron conductor and provides the pathway for oxidant and fuel to reach the membrane electrode assembly (MEA). CFD-based simulation tools can be effective in designing and optimization of flow field plates as they cab fully account for the complexity and coupling of various transport phenomena as well as the 3-D geometry. The objective of this paper is to report on the development of such a simulation platform and on its application to investigate the impact of several geometric parameters on fuel cell performance and detailed distribution of transport processes. The simulation tool is built upon a commercial computational fluid dynamics (CFD) code, CFD-ACE+, along with supporting software and script codes to automate the design workflow. A 3-D, straight channel model with material properties and model parameters validated with experimental data is used as the baseline for the present study. The workflow includes automated grid generation, model setup and job execution. Parametric study is performed for geometric parameters including (1) Channel width versus land area width (2) Channel height (3) Channel pitch and length, as well as material parameters including (4) Porosity and (5) Electrical conductivity of the gas diffusion layer (GDL). Among these parameters, it is found that predicted cell performance is most sensitive to the channel/land width ratio and to the anisotropy of the GDL property. When isotropic properties are used for the GDL, the predicted cell performance decreases with increasing channel/land width ratio. This is because the current distribution in the MEA is dictated by electrical conduction through the GDL and increasing channel width causes current to peak underneath the land area, which in turn increases ohmic losses. When the in-plane electrical conductivity is reduced, the effect of mass transfer on the current distribution becomes comparable to electron transfer and the predicted trend line of cell performance shows an optimum value as a function of the channel/land width ratio. The CFD based design tool developed in the present work has the advantage of providing more reliable prediction than methods based on reduced dimensionality or simplified transport models.
Transient Analysis and Modelling of Automotive PEM Fuel Cell System Accounting for Water Transport Dynamics
Authors: Miotti Alessandro , Di Domenico Alfonso , Esposito Angelo , Guezennec Yann G.
Published: September 2008

Dynamic behavior and transient analysis are one of the most critical issues for high performance polymeric electrolyte membrane fuel cells. An improvement of performance can be achieved both with hardware modifications and with more sophisticated control strategies. To this regard, the availability of a reliable dynamic fuel cell model plays an important role in the design of fuel cell control and diagnostic system. This paper presents a non-linear, iso-thermal, zero-dimensional model of a pressurized PEM fuel cell system used for automotive applications. The model was derived from a detailed, iso-thermal, steady-state, dimensional model which explicitly calculated (and subsequently captured as a multi-D look-up table) the relationship between cathode and anode pressures and humidity and stack average current. Since in the electrochemical model the single cell performance depends on the membrane ionic resistance, which is strictly related to the membrane water content, a dynamic estimation of the membrane water diffusion has been considered. This takes into account the dependence of the cell voltage on the unsteady membrane water concentration. A similar approach still allows the development of a simple zero-dimensional dynamic model suitable for control system development and amenable to control-oriented humidity modelling.
A Study of Water and Oxygen Distributions in the Cathode Flow Channels of a PEM Fuel Cell
Authors: Kim Han-Sang , Ha Taehun , Min Kyoungdoug
Published: September 2008

Water management is a critical operation issue for achieving the highest possible performance of proton exchange membrane (PEM) fuel cells. Quantitative determination of water and species distribution is needed to understand the water management and reactant distribution effects. In this study, the measurement of water and oxygen distributions along cathode flow channels was carried out using gas chromatography (GC). Generally, it is difficult to measure water distribution where water concentration is too high. Here, the measurement of high levels of water saturation in cathode channels was performed according to fuel cell operating conditions. GC measurement was also carried out for flooding and non-flooding conditions. To compare the experimental results with computational results, the three-dimensional CFD simulation of a unit fuel cell was performed using es-pemfc, which is the PEM fuel cell module of commercial CFD code STAR-CD. For the entrance of flow channel that has relatively lower level of water content, the calculated results showed good agreement with measured results. However, some discrepancy between calculated and experimental results was still found for the flow channels near the cathode outlet. The study provides the necessity of the development and adoption of a comprehensive multidimensional PEM fuel cell models including two-phase flow and cathode flooding phenomena for the optimization of fuel cell performance.
Partial Validation of a Proposed Rating Methodology for Residential Fuel Cell Systems
Authors: Davis Mark W. , Ellis Michael W. , Dougherty Brian P. , Fanney A. Hunter
Published: September 2008

The National Institute of Standards and Technology (NIST), in conjunction with Virginia Tech, has developed a rating methodology for residential-scale stationary fuel cell systems. The methodology predicts the cumulative electrical production, thermal energy delivery, and fuel consumption on an annual basis. The annual performance is estimated by representing the entire year of climate and load data into representative winter, spring/fall, and summer days for six different U.S. climatic zones. It prescribes a minimal number of steady state and simulated use tests, which provide the necessary performance data for the calculation procedure that predicts the annual performance. The procedure accounts for the changes in performance resulting from changes in ambient temperature, electrical load, and, if the unit provides thermal as well as electrical power, thermal load. The rating methodology addresses four different types of fuel cell systems: grid-independent electrical load following, grid-connected constant power, grid-connected thermal load following, and grid-connected water heating. This paper will describe a partial validation of the rating methodology for a grid-connected thermal load following fuel cell system. The rating methodology was validated using measured data from tests that subjected the fuel cell system to domestic hot water and space heating thermal loads for each of the three representative days. The simplification of a full year’s load and climate data into three representative days was then validated by comparing the rating methodology predictions with the prediction of each hour over the full year in each of the six cities.
Studies on Electrocatalysts, MEAs and Compact Stacks of Direct Alcohol Fuel Cells
Authors: Sun Gongquan , Wang Guoxiong , Wang Suli , Yan Shiyou , Yang Shaohua , Xin Qin
Published: September 2008

A number of carbon supported bi/multi-metallic Pt-based electrocatalysts with a metal particle-size and shape controllable in nanoscale and a narrow size distribution were prepared by the improved polyol method. Among the electrocatalysts prepared in-house, PtSn/C showed a high direct ethanol fuel cell performance and PtPd/C exhibited a favorable methanol-tolerant property and oxygen-reduction activity. Several MEA fabrication methods such as direct-spray, decal and screen-printing were developed, through which the pore structure and hydrophilic/hydrophobic properties in the MEAs could be controlled desirably. With multi-layer structured electrodes, the maximum power density of 300 mW/cm2 and 240 mW/cm2 for the single cells were achieved at 90 °C under 0.2 MPa pressures of oxygen and air, respectively. Several demonstrations of active and passive compact DMFC systems ranging from sub-watts to 200 watt were fabricated. Some of them were demonstrated in PDA, toy cars, mobile phones and laptop computers.
Component Failure Analysis From the U.S. Army ERDC-CERL Residential Proton Exchange Membrane Fuel Cells Demonstration
Authors: Kenner Scott A. , Josefik Nicholas M. , Lux Scott M. , Knight James L. , White Melissa K. , Holcomb Franklin H. , Ropp Gregory J.
Published: September 2008

Background: The U.S. Army Engineer Research and Development Center, Construction Engineering Research Laboratory (ERDC-CERL) continues to manage The Department of Defense (DoD) Residential Proton Exchange Membrane (PEM) Fuel Cell Demonstration Project. This project was funded by the United States Congress for fiscal years 2001 through 2004. A fleet of 91 residential-scale PEM fuel cells, ranging in size from 1 to 5 kW, has been demonstrated at various U.S. DoD facilities around the world. Approach: The performance of the fuel cells has been monitored over a 12-month field demonstration period. A detailed analysis has been performed cataloging the component failures, investigating the mean time of the failures, and the mean time between failures. A discussion of the lifespan and failure modes of selected fuel cell components, based on component type, age, and usage will be provided. This analysis also addresses fuel cell stack life for both primary and back-up power systems. Several fuels were used throughout the demonstration, including natural gas, propane, and hydrogen. A distinction will be made on any variances in performance based on the input fuel stock. Summary: This analysis will provide an overview of the ERDC-CERL PEM demonstration fuel cell applications and the corresponding data from the field demonstrations. Special emphasis will be placed on the components, fuel cell stack life, and input fuel characteristics of the systems demonstrated.