bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling PEM Fuel Cell Performance Using the Finite-Element Method and a Fully-Coupled Implicit Solution Scheme via Newton’s Technique
Authors: Chen Ken S. , Hickner Michael A.
Published: September 2008

A numerical model that employs the finite-element method and a fully-coupled implicit solution scheme via Newton’s technique is presented for simulating the performance of polymer-electrolyte-membrane (PEM) fuel cells. With our model, solved are the multi-dimensional momentum, mass & species, and charge conservation equations that govern, respectively, pressure-gradient driven flows along the gas flow channels (GFCs) and within the gas diffusion layers (GDLs), species transport along GFCs and within GDLs, and proton and water transport within the membrane as well as the ButlerVolmer constitutive equations describing the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR). For simplicity, the present version of our model considers PEM fuel cell operation as isothermal and water present as vapor, and treats the anode and cathode catalyst layers as respective interfaces at which HOR and ORR take place. With our numerical approach, all governing equations are solved simultaneously and quadratic convergence is ensured due to the use of Newton’s method with an analytical Jacobian. To demonstrate the utility of our computational approach, computed predictions of velocity field, contours of hydrodynamic pressure and molar concentrations of hydrogen, oxygen and water species, and current distribution and polarization (or I-V) curves from a two-dimensional case study of a simplified PEM fuel cell are presented. To help assess the validity of our PEM fuel cell model, measurements of current distribution and polarization curves were performed using a segmented PEM fuel cell, and the resultant experimental data as well as that from the literature are compared with computed predictions.
Manufacturing and Evaluation of Fiber-Reinforced Composite Bipolar Plate for PEM Fuel Cell
Authors: Lee Hee-Sub , Ahn Sung-Hoon , Jeon Ui-Sik , Ahn Sang-Yeoul , Ahn Byung-Ki
Published: September 2008

The fuel cell is one of promising environment-friendly energy sources for the next generation. The bipolar plate is a major component of the PEM fuel cell stack, which takes a large portion of stack cost. In this study, as alternative materials for bipolar plate of PEM fuel cells, graphite composites were fabricated by compression molding. Graphite particles mixed with epoxy resin were used as the main substance to provide electric conductivity. To achieve desired electrical properties, specimens were made with different mixing ratio, processing pressure and temperature and tested. To increase mechanical strength, one or two layers of woven carbon fabric were added to the original graphite and resin composite. Thus, the composite material was consisted of three phases: graphite particles, epoxy resin, and carbon fabric. By increasing mixing ratio of graphite, fabricated pressure and process temperature, electric conductivity of the composite were improved. The results of tensile test showed that the tensile strength of the two-phase graphite composite was about 4 MPa, and that of three-phase composite was increased to 57 MPa. As surface properties, contact angle and surface roughness were tested. Contact angles were higher than 100°. The average surface roughness was 0.96 μm.
Fabrication of Microchanneled Reformer for Portable Fuel Cell
Authors: Yu S. P. , Yim S. D. , Um S. , Lee W. Y. , Kim C. S.
Published: September 2008

Miniature PEFC (Proton Exchange Fuel Cell) needs to be supplied with hydrogen of relatively highly purity to produce electricity. Each microstructured metal (stainless steel and aluminum) foil for the purpose of micro reformer was brazed in vacuum for stacking. Inner surfaces of micro channels were coated with Al2O3 layer to support reforming catalysts by solgel method/sputtering (for stainless steel) and anodizing (for aluminum). Stainless steel foil was good to etch and braze, but oxide layer coating on the surface of foil was too difficult to maintain uniformity to induce stable catalytic reaction. On the other hand, aluminum foil was good to control oxide film on the surface and bonded for stacking at low temperature which can avoid catalyst degradation.
Shutdown and Startup of a SOFC/GT Hybrid System
Authors: Stiller Christoph , Thorud Bjo̸rn , Bolland Olav
Published: September 2008

During shutdown and startup trips, the SOFC/GT hybrid system and its components must be protected from critical incidents such as anode oxygen exposure, excessive temperature gradients and carbon deposition. A further task is to minimise the need for auxiliary equipment and resources. The paper shortly presents a previously published detailed model of a pressurised SOFC hybrid cycle for the analysis of transients and control strategies. Shutdown and startup procedures are proposed based on the possibility to use the GT system for temperature control of the SOFC. Air flow and SOFC system inlet temperature are controlled by using a combustion device upstream the turbine, turbine exhaust gas throttling and a variable bypass around the recuperative heat exchanger. During startup, a small amount of hydrogen for the ignition phase of the SOFC is used. A considerable nitrogen demand for anode flushing has been detected, though it is uncertain how much is required to safely protect the anode from oxygen exposure. In the simulation, shutdown takes app. 2 hours and startup takes app. 5.5 hours. It is, however, uncertain how quick temperature variations the SOFC can withstand. A more flexible control strategy would allow the system to follow a low load immediately after startup initiation by utilizing the gas turbine.
Ammonia as a Contaminant in the Performance of an Integrated SOFC Reformer System
Authors: Yi Yaofan , Rao Ashok , Brouwer Jacob , Samuelsen Scott
Published: September 2008

As supply of natural gas (NG) is limited, more attention is being given to operating fuel cells on syngas derived from gasification of feedstocks such as coal and biomass. Ammonia (NH3) is one of the problematic contaminants contained in syngas produced from these nitrogen containing feedstocks. NH3 can be easily oxidized to nitric oxide (NO) in a combustion process and thus if present in the anode exhaust gas would be problematic. The potential effects of NH3 (particularly at low levels) on fuel cell system performance have not been well studied. The former studies on NH3 have been limited to either the reforming process alone or testing the fuel cell at the cell level with NH3 containing gases. No studies have been accomplished on a fuel cell system level basis. Objectives of this work are to obtain a comprehensive understanding of fuel cell system performance on syngas containing NH3 using an integrated SOFC reformer system. Detailed analysis is conducted within the three major reacting components — indirect internal reformer, SOFC stack and combustion zone. Various simulation tools (etc., CHEMKIN, ASPEN, APSAT) are utilized for analysis. Results show that NH3 conversion (into N2 and H2) in the internal reformer is about 50% when temperature is 750° C. NH3 conversion (into N2 and H2) in the SOFC stack can affect NOx emissions significantly. More than 50% NH3 left from SOFC stack can convert into NOx in the combustion zone. Experimental study is also planned to validate the theoretical results.
The Potential Use of Liquid Oxidizer in PEM Cells
Authors: Erickson Paul , Grupp David
Published: September 2008

A novel method of using a liquid phase oxidizer in fuel cell applications has been discovered by researchers at UC Davis. This paper outlines potential implications for improving heat transfer and catalytic activity with this method. Experimental data have been collected and the results show that the proposed method of using liquid phase oxidizer does indeed allow operation of PEM fuel cell systems. Data indicate an improvement in overvoltage at low current but also clearly indicate a severely limited concentration polarization region with non-regenerated fluid. The preliminary data indicate the physical feasibility of the method but also show that more research and development is required.
A New Type of High Temperature Membrane for Proton Exchange Membrane Fuel Cells
Authors: Shi Jinjun , Guo Jiusheng , Jang Bor
Published: September 2008

The proton exchange membrane (PEM) fuel cell operated at high temperature is advantageous than the current low temperature PEM fuel cell, in that high temperature operation promotes electro-catalytic reaction, reduces the carbon monoxide poisoning, and possibly eliminates methanol crossover in Direct Methanol Fuel Cell (DMFC). However, current commercially viable membranes for PEMFC and DMFC, such as the de-facto standard membrane of Dupont Nafion membrane, only work well at temperatures lower than 80°C. When it is operated at temperatures of higher than 80°C, especially more than 100°C, the fuel cell performance degrades dramatically due to the dehydration. Therefore, high temperature proton exchange membrane material is now becoming a research and development focus in fuel cell industry. In this paper, a new type of high temperature PEM membrane material was investigated. This new type of membrane material was optimally selected from polyether ether ketone (PEEK)-based materials, poly (phthalazinon ether sulfone ketone) (PPESK). The performance of the sulfonated PPESK membrane with degree of sulfonation (DS) of 93% was studied and compared to that of Nafion (®Dupont) 117 membrane. The result showed SPPESK has a comparable performance to Nafion (®Dupont) 117 at low temperature (<80°C) and better performance at high temperature (>80°C). The other advantage of SPPESK is that it has much lower cost than that of Nafion. These characteristics make SPPESK an attractive candidate for high temperature proton exchange membrane material.
Computational Modeling of Thermal and Electrical Fields of a High Power Density Solid Oxide Fuel Cell
Authors: Iyengar Arun K. S. , DiGiuseppe Gianfranco , Desai Niranjan , Vora Shailesh , Shockling Larry
Published: September 2008

The electrical performance of solid oxide fuel cells (SOFC) has been traditionally characterized using isothermal cell tests and button cell tests. However, the evaluation of performance, operation, and structural integrity of cells in a typical SOFC stack are not only less amenable to confirmation through testing but are also significantly expensive than computational simulations. Computational models are invaluable in extending the measured isothermal cell test characteristics to predict both electrical performance and mechanical behavior of SOFCs in a stack under different operating conditions. The present investigation is part of an ongoing program of numerical developments and investigations to model the cell thermal and electrical characteristics in a stack environment. The ultimate objective is the development of an optimized cell geometry based on performance, structural integrity, and manufacturability. The flattened tubular high power density (HPD) cell, featuring five air channels fed by air feed tubes, was investigated. A CFD model of the HPD cell was developed using the commercial CFD software Fluent 6.2. A Fluent based SOFC model was used to simulate the electrochemical effects. The cathode, the anode, and the interconnection layers of the cell were resolved in the model and all modes of heat transfer, conduction, convection, and radiation were included. The results of the CFD model at isothermal conditions are presented and compared with experimentally measured isothermal cell V-J’s at 1000°C, 900°C, and 800°C. The model results agree well with the experimental data for cell temperatures of 1000°C and 900°C, after some tuning of exchange current density and tortuosity values. The agreement with the 800°C data however is not as good. The CFD model was then configured and analyzed with operating conditions typically encountered with a stack design that is currently under development. The resulting thermal, electrical, and flow fields are presented herein and discussed. It was found that the Fluent based SOFC model is a robust and effective tool for analyzing the complex and highly interactive three-dimensional electrical, thermal, and fluid flow fields, generally associated with the HPD cells. The computational time with the Fluent based model is however large in comparison with lumped-parameter approaches, mainly due to slow radiation convergence. Nevertheless, the comprehensive current density and thermal fields generated with the Fluent based model are necessary to enable a better prediction of thermal stresses within the cell, thereby permitting a more robust cell and module design.
An Investigation Into the Impact of the Performance Efficiency of PEM Fuel Cells From Coupling Channel Dimensions With Flow Configurations
Authors: Jindal Manish , Archambault Mark
Published: September 2008

Proton Exchange Membrane fuel cells are receiving a great deal of attention due to their low-temperature characteristics and environmental friendliness. Significant research has been conducted towards understanding and perfecting these devices so as to realize their potential to produce power with maximum efficiency and minimum cost. While much work has been done to refine the electrochemical and mass transport models describing the physics of the cell in the vicinity of the catalyst and membrane layers, comparatively little attention has been paid to the fluid dynamics phenomena within the cell and how it impacts the efficiency and performance of the device. The purpose of this work is to combine a subset of previously reported results and determine whether they can be incorporated into a single PEM fuel cell to further increase the performance above and beyond the increase obtained by implementing them separately. Several three-dimensional models with varying channel shapes, relative flow directions, and operating conditions were developed. Various inlet flow distributions were imposed to evaluate the most efficient fuel cell configuration. Results show that there are only minor differences in the average current density of the fuel cell with changes in the channel cross-sectional shape. Moreover, there is little impact on performance with variations in the relative flow directions of the inlet gases. While only slight increases in fuel cell performance were observed with most mass flow rate distributions across the channels, alternating high and low mass flow rates in adjacent channels provided almost a 3% increase in average current density over a uniform profile.
On the Nonlinear Behavior of a Glass-Ceramic Seal and Its Application in Planar SOFC Systems
Authors: Nguyen Ba Nghiep , Koeppel Brian J. , Vetrano John S. , Khaleel Mohammad A.
Published: September 2008

This paper studies the nonlinear behavior of a glass-ceramic seal used in planar solid oxide fuel cells (SOFCs). To this end, a viscoelastic damage model has been developed that can capture the nonlinear material response due to both progressive damage in the glass-ceramic material and viscous flow of the residual glass in this material. The model has been implemented in the MSC MARC finite element code, and its validation has been carried out using the experimental relaxation test data obtained for this material at 700°C, 750°C, and 800°C. Finally, it has been applied to the simulation of a SOFC stack under thermal cycling conditions. The areas of potential damage have been predicted.
Research and Development of Key Materials of PEMFC
Authors: Zhang Huamin , Zhu Xiaobing
Published: September 2008

In this paper, R & D on the electrocatalysts and the proton conductive membranes for proton exchange membrane fuel cells in our group is presented. It is shown that both the electrocatalysts and the proton conductive membranes have attained an enhanced performance.
Cycle Analysis of Low and High H2 Utilization SOFC/Gas Turbine Combined Cycle for CO2 Recovery
Authors: Onda Kazuo , Taniuchi Takuya , Sunakawa Daisuke , Nagahama Mitsuyuki , Araki Takuto , Kato Toru
Published: September 2008

A major factor in global warming is CO2 emission from thermal power plants, which burn fossil fuels. One technology proposed to prevent global warming is CO2 recovery from combustion flue gas and the sequestration of CO2 underground or near the ocean bed. Solid oxide fuel cell (SOFC) can produce highly concentrated CO2, because the reformed fuel gas reacts with oxygen electrochemically without being mixed with air in the SOFC. We therefore propose to operate multi-staged SOFCs with high utilization of reformed fuel to obtain highly concentrated CO2. In this study, we estimated the performance of multi-staged SOFCs considering H2 diffusion and the combined cycle efficiency of a multistage SOFC / gas turbine / CO2 recovery power plant. The power generation efficiency of our CO2 recovery combined cycle is 68.5%, whereas the efficiency of a conventional SOFC/GT cycle with the CO2 recovery amine process is 57.8%.
An Internal Water Management Scheme for Portable Polymer Electrolyte Fuel Cells
Authors: Fu Richard S. , Pasaogullari Ugur
Published: September 2008

Performance of polymer electrolyte fuel cells (PEFCs) is highly dependent on water content of the membrane and a humidification scheme becomes a necessity to operate PEFCs at a high efficiency. However, conventional humidification schemes require external humidifiers, which are usually bulky and impractical for portable PEFCs. In this paper we propose an innovative approach for humidification of the polymer electrolyte membrane, using an internally built-in mass (water) exchanger (MX) embedded in the bipolar plates. We present the validation of the concept using a multi-dimensional, isothermal computational fluid dynamics (CFD) solution of the water transport in the proposed MX. An optimal range of operation of the MX is investigated and effects on PEFC performance are studied.
A Unique Seal-Less Solid Oxide Fuel Cell Stack and Its CFD Analysis
Authors: Akbay Taner , Chitose Norihisa , Miyazawa Takashi , Murakami Naoya , Hosoi Kei , Nishiwaki Futoshi , Inagaki Toru
Published: September 2008

Combined Heat and Power (CHP) generation units based on intermediate temperature (600∼800°C) solid oxide fuel cell (SOFC) modules have been collaboratively developed by Mitsubishi Materials Corporation and The Kansai Electric Power Co., Inc. Currently, hydrocarbon fuel utilising units designed to produce modular power outputs up to 10 kWe-AC with overall efficiencies greater than 80% (HHV) are being tested. A unique seal-less stack concept is adopted to build SOFC modules accommodating multiple stacks incorporated of stainless steel separators and disk-type planar electrolyte-supported cells. In order to advance the current technology to achieve improved levels of efficiency and reliability, through design iterations, computational modelling tools are being heavily utilised. This contribution will describe the results of coupled computational fluid dynamics (CFD) analysis performed on our fourth-generation 1 kW class SOFC stack. A commercially available CFD code is employed for solving the governing equations for conservation of mass, momentum and energy. In addition, a local electrochemical reaction model is coupled to the rest of the transport processes that take place within the SOFC stack. It is found that the CFD based multi-physics model is capable of providing necessary and proper guidance for identifying problem areas in designing multi-cell SOFC stacks. The stack performance is also estimated by calibrating the computational model against data obtained by experimental measurements.
GDM Intrusion Into Reactant Gas Channels and the Effect on Fuel Cell Performance
Authors: Rapaport Pinkhas , Lai Yeh-Hung , Ji Chunxin
Published: September 2008

This paper reports on the study of gas diffusion media (GDM) intrusion into reactant gas channels and its effect on the performance of the proton exchange membrane (PEM) fuel cell. The PEM fuel cell under consideration consists of a membrane electrode assembly (MEA) sandwiched between two layers of gas diffusion media commonly made of carbon paper or cloth. The GDM/MEA/GDM assembly is then compressed between two adjacent bi-polar plates. In this configuration, the compression pressure is transmitted under the lands of the reactant gas flow-field onto GDMs on which the portion over the channels remain unsupported. Because of the relatively low bending and compressive stiffness, it is found that GDMs can easily intrude into the reactant gas channels. The direct consequence of GDM intrusion is the pressure drop increase in the reactant gases in the intruded channels. This is further compounded by cell-to-cell or channel-to-channel variation in GDM thickness and mechanical properties, which results in non-uniform reactant gas flow distribution and ultimately negatively impacts the fuel cell performance. In this study, we have developed a GDM intrusion model based on the finite element method (FEM. We have also devised an experimental setup to measure the GDM intrusion, in which we found good agreement between the model prediction and experimental measurement. Combining the FEM based intrusion model and a flow redistribution model we have investigated the effect of GDM channel intrusion on the reactant flow distribution and the impact on the fuel cell performance. It is found that a 20% reduction of reactant flow can be induced with a 5% additional blockage in channels by GDM intrusion. Based on the findings from the current study, we attribute the significant performance variation in a 30-cell fuel cell stack to the variation in reactant flow induced by the variation in GDM intrusion. The results from the analytical study and fuel cell testing both suggested that the product variations in GDM would need to be significantly reduced and the stiffness of the GDM would need to be increased if the PEM fuel cells of high power density were to be used reliably at a relatively low stoichiometry.
Numerical Simulation and Modeling of Liquid-Feed Direct Methanol Fuel Cell
Authors: Jen Tien-Chien , Yan Tuanzhou
Published: September 2008

A two-phase flow model was developed for liquid-feed methanol fuel cells (DMFC) to evaluate the effects of various operating parameters on the DMFC performance. In this study, a general homogenous two-dimensional model is described in details for both porous layers and fluid channels. This two-dimensional general model accounts for fluid flow, electrochemical kinetics, current density distribution, hydrodynamics, multi-component transport, and methanol crossover. It starts from basic transport equations including mass conservation, momentum transport, energy balance, and species concentration conservation in different elements of the fuel cell sandwich, as well as the equations for the phase potential in the membrane and the catalyst layers. These governing equations are coupled with chemical reaction kinetics by introducing various source terms. It is found that all these equations are in a very similar form except the source terms. Based on this observation, all the governing equations can be solved using the same numerical formulation in the single domain without prescribing the boundary conditions at the various interfaces between the different elements of the fuel cell. Detailed numerical formulations are presented in this paper. The numerical simulation results, such as velocity field, local current density distribution, and species concentration variation along the flow channel, under various operation conditions are computed. The performance of the DMFC affected by various parameters such as temperature, pressure, and methanol concentration is investigated in this paper. The numerical results are further validated with available experimental data from the published literatures.
Conversion of Syngas From Biomass in Solid Oxide Fuel Cells
Authors: Karl Ju¨rgen , Frank Nadine , Karellas Sotiris , Saule Mathilde , Hohenwarter Ulrich
Published: September 2008

Conversion of biomass in syngas by means of indirect gasification offers the option to improve the economic situation of any fuel cell systems due to lower costs for feedstock and higher power revenues in many European countries. The coupling of an indirect gasification of biomass and residues with highly efficient SOFC systems is therefore a promising technology for reaching economic feasibility of small decentralized combined heat and power production (CHP). The predicted efficiency of common high temperature fuel cell systems with integrated gasification of solid feedstock is usually significantly lower than the efficiency of fuel cells operated with hydrogen or methane. Additional system components like the gasifier, as well as the gas cleaning reduce this efficiency. Hence common fuel cell systems with integrated gasification of biomass will hardly reach electrical efficiencies above 30 percent. An extraordinary efficient combination is achieved in case that the fuel cells waste heat is used in an indirect gasification system. A simple combination of a SOFC and an allothermal gasifier enables then electrical efficiencies above 50%. But this systems requires an innovative cooling concept for the fuel cell stack. Another significant question is the influence of impurities on the fuel cells degradation. The European Research Project ‘BioCellus’ focuses on both questions — the influence of the biogenious syngas on the fuel cells and an innovative cooling concept based on liquid metal heat pipes. First experiments showed that in particular higher hydrocarbons — the so-called tars — do not have an significant influence on the performance of SOFC membranes. The innovative concept of the TopCycle comprises to heat an indirect gasifier with the exhaust heat of the fuel cell by means of liquid metal heat pipes. Internal cooling of the stack and the recirculation of waste heat increases the system efficiency significantly. This concept promises electrical efficiencies of above 50 percent even for small-scale systems without any combined processes.
Mechanical Response of 3-Layered MEA During RH and Temperature Variation Based on Mechanical Properties Measured Under Controlled T and RH
Authors: Solasi Roham , Huang Xinyu , Zou Yue , Feshler Matthew , Reifsnider Kenneth , Condit David
Published: September 2008

Mechanical fracture of Nafion® membrane limits the life of PEM FC stacks. This is likely a result of gradual strength degradation and mechanical stress/strain transients induced by the cycling relative humidity (RH). Mechanical properties of Nafion® membrane strongly depend on water content. The objectives of the authors’ work are (1) to understand the fundamental mechanical behavior of an ionomer membrane, i.e., Nafion®, as a function of RH and (2) to develop physically meaningful models to perform stress/strain analysis of membrane electrode assemblies under RH and temperature variations. To characterize the mechanical response of an ionomer as a function of temperature and relative humidity, an environment chamber capable of generating temperatures from 25 to 100 degrees Centigrade and relative humidities from 5 to 85 percent was designed and built. An electromechanical membrane test (load) frame was mounted as an integral part of the system. An optical strain measurement device was used to record axial extension and lateral contraction of the membrane specimens without contact. Extensive mechanical tests on a commercial ionomer membrane were conducted under carefully controlled hydration and temperature. Fully nonlinear, fully anisotropic elasto-plastic constitutive representation of this ionomer material was obtained as function of temperature and RH. Water content significantly affects the elastic modulus of the membranes. Experimental data show that the elastic modulus of the membrane continuously increases up to about twice the original value during dry out. Such has been taken into account in order to accurately model the stress/strain history of the membrane during dry-out. The collected experiment data were represented in material constitutive models for use in a finite element code, ABAQUS. A 3-layer membrane electrode assembly (MEA) structure has been modeled to observe stress/strain distribution during RH and T cycling. Non-uniform electrode/membrane interfaces have been modeled as well as uniform sections to see the effects of geometric irregularities on the extreme values of stress and strain.
Using a Knife Slitting Test to Characterize the Fracture Resistance of Proton Exchange Membranes
Authors: Li Yongqiang , Quincy Jennifer , Case Scott W. , Dillard David A. , Budinski Michael , Lai Yeh-Hung
Published: September 2008

Through-the-thickness flaws or “pinholes” in proton exchange membranes (PEM) can lead to gas crossover, reducing fuel cell efficiency, accelerating degradation, and raising safety issues. The multi-physics process that causes these flaws is not fully understood, but stress state, environmental exposure, and cyclic operation may all be contributing factors. Fracture mechanics has proven to be useful in characterizing degradation of many materials, including polymers subjected to environmental challenges. Although unclear if pinhole formation can be successfully characterized and predicted from a fracture perspective, this study continues our prior work to characterize PEMs in such a manner. Because of the lack of constraint, thin films often exhibit very high fracture energies and large plastic zones, features that are not consistent with observations of PEM failures. In an effort to obtain the fracture energy with very little dissipation, knife-slitting tests were conducted to reduce the crack tip plasticity. With modifications made to the systems used by Wang and Gent (1994) and by Dillard et al (2005), a slitter that maintains a constant tearing angle during the slitting process was developed. While fracture energies on the order of 104J/m2 were measured with double edge notched test samples, and on the order of 103J/m2 were measured with trouser tear samples, the knife slit test resulted in fracture energies as low as several hundred J/m2. An environmental chamber was used to enclose the slitting process so experiments at elevated temperature and moisture levels could be conducted. The relevance of these fracture energies to observed PEM failures in operating fuel cells is not fully understood. Nonetheless, the ability to obtain fracture energies approaching the intrinsic fracture energy of these ductile membranes is believed to be useful in studying what appear to be more brittle fracture modes that have been observed in PEMs.
Modeling of Shunt Current in Liquid Electrolyte Fuel Cells
Authors: Zhou Ge , Chen Lea-Der , Seaba James P.
Published: September 2008

A general electrolyte model for calculation of the liquid electrolyte transport in fuel cells is presented. A 2-D formulation is used to describe the transport in an alkaline fuel cell. Numerical results were obtained by using commercial CFD software, in conjunction with the user defined functions that calculate the source terms of the transport equations. An order of magnitude analysis is conducted of the energy transport in the separator and electrode regions. The numerical calculation also examines the local primary current at the anode and cathode electrodes. The calculated current flux showed a higher value near the separator entrance and it decreased along the stream-wise direction. The non-uniformity of the local primary current is caused mainly by the species transport resistance between the electrodes instead of the temperature difference. The effects of four different electrolytes were also studied. The results suggested that the cell voltage differences were due to the competing effects of electrolyte conductance and species diffusion. Numerical calculation also captured the presence of shunt current. A net shunt current as high as 0.1 A/cm2 is calculated at the separator inlet and exit. Provisions to reduce shunt currents seem to be warranted for AFC operated at a condition similar to that examined in this paper.
Analytical Solution for Two-Phase Flow in PEMFC Gas Diffusion Layer
Authors: Gan Mingfei , Chen Lea-Der
Published: September 2008

Thermal and water management is critical to fuel cell performance. It has been shown that gas diffusion layer (GDL) can impose the mass transport limit; for example, it can block the reactant transport to active layer when flooding occurs at high current density conditions. Micro porous layer (MPL) in conjunction with backing layer (BL) has been used as a GDL material and was shown to be effective for water management. To study the transport processes in GDL and MPL modified GDL, an analytical solution is derived current study for calculation of two-phase, multicomponent transport in GDL. Two models were considered, the unsaturated flow model (UFM) and the separate flow model (SFM). Comparison of the calculated saturation level and oxygen mass fraction shows that UFM calculation can underestimate, as well as overestimate the saturation and oxygen concentration. The SFM was used to study the effects due to GDL property variations. The calculation shows that increase in liquid water transport in an MPL modified GDL is due to the abrupt change of liquid water flow rate when a step change in porosity or permeability is imposed. The calculation further shows that particle size of around 1 μm would be a good choice for MPL as it results in higher oxygen concentration at active layer and lower saturation in GDL.
Shape Optimization of Fuel Cell Molded-on Gaskets for Robust Sealing
Authors: Vlahinos Andreas , Kelly Kenneth , Mease Kevin , Stathopoulos Jim
Published: September 2008

In typical Proton Exchange Membrane fuel cells, a compressed gasket provides a sealing barrier between cell and cooler bipolar plate interfaces. The gasket initially bears the entire bolt load, and its resisting reaction load depends on the cross-sectional shape of the gasket, bipolar plate’s groove depth, and the hyperelastic properties of the gasket material. A nonlinear, finite element analysis (FEA) model with various hyperelastic material models, large deformations, and contact was used to evaluate the load-gap curves. The deformed shapes and the distributions of stress, strain, and deflections are presented. Mooney-Rivlin and Arruda-Boyce hyperelastic material models were used, and a comparison of load-gap curves is shown. A process is presented that couples the computer-aided design geometry with the nonlinear FEA model that was used to determine the gasket’s cross-sectional shape, which achieves the desired reaction load for a given gap.
Analysis of Biomass Integrated Gasification Fuel Cell Plants in Industrial CHP Applications
Authors: Corradetti Alessandro , Desideri Umberto
Published: September 2008

The gasification of biomass wastes deriving from certain industrial processes is an interesting option for cogenerating heat and power. The utilization of the syngas in a high temperature fuel cell could lead to the improvement of electrical efficiency in comparison with traditional CHP plants. In this paper the performance of various Biomass Integrated Gasification Fuel Cell (BIGFC) plants are investigated. In particular an atmospheric down-draft gasifier has been considered for syngas production. The fuel cell used for power generation is a 250 kW solid oxide fuel cell, which has been simulated through a zero-dimensional steady-state model and integrated in Aspen Plus® software for evaluating the performance of the entire plant. Various system lay-outs have been investigated to analyze the effect on plant efficiency of the following parameters: (i) gasification air pre-heating; (ii) use of 90% pure oxygen for gasification; (iii) use of enriched air (55% O2) for gasification; (iv) recirculation of anodic gas flow; (v) installation of a SOFC/GT hybrid cycle for power production. BIGFC plants show an electrical efficiency in the range 20–27%, and a thermal efficiency of 39–59%. If a SOFC/GT hybrid cycle is installed electrical efficiency grows up to 39%.
Steady and Pulsed Flow Performance Trends of Higher Concentration DMFCs
Authors: McCarthy Larry , Haynes Comas
Published: September 2008

Direct methanol fuel cells (DMFCs) are a promising source of energy due to their potentially high energy density, facilitated fuel delivery and storage, and precluded fuel processing. However, DMFCs have several challenges which need to be resolved before they can replace existing energy sources. Some of these challenges include lower power density, relatively high cost, and uncertain reliability. These issues are all promoted, at least in part, by the methanol crossover phenomenon, wherein membrane permeability allows the undesirable species transport of methanol from the anode to the cathode. This phenomenon also causes the requirement of dilute fuel mixtures, which is undesirable from an energy density viewpoint. Prior research has shown that methanol crossover can be reduced by operating DMFCs in a transient mode [1,2]. Thus, a study has been performed to investigate the impact of hydraulic pulsing (HP) at different operating conditions, such as fuel concentration, current density, and number-of-stoichs (NOS). Furthermore, the cell’s performance is being characterized at different steady flow concentrations to highlight the impact of fuel dilution.
A New Highly-Efficient Direct Methanol Fuel Cell
Authors: Guo Jiusheng , Huang Wen-Chung , Jang Bor Z.
Published: September 2008

Direct Methanol Fuel Cell (DMFC) is often viewed as an ideal power source for microelectronics and portable devices such as cell phone, laptop computer, and sensor, etc. However, the drawbacks in conventional DMFC (e.g., methanol crossover through the proton exchange membrane and the low concentration of methanol and water mixture) impede the wide commercial applications of DMFC due to the dissatisfactory electrical output. Moreover, the complex system configuration in conventional DMFC increases fuel cell weight, size, and cost and also reduces the system reliability. In this paper, an innovative Local Vapor Fuel Cell (LVFC) was proposed to promote the electro-catalytic reaction and improve the fuel cell power output. The design of LVFC was based on locally vaporizing the mixture of methanol and water without the complex and bulky vaporizer and blower. The capillary-based fuel feeding in LVFC, instead of pumping, substantially reduced system complexity. The proposed design features the LVFC light in weight, compact in size and high fuel conversion efficiency. The thermally stable high temperature membrane materials and MEA for LVFC were also investigated and developed. After the high temperature membrane and MEA were integrated into the LVFC, the characterization of the LVFC was conducted as a function of temperatures. The experimental results demonstrated that LVFC had higher electrical output with the increase of temperature, and higher thermal and electro-chemical reliability and stability.
Proton Exchange Membrane Fuel Cell System Identification and Control: Part II — H-Infinity Based Robust Control
Authors: Wang F. C. , Yang Y. P. , Chang H. P. , Ma Y. W. , Huang C. W. , Weng B. J.
Published: September 2008

This paper applies robust control strategies to a PEM fuel-cell system. In Part I of this work [17], a PEM fuel cell was described as a two-input-two-output system with the inputs of hydrogen and air flow rates, and the outputs of cell voltage and current. From the responses, system identification techniques were adopted to model the system transfer function matrix. Then adaptive control methods were applied to control the system with encouraging results. In this paper, the H∞ robust control strategy is proposed due to the highly nonlinear and time-varying characteristics of the system. From the results, it is illustrated to be an efficient control method for the fuel cell systems.
Computational Modeling of PEM Fuel Cells With PBI Membranes
Authors: Cheddie Denver F. , Munroe Norman D. H.
Published: September 2008

A parametric model of a proton exchange membrane fuel cell (PEMFC) operating with a polybenzimidazole (PBI) membrane is presented. The model is three dimensional and applicable for PEMFCs operating at intermediate temperatures (120–150 °C). It accounts for all transport and polarization phenomena, and the results compare well with published experimental data for equivalent operating conditions. Results for oxygen concentration and temperature variations are presented. The model predicts the oxygen depletion, which occurs in the catalyst area under the ribs, and which gives an indication of the catalyst utilization. Results also predict that for an output power density of 1 kW m−2, a cell temperature rise of up to 30 K can be expected for typical laboratory operating conditions. Parametric analyses indicate that significant gain in fuel cell performance can be expected by increasing the conductivity of the PBI membrane. Further, results demonstrate that when the catalyst region is well utilized, increasing the catalyst activity results in only a small improvement in performance.
Performance Enhancement of PEM Fuel Cells by Use of Anode Gas Ultrahumidification via Ultrasonic Nebulization
Authors: Snyder Erik , Lalk Thomas R. , Appleby A. J.
Published: September 2008

A novel anode feed gas humidification method was investigated as part of an effort to reduce the mass, volume, and cost of the balance of plant for a commercial PEM fuel cell system. Ultrasonic fountain nebulization was utilized to ultrahumidify the anode feed gas for a PEM fuel cell. Ultrasonic nebulization ultrahumidification was found to increase the average voltage of the fuel cell by several percent, and reduce the amplitude of cyclic overvoltage. Most importantly, this humidification technique greatly increased the thermal fault tolerance of the PEM fuel cell; that is, this humidification technique allowed the PEM fuel cell to operate effectively at high temperatures without a need to increase the vapor pressure of the humidification water. In addition, this humidification technique shows potential to be used to increase the overall energy conversion efficiency of a PEM fuel cell system.
Molecular Dynamics of Proton Exchange Inside a Nafion® Membrane
Authors: Cheng Chin-Hsien , Lee Shu-Feng , Hong Che-Wun
Published: September 2008

The proton transfer mechanism is the fundamental principle of how the proton exchange membrane fuel cell (PEMFC) works. This paper develops a molecular dynamics technique to simulate the transfer mechanism of the hydrogen protons inside a Nafion 117 membrane. The realistic polymer structure of the Nafion is extremely huge and very complex, it is simplified to be a repeated structure with part of the major carbon-fluoride backbone and a side chain with radicals of SO3− in this paper. Water molecules were assigned to distribute between side chains randomly. The simulation package of DLPOLY was employed as the platform. Simulation results show that the water molecules will cluster together due to the polarization characteristics, and the clusters are attracted by the side chain of the membrane electrolyte. Hydrogen protons are then transferred from one side chain to another through the water clusters. The migration process of the hydrogen protons within the membrane is a function of the water uptakes and many other factors. They are investigated to further improve the ionic conduction of the fuel cell membrane.
Atomistic Analysis of Proton Diffusivity at Enzymatic Biofuel Cell Anode
Authors: Chiu Chuang-Pin , Chen Peng-Yu , Hong Che-Wun
Published: September 2008

This paper investigates the proton diffusion phenomenon between the anode catalyst and the electrode in an enzymatic bio-fuel cell. The bio-fuel cell uses enzymatic organism as the catalyst instead of the traditional noble metal, like platinum. The fuel is normally the glucose solution. The fuel cell is membrane-less and produces electricity from the reaction taken place in the organism. When the biochemical reaction occurs, the protons and electrons are released in the solution. The electrons are collected by the electrode plate and are transported to the cathode through an external circuit, while the protons migrate to the cathode by the way of diffusion. Unfortunately, protons are easy to dissipate in the solution because the enzyme is immersed in the neutral electrolyte. It is an important issue of how to collect the protons effectively. In order to investigate the diffusion process of the protons, a molecular dynamics simulation technique was developed. The simulation results track the transfer motion of the protons near the anode. The diffusivity was evaluated from the trajectory. The research concludes that the higher the glucose concentration, the better the proton diffusivity. The enzyme promotes the electrochemical reaction; however, it also plays an obstacle in the proton diffusion path.
Advanced Components for PEMFC Stacks
Authors: Fan Chinbay , Onischak Michael , Liss William
Published: September 2008

Currently, fuel cell cost reduction and long life are major priorities for fuel cells to be commercially successful for vehicle, stationary, or portable power applications. In the last five years, Gas Technology Institute (GTI) has formulated and developed a low cost, long lifetime, high conductivity proton exchange membrane (PEM) yielding state-of-the-art fuel cell performance. Additionally, a non-coated, corrosion-resistant metal alloy bipolar separator plate has been patented and tested for both hydrogen-fueled and direct methanol fueled PEMFC applications. Tests in fuel cells plus out-of-cell ASTM corrosion tests have shown very low corrosion rates under fuel cell operating conditions. Metal alloy separator plates have run for over 23,000 hours in cells with corrosion rates an order of magnitude less than the DOE target of 1 μA/cm2. GTI’s fuel cell polymer membrane research focused on three criteria: (1) use of low cost materials; (2) polymer structures stable under fuel cell operating conditions; and (3) performance equal or better than current Nafion membrane electrode assemblies (MEAs). Fluorine-containing polymers were eliminated due to cost issues, environmental factors, and the negative influence fluorine ion loss has on metallic separator plates. The polymer membrane material was synthesized and cast into films, then fabricated into MEAs. The cost of the membrane (raw materials plus film processing materials) is estimated to be less than $10/m2 — or less than 10% of available technology. A variety of out-of-cell testing showed the membrane has sufficient strength, flexibility, and conductivity to serve as an ion conducting membrane for fuel cells. A series of 60 cm2 active area single cells and short stacks were operated over a wide range of fuel cell conditions, showing state-of-the-art MEA performance with long-term polymer stability.
Integration of Fuel Cells in Multisource Multiproduct Energy Systems
Authors: Hemmes Kas
Published: September 2008

In the development of fuel cell and energy systems we can observe an increasing complexity, going from simple source-conversion-and product systems to single source multiproduct systems such as combined heat and power and so-called tri-generation systems in which for instance also chemicals can be produced simultaneously with electric power and heat. The logical next step would be to allow not only for multi products, but also for various sources supplied simultaneously to the system. This concept has been proposed by M. Geidl and was called an energy hub. In this paper examples are given of these MSMP systems with fuel cells. Examples are the integration of fuel cells in the existing natural gas infrastructure and in a possible future natural gas infrastructure in which hydrogen is mixed into the natural gas. Also a favorable example is given for the integration of wind energy and high temperature internal reforming fuel cells into a highly efficient system for the co production of hydrogen and electric power.