Update on numerical model for the performance prediction of a PEM Fuel Cell

A Computational Fluid Dynamics (CFD) model developed for a 50 cm² Fuel Cell with parallel and serpentine flow field bipolar plates was presented in an article published in the International Journal of Hydrogen Energy 35 (2010) 11,533-11,550 [1]. The experimental validation details were presented as well in an article published in the International Journal of Hydrogen Energy 35 (2010) 11,437-11,447 [2]. A good agreement between numerical results and experimental measurements were obtained except for the high current density region where mass-transport limitations dominate the voltage loss. This short communication presents an update on the last simulations performed, where an improved prediction of the polarization curve is obtained. The physical and computational aspects of the reasons underlying the improvement of the results are discussed.     

Three-dimensional computational fluid dynamics model of a tubular-shaped PEM fuel cell

A full three-dimensional, non-isothermal computational fluid dynamics model of a tubular-shaped proton exchange membrane (PEM) fuel cell has been developed. This comprehensive model accounts for the major transport phenomena in a PEM fuel cell: convective and diffusive heat and mass transfer, electrode kinetics, and potential fields. In addition to the tubular-shaped geometry, the model feature an algorithm that allows for more realistic representation of the local activation overpotentials which leads to improved prediction of the local current density distribution. Three-dimensional results of the species profiles, temperature distribution, potential distribution, and local current density distribution are presented. The model is shown to be able to understand the many interacting, complex electrochemical, and transport phenomena that cannot be studied experimentally.     

Optimal design and operational tests of a high-temperature PEM fuel cell for a combined heat and power unit

Development of new materials for polymer electrolyte membranes has allowed increasing the operational temperature of PEM fuel cell stacks above 120 °C. The present paper summarizes the main results obtained in a research devoted to the design, fabrication and operational tests performed on a high-temperature PEMFC prototype. A 5-cell stack has been assembled with commercial Celtec P-1000 high-temperature MEAs from BASF Fuel Cells, but the rest of elements and processes have been developed at LIFTEC research facilities. The stack includes different novelties, such as the way in which reactant gases are supplied to the flowfield, the design of the flowfield geometry for both anode and cathode plates, the concept of block that eases the assembling and maintenance processes, and the heating strategy for a very fast start-up. The different procedures comprising the assembly, closing and conditioning stages are also widely described and discussed. Results obtained in the preliminary operational tests performed are very promising, and it is expected that the 30-cells HT-PEMFC stack will deliver an electric power 2.3 times larger than the one initially predicted.     

New electroplated aluminum bipolar plate for PEM fuel cell

Further improvement in the performance of the polymer electrolyte membrane fuel cells as a power source for automotive applications may be achieved by the use of a new material in the manufacture of the bipolar plate. Several nickel alloys were applied on the aluminum substrate, the use of aluminum as a bipolar plate instead of graphite is to reduce the bipolar plate cost and weight and the ease of machining. The electroplated nickel alloys on aluminum substrate produced a new metallic bipolar plate for PEM fuel cell with a higher efficiency and longer lifetime than the graphite bipolar plate due to its higher electrical conductivity and its lower corrosion rate. Different pretreatment methods were tested; the optimum method for pretreatment consists of dipping the specimen in a 12.5% NaOH for 3 min followed by electroless zinc plating for 2 min, then the specimen is dipped quickly in the electroplating bath after rinsing with distilled water. The produced electroplate was tested with different measurement techniques, chosen based on the requirement for a PEM fuel cell bipolar plate, including X-ray diffraction, EDAX, SEM, corrosion resistance, thickness measurement, microhardness, and electrical conductivity.     

A hybrid model of cathode of PEM fuel cell using the interdigitated gas distributor

A two-dimensional (2D), single- and two-phase, hybrid multi-component transport model is developed for the cathode of PEM fuel cell using interdigitated gas distributor. The continuity equation and Darcy's law are used to describe the flow of the reactant gas and production water. The production water is treated as vapor when the current density is small, and as two-phase while the current density is greater than the critical current density. The advection–diffusion equations are utilized to study species transport of multi-component mixture gas. The Butler–Volmer equation is prescribed for the domain in the catalyst layer. The predicted results of the hybrid model agree well with the available experimental data. The model is used to investigate the effects of operating conditions and the cathode structure parameters on the performance of the PEM fuel cell. It is observed that liquid water appears originally in the cathodic catalyst layer over outlet channel under intermediate current and tends to be distributed uniformly by the capillary force with the increase of the current. It is found that reduction of the width of outlet channel can enhance the performance of PEM fuel cell via the increase of the current density over this region, which has, seemingly, not been discussed in previous literatures.     

Chemical reacting transport phenomena in a PEM fuel cell

A three-dimensional mathematical model for the PEM fuel cell including gas channel has been developed to simulate fuel cell performance. A set of conservation equations and species concentration equations are solved numerically in a coupled gas channel and porous media domain using the vorticity-velocity method with power law scheme. Detailed development of axial velocity and secondary flow fields are presented at various axial locations. Polarization curves are demonstrated by solving the equations for electrochemical reactions and the membrane phase potential. Compared with experimental data from published literatures, numerical results of this model agree closely with experimental results.     

Degradation prediction of PEM fuel cell based on artificial intelligence

In the last years, Proton Exchange Membrane Fuel Cells (PEMFC) became a promising energy converter for both transportation and stationary applications. However, durability of fuel cells still needs to be improved to achieve a widespread deployment. Degradation mechanisms and aging laws are not yet fully understood. Therefore, long-term durability tests are necessary to get more information. Moreover, degradation models are requested to estimate the remaining useful life of the system and take adequate corrective actions to optimize durability and availability. This paper presents in a first part the results of a long-term durability test performed on an open cathode fuel cell system operated during 5000 h under specific operating conditions including start/stop and variable ambient temperature. Performance evolution and degradation mechanisms are then analyzed to understand influence of operating conditions and how to extend the durability. In a second part of the paper, the results are used to build a degradation model based on echo state neural network in order to predict the performance evolution. Results of the degradation prediction are very promising as the normalized root mean square error remains very low with a prediction time over 2000 h.     

Development of bipolar plates with different flow channel configurations for fuel cells

Bipolar plates include separate gas flow channels for anode and cathode electrodes of a fuel cell. These gases flow channels supply reactant gasses as well as remove products from the cathode side of the fuel cell. Fluid flow, heat and mass transport processes in these channels have significant effect on fuel cell performance, particularly to the mass transport losses. The design of the bipolar plates should minimize plate thickness for low volume and mass. Additionally, contact faces should provide a high degree of surface uniformity for low thermal and electrical contact resistances. Finally, the flow fields should provide for efficient heat and mass transport processes with reduced pressure drops. In this study, bipolar plates with different serpentine flow channel configurations are analyzed using computational fluid dynamics modeling. Flow characteristics including variation of pressure in the flow channel across the bipolar plate are presented. Pressure drop characteristics for different flow channel designs are compared. Results show that with increased number of parallel channels and smaller sizes, a more effective contact surface area along with decreased pressured drop can be achieved. Correlations of such entrance region coefficients will be useful for the PEM fuel cell simulation model to evaluate the affects of the bipolar plate design on mass transfer loss and hence on the total current and power density of the fuel cell.     

Numerical investigation of the performance of symmetric flow distributors as flow channels for PEM fuel cells

This work reports on the performance of a single PEM fuel cell using symmetric flow patterns as gas delivery channels. Three flow patterns, two symmetric and one serpentine, are taken from the literature on cooling of electronics and they are implemented in a computational model as gas flow channels in the anode and cathode side of a PEMFC. A commercial CFD code was used to solve the physics involved in a fuel cell namely: the flow field, the mass conservation, the energy conservation, the species transport, and the electric/ionic fields under the assumptions of steady state and single phase. An important feature of the current modeling efforts is the analysis of the main irreversibilities at different current densities showing the main energy dissipation phenomena in each cell design. Also, the hydraulic performance of the flow patterns was studied by evaluating the pressure drop and pumping power. The first part of this work reveals the advantages of using a serpentine pattern over the base symmetric distributors. The second part is an optimization of the symmetric patterns using the entropy minimization criteria. Such an optimization led to the creation of a flow structure that promotes an improved performance from the point of view of power generation, uniformity of current density, and low pumping power.     

New insights into the temperature-water transport-performance relationship in PEM fuel cells

Three-dimensional numerical simulations of a single straight-channel PEMFC at three different operating temperatures (343 K, 353 K, and 363 K) and at a relative humidity RH = 90% were carried out, by using potentiostatic conditions ranging from 0.27 to 1.0 V. This study aimed at gaining further insights into the complex and tightly coupled interactions taking place inside the fuel cell, relating water generation and transport with local temperature distributions and cell performance. A sensitivity analysis concluded that the higher the operating temperature is, the better the electrical performance of the PEMFC, for the range of operating temperatures analyzed. This feature was further investigated at high current densities (j = 2.25 and 2.57 A/cm²), where the increase of the operating temperature (in the range of study) resulted in an enhancement of the water diffusivity and the electro-osmotic drag, improving the ionic conductivity. Additionally, the dimensionless temperature distribution across the cell width was found to be similar in all the cases. Profile-like curves displaying under-rib/under-channel characteristics are presented and analyzed to understand the role of water and its interaction with the different phenomena occurring within the cell. It was demonstrated that colored scatter plots are convenient tools that contribute to explain existing relationships between the water-related magnitudes.     

Computational model of a PEM fuel cell with serpentine gas flow channels

A three-dimensional computational fluid dynamics model of a PEM fuel cell with serpentine flow field channels is presented in this paper. This comprehensive model accounts for the major transport phenomena in a PEM fuel cell: convective and diffusive heat and mass transfer, electrode kinetics, and potential fields. A unique feature of the model is the implementation of a voltage-to-current (VTC) algorithm that solves for the potential fields and allows for the computation of the local activation overpotential. The coupling of the local activation overpotential distribution and reactant concentration makes it possible to predict the local current density distribution more accurately. The simulation results reveal current distribution patterns that are significantly different from those obtained in studies assuming constant surface overpotential. Whereas the predicted distributions at high load show current density maxima under the gas channel area, low load simulations exhibit local current maxima under the collector plate land areas.     

CFD modelling and experimental validation of cell performance in a 3-D planar SOFC

Fuel cells can be used to provide power for most electrical or electronic devices designed for operation from batteries or from conventional utility power sources. In this study, a three dimensional Computational Fluid Dynamics (CFD) simulation model has been developed and experimentally tested for an anode-supported planar SOFC that has bipolar plated for corrugation which serving as a gas channel and current collector. Experiments were performed on planar cross-flow type at different reactant flow rates, cell temperatures and pressures. In the experimental analysis, values varied from 0.12 L/min to 2 L/min for reactant and from 700 °C to 800 °C SOFC cell temperature. Thereby divergent operating parameters about cell parameters have been addressed. The conservation equations of momentum, energy and mass types are solved with the ANSYS FLUENT software in the proposed model. The maximum power density measured as 6 kW/m² under optimum working conditions. The results also show that the current density and the inlet velocity of fuel gassed are the main parameters that drive the fuel utilization and the total conversion efficiency. All the experimental and numerical findings, which were in good agreement with each other, showed that for Current density – Potential difference characteristic of SOFC cell graphs.     

Data driven models for a PEM fuel cell stack performance prediction

The operating principles of polymer electrolyte membrane (PEM) fuel cells system involve electrochemistry, thermodynamics and hydrodynamics theory for which it is not always easy to establish a mathematical model. In this paper two different methods to model a commercial PEM fuel cell stack are discussed and compared. The models presented are nonlinear, derived from a black-box approach based on a set of measurable exogenous inputs and are able to predict the output voltage and cathode temperature of a 5 kW module working at the CNR-ITAE. A PEM fuel cell stack fed with H₂ rich gas is employed to experimentally investigate the dynamic behaviour and to reveal the most influential factors. The performance obtained using a classical Neural Networks (NNs) model are compared with a number of stacking strategies. The results show that both strategies are capable of simulating the effects of different stoichiometric ratio in the output variables under different working conditions.     

Neural network model of 100 W portable PEM fuel cell and experimental verification

The inherent properties of artificial neural networks (ANNs) such as low sensitivity to noise and incomplete information make the ANN a promising candidate to model the fuel cell system. In this paper, an ANN-based model of 100 W portable direct hydrogen fed proton exchange membrane fuel cell (PEMFC) is presented. The model is built based on experimentally collected data from a portable 100 W direct hydrogen fed PEMFC in the authors’ laboratory. A multilayer feedforward ANN with back-propagation training algorithm is used to model the portable PEMFC. The ANN consists of fully connected four layers network with two hidden layers. The PEMFC ANN model is trained using extracted data from experimentally measured and calculated parameters. To validate the model, the outputs of the PEMFC ANN are compared against experimental data and results from a dynamic model of portable direct hydrogen fed PEMFC. In addition, three statistical indices to measure variations, unbiasedness (precision), and accuracy in voltage, power, and hydrogen flow are used to evaluate the PEMFC ANN model performance. The indices indicate that the maximum variations, unbiasedness, and accuracy of the voltage, power, and hydrogen flow are 1.45%, 2.04%, and 1.90%, respectively, which shows a close agreement between the outputs of the PEMFC ANN and the experimental results.     

Development of a numerical model for natural gas steam reforming and coupling with a furnace model

This paper presents a numerical model (SRP) that was developed to describe the steam reforming process within tubes or channels. This model was implemented in C language and is used as a User-Defined Function (UDF) in the commercial program Fluent. The SRP model is one-dimensional representing mass and energy balances along the tubes/channels assuming uniform conditions in the cross section, except for temperature within porous regions. The model calculates the gas species concentrations and temperature profiles along the tubes/channels and since it is coupled with the Fluent furnace calculation, the boundary temperature is continuously updated and is a model result.     

Fabrication of stainless steel bipolar plates for fuel cells using dynamic loads for the stamping process and performance evaluation of a single cell

In this study, a dynamic load (square wave) is applied to bipolar plates in order to reduce forming defects from the stamping process. Four round (R) sizes of die (R 0.05, 0.1, 0.2, 0.3 mm) are applied to edges that ran from the channel to the rib of the stamping die. Fuel cell performance tests are carried out to analyse the depth and shape of bipolar plate channels formed according to the load conditions, and the effect of the die size on the fuel cell performance is evaluated. The depth of the bipolar plate channel increase with the round size of die regardless of the load type. The shape of the channel formed with a die of R 0.05 mm is trapezoidal, while that formed with a die of R 0.3 mm is triangular. Triangular channels have a higher current density than trapezoidal channels. A higher current density can be obtained with a square load than with a conventional straight load because the former produces a deeper and more uniform bipolar plate channel. The current density of a bipolar plate with a triangular channel formed by a square load with a die of R 0.3 mm is 531 mA cm⁻². After TiN coating, the current density is 784 mA cm⁻², which is about 58% of that of a graphite bipolar plate.     

Numerical investigation of flow field configuration and contact resistance for PEM fuel cell performance

A steady-state three-dimensional non-isothermal computational fluid dynamics (CFD) model of a proton exchange membrane fuel cell is presented. Conservation of mass, momentum, species, energy, and charge, as well as electrochemical kinetics are considered. In this model, the effect of interfacial contact resistance is also included. The numerical solution is based on a finite-volume method. In this study the effects of flow channel dimensions on the cell performance are investigated. Simulation results indicate that increasing the channel width will improve the limiting current density. However, it is observed that an optimum shoulder size of the flow channels exists for which the cell performance is the highest. Polarization curves are obtained for different operating conditions which, in general, compare favorably with the corresponding experimental data. Such a CFD model can be used as a tool in the development and optimization of PEM fuel cells.     

The empirical validation of a model for simulating the thermal and electrical performance of fuel cell micro-cogeneration devices

Fuel cell micro-cogeneration is a nascent technology that can potentially reduce the energy consumption and environmental impact associated with serving building electrical and thermal demands. Accurately assessing these potential benefits and optimizing the integration of micro-cogeneration within buildings requires simulation methods that enable the integrated modelling of fuel cell micro-cogeneration devices with the thermal and electrical performance of the host building and other plant components. Such a model has recently been developed and implemented into a number of building simulation programs as part of an International Energy Agency research project. To date, the model has been calibrated (tuned) for one particular prototype solid-oxide fuel cell (SOFC) micro-cogeneration device. The current paper examines the validity of this model by contrasting simulation predictions to measurements from the prototype device. Good agreement was found in the predictions of DC power production, the rate of fuel consumption, and energy conversion efficiencies. Although there was greater deviation between simulation predictions and measurements in the predictions of useful thermal output, acceptable agreement was found within the uncertainty of the model and the measurements. It is concluded that the form of the mathematical model can accurately represents the performance of SOFC micro-cogeneration devices and that detailed performance assessments can now be performed with the calibrated model to examine the applicability of the prototype device for supplying building electrical and thermal energy requirements.     

2-D + 1-D PEM fuel cell model for fuel cell system simulations

The water management is critical for the operation of PEM fuel cells and has a strong impact on its performance and durability. The aim of this work is the simulation-based investigation of the operation of a PEM fuel cell system with the special focus on its water management.In order to analyze these dependencies correctly, a 2-D + 1-D PEM fuel cell stack model has been developed, which on the one hand has a high level of modelling details and on the other hand meets high requirements concerning its runtime, to enable acceptable simulation times for fuel cell system simulations. The fuel cell model is integrated into an AVL Cruise-M fuel cell system simulation.An analysis is presented comparing a system operation with a fuel cell in co- and counter-flow configuration with a special focus on the local and overall water management.     

Transient response of high temperature PEM fuel cell

A transient three-dimensional, single-phase and non-isothermal numerical model of polymer electrolyte membrane (PEM) fuel cell with high operating temperature has been developed and implemented in computational fluid dynamic (CFD) code. The model accounts for transient convective and diffusive transport, and allows prediction of species concentration. Electrochemical charge double-layer effect is considered. Heat generation according to electrochemical reaction and ohmic loss are involved. Water transportation across membrane is ignored due to low water electro-osmosis drag force of polymer polybenzimidazole (PBI) membrane. The prediction shows transient in current density which overshoots (undershoots) the stabilized state value when cell voltage is abruptly decreased (increased). The result shows that the peak of overshoot (undershoot) is related with cathode air stoichiometric mass flow rate instead of anode hydrogen stoichiometric mass flow rate. Current is moved smoothly and there are no overshoot or undershoot with the influence of charge double-layer effect. The maximum temperature is located in cathode catalyst layer and both fuel cell average temperature and temperature deviation are increased with increasing of current load.