Polymer Electrolyte Fuel Cell Model Research Articles

Polymer electrolyte fuel cell operating with nickel foam-based gas diffusion layers: A numerical investigation

Due to their outstanding structural, transport and electrical characteristics, nickel foams serve as excellent candidate materials for gas diffusion layers (GDLs) in polymer electrolyte fuel cells (PEFCs). In this work, a new three-dimensional PEFC model was developed to explore the local and global fuel cell performance with nickel foam-based GDLs. The fuel cell operating with nickel foam GDLs was shown to have, due to its superior mass and charge transport properties, higher oxygen and water concentration and current density compared to that operating with the conventional carbon fibre-based GDLs. The results show that the pumping power should be taken into account when optimising the dimensions of the flow channels and as such the net power density must be the criterion for optimisation. The optimal dimensions of the flow channels for the fuel cell operating with nickel foam based GDLs were found to be 0.25 mm for the channel height and 1 mm for the channel width; the maximum net power density with these dimensions was around 0.95 W/cm2 which is two times higher than that operating with carbon fibre based GDLs. All the results have been presented and critically discussed.

WO x /Pt(111) Prepared As PEFC Model Anode Catalyst: Surface Structure and Suppressed Hydrogen Peroxide Generation

Introduction To achieve prolonged lifetime of polymer electrolyte fuel cell (PEFC), hydrogen-peroxide (H2O2)-induced chemical degradation of polymer electrolyte membrane (PEM) is a crucial problem. In general, oxygen (O2) crossover from cathode to anode through the PEM yields H2O2 generation on Pt/C anode catalyst surface through 2-electron pathway of O2 reduction reaction. Thus, mitigation of H2O2 generation on Pt/C surface is a key to suppress the PEM degradation. Trogadas and Ramani reported tungsten trioxide (WO3) addition to Pt/C suppressed H2O2 generation.1 The results suggest that the cooperation of Pt nanoparticles and WO3 located near-by should be effective for suppression of H2O2 generation. However, influence of the oxidation states of tungsten oxide (WO x ) on H2O2 generation at the Pt surface is not fully resolved. Furthermore, it was reported that, although fully oxidized WO3 is stable in acid solution (pH < 2),2 sub-oxides of tungsten (WO x ) could dissolve in Pt-WO x electrochemical system.3 Thus, electrochemical dissolution behaviors of WO x located on Pt substrate surface should be investigated in detail. In this study, we prepare Pt(111) surface that modified by WO x having different oxidation states, and investigated the electrochemical H2O2 generations. Experimental Pt(111) single crystal substrate surface was cleaned by repeated cycles of Ar+ sputtering and annealing in an ultrahigh vacuum (UHV; ~10-8Pa). Subsequently, WO x was deposited on the cleaned Pt(111) via an arc-plasma deposition (APD) method using a W target under partial pressures of O2 (p(O2) = 1×10-1 or 1×10-3 Pa) at ca. 298 K. Deposition amounts of the WO x was estimated to be ca. 1.5 µg/(cm2 of substrate) by using a quartz crystal microbalance installed in the UHV chamber. Then, WO x -modified Pt(111) were annealed at 703 K for 10 min. in UHV. Hereafter, the fabricated samples are referred to as p(O2)-WO x /Pt(111). X-ray photoelectron spectroscopy (XPS) was conducted for the as-fabricated samples in situ in UHV.H2O2 generation amounts were evaluated by the tip generation/substrate collection mode of scanning electrochemical microscope (SECM)4 in O2-saturated 0.1 M HClO4. Generated H2O2 was detected by a Pt tip micro-electrode (diameter: ca. 20 µm, tip potential: 1.26 V vs. RHE) positioned ca. 50 µm at surface normal of the sample electrodes, with sweeping sample electrode potential (E S) at sweep rate of 2 mV/s in negative going direction. Thereafter, potential cycles (PCs: 0.05–1.0 V vs. RHE, sweep rate: 100 mV/s, 100 cycles) were applied to the sample surfaces; then, H2O2 generation was re-evaluated. Finally, the PCs-applied sample surfaces were re-introduced to the UHV chamber to perform XPS measurements. Results and Discussion XP spectra of W4f bands for the as-fabricated and PCs-applied sample surfaces are summarized in Figure. 1 (A). Considering peak areas of deconvoluted components (solid lines), the oxidation states of WO x as-fabricated can be judged mainly to be W6+ and Wx+ (x < 4) for 10-1 Pa-WO x /Pt(111) (a) and 10-3 Pa-WO x /Pt(111) (c), respectively.Figure. 1 (B) shows SECM-estimated H2O2 generations of the WO x /Pt(111) surfaces before (as-fabricated) and after the 100 PCs. As for the as-fabricated surfaces (solid lines), H2O2 detection current (i T) of the Pt tip micro-electrode normalized by respective sample electrode current (i S) is lower for 10-1 Pa-WO x /Pt(111) than 10-3 Pa-WO x /Pt(111), yet normalized i T/|i S|-values for both surfaces are smaller than that of clean Pt(111). The results show that surface modification of Pt(111) by the small amount of WO x , particularly with higher oxidation states, effectively suppressed H2O2 generations. However, the suppression effect degraded by the 100 PCs application for both the electrode surfaces (dotted lines). Compared of W4f bands for the PCs-applied surfaces (Figure. 1 (A) (b, d)) with corresponding as-fabricated ones (a, c), the bands shifted to negative- and positive-binding-energies for 10-1 Pa-WO x /Pt(111) and 10-3 Pa-WO x /Pt(111), respectively, indicating respective reduction and oxidation of the surface WO x by the PCs. In addition, W4f bands for both surfaces decreased in intensity by the PCs application, suggesting decrease in surface amount of the WO x , probably through electrochemical dissolution during the PCs. The PCs-induced changes in oxidation states and amounts of surface WO x should correlate to the degraded H2O2 generation suppressions. Acknowledgement This study was supported by the new energy and industrial technology development organization (NEDO) of Japan, JSPS KAKENHI Grant Number JP21H01645, and JST SPRING Grant Number JPMJSP2114. References P. Trogadas and V. Ramani, J. Electrochem. Soc., 155, B696–B703 (2008).M. Anik and K. Osseo-Asare, J. Electrochem. Soc., 149, B224 (2002).A. J. Martín, A. M. Chaparro, and L. Daza, J. Power Sources, 196, 4187–4192 (2011).C. M. Sánchez-Sánchez and A. J. Bard, Anal. Chem., 81, 8094–8100 (2009). Figure 1

The effects of GDL anisotropic transport properties on the PEFC performance

PurposeThis paper aims to numerically investigate the impact of gas diffusion layer (GDL) anisotropic transport properties on the overall and local performance of polymer electrolyte fuel cells (PEFCs).Design/methodology/approachA three-dimensional numerical model of a polymer electrolyte fuel cell with a single straight channel has been developed to investigate the sensitivity of the fuel cell performance to the GDL anisotropic transport properties – gas permeability, diffusivity, thermal conductivity and electrical conductivity. Realistic experimentally estimated GDL transport properties were incorporated into the developed PEFC model, and a parametric study was performed to show the effect of these properties on fuel cell performance and the distribution of the key variables of current density and oxygen concentration within the cathode GDL.FindingsThe results showed that the anisotropy of the GDL must be captured to avoid overestimation/underestimation of the performance of the modelled fuel cell. The results also showed that the fuel cell performance and the distributions of current density and oxygen mass fraction within the cathode GDL are highly sensitive to the through-plane electrical conductivity of the GDL and, to a lesser extent, the through-plane diffusivity, and the thermal conductivity of the GDL. The fuel cell performance is almost insensitive to the gas permeability of the GDL.Practical implicationsThis study improves the understanding of the importance of the GDL anisotropy in the modelling of fuel cells and provides useful insights on improving the efficiency of the fuel cells.Originality/valueRealistic experimentally estimated GDL transport properties have been incorporated into the PEFC model for the first time, allowing for more accurate prediction of the PEFC performance.

Modeling of Fuel Cell Stack for High-Speed Computation and Implementation to Integrated System Model

:1-dimentional (1D) modeling methods of fuel cell stack are investigated. To ensure numerical simulation of life-long system operation in permissible calculation time and accuracy, physical/empirical models of mass transfer, heat transfer, and electrochemistry in fuel cell stack with proper resolution are developed. These models are validated and verified by the actual fuel cell system data collected in a variety of operating conditions, such as low to high loads, operating temperatures, and total pressures. Modeling and implementation: For a high-speed computation, 2D (along-the-channel + across-the-channel distribution) model was reduced to 1D (across-the-channel distribution) model by introducing weighting function for state variables at inlet and outlet of the fuel cell stack (flowrate, pressure, temperature, and molar fractions of gaseous species), as shown in Fig.1.The physics implemented in the fuel cell stack model are listed in Table 1. Of the models listed in the table, the short-circuit current model, effective enthalpy voltage model, and direct-combustion reaction model were newly developed and implemented. The other models were employed from the representative literature [1][2][3][4]. The model parameters were calibrated by the microscopic measurement results of geometrical structures as well as electrochemical test results measured at a variation of current, gas composition, humidity, and temperature using small cells [5][6].For reducing the computational load, the models were integrated based on a discrete-time explicit numerical solver without any iterative calculations for numerical convergence. To achieve high accuracy even in such a simple framework of the numerical solving methods, the features of mass transport dynamics were expressed by discrete first-order lag model with the unique time-constants, which were determined empirically. All the models were implemented on MATLAB/SIMULINK platform and the interface of the fuel cell stack model was designed so that it could be easily integrated with the balance-of-plants models (air-supply, hydrogen-supply, and cooling subsystems) and the existing libraries of the fuel cell system controllers. Results and discussion Extensive testing was conducted and a lot of validation data were collected in the variety of operating conditions such as low to high loads, operating temperatures, and total pressures. The validation data were utilized for the validation of the fuel cell stack model accuracy and modeling strategies.An example of the validation results is shown in Fig.2. Time-series data of the interfacial conditions of the fuel cell stack (current, temperature, flowrate, pressure, and gas composition) are inputted to the fuel cell stack model, and voltage and resistance are calculated by the model. Then, calculated and measured values are compared. Newly developed models (the short-circuit current model, effective enthalpy voltage model, and direct-combustion reaction model) were found to be beneficial to close a gap of the acceleration / deceleration transient features between dynamic fuel stack responses in the validation data and the calculation results.The computational time of the numerical simulation is listed in Tables 2 and 3. A considerable reduction in computation time (more than 50-times faster than real time) was confirmed even under the standard-performance computational resources. References R.B. Bird, W.E. Stewart, E.N. Lightfoot, Transport Phenomena, Revised Second Edition, John Wiley & Sons, New York (2006).S.V. Patankar, Numerical Heat Transfer and Fluid Flow, McGraw–Hill, New York (1980).T.E. Springer, T.A. Zawodzinski, and S. Gottesfeld, “Polymer electrolyte fuel cell model”, J. Electrochem. Soc., 138(8), 2334–2342 (1991).D.M. Bernardi and M.W. Verbrugge, “A mathematical model of the solid-polymer-electrolyte fuel cell,” J. Electrochem. Soc., 139(9), 2477–2491 (1992).T. Tsukamoto et al., “Three-dimensional numerical simulation of full-scale proton exchange membrane fuel cells at high current densities,” J. Pow. Sour., 588, 229412 (2021).N. Nonoyama et al., “Analysis of oxygen-transport diffusion resistance in proton-exchange-membrane fuel cells,” J. Electrochem. Soc., 158(4), B416–B423 (2011). Figure 1

Temperature control strategy for polymer electrolyte fuel cells

A polymer electrolyte fuel cell (PEFC) is an electrochemical device that converts chemical energy directly to electrical energy, and its performance greatly depends on its operating temperature. Therefore, in this paper, a novel thermodynamic PEFC model with the airflow cooling method is firstly developed for the PEFC system. Then, a novel model predictive control (MPC) controller is designed to control the stack temperature at an optimal value by adjusting the air flow rate on the basis of the developed thermodynamic PEFC model. The thermodynamic PEFC model and the designed controlling strategies are simulated and analysed in Matlab/Simulink. Three tests are conducted to estimate the reliability of the developed controllers concerning different operating conditions: (a) typical perturbation in the current load, (b) any perturbation in the current load, and (c) variation of the ambient temperature. The simulation results demonstrate that the MPC controller can effectively control the stack temperature at the desired value. Moreover, the MPC controller shows much superior effects compared with the conventional proportional integral derivative (PID) controller. In addition, the developed coolant circuit model can be easily applied to various PEFC systems. The MPC controller shows potential also for other controlling issues of PEFC systems due to its strong robustness and fast response.

Dynamic modelling and controlling strategy of polymer electrolyte fuel cells

A comprehensive dynamic control oriented model of a polymer electrolyte fuel cell (PEFC) is developed, considering the mixed effects of temperature, gas flow and capacitance. The fractional relationship between the dynamic output voltage and the capacitance, which escaped the attention in most previous studies is also addressed. Moreover, based on the developed PEFC model, a proportional integral and derivative (PID) controller is designed to stabilize the output voltage at a determined value by regulating the input hydrogen mass flow rate under a series of disturbance in the input. The dynamic PEFC model and controller are simulated in Matlab/Simulink. The simulation results illustrate that the PEFC system model is capable of characterizing dynamic properties of PEFCs. Additionally, the developed PID controller is effective in stabilizing the output voltage with a rather small overshoot and rather faster response, which also proves that the developed model is suitable for PEFC control algorithms development.

(Invited) Perspective on Modeling in Proton Exchange Membrane Fuel Cells

Following their use in the Gemini space program (1965-66), proton exchange membrane fuel cell (PEMFC) technology languished. Los Alamos National Laboratory (LANL), and more specifically Shimshon Gottesfeld’s group, was instrumental in the resurgence of PEMFCs. Polymer Electrolyte Fuel Cell Model,[i] has been cited more than 2000 times since 1991 and exemplifies the influence that Gottesfeld’s group had on the community during his roughly two decades at LANL. Remarkable advances have subsequently been made in modeling of PEMFCs, arguable greater than those seen in the lithium-ion battery field. The focus of this presentation is to connect the broader work of Gottesfeld’s group on PEMFCs to the field of modeling of fuel cells and to offer a perspective on the remaining barriers and opportunities, and specifically those for the catalyst layer, nearly 30 years after Springer et al.’s seminal paper. [i] Springer, T. E., Zawodzinski, T. A. & Gottesfeld, S. Polymer Electrolyte Fuel-Cell Model. J Electrochem Soc 138, 2334-2342 (1991).

Implications of inherent inhomogeneities in thin carbon fiber-based gas diffusion layers: A comparative modeling study

Thin porous media are present in multiple electrochemical energy devices, where they provide key transport and structural functions. The prototypical example is gas diffusion layers (GDLs) in polymer-electrolyte fuel cells (PEFCs). While modeling has traditionally been used to explore PEFC operation, this is often accomplished using volume-averaged (VA) formulations, where the intrinsic inhomogeneities of the GDL are smoothed out and the lack of defining a representative elementary volume is an ever-present issue. In this work, the predictions of a single-phase VA PEFC model are compared to those of a pore-scale PEFC model using GDL tomograms as a part of the meshed domain to delineate important aspects that VA models cannot address. The results demonstrate that while VA models equipped with suitable effective properties can provide a good average estimate for overall performance, the lack of accounting for real structures limits their predictive power, especially for durability and degradation behavior where large deviations are found in the spatial distributions. Furthermore, interfacial effects between the GDL and the microporous layer are explored with the pore-scale model to understand the implications of the layered geometry. It is shown that the actual microstructure of the GDL/MPL transition region can significantly affect the fluxes across the sandwich, something that VA models cannot easily consider. Interfacial design is recognized as a key quality control parameter for large-scale MEA manufacturing and assembly.

(Invited) Open-Source Macro- and Meso-Scale Modeling of PEFCs

Since the early polymer electrolyte fuel cell (PEFC) mathematical modeling studies of Springer and Bernardi and Verbrugge [1], a variety of steady-state and transient PEFC models have emerged in the literature, see [2] and references within. Fuel cell modeling results have highlighted the importance of multi-dimensional effects (e.g., dead-zones under the land area [3]), coupled physical processes (e.g., heat-pipe effects [4]), liquid water accumulation, and interfacial effects (e.g., water/channel/porous media interactions [5]). Even though substantial progress has been made in developing meso- and macro-scale models, a generally accepted PEFC model does not yet exist, even for dry conditions. The absence of such model is due to: a) multiple scales under consideration, i.e., from nanometers in the catalyst layer to millimeters in the channel; b) the complex heterogeneous materials used; and, c) the coupled physical processes occurring inside the PEFC. The small number of experimental validation techniques used, and the limited number of comparative numerical modeling studies has also contributed to the disagreement between modeling approaches. A common platform for numerical modeling of fuel cells is essential in order to integrate new models, compare and assess the validity of existing ones on a one-to-one basis, and eventually, to perform fuel cell design and optimization studies. Our research group has developed an open-source mathematical modeling platform for the analysis of polymer electrolyte fuel cells, i.e., OpenFCST [6]. This modeling platform has been implemented using object-oriented concepts in order to develop a toolbox with multitude of physical models, such as multi-step reaction kinetics, gas, liquid and ion transport equations. It is also capable of handling various theoretical representations of the main layers in a fuel cells, for example, the catalyst layer can be analyzed with either a macro-homogeneous or an agglomerate model. Users can easily modify the mathematical formulation for an individual physical model while maintaining all other models and parameters the same. In this talk, the general architecture of OpenFCST and the new models implemented since its first release in 2013 [6] will be discussed. OpenFCST will be used to analyze several recently proposed mathematical models for fuel cells. Critical to improving PEFC mathematical models is the development of: 1) methodologies to estimate macro-scale reaction and transport properties based on meso- and micro-scale information of the heterogeneous materials, such as micro-scale imaging, electrode kinetic mechanisms, and pore-size distributions; 2) accurate transport models for multi-component gas transport, and multi-phase flow; and, 3) improved models for the interfaces between layers in the membrane electrode assembly (MEA) and also between the MEA and the channel. In this talk, new advances in micro-scale simulations using FIB-SEM data in OpenFCST that include voxel meshing and a morphological image opening algorithms will be presented and used to estimate effective transport properties of CL under dry and wet conditions [8]. A multi-dimensional, two-phase, non-isothermal membrane electrode assembly model in OpenFCST that includes a dual wettability pore-size distribution model will be described and compared to: a) experimental performance, water fluxes and temperature and saturation distributions, and b) to the common saturation-based, two-phase flow transport model in porous media. The pore-size distribution model is shown to be able to identify when liquid water would start leaving the cell, and possible discontinuities in the saturation profiles inside the MEA. A key issue in two-phase flow models is the channel/GDL interface. A two-phase flow finite element formulation that uses two independent meshes for air and liquid will also be described and used to study droplet dynamics in a channel [5].

Evaluate the Validity of Electrochemical Impedance Measurements of Polymer Electrolyte Fuel Cells using a Computational Algorithm based on Fast Fourier Transform

The validity of electrochemical impedance measurements of polymer electrolyte fuel cells (PEFCs) have to be evaluated before an attempt is made to interpret the electrochemical mechanisms represented in the Nyquist plot. This evaluation can be carried out by data transformation of impedance measurements using Kramers-Kronig (K-K) relations. However, this evaluation has been commonly neglected in the fuel cell area due to the complexity of applying the mathematical K-K relations to real-world impedance measurements. In this study a computational algorithm, based on the Fast Fourier Transform (FFT) theory, the Hilbert transformation of impedance data, and a validated impedance model for PEFCs, for evaluating data transformation (real to imaginary Z’→Z’’ and imaginary to real Z’’→Z’) and hence validity of impedance measurements of PEFCs has been developed in Matlab®. With this computational algorithm it is possible to identify the factors that lead to incorrect EIS measurements of PEFCs such as inductance effect from the electrical cables of the measurement system, incorrect AC amplitude signal, and instability during EIS measurements. The computational algorithm developed in this study enables more accurate impedance results to be obtained to study the performance and state of health of PEFCs.

Numerical evaluation of a dual-function microporous layer under subzero and normal operating temperatures for use in automotive fuel cells

In a previous study, we proposed a dual-function microporous layer (MPL) to improve the cold-start capability of polymer electrolyte fuel cells (PEFCs). The conceptual MPL design is to use an ionomer-based binder with low Pt loading, thereby allowing the MPL to provide additional volume for ice storage during cold-start PEFC operations. Although the benefit of using a dual-function MPL was numerically elucidated in our previous study, the question regarding the use of this new MPL under normal PEFC operation remains to be addressed. In this paper, we extend our discussion to the effects of a dual-function MPL under subzero to normal operating temperatures. The three-dimensional (3D) cold-start PEFC model developed in our previous study is modified for transient PEFC simulations to consider a wide range of operating temperatures from −20 °C to 80 °C. Simulation results show a negligible performance drop at the normal PEFC temperature of 80 °C, because of the presence of the dual-function MPL in a PEFC membrane electrode assembly. In addition, water back flow from the cathode to anode is reduced on using the dual-function MPL, owing to the additional water uptake driven by its ionomer content. This study clearly demonstrates that this dual-function MPL technology may be applied to automotive PEFC stack development without sacrificing fabrication cost and cell performance during normal PEFC operations.

A domain decomposition method for a two‐phase transport model of polymer electrolyte fuel cell containing micro‐porous layer

SUMMARYIn this paper, a nonlinear Dirichlet–Robin iteration‐by‐subdomain domain decomposition method is studied for a multidimensional, multiphysics, and multiphase model of polymer electrolyte fuel cell (PEFC) containing micro‐porous layer (MPL). Across the interface of gas diffusion layer and MPL in PEFC, it is well known that the capillary pressure is continuous, whereas liquid saturation is discontinuous, by which the liquid‐water removal in the porous electrodes can be significantly enhanced. We design a type of non‐overlapping domain decomposition method to deal with water transport in such multi‐layer diffusion media, where Kirchhoff transformation and its inverse techniques are employed to conquer the discontinuous and degenerate water diffusivity in the coexisting single‐phase and two‐phase regions. In addition, the conservation equations of mass, momentum, charge, and hydrogen and oxygen transport are also solved by the combined finite element–upwind finite volume method (FEM/FVM) to overcome the dominated convection effect in gas channels. Numerical simulations demonstrate that the presented techniques are effective in obtaining a fast and convergent nonlinear iteration for such a 3D PEFC model within around 50 steps, in contrast with the oscillatory and nonconvergent iteration conducted by standard FEM/FVM. A series of numerical convergence tests are also carried out to verify the efficiency and accuracy of the present numerical techniques. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Evaluating cold-start behaviors of end and intermediate cells in a polymer electrolyte fuel cell (PEFC) stack

In a polymer electrolyte fuel cell (PEFC) stack, the end cells immediately adjacent to the end plates of a stack usually exhibit different cell behaviors compared to its intermediate cells. In this study, cold-start behaviors of end and intermediate cells in a fuel cell stack are numerically examined by using the three-dimensional cold-start PEFC model. The cold-start simulations show that the ice fraction in the end cell grows much faster than in the intermediate cell, indicating that the heat loss through stack end plate to the ambient is critical, determining the fate of cold-start whether cell shutdown or successful startup. As a consequence, under the assumed cold-start condition (start-up from −20°C and 100mA/cm2), the end cell experiences a sudden voltage drop and cold-start failure due to considerable ice filling in the cathode catalyst layer (CL) whereas a successful startup is achieved in the intermediate cell because its temperature increases faster than the rate of ice growth and finally exceeds freezing temperature.

Performance evaluation of a polymer electrolyte fuel cell with a dead-end anode: A computational fluid dynamic study

The operation of polymer electrolyte fuel cell (PEFC) with a dead-end anode requires careful gas and water management to achieve optimal operating performance. The amount of water accumulated in the anode and nitrogen crossover are particularly important factors. To ascertain ( i) the behavior of a PEFC with a dead-end anode, ( ii) the accumulation of water and nitrogen in the anode cell with time, and ( iii) efficient purging strategies to manage the gas and water, a transient PEFC model with a dead-end anode was developed and analyzed. The model assumes a two-phase flow and solves the governing equations of conservation of mass, momentum, species, energy, charge, coupled with a phenomenological membrane model and agglomerate model for catalyst layer. The model results indicate that water and nitrogen can accumulate in the anode region with time, such that the amount of available hydrogen decreases and hence the cell performance drops. The accumulation rate is found to be closely linked to the current that is drawn from the cell. Further, it is found that to alleviate the problem of build-up of nitrogen and water, the purge frequency and duration of the purge play important roles in affecting cell performance. The transient behavior and impact of the relevant operating conditions obtained from the simulation results can be used for development of efficient purging strategies.

A numerical investigation of the effects of GDL compression and intrusion in polymer electrolyte fuel cells (PEFCs)

The purpose of this work is to numerically investigate the effects of non-uniform compression of the gas diffusion layer (GDL) and GDL intrusion into a channel due to the channel/rib structure of the flow-field plate. The focus is placed on accurately predicting two-phase transport between the compressed GDL near the ribs and uncompressed GDL near the channels, and its associated effects on cell performance. In this paper, a GDL compression model is newly developed and incorporated into a comprehensive three-dimensional, two-phase PEFC model developed earlier. To assess solely the effects of GDL compression and intrusion, the new fuel cell model is applied to a simple single-straight channel fuel cell geometry. Numerical simulations with different levels of GDL compression and intrusion are carried out and simulation results reveal that the effects of GDL compression and intrusion considerably increase the non-uniformity, particularly, the in-plane gradient in liquid saturation, oxygen concentration, membrane water content, and current density profiles that in turn results in significant ohmic and concentration polarizations. The present three-dimensional GDL compression model yields realistic species profiles and cell performance that help to identify the optimal MEA, gasket, and flow channel designs in PEFCs.

Polymer Electrolyte Fuel Cell Transport Mechanisms: A Universal Approach to Multilayer Two-Phase Modeling Through the General Transport Equation

A mathematical multilayer, multispecies two-phase model for polymer electrolyte fuel cells (PEFCs) is presented based on fundamental molecular theory using the general transport equation (GTE). The GTE was previously developed and applied to bridge the gap that exists between the benchmark modeling philosophies in the literature for transport across the PEFC. In the current work, the GTE is applied with Darcy’s law to describe water transport and water uptake through the porous and quasiporous layers of a PEFC under single- and two-phase operating conditions. The characteristic transport equations and available material properties from the literature are translated into a single-cell fuel cell model, which is implemented using the object modeling technique. The PEFC model is applied to predict and validate the net water transport ratio and water content under a range of operating conditions. The numerical model exhibits good agreement with experimental data under both vapor- and liquid-equilibrated conditions. The model is then applied in a water transport study to determine the effects of cell compression on local water content, liquid water intrusion, water transport, and Ohmic resistance across nonreinforced polymer electrolyte membranes (PEMs) under two-phase operating conditions. The modeling results suggest that the presence of liquid water at the cathodic boundary of the PEM and a well-established liquid water network can affect water uptake and water transport and can reduce the Ohmic resistance of the PEM.

Numerical analysis of gas crossover effects in polymer electrolyte fuel cells (PEFCs)

The gas crossover phenomenon in polymer electrolyte fuel cells (PEFCs) is an indicator of membrane degradation. The objective of this paper is to numerically investigate the effects of hydrogen and oxygen crossover through the membrane in PEFCs. A gas crossover model is newly developed and implemented in a comprehensive multi-dimensional, multi-phase PEFC model developed earlier. A parametric study is carried out to investigate the effects of the crossover diffusion coefficients for hydrogen and oxygen as well as the membrane thickness. The simulation results demonstrate that the hydrogen crossover induces an additional oxygen reduction reaction (ORR) and consequently causes an additional voltage drop, while the influence of oxygen crossover on PEFC performance is relatively insignificant because it leads to the hydrogen/oxygen chemical reaction at the anode side. Finally, using the time-dependent gas crossover data that are available in the literature (measured in days), we conduct gas crossover simulations to examine the effects of increased gas crossover due to membrane degradation on PEFC performance and successfully demonstrate decaying polarization curves with respect to time. This study clearly elucidates the detailed mechanisms of the hydrogen and oxygen crossover phenomena and their effect on PEFC performance and durability.

Modeling the cation transport in an operating polymer electrolyte fuel cell (PEFC)

A computational fluid dynamics model is developed to investigate the multicomponent cation transport in polymer electrolyte membranes and to predict the performance degradation of the polymer electrolyte fuel cell (PEFC) due to the cationic contamination. A Maxwell–Stefan approach is implemented by modifying the Nernst–Planck equations to model the multicomponent cationic species transport in the membrane. Langmuir isotherms are used to model the non-ideal species adsorption in the membrane. Cation transport model shows good agreement with the experimental data found in the literature. Following the validation of the cation transport model, it is incorporated in a PEFC model framework, which solves for mass, momentum, species and charge conservations. Both fuel side and air side impurities are considered in analyses, which show that for air side impurities current density drops from 0.9 to 0.7 A/cm 2 whereas for fuel side impurities current density drops to impractical values as low as 0.05 A/cm 2, at the steady-state. Effect of cationic impurity on water transport in the membrane is also investigated and found that cathode dry-out occurs due to decreased water generation in case of fuel side contamination.

On a Pioneering Polymer Electrolyte Fuel Cell Model

Polymer Electrolyte Fuel Cell Model is a seminal work that continues to form the basis for modern modeling efforts, especially models concerning the membrane and its behavior at the continuum level. The paper is complete with experimental data, modeling equations, model validation, and optimization scenarios. While the treatment of the underlying phenomena is limited to isothermal, single-phase conditions, and one-dimensional flow, it represents the key interactions within the membrane at the center of the PEFC. It focuses on analyzing the water balance within the cell and clearly demonstrates the complex interactions of water diffusion and electro-osmotic flux. Cell-level and system-level water balance are key to the development of efficient PEFCs going forward, particularly as researchers address the need to simplify humidification and recycle configurations while increasing the operating temperature of the stack to minimize radiator requirements.

Empirical modeling of a polymer electrolyte fuel cell based on water transport investigation and current interrupt measurement

Water management is an important factor in the optimal performance of a polymer electrolyte fuel cell (PEFC). In this paper, a PEFC model that facilitates the control of PEFC membrane humidity is presented. An efficient modeling procedure using a combination of mathematical and experimental techniques is proposed. A simple mathematical structure for the model is adopted, and experiments to measure PEFC irreversibilities and net water transport across the membrane electrode assembly (MEA) are performed. The developed PEFC model effectively quantifies the irreversibilities in the PEFC output voltage and clarifies the relationship between PEFC performance and steady state water transport through the MEA. The proposed modeling procedure can effectively save time and cost during the controller / control algorithm design phase in PEFC system development.