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The work is devoted to a computational study of three types of cationic polymeric membranes in Li + -ionic form, in water and methanol environments, at various solvation levels. The studied membranes Nafion, IonClad, and M3 possess the perfluorinated backbone; however, various side chains were terminated with the functional groups of distinctly different ionic strength. The paper discusses the structural features of the membrane-solvent clusters as well as an influence of the side chain nature on the dissociation of the functional groups and the binding energy of the solvent molecules. Additionally, the paper compares the obtained results for Li + -Nafion membrane in water with the results published earlier for H + and Na + forms.

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Available online xxxKeywords: Polymer electrolyte fuel cell Nafion degradation Modelling Computational fluid dynamics Local operating condition a b s t r a c t The paper describes a development of a degradation model, which enables to predict timedependent changes in performance of a polymer electrolyte fuel cell. The developed model consists of two main parts: 1) a new semi-empirical model taking into account changes in physico-chemical properties of a polymer electrolyte membrane operating in the fuel cell, 2) a validated CFD model computing the 3D performance of the cell. In the semi-empirical model, the degradation rates of the membrane thickness and conductivity depend on the oxygen crossover rate. The acid group concentration is calculated from the membrane conductivity based on the percolation theory approach. The gas diffusion coefficients are modelled empirically as a function of the membrane thickness. The model of the membrane degradation is coupled with the CFD model and applied to analyse the cell behaviour as a function of time. The simulation shows that the cell current density decreases faster with lowering relative humidity and increasing temperature. The in-plane degradation of the membrane is non-uniform and depends on the local operating condition.

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The PEM fuel cell simulation package developed by AVL List GmbH is coupled with a semi‐empirical degradation model describing the dependency of material parameters on operating conditions. The CFD model calculates the 3D distributions of electronic/ionic potentials, velocity, pressure, phase volume fractions, gas species mass fractions, and temperature in all solids and fluids of PEM fuel cell stacks, as well as water concentration and hydraulic pressure in the membrane. The degradation model modifies membrane and catalyst layer parameters according to local operating conditions and given operating time during the simulation run‐time. Calculated distributions of current density and temperature are compared to experimental data of an air‐cooled PEM fuel cell stack obtained with segmented measurement plates. For the validation of the degradation model, calculated current density decay vs. operating time are compared to through‐life polarization measurements. The good agreement between measurement and simulation demonstrates the ability of the model to predict the complex physical phenomena taking place in PEM fuel cells with high accuracy.