Simulation for water management in membranes for polymer electrolyte fuel cells

Water management in membranes for polymer electrolyte fuel cells during their operational conditions is considered theoretically. Using a linear transport equation based on the diffusion of water and the electroosmotic drag, analytical solutions for water concentration profiles in the membrane are obtained from which membrane resistance overvoltage and other characteristic values are calculated. Specific parameters of the membranes such as water transference coefficient t(H2O), water permeability L-p, specific membrane conductivity kappa etc., at cell operating temperatures (50 to 80 degrees C) have been obtained from the experiment, and used as input parameters to the analytically derived expressions for water balance calculations. Hydration states of the membrane are simulated for various current densities at the fuel cell operation conditions. The effects of several operational factors of fuel cells on the membrane water content are discussed systematically, among which the membrane thickness and humidification conditions are shown to be the most significant. Contamination of the membrane by foreign impurities turned out to cause a serious problem of the water depletion at the anode side of the membrane. For the purpose of testing the validity of the method, the net water flux and the change in electric resistance inside the membrane are calculated extensively and compared with reported experimental results. The present method turned out to be fairly satisfactory for predictive water management, in spite of its simplicity of the simulation procedure. (C) 1998 Elsevier Science Ltd. All rights reserved.