SIMULATION FOR WATER MANAGEMENT IN MEMBRANES FOR POLYMER ELECTROLYTE FUEL-CELLS

Water management in membranes for polymer electrolyte fuel cells durin g their operational conditions is considered theoretically. Using a li near transport equation based on the diffusion of water and the electr oosmotic drag, analytical solutions for water concentration profiles i n the membrane are obtained from which membrane resistance overvoltage and other characteristic values are calculated. Specific parameters o f the membranes such as water transference coefficient t(H2O), water p ermeability L-p, specific membrane conductivity kappa etc., at cell op erating temperatures (50 to 80 degrees C) have been obtained from the experiment, and used as input parameters to the analytically derived e xpressions for water balance calculations. Hydration states of the mem brane are simulated for various current densities at the fuel cell ope ration conditions. The effects of several operational factors of fuel cells on the membrane water content are discussed systematically, amon g 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 depletio n at the anode side of the membrane. For the purpose of testing the va lidity of the method, the net water flux and the change in electric re sistance inside the membrane are calculated extensively and compared w ith 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.