Two-dimensional finite-element method study of the resistance of membranes in polymer electrolyte fuel cells

A two-dimensional model of fluid flow, mass transport and electrochemistry is presented to examine the effect of current density and cell pressure on the resistance of Nation 117 membranes in polymer electrolyte fuel cells. The finite element method is used to solve the continuity, potential and Stefan-Maxwell equations in the flow channel and gas diffusion electrode regions and the concentrated solution theory equations in the membrane region. Model calculations for concurrent flow indicate that current density and water flux through the membrane are non-uniform and reach a minimum at the bottom of the membrane near the gas exit. A comparison of model results to membrane resistance measurements in the literature is discussed. The multidimensional nature of transport within the fuel cell is described and plots of flow streamlines, gas mole fractions and membrane water content are shown. The boundary condition for water transport across the active catalyst layer is examined.