A two-dimensional analysis of mass transport in proton exchange membrane fuel cells

A theoretical model is developed to simulate transport phenomena in a proton exchange membrane fuel cell (PEMFC). The primary focus of this paper is the modelling and assessment of two-dimensional effects neglected in previous studies. The work is motivated by the need to understand the transport processes in fuel cells in order to improve heat and water management, and to alleviate mass transport limitations. The model takes into account diffusion of the humidified fuel (H-2, CO2 and H2O(v)) and oxidant gases (O-2, N-2 and H2O(v)) through the porous electrodes, and convective and electro-osmotic transport of liquid water in the electrodes and the membrane. The thermodynamic equilibrium potential is calculated using the Nernst equation, and reaction kinetics are determined using the Butler-Volmer equation. A finite volume procedure is developed to solve the system of differential equations. The model is validated against available experimental data, and numerical simulations are presented for various one- and two-dimensional isothermal cases. The results indicate that the cathode potential loss, associated with the slow O-2 reaction rate, is dominant at all practical current densities. The simulations also show that two-dimensionality has a significant effect on water management and on some aspects of fuel cell performance. In particular, the anode and cathode water fluxes are found to vary considerably along the oxidant and fuel flow channels, and two new transitional water transport regimes are revealed by the two-dimensional simulations. The influences of flow configuration and electrode porosity on predicted cell performance are also discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.