A two dimensional agglomerate model for a proton exchange membrane fuel cell

A two dimensional steady state and isothermal model of a proton exchange membrane fuel cell is presented. This model is applied to a fuel cell with a counter-flow mode of hydrogen and air along parallel flow channels. In the flow channel and porous media, reactant flow is modelled using the continuity and Navier-Stokes equation. Reactant diffusion and convection are modelled by the Maxwell-Stefan and Navier-Stokes equation, respectively. Water transport is described by the combined mechanism of electro-osmotic drag, back diffusion and hydraulic permeation. The catalyst layer is modelled as a spherical-agglomerate structure in which ionomer and liquid water partially occupy the void space to form a so-called carbon-ionomer-liquid water film inside the agglomerate. A mathematical relationship for the variation in film thickness with the current density is also developed. The effect of platinum and carbon loadings on the cell performance and effectiveness are simulated. The fuel cell polarisation curve based on the agglomerate with a film model gives good agreement to experimental data while the agglomerate without a film model overestimates the current density. The modelling results show that the rapid fall in current density at lower cell voltage is due to an increased oxygen diffusion resistance through the film.