Two‐phase flow model of the cathode of PEM fuel cells using interdigitated flow fields

Abstract

When interdigitated gas distributors are used in a PEM fuel cell, fluids entering the fuel cell are forced to flow through the electrodes porous layers. This characteristic increases transport rates of the reactants and products to and from the catalyst layers and reduces the amount of liquid water entrapped in the porous electrodes thereby minimizing electrode flooding. To investigate the effects of the gas and liquid water hydrodynamics on the performance of an air cathode of a PEM fuel cell employing an interdigitated gas distributor, a 2‐D, two‐phase, multicomponent transport model was developed. Darcy's law was used to describe the transport of the gas phase. The transport of liquid water through the porous electrode is driven by the shear force of gas flow and capillary force. An equation accounting for both forces was derived for the liquid phase transport in the porous gas electrode. Higher differential pressures between inlet and outlet channels yield higher electrode performance, because the oxygen transport rates are higher and liquid water removal is more effective. The electrode thickness needs to be optimized to get optimal performance because thinner electrode may reduce gas‐flow rate and thicker electrode may increase the diffusion layer thickness. For a fixed‐size electrode, more channels and shorter shoulder widths are preferred.