A Study on the Bypass Flow in a Gas Diffusion Layer of a PEMFC With Serpentine Flow Channels

The serpentine channel widely employed in fuel cells has a strong pressure gradient between adjacent channels in specific regions. Due to the pressure gradient, some amount of reactant gas can be delivered to a catalyst layer by convection as well as diffusion processes in a gas diffusion layer (GDL). The enhancement of the convective flow, so-called bypass flow affects performance of a PEMFC since the bypass flow can lead to significant concentration loss at the downstream of the gas channel. The purpose of the present paper is to examine the effect of the bypass flow in the GDL on performance of a PEMFC with serpentine channels. By performing three-dimensional numerical simulation, we have investigated the bypass flow in the GDL and its effects on the distribution of reactant concentration and local current density. Three-dimensional Navier-Stokes equations are solved with the source and sink terms associated with the electrochemical reactions in the fuel cell. Several values of GDL permeability have been tested to see the effects of GDL permeability on the bypass flow for different cathode stoichiometry rate. The present numerical results show that, with increasing GDL permeability, local current density distribution changes significantly and becomes more inhomogeneous.