Numerical analysis of gas cross-over through the membrane in a proton exchange membrane fuel cell

Mass transport phenomena through the membrane have the major role in performance of a proton exchange membrane (PEM) fuel cell. Water is transported through the membrane due to diffusion, convection and electro-osmotic drag. Normally it is assumed that the membrane is impermeable against gases. Strictly speaking there are some amount of solute gases in liquid water which move within the membrane and reach to the other side. For example, oxygen dissolves into the water at cathode catalyst. Most of this oxygen reacts with proton and produces electricity. But some oxygen molecules diffuse toward anode side and react directly with hydrogen at anode catalyst. This process leads to waste of energy since direct reaction releases energy in form of heat. In this paper these processes have been studied. We have developed a two-dimensional numerical model using full Navier-Stokes equations and species transport equations of hydrogen, oxygen and water. It was found that cross-over of reactant gases has a considerable effect on cell energy efficiency in some common cases.