On the permeability of gas diffusion media used in PEM fuel cells

The current work investigates laminar channel flow in square serpentine channels mounted on a permeable gas diffusion media (GDM) as in the case of a PEM fuel cell. Computational fluid dynamics is used to determine the importance of convective transport as a function of GDM permeability. Both isotropic and orthotropic permeabilities are considered and it is found that the in-plane permeability is the parameter of importance. For typical flow field dimensions and fuel cell operating conditions, it is found that convective transport will occur in the GDM when the permeability exceeds 1×10−13 m2. This value is lower than that reported experimentally, meaning that convection is significant in fuel cell GDM. Currently, virtually all fuel cell modelling work either implicitly or explicitly ignores this effect. Finally, it is noted that the in-plane permeability is the relevant parameter in these configurations. This is particularly relevant in the case of GDM with micro-porous layers which decrease the through-plane permeability by several orders of magnitude but do not change in the in-plane permeability.