  This paper explores the mathematical formulations of Fick and Maxwell-Stefan
diffusion in the context of polymer electrolyte membrane fuel cell cathode gas
diffusion layers. Formulations of diffusion combined with mass-averaged Darcy
flow are considered for three component gases. Fick formulations can be
considered as approximations of Maxwell-Stefan in a certain sense. For this
application, the formulations can be compared computationally in a simple, one
dimensional setting. We observe that the predictions of the formulations are
very similar, despite their seemingly different structure. Analytic insight is
given to the result. In addition, it is seen that for both formulations,
diffusion laws are small perturbations from bulk flow. The work is also
intended as a reference to multi-component gas diffusion formulations in the
fuel cell setting.
