The regimes of catalyst layer operation in a fuel cell

A generalized Perry–Newman–Cairns model for performance of a generic catalyst layer (CL) with the Butler–Volmer conversion function is considered. The CL polarization curve, the rate of electrochemical conversion S(x) and the thickness of the conversion domain l∗ are derived for the cases of ideal transport of ions or feed molecules. In both cases, the CL may work in the low- or high-current regime. In the low-current regime with poor ionic transport, l∗ is given by the Newman’s current-independent reaction penetration depth. In the high-current regime, l∗ is inversely proportional to the cell current, regardless of the origin of transport loss. The position and width of the transition region between the low- and high-current branches of the polarization curve are calculated. Based on these results, the features of catalyst layer performance in PEMFC, HT-PEMFC, DMFC and SOFC are discussed.