Oxygen Transport Resistances Induced by Rib/Channel Geometry

The influences of rib/channel geometries on the oxygen transport resistances in a polymer electrolyte fuel cell (PEFC) were investigated through experimental and numerical analyses. A limiting current method was used for evaluating the oxygen transport resistances, which could be separated into two parts. One was macro transport resistances, which were defined as pressure-dependent resistances and the other was micro transport resistances, which were defined as pressure-independent resistances. Both of resistances significantly increased with wider rib/channel widths. Also, the increase in micro transport resistances was more significant than that in macro transport resistances in the lower Platinum (Pt) loading. The numerical model implementing oxygen transport resistances near Pt surface was well correlated with experimental results. The validation results revealed that both in-plane and through-plane reaction distribution became inhomogeneous due to the oxygen concentration distribution induced by rib/channel geometry, resulting in the increase in both oxygen transport resistances. The through-plane reaction distribution also suggested that the micro transport resistances increased due to larger oxygen flux per Pt surface area under low Pt loading. Moreover, the model was applied to verify the impact of oxygen transport resistances on cell performance with lower Pt loading. It was found that the increase in oxygen transport resistances due to larger oxygen flux per Pt surface area lowered the cell performance under high current density operation.