PEMFC Reactant Mass Transfer Coefficient Measurement and Separation – Method Extension to the Mixed Kinetic and Mass Transfer Control Regime

Abstract

A kinetic and mass transfer model for a proton exchange membrane fuel cell (PEMFC) current distribution was derived and validated with data obtained with a dilute oxygen stream and three diluents (5 % O2 + 95 % He, N2 or C3F8). The overall mass transfer coefficient k increased by a factor of ~2 to ~4 with a decrease in cell potential from 0.75-0.8 to 0.2 V. Mass transfer coefficients pertaining to gas phase molecular diffusion km , and, gas phase Knudsen and solid phase ionomer diffusion ke +K respectively increased by 20 % and a factor of ~2. Below 0.6 V, the km and ke +K increase is relatively smaller and is ascribed to the larger heat generation, local temperature and diffusion coefficients. The increase in km and ke +K between 0.75 and 0.6 V is relatively larger and is attributed to the development of steep oxygen and diluent concentration gradients affecting oxygen movement.