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

摘要

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% O_2 + 95% He, N_2 or C_3F_8). 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 k_m, and, gas phase Knudsen and solid phase ionomer diffusion k_(e+K) respectively increased by 20% and a factor of ～2. Below 0.6 V, the k_m and k_(e+K) increase is relatively smaller and is ascribed to the larger heat generation, local temperature and diffusion coefficients. The increase in k_m and k_(e+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.