Transport phenomena in elevated temperature PEM fuel cells

There is a recognized need for operation of polymer electrolyte membrane (PEM) fuel cells at higher than 80°C for automotive applications. Electrochemically, higher temperature results in better kinetics of oxygen oxidation reaction but more difficult membrane hydration. These consequences call for a detailed study of electrochemical and transport phenomena at such operating temperatures. In this work, a three-dimensional, nonisothermal model was used to investigate the performance of PEM fuel cells operating at 95°C under various operating conditions. The numerical model is first validated against experimental data for a 25 cm2 cell, after which a detailed analysis of species, heat, and charge transport is presented based on a single-channel unit cell. A brief study of the effect of flow-field design on cell performance is also presented. Numerical studies reveal that at 95°C operation, oxygen transport and its depletion along the flow direction play a critical role in cell performance, even under low humidity conditions.