Gas Purge in a Polymer Electrolyte Fuel Cell

Gas purge intended to minimize residual water in the membrane, porous electrodes, and gas diffusion layers is critical for successful start-up of a polymer electrolyte fuel cell (PEFC) from subfreezing temperatures. A basic understanding of the physical phenomena involved in gas purge, required to establish effective and energy-saving purge protocols, is necessary. In this work, we present a physical model describing water removal from a PEFC during gas purge. Various stages of gas diffusion layer (GDL) and membrane drying are characterized, and the variations along the flow direction are considered and emphasized. The predicted GDL drying time constant is compared to the tomographic experiments with good agreement. The effect of purge conditions on purge effectiveness is elucidated. It is found that low relative humidity of purge gas, high gas flow rate, and high cell temperature favor effective purge.