Effect of Flow Conditions of Anode Hydrogen on Net Water Drag Coefficient of Polymer Electrolyte Fuel Cells

The net water drag coefficient (alpha(NWD)) is supposedly an essential index in water management, and must be negative for system operation for polymer electrolyte fuel cell (PEFC) systems. In this study, alpha(NWD) is carefully examined by measurement of the water content in the gases supplied to and those discharged from the cell/stack under gas supply conditions similar to those in a real PEFC system. We focus on the effect of anode hydrogen (H-2) flow conditions (i.e., flow rate and relative humidity) on alpha(NWD) under a constant flow condition of cathode air. Measured characteristics of current density (i)-alpha(NWD) in which the relative humidity of discharged H-2 from the anode is constant at around 100%, show that alpha(NWD) is stable when i exceeds a certain threshold. The value of alpha(NWD) in this stable region is particularly sensitive to changes in the stoichiometric ratio of H-2. These measurements also suggest that in the alpha(NWD) stable region, almost the entire area of the membrane is fully hydrated, and the effect of back diffusion on alpha(NWD) becomes negligible. Analysis of the observed relationships between alpha NWD and several variables indicate that increasing the H-2 circulation flow rate effectively prevents anode dry-out. (c) 2022 The Electrochemical Society ( "ECS "). Published on behalf of ECS by IOP Publishing Limited.