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

Abstract

The net water drag coefficient () 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, 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 (H2) flow conditions (i.e., flow rate and relative humidity) on under a constant flow condition of cathode air. Measured characteristics of current density ()- in which the relative humidity of discharged H2 from the anode is constant at around 100%, show that is stable when exceeds a certain threshold. The value of in this stable region is particularly sensitive to changes in the stoichiometric ratio of H2. These measurements also suggest that in the stable region, almost the entire area of the membrane is fully hydrated, and the effect of back diffusion on becomes negligible. Analysis of the observed relationships between and several variables indicate that increasing the H2 circulation flow rate effectively prevents anode dry-out.