Net Water Drag Coefficient during High Temperature Operation of Polymer Electrolyte Fuel Cells

Abstract

For polymer electrolyte fuel cell (PEFC) systems in vehicle applications, net water drag coefficient ( α NWD ) is an essential index and must be negative for system operation. The feasibility of PEFC operation at temperatures over 100 °C was examined here by measuring and comparing the current density (j)— α NWD characteristics using PEFCs with either an Aquivion or Nafion membrane. The effect of cell temperature ( T cell ) on α NWD was evaluated at T cell range from 80 °C to 120 °C. Results clearly demonstrated that, for both membrane types, α NWD significantly increased with increasing T cell . Results also confirmed that, at a constant flow rate of H2 at the anode, α NWD decreased with decreasing stoichiometric ratio of air ( γ air ), although the effect of γ air on α NWD was relatively small. Finally, the effect of relative humidity (RH) balance of supplied gases in both sides (anode/cathode) on water transport at temperature up to 120 °C was examined for the Aquivion cell. Results revealed that α NWD could be significantly decreased by decreasing the RH of hydrogen supplied to the anode (RHA) and that the control of RHA is an effective method for lowering α NWD at elevated temperature operation.