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

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 H ₂ 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 (RH _A ) and that the control of RH _A is an effective method for lowering {α}_NWD at elevated temperature operation.