Electro‐osmotic Drag Coefficient of Water and Methanol in Polymer Electrolytes at Elevated Temperatures

The electro‐osmotic drag coefficient of water in two polymer electrolytes was experimentally determined as a function of water activity and current density for temperatures up to 200°C. The results show that the electro‐osmotic drag coefficient varies from 0.2 to 0.6 in Nafion®/ membrane electrolyte, but is essentially zero in phosphoric acid‐doped FBI (polybenzimidazole) membrane electrolyte over the range of water activity considered. The near‐zero electro‐osmotic drag coefficient found in PBI indicates that this electrolyte should lessen the problems associated with water redistribution in proton exchange membrane fuel cells.