(Invited) Stable and Conductive Anhydrous Proton Conducting Membranes Based on Polycations Blended with Polybenzimidazole

Abstract

This talk primarily focuses on anhydrous, mild temperature (100 to 250 °C) proton conductors composed of polycation polymers, typically used as anion exchange membranes, blended with polybenzimidazole (PBI). These moderate temperature membranes are envisioned for fuel cell systems that operate with hydrogen from steam-reformed methane. Evaluating polycation membrane variants alone demonstrated lower proton conductivity when compared to PBI doped with phosphoric acid (H3PO4) and sulfuric acid. PBI doped with phosphoric acid, on the other hand, was observed to be unstable above 160 °C because of H3PO4 boiling and evaporation. Plus, the PBI-H3PO4membrane loses its acid due to leaching if condensed water is present (i.e., lack of robust operation if the cell drops below 100 °C). To overcome these problems, polycation polymers, were blended with polybenzimidazole (PBI) and these membranes routinely showed conductivity values as high as 0.18 S cm-1and were stable under dry and wet conditions and with thermal stability up to 250 °C. These membrane composites were also assessed with other types of doped acids (e.g., phosphoric acid, methanesulfonic acid, p-toulenesulfonic acid, trifluoroacetic acid, and sulfuric acid) to promote the Faradaic reaction kinetics at low pH (i.e., pH values below 0). The talk will close with our recent efforts to pattern polymer electrolyte membrane surfaces to make high surface area bipolar junction interfaces. It is envisaged that an acidic anode and alkaline cathode with a bipolar membrane offers a pathway forward for very low platinum loading fuel cells. Figure 1