(20f) High Temperature Proton Exchange Membrane Based on Polycation – Polybenzimidazole Blends

Phosphoric acid doped polybenzimidazole (PA – PBI) has been the most commonly used membrane for high temperature polymer electrolyte membrane fuel cell and hydrogen pump applications. Some of the limitations of PA – PBI arise from their weak acid – base interaction leading to PA loss under two scenarios: i.) temperatures above 180 °C that causes PA evaporation and ii.) low humidity operations were water supplants PA favorably within the acid-doped membrane matrix. PA doped polycation based membranes exhibit strong cation-anion pair electrostatic interactions that aid in PA retention up to 220 °C and curtail PA loss in the presence of water. However, several PA-polycations variants examined in our lab display lower proton conductivity when compared to PA – PBI because the PBI host features a higher PA loading and in essence a higher effective ion-exchange capacity (i.e., more imidazole groups per tethered cation groups).

This talk will discuss a new class of high temperature anhydrous proton conducting membrane based upon PA – PBI – polycation blends. The polycation is based upon quaternary benzyl pyridinium polysulfone. The blended membranes doped with PA displayed proton conductivity up to 0.28 S cm^-1 with stability up to 240 °C. Similar proton conductivity results were attained for thin film ionomer variants implying that this material, unlike Nafion, does not lose its proton conductivity under thin film confinement in electrode layers. Finally, the talk will present fuel cell, electrolysis, and supercapacitor device performance at temperatures well above 100 °C demonstrating the versatility and effectiveness of these new membrane and solution processable ionomer binder materials.