Polybenzimidazole and Phosphonic Acid Groups-Functionalized Polyhedral Oligomeric Silsesquioxane Composite Electrolyte for High Temperature Proton Exchange Membrane

Here, we report composite membrane consisting of poly[2,2'-(m-phenylene)-5,5'-(bibenzimidazole)] (PBI) and polyhedral oligomeric silsesquioxane functionalized with phosphonic acid groups (PO(OH)(2)-POSS) for high temperature proton exchange membrane. similar to 7 phosphonic acid groups are incorporated into the phenyl rings of POSS via bromination in a high yield (similar to 93%), followed by substitution of the bromine elements by phosphonate ester groups via a Pd(0) catalyzed P-C coupling reaction. Phosphonic acid groups are formed by the hydrolysis of the phosphonate ester groups in hydrobromic acid solution. At a 50 wt% of PA content in the membranes, PBI/PO(OH) 2-POSS composite membrane shows larger proton conductivity of 3.2 x 10(-3) S cm(-1) than 2.8 x 10(-3) S cm(-1) of PBI membrane at 150 degrees C and anhydrous conditions, owing to the multiple phosphonic acid groups of PO(OH)(2)-POSS that can function as proton transport medium at high temperature and low humidity conditions.