Synthesis and properties of phenylindane-containing polybenzimidazole (PBI) for high-temperature polymer electrolyte membrane fuel cells (PEMFCs)

A thermally stable and organo-soluble phenylindane-containing polybenzimidazole (phenylindane-PBI) was synthesized from 3,3′,4,4′-tetraaminobiphenyl and 1,1,3-trimethyl-3-phenylindan-4′,5-dicarboxylic acid using polyphosphoric acid (PPA) as both solvent and dehydrating agent. Polymerization conditions were carefully investigated to achieve high molecular weight polymers (IV = 1.00 dL g−1). To study the effects of backbone structure on properties, meta-PBI was also synthesized in PPA. It was found the introduction of rigid bent phenylindane moiety into the polymer backbone greatly improved the polymer solubility in polar aprotic solvents. The fabrication of acid-doped phenylindane-PBI membranes was attempted by both sol-gel and acid imbibing processes. The membranes prepared by the latter method showed a maximum proton conductivity of 0.061 S cm−1 at 180 °C with a phosphoric acid doping level of 10.0 PA/RU. Both phenylindane-PBI and meta-PBI membranes were fabricated into membrane electrode assemblies (MEAs) and tested to evaluate their fuel cell performance. The phosphoric acid doped phenylindane-PBI membrane exhibited comparable fuel cell performance as meta-PBI under similar testing conditions, demonstrating that it is a promising polymer electrolyte membrane candidate for high-temperature fuel cell applications.