Enhancing Proton Conductivity and Durability of Crosslinked PBI-Based High-Temperature PEM: Effectively Doping a Novel Cerium Triphosphonic-isocyanurate

Abstract

Acid doping is an effective way to enhance the proton conduction of high temperature polybenzimidazole (PBI) based proton exchange membranes (HTPEMs). To overcome the problem of acid leaching from the membranes, a cerium triphosphonic-isocyanurate (Ce-TOPT) proton conductor was synthesized and doped into a crosslinked PBI backbone (c-mPBI). The TOPT organic compound contains three –PO3H2 groups, which can be complexed with high valent metal ions (Ce4+/3+, Zr4+, Fe3+) to ensure its water-insolubility. Ce-TOPT(1:2) exhibited high ion exchange capacity (IEC, up to 2.2 meq. g−1) and good thermal stability. The organic-inorganic Ce-TOPT shown a high doping level in c-mPBI/CeTOPT membranes and consequently high proton conductivity of the membranes at high temperature and low relative humidity (RH). At 180 °C, the conductivity of c-mPBI/CeTOPT(50) could reach 0.125, 0.0885 and 0.0363 S cm−1 at 100% RH, 50% RH and anhydrous conditions, respectively. After water-washing for 48 h, the proton conductivity loss of c-mPBI/CeTOPT(50) was 4.6%. The good mechanical properties, proton conductivity, durability and membrane selectivity indicate that the crosslinked PBI-based membrane doped with Ce-TOPT is a potential candidate as HTPEMs.