Cyano crosslinked polybenzimidazole membranes containing 4,5-diazafluorene and pyridine for high temperature proton exchange membranes

Cross-linking is an effective way to enhance the mechanical strength of high-temperature proton exchange membranes (HTPEMs). In this study, a series of HTPEMs based on cyano-thermal cross-linked polybenzimidazole (C-PBPBI-xCN) were formulated and synthesized using cyano to achieve cross-linking via a simple heat treatment for the first time. The 4-fluorobenzonitrile was grafted onto the synthesized polybenzimidazole (PBI) containing 4,5-diazafluorene and pyridine, and the cyano-grafted PBI (PBPBI-xCN) membranes were then heat-treated to cross-link the cyano groups to improve the mechanical strength of PBI, resulting in HTPEMs with good mechanical properties without sacrificing considerable proton conductivity. The prepared cyano cross-linked membranes have high oxidative stability, thermal stability, mechanical strength and phosphoric acid retention properties. The proton conductivity of the C-PBPBI-3CN membrane achieved 52.8 mS cm−1 in an anhydrous environment at 180 °C, which is much higher than that of uncured PBPBI-xCN. The maximum output power density of the single cell based on the C-PBPBI-3CN reached 496.2 mW cm−2 at 140 °C.