Superprotonic Conduction of Acidified Benzimidazole-Linked Covalent Organic Framework

The development of fast proton-conducting materials above 100 °C with high chemical stability is very challenging but of great significance for proton-exchange membrane fuel cells (PEMFCs). Herein, we demonstrate the first example of benzimidazole-linked COF (PBI-COF) exploited as a fast proton conductor above 100 °C toward PEMFC application. Our PBI-COF integrates the outstanding chemical stability of polybenzimidazoles (PBIs) and the ordered channel structure of COFs to provide a powerful platform to confine and stabilize H3PO4 molecules for proton transport. Upon impregnation with H3PO4, H3PO4@PBI-COF exhibits high proton conductivity (>10–1 S cm–1 above 100 °C), low water swelling, and good long-term durability that is superior to many reported proton conductors. Furthermore, PEMFC with H3PO4@PBI-COF as a solid electrolyte achieves 0.936 V open-circuit voltages and 125 mW cm–2 maximum power densities.