A Sulfonated Polybenzimidazole Membrane Incorporating a Sulfonated Covalent Organic Framework to Enhance Proton Conductivity for Water Electrolysis

Proton exchange membranes (PEMs) featuring exceptional proton conductivity and robust mechanical strength are essential for diverse electrochemical energy devices. Herein, we synthesized sulfonated polybenzimidazole (SPBI) and incorporated a sulfonated covalent organic framework (COF) with densely aligned sulfonic acid (−SO 3 H) groups into the SPBI to fabricate hybrid membranes. The abundant –SO 3 H groups on the COF backbone not only construct continuous hydrogen-bond networks but also form acid–base pairs with the imidazole groups on SPBI, synergistically enhancing proton conductivity. Besides, the hydrogen-bonding and electrostatic interactions between the COF and SPBI improve the mechanical strength of the PEMs. Consequently, the optimal hybrid membrane achieves a proton conductivity of 588.0 mS cm –1 (80 °C, 100% RH) and a mechanical strength of 119.3 MPa, which enables it to deliver 1.04 A cm –2 at 2.0 V in PEM water electrolysis and maintain stable operation over 220 h in pure water at 1 A cm –2 and 80 °C.