Constructing unique carboxylated proton transport channels via the phosphoric acid etching of a metal–organic framework in a crosslinked branched polybenzimidazole

Abstract

The construction of proton transport channels in proton exchange membranes (PEMs) is an effective strategy by which to improve their performance. In this work, the metal–organic framework (MOF) UIO-66-NH₂ was introduced to a branched polyether polybenzimidazole (BOPBI) to achieve their crosslinking using a silane crosslinking agent. The structure of the designed MOF can be destroyed using phosphoric acid (PA), with the complete release of the carboxyl groups in the ligand from the surface of Zr²⁺. This preparation resulted in unique carboxylated proton transport channels being constructed in a crosslinked branched PBI membrane for the first time. The combination of unique carboxylated proton transport channels and a silica crosslinked structure led to the formation of a membrane with a high proton conductivity (0.084 S cm⁻¹) and PA retained in the structure. A hydrogen/oxygen (H₂/O₂) cell based on the membrane exhibited a high peak power density of 750 mW cm⁻² at 180 °C and outstanding long-term stability, with a loading voltage drop rate of 10 μV h⁻¹ at 160 °C over 387 h of operation. Furthermore, these excellent characteristics of the novel porous PBI membranes with carboxylated proton transport channels enabled the resulting high-temperature PEMs (HT-PEMs) to operate under a wide range of conditions at temperatures in the range of 80–180 °C without external humidification. This work is thus of great significance to accelerating the commercialization application of PA–PBI HT-PEMs.