Low hydrogen permeability and high durability proton exchange membrane with three-dimensional acid-base crosslink structure for water electrolysis

Introducing a acid–base cross-linked network structure and reinforcement layer into a proton exchange membrane (PEM) can effectively improve its performance, durability, and hydrogen permeability for high-pressure PEM water electrolysis (PEMWE). Here, a hyperbranched polymer containing imidazole terminal groups (HBP-MZ) is designed and prepared, then is used to form a novel PEM possessing a cross-linked network structure consisting of HBP-MZ, perfluorosulfonic acid (PFSA) and reinforced with a poly(ether-ether-ketone) (PEEK) mesh. The microstructure of the PEM is characterized using thermal performance analysis. Benefiting from the acid–base crosslinked structure, the obtained PEM has a more compact structure, induces a drastic increase in dimensional stability, mechanical properties, proton conductivity and stability in water. The HBP-MZ/PFSA@PEEK membrane exhibits excellent water electrolysis performance, low high-frequency impedance, and superior stability: the HBP-MZ/PFSA@PEEK membrane provides an electrolytic performance of up to 1.76 V at 2.0 A cm−2 and 1.84 V at 3.0A cm−2 (60 °C, with an IrO2 loading of 1.0 mg cm−2), and exhibits a 6.2 μV h−1 average voltage degradation rate during durability testing. Benefiting from the characteristics of HBP and the existing cross-linked structures, the obtained HBP-MZ/PFSA@PEEK membrane exhibits a lower hydrogen crossover current density of 1.06 mA cm−2 and maintains a lower hydrogen content in oxygen under conditions of high current density and high pressure. This work provides a promising way to prepare a PEM with high durability and low gas permeability that could be applied in high-pressure water electrolysis.