Constructing Zn (II)-based MOF1-assisted sulfonated polyether ether ketone electrolyte membrane for excellent proton conductivity and stability toward PEM fuel cell applications

Developing a highly conductive proton exchange membrane (PEM) with high thermal and mechanical stability is crucial for enhanced fuel cell performance and durability. In this work, a highly efficient SPEEK/MOF1 PEM was fabricated by incorporating a thermally and dimensionally stable zinc-based proton-conductive MOF1 with a uniform distribution and early water evaporation inhibition, due to the strong hydrogen bonding interaction, and compact and nanoporous structure. The extra proton sites and the three-dimensional hydrogen bonding network of the anionic [Zn2(ox)3]2− and cationic [(Me2NH2)3(SO4)]+ framework in MOF1 enhance proton transfer during hydrous, anhydrous, and partially hydrated states through Grotthuss and vehicle mechanisms. Impedance spectroscopy analysis showed that one wt% MOF1 in SPEEK (SPEEK/1% MOF1 membrane) obtained 25% and 106% higher hydrous proton conductivity over the neat SPEEK membrane at 25 and 80 °C, respectively. Interestingly, at 150 °C and 0, 30, and 60% RH, the binary membrane yielded 5.6, 10, and 1.4 times more conductivity than the pure membrane, respectively. Consequently, the SPEEK/1% MOF1 membrane displayed 2.9-fold higher power density along with superior voltage stability than the pure membrane. Furthermore, reduced water absorption and swelling were observed, which increases the membrane's dimensional stability. Mechanical testing reveals an improvement in maximum tensile strength, from 40.6 MPa for the plain SPEEK to 48.95 MPa for the hybrid membrane, due to the reinforcement effect of the well-dispersed MOF1 filler in the SPEEK backbone. This work demonstrates a facile synthesis of MOF1-doped SPEEK to develop a composite PEM with remarkable properties, offering a promising alternative to PEMFCs.