Covalently cross-linked proton exchange membranes based on sulfonated poly(arylene ether ketone) and polybenzimidazole oligomer

To prepare a novel covalently cross-linked proton exchange membrane with high proton conductivity, sulfonated poly(arylene ether ketone)s bearing carboxylic acid groups (SPAEK-C) and o-diamino functional polybenzimidazole oligomers (PBI) were consequently synthesized. Then the SPAEK-C/PBI blend membranes were dried at 110 °C for 3 h to induce cross-links between amino groups of PBI oligomer and carboxylic acid groups of SPAEK-C. 1H NMR measurements and Fourier transform infrared spectroscopy were used to characterize and confirm the structures of SPAEK-C, PBI oligomers and the cross-linked membranes. The cross-linked membranes were immersed in various concentrations of phosphoric acid solution to enhance proton conductivity. These H3PO4 doped SPAEK-C/PBI membranes displayed comparable or even higher proton conductivity than that of Nafion 117, especially under low humidity conditions. Moreover, the water uptake, acid uptake, mechanical and thermal stability were also investigated in detail.