Benzimidazole-cross-linked proton exchange membranes for direct methanol fuel cells

Sulfonated poly(ether ether ketone)s with pendent amino groups (Am-SPEEKs) have been prepared for direct methanol fuel cells (DMFCs). With the goal of improving the dimensional stability and reducing the methanol permeability of membranes, Benzimidazole trimer is synthesized as a cross-linker. The cross-linking reaction is induced by heating at 120 °C for 6 h and then the effects of different contents of cross-linker on the properties of the cross-linking membranes are investigated in detail. Combining covalent cross-linking with ionic cross-linking, the cross-linking network structure causes significant enhancement in oxidative and mechanical property. Meanwhile, water uptake, swelling ratio and methanol permeability of the membranes substantially decrease with increasing the content of cross-linker. Although the conductivity of the membranes is lower than that of the pristine membrane, the relative selectivity is much higher. All the results indicate that the cross-linked membrane is potential candidate as membrane for applications in fuel cells.

► Am-SPEEK with active sites for cross-linking was synthesized successfully.
► Carboxyl-terminated benzimidazole trimer was prepared as cross-linker.
► The cross-linked membranes showed high dimensional stability and fuel resistance.
► The cross-linked membranes showed relative high proton conductivity.