Novel hydroxide conducting sulfonium-based anion exchange membrane for alkaline fuel cell applications

•We synthesized sulfonated sulfonium based alkaline polymers.•We achieved 100% conversion of chloromethylation with ZnCl2 and SOCl2.•Increasing concentration of sulfonium improves ionic conductivity.•Membranes showed good performance with high ion conductivity.

Sulfonium-based high performance alkaline polymer electrolyte was successfully synthesized from commercial poly (ether sulfone) by first inducting the chloromethyl groups and thereby functionalization with dimethyl sulfide. Novel anion exchange membranes were obtained by an anion exchange with 1.0 M KOH. Lewis acid (zinc chloride, ZnCl2) catalyzed chloromethylation reaction was performed using chloromethyl methyl ether and thionyl chloride. The prepared tertiary sulfonium functionalized alkaline poly(ether sulfone) membrane exhibited outstanding solubility in polar aprotic solvents; thus, the flexible and tough membranes could be prepared by casting from the DMSO solution. The resulting ionomer membrane showed hydroxide conductivity above 10−2 mS cm−1 at room temperature with the ion exchange capacity value of 1.37 mmol g−1. The chemical structure of the chloromethylated polymer and polymer electrolyte were identified by 1H NMR. The polymer membrane will be characterized by FT-IR, thermogravimetric analysis (TGA), ion exchange capacity (IEC), water uptake and hydroxide conductivity assessment.

Graphical abstractAnion conductive copolymer membrane was synthesized by successive chloromethylation, substitution with dimethyl sulfide and ion exchange reactions of the commercially available poly(ether sulfone) PES. Chloromethylation was important in giving quantitative tertiary sulfonium cation and also the subsequent ion exchange reactions. We performed the chloromethylation reaction using thionyl chloride as an activating agent of the Lewis acid ZnCl2 catalyst. This makes the chloromethylation reaction faster and 100% conversion to target yield. the tertiary sulfonium functionalized poly (ether sulfone) membranes developed here could potentially be more effective in fuel cells under basic conditions.Figure optionsDownload full-size imageDownload as PowerPoint slide