Hydrogen fuel cells and water electrolysers that use proton exchange membranes as their electrolyte are well established, but the alternative alkaline anion exchange membrane (AEM) devices offer several advantages, principally the ability to use a broader range of cheaper, non-platinum-group metal electrocatalysts. The two main challenges associated with the design of AEMs are sufficient hydroxide ion conductivity and chemical stability at operational temperatures up to 90 °C. The latter is particularly difficult given that cationic organic head groups are covalently bound to the membrane and these traditionally make good leaving groups for nucleophilic attack or elimination by hydroxide anions. We are engaged in the synthesis of new anion-exchange polymers containing various linkers and cationic groups to yield improved alkali stabilities and conductivities. To achieve this, inexpensive, commercially available ethylene tetrafluoroethylene (ETFE) and low density polyethylene (LDPE) membranes of varying thicknesses are activated by passage through an industrial electron beam in the presence of air. This produces hydroperoxy groups throughout the ETFE membranes, which can be later reacted in radical chain-growth graft polymerisation of vinylbenzylchloride (VBC) monomers and analogues. Subsequent amination yields quaternary ammonium-based AEMs that can conduct hydroxide anions. Recently, we have demonstrated that this grafting process can be carried out in water emulsions which reduces costs and environmental impact and produces higher performance AEMs giving enhanced power densities in H2/O2 fuel cells. We have also shown that N-methylpyrrolidinium is a promising cationic alternative to the benchmark trimethylammonium head group, showing slower alkali degradation at 80 °C. Overall, the development and testing of AEMs with improved alkali stability using improved methods will be reported.

Development of new radiation-grafted alkali-stable anion-exchange membranes for use in alkaline fuel cells and electrolysers

254th National Meeting (2017)

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