Alkaline imidazolium- and quaternary ammonium-functionalized anion exchange membranes for alkaline fuel cell applications

Alkaline imidazolium-type ionic liquids (ILs) and quaternary ammonium salt functionalized alkaline anion-exchange membranes (AEMs), with the same ion exchange capacity (IEC), were synthesized via in situ cross-linking of styrene, acrylonitrile, 1-methyl-3-(4-vinylbenzyl)imidazolium chloride ([MVBIm][Cl]), and N,N,N-trimethyl-1-(4-vinylphenyl) methanaminium chloride ([TMVPMA][Cl]), respectively. The water uptake, swelling ratio, conductivity, and alkaline stability of resultant cross-linked copolymer membranes were investigated. Both types of copolymer membranes exhibit hydroxide conductivity above 10−2 S cm−1 at room temperature. Alkaline imidazolium-type IL functionalized membranes showed an excellent chemical stability of up to 1000 h without obvious loss of ion conductivity, whereas the membranes based on quaternary ammonium salts degraded in high pH solution because of nucleophillic substitution on quaternary ammonium cations. The results of this study suggest that the AEMs based on alkaline imidazolium-type ILs are expected to promote the widespread use of alkaline fuel cells.