Stable hydroxide anion exchange polymerized ionic liquid
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abstract
Recently, anion exchange membranes (AEMs) that can conduct hydroxide (OH) anions have been explored for use in alkaline fuel cells (AFCs) due to their potential advantages over proton exchange membrane fuel cells (PEMFCs), such as facile electrokinetics allowing the use of non-noble metal catalysts and a wider range of fuels. Other benefits include reduced fuel crossover and improved water management. However, one critical issue limiting the application of AEMs in AFCs is the stability due to the nucleophilicity and basicity of the hydroxide anion that can lead to known degradation pathways for the cation, such as b-hydrogen elimination (Hofmann), direct nucleophilic attack of the a-carbon (SN2), and ylide formation. In particular, in the absence of water, OH- ions are not well solvated and can lead to faster degradation of the counter cation. As a consequence, AEMs are usually stored in the presence of water to prevent fast degradation. In this work, we report a dry-stable imidazolium-based polymerized ionic liquid (PIL), 1-[(2-methacryloyloxy)ethyl]-3-butylimidazolium hydroxide (poly(MEBIm-OH)), which shows considerably enhanced stability under dry conditions. Carbonate (CO32-) and bicarbonate (HCO3-) anion exchange PILs, which are known to form in the presence of carbon dioxide, were also investigated to compare with poly(MEBIm-OH).
