Alkaline durable 2-methylimidazolium containing anion-conducting electrolyte membranes synthesized by radiation-induced grafting for direct hydrazine hydrate fuel cells

Through the radiation-induced grafting of 2-methyl-N-vinylimidazole (MNVIm) and styrene (St) into a poly(ethylene-co-tetrafluoroethylene) film, polyvinylimidazolium hydroxide-grafted anion-conducting polymer electrolyte membranes (AEMs) (MNVIm/St-AEM (OH)) were prepared to prevent two main degradation routes of an imidazolium group (i.e., β-elimination and ring opening hydrolysis reactions). The treatment of MNVIm/St-AEM with a MNVIm/St molar ratio of 6/4 and an ion-exchange capacities (IEC) of 2.08 mmol g−1 in short time in 1 M potassium hydroxide (KOH) at 80 °C converted part of imidazolium units to ethene monomer units (En), resulting in the formation of terpolymer-grafted membranes (MNVIm/En/St-AEM) (41/26/33) with an IEC of 1.05 mmol g−1. The MNVIm/En/St-AEM (initial conductivity: 53 mS cm−1) maintained conductivity levels of higher than 10 mS cm−1 for 600 h in 1 M KOH and 1300 h with an actual fuel of 5% hydrated hydrazine in 1 M KOH at 80 °C, respectively. By using copoly(N-vinyl-2-methyl-3-hexylimidazolium hydroxide-co-St) ionomer with a polymer structure similar to that of the MNVIm/St-AEM graft copolymer, the MNVIm/St-AEM demonstrated a maximum power density of 230 mW cm−2 in a direct hydrazine hydrate fuel cell. This power density is more than three times higher than that assembled with the N-vinylimidazole containing AEM (NVIm/St-AEM).