Anion-exchange membranes for alkaline polymer electrolyte fuel cells: comparison of pendent benzyltrimethylammonium- and benzylmethylimidazolium-head-groupsElectronic supplementary information (ESI) available: Additional details of the methodologies used, additional spectroscopic characterisation data for the membranes, and additional data in support of the small molecule FT-Raman stability tests. A zip file containing the raw spectra (in text format - intensity versus wavenumber) is available.

Radiation-grafted alkaline anion-exchange membranes (AAEM) containing pendent groups with either benzyltrimethylammonium (BTM) or benzylmethylimidazolium (BMI) functionality were successfully synthesised from the same base membrane and with identical ion-exchange capacities. The conductivity of the new BMI-AAEM is comparable to the BTM-benchmark AAEM. The fuel cell performance obtained with the BMI-AAEM was, however, significantly poorer due to in situ AAEM degradation. FT-Raman spectroscopic studies on the stability of the two head-groups at 60 °C in aqueous potassium hydroxide (1 mol dm 3 ) indicates that the BMI-group is intrinsically less chemically stable in strongly alkaline conditions compared to the BTM-benchmark head-group. However, the stabilities of both head-groups are improved when treated at 60 °C in lower pH aqueous carbonate and bicarbonate solutions (1 mol dm 3 ). Contrary to a portion of the prior literature, there appears to be no real advantage in using anion-exchange polymer electrolytes containing pendent imidazolium groups in highly alkaline systems. Alkali stable head-groups for anion-exchange polymer electrolytes. Resolving the conflict in the literature: pendant imidazolium groups are not the answer.