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 À3) 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 À3). 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.

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Novel anion exchange membranes (AEMs), based on poly(phenylene oxide) (PPO) chains linked to pendant 1,2-dimethylimidazolium (DIm) functional groups, have been prepared for evaluation in alkaline polymer electrolyte membrane fuel cells (APEFCs). Successful functionalisation of the PPO chains was confirmed using H-NMR and FT-IR spectroscopies. The ionic conductivities of the resulting DIm-PPO AEMs at 30 °C are in the ranges of 10-40 mS cm and 18-75 mS cm at 60 °C. The high ionic conductivities are attributed to the highly developed microstructures of the membranes, which feature well-defined and interconnected ionic channels (confirmed by atomic force microscopy, AFM, measurements). Promisingly, the ion-exchange capacities (IECs) of the DIm-PPO AEM are maintained after immersion in an aqueous KOH solution (2 mol dm) for 219 h at 25 °C; a previously developed monomethyl imidazolium PPO analogue AEM (Im-PPO) showed a significant decline in IEC on similar treatment. This reduction in undesirable attack by the OH conducting anions is ascribed to an increase in steric interference and removal of the acidic C2 proton [in the monomethyl Im-groups] by the methyl group in the DIm cationic ring. Moreover, the maximum power densities produced in simple beginning-of-life single cell H /O fuel cell tests increased from 30 mW cm to 56 mW cm when switching from the Im-PPO AEM (fuel cell temperature = 50 °C) to the DIm-PPO-0.54 AEM (fuel cell temperature = 35 °C) respectively (even with the use of lower temperatures). This journal is © The Royal Society of Chemistry 2013

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