Stable alkoxy chain enhanced anion exchange membrane and its fuel cell

In order to investigate the effect of side-chain position and polarity on the performance of anion exchange membrane (AEM), we design and fabricate a series of AEMs with alkyl extender (i.e. the cation's “tail”), alkyl additional side-chain (i.e. the cation's “neighbor”), alkoxy extender, alkoxy additional side-chain, and side-chain-free structure, which are named MImPSf-EC (EC = alkyl extender), MImPSf-AC (AC = alkyl additional side-chain), MImPSf-EO (EO = alkoxy extender), MImPSf-AO (AO = alkoxy additional side-chain) and MImPSf (side-chain-free), respectively. Our results indicate that both additional side-chain and alkoxy chain can promote micro-phase separation, and improve water uptake and conductivity of AEMs, which follow the order of MImPSf-AO > MImPSf-EO > MImPSf-AC > MImPSf > MImPSf-EC at similar ion exchange capacity (IEC). The AEM containing additional alkoxy chain, i.e. MImPSf-AO-150% exhibits the highest water uptake (77.6%) and hydroxide conductivity (23.7 mS/cm) at 30 °C. Compared with others, the alkoxy-containing AEM gives rise to higher H2/O2 fuel cell peak power density (404 mW/cm2 for MImPSf-AO and 383 mW/cm2 for MImPSf-EO) and longer durability (137 min for MImPSf-AO and 133 min for MImPSf-EO at 100 mA/cm2) at similar IEC due to its good hydrogen bond network and high stability of alkoxyl chain (both experimentally and theoretically confirmed). Our work demonstrates the advantage of alkoxy chain in AEMs as a partial replacement of degraded cationic groups so that the integrity of ion transport channel can be maintained, and fuel cell durability can be improved.