Highly alkali-stable polyolefin-based anion exchange membrane enabled by N-cyclic quaternary ammoniums for alkaline fuel cells

Polyolefin-based anion exchange membranes (AEMs) have shown great promise in AEM fuel cells thanks to the excellent membrane-forming ability and chemical inertness of all-carbon backbones. Here, we attached alkalistable N-cyclic cations, dimethyl piperidinium (DMP), or 6-azonia-spiro [5.5] undecane (ASU), onto soluble polyolefin backbones to produce highly alkali-stable AEMs. The synthetic procedure included Ziegler-Natta polymerization, azidation, and Cu(I)-mediated azide-alkyne cycloaddition reaction. The as-prepared PBFBDMP or PBFB-ASU copolymers were blended with poly (2,2'-(1,4-naphthalene)-5,5' -bibenzimidazole) (NPBI) polymer to achieve mechanical robust and flexible membranes. Polyolefin-based AEMs and their blend AEMs containing DMP or ASU cations showed superior alkali-resistance with over 91.9% of initial conductivities remaining and no obvious chemical degradation after 95 days (2280 h) of immersion in 1 M NaOH alkaline solution at 80 degrees C as proved by NMR spectroscopy. The blend AEM bearing DMP cations (B-PBFB-DMP) with an ion exchange capacity of 1.54 mmol g(-1) displayed a higher hydroxide conductivity of 65.1 mS cm(-1) at 80 degrees C than the analogue with ASU cations. In a single H-2/O-2 fuel cell, the integration of the B-PBFB-DMP membrane into membrane electrode assemblies resulted in a peak power density of 402 mW cm(-2) under optimized anode humidification. Moreover, the short-term durability of the cell under reduced anode humidification was carried out at 200 mA cm(-2) for 6 h, and post-cell analysis confirmed that no chemical degradation took place for the blend membrane.