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

Abstract

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 alkali-stable 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 PBFB-DMP 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 °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 °C than the analogue with ASU cations. In a single H2/O2 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.