Optimized Ion-Transport Properties of Diallylammonium-Cyclopolymerized Anion-Exchange Membranes for High-Performance Water Electrolysis

Abstract

Anion-exchange membranes (AEMs) are the key components of AEM-based water electrolysis (AEMWE) for green hydrogen production. Unfortunately, many AEMs have unsatisfactory ion conductivity, and the factors governing their ion transport remain unclear. To address these limitations, herein, a new pyrrolidinium-containing diallylammonium-cyclopolymerized (PDT) AEM is proposed. Cyclopolymerization between diallyldimethylammonium chloride and tetraallylammonium bromide (TAAB, crosslinker) monomers in a porous polytetrafluoroethylene support yielded a pore-filled crosslinked PDT membrane, whose structure is controlled by adjusting its TAAB content. The OH⁻ conductivity of the PDT membrane is more strongly correlated with its OH⁻ diffusivity (determined by its internal water content) than its OH⁻ partitioning (determined by its internal charge content). The optimized PDT membrane exhibited low gas crossover and high thermomechanical stability. Importantly, it displayed excellent AEMWE performance in both pure water (0.71 A cm⁻² at 1.8 V) and 1 m KOH (5.25 A cm⁻² at 1.8 V) at 80 °C with half-platinum-group metal electrodes, outperforming many previously reported and commercial AEMs, owing to its significantly high OH⁻ conductivity. The PDT membrane also demonstrated stable AEMWE performance in 1 m KOH at 60 °C for 300 h. This study offers an effective means to fabricate high-performance AEMs and sheds light on their ion-transport mechanisms.