Side-chain sterically induced directional units construct stable and continuous ion transport channels for anion exchange membranes

Abstract

Improving the hydroxide conductivity and dimensional stability of anion exchange membranes (AEMs), while retaining their high alkaline stability, is essential for AEM water electrolysis (AEMWE). Herein, a novel design strategy is proposed for perfluorinated ionomer by introducing sterically induced directional units (SIDUs) at the termini of pendant side chains to achieve superior performance in both conductivity and stability. The design is centered on introducing an appropriate amount of rigid bulk benzyl groups based on fluorinated ionomer segments to driven the directional aggregation of cationic groups, thus enabling the construction of continuous and stable ion transport channels. The resulting Perfluorinated-tribenzyls AEM (PFTQ), by forming continuous and stable ionic channels that significantly enhance OH⁻ and H₂O mobility, exhibit an over 46 % and 65 % increase in self-diffusion coefficient compared to Perfluorinated-propyl AEM (PFPQ), achieving an exceptional conductivity of 167 mS cm⁻¹ at 80 °C with a swelling ratio as low as 19 %. Moreover, the robust C–F bond backbone, coupled with the protective effects of SIDUs through electron-donating and steric hindrance on the cationic groups, allows the PFTQ with negligible degradation at 80 °C in 6 M KOH over 400 h. Based on this rational design, we achieved a high alkaline water electrolysis performance of 3.6 A cm⁻² at 2.0 V and demonstrated durability of over 500 h at 1 A cm⁻² at 80 °C. This study demonstrates that the AEM design strategy based on the introduction of SIDUs has significant potential in achieving excellent energy efficiency and extended stability for electrolyzers.