Engineering crystallinity and hydrated ion clusters via branched design for anion exchange membranes in water electrolysis

The shortage of anion-exchange membranes (AEMs) with both high hydroxide conductivity and stable physicochemical properties remains a major impediment to the development of high-performance anion-exchange membrane water electrolysis (AEMWE) technology. Herein, we designed a series of branched AEMs with specific spatial configurations at the molecular level to tackle such a dilemma. The core of rational design is incorporated rigid, non-rotatable, single-bonded branched monomers and spirobisindane-co-terphenyl structures to modulate branched rotational freedom and microphase separation. The low rotational freedom branched structure improves local chain stacking, enhances the crystallinity, and forms a dense network of interconnected micropores. Furthermore, the delicate design regulates the hydrated ionic cluster aggregation state, reducing the OH^- diffusion barriers within the polymer networks. Well-designed AEMs exhibit a low swelling ratio (<18.0%) even with high water uptake (94.2%-101.3%) at 80°C, while possessing high conductivity (165.4 mS cm⁻¹) and stabilizing in 1 M KOH for 1200 h. Impressively, the AEM was used to construct an IrO₂ anode AEMWE cell, which exhibits a performance of 4 A cm^-2 at 2.0 V and more than 500 h of stable operation at 1 A cm^-2. This study provides insights into the design of high-performance AEMs for energy conversion devices.