Polymer Nanosphere-Induced Heterogeneous Crosslinking toward Robust Anion Exchange Membranes for Water Electrolysis

Abstract

Anion exchange membranes (AEMs) frequently face trade-off between high hydroxide conductivity and dimensional stability under hydration. Conventional homogeneous crosslinking improves the dimensional stability and mechanical strength of AEMs. However, an excessively high crosslink density may compromise hydroxide conductivity. Here, we propose a polymer nanosphere-induced heterogeneous crosslinking strategy that spatially confines crosslinking to the nanosphere-matrix interfaces, enabling comparable enhancement of dimensional stability with a substantially reduced conductivity penalty relative to conventional homogeneous crosslinking. The ∼16 nm nanospheres, which possess benzyl chloride-rich surfaces, are embedded in a rigid aromatic cationic polymer matrix, where interfacial reactions lead to interface-localized crosslinking at the nanosphere-matrix boundary. The optimized membrane shows a strongly suppressed swelling ratio (SR) of 5.0% at 80 °C (∼70% lower than that of the control) together with a markedly enhanced wet tensile strength of 55.1 MPa (fully hydrated state; 2.7 times that of the control), without compromising hydroxide conductivity (205.7 mS cm^–1 at 80 °C) or alkaline stability. In anion exchange membrane water electrolysis (AEMWE), the optimized membrane delivers 5.29 A cm^–2 at 2.0 V in 1 M KOH at 80 °C.