Synergistic coupling of spirobifluorene-based 3D rigid branched backbone and flexible ethoxy-containing side chains for anion exchange membranes

Abstract

The creation of anion exchange membranes (AEMs) that integrate high ionic conductivity with excellent dimensional stability is crucial for facilitating the efficiency improvement of AEM fuel cell systems. We proposed a molecular synergistic strategy to fabricate high-performance AEMs, which combines the directed dipole behavior of flexible ethoxy side chains with the steric hindrance originating from three-dimensional (3D) rigid branched monomers. A three-dimensional rigid polymer backbone containing spirobifluorene units was grafted with cationic ethoxy side chains. The cation-dipole interaction induces microphase separation and builds continuous, efficient hydroxide (OH − ) ion transport channels. Based on this strategy, a range of poly(p-terphenyl-isatin-spirobifluorene) PTI-SP X -O AEMs were successfully prepared. The 3D branched structure restricts polymer chain movement, endowing the membrane with a low swelling ratio of 14.86% under 80 °C and a high peak power density of 811.33 mW cm −2 in single-cell tests. This work offers new insights into the rational design of high-efficiency AEMs.