Enhanced hydroxide conductivity in zwitterionic polyacrylate-based anion exchange membranes via side-chain length optimization

Developing advanced ion-conductive networks is crucial for anion exchange membranes (AEMs). A flexible molecular structure facilitates the formation of ion clusters and results in enhanced ionic conductivity. Polyacrylates, known for their outstanding flexibility and chemical stability, hold significant potential as polymer electrolyte membranes. In this work, we innovatively constructed a series of polyacrylate-based AEMs decorated with pendant zwitterions (designated as PSBPA-X, BSBPA-X, where X=20, 30, 40). Specifically, the spacer length between the zwitterions is strategically optimized to enhance the ionic conductivity. Atomic force microscopy reveals that a longer spacer length between the zwitterions promotes the microphase separation and the formation of advanced water channels, which facilitates the OH - transport in the BSBPA-40 membrane. Moreover, the stronger electrostatic potential and lower interaction energy between the BSBPA-40 and OH - further contributes to efficient OH - hopping transmission. Consequently, the BSBPA-40 membrane demonstrates the highest OH - conductivity, achieving 102.1 mS/cm at 80 °C and 90% relative humidity, significantly surpassing that of the PSBPA-40 membrane (75.2 mS/cm). Additionally, the BSBPA-40 membrane exhibits remarkable flexibility with an improved breaking elongation of 480.5% due to the ionic cross-linking between the zwitterions. Notably, the BSBPA-40 membrane-based zinc-air battery achieves an outstanding power density of 156.7 mW/cm 2 at room temperature, while its water electrolysis performance reaches 2.1 A/cm 2 at 2.0 V. These results indicate that the developed membranes hold great promise for applications in sustainable and clean energy technologies. This study reports a series of zwitterionic polyacrylates with meticulously designed molecular architectures, wherein the spacer length of the zwitterion is optimized. The BSBPA-40 membrane, featuring a longer spacer length, demonstrates more distinct microphase separation and exceptional OH - conductivity, reaching 102.1 mS/cm at 80 °C and 90% RH. Specifically, the BSBPA-40 membrane-based zinc-air battery achieves an exceptional power density of 156.7 mW/cm 2 at room temperature, while its water electrolysis performance reaches 2.1 A/cm 2 at 2.0 V. • Side-chain length of zwitterionic polyacrylate-based AEMs is optimized. • Longer side-chain contributes to more pronounced phase separation and higher OH - conductivity. • BSBPA-40 based ZAB achieves an outstanding power density of 156.7 mW/cm 2 at 25 °C. • Water electrolysis of BSBPA-40 exhibits a superior current density of 2.1 A/cm 2 at 2.0 V.