Highly durable anion exchange membranes with sustainable mitigation of hydroxide attacks for water electrolysis

Abstract

Low hydroxide conductivity and insufficient alkaline stability are the main problems currently facing anion exchange membranes (AEMs). Conventional quaternary ammonium groups have limited resistance to attack by hydroxide roots. In this paper, quaternary ammonium-type (Cn-PFCO (n = 2, 5)) perfluoroanion exchange polymers with carbonyl side chains were synthesized. The C5–PFCO exhibited an impressive conductivity of 113.4 mS cm−1 at 80 °C, and remarkably, it retained 86.87% of its initial conductivity even after 15 days of immersion in a 1 M KOH aqueous solution. This excellent alkali resistance is due to the generation of intermediate oxygen anions from OH− and carbonyl groups through a reversible reaction. These anions effectively reduce the likelihood of SN2 attack by diminishing the electrostatic potential of the QA groups from Density Functional Theory (DFT) calculations. The electrostatic potential of C2–PFCO is 6.28 eV, while it decreases to 2.69 eV after the formation of intermediate anions. Furthermore, we also used the prepared AEM for pure water electrolysis to explore its performance. The electrochemical performance of AEMWE exhibited remarkable results when supplied with pure water, demonstrating an impressive current density of 262 mA cm−2 at 1.9 V. This study introduces a novel strategy for concurrently enhancing hydroxide conductivity and alkali resistance in AEMs by analyzing the potential for further improvement in AEMs' alkali resistance.