Reductive amination–engineered dual-function networks enhance alkaline stability and hydroxide conductivity in polyvinylpyrrolidone AEMs

Abstract

While ether-free anion exchange membranes (AEMs) have demonstrated enhanced alkaline stability, the simultaneous enhancement of hydroxide conductivity and dimensional stability remains a challenging aspect to address. This study proposes a reductive amination strategy for synthesizing cross-linked polyvinylpyrrolidone (PVP)-based AEMs. The strategy involves controlled molecular weight variation (K16, K30, and K60) and alkylamine functionalization. The employment of n-propylamine, 3-(Dimethylamino)propylamine (DMAPA), and hexadecylamine in conjunction with a 1,6-dibromohexane cross-linker has enabled the systematic tailoring of membrane architectures. The K16-PVP grafted with DMAPA demonstrated the highest grafting degree, as confirmed by FT-IR and ¹H NMR analyses, and exhibited enhanced cross-linking density. This synergy resulted in a significant improvement in ion transportation and mechanical stability. The optimized membrane performed exceptionally, with 94.15 mS·cm⁻¹ of hydroxide conductivity at 80 °C, surpassing PVP-based AEM reports, while still maintaining 85.3% conductivity after 240 h in 2 M NaOH at 80 °C. These results establish molecular weight-controlled reductive amination as an effective approach to resolve the critical conductivity-stability trade-off in anion exchange membranes.

Graphical Abstract