The impact of double crosslinking and alkaline activation strategies on the multifaceted characteristics of quaternized poly(vinyl alcohol) anion exchange membranes

This study investigates the effects of crosslinking strategies and KOH activation on the multifaceted characteristics of quaternized poly(vinyl alcohol) (QPVA) membranes for anion exchange membrane (AEM) applications. In situ and combined in situ/ex situ crosslinking with glutaraldehyde were evaluated at 5 M, 6 M, and 8 M KOH concentrations. Multifaceted characteristics on the membranes including ionic conductivity, swelling degree, thermal and oxidative stability are studied. Four types of membranes: M1 (in situ crosslinked, heated), M2 (in situ crosslinked, no heating), M1 2x (in situ, heated and ex situ crosslinked), and M2 2x (in situ, no heating and ex situ crosslinked) were synthesized. The M1 5 M KOH membrane (in situ crosslinked, heated activation) demonstrated the highest ionic conductivity (40.93 mS cm-1 before equilibrium, 33.41 mS cm-1 after equilibrium) and moderate oxidative stability (81.10%). Combined crosslinking and higher activation temperatures improved the membrane stability and mechanical properties but reduced the oxidative stability owing to potential alkaline attack on glutaraldehyde crosslinked groups. Oxidative stability is critical for AEMs because they are exposed to reactive oxygen species (ROS) generated during fuel cell operation or electrolysis. Poor oxidative stability can lead to degradation of the membrane, reducing its lifespan and overall performance in these applications. The novelty of this work lies in the dual crosslinking strategy, which significantly enhances the mechanical and thermal properties of QPVA membranes, while also highlighting the impact of KOH activation on crystallinity and ion transport. This study emphasizes the importance of optimizing crosslinking and activation conditions to develop high-performance QPVA membranes for energy conversion and storage applications such as fuel cells and electrolyzers.