Investigating the effect of hydration ratios on hydroxide conductivity in anion exchange membranes from non-reactive molecular dynamics simulations

Anion exchange membranes (AEMs) used in alkaline fuel cells rely on the selective transport of hydroxide ions through the membrane to produce electricity. The transport of hydroxide ions depends on hydroxide-polymer, hydroxide-water and hydroxide-hydroxide cooperative interactions. In this study, we implement atomistic molecular dynamics (MD) simulations across three different AEM chemistries with ion contents ranging from 20% to 50%, and water/hydroxide ratios ranging from 0 – 40. We compute the microstructure of the polymer using the cavity energetic sizing algorithm. We calculate conductivity using both Nernst-Einstein and Onsager transport coefficients. We find that at high hydration ratios, trends in conductivity agree well with experiments. We are able to decorrelate the contributions of polymer dynamics, microstructure, and water dynamics on the ion conductivity in these materials and provide design rules that can be used to optimize AEMs in the future.