Hydroxide transport and chemical degradation in anion exchange membranes: a combined reactive and non-reactive molecular simulation study

Abstract

Investigating the structural and dynamical properties, charge transport and membrane degradation in anion exchange membranes (AEMs) using atomistic-scale simulations provides a guideline for the design of new high-performance membrane fuel cells. In this work, we demonstrate a multiscale simulation strategy that combines molecular dynamics simulations using non-reactive polarizable (APPLE&P) and reactive (ReaxFF) force fields. From the comparison of APPLE&P and ReaxFF results for four model AEMs with different functional groups, we show the significance of the Grotthuss mechanism for the OH⁻ diffusion, as well as for water self-diffusion in high OH⁻ concentration environments. With the incorporation of proton hopping into ReaxFF, the OH⁻ diffuses much easier through the bottlenecks in the water channels, without losing some coordinating water molecules. Furthermore, investigation of the chemical degradation selectivity in different membranes with ReaxFF indicates that AEMs with cations connected to large hydrophobic groups have better chemical stability. Considering the balance of transport and stability properties of AEMs, we propose a potential candidate for high performance membranes.