Molecular dynamics insight into phase separation and transport in anion-exchange membranes: Effect of hydrophobicity of backbones

Anion exchange membranes (AEMs) are essential components in anion exchange membrane fuel cells (AEMFCs), which can effectively convert chemical energy into electricity. Among the existing backbones of AEMs, poly(aryl piperidinium) (PAP), an emerging AEM backbone, vastly improved the power density of AEMFCs, far exceeding the other traditional backbones. Hence, a deep understanding of the correlation between the PAP backbone and the performance of the corresponding AEMs is vital for designing the next generation AEM. In this study, we select three typical AEM backbones and find that the hydrophobicity of the backbone plays a vital role in dominating the ion conductivity of the membrane. The molecular dynamics simulation analysis suggests that the hydrophobic PAP backbones form more connective ion channels. In addition, PAP backbones repulse water molecules and hydroxides. This causes water molecules and hydroxides to move into the hydrophilic phase more and remain for a shorter time around PAP backbones, which is conducive to the efficient transportation of hydroxides. With increasing temperature, hydrophobic and rigid PAP-BP shows lower hydroxide residence time and better swelling resistance, which is highly consistent with the experimental results and explains the excellent performance of PAP-BP in AEMFCs. © 2022 Elsevier B.V.