Hydroxide ion transfer in anion exchange membrane: A density functional theory study

• The OH− transport mechanism in quaternary ammonium functionalized polystyrene was studied by DFT.
• There were two steps in the OH− transport process in anion exchange membrane.
• The role of hydrogen bonding was investigated by DFT.
• The rotation about ionic groups was studied in detail during OH− transport.

A theoretical investigation of hydroxide ion transport mechanism in quaternary ammonium functionalized polystyrene (QAPS) anion exchange membrane (AEM) was studied by density functional theory (DFT). The results showed that there were two steps for OH− transferring through QAPS-AEM. The first step was the movement of OH− in water channel, which was induced by frequently forming and breaking of hydrogen bonds (H-bonds) between H2O and OH−. The second step was that OH− transferred across the quaternary ammonium (QA) groups by following the rotation about CC single bond, which was the rate-determining step for OH− transferring in QAPS-AEM. We presented that the ionic groups on the side chain of polymer with smaller space steric should provide higher ion conductivity due to their lower rotation energy barriers.

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