A Theoretical Study of the Effect of Hydrophobicity on Ion Transport in Polyarylpiperidine Anion Exchange Membranes

The introduction of hydrophobic substances has a positive effect on the OH– transport of anion exchange membranes (AEMs). This study designs four fluorinated AEMs and investigates the effects of changes in the fluorinated structures on ion transport with molecular dynamics (MD) simulations. The simulation results indicate that the self-diffusion coefficient of OH– first increased and then decreased with increasing hydrophobicity at the same hydration number. As the hydrophobicity increases, the possibility of OH– dissociation from the cations within the AEMs gradually increases. However, the domain barriers resulting from excess hydrophobicity are not conducive to ion transport. In addition, increases in the hydrophobicity lead to increases and then decreases in the widths of the channels within the AEMs, while aggregation of adjacent cations within the intrachains facilitates OH– transport between the cations. Therefore, the introduction of fluorinated structures with moderate hydrophobicity into the main chain is an effective strategy for improving the AEMs.