Designing Anion Exchange Membranes with Enhanced Hydroxide Ion Conductivity by Mesoscale Simulations

This work studied polyphenylene oxide tetramethylammonium (PPO-TMA) anion exchange membrane by dissipative particle dynamics (DPD) simulations. The simulation method is validated by semiquantitatively reproducing the ion conductivity of a standard PPO-TMA and then applied to systematically explore the microstructure and ion diffusivity of modified PPO-TMA influenced by alkyl chain length, side-chain structure, and side-chain distribution. The nanosegregation of hydrophobic and hydrophilic domains is driven by alkyl side-chain modifiers, and the ionic pathways formed in lamellar structure are observed if the side chains are distributed normally as comblike structure. In these systems, ion conductivity has been elevated to 17 mS/cm compared to 11 mS/cm for nonmodified PPO-TMA. The solvation of cationic groups is also crucial for forming effective ion transport pathways. The percolated water domain breaks into smaller clusters if the charged TMA groups are moved toward PPO backbones, indicating that the alkyl spacer modification outperforms the alkyl extender design. By further altering the tethering style of side chains from comblike to block-copolymer-like, the lamellar water percolation transforms into interconnective water framework, which promotes the ion conductivity to 22 mS/cm.