Molecular dynamics simulation on the effect of water uptake on hydrogen bond network for OH- conduction in imidazolium-g-PPO membrane

OH- conduction involved in the hydrophilic channel of anion exchange membrane strongly depends on the water uptake. To investigate the effect of water uptake on the hydrogen bond network for OH- conduction, a series of molecular dynamics simulations based on all-atom force field were performed on the hydrated imidazolium-g-PPO membranes with different water uptakes. The systems were well verified by comparing the membrane density and OH- conductivity with previous experiments. By means of local structural properties and pair-potential energy, reasonable hydrogen bond criteria were determined to describe the hydrogen bond network confined in the membrane. Increasing water uptake enhances the hydration structures of water and OH-, and facilitates the reorganization of the hydrogen bond network. Water and OH- are nearly saturated with water when the water uptake reaches lambda = 10, where well-connected hydrogen bond network is produced. Further increasing water uptake has much less contribution to improving the hydrogen bond network, but inevitably swells the membrane channel. This work provides a molecular-level insight into the effect of water uptake on the hydrogen bonding structures and dynamics of OH- and water confined in the imidazolium-g-PPO membrane. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.