(389h) Role of Water Molecules in Enabling Vehicular Transport Mechanism in Polynorbornene-Based Anion Exchange Membrane

The lack of understanding in ion transport mechanisms of an anion exchange membrane hinders the rational design of membrane electrode assemblies (MEAs) with efficient water management. Here we investigate site hopping and vehicular transport mechanisms using anion exchange thin films, interdigitated electrodes, and atomistic molecular dynamics simulations. Bromide ion conductivities in polynorbornene-based thin films are measured as a function of temperature and relative humidity using electrochemical impedance spectroscopy. Bromide ion transport shows Arrhenius behaviors, and activation energy (E_a) is for the first time used as an indicator for detecting the transition of site hopping and vehicular transport mechanisms. Using atomistic molecular dynamics simulation, we quantitatively demonstrate that the transition of site hopping and vehicular mechanisms is aided by better solvation environments of anions and more percolated water pathways at 55% RH. These results have important implications for the design of MEAs that enables high-performance and durable fuel cells.