(546c) Molecular Dynamics Simulation of Quaternary Ammonium Polycation Exchange Membrane Fuel Cell: Nanophase-Segregated Structure and Transport Properties

Harris, A., Georgia Institute of Technology
Jang, S. S., Georgia Institute of Technology
The nanophase-segregated structure and transport properties of quaternary ammonium grafted polycation membranes are investigated using a molecular dynamics simulation method. For this, we develop a new force field from a reference density functional theory modeling with B3LYP and 6-31G** in order to describe the hydroxide anion. The bond stretching force constant is determined to reproduce the quantum mechanical vibrational frequency. The atomic charges are determined by Mulliken population analysis. Through the annealing procedure, the nanophase-segregated structure is developed as a function of water contents, such as 10 wt % and 20 wt %. The extent of nanophase-segregation is evaluated by the structure factor analysis, which can be compared with the experimental small angle scattering data. Once the equilibrium structures are obtained, we will run long MD simulations to analyze the diffusion of water and hydroxide using the mean-square displacement analysis with an assumption of Gaussian diffusion. Previous processes were modified from past results to minimize potential sources of error and better compare the anion exchange membrane fuel cell with the proton exchange membrane fuel cell.