Large-scale Molecular Dynamics Simulations for Analyses of Transport Phenomena in Polymer Electrolyte Fuel Cell

Abstract

Computer simulation is a very powerful tool to analyze transport phenomena in the membrane electrode assembly (MEA) of polymer electrolyte fuel cells (PEFCs). In particular, there are many nanoscale structures in this flow field, and therefore the phenomena should be analyzed from the microscopic point of view rather than computational fluid dynamics. In this paper, we report large-scale molecular dynamics (MD) simulations to analyze these flows. In particular, dissociation phenomena of a hydrogen molecule on a Pt catalyst, transport phenomena of proton and water in a polymer electrolyte membrane (PEM), oxygen permeability of ionomers in a catalyst layer (CL), and transport phenomena of a water droplet in a nanopore were simulated, and their characteristics are discussed. In the analysis of the dissociation phenomena of the hydrogen molecule, it was found that the trend of dissociation probability as a function of impinging energy considering the motion of the molecule differs from that without considering the motion of the molecule. In the analysis of proton transfer in a PEM, the diffusion coefficients obtained by this simulation were consistent with the experimental data. In the analysis of oxygen permeability of ionomers, the dependence of water content on the permeability was estimated and the difference between ionomer on catalyst layer and that in bulk state was clarified. In the analysis of transport phenomena of a water droplet in a nanopore, we compared the results of our simulation with the macroscopic governing equation.