(635d) Multi-Scale First-Principles Approach to Three-Phase Model of Polymer Electrolyte Membrane Fuel Cell

Giuseppe F. Brunello, Ji Il Choi and Seung Soon Jang

Computational NanoBio Technology Laboratory, School of Materials Science and Engineering, Georgia Institute of Technology, 771 Ferst Drive NW, Atlanta, GA 30332-0245

It is desirable to achieve fundamental understanding of the three-phase system consisting of carbon support, polymeric ionomer, and Pt catalyst nanoparticle, where the most essential electrochemical events for fuel cell operation take place in the presence of other molecular species such as water, proton, and oxygen. Although variety of cutting-edge in-situ and time-resolved probing techniques would be available to investigate nanometer-scale systems, the structure and dynamic behavior of the three-phase system of fuel cell has not been thoroughly analyzed at molecular level, which is mainly due to such complicated multi-component feature of the three-phase system in several tens of nanometers. In this context, we simulate the three-phase system using multi-scale first-principles modeling approach consisting of quantum mechanical density functional theory (DFT) and molecular dynamics (MD) simulations in order to investigate the nanophase-segregation of polymeric ionomers and water molecules, surrounding Pt nanoparticle on graphitic carbon support. For this, we develop a force field based on DFT computations and ran large-scale MD simulations. The nanophase-segregated structures and transport properties of water, proton, and oxygen are analyzed, and especially the spatial arrangement of molecular species around Pt particle is characterized in detail. All the simulation results are compared to those of bulk Nafion phase with the same water contents.