Multi-scale First-Principles Modeling of Three-Phase System of Polymer Electrolyte Membrane Fuel Cell

It is desirable if we can achieve fundamental under-standing 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 molecu-lar 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 have simulated the three-phase systems using multi-scale first-principles modeling approach consisting of quantum mechanical density functional theory (DFT) and molecu-lar dynamics (MD) simulations in order to investigate the nanophase-segregation of polymeric ionomers and water molecules, surrounding Pt nanoparticle on graphitic car-bon support. For this, we developed a force field based on DFT computations and ran large-scale MD simulations. Another topic we would like to address is the Pt dissolu-tion that degrades the fuel cell performance by decreasing the active catalyst surface area. In order to elucidate the Pt dissolution mechanisms under a certain surface potential condition, we implemented the DFT computation of vari-ous charged Pt surface in the presence of water. Modeling of Three-Phase System. To achieve accurate analyses from the three-phase system, first, we built prob-able structures consisting of all the components in the simulated three-phase system. To prepare the accurate force field describing the molecular interactions between components in the three-phase system, we performed DFT computations using model systems. Figure 1 shows an example for the water-Pt nanoparticle pair