Molecular Dynamics Simulation to Reveal Effects of Binder Content on Pt/C Catalyst Coverage in a High-Temperature Polymer Electrolyte Membrane Fuel Cell

Abstract

Full atomistic molecular dynamics simulations were performed to provide detailed information on the morphologies of Pt/C catalyst with varying poly(tetrafuoroethylene) (PTFE) binder contents. Changes in the surface configuration and PTFE coverage on Pt particles with changing binder content were examined on the molecular level; this coverage can affect the catalytic performance of Pt particles and PTFE binding. The PTFE binder content in the prepared solutions ranged from 4.0 to 35.1 wt %. From Pt-PTFE pair correlation analysis, the coordination number of this pair increased from 0.43 to 1.23 as the PTFE binder content increased from 4.0 to 35.1 wt %, with a concomitant 40.0 to 84.0% change in coverage over the Pt surface. At low PTFE content, the PTFE binder was dispersed between Pt particles and the carbons on the Pt/C surface to form a triple-phase boundary. Subsequently, Pt particles become increasingly covered by PTFE with increasing binder content. However, no significant changes were observed when the PTFE content exceeded 20.0 wt %; we expect that the catalytic performance of Pt will significantly decrease at PTFE binder contents greater than 20.0 wt %. Considering the Pt-retaining role of the binder, we conclude that the optimum PTFE binder content is less than 20.0 wt % for the ∼2.6 nm diameter Pt particle used in this study. This investigation provides detailed information on polymer properties and electrode morphologies for high-temperature polymer electrolyte membrane fuel cells applications at various PTFE binder contents.