Impact of oxidation on nanoparticle adhesion to carbon substrates

Abstract

Carbon supported platinum (Pt/C) catalysts are of vital importance to today's fine chemical industry. However, both Pt and its carbon support surface undergo oxidation during operation. There is a lack of information on how surface oxidation affects the durability of Pt/C catalysts. In this study, we report the impact of oxidation of Pt/C on the binding energy and nanoparticle adhesion force. Classic molecular dynamics simulations are performed on systems containing PtO nanoparticles of 4 nm and graphite surfaces oxidized with either epoxy or hydroxyl groups at several oxidation extents (10%, 25% and 50%). Appropriate for service in polymer electrolyte membrane fuel cells (PEMFC), the effect of a thin Nafion film (1 nm thick) at different hydration levels (λ = 3, 6, 9 and 15) is also included in the system to study the impact of oxidation on the interface structure of the electrolyte and the electrode. This study shows that the adhesion of both the Nafion film and the PtO nanoparticle is drastically affected by the type and degree of oxidation on the carbon surface. The oxidation with hydroxyl groups on the graphite surface enhanced the binding energy between the polymer electrolyte and the carbon electrode, while oxidation with the epoxy group beyond a certain amount caused delamination of the film. The adhesion of the PtO nanoparticle was similarly enhanced by the hydroxylated surface and diminished by the epoxidized surface. The binding energies and adhesive forces are reported for all systems studied.