Investigation of oxidation mechanisms of Pt nanoparticles in water – a molecular dynamics study

Platinum oxide (PtO) formation has a direct link to nanoparticle passivation as well as Pt dissolution in proton exchange membrane fuel cells (PEMFCs). During potential sweep, place exchange mechanism between Pt and O atoms is first triggered followed by irreversible Pt surface roughening at high potential. In this work, we employ molecular dynamics (MD) to capture atomic level processes of Pt extraction by O atoms from Pt(111) surface. As a benchmarking system, we correlate oxygen coverage with the onset of different Pt surface evolution mechanisms in the presence of water. Local O coordination of Pt atoms, concurrent Pt extraction, and generation of surface vacancies are major factors shaping the final surface structure. In addition, the MD simulation is employed to investigate the oxidation process of Pt nanoparticles. Our results show that in addition to PtO formation on faceted surfaces, Pt atoms desorption into water is a strong function of oxygen coverage. This is particularly true for under-coordinated atoms at edges and corners. The atomistic details described by the MD setup provides valuable insights into Pt-O interaction and stability of Pt nanoparticles in a complex environment.