Molecular Dynamics Simulations of Surface Oxidation on Pt and Pt/PtCo/Pt<sub>3</sub>Co Nanoparticles Supported over Carbon

Simulations of surface oxidation on pure Pt and Pt/PtCo/Pt<sub>3</sub>Co nanoparticles supported over carbon in the presence of water and acid molecules are performed through classical molecular dynamics. The water molecules are represented using the CF1 central force model to allow their dissociation. It is found that water molecules near the nanoparticle surface dissociate only in the presence of acid molecules. The presence of the acid species does not modify the relaxed structure of the nanoparticles but they cause breaking of the OH bonds of water molecules due to electrostatic interactions. The Pt/PtCo/Pt<sub>3</sub>Co nanoparticle is more active in terms of water dissociation and less stable after 10 cycles of reduction and oxidation than the pure Pt nanoparticle. The metal dissolution mechanism after reduction–oxidation cycles in the alloy nanoparticle involves the surface segregation of alloy atoms, oxygen absorption in the subsurface, destabilization of the oxide phase through electrostatic interactions with ions in the solvent, and detachment of single metal atoms bonded to oxygen atoms.