Development of a ReaxFF potential for Pt-O systems describing the energetics and dynamics of Pt-oxide formation.

ReaxFF force field parameters describing Pt-Pt and Pt-O interactions have been developed and tested. The Pt-Pt parameters are shown to accurately account for the chemical nature, atomic structures and other materials properties of bulk platinum phases, low and high-index platinum surfaces and nanoclusters. The Pt-O parameters reliably describe bulk platinum oxides, as well as oxygen adsorption and oxide formation on Pt(111) terraces and the {111} and {100} steps connecting them. Good agreement between the force field and both density functional theory (DFT) calculations and experimental observations is demonstrated in the relative surface free energies of high symmetry Pt-O surface phases as a function of the oxygen chemical potential, making ReaxFF an ideal tool for more detailed investigations of more complex Pt-O surface structures. Validation for its application to studies of the kinetics and dynamics of surface oxide formation in the context of either molecular dynamics (MD) or Monte Carlo simulations are provided in part by a two-part investigation of oxygen diffusion on Pt(111), in which nudged elastic band (NEB) calculations and MD simulations are used to characterize diffusion processes and to determine the relevant diffusion coefficients and barriers. Finally, the power of the ReaxFF reactive force field approach in addressing surface structures well beyond the reach of routine DFT calculations is exhibited in a brief proof-of-concept study of oxygen adsorbate displacement within ordered overlayers.

Ab initio study of the electrochemical H2SO4/Pt(111) interface.

The co-adsorption of H(3)O(+) and/or H(2)O on SO(4)(2-)/Pt(111) has been studied on the basis of DFT calculations. Several combinations of co-adsorbates have been considered in order to determine the most stable configuration. We find an adlayer of H(3)O(+) coadsorbed with SO(4)(2-)/Pt(111) having either none or one additional H(2)O molecule. When including the effects of an external electrode potential the nature of the adlayer is modified. This is also reflected in the behavior of the electrostatic potential normal to the surface, which should be directly comparable to future distance tunneling spectroscopy measurements.