DFT calculations on H, OH and O adsorbate formations on Pt(111) and Pt(332) electrodes

Density functional theory combined with a modified Poisson–Boltzmann theory (DFT-MPB) is applied to H, OH and O adsorbate formations on electrified Pt(111) and Pt(332) surfaces in an acid aqueous solution. In this method, the chemical bonds between adsorbates and electrodes are quantitatively described by the DFT, and solvation and electric field effects by the electric double layer are described by combining explicit water adlayer models and modeled continuum electrolyte. The results indicated that H, OH and O are bound less strongly to (110)-step on Pt(332) than to terrace on Pt(111) in the electric double layer while the trend is opposite in vacuum. The trend in the electric double layer is consistent with our experimentally-obtained cyclic voltammograms, in which H and (hydr)oxides are formed less easily (at lower and higher potentials, respectively) on Pt(332) than on Pt(111). The small binding energies in the modeled electric double layer mainly stem from destabilizations of adsorbates by the presence of strongly adsorbed water molecules forming 1D H-bond networks on the step. Other effects also are found to contribute to the destabilizations: the strain on the Pt(332) terrace, the confinement by the Pt atoms near the step and the water orientation changes by the formations of adsorbates.