B3LYP study of water adsorption on cluster models of Pt(1 1 1), Pt(1 0 0) and Pt(1 1 0): Effect of applied electric field

A density functional theory (DFT) study of the adsorption of a water molecule on Pt(1 1 1), Pt(1 0 0) and Pt(1 1 0) surfaces has been carried out using cluster models, at the B3LYP/LANL2DZ,6-311++G(d,p) level. The water molecule binds preferentially at the top site on Pt(1 1 1) and Pt(1 0 0) with adsorption energy around −27 kJ mol⁻¹, and is oriented with the molecular plane nearly parallel to the metal surface and the H atoms pointing away from it. On Pt(1 1 0) a hollow site is preferred, with adsorption energy of −32 kJ mol⁻¹. Potential energy barriers for the rotation around an axis normal to the surface have been estimated to be below 1 kJ mol⁻¹ for Pt(1 1 1) and Pt(1 0 0) when water is adsorbed on top. Upon application of an external electric field (inducing positive charge density on the metal) adsorbed water is additionally stabilized on the three surfaces, especially at the top adsorption site, and adsorption on Pt(1 1 1) and Pt(1 0 0) becomes more favoured than on Pt(1 1 0). Good agreement has been found between harmonic vibrational frequencies calculated at the B3LYP/LANL2DZ,6-311++G(d,p) level and experimental frequencies for adsorbed water monomers on Pt(h k l) surfaces.