Density Functional Theory Study of the Alkali Metal Cation Adsorption on Pt(111), Pt(100), and Pt(110) Surfaces

We used density functional theory to study the adsorption of hydrogen, lithium, sodium, and potassium cations on different surfaces of platinum, namely the Pt(111), Pt(110), and Pt(100) surfaces. It was found that at low H+ concentrations alkali metal cations can compete with hydrogen for adsorption on all the studied platinum surfaces leading to a site blocking effect during the electrochemical processes involving adsorption of hydrogen in alkaline media. The strongest site blocking effect is predicted to occur on the Pt(111) surface as hydrogen and alkali metal cations adsorb in the same fcc-hollow adsorption site. On the Pt(110) and Pt(100) surface hydrogen and alkali cations adsorb on different sites and can co-exist on the surface - the most favorable adsorption site for hydrogen is a bridge site, while the hollow site is favored for all the studied alkali metal cations. Based on the calculated adsorption Gibbs free energies and the number of available adsorption sites on different surfaces, the probability of the site blocking effect by alkali cations on different surfaces of platinum was determined as Pt(111)>Pt(110)>Pt(100).