Effects of Adsorbed OH on Pt(100)/Water Interfacial Structures and Potential

Adsorbates at the electrode change the structure of the electrode/electrolyte interface. Despite the important influence of the interfacial structure on electrochemical processes, computational investigations targeting this influence are still lacking. Even the impact of one of the most common adsorbates, namely, adsorbed OH, is so far largely unknown. In this study, we choose the Pt(100)/water interface as a model system to investigate the interfacial water structure at various OH coverages with ab initio molecular dynamics. We find that the interfacial water structure is highly sensitive to the adsorption site of OH (namely, top or bridge site) and that the preference of adsorption sites of OH is, in turn, strongly influenced by the solvation caused by interfacial water. This indicates that the structure of water is correlated with that of OH. Based on a detailed analysis, we attribute these observations to a strong hydrogen-bonding network between OH and the interfacial water. This hydrogen-bonding network also results in a complicated dependence of the interfacial potential on the OH coverage, which is governed not only by the dipole induced by OH but also by the influence the OH species have on the interfacial water structure.