Site dependent reactivity of Pt single atoms on anatase TiO₂(101) in an aqueous environment

The TiO₂-Pt-water interface is of great relevance in photocatalysis where Pt is widely used as a co-catalyst for enhancing hydrogen evolution in aqueous TiO₂. Using ab initio molecular dynamics, we investigated this interface focusing on Pt single atoms supported on anatase TiO₂(101) in a water environment. Based on recent experiments showing a broad distribution of Pt coordination sites in TiO₂, we examined six distinct single-Pt supported species with different nominal Pt oxidation states, namely: Pt, PtOH, and PtO₂ species adsorbed on the stoichiometric surface; Pt adsorbed at a surface oxygen vacancy (O_v); and Pt substituting a surface Ti cation (Pt_Ti), both without and with an accompanying O_v (Pt_Ti + O_v). As found for the pristine anatase surface, interfacial water remained intact in the presence of a nearly neutral Pt adatom within the time duration of our simulations (∼15 ps). Similarly, no (or only temporary) water dissociation was observed at the Pt_Ti + O_v and PtO₂ interfaces, due to the formation of very stable planar Pt coordination structures that interact only weakly with water. In contrast, water dissociated with OH^- (H⁺) on the Pt atom when this substituted a surface Ti (oxygen) ion as well as on PtOH.