Au (Core)–Pt (Shell) Nanocatalysts with the Shell Thickness Controlled at a Monolayer Level: Extremely High Activity for Hydrogen Peroxide Decomposition

Au and Pt nanoparticle-loaded anatase TiO₂ particles (Au/TiO₂ and Pt/TiO₂) were separately prepared by the deposition–precipitation method. Also, selective Pt photodeposition on the Au surface of Au/TiO₂ yielded Au (core)–Pt (shell) bimetallic NP-loaded TiO₂ particles. In Au (core)–Pt (shell)/TiO₂, the mean Pt-shell thickness was controlled at an atomic layer level by irradiation time. The thermocatalytic activities of Au/TiO₂, Pt/TiO₂, and Au (core)–Pt (shell)/TiO₂ for the decomposition of H₂O₂ were evaluated in the dark at 25 °C. Au (core)–Pt (shell)/TiO₂ exhibits a much higher activity than that of Au/TiO₂ and even Pt/TiO₂ in spite of that Pt has the highest activity among the metals. The turnover frequency depends on the mean number of Pt layers, reaching a maximum of 1.1 × 10⁶ around the monolayer. Density functional theory simulations were performed to analyze the potential-energy surfaces in metal-cluster-catalyzed H₂O₂ decomposition with Au₅₀, Pt₅₀, and Au₁₄ (core)–Pt₃₆ (shell) used as model metal clusters. The results explain the relative catalytic activities of Au/TiO₂ ≪ Pt/TiO₂ < Au@Pt/TiO₂, further indicating the affinity of the metal clusters for oxygen atom produced in the course of reaction.