Atomic-Level Understanding of the Effect of Heteroatom Doping of the Cocatalyst on Water-Splitting Activity in AuPd or AuPt Alloy Cluster-Loaded BaLa₄Ti₄O₁₅

Various studies on functionalization of water-splitting photocatalysts have been performed toward their practical usage. Control of the cocatalyst has been investigated, and recently, in addition to particle-size control, alloying has been extensively used to achieve this goal. It is essential to investigate photocatalysts with precisely controlled cocatalysts to obtain a detailed understanding of the effect of heteroatom doping of the cocatalyst on the photocatalytic activity and thereby establish clear design guidelines for functionalization. However, previous studies have investigated photocatalysts with a variety of particle sizes and doping ratios (chemical compositions). In this study, we succeeded in loading precisely controlled Au₂₄Pd and Au₂₄Pt clusters on BaLa₄Ti₄O₁₅, which is one of the most advanced photocatalysts, using precisely synthesized alloy clusters as the precursor. Experiments with the photocatalysts loaded with precisely controlled cocatalysts revealed the following three features of heteroatom doping of cocatalysts: (1) Pd is located at the surface of the metal-cluster cocatalyst, whereas Pt is located at the interface between the metal-cluster cocatalyst and the photocatalyst. (2) Pd doping decreases the water-splitting activity, whereas Pt doping improves the water-splitting activity. (3) This opposite doping effect is strongly related to the doping position of the heteroatom. Furthermore, when Pt doping is combined with surface protection of the cocatalyst with a Cr₂O₃ shell, a photocatalyst with higher activity and stability can be obtained. These results will lead to clear design guidelines for creating water-splitting photocatalysts with high activity and stability.