Species Heterogeneity and Synergy to Boost Photocatalytic Hydrogen Evolution

Integrating different reaction sites, such as single atom (SA), nanocluster (NC), and oxygen vacancy (Ov), in a specific photocatalyst affords a new prospect to break through the limitations of SA catalysis. However, the intrinsic influence mechanisms of cocatalyst size and Ov on the photocatalytic performance and synergy are still not well unraveled. Herein, we report the synthesis and investigation of atomically dispersed Pt-based photocatalysts surface-confined in Ov-containing porous TiO₂ nanoflowers via atomic layer deposition. The SA–NC coexisting Pt_SA+NC@TiO₂ photocatalysts exhibit optimized hydrogen evolution activity (2260 h^–1), which is 3.6-fold higher than that of Pt_SA@TiO₂ counterparts. Moreover, the activity can be further remarkably enhanced to 3645 h^–1 by engineering the cocatalyst size and Ov concentration. We identify the ad-/desorption sites of the reacting molecules and unravel the synergistic catalytic mechanisms of the active speciesthrough characterizations and density functional theory calculations: Pt NC is responsible for the adsorption–dissociation of H₂O molecules preferentially adsorbed on Ti sites and meanwhile lowers the d-band center of Pt SA responsible for the desorption of H₂ molecules, and the adjacent Ov can stabilize the cocatalysts and modify the electronic energy distribution of Pt NC, achieving the optimized adsorption state toward the *OH intermediate. The present multiple-site engineering concept and mechanistic insights are expected to shed light on the rational design of atomically dispersed photocatalysts.