Platinum Single Atoms Anchored on a Covalent Organic Framework: Boosting Active Sites for Photocatalytic Hydrogen Evolution

It is of great importance to explore and achieve a more effective approach toward the controllable synthesis of single-atom-based photocatalysts with high metal content and long-term durability. Herein, single-atom platinum (Pt) with high loading content anchored on the pore walls of two-dimensional β-ketoenamine-linked covalent organic frameworks (TpPa-1-COF) is presented. Aided by advanced characterization techniques of aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC HAADF-STEM) and X-ray absorption fine structure (XAFS) spectroscopy, it has been demonstrated that atomically dispersed Pt is formed on the TpPa-1-COF support through a six-coordinated C₃N–Pt–Cl₂ species. The optimized Pt₁@TpPa-1 catalyst exhibits a high photocatalytic H₂ evolution rate of 719 μmol g^–1 h^–1 under visible-light irradiation, a high actual Pt loading content of 0.72 wt %, and a large turnover frequency (TOF) of 19.5 h^–1, with activity equivalent to 3.9 and 48 times higher than those of Pt nanoparticles/TpPa-1 and bare TpPa-1, respectively. The improved photocatalytic performance for H₂ evolution is ascribed to the effective photogenerated charge separation and migration and well-dispersed active sites of single-atom Pt. Moreover, density functional theory (DFT) calculations further reveal the role of Pt single atoms in the enhanced photocatalytic activity for H₂ evolution. Overall, this work provides some inspiration for designing single-atom-based photocatalysts with outstanding stability and efficiency using COFs as the support.