<i>In situ</i> fabrication of Cu ^II-tetrapyridylporphyrin derived single-atom CuN _<i>x</i> cluster-modified TiO ₂ for efficient hydrogen evolution reaction

Photocatalytic hydrogen evolution reaction (HER), which can convert solar energy into hydrogen energy, offers a viable green energy solution to the current energy shortages. Herein, Cu^II-tetrapyridylporphyrin (CuTPyP) molecules are decorated onto an amino-functionalized Ti-based metal organic framework (NH₂-MIL-125(Ti) MOF) to form CuTPyP/NH₂-MIL-125(Ti) precursor <em>via</em> an impregnation method, which is then pyrolyzed to fabricate a novel single-atom CuN<em>_x</em> cluster-modified TiO₂ composite (CuN<em>_x</em>/TiO₂). Under the full spectrum irradiation of Xe-lamp, the resultant CuN<em>_x</em>/TiO₂ exhibits slightly better photocatalytic performance than the Pt-loaded TiO₂ product, with an optimal HER activity of 581 μmol h^-1, which is 38 and 20 times higher than that of the TiO₂ (15 μmol h^-1) pyrolyzed from of the bare NH₂-MIL-125(Ti) and the N<em>_x</em>/TiO₂ (28 μmol h^-1) pyrolyzed from the H₂TPyP/NH₂-MIL-125(Ti) precursor, respectively. The characterization results confirm that the Cu species in CuN<em>_x</em>/TiO₂ can maintain the single-atom dispersed CuN<em>_x</em> clusters, thereby extending the spectral absorption region, promoting the photoexcited charge separation, and then enhancing the activity of TiO₂. These results demonstrate that the CuN<em>_x</em> clusters exhibit comparable effectiveness to Pt cocatalyst, providing a feasible approach for developing efficient non-precious metal single-atom photocatalysts.