Cu Atomic Subnanoclusters on TiO₂ for Photocatalytic Hydrogen Evolution

Subnanocluster (SNC) cocatalysts are considered to be promising cocatalysts for photocatalytic hydrogen evolution reaction (HER) due to their rich surface-active sites and high atom utilization efficiency. Herein, a reductant-mediated in situ growth of the atomic clusters procedure is developed to synthesize SNC-Cu serving as advanced cocatalysts on TiO2 nanoparticles for HER. The optimized SNC-Cu/TiO2 catalyst, with 1.8 wt % metal mass loading, exhibits a remarkable hydrogen evolution rate of 6832 μmol g–1 h–1, which is ca. 25-fold that of bare TiO2 (273 μmol g–1 h–1 and comparable to that of 1 wt % Pt-modified TiO2 (7754 μmol g–1 h–1). Meanwhile, decent photostability and recyclability are also certified via a 20 h durability test. Comprehensive electron microscopy and spectroscopy characterizations unveil that the outstanding performance of SNC-Cu/TiO2 can be attributed to accelerated charge separation/transfer and suppressed photoinduced electron–hole recombination. Furthermore, in situ X-ray photoelectron spectroscopy and first-principle calculations reveal that the electron-localized SNC-Cu, with its abundant surface sites, facilitates *H adsorption and desorption, thus enhancing the HER activity significantly. This work highlights the promising potential of constructing noble-metal-free SNCs in semiconductors for photocatalytic HER.