Effect of Ultra-Small Platinum Single-Atom Additives on Photocatalytic Activity of the CuOx-Dark TiO2 System in HER

Improving the efficiency of photocatalysts for hydrogen production while minimizing the amount of noble metals used is a pressing issue in modern green energy. This study examines the effect of ultra-small Pt additives on increasing the efficiency of the CuOx-dark TiO2 photocatalyst used in the hydrogen evolution reaction (HER). Initially, Pt was photoreduced from the hydroxonitrate complex (Me4N)2[Pt2(OH)2(NO3)8] onto the surface of nanodispersed CuOx powder obtained by pulsed laser ablation. Then, the obtained Pt-CuOx particles were dispersed on the surface of highly defective dark TiO2, so that the mass content of Pt in the samples varied in the range from 1.25 × 10−5 to 10−4. The prepared samples were examined using HRTEM, XRD, XPS, and UV-Vis DRS methods. It has been established that in the Pt-CuOx particles, platinum is mainly present in the form of single atoms (SAs), both as Pt2+ (predominantly) and Pt4+ species, which should facilitate electron transfer and contribute to the manifestation of the strong metal–support interaction (SMSI) effect between SA Ptn+ and CuOx. In turn, in the Pt-CuOx-dark TiO2 samples, surface defects (Ov) and surface OH groups on dark TiO2 particles act as “anchors”, promoting the spontaneous dispersion of CuOx in the form of sub-nanometer clusters with the reduction of Cu2+ to Cu1+ when localized near such Ov defects. During photocatalytic HER in aqueous glycerol solutions, irradiation was found to initiate a large number of catalytically active Pt0-CuOx-Ov-dark TiO2 centers, where the SMSI effect causes electron transfer from titania to SA Pt, thus promoting better separation of photogenerated charges. As a result, ultra-small additives of Pt led to up to a 1.34-fold increase in the amount of released hydrogen, while the maximum apparent quantum yield (AQY) reached 65%.