Enhanced photocatalytic hydrogen production on Au/TiO2-CeO2 through the formation of oxygen vacancies

TiO₂-CeO₂ (TC) materials superficially modified with Au nanoparticles (AuNPs) were prepared using the sequential deposition-precipitation with urea method. EDS revealed the effective deposition of Ce and Au and a well-distributed CeO₂ phase on TiO₂. STEM-HAADF showed proximity between the TiO₂ and CeO₂ phases and the formation of AuNPs with a size of 3.6 ± 0.7 nm. The TiO₂ band gap (E_g) decreased slightly with the increase in the CeO₂ concentration. For the TC materials, XPS confirmed a slight increase in the Ti³⁺ concentration and the predominant presence of Ce³⁺, which increased the oxygen vacancies (OVs).

Furthermore, the AuNPs were mainly composed of Au⁰ (80.2 %). XPS and photoelectrochemical characterizations revealed higher valence band-edge energy after the CeO₂ and AuNP incorporation, making proton reduction in the material more thermodynamically favorable. As for the hydrogen evolution reaction, the TC material with optimal Ce loading of 0.9 wt% increased the photocatalytic hydrogen production rate to 2.3 mmol g⁻¹ h⁻¹, 20 % higher than that of pristine TiO₂. Additionally, adding 0.7 wt% of AuNPs led to a substantial improvement in hydrogen photocatalytic production, reaching 10.7 mmol g⁻¹ h⁻¹. This enhancement was ascribed to the ability of AuNPs to act as electron traps, reducing the electron-hole recombination. Photoelectrochemical characterization showed a decrease in the flat-band potential upon incorporation of CeO₂ and AuNPs, which could also be associated with the formation of OVs. AuNPs on the surface improved the stability of the electrons in the CB through the formation of a Schottky junction.