New evidence for the regulation of photogenerated electron transfer on surface potential energy controlled co-catalyst on TiO2 – The investigation of hydrogen production over selectively exposed Au facet on Au/TiO2

In this study, Au/TiO2 samples with different exposed facets ({100}, {100/111}, and {111}) of Au were employed as catalysts for the examination of facet-dependent catalytic activity toward photocatalytic hydrogen evolution from water. By photosensitized using Eosin Y as antenna molecule, Au/TiO2 series photocatalysts exhibited different photocatalytic hydrogen evolution performances under visible light irradiation. Au{111}/TiO2 photocatalyst presented the highest photocatalytic hydrogen generation activity among Au/TiO2 series samples. As evidenced by photoluminescence spectra, photocurrent, electrochemical impedance spectra, and Mott–Schottky characterizations, the difference in photocatalytic activities resulted from the different electron transfer rates from the conduction band of TiO2 to Au nanoparticles. Au nanoparticles with exposed {111} facets were more effective in trapping electrons due to their higher Fermi level. In addition, the apparent activation energy of Au{111}/TiO2 sample was the lowest, resulted from the biggest uncoordinated numbers of Au atoms on Au{111} nanoparticles, which was favor in forming the hydrogen–metal bond. This study discloses the facet-dependent effect of noble-metal cocatalyst on semiconductor photocatalysts in photocatalytic water reduction, and will give an insight into design and synthesis of high-efficient noble metal/semiconductor hybrid photocatalysts.