Effect of Metal Work Function on Hydrogen Production from Photocatalytic Water Splitting with MTiO2 Catalysts

Photocatalytic water splitting was performed on TiO2 and metal-containing TiO2 (MTiO2) catalysts under UV light irradiation. TiO2 was added with various metals of different work functions, namely, Pt (5.93 eV), Pd (5.60 eV), Cu (5.10 eV), Ru (4.71 eV), and Ag (4.26 eV). The hydrogen production was found to increase linearly with increasing metal work function. The rate of charge recombination increases with decreasing work function difference between the metal and TiO2. Pt and Pd were highly efficient co-catalysts to TiO2 for hydrogen generation from water due to their larger work function and upward-bent band causing the photoelectrons to be trapped in those metal sites that are eventually consumed during water reduction. Co-catalysts such as Ag, Ru, and Cu were less effective towards water splitting due to downward-bent band gaps that allow the photoelectrons to flow back to TiO2 from the metal which leads to faster charge recombination.