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.