Roles of various Ni species on TiO2 in enhancing photocatalytic H2 evolution

Low-cost nickels can be used as cocatalyst to improve the performance of photocatalysts, which may be promising materials applied in the field of photocatalytic water splitting. In this study, different nickel species Ni, Ni(OH)₂, NiO, NiO_x, and NiS are used to modified titanium dioxide (P25) to investigate their roles on the photocatalytic hydrogen evolution activities. UV-visible, X-ray diffraction (XRD), Brunner-Emmet-Teller (BET) measurements, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) analysis etc. are employed to characterize the physical and chemical properties of catalysts. The results indicate that all the nickel species can improve the photocatalytic hydrogen production activity of P25. The P25 modified with NiO_x and NiS has more superior photocatalytic hydrogen evolution activities than those modified with other nickel species. The reason for this is that NiO_x and NiS can form p-n junctions with P25 respectively. In addition, NiO_x can be selectively deposited on the active sites of P25 via in situ the photodeposition method and NiS is beneficial for H⁺ reacting with photo-excited electrons.