Physical and photoelectrochemical properties of the ilmenite NiTiO3 prepared by wet chemical method and its application for O2 evolution under visible light

The ilmenite NiTiO3 prepared by wet chemical method is characterized by thermal gravimetry (TG), X-ray diffraction (XRD), FTIR and Scanning Electron Microscopy (SEM). The oxide crystallizes in the hexagonal symmetry with grains size in the range [200-300 nm]. The BET analysis gives a specific surface area of ~ 4 m2 g−1. The UV-vis diffuse reflectance analysis gives a direct transition at 2.57 eV well matched to the solar spectrum. The transport properties exhibit n-type semiconductor with an activation energy of 0.11 eV and an electron mobility of 5.82 × 10−4 cm2 V−1 s−1. The physical and chemical characterizations are correlated for the construction of the energy diagram in order to assess the photoelectrochemical properties for the oxygen evolution. The valence band, deriving from O2-: 2p orbital (2.19 VSCE), is located above the O2/H2O potential (~ 1.5 VSCE), allowing O2-evolution upon visible light (15 mW cm−2) and the oxide is photocathodically protected against corrosion. An evolution rate of 0.046 mL mg−1 h−1 is obtained within 20 min upon visible light and under optimal conditions (200 mg of catalyst, pH ~ 3 and 50 °C).