Photocatalytic Hydrogen Production Enhancement of NiTiO₃ Perovskite through Cobalt Incorporation

In this study, we synthesized pure and cobalt-doped NiTiO₃ perovskite nanostructures using a sol–gel method and characterized them to investigate the impact of cobalt incorporation on their photocatalytic hydrogen production under UV light. XRD analysis confirmed the formation of the hexagonal ilmenite structure, with lattice parameters increasing with cobalt doping, indicating the substitution of larger Co²⁺ ions onto smaller Ni²⁺ sites. Raman spectroscopy revealed a decrease in the intensity of active modes, suggesting crystal structure distortion and oxygen vacancy generation. UV-vis spectroscopy showed a decrease in bandgap energy from 2.24 to 2.16 eV with cobalt doping up to 5%, enhancing UV light absorption. SEM and TEM images revealed nanoparticle agglomeration, while cobalt doping did not significantly alter particle size up to 5% doping. Photoluminescence spectroscopy revealed an initial increase in PL intensity for NiTiO₃-1%Co, followed by a systematic decrease with higher cobalt concentrations, with NiTiO₃-10%Co exhibiting the lowest intensity. Photocatalytic experiments demonstrated a remarkable improvement in hydrogen evolution rate with increasing cobalt doping, with NiTiO₃-10%Co exhibiting the highest rate of 940 μmol∙g⁻¹·h⁻¹, a 60.4% increase compared to pure NiTiO₃. This enhanced performance is attributed to the substitution of Co²⁺ on Ni²⁺ sites, the modification of electronic structure, the suppression of electron–hole recombination, and the creation of surface catalytic sites induced by cobalt incorporation. The proposed mechanism involves the introduction of Co²⁺/Co³⁺ energy levels within the NiTiO₃ bandgap, facilitating charge separation and transfer, with the Co⁺/Co²⁺ redox couple aiding in suppressing electron–hole recombination. These findings highlight the potential of cobalt doping to tune the properties of NiTiO₃ perovskite for efficient hydrogen production under UV light.