Photocatalytic Hydrogen Production Enhancement of NiTiO3 Perovskite through Cobalt Incorporation

Abstract

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.