Constructing Particulate p–n Heterojunction Mo:SrTiO₃/NiO@Ni(OH)₂ for Enhanced H₂ Evolution under Simulated Solar Light

Abstract

The global environmental issues associated with the use of fossil fuels lead to an urgent need for renewable energy sources, especially those free of CO2 emissions, such as green hydrogen. In this work, we successfully synthesized Mo-doped SrTiO3 by a molten salt method for photocatalytic hydrogen production under simulated solar light (AM 1.5G illumination). As a strategy to enhance the photocatalytic performance of Mo:SrTiO3, nickel-based nanoparticles (NiO@Ni­(OH)2) were deposited onto the surface of the particles by modified magnetron sputtering to form a p–n heterojunction (HJ), resulting in the photocatalytic improvement of around 30-fold concerning pristine SrTiO3. Theoretical investigation of the electronic band structure, by DFT, reveals that the addition of Mo as a dopant leads to the formation of midgap states near the conduction band, further attributed to the photoactivity of Mo:SrTiO3 under visible-light illumination (>400 nm). The obtained structure, Mo:SrTiO3/NiO@Ni­(OH)2, had its electronic behavior studied by XPS, Mott–Schottky analysis, and UV–vis spectroscopy, leading to the construction of a band diagram that confirms type-II p–n HJ formation. Remarkably, the formation of the HJ was responsible for establishing an internal electric field, which drives the photogenerated holes to the NiO@Ni­(OH)2 structure, leading to the suppression of electron–hole recombination, observed by the reduction of the PL signal.

Critical Role of the NiO–Ni(OH)2 Species Loaded Onto TiO2 Photocatalyst in the Enhancement of H2 Evolution Activity

“…The peak positions (binding energies) are approximately the same with those reported earlier. 40,41 The presence of a mixture of NiO-Ni(OH) 2 is consistent with TEM observation shown in Fig. S3.…”