Ni/NiSe_x@N-doped carbon/TiO₂ heterostructures for enhanced photocatalytic hydrogen evolution

Titanium dioxide (TiO₂) is extensively implemented in photocatalytic hydrogen (H₂) production. However, the rapid recombination rate of photogenerated electron–hole pairs in TiO₂ limits the potential to catalyze H₂ photogeneration. In this study, we rationally designed nickel/nickel selenide@nitrogen-doped carbon/TiO₂ (Ni/NiSe_x@NC/TiO₂) heterostructures via impregnation assisted by ultrasonication to enhance the photocatalytic activity of TiO₂ in H₂ production. This strategy yields a high interfacial contact between TiO₂ and Ni/NiSe_x@NC, which reduces the band gap energy and enhances the surface area. This combination yields a type-II heterojunction, as evidenced by X-ray photoelectron spectroscopy analysis of used Ni/NiSe_x@NC/TiO₂ and OH radical trapping via fluorescence analysis, with high conductive features due to the presence of NC. The presence of Ni metal provides additional sites for H₂ photogeneration. Such features significantly enhance the transfer and separation of electrons, as evidenced by a series of electrochemical analyses. Consequently, the photocatalytic H₂ generation of Ni/NiSe_x@NC/TiO₂ nanocomposites is enhanced compared with TiO₂, NiSe/TiO₂, and Ni/NiSe_x@NC. Moreover, the highest H₂ production rate is achieved by incorporating 3 wt% Ni/NiSe_x@NC on TiO₂ with the highest H₂ rate of 5985 μmol·g⁻¹. Different sacrificial agents show that glycerol exhibits the highest photocatalytic H₂ production rate compared to methanol and glucose. More importantly, Ni/NiSe_x@NC/TiO₂ shows good stability test until four cycles of photocatalytic reaction. This finding provides an insight into the formation of type-II heterojunction with conductive layers via simple preparation to enhance the photocatalytic H₂ generation.