Boosting photocatalytic hydrogen evolution through efficient charge separation in NiSe₂ nanooctahedra-TiO₂...

The transition to clean energy has recently become the primary focus of researchers. Photocatalytic hydrogen evolution from aqueous sacrificial solutions using TiO₂ as the photocatalyst has emerged as a viable approach. However, TiO₂ is limited by its large band gap and rapid charge recombination. To overcome these limitations, we investigate the non-noble metal nickel diselenide (NiSe₂), synthesized by a simple hydrothermal method, and a series of NiSe₂/TiO₂ (P25) composites prepared by a wet impregnation method. The intrinsic structural, morphological, optical, and electronic properties of the as-prepared NiSe₂/TiO₂ composites were investigated using a variety of characterization techniques. The introduction of nanooctahedral NiSe₂ led to a 258-fold enhancement in hydrogen evolution compared to pristine TiO₂ under UV irradiation. The optimized catalyst exhibited a hydrogen evolution rate of ≈129.4 µmol h^-1 and an apparent quantum efficiency (AQE) of ≈4% at 365 nm. This enhancement is attributed to improved charge separation and transfer arising from the morphology, high conductivity, and promising catalytic activity of NiSe₂, enabling efficient hydrogen production. Furthermore, the comparison of sacrificial agents shows that for methanol, CO₂ was the only detected carbon-containing gaseous product under the applied conditions, whereas glycerol reforming resulted in the formation of both CO and CO₂. During glycerol reforming, post-reaction ¹H NMR analysis did not reveal major detectable liquid-phase intermediates within the sensitivity limits of the measurement. To further investigate the effect of NiSe₂ on the photocatalytic hydrogen evolution of TiO₂, a reaction mechanism is proposed. This study demonstrates the potential of nanooctahedral NiSe₂ as a cost-effective, stable, and efficient non-noble metal co-catalyst for hydrogen evolution.