A direct Z-scheme NiCo₂O₄/ZnIn₂S₄ heterojunction for highly efficient visible-light-driven H₂ evolution

Exploiting efficient and stable photocatalysts is the primary goal of photocatalytic water splitting for H₂ production. In this work, a sea urchin-like bimetallic NiCo₂O₄-decorated ZnIn₂S₄ heterojunction was fabricated via a solvent evaporation method. Investigation shows that the introduction NiCo₂O₄ can expand the UV-vis absorption range, enhance the absorption intensity, promote the charge separation, decrease the charge transfer resistance, induce more active sites, and decrease the H₂ evolution overpotential of the composite. Besides, the charge transfer between NiCo₂O₄ and ZnIn₂S₄ follows a Z-scheme route based on the ˙OH radical capture experiments; this can preserve the strong oxidation-reduction reaction ability of photogenerated electrons and holes, leading to a faster H₂ evolution rate, which reaches 17.28 mmol g^-1 h^-1 over the 4.8%-NiCo₂O₄/ZnIn₂S₄ composite under 300 W Xe lamp irradiation in 20 vol% triethanolamine (TEOA) solution and is 3.0 times higher than that of ZnIn₂S₄. In addition, NiCo₂O₄/ZnIn₂S₄ also has excellent stability during 5 consecutive cycles. This work provides an effective method for constructing a highly effective Z-scheme heterojunction system for photocatalytic H₂ production.