Novel noble-metal-free NiCo2O4/CdIn2S4 S-scheme heterojunction photocatalyst with redox center for highly efficient photocatalytic H2 evolution

The exploration of efficient and noble-metal-free photocatalysts for photocatalytic H2 production is still a hot topic. Herein, a novel NiCo2O4/CdIn2S4 S-scheme heterojunction composites were successfully synthesized. Morphology characterization manifests that CdIn2S4 nanoparticles are tightly bound to the rod NiCo2O4 to form S-scheme heterojunction. Besides, X-ray photoelectron spectroscopy (XPS) results verify the existence of coexisting cobalt and nickel ions with multivalent state, which could provide H2 evolution active site and form redox centers. The S-scheme heterojunction and redox centers prompt the transfer of photogenerated e- from CdIn2S4 to NiCo2O4 for improving carrier separation efficiency, which is confirmed by a series of electrochemical experiments and photoluminescence (PL). The specific surface area and transmission electron microscope (TEM) results show that NiCo2O4 possesses a high specific surface area and porous structure, which could provide more active sites and facilitate H2O adsorption for further reduction reaction. The optimal NiCo2O4/CdIn2S4 composites possess maximum H2 evolution rate of 624 mu mol center dot g- 1 center dot h- 1, which is about 3.2 times than CdIn2S4-1 %Pt (198 mu mol center dot g- 1 center dot h- 1). After three cycles, the activity of NiCo2O4/CdIn2S4 shows no significant weaken. Moreover, the possible H2 evolution mechanism of NiCo2O4/CdIn2S4 S-scheme heterojunction composites is discussed. This research offers an idea for bimetallic oxide (NiCo2O4 etc.) modified sulfide to improve photocatalytic hydrogen production.