A novel dual S-scheme CoS/MnCdS/CoO heterojunction for photocatalytic hydrogen evolution under visible light irradiation.

Rational design and synthesis of a unique heterojunction photocatalyst structure is an important strategy to enhance its performance and structural stability. Herein, CoS/MnCdS/CoO photocatalysts with double S-scheme heterojunctions were successfully prepared by coupling CoS and CoO sheet structures with n-type MnCdS nanoparticles through a simple solvothermal and mechanical mixing method. The construction of the dual S-scheme heterostructure offers the possibility to expand the light absorption range, extend the carrier lifetime and maximise the redox capacity. In addition, the mechanism of charge transfer and the reason for the improvement of photocatalytic activity were explored through photoelectrochemical characterization. The lamellar structures of CoS and CoO not only provide excellent dispersion and slow down the agglomeration of MnCdS nanoparticles, but also promote charge transfer, which improves the photocatalytic hydrogen production effect. Under simulated solar irradiation, the evolution rate of H after 5 h was as high as 46.44 μmol, which was 3.49 and 1.49 times higher than those of pristine MnCdS and MnCdS/CoO, respectively. Meanwhile, it has good stability under 20 h irradiation. This work demonstrates a novel idea for the rational design of double S-scheme photocatalysts with efficient space separation.