Defect Mediated Improvements in the Photoelectrochemical Activity of MoS₂/SnS₂ Ultrathin Sheets on Si Photocathode...

Solar-driven water electrolysis to produce hydrogen is one of the clean energy options for the current energy-related challenges. Si as a photocathode exhibits a large overpotential due to the slow hydrogen evolution reaction (HER) kinetics and hence needs to be modified with a cocatalyst layer. MoS₂ is a poor HER cocatalyst due to its inert basal plane. Activation of the MoS₂ basal plane will facilitate HER kinetics. In this study, we have incorporated SnS₂ into MoS₂ ultrathin sheets to induce defect formation and phase transformation. MoS₂/SnS₂ composite ultrathin sheets with a Sn²⁺ state create a large number of S vacancies on the basal sites. The optimized defect-rich MoS₂/SnS₂ ultrathin sheets decorated on surface-modified Si micro pyramids as photocathodes show a current density of -23.8 mA/cm² at 0 V with an onset potential of 0.23 V under acidic conditions, which is higher than that of the pristine MoS₂. The incorporation of SnS₂ into 2H-MoS₂ ultrathin sheets not only induces a phase but also can alter the local atomic arrangement, which in turn is verified by their magnetic response. The diamagnetic SnS₂ phase causes a decrease in symmetry and an increase in magnetic anisotropy of the Mo³⁺ ions.