Defect Mediated Improvements in the Photoelectrochemical Activity of MoS 2 /SnS 2 Ultrathin Sheets on Si Photocathode for Hydrogen Evolution.

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. MoS is a poor HER cocatalyst due to its inert basal plane. Activation of the MoS basal plane will facilitate HER kinetics. In this study, we have incorporated SnS into MoS ultrathin sheets to induce defect formation and phase transformation. MoS/SnS composite ultrathin sheets with a Sn state create a large number of S vacancies on the basal sites. The optimized defect-rich MoS/SnS ultrathin sheets decorated on surface-modified Si micro pyramids as photocathodes show a current density of -23.8 mA/cm at 0 V with an onset potential of 0.23 V under acidic conditions, which is higher than that of the pristine MoS. The incorporation of SnS into 2H-MoS 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 SnS phase causes a decrease in symmetry and an increase in magnetic anisotropy of the Mo ions.