Self-Assembled p–n Homojunction in SnS2 Nanosheets for Electrocatalytic Hydrogen Evolution: The Role of Sulfur Defects

In this study, we demonstrate the impressive electrocatalytic hydrogen evolution (HER) capabilities of a self-assembled p–n homojunction in SnS2 nanosheets enriched with sulfur vacancies (VS) and tin vacancies (VSn). Our experiments demonstrate that after aqueous washing, SnS2 nanosheets washed ten times (S10) contain more VS and VSn than those washed three times (S3). As a result, S10 exhibits a significantly better HER performance than S3, with an overpotential of 119 mV at 10 mA/cm2, a Tafel slope of 140 mV/dec, a turnover frequency of 10.9 m/s, and faster H+ mass transport. S10 exhibits improved HER performance with an overpotential of 116 mV at 10 mA/cm2 and a Tafel slope of 96 mV/dec in the visible spectrum due to VS and better interfacial carrier separation from the p–n homojunction. Our partial density of states and Gibbs free energy calculation for H adsorption (ΔGH) reveal that undercoordinated Sn atoms near VS contribute to H adsorption in both S3 and S10. However, as S10 contains more VS than S3, its HER activity is superior. Our findings suggest that defect engineering through a simple and effective chemical synthesis approach can optimize the electro- and photoelectrochemical HER activity of layered two-dimensional SnS2 nanosheets.