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 SnS 2 nanosheets enriched with sulfur vacancies (V S ) and tin vacancies (V Sn ). Our experiments demonstrate that after aqueous washing, SnS 2 nanosheets washed ten times (S10) contain more V S and V Sn 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/cm 2, 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/cm 2 and a Tafel slope of 96 mV/dec in the visible spectrum due to V S and better interfacial carrier separation from the p–n homojunction. Our partial density of states and Gibbs free energy calculation for H adsorption (Δ G H ) reveal that undercoordinated Sn atoms near V S contribute to H adsorption in both S3 and S10. However, as S10 contains more V S 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 SnS 2 nanosheets.