High performance photocatalytic water splitting in two-dimensional BN/Janus SnSSe heterojunctions: ab initio study

Designing and exploring a photocatalyst with interfacial electric fields for hydrogen production via water splitting is a critical area of research. To achieve efficient hydrolysis reactions, heterojunction materials have garnered significant attention due to their excellent electronic structures and interfacial properties. In this study, we designed a 2D BN/SnSSe heterojunction and investigated its photovoltaic properties through first-principles calculations. We found that the BN/SSnSe heterojunction is a type-II structure, with electron mobility (μ_e) and hole mobility (μ_h) of 1257.32 and 439.73 cm² V^-1 s^-1, respectively. By modulating the interlayer spacing to 2.7 Å, we successfully achieved the desired photocatalytic band-edge positions (CBM > -4.44 eV, VBM < -5.67 eV). Additionally, we discovered a unique phenomenon in the oxygen evolution reaction (OER), where the peroxide groups (OOH) automatically detach when H⁺ is adsorbed on the reaction intermediate *OOH, leading to the production of O₂ and H₂. We refer to this process as the H-ion induced desorption mechanism (H-IIDM). This mechanism not only enables the separation of the OER and hydrogen evolution reaction (HER) on different surfaces but also further enhances the photocatalytic efficiency. Furthermore, the BN/SnSSe heterojunction exhibits excellent visible-light absorption with a high optical absorption coefficient (10⁵ cm^-1), and BN/SSnSe has a high solar hydrogen production efficiency (32.61%), significantly outperforming conventional 2D photocatalysts. These findings suggest that the BN/SnSSe heterojunction holds great potential as a photocatalyst for water splitting applications.