Interfacial Electronic Properties and Photocatalytic CO₂ Reduction of a Z-Scheme SnS/(CH₃NH₃)₂AgBiI₆ Double Perovskite Heterostructure

The conversion of CO2 into energy fuel is an effective strategy to address energy shortages and environmental problems. To enhance the photocatalytic activity of CO2 reduction, the lead-free halide double perovskite (CH3NH3)2AgBiI6 (010) surface is combined with a SnS monolayer to construct a stable SnS/(CH3NH3)2AgBiI6 photocatalyst. The bandgap of SnS/(CH3NH3)2AgBiI6 is narrow (1.566 eV) compared with the (CH3NH3)2AgBiI6 (010) surface, which enhances the absorption of visible light and leads to the redshift of the absorption edge. The interface interaction between the (CH3NH3)2AgBiI6 (010) surface and the SnS monolayer causes electron flow from the SnS monolayer to the (CH3NH3)2AgBiI6 (010) surface. SnS/(CH3NH3)2AgBiI6 has a good Z-scheme band alignment, which facilitates the separation of electron–hole pairs. The electrons accumulate at the CB of the SnS monolayer and participate in the CO2 reduction reaction. In comparison with the (CH3NH3)2AgBiI6 (010) surface, SnS/(CH3NH3)2AgBiI6 changes the rate-determination step and reduces the Gibbs free energy from 2.17 to 1.72 eV. The results indicate that SnS/(CH3NH3)2AgBiI6 improves the photocatalytic activity of CO2 reduction.