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)(2)AgBiI6 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.