Interfacial Ni–S–Zn Bond-Reinforced CoNi2S4/Zn0.8Cd0.2S S-Scheme Heterojunction for Enhanced CO2 Photoreduction

Photocatalytic CO₂ conversion is regarded as an effective strategy to tackle energy-related and ecological issues by generating sustainable fuels. Herein, we develop CoNi₂S₄/Zn_0.8Cd_0.2S S-scheme heterojunctions constructed via an in situ sulfurization approach. Through combined density functional theory calculations and experimental investigations, we demonstrate that electron transfer from CoNi₂S₄ to Zn_0.8Cd_0.2S establishes an internal electric field (IEF) directed from CoNi₂S₄ to Zn_0.8Cd_0.2S. Both in situ X-ray photoelectron spectroscopy and Kelvin probe force microscopy analyses demonstrate that the IEF promotes the migration of photoinduced electrons via interfacial Ni–S–Zn bonds, thereby verifying the establishment of an S-scheme heterojunction that markedly improves charge separation efficiency. The optimized heterojunction exhibits exceptional CO₂ photoreduction performance, accomplishing a CO yield rate of 3.60 μmol g^–1 h^–1, which is 9.0 and 4.9 times higher than those of the original state CoNi₂S₄ (0.40 μmol g^–1 h^–1) and Zn_0.8Cd_0.2S (0.73 μmol g^–1 h^–1), respectively. This study provides critical insights for designing high-performance metal sulfide-based S-scheme heterojunctions toward efficient CO₂ photoreduction.