Cu Sites d Orbital Regulation Enables Highly Efficient Photocatalytic CO ₂ ‐to‐Ethylene Conversion

Abstract The core challenge in achieving efficient and targeted photocatalytic CO ₂ reduction to C2 compounds lies in the inherent kinetic barriers related to the C─C dimerization process. This study lowers the energy barrier from 0.73 to 0.50 eV by modifying the CuIn ₅ S ₈ /CuInS ₂ (CIS) heterojunction with Pt atoms, which function as a bridge for C─C coupling. The inhomogeneous local electric field formed between Pt and the CIS heterojunction synergistically enhances the built‐in electric field (BEF) at the CIS interface, thereby promoting the separation of photogenerated carriers. The introduction of Pt promotes strong hybridization between the d orbitals of Cu and Pt with CO ₂ , activating the bending of the CO ₂ molecule. The highest occupied orbital of Cu active sites is modulated from 3 d _xz to 3 d _x2‐y2 by electron injection, improving the alignment with the lowest unoccupied molecular orbital (LUMO) of CO ₂ . This dual regulation ( d‐p hybridization and orbital modulation) facilitates ^* COOH over ^* OCHO formation, enhancing ethylene selectivity. As a result, Pt decorated CuIn ₅ S ₈ /CuInS ₂ catalyst achieves an ethylene production rate of 38.93 µmol g ⁻¹ h ⁻¹ and electron selectivity of 94.28% in photocatalytic CO ₂ reduction. This work offers a new approach to design highly selective photocatalysts for CO ₂ reduction to C2 compounds.