Vacancy-guided dual sites help turn CO2 into ethylene with sunlight

Converting carbon dioxide into valuable chemicals using sunlight is an attractive route toward carbon recycling. Among possible products, ethylene is especially important because it is a key building block for the chemical industry. However, producing ethylene from CO₂ is difficult: it requires multiple proton-coupled electron transfer steps and, more importantly, the formation of a new carbon–carbon bond.

A research team led by Prof. Lei Ge from China University of Petroleum Beijing has now developed a zinc-doped CuInS₂ photocatalyst that addresses this challenge by combining defect engineering with dual-site catalysis. The study was published in Chinese Journal of Catalysis.

The catalyst, named Zn-CIS, was prepared by a simple one-step solvothermal method. Structural characterization and theoretical calculations showed that Zn²⁺ preferentially replaces In³⁺ in the CuInS₂ lattice. This substitution creates a charge imbalance, which promotes the spontaneous formation of sulfur vacancies through charge compensation.These sulfur vacancies play two roles. First, they act as shallow donor defects and improve the separation and transport of photogenerated charge carriers. Second, they redistribute electrons toward nearby Zn sites, turning the Zn-centered environment into an electron-rich region that is favorable for CO₂ activation.

The key catalytic feature of Zn-CIS is the formation of neighboring Cu–Zn dual sites. In this configuration, CO₂ is captured through asymmetric Cu–C and Zn–O interactions. This dual-site binding bends the originally linear CO₂ molecule, weakens the C–O bonds, and prepares it for further reduction. The Cu–Zn distance also shortens the spacing between C–C coupling sites, helping key intermediates approach each other and form the *COCHO intermediate required for ethylene production.

In situ infrared spectroscopy and density functional theory calculations revealed the likely reaction pathway:*CO₂ → *COOH → *CO → CHO → COCHO → C₂H₄. At the orbital level, Cu 3d orbitals hybridize with the CO₂ 2π* antibonding orbital, promoting electron injection into CO₂ and weakening the C–O bond. Meanwhile, sulfur-vacancy-induced charge redistribution activates Zn 3d orbitals, allowing them to couple with CO₂ bonding orbitals and stabilize the bent adsorption configuration. This “Cu-site electron injection and Zn-site configuration anchoring” mechanism is central to the enhanced CO₂ activation and C–C coupling.

The optimized 3Zn-CIS photocatalyst achieved a C₂H₄ production rate of 15.9 μmol g^-1 h^-1 under visible light without sacrificial agents, 5.9 times higher than pristine CuInS₂. The electron selectivity toward C₂H₄ reached 77.5%. Cycling tests confirmed good stability, while control and isotope-labeling experiments verified that the detected carbon-containing products originated from CO₂ reduction. This work provides an orbital-level understanding of how dopants and vacancies cooperate to regulate active sites. More broadly, it offers a design strategy for developing photocatalysts that can steer CO₂ reduction toward high-value C2 products. The results were published in Chinese Journal of Catalysis (DOI: 10.1016/S1872-2067(24)60168-3)

About the Journal

Chinese Journal of Catalysis is co-sponsored by Dalian Institute of Chemical Physics, Chinese Academy of Sciences and Chinese Chemical Society, and it is currently published by Elsevier group. This monthly journal publishes in English timely contributions of original and rigorously reviewed manuscripts covering all areas of catalysis. The journal publishes Reviews, Accounts, Communications, Articles, Highlights, Perspectives, and Viewpoints of highly scientific values that help understanding and defining of new concepts in both fundamental issues and practical applications of catalysis. Chinese Journal of Catalysis ranks among the top one journals in Applied Chemistry with a current SCI impact factor of 17.2. The Editors-in-Chief are Profs. Can Li and Tao Zhang.

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