The electrochemical CO₂ reduction reaction (CO₂RR) plays an important role in addressing climate-change issues and global energy demands as part of a carbon-neutral energy cycle. Selective conversion of CO₂ to multi-carbon products remains a challenge due to the sluggish kinetics during C-C coupling.  

Cu-based materials, including metallic Cu, Cu oxides, and Cu-containing molecules, have been proved to be capable of producing C₂/C₂₊ hydrocarbons in considerable amounts. However, these conventional Cu-based electrocatalysts usually suffer from the insufficient clarity of the active sites and low selectivity. Copper-based tandem catalysts with well-defined Cu coordination environment for CO₂RR are highly desirable, due to their unique geometric-electronic properties and helpfulness for revealing structure-property correlation. 

In a study published in Advanced Energy Materials, the research group led by Prof. ZHANG Jian from Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences constructed a tandem catalyst Ag@BIF-104NSs(Cu) at atomic configuration scale to enhance the selectivity and activity for CO₂RR to C₂H₄, providing fundamental comprehension for the C-C coupling in the CO₂ reduction process. 

The researchers constructed the composite material Ag@BIF-104NSs(Cu) as a tandem catalyst. The support of BIF-104(Cu) nanosheet provided the well-defined environment of Cu atoms. Ag nanoparticles were attached to Cu atoms via coordination effect with the abundant carboxylic functional ligands in the BIF-104NSs(Cu) surface.  

By electrochemistry performance test, the researchers found that this tandem catalyst Ag@BIF-104NSs(Cu) could efficiently enhance the faradic efficiency of C₂H₄ products (FE of 21.43 %), which is almost 6-folds enhancements of BIF-104NSs(Cu) alone (3.82 %).  

Through electrochemistry mechanism analysis, they discovered that Ag@BIF-104NSs(Cu) tandem catalysts provide more effective active sites and faster electron transfer in electroreduction CO₂ process, leading to enhanced CO₂RR activity and C₂H₄ selectivity. 

Besides, density functional theory calculations revealed that the Ag sites in the Ag@BIF-104NSs(Cu) catalysts can efficiently reduce CO₂ and enrich surface coverage of *CO, which subsequently migrated to the atomic proximity Cu sites. Therefore, the Cu-Ag atom pair is responsible for the C-C coupling of the local enriched *CO and further production of C₂H₄. 

This study provides a new approach for developing high-performance electrochemical CO₂ reduction tandem catalysts to prepare C₂ products.