A Tandem Strategy for Enhancing Electrochemical CO₂ Reduction Activity of Single‐Atom Cu‐S₁N₃ Catalysts via Integration with Cu Nanoclusters

We developed a tandem electrocatalyst for CO₂ -to-CO conversion comprising the single Cu site co-coordinated with N and S anchored carbon matrix (Cu-S₁ N₃ ) and atomically dispersed Cu clusters (Cux ), denoted as Cu-S₁ N₃ /Cux . The as-prepared Cu-S₁ N₃ /Cux composite presents a 100 % Faradaic efficiency towards CO generation (FECO ) at -0.65 V vs. RHE and high FECO over 90 % from -0.55 to -0.75 V, outperforming the analogues with Cu-N₄ (FECO only 54 % at -0.7 V) and Cu-S₁ N₃ (FECO 70 % at -0.7 V) configurations. The unsymmetrical Cu-S₁ N₃ atomic interface in the carbon basal plane possesses an optimized binding energy for the key intermediate *COOH compared with Cu-N₄ site. At the same time, the adjacent Cux effectively promotes the protonation of *CO₂ ⁻ by accelerating water dissociation and offering *H to the Cu-S₁ N₃ active sites. This work provides a tandem strategy for facilitating proton-coupled electron transfer over the atomic-level catalytic sites.