A Tandem Strategy for Enhancing Electrochemical CO Reduction Activity of Single-Atom Cu-S N Catalysts via Integration with Cu Nanoclusters.

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