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

Abstract

Electrochemical CO 2 -to-CO conversion is an advanced technology for converting waste CO 2 and closing carbon cycle. This process was usually obstructed by large energy barriers for *COOH formation. In this study, we developed a novel tandem electrocatalyst for CO 2 -to-CO conversion comprising the single Cu site co-coordinated with N and S anchored carbon matrix (Cu-S 1 N 3 ) and atomically dispersed Cu clusters (Cu x ), denoted as Cu-S 1 N 3 /Cu x . The configuration of Cu-S 1 N 3 /Cu x was clearly confirmed by X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analysis. The as-prepared Cu-S 1 N 3 /Cu x composite presents a 100% Faradaic efficiency towards CO generation (FE CO ) at -0.65 V vs. RHE and high FE CO over 90% from -0.55 to -0.75 V, outperforming the analogue with a Cu-N 4 coordination sphere (FE CO only 54% at -0.7 V). Experimental and density functional theory (DFT) calculations revealed that the unsymmetrical Cu-S 1 N 3 atomic interface in the carbon basal plane possesses an optimized binding energy for the key intermediate *COOH compared with Cu-N 4 site. At the same time, the adjacent Cu x effectively promotes the protonation of *CO 2 - by accelerating water dissociation and offering *H to the Cu-S 1 N 3 active sites. Consequently, the fine-tuned single Cu atoms and Cu clusters integrated in carbon matrix play a synergistic role in lowering the energy barrier of the rate-determining step (*COOH formation) and cooperatively improving the reductive conversion of CO 2 to CO. This work provides a tandem strategy for facilitating proton-coupled electron transfer over the atomic-level catalytic sites.