Adjacent Copper Single Atoms Promote C-C Coupling in Electrochemical CO₂ Reduction for the Efficient Conversion of Ethanol

The electrochemical CO₂ reduction reaction (CO₂RR) using renewable electricity is one of the most promising strategies for reaching the goal of carbon neutrality. Multicarbonous (C₂₊) products have broad applications, and ethanol is a valuable chemical and fuel. Many Cu-based catalysts have been reported to be efficient for the electrocatalytic CO₂RR to C₂₊ products, but they generally offer limited selectivity and current density toward ethanol. Herein, we proposed a silica-mediated hydrogen-bonded organic framework (HOF)-templated approach to preparing ultrahigh-density Cu single-atom catalysts (SACs) on thin-walled N-doped carbon nanotubes (TWN). The content of Cu in the catalysts prepared by this method could be up to 13.35 wt %. It was found that the catalysts showed outstanding performance for the electrochemical CO₂RR to ethanol, and the Faradaic efficiency (FE) of ethanol increased with the increase in Cu-N₃ site density. The FE of ethanol over the catalysts with 13.35 wt % Cu could reach ∼81.9% with a partial current density of 35.6 mA cm^-2 using an H-type cell, which is the best result for electrochemical CO₂RR to ethanol to date. In addition, the catalyst could be stably used for more than 25 h. Experimental and density functional theory (DFT) studies revealed that the adjacent Cu-N₃ active sites (one Cu atom coordinates with three N) were the active sites for the reaction, and their high density was crucial for the high FE of ethanol because the adjacent Cu-N₃ sites with a short distance could promote the C-C coupling synergistically.