Enhanced Local CO Coverage on Cu Quantum Dots for Boosting Electrocatalytic CO₂ Reduction to Ethylene

Abstract Ethylene (C₂H₄) electrosynthesis from the electrocatalytic CO₂ reduction process holds enormous potential applications in industrial production. However, the sluggish kinetics of C─C coupling often result in low yield and poor selectivity for C₂H₄ production. Herein, the performance of Cu catalysts of varying sizes is investigated, prepared via a cryo‐mediated liquid phase exfoliation technique, for the electrochemical CO₂ reduction to C₂H₄. The activity and selectivity of C₂H₄ gradually increase as the size of the Cu catalysts decreases from tens of nanometers to a few nanometers. Impressively, the 5 nm Cu quantum dots (Cu‐5) achieve a maximum C₂H₄ Faradaic efficiency (FE) of 81.5% and a half‐cell cathodic energy efficiency (CEE) of 42.2% with a large partial current density of 1.1 A cm⁻² at −0.93 V versus the reversible hydrogen electrode. Structural characterization and in situ spectroscopic analysis reveal that the Cu‐5 quantum dots, dominated by the (100) facet, provide an abundance of active sites that enhance CO₂ adsorption and activation, promoting the formation of *CO intermediates. The accumulation of *CO intermediates on the Cu active sites facilitates the CO‐CHO coupling reaction, thus enhancing the C₂H₄ production rate.