Ag-mediated in situ reconstruction of Cu/Cu₂O interfaces for selective CO₂ electroreduction to ethanol

The electrochemical reduction of carbon dioxide (CO₂) into multi‑carbon products offers a promising route for sustainable fuel and chemical synthesis, yet achieving high selectivity toward ethanol (C₂H₅OH) remains challenging. Herein, through a unique in situ transformation strategy, copper quantum dots could convert into Ag₃PO₄/Cu₃(PO₄)₂ nanosheet pre-catalysts by sonicating in phosphate buffer solution (PBS) and silver nitrate. Under electroreduction conditions, this Ag-modified precursor undergoes dynamic reconstruction into a Cu/Cu₂O/Ag, whereas the Ag-free analogue is completely reduced to metallic Cu. The resulting catalyst exhibits remarkable C₂H₅OH selectivity with a Faradaic efficiency (FE) of 54.8% and a high partial current density of 262.6 mA cm^-2 at -1.05 V (relative to reversible hydrogen electrode, RHE), corresponding to a half-cell cathode energy efficiency (CEE) of 27.2%, and alongside with excellent stability of 120 h. The in situ spectroscopy and structural analysis reveal that the incorporation of Ag plays a crucial role in stabilizing Cu(I) species under working conditions, which enriches the surface CO coverage and facilitates the critical CC coupling step toward C₂H₅OH. Furthermore, the residual copper quantum dots within the structure enhance the overall electrical conductivity. This work highlights the dynamic role of Ag in modulating the oxidation state and interfacial environment of Cu, providing a design principle for CO₂-to-C₂₊ electrocatalysts through controlled precursor transformation and electronic engineering.