Lattice Oxygen-Driven Co-Adsorption of Carbon Dioxide and Nitrate on Copper: A Pathway to Efficient Urea Electrosynthesis

Abstract

The electrochemical coupling of CO₂ and NO₃^– on copper-based catalysts presents a sustainable strategy for urea production while simultaneously addressing wastewater denitrification. However, the inefficient random adsorption of CO₂ and NO₃^– on the copper surface limits the interaction of the key carbon and nitrogen intermediates, thereby impeding efficient C–N coupling. In this study, we demonstrate that the residual lattice oxygen in oxide-derived copper nanosheets (O_L-Cu) can effectively tune the electron distribution, thus activating neighboring copper atoms and generating electron-deficient copper (Cu^δ+) sites. These Cu^δ+ sites enhance CO₂ adsorption and stabilize *CO intermediates, which enables the directional NO₃^– adsorption at adjacent Cu^δ+ sites. This mechanism shortens the C–N coupling pathway and achieves a urea yield of up to 298.67 mmol h^–1 g^–1 at −0.7 V versus RHE, with an average Faradaic efficiency of 31.71% at a high current density of ∼95 mA cm^–2. In situ spectroscopic measurements confirmed the formation of Cu^δ+ sites and tracked the evolution of the key intermediates (i.e., *CO, *NO, *OCNO, and *NOCONO) during urea synthesis. Density functional theory calculations revealed that Cu^δ+ sites promote adjacent coadsorption of *CO and *NO₃, as well as *OCNO and *NO₃, significantly improving C–N coupling kinetics. This study underscores the critical role of lattice oxygen in facilitating adjacent coadsorption and improving C–N coupling selectivity.