Understanding the potential of metal oxides for electrochemical co-reduction of carbon dioxide and nitrite

Understanding the formation of reaction intermediates is critical to developing active electrocatalysts that can convert carbon dioxide (CO 2 ) and nitrite (NO 2 − ) into valuable carbon–nitrogen (C–N) compounds under ambient conditions. Herein, we investigate a series of transition metal-oxides prepared using scalable flame spray pyrolysis (FSP) to evaluate their activity toward the electrochemical C–N coupling. Among the tested materials (ZnO x , SnO x , MoO x , InO x , and CeO x ), only ZnO x exhibits selective C–N bond formation, producing ammonium carbamate. In situ Fourier-transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculations reveal a previously unreported Eley-Rideal mechanism, where gaseous CO 2 directly interacts with adsorbed NO 2 RR-derived intermediates on the ZnO x . The intermediate *CO 2 NH 2 is identified as a key species in this pathway. DFT analysis further shows that desorption of *CO 2 NH 2 to form ammonium carbamate is more thermodynamically favorable than its protonation toward urea, explaining the selectivity observed. The superior performance of ZnO x is attributed to its strong NO 2 RR activity, suppressed hydrogen evolution reaction (HER), and favorable thermodynamics for C–N coupling, unlike other metal oxides tested. These findings provide deeper insights into the electrochemical C–N coupling mechanisms and offer design strategies for advanced catalysts targeting sustainable C–N product synthesis. The electrochemical C–N coupling from CO2 and nitrite (NO2−) on ZnOx surface produce ammonium carbamate via Eley-Rideal mechanism, in which the direct interaction between gaseous CO2 and *NO2 intermediate forms C–N bond. • New C–N bond formation mechanism via direct interaction between gaseous CO 2 and *NO 2 intermediate • Ammonium carbamate is the main C–N product from electrochemical co-reduction of CO 2 and NO 2 − • *NH 2 CO 2 is a crucial intermediate in this pathway and its protonation is the key for urea formation • ZnO x exhibits the highest C–N coupling efficiency among tested materials