(329d) Empowering Urea Electrosynthesis from Carbon Dioxide and Nitrate: Modulating *NO2 Adsorption on Copper for Enhanced Performance

In conventional electrochemical coupling reactions involving two distinct reactants, catalysts are typically required to exhibit high activity for both half-reactions while ensuring kinetic compatibility. However, in C-N coupling reactions where the valency of carbon or nitrogen remains constant in the reactants and products, achieving high production performance may not necessitate the catalyst to be equally active for both half-reactions. As the typical C-N bond-involved high-value chemical, urea commands significant market demand, which is a prominent fertilizer for agriculture. This study investigates this hypothesis within the framework of urea electrosynthesis, a process that directly converts carbon dioxide (CO₂) and nitrate (NO₃⁻) into urea without altering the valence state of carbon.

Utilizing copper (Cu) as a catalyst, capable of catalyzing both CO₂ reduction and NO₃⁻ reduction, urea synthesis can occur within a potential region where merely NO₃⁻ reduction takes place, contrary to the expectation of kinetic matching. Through the implementation of density functional theory, we predict that the carbon intermediate involved in the C-N coupling process primarily originates from CO₂ rather than from CO₂ reduction. Moreover, we elucidate the pivotal approach to achieve high urea selectivity is regulating the competition of *NO₂ for coupling with CO₂ and H.

Furthermore, by incorporating a minute quantity of non-metallic atoms with high electronegativity, Cu-based catalysts are synthesized, significantly enhancing selectivity towards urea from below 20% to 80% with the highest yield rate of 6075 μg h⁻¹ cm⁻² for 100 h in a typical flow cell. The improvement predominantly stems from the mitigated adsorption of intermediates, making *NO₂ more predisposed to couple with CO₂ rather than undergoing hydrogenation. The reaction mechanism is further investigated through in-situ Fourier-transform infrared techniques. Scaling up the electrode into a 10 × 10 cm² flow cell, the overall current can escalate to 3.5 A while maintaining approximately 50% selectivity towards urea for a duration of 10 hours. This work provides an alternative strategy for designing catalysts for electrochemical coupling reactions.