Unveiling the Electrooxidation of Urea: Intramolecular Coupling of the N-N Bond

The nitrogenous nucleophile electrooxidation reaction (NOR) plays a vital role in the degradation and transformation of available nitrogen. Focusing on the NOR mediated by the beta-Ni(OH)(2) electrode, we decipher the transformation mechanism of the nitrogenous nucleophile. For the two-step NOR, proton-coupled electron transfer (PCET) is the bridge between electrocatalytic dehydrogenation from beta-Ni(OH)(2) to beta-Ni(OH)O, and the spontaneous nucleophile dehydrogenative oxidation reaction. This theory can give a good explanation for hydrazine and primary amine oxidation reactions, but is insufficient for the urea oxidation reaction (UOR). Through operando tracing of bond rupture and formation processes during the UOR, as well as theoretical calculations, we propose a possible UOR mechanism whereby intramolecular coupling of the N-N bond, accompanied by PCET, hydration and rearrangement processes, results in high performance and ca. 100 % N-2 selectivity. These discoveries clarify the evolution of nitrogenous molecules during the NOR, and they elucidate fundamental aspects of electrocatalysis involving nitrogen-containing species.

Automated summary

This study delves into the crucial role of nitrogenous nucleophile electrooxidation reaction (NOR) in the degradation and transformation of available nitrogen, particularly focusing on the transformation mechanism mediated by the beta-Ni(OH)(2) electrode. The study proposes the role of proton-coupled electron transfer (PCET) in bridging the electrocatalytic dehydrogenation and spontaneous nucleophile dehydrogenative oxidation reaction, with a specific focus on the urea oxidation reaction (UOR). Through both operando tracing and theoretical calculations, a mechanism for UOR involving intramolecular coupling of the N-N bond, accompanied by PCET, hydration, and rearrangement processes, is proposed to achieve high performance and approximately 100% N-2 selectivity. These findings shed light on the evolution of nitrogenous molecules during NOR, as well as fundamental aspects of electrocatalysis involving nitrogen-containing species.