Pairing N-Vacancy and Adjacent Ni-Sites in the Local Microenvironment to Regulate the Urea Oxidation Reaction Pathway...

The urea oxidation reaction (UOR) is a promising approach for replacing the oxygen evolution reaction in hydrogen production, offering lower energy consumption. However, the kinetics of Ni-based catalysts for UOR are hindered by the high formation potential of NiOOH and its repeated transition with Ni(OH)₂. In this study, a local microenvironment featuring electron-deficient N-vacancies (V_N) paired with adjacent electron-rich Ni-sites on Ni₃N (Ni₃N-V_N) to enhance UOR kinetics is constructed. The electron-rich Ni-sites significantly reduce the energy barrier for NiOOH formation and promote the conversion of Ni(OH)₂ to NiOOH. Meanwhile, the V_N sites induce low charge transfer resistance in Ni₃N, facilitating efficient electron transfer and boosting UOR performance while ensuring the stability of the active NiOOH phase. The V_N sites promote the adsorption of the urea N atom at the active site, favoring the reaction pathway toward "NCO⁻" formation without requiring complete urea dissociation. This pathway alleviates the NiOOH/Ni(OH)₂ conversion cycle, lowers charge transfer resistance, and improves reaction kinetics. Ni₃N-V_N demonstrates excellent UOR activity (low potential of 1.46 V at 1000 mA cm^-2) and industrial prospects (integrating into an anion exchange membrane flow electrolyzer with 20% Pt/C, producing 600 mA cm^-2 at 1.84 V), highlighting its potential for practical applications.