Abstract:

Developing efficient electrocatalysts for the urea oxidation reaction (UOR) is a promising strategy for purifying urea-laden wastewater and promoting energy-efficient hydrogen production. However, the strong binding of the hydroxyl group to Fe sites in the NiFe layered double hydroxide (NiFe-LDH) impedes the generation of active Ni³⁺-O, thus raising the onset potential of UOR. Moreover, identifying and tracking the active sites in NiFe-LDH at the molecular level remains a considerable challenge during the UOR process. Herein, we modified NiFe-LDH by incorporating the low-electronegativity S element to create S-NiFe-LDH, thereby optimizing the electron structure and facilitating the transfer of active sites from Ni²⁺ and Fe³⁺ in the original NiFe-LDH to high-valence Ni intermediates in S-NiFe-LDH at a low applied potential. Moreover, the incorporation of S into NiFe-LDH significantly reduces the thermodynamic barrier of the Ni active sites, advancing the intrinsic activity and kinetic process of the active sites for the decomposition of urea by facilitating the Ni³⁺-O formation because of the facile dehydrogenation steps at the Ni sites. As a result, the S-NiFe-LDH achieved excellent electrochemical UOR activity, with a low potential of 1.36 V and long-term durability at 100 mA cm^‒2, demonstrating promising prospects for practical application. Overall, this work unscrambles the immediate active sites during electrocatalysis and paves a new avenue for the electronic engineering of NiFe-based catalysts in the UOR process.

Key words: Urea oxidation reaction, S doping, NiFe layered hydroxide, Surface reconstruction, Active sites