Remarkable roles of electron-rich Mo and electron-deficient Ni active pairs in MoN/Ni heterostructures in promoting efficient urea oxidation reaction

Abstract

The application of urea oxidation reaction (UOR) can assist in hydrogen production through water electrolysis and reduce energy consumption. Ni-based catalysts have received widespread attention in the field of water electrolysis due to their low cost and high catalytic activity. However, the unavoidable Ni self-oxidation reaction (NSOR) of Ni-based catalysts will lead to unnecessary energy waste and strong adsorption of CO₂ during UOR, which will affect the activity of the active sites. Herein, we designed the MoN/Ni heterostructure to optimize the electronic structure of Ni sites in Ni-based catalysts to avoid NSOR. The X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) verified that the MoN/Ni heterostructure could induce the generation of electron-rich Mo sites and electron-deficient Ni sites active pairs in the catalyst. In-situ spectroscopic characterizations, electrochemical tests, and theoretical calculations all demonstrated that the electron-rich Mo sites promoted urea adsorption, and the electron-deficient Ni sites prevented the occurrence of NSOR, thereby promoting the activation of urea, rapid conversion of intermediate species, and desorption of CO₂ (the product of UOR). The synergistic effect of electron-rich Mo and electron-deficient Ni active pairs endows the catalyst with high catalytic activity for UOR, and can achieve a current density of 100 mA cm⁻² at only about 1.39 V vs. RHE, which is superior to many catalysts with NiOOH as the active site. This work has developed a novel high-performance catalyst with electron-rich and electron-deficient active pairs, which can be used for efficient urea oxidation.