Nickel-Based Hollow Spheres with Optimized Interfacial Electronic Structures by Highly Dispersed MoN for Efficient Urea Electrolysis

Abstract

Ni-Mo-based catalysts that exhibit well-synergized and readily accessible catalytic sites are ideal catalysts for achieving efficient electrocatalysis. Herein, the synthesis of hollow Ni spheres with a hierarchical nanosheet surface modified by highly dispersed MoN for efficient urea electrolysis is reported. This synthesis is based on the design of hollow Mo-Ni precursors featuring a nanosheet array surface, achieved through the phosphomolybdic acid (PMo₁₂)-mediated reconstruction of hollow Ni-BTC spheres. The optimized MoN-Ni catalyst can effectively drive both the urea oxidation reaction (UOR) and hydrogen evolution reaction at low potentials of 1.37 V and 191 mV, respectively, achieving a current density of 100 mA cm⁻². The electrolytic cell utilizing these catalysts can sustain 100 mA cm⁻² at a low voltage of 1.53 V and can operate continuously for over 220 h. The X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) analyses demonstrate the established built-in electric field facilitates electron transfer from MoN to Ni, optimizing the d-band center and consequently reducing the reaction barrier for the UOR. In situ electrochemical impedance spectroscopy (EIS) and in situ Fourier-transform infrared spectroscopy analyses indicate that MoN promotes the formation of high-valent Ni sites, which accelerates the UOR and facilitates the urea eletrolysis through a more environmentally friendly “carbonate” pathway.