Unlocking Efficient Electrochemical Urea Oxidation and Understanding Mechanism Insights of Co-Doped NiS

Abstract

Urea electrooxidation serves as the core of urea-based fuel cells, urea electrolysis for energy generation, and urea-based wastewater treatment for environmental applications. This study emphasizes the development of electrocatalysts made from nickel–cobalt bimetallic sulfide, synthesized through an ultrasonic-assisted hydrothermal synthesis method, focusing on their capacity to oxidize urea under alkaline conditions. The objective was to reduce the onset potential for this reaction. These nickel–cobalt bimetallic sulfide catalysts were characterized by using various techniques, including X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). A notable decrease in overpotential was observed: 70 mV for Ni_0.75Co_0.25S and 130 mV for Ni_0.50Co_0.50S, compared to a Ni₁Co₀S electrode. Furthermore, the XPS analysis indicates that the ratio of Ni³⁺/Ni²⁺ is higher for Ni_0.75Co_0.25S than for other combinations, with Ni³⁺ acting as the primary active center for urea electrooxidation. This reduction in the onset potential for urea oxidation and the increase in Ni³⁺ on the nickel–cobalt bimetallic sulfide electrodes reveal significant potential for future applications in urea electrooxidation.