Tuning of Oxygen Vacancies in Co₃O₄ Electrocatalyst for Effectiveness in Urea Oxidation and Water Splitting

The development of an excellent multifunctional electrocatalyst that is based on non-precious metal is critical for improving the electrochemical processes of the hydrogen evolution reaction (HER), the oxygen evolution reaction (OER), and the urea oxidation reaction (UOR) in alkaline media. This study demonstrates that incorporating Mo into Co₃O₄ facilitated the formation of rich oxygen vacancies (Vo), which promotes effective nitrate adsorption and activation in urea electrolysis. Subsequently, in situ/operando X-ray absorption spectroscopy is used to explore the active sites in Mo-Co₃O₄-3 under OER, indicating the oxygen vacancies are first filled with OH^• in Mo-Co₃O₄; facilitated the pre-oxidation of low-valence Co, and promoted the reconstruction/deprotonation of intermediate Co-OOH^•. Mo-Co₃O₄-3 electrocatalysts show impressive HER, OER, and UOR with low overpotentials of 141 mV, 220 mV, and 1.32 V, respectively, at 10 mA cm^-2 in an alkaline medium. Furthermore, in situ/Operando Raman spectroscopy results reveal the importance of CoOOH active sites for enhanced electrochemical performance in Mo-Co₃O₄-3 compared to the pure Co₃O₄. The urea electrolyzer with Mo-Co₃O₄ electrocatalysts acts as an anode and the cathode delivers 1.42 V at 10 mA cm^-2. A viable approach to creating effective UOR electrocatalysts involves synergistic engineering exploiting doping and oxygen vacancies.