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

Abstract

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.