Transition-metal oxides with peak oxygen vacancy content for oxygen electrocatalysis

Introducing oxygen vacancies in transition-metal oxides is an effective method to improve electrocatalytic water oxidation activity. However, controlled defect engineering in metal oxides remains a challenge. In this study, high oxygen vacancy content is achieved in transition-metal oxides by regulating the pyrolysis temperature of corresponding metal hydroxides. Specifically, Co3O4 nanoflowers with a large amount of oxygen vacancies were obtained by pyrolysis of Co(OH)2 in air at 400°C. The high oxygen vacancy content may be due to the rich porous structure and atomic rearrangement of Co and O. Electrochemical results showed that oxygen vacancy defect-rich Co3O4 prepared at 400°C (Co3O4-400) has the lowest overpotential η of 321 mV for oxygen evolution reaction at a current density j of 10 mA cm−2 in 1.0 mol L−1 KOH compared with Co3O4-300 (348 mV) and Co3O4-500 (366 mV). Theoretical calculations and experiments verified the beneficial effect of oxygen vacancies in Co3O4. This study offers an efficient strategy to develop highly active transition-metal oxides with optimized oxygen vacancies.