Oxygen vacancies modulated Co3O4 toward highly efficient electrooxidation of 5-hydroxymethylfurfural

Electrochemical oxidation of 5-hydroxymethylfurfural (HMF) has emerged as a promising method to produce highly valuable chemicals. Co-based electrocatalysts with oxygen vacancies are one of the most promising candidates. However, the relationship between their electrocatalytic behavior and the vacancy concentration is still ambiguous. In this work, the diverse oxygen vacancy contents of Co3O4 were realized via a simple adsorption-pyrolysis method and confirmed by X-ray diffraction, Raman, transmission electron microscopy, Xray photoelectron spectroscopy and X-ray absorption spectroscopy, respectively. It was found that the Co3O4 with proper oxygen vacancies prepared at optimized conditions exhibits a superior catalytic activity for HMF oxidation reaction (HMFOR) in 1.0 M KOH with 50 mM HMF electrolyte (with the potential of 1.35 V vs. RHE at 10 mA cm-2). Correlational characterizations and density functional theory calculations demonstrate that appropriate oxygen vacancies can promote HMF electrooxidation performance, whereas excessive oxygen vacancies can hinder electron transport and result in a significant decline in HMF electrooxidation performance. This study reveals the significance of appropriate oxygen vacancies in catalytic oxidation activity and provides important insights into the role of oxygen vacancies in catalytic oxidation reactions for the synthesis of defective material.