Accurate construction of cobalt vacancies in Co3O4 to promote oxyhydroxide formation for water oxidation

The introduction of defect sites has been widely reported to enhance electrocatalysts' abilities by increasing their affinity for reaction intermediates. Many different defect types, such as cation and anion vacancies, can exist in nano-materials. The different defect sites can make different contributions to the electrochemical ability. Therefore, a constructed defect should be accurate and specific, which makes it easy to identify the optimal defect type to facilitate electrochemical reactions. In this work, we used cobalt vacancies in Co3O4 as an example and synthesized Co3O4 with bivalent cobalt vacancies (Co3O4-VCo(II)) and trivalent cobalt vacancies (Co3O4-VCo(III)). Electrochemical results demonstrate that introducing cobalt vacancies considerably enhances the electrocatalytic activity of Co3O4. Furthermore, Co3O4-VCo(II) exhibits the most outstanding oxygen evolution ability with the fastest reaction kinetic rate. Quasi-operando X-ray photoelectron microscopy spectrum analysis results indicate that the presence of VCo(II) can accelerate CoOOH active site formation during the oxygen evolution reaction process. Density functional theory calculations reveal that introducing cobalt vacancies can endow Co3O4 with metal-like conductivity. The O p-band center can be moved near the Fermi level, and the free energy barrier can be the lowest with the presence of VCo(II), resulting in a fast kinetics rate of oxygen exchange at the electrocatalyst surface and optimal adsorption energy to reaction intermediates to display excellent electrochemical ability. This work provides substantial guidance for designing efficient defect-rich electrocatalysts.