Oxygen defect functionalized cobalt oxide towards high-efficient reaction with OH− for aqueous energy storage devices

The ever-growing environmental contamination and energy crisis have promoted the development of modern renewable energy resources. New generation aqueous energy storage devices have attracted increasing interest due to their excellent performance, high safety, and environmental friendliness. Here, the high-performance binder-free hierarchical defect-Co3O4 (D-Co3O4) nanosheets have been successfully designed and in-situ grown on Ni foam. By using NaBH4 as a reductant, the obtained hierarchical structure composed of ultrafine nanoparticles with massive oxygen defects has superior performance due to the high-efficiency reaction with OH−. The double optimization strategies are shown below: improving the diffusion of active species and bringing more exposed active sites to strengthen the Co3O4 electrode electrochemical performance. Eventually, the electrochemical properties of oxygen-defect-rich Co3O4@Ni (D-Co3O4@Ni) for supercapacitors and alkaline Zn–Co batteries have been systematically investigated. An asymmetric supercapacitor (ASC) device exhibited a remarkable energy density of 64.6 Wh/kg with excellent cycling stability (negligible decay after 5000 cycles). In addition, as the cathode for alkaline zinc battery, the D-Co3O4@Ni exhibits excellent cycling stability performance with no capacity decay after 400 cycles at 1.5 A/g. Effective hierarchical structure constructing, bind-free design, and introducing oxygen vacancies are practical modification approaches to meet new usage demands for supercapacitors and alkaline zinc batteries.