Cobalt oxide nanoparticles combine Co²⁺/Co³⁺ redox chemistry with high catalytic and electrochemical activity, which is amplified by their large surface-to-volume ratio. The material can promote both oxidation reactions and oxygen evolution and reduction processes. Co₃O₄ is widely used in catalytic oxidation, gas sensors, supercapacitor electrodes, and rechargeable battery cathodes and anodes.