Graphene In Situ Coated High-Oxygen Vacancy Co₃O_4−x Sphere Composites for High-Stability Supercapacitors

In this paper, the graphene in situ coated Co₃O₄ core–shell heterogeneous composites have been facilely fabricated via microwave plasma-enhanced chemical vapor deposition method. The graphene thin-shell-layer-covered Co₃O_4−x particles were revealed by FE-SEM, XRD, XPS and Raman spectra. And the ratio of Co²⁺/Co³⁺ is adjusted, and abundant surface oxygen vacancies are created by the microwave plasma etching, which can contribute to the improvement of electrochemical performance for the Co₃O₄/graphene core–shell composites. Results present that the graphene in situ coated Co₃O_4−x has a specific capacitance of 192.8 F g⁻¹ under the current density of 0.5 A g⁻¹, which is 4.5 times than that of the original Co₃O₄ sphere. Meanwhile, the core–shell heterogeneous composite displays excellent cyclic stability with ~ 98.5% specific capacitance retained after 20,000 cycle tests.