In situ encapsulation of Co3O4 polyhedra in graphene sheets for high-capacitance supercapacitors

Abstract

Co₃O₄ polyhedra were well encapsulated in reduced graphene oxide (rGO) sheets by in situ growth of Co-based zeolitic imidazolate framework (ZIF-67) polyhedra in the presence of graphene oxide followed by thermal annealing. The resultant rGO/Co₃O₄ composites consist of a continuously-conductive double-network constructed from graphene sheets and the derived N-doped carbons from ZIF-67, showing a large specific surface area of 523 m² g⁻¹. The as-fabricated symmetrical supercapacitor based on rGO/Co₃O₄ exhibits a high specific capacitance of 277.5 F g⁻¹ at 25 A g⁻¹ and an energy density of 24.7 W h kg⁻¹ at a power density of up to 40 kW kg⁻¹. The supercapacitor also retains 87.5% of the initial capacitance over 5000 cycles at 5 A g⁻¹. Such large capacitance, high energy density, and excellent cycling stability for rGO/Co₃O₄ are attributable to the 3D double conductive network from 2D graphene sheets and porous channels of pseudo-capacitive Co₃O₄ polyhedra.