Hierarchical core–shell Co₃O₄/graphene hybrid fibers: potential electrodes for supercapacitors

Toward the fast development of portable devices, the lightweight, flexible, and even wearable energy storage devices are very required. One effective device is the graphene-based fiber supercapacitors. Here we present the core–shell Co₃O₄/graphene hybrid fibers by hydrothermal method for the first time, where Co₃O₄ directly grows on the surface of graphene forming excellent hierarchical nanostructures. The combination of the Co₃O₄ shell and graphene core evidently improves the capacitive behaviors of the hybrid fibers. The Co₃O₄/graphene hybrid fibers are lightweight, flexible, and wearable, showing ultrahigh electrochemical performances such as large specific capacitance of 236.8 F g⁻¹ (196.3 mF cm⁻²) at current density of 0.2 A g⁻¹, outstanding rate capability, and excellent cycling stability (72.7% retention after 10000 cycles). The high electrochemical performances reveal the great potential of core–shell Co₃O₄/graphene hybrid fibers as electrodes in the energy storage system.