3D Hierarchical Co3O4 Twin-Spheres with an Urchin-Like Structure: Large-Scale Synthesis, Multistep-Splitting Growth, and Electrochemical Pseudocapacitors

Novel, 3D hierarchical Co3O4 twin-spheres with an urchin-like structure are produced successfully on the large scale for the first time by a solvothermal synthesis of cobalt carbonate hydroxide hydrate, Co(CO3)0.5(OH)center dot 0.11H2O, and its subsequent calcination. The morphology of the precursor, which dominates the structure of the final product, evolves from nanorods to sheaf-like bundles, to flower-like structures, to dumbbell-like particles, and eventually to twin-spheres, accompanying a prolonged reaction time. A multistep-splitting growth mechanism is proposed to understand the formation of the 3D hierarchical twin-spheres of the precursor, based on the time effect on the morphologies of the precursor. The 3D hierarchical Co3O4 twin-spheres are further used as electrode materials to fabricate supercapacitors with high specific capacitances of 781, 754, 700, 670, and 611 F g-1 at current densities of 0.5, 1, 2, 4, and 8 A g-1, respectively. The devices also show high charge-discharge reversibility with an efficiency of 97.8% after cycling 1000 times at a current density of 4 A g-1.