Facile synthesis of carbon-NiCoO₂ composite microspheres with pitaya-type structure and their application in supercapacitors

Three-dimensionally porous oxide composite materials have recently attracted increasing interest because of their exciting potential in electrochemical energy conversion and storage. Herein, novel carbon-NiCoO₂ microsphere composites with a pitaya-type structure have been prepared for the first time via a one-pot hydrothermal synthesis followed by annealing treatment. These composite microspheres are composed of NiCoO₂ nanoparticles inserted into porous carbon microspheres. Furthermore, the prepared carbon-NiCoO₂ electrodes exhibit excellent rate capacity when used as supercapacitor electrodes. Under a current density of 1 and 10 A g^-1, the optimized composite electrode exhibits specific capacitance of 507 and 390 F g^-1, respectively. The excellent electrochemical properties can possibly be attributed to the intrinsic nature of NiCoO₂, the ultrafine NiCoO₂ particles, and sufficient space being available to interact with the electrolyte. This facile synthesis method may be extended to prepare other carbon-based metal oxides, which may find application in catalysts and adsorption due to their unique structural features.