A facile and cost-effective synthesis of mesoporous NiCo2O4 nanoparticles and their capacitive behavior in electrochemical capacitors

Mesoporous nickel cobaltite (NiCo2O4) nanoparticles were synthesized via a facile and cost-effective ball milling solid-state method and followed by a simple thermal treatment. The physical structures of the materials were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectrum, and Brunauer-Emmett-Teller methods. The electrochemical performances of the materials were investigated by cyclic voltammetry, chronopotentiomerty, electrochemical impedance spectra, and cycling life measurements. The physical characterizations show that the obtained materials consist of nanostructured NiCo2O4 spinels of hexagonal morphology and a spot of nanosized NiO spherical particles and display a layer-stacked mesoporous structure. Electrochemical measurements display that the NiCo2O4 electrode exhibits mainly a Faradaic pseudocapacitive behavior and possesses high performance even after 5,000 cycles with a specific capacitance value of 554 F g(-1) at 2 mV s(-1) in 1 M KOH electrolytes, a power density and energy density respective value of 2,318 W kg(-1) and 5.15 W h kg(-1) at a current density of 8 A g(-1) in 1 M KOH electrolytes, and an excellent cycling behavior with no capacitance decays and high coulombic efficiency close to 100 % during 5,000 cycles at a current density of 2 A g(-1) in 1 M KOH electrolytes, indicating a promising application for electrochemical capacitors.