Microwave Assisted Synthesis of Porous NiCo₂O₄ Microspheres: Application as High Performance Asymmetric and Symmetric Supercapacitors with Large Areal Capacitance

Large areal capacitance is essentially required to integrate the energy storage devices at the microscale electronic appliances. Energy storage devices based on metal oxides are mostly fabricated with low mass loading per unit area which demonstrated low areal capacitance. It is still a challenge to fabricate supercapacitor devices of porous metal oxides with large areal capacitance. Herein we report microwave method followed by a pyrolysis of the as-prepared precursor is used to synthesize porous nickel cobaltite microspheres. Porous NiCo₂O₄ microspheres are capable to deliver large areal capacitance due to their high specific surface area and small crystallite size. The facile strategy is successfully demonstrated to fabricate aqueous-based asymmetric and symmetric supercapacitor devices of porous NiCo₂O₄ microspheres with high mass loading of electroactive materials. The asymmetric and symmetric devices exhibit maximum areal capacitance and energy density of 380 mF cm^-2 and 19.1 Wh Kg^-1 and 194 mF cm^-2 and 4.5 Wh Kg^-1 (based on total mass loading of 6.25 and 6.0 mg) respectively at current density of 1 mA cm^-2. The successful fabrication of symmetric device also indicates that NiCo₂O₄ can also be used as the negative electrode material for futuristic asymmetric devices.