Facile and large-scale chemical synthesis of highly porous secondary submicron/micron-sized NiCo2O4 materials for high-performance aqueous hybrid AC-NiCo2O4 electrochemical capacitors

Highly porous nickel cobaltite (NiCo2O4) materials have been synthesized via a facile and scalable chemical synthesis route. The obtained NiCo2O4 material displays a typical secondary submicron/micron-sized (0.1-2 μm) agglomerate morphology, exhibiting large surface area (190.1 m2 g−1) and high porosity (1.136 cm3 g−1). The fabricated NiCo2O4 electrode shows high specific capacitance (351 F g−1 at 1 A g−1) and high-rate capability (82.1% capacitance retention at 8 A g−1), which is superior to many reported NiCo2O4 materials. Further, the assembled AC-NiCo2O4 aqueous hybrid capacitor exhibits high power and energy densities (2805 W kg−1, 6.8 Wh kg−1 at 8 A g−1) and high cycling stability (15% loss after 5000 cycles at 1.5 A g−1). The high-performance of the NiCo2O4 materials is attributed to their large surface area and highly porous structure which contribute to rich surface electroactive sites and easy ions transport pathways for facile electrochemical reactions.