Porous NiCo2O4 spheres tuned through carbon quantum dots utilised as advanced materials for an asymmetric supercapacitor

Abstract

Carbon quantum dots (CQDs) tuned porous NiCo₂O₄ sphere composites are prepared for the first time via a reflux synthesis route followed by a post annealing treatment. Benefiting from the advantages of the unique porous structure with a large specific surface area, high mesoporosity and superior electronic conductivity, the as-obtained CQDs/NiCo₂O₄ composite electrode exhibits high specific capacitance (856 F g⁻¹ at 1 A g⁻¹), excellent rate capability (83.9%, 72.5% and 60.8% capacity retention rate at 20, 50 and 100 A g⁻¹, respectively) and exceptional cycling stability (98.75% of the initial capacity retention over 10 000 cycles at 5 A g⁻¹). Furthermore, the assembled AC//CQDs/NiCo₂O₄ asymmetric supercapacitor manifests a high energy density (27.8 W h kg⁻¹) at a power density of 128 W kg⁻¹ or a high power density (10.24 kW kg⁻¹) at the reasonable energy density of 13.1 W h kg⁻¹ and remarkable cycling stability (101.9% of the initial capacity retention over 5000 cycles at 3 A g⁻¹). The results above suggest a great potential of the porous CQDs/NiCo₂O₄ composites in the development of high-performance electrochemical energy storage devices for practical applications.