A facile and scalable strategy for synthesis of size-tunable NiCo₂O₄ with nanocoral-like architecture for high-performance supercapacitors

Graphical abstract: We reported a facile and scalable strategy for synthesis of size-tunable NiCo₂O₄ with nanocoral-like architecture. The unique structure will improve faradaic redox reaction and mass transfer, NiCo₂O₄ offers excellent electrochemical performance for supercapacitors. - Highlights: • We reported a facile and scalable strategy for synthesis of size-tunable NiCo₂O₄ withnanocoral-lide architecture. • Combination of microwave and tertbutanol as medium creates ultrathin nickel/cobalt double hydroxide with flowerclusters. • The method is very simple, rapid and efficient, it can be used for large scale productionof nanomaterials. • The size of NiCo₂O₄ nanocorals is easy to be can be controlled by adjusting calcination temperature. • Unique structure enhances rates of electron transfer and mass transport, NiCo₂O₄shows high electrochemical performance. - Abstract: There is a great need to develop high-performance electroactive materials for supercapacitors. The study reported a facile and scalable strategy for synthesis of size-tunable NiCo₂O₄ with nanocoral-like architecture. Cobalt nitrate and nickel nitrate were dissolved in a tertbutanol solution and heated to reflux state under microwave radiation. The amounts of ammonia was dropped into the mixed solution to form nickel/cobalt double hydroxides. The reaction can complete within 15 min with the productivity of 99.9%. The obtained double hydroxides display flowercluster-like ultrathin nanostructure. The double hydroxide was calcined into different NiCo₂O₄ products using different calcination temperature, including 400 °C, 500 °C, 600 °C and 700 °C. The resulting NiCo₂O₄ is of nanocoral-like architecture. Interestingly, the size of coral can be easily controlled by adjusting the temperature. The NiCo₂O₄ prepared at 400°C gives a minimum building block size (10.2 nm) and maximum specific surface area (108.8 m²·g⁻¹). The unique structure will greatly improve faradaic redox reaction and mass transfer, the NiCo₂O₄ electrode exhibits excellent electrochemical performances for supercapacitors. Its maximum specific capacitance was 870.7 F g⁻¹ at the current density of 1A g⁻¹. The specific capacitance can remain 805.8 F g⁻¹ at the current density of 10 A g⁻¹, which offers an increase of about 4.6% after 1500 cycles. Moreover, the study also provides prominent approach to fabricate various size-adjustable nano-materials with three-dimensional network framework for supercapacitors, Li-ion batteries and other energy storge devices