Rationally stabilized hierarchical NiCo2O4 hollow nanoballs for high-performance asymmetric supercapacitors and excellent methanol oxidation

Abstract

An emergent theme of constructing intriguing morphologies of mono/multivalent materials, exhibiting a low diffusion length and large interfacial electrode–electrode cross section, along with low cost, improved performance and eco-effectiveness is essentially required for the growing energy sector. Hierarchically assembled spherical nanostructures possessing a hollow cavity facilitate ion accommodation over and inside the structure. However, a robust and generic strategy for the scalable synthesis of these hierarchical hollow morphologies is still lacking. Herein, we report an optimized strategy for the synthesis of perfect hollow bi-metallic oxide (NiCo₂O₄) nanoballs and discuss the involved growth mechanism following a series of chemical reactions/phenomena. Furthermore, the effectiveness of the synthesized hollow nanoballs as a model electrode material in an asymmetric supercapacitor and electro-oxidation of methanol is investigated. The fabricated electrodes exhibit a maximum specific capacitance of ∼721 F g⁻¹ and shows a high energy density of ∼40 W h kg⁻¹ in an asymmetric device configuration with activated carbon. The opening of the cavity evidently explains the high cycling stability and coulombic efficiency shown by the respective electrodes and device. Additionally, the hollow hosts showed a long lasting stable performance (7000 s and 500 cycles) with high currents for detecting 0.5 M methanol in 1 M KOH. The current strategy improves and optimizes the parameters to substantially improve the nano-chemistry at the reaction scale for batch synthesis. Such plausible strategies, which result in stabilizing greener and economically intriguing morphologies exhibiting exceptional interfacial electrochemistry, are actually path-breaking for pilot-scale integrated energy-storage and electro-oxidation systems.