A ZIF-67 derived NiCo-LDH nanosheet–nanourchin 3D hierarchical nanostructure for high-performance supercapacitors

Abstract

Nickel–cobalt layered double hydroxide (NiCo-LDH) is a promising electrode material for supercapacitors due to its high electrochemical activity. However, it easily restacks and aggregates due to its nanosheet structure, which limits the effective utilization of redox active sites. Herein, the NiCo-LDH nanosheets derived from ZIF-67 were in situ grown on the surface of a basic copper cobalt carbonate (CoCu) urchin-like skeleton and supported by nickel foam (CoCu@NiCo-LDH). The well-designed three-dimensional (3D) hierarchical nanostructure not only effectively prevents the aggregation of NiCo-LDH nanosheets, but also provides a rapid charge transport channel, which facilitates ion diffusion and electron transport, therefore enhancing the utilization of NiCo-LDH redox active sites to a greater extent. Besides, the synergistic interactions between NiCo-LDH nanosheets and CoCu nanoneedles further enrich the redox reactions and increase the electrical conductivity and reaction kinetics of the electrode at the same time. As a result, the CoCu@NiCo-LDH electrode exhibits outstanding electrochemical performance with an ultrahigh mass loading of 14 mg cm⁻², including excellent specific capacitance (18.71 F cm⁻² or 1346 F g⁻¹ at 3 mA cm⁻²) and distinguished rate capability of 87.3% from 3 mA cm⁻² to 50 mA cm⁻². When the CoCu@NiCo-LDH electrode was assembled with active carbon (AC) to form an asymmetric supercapacitor (ASC), the CoCu@NiCo-LDH//AC ASCs display outstanding energy density (1.98 mW h cm⁻²) and power density (97.5 mW cm⁻²) with excellent cycling stability (86.0% initial capacitance after 5000 cycles), and could keep an LED light bulb working for 90 min after only charging for 60 s. This work provides an effective strategy for the design and application of layered double hydroxide based pseudocapacitors.