Self-assembly of CNTs on Ni foam for enhanced performance of NiCoO2@CNT@NF supercapacitor electrode

Abstract Supercapacitors possess an essential application in storing intermittent energy and powering electric vehicles or wearable electronics. It should be a promising approach by combining carbon nanomaterials with metal oxides to promote energy density and maintain high power density and durable stability. Herein, carbon nanotubes (CNTs) were firstly organized on the surface of nickel foam (NF) by a facile and mild (room temperature) metal-induced self-assembly process. Afterward, NiCoO2 nanosheets are bonded by CNTs films via hydrothermal method, and then the integrated NiCoO2@CNTs@NF electrodes were successfully fabricated. The kinds of self-supporting electrodes have some advantages of hierarchical three-dimensional (3D) network structure, strong binding force between NiCoO2 nanosheets and Ni foam substrate, excellent conductivity tunnel for ions and electrons transport, and abundant active sites for ions adsorption and fast faradic redox reaction. Accordingly, the NiCoO2@CNTs@NF integrated electrode present the superior capacitive properties and stabilities because of outstanding synergistic effect between CNTs as electric double-layer capacitance (EDLC) materials and NiCoO2 nanosheets as Faradic pseudocapacitance materials. Asymmetric supercapacitors (ASCs) were also fabricated based on NiCoO2@CNTs@NF electrodes and active carbon supported on Ni foam electrodes. The ASCs show prominent performances of a high special capacitance (151 F g−1 at 5 mA cm−2), an outstanding rate capability (83.8% when current densities changed from 5 to 50 mA cm−2), durable stability (above 90% after 5000 cycles), and a high energy density (56.0 Wh kg−1). Such three ASCs devices connected in series can light up four blue light-emitting diodes (LEDs) that operates at a minimum voltage of 2 V. The presented work provides an efficient approach to design an outstanding electrode by combining active materials with a metal substrate.