Porous NiCo2O4–FeCo2O4 Nanowire Arrays as Advanced Electrodes for High-Performance Flexible Asymmetric Supercapacitors

Efficient supercapacitors have attracted wide attention by the exploration of hybrid materials integrating the merits of individual components as promising electrode materials. However, the construction of advanced hybrid structures for highly enhanced electrochemical energy storage is still challenging. Herein, integration of a strong compositional synergy between various bimetallic oxides, MCo2O4 (M = Ni, Fe, and so on), and inducing rich defects for more redox sites are proposed. A novel NiCo2O4–FeCo2O4 hybrid array of nanowires with a large number of nanopores and crystal interfaces is synthesized via hydrothermal reactions and fast calcination. The performance of the NiCo2O4–FeCo2O4/carbon cloth electrode is good and is far beyond that of single-component MCo2O4 electrodes, which exhibits a specific capacity of 490 F/g at 4.0 A/g. The integration of bimetallic redox centers reconstructing the electronic coordination and the nanopores providing highly exposed active surfaces and active sites for highly efficient electrolyte ion diffusion contribute to the enhanced performance. An asymmetric solid-state supercapacitor composed of NiCo2O4–FeCo2O4 and graphene (both using carbon cloth as substrates) as the anode and cathode electrodes, respectively, exhibits a high energy density of 88.9 Wh/cm2 (at a power density of 800 mW/cm2). In particular, the flexible asymmetric device exhibits excellent deformation-tolerant electrochemical stability with nearly overlapping cyclic voltammetry curves at varying bending angles. This work proposes additional methodologies to the fabrication of excellent-performance flexible all-solid-state devices for wearable devices.