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

Abstract

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.

Asymmetrical Supercapacitor Fabricated Using Sodium Nickel Phosphate and Transition Metal-Carbon Nitride Nanocomposite as Electrodes

“…Asymmetric stretching of the P–O–P bonds is detected at 905 cm –1 . M–OH absorbs in the regime 700–500 cm –1 , and the peak at 573 cm –1 can be correlated to the bending of Ni–O–H and due to the asymmetric bending vibration of PO 4 . − …”

“…The peak at 1116 cm –1 is owing to the asymmetric stretching of PO 4. − Vibrational bands of PO 4 3– are observed around 1093, 1026, and 994 cm –1 , corresponding to tetrahedral stretching vibrations. Asymmetric stretching of the P–O–P bonds is detected at 905 cm –1 .…”

“…8 Moreover, bimetallic compounds exhibit synergistic effects of metal cations to improve the electrochemical performance. 9,10 The primary concern of using these materials in supercapacitor applications is the volume change during the charging− discharging process, which disrupts the contact between particles and increases the material's resistance, resulting in inferior cyclic stability.…”

“…Nickel–manganese oxides are extensively being investigated due to their excellent electrical conduction, higher electrochemical performance, and presence of oxidation–reduction couples of Ni 2+ /Ni 3+ and Mn 3+ /Mn 4+ . Moreover, bimetallic compounds exhibit synergistic effects of metal cations to improve the electrochemical performance. , The primary concern of using these materials in supercapacitor applications is the volume change during the charging–discharging process, which disrupts the contact between particles and increases the material’s resistance, resulting in inferior cyclic stability.…”

Freestanding carbon‐based hybrid anodes for flexible supercapacitors: Part I—An inclusive outlook on current collectors and configurations

“…For example, Tong et al constructed a hierarchically constructed anode where a Fe 2 O 3 shell anchored on a CuO core has been deposited onto a carbon cloth current collector. Here the carbon cloth was chosen as a current collector, due to its efficient conductive pathways for electronic conduction (T. Wu, Zhou, et al, 2021). Xinyi et al reported an asymmetric supercapacitor by employing an anode of FeCo 2 O 4 @Ppy (polypyrrole) core/shell nanowires grown onto carbon cloth in a flexible supercapacitor.…”