Controlled synthesis of Ni(OH)2/graphene composites and their transformation to NiO/graphene for energy storage

Electrode Materials, Structural Design, and Storage Mechanisms in Hybrid Supercapacitors

Currently, energy storage systems are of great importance in daily life due to our dependence on portable electronic devices and hybrid electric vehicles. Among these energy storage systems, hybrid supercapacitor devices, constructed from a battery-type positive electrode and a capacitor-type negative electrode, have attracted widespread interest due to their potential applications. In general, they have a high energy density, a long cycling life, high safety, and environmental friendliness. This review first addresses the recent developments in state-of-the-art electrode materials, the structural design of electrodes, and the optimization of electrode performance. Then we summarize the possible classification of hybrid supercapacitor devices, and their potential applications. Finally, the fundamental theoretical aspects, charge-storage mechanism, and future developing trends are discussed. This review is intended to provide future research directions for the next generation of high-performance energy storage devices.

Free-Standing rGO-CNT Nanocomposites with Excellent Rate Capability and Cycling Stability for Na2SO4 Aqueous Electrolyte Supercapacitors

Facing the increasing demand for various renewable energy storage devices and wearable and portable energy storage systems, the research on electrode materials with low costs and high energy densities has attracted great attention. Herein, free-standing rGO-CNT nanocomposites have been successfully synthesized by a facile hydrothermal method, in which the hierarchical porous network nanostructure is synergistically assembled by rGO nanosheets and CNT with interlaced network distribution. The rGO-CNT composite electrodes with synergistic enhancement of rGO and CNT exhibit high specific capacitance, excellent rate capability, exceptional conductivity and outstanding long-term cycling stability, especially for the optimal rGO-CNT₃₀ electrode. Applied to a symmetric supercapacitor systems (SSS) assembled with an rGO-CNT₃₀ electrode and with 1 M Na₂SO₄ aqueous solution as the electrolyte, the SSS possesses a high energy density of 12.29 W h kg⁻¹ and an outstanding cycling stability, with 91.42% of initial specific capacitance after 18,000 cycles. Results from these electrochemical properties suggest that the rGO-CNT₃₀ nanocomposite electrode is a promising candidate for the development of flexible and lightweight high-performance supercapacitors.

Effects of high-shear mixing and the graphene oxide weight fraction on the electrochemical properties of the GO/Ni(OH)2 electrode

High-shear mixing can efficiently enhance the homogeneity and the electrochemical performances of the GO/Ni(OH)₂ composite.

Porous nanorods of nickel-cobalt double hydroxide prepared by electrochemical co-deposition for high-performance supercapacitors

Nickel-cobalt double hydroxides (Ni-Co DHs) combined with cost-effectively commercial expanded graphite (EG) was prepared via a facile in-situ electrodeposition in mixed solvents of N,N-dimethylformamide and water. By simply adjust molar ratios of Ni²⁺/Co²⁺, a Ni-Co DHs/EG electrode in which Ni-Co DHs showing a porous-nanorod microstructure was fabricated. Thanks to synergistic effects between Ni(OH)₂ and Co(OH)₂ as well as the unique morphology of porous nanorods, an optimal Ni-Co DHs/EG electrode with a total mass loading of 4.0 mg cm^-2 can deliver a specific capacitance of 1246 F g^-1 at 1 A g^-1, a rate capability of 91.8% as the discharging current density increasing from 1 to 10 A g^-1, and a capacitance retention of 80.1% after 1000 cycles charged/discharged at 10 A g^-1. Thus we can draw a conclusion that the Ni-Co DHs/EG electrode possesses a satisfactory specific capacitance, extremely superior rate performance, and good cycle stability, therefore it can be very competitive for practical applications in supercapacitors.

Two-step controllable preparation of NiO nanocrystal anchored reduced graphene oxide sheets and their electrochemical performance as supercapacitors

A feasible and expandable way to prepare homogenous NiO nanocrystal coated reduced graphene oxide (rGO-NiO) for high performance supercapacitor electrodes.