Au-incorporated NiO nanocomposite thin films as electrochromic electrodes for supercapacitors

Electrode materials for electrochromic supercapacitors

Smart energy storage systems, such as electrochromic supercapacitor (ECSC) integrated technology, have drawn a lot of attention recently, and numerous developments have been made owing to their reliable performance. Developing novel electrode materials for ECSCs that embed two different technologies in a material is an exciting and emerging field of research. To date, the research into ECSC electrode materials has been ongoing with excellent efforts, which need to be systematically reviewed so that they can be used to develop more efficient ECSCs. This mini-review provides a general composition, main evaluation parameters and future perspectives for electrode materials of ECSCs as well as a brief overview of the published reports on ECSCs and performance statistics on the existing literature in this field.

Unveiling the Multistep Electrochemical Desorption Mechanism of Cubic NiO Films for Transmissive-to-Black Electrochromic Energy Storage Devices

Electrochromic smart windows offer dynamic control of sunshine and solar heat in modern architecture. Yet, how to obtain aesthetically pleasing color tuning states such as gray and black is a great challenge, and the corresponding desorption mechanism in electrochromism is still not well understood. Here, we report one transmissive-to-black NiO electrochromic film assembled by a facile and low-cost electrostatic spray technology, which achieves ultralarge optical modulation, high coloration efficiency, and remarkable energy storage capacity. By in-depth experimental analyses and the first-principle calculations, multistep electrochemical desorption mechanisms of OH^- and electrochromic switching kinetics of the NiO film were unveiled. Additionally, the assembled NiO film-based smart energy storage indicator can visually display its energy storage level in real time. Our obtained NiO films and subsequent devices can serve as potential candidates in a broad range of innovative electrochromic applications including multifunctional smart windows, energy-efficient displays, energy-storage indicators, electronic labels, etc.

One-step electrodeposition of a polypyrrole/NiO nanocomposite as a supercapacitor electrode

An electrochemical deposition technique was used to fabricate polypyrrole (Ppy)/NiO nanocomposite electrodes for supercapacitors. The nanocomposite electrodes were characterized and investigated by Fourier transform infrared spectroscopy (FTIR), X-ray Diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). The performance of supercapacitor electrodes of Ppy/NiO nanocomposite was enhanced compared with pristine Ppy electrode. It was found that the Ppy/NiO electrode electrodeposited at 4 A/cm-2 demonstrated the highest specific capacitance of 679 Fg-1 at 1 Ag-1 with an energy density of 94.4 Wh kg-1 and power density of 500.74 W kg-1. Capacitance retention of 83.9% of its initial capacitance after 1000 cycles at 1 Ag-1 was obtained. The high electrochemical performance of Ppy/NiO was due to the synergistic effect of NiO and Ppy, where a rich pores network-like structure made the electrolyte ions more easily accessible for Faradic reactions. This work provided a simple approach for preparing organic-inorganic composite materials as high-performance electrode materials for electrochemical supercapacitors.

Synthesis of novel Co3O4 nanocubes-NiO octahedral hybrids for electrochemical energy storage supercapacitors

Fabrication of novel metal oxide nanostructured composites is a proficient approach to develop efficient energy storage devices and development of cost-free and eco-friendly metal oxide nanostructures for supercapacitor applications received considerable attention in recent years. The Co₃O₄ nanocubes-NiO octahedral structured composite was constructed using facile and one-step calcination process. Cyclic voltammetry, charge-discharge, and electrochemical impedance spectral techniques have been employed to analyze the specific capacitance of the synthesized nanostructures and the composites. Specific capacitance and cycling stability of the composites were evaluated with the pristine Co₃O₄ and NiO nanostructures. The composite showed a specific capacitance of 832 F g^-1 at a current density of 0.25 A g^-1, which was ~1.5 and ~1.9-times higher than pristine Co₃O₄ nanocubes and NiO octahedral structure, respectively. On the other hand, electrode showed approximately 50 % capacity retention at a higher current density (5 Ag^-1) because of the uniform morphology of Co₃O₄ and NiO. The charge-discharge stability measurements of the composite showed an admirable specific capacitance retention capability, which was 94.5 % after 2000 continuous charge-discharge cycles at a current density of 5 A g^-1. The superior electrochemical performance of the nano-composite was ascribed to synergistic effects and uniform morphology. Efficient nanostructure development using facile and one-step calcination process and electrochemical performance make the synthesized composite a promising device for supercapacitor applications.

Construction of hierarchical Co9S8@NiO synergistic microstructure for high-performance asymmetric supercapacitor

Metal-organic frameworks (MOFs) become a research hot-spot owing to their unique properties originating from the ultra-high porosity and large specific surface area with highly accessible active sites. However, the electrochemical performance of a single component is unsatisfied when MOFs are applied as electrode material in a supercapacitor. In this work, the hierarchical hollow framework involving interconnected Co₉S₈ structure and NiO nanosheets (Co₉S₈@NiO) are successfully prepared by MOFs derived methods and proposed to electrode materials. As a result, the prepared Co₉S₈@NiO electrode materials exhibit a superior specific capacitance of 1627 F g^-1 at a current density of 1 A g^-1. Moreover, an assembled hybrid supercapacitor shows a high energy density of 51.65 Wh Kg^-1 at a power density of 749.8 W Kg^-1 as well as excellent long-term cycling stability with 81.79% capacity retention after 10,000 cycles. Meanwhile, we concluded that the marvelous electrochemical performance is closely associated with the unique structure of NiO, in particular, the nanosheet surface provides a superior specific surface area and rich accessible redox reaction sites, thus enlarged the contact between the surface and interface of the electrode material. Finally, two supercapacitor devices connected in series can light up four light-emitting diodes (LEDs) for about 30 min. Hence, the presented strategy represents a general route for supercapacitor electrode material with promising electrochemical performance, which can combine the MOFs template and other hierarchical nanosheets together.

In-Situ Synthesis of Heterostructured Carbon-Coated Co/MnO Nanowire Arrays for High-Performance Anodes in Asymmetric Supercapacitors

Structural design is often investigated to decrease the electron transfer depletion in/on the pseudocapacitive electrode for excellent capacitance performance. However, a simple way to improve the internal and external electron transfer efficiency is still challenging. In this work, we prepared a novel structure composed of cobalt (Co) nanoparticles (NPs) embedded MnO nanowires (NWs) with an N-doped carbon (NC) coating on carbon cloth (CC) by in situ thermal treatment of polydopamine (PDA) coated MnCo₂O_4.5 NWs in an inert atmosphere. The PDA coating was carbonized into the NC shell and simultaneously reduced the MnCo₂O_4.5 to Co NPs and MnO NWs, which greatly improve the surface and internal electron transfer ability on/in MnO boding well supercapacitive properties. The hybrid electrode shows a high specific capacitance of 747 F g⁻¹ at 1 A g⁻¹ and good cycling stability with 93% capacitance retention after 5,000 cycles at 10 A g⁻¹. By coupling with vanadium nitride with an N-doped carbon coating (VN@NC) negative electrode, the asymmetric supercapacitor delivers a high energy density of 48.15 Wh kg⁻¹ for a power density of 0.96 kW kg⁻¹ as well as outstanding cycling performance with 82% retention after 2000 cycles at 10 A g⁻¹. The electrode design and synthesis suggests large potential in the production of high-performance energy storage devices.