One-pot microwave synthesis of NiO/MnO2 composite as a high-performance electrode material for supercapacitors

Hydrothermal synthesis of NiO nanoparticles decorated hierarchical MnO2 nanowire for supercapacitor electrode with improved electrochemical performance

In this work, MnO2/NiO nanocomposite electrode materials have been synthesized by a cost-effective hydrothermal method. The effect of the concentrations (0, 1, 3, 5, and 7 wt%) of NiO nanoparticles on the surface morphology, structural properties, and electrochemical performance of the nanocomposites was characterized by different characterization techniques. The scanning electron micrographs (SEM) reveal that the as-prepared NiO nanoparticles are well connected and stuck with the MnO2 nanowires. The transmission electron microscopy (TEM) analysis showed an increase in the interplanar spacing due to the incorporation of NiO nanoparticles. The different structural parameters of MnO2/NiO nanocomposites were also found to vary with the concentration of NiO. The MnO2/NiO nanocomposites provide an improved electrochemical performance together with a specific capacitance as high as 343 F/g at 1.25 A/g current density. The electrochemical spectroscopic analysis revealed a reduction in charge transfer resistance due to the introduction of NiO, indicating a rapid carrier transportation between the materials interface. The improved electrochemical performance of MnO2/NiO can be attributed to good interfacial interaction, a large interlayer distance, and low charge transfer resistance. The unique features of MnO2/NiO and the cost-effective hydrothermal method will open up a new route for the fabrication of a promising supercapacitor electrode.

Impact of mesoporous SiO2 support for Ni/polypyrrole nanocomposite particles on their capacitive performance

The inclusion of mesoporous H2N-SiO2 support in H2N-SiO2/Ni/PPy nanocomposite particles improved their electrochemical performance, suitable for energy storage devices.

Cost-Effective Synthesis of Efficient CoWO4/Ni Nanocomposite Electrode Material for Supercapacitor Applications

In the present study, the synthesis of CoWO4 (CWO)-Ni nanocomposites was conducted using a wet chemical method. The crystalline phases and morphologies of the Ni nanoparticles, CWO, and CWO-Ni composites were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDAX). The electrochemical properties of CWO and CWO-Ni composite electrode materials were assessed by cyclic voltammetry (CV), and galvanostatic charge-discharge (GCD) tests using KOH as a supporting electrolyte. Among the CWO-Ni composites containing different amounts of Ni1, Ni2, and Ni3, CWO-Ni3 exhibited the highest specific capacitance of 271 F g-1 at 1 A g-1, which was greater than that of bare CWO (128 F g-1). Moreover, the CWO-Ni3 composite electrode material displayed excellent reversible cyclic stability and maintained 86.4% of its initial capacitance after 1500 discharge cycles. The results obtained herein demonstrate that the prepared CWO-Ni3 nanocomposite is a promising electrode candidate for supercapacitor applications.

Enhanced Activity of Hierarchical Nanostructural Birnessite-MnO2-Based Materials Deposited onto Nickel Foam for Efficient Supercapacitor Electrodes

Hierarchical porous birnessite-MnO₂-based nanostructure composite materials were prepared on a nickel foam substrate by a successive ionic layer adsorption and reaction method (SILAR). Following composition with reduced graphene oxide (rGO) and multiwall carbon nanotubes (MWCNTs), the as-obtained MnO₂, MnO₂/rGO and MnO₂/rGO-MWCNT materials exhibited pore size distributions of 2-8 nm, 5-15 nm and 2-75 nm, respectively. For the MnO₂/rGO-MWCNT material in particular, the addition of MWCNT and rGO enhanced the superb distribution of micropores, mesopores and macropores and greatly improved the electrochemical performance. The as-obtained MnO₂/rGO-MWCNT/NF electrode showed a specific capacitance that reached as high as 416 F·g^-1 at 1 A·g^-1 in 1 M Na₂SO₄ aqueous electrolyte and also an excellent rate capability and high cycling stability, with a capacitance retention of 85.6% after 10,000 cycles. Electrochemical impedance spectroscopy (EIS) analyses showed a low resistance charge transfer resistance for the as-prepared MnO₂/rGO-MWCNT/NF nanostructures. Therefore, MnO₂/rGO-MWCNT/NF composites were successfully synthesized and displayed enhanced electrochemical performance as potential electrode materials for supercapacitors.

Nanofiber NiMoO4/g-C3N4 Composite Electrode Materials for Redox Supercapacitor Applications

NiMoO₄/g-C₃N₄ was fabricated by a hydrothermal method and used as an electrode material in a supercapacitor. The samples were characterized by XRD, FTIR, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to study the physical and structural properties of the as-prepared NiMoO₄/g-C₃N₄ material. The electrochemical responses of pristine NiMoO₄ and the NiMoO₄/g-C₃N₄ nanocomposite material were investigated by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). From the CD studies, the NiMoO₄/g-C₃N₄ nanocomposite revealed a higher maximum specific capacitance (510 Fg⁻¹) in comparison to pristine NiMoO₄ (203 Fg⁻¹). In addition, the NiMoO₄/g-C₃N₄ composite electrode material exhibited high stability, which maintained up to 91.8% capacity even after 2000 charge-discharge cycles. Finally, NiMoO₄/g-C₃N₄ was found to exhibit an energy density value of 11.3 Whkg⁻¹. These findings clearly suggested that NiMoO₄/g-C₃N₄ could be a suitable electrode material for electrochemical capacitors.

Fiber-Shaped Supercapacitors Fabricated Using Hierarchical Nanostructures of NiCo2O4 Nanoneedles and MnO2 Nanoflakes on Roughened Ni Wire

Electrostatic capacitors have high power density but low energy density. In contrast, batteries and fuel cells have high energy density but low power density. However, supercapacitors can simultaneously achieve both high power density and energy density. Herein, we propose a supercapacitor, in which etched nickel wire was used as a current collector due to its high conductivity. Two redox reactive materials, MnO2 nanoflakes and NiCo2O4 nanoneedles, were used in a hierarchical structure to cover the roughened surface of the Ni wire to maximize the effective surface area. Thus, a specific capacitance, energy density, and power density of 14.4 F/cm3, 2 mWh/cm3, and 0.1 W/cm3, respectively, was obtained via single-electrode experiments. A fiber-shaped supercapacitor was prepared by twisting two electrodes with solid electrolytes made of KOH and polyvinyl alcohol. Although the solid electrolyte had a low ionic conductivity, the energy density and power density were determined to be 0.97 mWh/cm3 and 49.8 mW/cm3, respectively.

Unusual formation of NiCo2O4@MnO2/nickel foam/MnO2 sandwich as advanced electrodes for hybrid supercapacitors

A facile three-step method is designed for large-scale preparation of a NiCo₂O₄@MnO₂/nickel foam/MnO₂ sandwich architecture with robust adhesion as an advanced electrode for high-performance supercapacitors. The synthesis contains the hydrothermal reaction of a cobalt-nickel hydroxide precursor on a nickel foam (NF) support and subsequent thermal conversion into spinel mesoporous NiCo₂O₄ nanowire arrays, followed by a hydrothermal oxidation reaction to synthesize NiCo₂O₄@MnO₂/nickel foam/MnO₂ sandwiches. Moreover, the tactics reported in this study enable easy control of the growth of NiCo₂O₄ on one side of the NF and MnO₂ nanosheets on both sides of the NF to obtain novel NiCo₂O₄@MnO₂/nickel foam/MnO₂ sandwiches. Because of the unusual structural and compositional features, the obtained NiCo₂O₄@MnO₂/nickel foam/MnO₂ sandwiches manifest excellent performance with high specific capacitance (1.70 C cm^-2 at 2 mA cm^-2), exceptional rate capability (78.5% retention at 20 mA cm^-2) and ultralong cycling stability (91% retention over 30 000 cycles at 20 mA cm^-2) as a battery-type electrode material for supercapacitors. When further assembled into an aqueous hybrid supercapacitor, it can deliver an energy density of 53.5 W h kg^-1 at a power density of 80 W kg^-1 and 20.7 W h kg^-1 at 8 kW kg^-1. This novel sandwich electrode provides a new idea for improving the electrochemical performance of hybrid supercapacitors.

Facile synthesis of polypyrrole nanofiber (PPyNF)/NiOx composites by a microwave method and application in supercapacitors

In this study, polypyrrole nanofiber (PPyNF)/NiO_x composites were synthesized by a simple and fast microwave method. The samples were characterized using differential scanning calorimetry and thermal gravimetric analysis (DSC/TGA), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Furthermore, the synthesized PPyNF/NiO_x nanocomposites were electrochemically characterized using galvanostatic charge–discharge, cyclic voltammetry and electrochemical impedance spectroscopy (EIS) techniques. They showed the highest specific capacitance of 657 F g⁻¹ at 0.5 A g⁻¹, demonstrating their potential application in supercapacitors.

In this study, polypyrrole nanofiber (PPyNF)/NiO_x composites were synthesized by a simple and fast microwave method.