Controlled-Synthesis of Hierarchical NiCo2O4 Anchored on Carbon Nanofibers Mat for Free-Standing and Highly-Performance Supercapacitors

In this work, a versatile one-step hydrothermal technique was used to produce a hybrid standalone electrode of NiCo2O4 hierarchical nanostructures anchored on CNFs mat for highly-performance and substrate-free supercapacitors. The CNFs mat was working as a conductive and a three-dimensional template for hierarchical NiCo2O4 nanostructures deposition at the same time. The morphological and structural data analysis revealed a pure spinel NiCo2O4 nanostructures with a unique surface morphology comprising interconnected ultrathin nanoneedles and nanoflowers were successfully anchored to the CNFs mat. Real supercapacitors consist of two-symmetrical hybrid electrodes with different NiCo2O4 loading ratios were assembled and tested. The electrochemical performances of the assembled devices in terms of specific capacitance, energy, and power densities were systematically evaluated. Increasing the NiCo2O4 loading on the CNFs mat had shown a positive impact on improving the overall electrochemical performance of the assembled supercapacitors. A hybrid electrode loaded with NiCo2O4 twice as much as CNFs possess a specific capacitance value of 540 F g−1 along with an energy density of 30 Wh kg−1 at a power density of 515.6 W kg−1. In addition, the device showed excellent cycling stability and high capacitance retention against 6000 charge-discharge cycles at a charging current of 1.0 A g−1.

NiCo2O4/RGO Hybrid Nanostructures on Surface-Modified Ni Core for Flexible Wire-Shaped Supercapacitor

In this work, we report surface-modified nickel (Ni) wire/NiCo2O4/reduced graphene oxide (Ni/NCO/RGO) electrodes fabricated by a combination of facile solvothermal and hydrothermal deposition methods for wire-shaped supercapacitor application. The effect of Ni wire etching on the microstructural, surface morphological and electrochemical properties of Ni/NCO/RGO electrodes was investigated in detail. On account of the improved hybrid nanostructure and the synergistic effect between spinel-NiCo2O4 hollow microspheres and RGO nanoflakes, the electrode obtained from Ni wire etched for 10 min, i.e., Ni10/NCO/RGO exhibits the lowest initial equivalent resistance (1.68 Ω), and displays a good rate capability with a volumetric capacitance (2.64 F/cm3) and areal capacitance (25.3 mF/cm2). Additionally, the volumetric specific capacitance calculated by considering only active material volume was found to be as high as 253 F/cm3. It is revealed that the diffusion-controlled process related to faradaic volume processes (battery type) contributed significantly to the surface-controlled process of the Ni10/NCO/RGO electrode compared to other electrodes that led to the optimum electrochemical performance. Furthermore, the wire-shaped supercapacitor (WSC) was fabricated by assembling two optimum electrodes in-twisted structure with gel electrolyte and the device exhibited 10 μWh/cm3 (54 mWh/kg) energy density and 4.95 mW/cm3 (27 W/kg) power density at 200 μA. Finally, the repeatability, flexibility, and scalability of WSCs were successfully demonstrated at various device lengths and bending angles.

Effect of precursor ultrasonic treatment on synthesis, texture characteristics and electrical conductivity of NiCo2O4

The high-dispersed powder−precursors of nickel−cobalt spinel (NiCo2O4) was synthesized by the method of coprecipitation of the nickel and cobalt hydroxides with followed by drying (150 °C) and ultrasonic (US) treatment of the precipitate. The influence of US−treatment on the texture characteristics of the precursors and NiCo2O4 powders was established. The possibility of obtaining nanodispersed (crystallite size < 20 nm), mesoporous powders (pore size 3 − 15 nm) of nickel−cobalt spinel at a temperature of 700 °C is shown. The change in the specific electrical conductivity of sintered NiCo2O4 samples in the temperature range of 100 – 800 °C was studied, the value of σ can vary from 0.1 to 7.0 Sm/cm.

Enrichment in the field emission properties of NiCo2O4 nanostructures by UV/Ozone treatment

Herein, UV/O3 treatment was imposed on the hydrothermally synthesized spinel NiCo2O4 urchin like structure to study its enhancement effect in the field electron emission properties. The as prepared sample was...