NiO nanomaterial was synthesized at different calcination temperatures using cetyltrimethyl ammonium bromide (CTAB) as surfactant via microwave method. Thermogravimetric studies revealed the decomposition details of Ni(OH)2 precursor. The structure and morphology of the NiO was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). NiO calcined at 300 °C shows a nanoflake-like structure. A possible formation mechanism has been discussed with time evolution study. Electrochemical studies indicate that the sample calcined at 300 °C exhibits better charge storage. The NiO nanoflakes exhibit maximum specific capacitance of 401 F g(-1) at a current density of 0.5 mA cm(-2). The energy generated and hence the charges collected from wind and solar panels are slow but in many applications the power delivery has to be at a faster rate. Considering this aspect, slow-charge and fast-discharge tests have been performed and reported. The NiO nanoflakes appear to be a promising electrode material for supercapacitor application.

Vanadium pentoxide (V(2)O(5)) has attracted attention for supercapcitor applications because of its extensive multifunctional properties. In the present study, V(2)O(5) nanoporous network was synthesized via simple capping-agent-assisted precipitation technique and it is further annealed at different temperatures. The effect of annealing temperature on the morphology, electrochemical and structural properties, and stability upon oxidation-reduction cycling has been analyzed for supercapacitor application. We achieved highest specific capacitance of 316 F g(-1) for interconnected V(2)O(5) nanoporous network. This interconnected nanoporous network creates facile nanochannels for ion diffusion and facilitates the easy accessibility of ions. Moreover, after six hundred consecutive cycling processes the specific capacitance has changed only by 24%. A simple cost-effective preparation technique of V(2)O(5) nanoporous network with excellent capacitive behavior, energy density, and stability encourages its possible commercial exploitation for the development of high-performance supercapacitors.

Via the green chemistry route, Mn3O4/amorphous carbon nanoparticles have been synthesized. Dextrose was used as the reducing agent, and starch was used as the capping agent. The X-ray diffraction patterns reveal the Hausmannite tetragonal structure of the synthesized Mn3O4 particles. EDAX analysis confirms the presence of carbon and stoichiometry of Mn3O4. Morphological studies reveal the nanospherical nature of the synthesized particles. The FTIR spectra confirm the presence of Mn–O bonds. Mn3O4/AC 500 exhibits highest specific capacitance of 522 F g–1 at a specific current of 1 A g–1, when measured from the charge–discharge process. This value is superior to previous reports on Mn3O4 nanoparticles as an electrode for supercapacitors. Higher energy density of 58.72 W h kg–1 could be observed for Mn3O4/AC 500, which is higher than lead acid batteries and comparable to those for the nickel hydride batteries. These results indicate that Mn3O4/AC 500 is a promising electrode for supercapacitor applications.

Nanosheet-assembled NiO microstructures have been synthesized via a hydrothermal method. The presence of anionic surfactant in the fabrication process initiates the formation of lamellar micelles and a self-assembling process. This leads to the formation of NiO nanosheets and organizes it into microstructures. The effect of preparation temperature on the morphological, structural, and electrochemical properties and stability upon continuous charge/discharge cycles has been examined for supercapacitor applications. Electrochemical analysis demonstrated that NiO nanosheets prepared at 160 °C are capable of delivering a specific capacitance of 989 F g(-1) at a scan rate of 3 mV s(-1) for the potential window of 0-0.6 V. The nanosheets exhibit excellent capacity retention, 97% retention after 1000 continuous charge/discharge cycles, and an energy density of 49.45 W h kg(-1).

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