Synthesis of Ag/NiO Honeycomb Structured Nanoarrays as the Electrode Material for High Performance Asymmetric Supercapacitor Devices.

Metallic silver nickel oxide honeycomb nanoarrays were synthesized via a surfactant-assisted hydrothermal route. The crystal structure of the Ag/NiO nanoarrays was confirmed by X-ray diffraction. X-ray photoelectron spectroscopy confirmed the valance state of the nickel, oxygen, and metallic silver. The morphological studies and energy dispersive X-ray spectroscopy revealed the honeycomb structured nanoarrays and the elemental distribution of the prepared sample, respectively. The three-electrode measurements showed that the Ag/NiO nanoarray is a suitable electrode material for supercapacitor applications, which delivers the maximum specific capacity of 824 C g-1 at a specific current of 2.5 A g-1. An Ag/NiO positive electrode-based asymmetric device was fabricated and tested. The asymmetric device yielded a high specific cell capacity of 204 C g-1 at a specific current of 2.5 A g-1 as well as a maximum energy density of 63.75 W h kg-1 at a power density of 2812.5 W kg-1. These results are comparable to those of (NiMH) metal hydride batteries.

In situ preparation of MgCo2O4 nanosheets on Ni-foam as a binder-free electrode for high performance hybrid supercapacitors.

A binder-free, MgCo2O4 nanosheet-like architecture was prepared on Ni-foam using a hydrothermal method. MgCo2O4/Ni-foam was characterized by X-ray diffraction, field emission scanning electron microscopy (FESEM), and transmission electron microscopy techniques. The FESEM image revealed a nanosheet array-like architecture. The MgCo2O4 nanosheets grown on Ni-foam exhibited the maximum specific capacity of 947 C g-1 at a specific current of 2 A g-1. Approximately 96% of the specific capacity was retained from the maximum specific capacity after 5000 continuous charge-discharge cycles. This hybrid device exhibited a maximum specific capacity of 52 C g-1 at a specific current of 0.5 A g-1, and also exhibited a maximum specific energy of 12.99 W h kg-1 at a specific power of 448.7 W kg-1. These results confirmed that the binder-free MgCo2O4 nanosheets grown on Ni-foam are a suitable positive electrode material for hybrid supercapacitors.

Supercapacitor studies on NiO nanoflakes synthesized through a microwave route.

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.