Herein, we demonstrate the synthesis of rGO/BiVO hybrid nanostructures by facile hydrothermal method. Morphological studies reveal that rGO sheets are embedded in the special dendritic fern-like structures of BiVO. The rGO/BiVO hybrid architecture shows the way to a rational design of supercapacitor, since these structures enable easy access of electrolyte ions by reducing internal resistance. Considering the unique morphological features of rGO/BiVO hybrid nanostructures, their supercapacitive properties were investigated. The rGO/BiVO electrode exhibits a specific capacitance of 151 F/g at the current density of 0.15 mA/cm. Furthermore, we have constructed rGO/BiVO symmetric cell which exhibits outstanding volumetric energy density of 1.6 mW h/cm (33.7 W h/kg) and ensures rapid energy delivery with power density of 391 mW/cm (8.0 kW/kg). The superior properties of symmetric supercapacitor can be attributed to the special dendritic fern-like BiVO morphology and intriguing physicochemical properties of rGO.
The preparation of nanostructured hierarchical MnxNi1-xCo2O4 metal oxides as efficient supercapacitors of different structures and configurations especially for the miniaturized electronics is still a challenge. In this context, we report template free facile hydrothermal synthesis of hierarchical nanostructured MnxNi1-xCo2O4 with excellent supercapacitive performance. Significantly, the morphology of pure MnCo2O4 transformed from 3D microcubes to 1D nanowires with incorporation of Ni. The electrochemical study shows highest specific capacity i.e. 734 C/g for Mn0.4Ni0.6Co2O4 with high cycling stability of 89.2 % which is much higher than pristine MnCo2O4 and NiCo2O4. Later, asymmetric capacitor has been fabricated successfully using Mn0.4Ni0.6Co2O4 nanowires as positive electrode and activated carbon (AC) as negative electrode in a KOH aqueous electrolyte. An asymmetric cell could be cycled reversibly in the high-voltage range of 0 to 1.5 V and displays intriguing performances with a specific capacitance of 112.8 F/g (6.87 F/cm3) and high energy density of 35.2 Wh/kg (2.1 mWh/cm3). Importantly, this asymmetric capacitor device exhibits an excellent long cycle life along with 83.2 % specific capacitance retained after 2000 cycles.
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