G. Muralidharan

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.

Nanosheet-Assembled NiO Microstructures for High-Performance Supercapacitors

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).

Nanostructured CuO/reduced graphene oxide composite for hybrid supercapacitors

To address the issues such as low ionic conductivity, poor electrode kinetics and cyclic stability, the strategy of combining carbon-based materials with transition metal oxide (TMO) is adopted. In this article, the preparation of CuO/reduced graphene oxide (RGO) nanocomposite electrodes by a simple, low cost hydrothermal method is described. This hybrid nanocomposite exhibits a high specific capacitance of 326 F g−1 at a current density of 0.5 A g−1. It shows a high energy density of 65.7 W h kg−1 at a power density of 302 W kg−1. Further, this material does not exhibit any measureable degradation in electrochemical performance, even after 1500 cycles. Symmetric hybrid capacitors exhibit a specific capacitance of 97 F g−1 at 0.2 A g−1 with a power density of 72 W kg−1. These superior electrochemical features demonstrate that the CuO/RGO hybrid nanocomposite is a promising material for next-generation supercapacitor systems.

Synthesis of mesh-like Fe2O3/C nanocomposite via greener route for high performance supercapacitors

A facile and template free greener route is used to fabricate natural polysaccharide based biocompatible mesh-like Fe2O3/C nanocomposites for supercapacitor application. Thermal, structural and morphological properties of iron oxide–carbon composites prepared at different annealing temperature have been analyzed and the electrochemical properties of composites are evaluated. The nanocomposite prepared at 500 °C with mesh-like structure reveals maximum specific capacitance of 315 F g−1 in 2 M KOH solution at a scan rate of 2 mV s−1 and good capacity retention (88.9%) after 1500 continues charge–discharge cycles with energy density of 37 W h kg−1, indicating that the Fe2O3/C composite can be a promising electroactive material for a supercapacitor.

V2O5/functionalized MWCNT hybrid nanocomposite: the fabrication and its enhanced supercapacitive performance

The vanadium pentoxide (V2O5) has been attached to functionalized multiwall carbon nanotube (f-MWCNT) networks by simplified solution based approach. The product V2O5/f-MWCNT hybrid nanocomposite has been exploited for supercapacitor electrode application. The addition of f-MWCNT with V2O5 significantly improves the surface area and conductivity, which leads the high energy and power densities. This nanocomposite shows highest specific capacitance up to 410 F g−1 and 280 F g−1 at current densities of 0.5 and 10 A g−1 respectively. Moreover, this nanocomposite provides excellent energy density (∼57 W h kg−1), better rate capacity, and a good retention of capacity (∼86%) up to 600 cycles of charge–discharge. Further a symmetric supercapacitor was fabricated using V2O5/f-MWCNT nanocomposite as electrodes. It shows a specific capacitance of 64 F g−1 at a current density of 0.5 A g−1.

MnO2 grafted V2O5 nanostructures: formation mechanism, morphology and supercapacitive features

This article details an approach for the fabrication of MnO2 grafted V2O5 nanostructures to function as supercapacitor electrode. The MnO2 and V2O5 combined to form profitable hierarchical network morphology. Most importantly, both MnO2 and V2O5 contributed to energy storage. This type of synergetic architecture exhibits elevated specific capacitance (450 F g−1 at 0.5 A g−1), good rate capacity (251 F g−1 at 5 A g−1) and provides better cycling stability (retaining 89% of capacitance after 500 cycles). An asymmetric supercapacitor using MnO2 grafted V2O5 and activated carbon (AC) as electrodes was assembled. It exhibits a specific capacitance of 61 F g−1 with an energy density of 8.5 Wh kg−1. The electrochemical feature of MnO2 grafted V2O5 nanostructure can be useful for the fabrication of high performance supercapacitor systems.

Ag3O4 grafted NiO nanosheets for high performance supercapacitors

Ag3O4 grafted NiO nanosheets were successfully synthesized via hydrothermal route. The morphological and structural analysis was performed using scanning transmission electron microscopy (STEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) studies. The grafting of Ag3O4 on NiO nanosheets enhanced the conductivity of the nanosheets and resulted in a maximum specific capacitance of 1504 F g−1 for 5 wt% of Ag on NiO (AGN2) at a scan rate of 3 mV s−1. The porous nature of AGN2 provides larger paths for ions, which significantly increases the intercalation of ions and utilization rate of electrode materials. Galvanostatic charge discharge (GCD) analysis reveals a specific capacitance of 1524 F g−1 for AGN2 at a current density of 1 A g−1 with excellent cyclic stability (12% loss after 1500 cycles). An asymmetric supercapacitor device (AGN2//RGO) achieved a specific capacitance of 274 F g−1 with an energy density of 37 Wh kg−1 and the power density of 499 W kg−1 at a discharge current of 0.2 A g−1.

EFFECT OF FLUORINE CONTENT ON THE MORPHOLOGICAL, STRUCTURAL, OPTICAL AND ELECTRICAL PROPERTIES OF NANOSTRUCTURED SnO2 FILMS

This paper reports morphological and structural details, optical and electrical properties of fluorine doped SnO2 thin films prepared via spray pyrolysis route using SnCl2·2H2O as precursor and methanol as a solvent. The effect of fluorine concentration on the properties of the films is presented and discussed. X-ray diffraction pattern reveals the presence of SnO2 films in the rutile structure with a preferential growth along the (200) direction. FTIR spectrum confirms the films to be made of SnO2. EDS was used to estimate the fluorine concentration. SEM reveals the surface of FTO to be made of nanocrystalline particles. The grain size calculated using Debye–Scherrer formula is in the range of 8–34 nm. Film thickness measured using optical transmission method is in the range of 425–538 nm. The sheet resistance was found to decrease with increase in fluorine concentration, to a minimum of 6.35 Ω/□ for 7.5 mol% of NH4F, and it showed an increase beyond this concentration. The 2.5 mol% of F doped films gave 95.20% transmission at 704 nm. The calculated reflectivity in the IR region is 93.57% for 7.5 mol% of F doping, and figure of merit for the same film is 0.025(Ω/□)-1 at 550 nm. The total work was optimized by fixing the temperature at 550°C for the usage of Electrochromic Device preparations on FTO coated glass substrates.

Thickness dependent supercapacitor behaviour of sol-gel spin coated nanostructured vanadium pentoxide thin films

Vanadium pentoxide thin films of various thicknesses have been prepared by sol-gel spin coating method on glass and conducting substrates. X-ray diffraction analysis reveals crystalline nature for the 6–12 layered films (170–310 nm). The crystalline films indicate a preferential orientation of the crystallites along the (200) plane. FTIR studies of the V2O5 xerogel show the presence of V–O–V and V= O bond confirming the formation of V2O5. The scanning electron microscope images reveal formation of nanostructures in the 6–12 layered films. Optical absorption studies indicate a band gap of 2.2–2.5 eV. Pseudocapacitance behaviour of the V2O5 films was studied using cyclic voltammetric technique and impedance analysis. V2O5 films of thickness 202 nm (8 layers) exhibit a specific capacitance of 346 F/g at a scan rate of 5 mV/s.

Role of annealing duration on the microstructure and electrochemical performance of β-V2O5thin films

Vanadium pentoxide thin films have been prepared by sol–gel spin coating method. The eight-layered films coated on fluorine-doped tin oxide substrate and glass substrate were subjected to different durations of annealing under a constant annealing temperature of 300 °C from 30  to 120 min. The X-ray diffraction spectrum reveals crystallinity along (2 0 0) direction. The SEM images of these films show the variation in the surface morphology with increase in annealing duration. The supercapacitor behaviour has been studied using cyclic voltammetry technique and electrochemical impedance spectroscopy. The film annealed for 60 min exhibits a maximum specific capacitance of 346 F/g at a scan rate of 5 mV/s with a charge transfer resistance of 172 Ω.