Search

Bimetallic oxide/graphene nanocomposite has been recognised as a promising electrode material owing to its admirable electrochemical activity and excellent electrical conductivity. Herein, a distinctive approach has been applied on exploiting the graphene/MnV2O6 nanomaterial as a promising electrode for supercapacitor. In order to achieve fascinating supercapacitive behaviours, an efficient liquid phase exfoliation coupled with solvothermal process is offered to construct these graphene/MnV2O6 nanocomposites for symmetric supercapacitor analysis. The hybrid G-8MVO electrode benefited from its optimal graphene/manganese vanadate ratio (1:8), interconnecting network architecture, rich redox activity and superior conducting feature exhibited the maximum specific capacitance of 348 Fg-1 at 0.5 Ag-1. Moreover, 88% of its initial capacitance was retained and columbic efficiency of nearly 100% was achieved after 3000 cycles at 1 Ag-1. Moreover, the symmetric supercapacitor provided a maximum specific energy of 48.33 Wh/kg at specific power of 880.6 W/kg. The comprehensive electrochemical output of the graphene/MnV2O6 nanocomposite advocates its potential as a high performance supercapacitor electrode.

3D lion's mane like AlV3O9 microspheres deposited on the well-exfoliated graphene were successfully synthesised through a facile solvothermal method where the graphene sheet was prepared solely via the liquid phase exfoliation process. The highly electrical conductive graphene was introduced as a conductive substrate or a backbone to support the diffusion of the electrolyte ions (OH−). In order to achieve the optimum electrochemical performance, graphene/AlV3O9 nanocomposites with different weight ratios were fabricated wherein G-5AlV possessed an exceptional charge storage ability which surpasses that of other nanocomposites. The G-5AlV sample was found to possess a magnificent specific capacitance of 551.72 F∙g−1 at 0.5 A∙g−1 and achieve a remaining capacitance of 468.97 F∙g−1 as the current density was increased. After 5000 continuous intercalation/de-intercalation processes, G-5AlV delivered a specific capacitance of 441.38 F∙g−1 and a coulombic efficiency of 95%, confirming its remarkable cycling stability and coulombic efficiency. More importantly, it exhibits good energy and power densities as a symmetric supercapacitor, further suggesting itself as a potential candidate for use in high-performance charge storage devices.

The electrochemical capability for the charge and energy storage of supercapacitors can be augmented by fabricating the hybrid and binder-free electrodes. In this work, the novel graphene/Co3V2O8 micro-pencils nanohybrids were successfully developed via the one-pot solvothermal method. The interactive effect between graphene and Co3V2O8 was investigated by varying their mass ratios. Benefiting from the peculiar morphology of Co3V2O8 micro-pencils and the homogenous distribution of Co3V2O8 on the graphene sheets, G-4CVO manifested a relatively promising specific capacitance of 528.17 F·g−1 at 0.5 A·g−1 while 80% of the charge storage capability was still retained even after 5000 continuous cycles. G-4CVO also delivered a remarkable energy density of 73 Wh/kg and these advanced electrochemical performances could be explicated by the integration of graphene sheets which shortens the ions and electrons transportation pathway and at the same time acts as a scaffold to alleviate the volume variation during the inter/de-intercalation process. Keywords: One-pot solvothermal, Graphene, Graphene/Co3V2O8, Supercapacitor

In order to improve the energy density of the supercapacitor, fabrication of next-generation materials with inimitable morphology and superior electrochemical performance is highly desired. Herein, a novel hybrid electrode material, namely graphene-Zn3V2O8 nanocomposites, were successfully prepared via facile solvothermal process followed by thermal annealing treatment. Graphene sheets were synthesised through the eco-friendly liquid phase exfoliation approach with optimised ethanol to water volume ratio (2:3). Optimisations on the weight ratio between the graphene and Zn3V2O8 were performed to determine the synergistic effect between them. The morphogenesis of the graphene-Zn3V2O8 nanohybrid manifests “sheet on sheet” nanostructures that intertwined with each other to form a 3D network architecture, which provides sufficient electroactive sites and shortens the ions diffusion pathway, leading to eminent electrochemical properties. The electrochemical properties of these materials were evaluated by cyclic voltammetry and galvanostatic charge-discharge tests in 2 M KOH aqueous electrolyte. Among the nanocomposites studied, G-3ZVO (weight ratio of 1:3) exhibited a specific capacitance of 564 Fg-1 at 0.8 Ag-1, outstanding rate capability and good cycling stability even after 5000 cycles. Furthermore, this symmetrical supercapacitor delivered an impressive energy density of 78 Wh/kg at power density of 75.5 kW/kg.

Nowadays, imminent deficiency of fossil fuels and arising environmental concerns have triggered immense research enthusiasm for the development of green and renewable energy sources. Particularly, supercapacitors are emerging as one of the competent energy storage devices owing to their excellent capacitive properties, long term cycling stability as well as remarkable power density. In this sense, the promising family of transition metal oxides (TMO) and mixed transition metal oxides (MTMO) are felicitous as active electrode materials for supercapacitor due to their multiple oxidations states and ions possess, leading to superior specific capacitance. Moreover, hybridisation of MTMO with graphene nanosheets has received tremendous research interest owing to the peculiar intrinsic properties of graphene, which ameliorate the electrical conductivity and enlarge the specific surface area of the nanocomposite for faradiac redox reaction. In this review article, we emphasised on the current evolution of MTMO and the hybridisation of MTMO with graphene nanosheets as active electrode materials, with a comprehensive study on their synthetic approaches. In addition, the critical factors that influence the electrochemical activities of mixed transition metal oxide based materials are also delineated.

In the present study, graphene/Ni3V2O8 nanocomposites were successfully synthesised by a facile solvothermal approach in which the graphene sheets were fabricated via the environmentally benign liquid phase exfoliation with optimised ethanol to water volume ratio (2:3). The nanocomposites integrated separately the advantages of graphene sheet and pseudocapacitive nature of Ni3V2O8 and hence possessed electrochemical performance which outperformed the pristine Ni3V2O8. Optimizations on the weight ratio between the graphene and Ni3V2O8 were performed to determine the synergistic effect between the highly conductive graphene sheet and Ni3V2O8. Among the graphene/Ni3V2O8 nanocomposites, G-4NVO (graphene/Ni3V2O8 with the weight ratio of 1:4) was proved to be a promising electrode material, as it delivered eminent specific capacitance of 748 Fg−1 at current density of 0.5 Ag-1, remarkable energy density of 103.94 Wh/kg at power density of 45.61 kW/kg, reasonable cycling stability with 71% capacitance retention and superior coulombic efficiency of 83% after 3000 charge-discharge cycles at 0.5 Ag-1.

NiMoO 4 nanorods have been directly synthesised on graphene sheet using a facile solvothermal method with subsequent calcination treatment. As an electrode for electrochemical capacitors, the graphene-NiMoO 4 composite electrode prepared at a mass ratio of 1:8 exhibited a specific capacitance of 670 F/g at 0.3 A/g and good rate capability. When cycled at 0.5 A/g for 3000 cycles, it retained 88% of its initial capacitance with a Coulombic efficiency of ~ 80%. This study presents a pungent and environmental benign research strategy for the development of graphene-NiMoO 4 ternary based electrochemical capacitors.

For the first time, a sonochemical process has been used to synthesis cobalt oxide Co3O4 nanoflowers and nanorods morphology in the presence of the ionic liquid 1-Ethyl-3-methylimidazolium tetrafluoroborate [EMIM][BF4] as reaction media and morphology template. Different sonication time periods and different molar ratios of the ionic liquid (IL) were used to investigate their effects on the structural, optical, chemical and magnetic properties of the produced Co3O4 nanoparticles. During synthesis process brown powder contains cobalt hydroxide Co(OH)2 and cobalt oxyhydroxide (Cobalt hydroxide oxide) CoO(OH) was formed, after calcination in air for 4 h at 400 °C a black powder of Co3O4 nanoparticles was produced. The produced Co3O4 nanoparticles properties were characterized by X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), transmission electron microscopy (TEM), FTIR spectroscopy, UV–vis spectroscopy, and Vibrating Sample Magnetometer (VSM). To explain the formation mechanism of Co3O4 NPs some investigations were carried on the brown powder before calcination.

Graphene was synthesised by an efficient, facile and green method of liquid phase exfoliation of highly pyrolytic graphite in an apt ratio of water and ethanol and subsequently used to produce graphene-NiCo 2 O 4 nanocomposites via solvothermal method using urea as a hydrolysis agent. X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and Raman spectroscopy revealed the formation of pure NiCo 2 O 4 composites. Transmission electron microscope (TEM), field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscope (HR-TEM) demonstrated that NiCo 2 O 4 was successfully anchored on the graphene sheets. The electrochemical analysis performed on the prepared graphene-NiCo 2 O 4 electrodes showed that the addition of graphene to the NiCo 2 O 4 nanomaterials is paramount to the charge storage performance. Different ratios of graphene to NiCo 2 O 4 varied to form nanocomposites under the same reaction conditions were analysed to reveal the best synergistic effect of the pseudocapacitance of NiCo 2 O 4 nanomaterial and the excellent conductivity of graphene. The capacitive performance of the graphene-NiCo 2 O 4 composites electrode prepared at a mass ratio (1:8) exhibited superior specific capacitance of 698 F/g at a current density of 0.5 A/g, with an energy density of 96.9 Wh/kg at power density of 13.9 kW/kg. The electrode also showed good cycling performance, with about 74% retention of the capacitance after 5000 cycles.

Highly pyrolytic graphite (HOPG) was used as a precursor to produce graphene in an apt ratio of ethanol and water. The as-synthesised graphene was subsequently used to produce graphene-Cobalt oxide (Co3O4) composites via solvothermal method. Morphological and structural characterizations of the prepared composites demonstrated that Co3O4 was successfully formed on the graphene sheet. Electrochemical measurements of graphene-Co3O4 composites from cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy indicated that the mass ratio of graphene to cobalt oxide precursors is crucial to affect their electrochemical performance. The capacitive performance of the graphene-Co3O4 composites electrode prepared at a mass ratio (1:4) exhibited superior specific capacitance of 384 F/g at a current density of 0.3 A/g, with an energy density of 64 Wh/kg and a power density of 103 kW/kg. The electrode also showed good cycling performance, with about 80% retention of the capacitance after 1000 cycles.

The present work reports the facile and green synthesis of silver nanoparticles from Catharanthus Roseus (C. Roseus) dried barks extract doped with graphene oxide (AgNPs/GO). The deposition of silver nanoparticles onto graphene oxide sheets were confirmed by UV–vis spectrometer and X-ray diffraction analysis. The synthesized AgNPs/GO displayed high crystallinity with absorption peak at about 400 nm. TEM analysis showed that biosynthesized AgNPs are mostly in a spherical form with particles size ranging from 1 to 26 nm. The existence of functional groups such as hydroxyl, epoxy and carboxylic in GO are believed to be the reason for the anionic character of the synthesised nanocomposite. Whilst, AgNPs functions as spacers assisting the segregation of stacked GO sheets thus promoting larger surface area. The evaluation of its adsorption capacity was carried out against methylene blue (MB) dye. The addition of biosynthesized AgNPs on GO sheets synergistically envisages the best adsorption capacity at 100 mM of AgNPs with almost a complete removal of MB in less than 5 min. Based on the pseudo second-order kinetic approach, the highest adsorption rate constant of 1.4563 g mg−1 min-1 was obtained. The overall adsorption capacity was enhanced due to the presence porous nanocomposite with highly disperse AgNPs anchored onto the surface of GO sheets.

This study reports a facile, environmentally-friendly and scalable liquid-phase exfoliation of HOPG process combined with a simple solvothermal method, consequently with calcination for the synthesis of highly porous graphene/Zinc–Nickel–Cobalt (ZNC) nanosheets arrays. The crystallographic and morphological information of the nanostructures were evaluated by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) Transmission electron microscope (TEM), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscope (HR-TEM). Given its unique architecture and composition, the nanocomposites were analysed as electrode materials for electrochemical capacitor. Additionally, different graphene/(ZNC) nanocomposites composed of various mass loading of graphene to ZNC were prepared under the same synthesis conditions and the results revealed that the mass loading of the precursors significantly influenced the electrochemical behaviour of the active electrode materials. The electrochemical performance of the graphene-(ZNC) electrode prepared at a mass loading of 0.3 of graphene and labelled G3-(ZNC), exhibited fascinating specific capacitance of 502 Fg-1 at current density of 0.2 Ag-1 and with excellent cycling stability of 82% capacitance retention after 2600 cycles.