Enhanced electrochemical performance of supercapattery derived from sulphur-reduced graphene oxide/cobalt oxide composite and activated carbon from peanut shells

Sulphur-reduced graphene oxide/cobalt oxide composites (RGO-S/Co₃O₄) were successfully synthesized by varying mass loading of Co₃O₄ through a simple hydrothermal method. Structural, morphological, chemical compositional and surface area/pore-size distribution analysis of the materials were obtained by using XRD, Raman spectroscopy, SEM, TEM, EDX, FTIR, XPS and BET techniques, which reveal an effective synthesis of the RGO-S/Co₃O₄ composites. Electrochemical performance of the materials was evaluated using a three- and two-electrode system in 1 M KOH electrolyte. An optimized RGO-S/200 mg Co₃O₄ composite displayed the highest specific capacity of 171.8 mA h g⁻¹ and superior cycling stability of 99.7% for over 5000 cycles at 1 and 5 A g⁻¹, respectively, in a three-electrode system. A fabricated supercapattery device utilizing RGO-S/200 mg Co₃O₄ (positive electrode) and activated carbon from peanut shells (AC-PS) (negative electrode), revealed a high specific energy and power of 45.8 W h kg⁻¹ and 725 W kg⁻¹, respectively, at 1 A g⁻¹. The device retained 83.4% of its initial capacitance for over 10, 000 cycles with a columbic efficiency of 99.5%. Also, a capacitance retention of 71.6% was preserved after being subjected to a voltage holding test of over 150 h at its maximum potential of 1.45 V.     

Core-shell structured ZIF-7@ZIF-67 with high electrochemical performance for all-solid-state asymmetric supercapacitor

Zeolitic imidazolate frameworks (ZIFs) are considered as a promising material for energy storage in recent years. Here, core-shell structured ZIF-7@ZIF-67 is synthesized in this work. The core-shell structured material can promote electron transfer of inner-outer metals ions of ZIF-7@ZIF-67, quicken diffusion of electrolyte ions and improve the capacitance performance compared to the ZIF-7 and ZIF-67. ZIF-7@ZIF-67 delivers good energy storage ability with a specific capacitance of 518.9 F g⁻¹ at a current density of 1 A g⁻¹ and remarkable stability with a retention of 99.6% after 4000 cycles in the three-electrode system. Furthermore, an all-solid-state asymmetric supercapacitor (ASC) device is assembled based on core-shell structured ZIF-7@ZIF-67 as positive electrode. Impressively, the ASC device displays an energy density of 31 Wh kg⁻¹ at a power density of 400 W kg⁻¹ and an excellent cyclic stability with 99.5% retention after 10,000 cycles at a current density of 10 A g⁻¹. Finally, two all-solid-state ASCs are contacted to power various lighting-emitting diodes (LED). The red LED can be kept glowing for over 10 min. These electrochemical characteristics suggest that core-shell structured ZIF-7@ZIF-67 is a potential material for energy storage device with long-life cyclic stability.     

Interconnected NiS-nanosheets@porous carbon derived from Zeolitic-imidazolate frameworks (ZIFs) as electrode materials for high-performance hybrid supercapacitors

Nickel sulfide-based materials have shown great potential for electrode fabrication owing to their high theoretical specific capacitance but poor conductivity and morphological aggregation. A feasible strategy is to design hybrid structure by introducing highly-conductive porous carbon as the supporting matrix. Herein, we synthesized hybrid composites consisting of interconnected NiS-nanosheets and porous carbon (NiS@C) derived from Zeolitic-imidazolate frameworks (ZIFs) using a facile low-temperature water-bath method. When employed as electrode materials, the as-prepared NiS@C nanocomposites present remarkable electrochemical performance owing to the complex effect that is the combined advantages of double-layer capacitor-type porous carbon and pseudocapacitor-type interconnected-NiS nanosheets. Specifically, the NiS@C nanocomposites exhibit a high specific capacitance of 1827 F g⁻¹ at 1 A g⁻¹, and excellent cyclic stability with a capacity retention of 72% at a very high current density of 20 A g⁻¹ after 5000 cycles. Moreover, the fabricated hybrid supercapacitor delivers 21.6 Wh kg⁻¹ at 400 W kg⁻¹ with coulombic efficiency of 93.9%, and reaches 10.8 Wh kg⁻¹ at a high power density of 8000 W kg⁻¹, along with excellent cyclic stability of 84% at 5 A g⁻¹ after 5000 cycles. All results suggest that NiS@C nanocomposites are applicable to high-performance electrodes in hybrid supercapacitors and other energy-storage device applications.     

Facile one pot sonochemical synthesis of CoFe2O4/MWCNTs hybrids with well-dispersed MWCNTs for asymmetric hybrid supercapacitor applications

In this study, a facile sonochemical strategy is used for the fabrication of CoFe₂O₄/MWCNTs hybrids as an electrode material for supercapacitor applications. FE-SEM image demonstrates the uniformly well-distributed MWCNTs as well as porous structures in the prepared CoFe₂O₄/MWCNTs hybrids, suggesting 3D network formation of conductive pathway, which can enhance the charge and mass transport properties between the electrodes and electrolytes during the faradic redox reactions. The as-fabricated CoFe₂O₄/MWCNTs hybrids with the MWCNTs concentration of 15 mg (CFC15) delivers maximum specific capacitance of 390 F g⁻¹ at a current density of 1 mA cm⁻², excellent rate capability (275 F g⁻¹ at 10 mA cm⁻²), and outstanding cycling stability (86.9% capacitance retention after 2000 cycles at 3 mA cm⁻²). Furthermore, the electrochemical performance of the CFC15 is superior to those of pure CoFe₂O₄ and other CoFe₂O₄/MWCNTs hybrids (CFC5, CFC10 and CFC20), indicating well-dispersion MWCNTs and uniform porous structures. Also, as-fabricated asymmetric supercapacitor device using the CoFe₂O₄/MWCNTs hybrids as the positive electrode and activated carbon as the negative electrode materials shows the outstanding supercapacitive performance (high specific capacitance, superior cycling stability and good rate capability) for energy storage devices. It delivers a capacitance value of 81 F g⁻¹ at 3 mA cm⁻², ca. 92% retention of its initial capacitance value after 2000 charge-discharge cycles and excellent energy density (26.67 W h kg⁻¹) at high power density (~319 W kg⁻¹).     

Hierarchical design of Ni(OH)2/MnMoO4 composite on reduced graphene oxide/Ni foam for high-performances battery-supercapacitors hybrid device

Design and synthesis advanced battery-type electrode materials with outstanding electrical conductivity and remarkable theoretical specific capacity are crucial to enhance the comprehensive performances for battery-supercapacitors (SCs). Herein, Ni(OH)₂/MnMoO₄ composite on reduced graphene oxide/Ni foam (rGO/NF) was successfully fabricated through the hydrothermal method and potentiostatic electrodeposition (Ni(OH)₂/MnMoO₄/rGO/NF). The unique honeycomb structure and the efficient synergistic effects among MnMoO₄ and Ni(OH)₂ of the as-prepared battery type electrode, as well as outstanding electronic conductivity of the reduced graphene oxide, were beneficial to the enhanced electrochemically active sites and increased specific capacity. Ni(OH)₂/MnMoO₄/rGO/NF composite employed for SCs yielded the maximum specific capacity of 1329.1 C g⁻¹ and a superb cycle property of 86.8% during 5000 cycles. Furthermore, the battery-supercapacitor hybrid (BSH) device with the Ni(OH)₂/MnMoO₄/rGO/NF and active carbon (AC) as-prepared samples showed the energy density of 61.4 W h kg⁻¹ at the power density of 428.4 W kg⁻¹. The capacity retention of the as-fabricated hybrid device reached 96.4% over 7000 cycles. Those consequences tested that the Ni(OH)₂/MnMoO₄/rGO/NF composite should be the promising category of battery-type electrodes materials of the next generation energy storage devices for the high-performances SCs.     

A comparative study of various polyelectrolyte/nanocomposite electrode combinations in symmetric supercapacitors

A more practical, nontoxic and cheaper electrolyte, poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) was used to construct supercapacitors with different nanocomposite electrodes. The flexible devices were fabricated including active carbon (AC) electrode and nanocomposites electrodes of AC/nano-silica (nano-SiO₂) and AC/multiwalled carbon nanotubes (MWCNTs) at various weight percentages. The symmetrical cell made from AC electrodes generated a maximum specific capacitance (Cs) of 315 F g⁻¹ at 0.5 A g⁻¹. The energy density of this device was 55.5 Wh kg⁻¹ at a power density of 690 W kg⁻¹. Excellent performance was achieved after 5000 charge-discharge cycles where the supercapacitor maintains 92% of its activity. The energy storage capability of the supercapacitors was also investigated with the addition of nano-SiO₂ and MWCNTs. The Cs of the supercapacitors made with the electrodes AC/nano-SiO₂ (5%, 10%, 25% and 50%) were 172, 228, 247 and 55 F g⁻¹, respectively. Similarly, the capacity of the device including the electrodes of AC/MWCNTs (5%, 10%, 25% and 50%) varied as 191, 244, 93 and 20 F g⁻¹ at 0.5 A g⁻¹. The maximum energy density of the devices having nano-SiO₂ and MWCNT were 44.4 Wh kg⁻¹ and 43.8 Wh kg⁻¹, respectively at a power density of 520 W kg⁻¹. A supercapacitor with certain dimension successfully operated a light-emitting diode (LED).     

Transforming waste sugar solution into N-doped hierarchical porous carbon for high performance supercapacitors in aqueous electrolytes and ionic liquid

Waste sugar solution is a by-product in the process of manufacturing vitamin C. Nowadays, the unused industrial waste residues are transformed into high efficient energy storage devices, such as supercapacitors electrodes, which are worth exploring because they are consistent with the concept of green and sustainable development. In this paper, a nitrogen-doped hierarchical porous carbon are obtained via pre-carbonization and KOH activation. The as-prepared material, possessed proper pore size distribution, large specific surface area and nitrogen-doping, exhibits good electrochemical performance, such as a high specific capacitance of 342 F g⁻¹ (0.1 A g⁻¹), good stability with 95% capacitance retention after 15,000 cycles in 6 M KOH. Moreover, the supercapacitors deliver a high energy density of 25.6 and 65.9 W h kg⁻¹ in the 1 M Na₂SO₄ and EMIMBF₄, respectively. The good electrochemical performance illustrates that the nitrogen-doped hierarchically porous carbon derived from the waste sugar solution is a potential candidate for energy storage.     

One-pot sonochemical synthesis of hierarchical MnWO4 microflowers as effective electrodes in neutral electrolyte for high performance asymmetric supercapacitors

In this article, manganese tungstate (MnWO₄) microflowers as electrode materials for high performance supercapacitor applications are prepared by a one-pot sonochemical synthesis. The crystalline structure and morphology of MnWO₄ microflowers are characterized through X-ray diffraction, field emission scanning electron microscopy. The electrochemical properties of the MnWO₄ microflowers are investigated using cyclic voltammograms, galvanostatic charge/discharge and electrochemical impedance spectroscopy. The MnWO₄ microflowers as electrode materials possess a maximum specific capacitance of 324 F g⁻¹ at 1 mA cm⁻² in the potential window from 0 to +1 V and an excellent cycling stability of 93% after 8000 cycles at a current density of 3 mA cm⁻². An asymmetric supercapacitor device is fabricated using the MnWO₄ and iron oxide (Fe₃O₄)/multi-wall carbon nanotube as the positive and negative electrode materials, it can be cycled reversibly at a potential window at 1.8 V. The fabricated ASC device can deliver a high energy density of 34 Wh kg⁻¹ at a power density of 500 W kg⁻¹ with cycling stability of 84% capacitance retained after 3000 cycles. The above results demonstrate that MnWO₄ microflowers can be used as promising high capacity electrode materials in neutral electrolyte for high performance supercapacitors.     

Microwave-synthesized self-supporting CoSe2/carbon fiber felt electrode for ultra–high cycling life flexible supercapacitors

Flexible electrodes are candidate for portable and wearable electronic storage devices. In this work, high-performance flexible self-supporting CoSe₂/carbon fiber felt (CoSe₂/CFF) electrode was prepared via the microwave method without any binder. The CoSe₂/CFF electrodes exhibited superior electrochemical performance (621 F g^?1 at 1 A g^?1) and an ultra-high cycling life (84.7% capacitance retention after 100,000 cycles). When the CoSe₂/CFF was used as the positive electrode for the flexible supercapacitor, the assembled device exhibited an outstanding energy density of 22.43 W h Kg^?1 at a power density of 823.12 W kg^?1. Because of the excellent mechanical stability of the device, it maintained 91.3% of its initial C after bending from 0° to 180°. The CoSe₂/CFF proposed in this work shows electrode promising applicability to a low-cost, small-sized wearable and portable energy storage device.     

Construction of MnO2 nanosheets@graphenated carbon nanotube networks core-shell heterostructure on 316L stainless steel as binder-free supercapacitor electrodes

Carbon nanotubes are regarded as typical and promising electrode materials in supercapacitors. However, small specific capacitance of carbon nanotubes restricts the practical application in high energy density devices. Herein, MnO₂ nanosheets@graphenated carbon nanotube networks are synthesized directly on 316L stainless steel as binder-free electrodes for high-performance supercapacitors. Graphenated carbon nanotube networks are grown in-situ on stainless steel by chemical vapor deposition method followed by annealing treatment. Subsequently, MnO₂ nanosheets are uniformly deposited on graphenated carbon nanotube networks to construct core-shell heterostructure based on the facile hydrothermal reaction using KMnO₄ as the precursor. Core carbon nanotube networks can offer a stable structural backbone and shell MnO₂ nanosheets can shorten diffusion paths of ions. The MnO₂ nanosheets@graphenated carbon nanotube networks exhibit a high specific capacitance of 575.4 F g⁻¹ (areal capacitance of 274 mF cm⁻²) at the current density of 0.5 mA cm⁻² and good cycling stability (93% of capacity retention after 6000 cycles), due to the synergistic effects between pseudocapacitive MnO₂ nanosheets and conductive carbon nanotube networks. The developed synthetic strategy offers design guidelines for the construction of advanced binder-free electrodes for high-performance supercapacitors.     

Formation of hierarchical 3D cross-linked porous carbon with small addition of graphene for supercapacitors

In the present paper, starch was used as raw material to prepare carbon material with low-temperature hydrothermal route and hierarchical three-dimensional cross-linked porous carbon was successfully synthesized with the help of a small amount of graphene for high-performance supercapacitors. It's found that presence of graphene is a crucial condition for the formation of 3D porous carbon and graphene acts as a skeleton in the porous carbon. This kind of carbon material exhibited very high surface area of 1887.8 m² g⁻¹ and delivered excellent electrochemical performance. Its specific capacitance can reach 141 F g⁻¹ at 0.5 A g⁻¹ and more importantly, after 10,000 cycles 98.6% of initial specific capacitance can be maintained. To explore the practical application of the 3D porous carbon, an asymmetric supercapacitor coin-type device was assembled with 3D porous carbon and graphene as electrode materials in organic electrolyte. The constructed device exhibited high energy density of 48.5 Wh·kg⁻¹ at a power density of 1.5 kW kg⁻¹ and still maintains 39.625 Wh·kg⁻¹ under the high power density (15 kW kg⁻¹). These results will promote the rapid development of 3D porous carbon prepared by low-temperature route and the application in supercapacitors.     

Constructing 3D honeycomb-like CoMn2O4 nanoarchitecture on nitrogen-doped graphene coating Ni foam as flexible battery-type electrodes for advanced supercapattery

Reasonable structural design is significant to enable the performance in advanced energy storage devices. Herein, a 3D honeycomb-like CoMn₂O₄ nanoarchitecture (CMO) on nitrogen-doped graphene (NG) coating Ni foam (denoted as Ni/NG/CMO) flexible battery-type electrode was prepared by a facile two-step hydrothermal strategy. The honeycomb-like CoMn₂O₄ arrays not only provide abundant active sites but can also be closely combined with the Ni foam/NG substrate, which enables high reversible capacity and good cycle stability during the long cycles. Benefiting from the compositional features and 3D honeycomb-like nanoarchitecture, the Ni/NG/CMO composite electrode displays improved electrochemical performance with remarkable specific capacity of 527.0C g⁻¹ at a current density of 1 A g⁻¹, outstanding rate capability (338.6C g⁻¹ even at 20 A g⁻¹). In addition, a flexible binder-free supercapattery device has been assembled with Ni/NG/CMO as positive electrode and 3D Ni/NG as negative electrode. Such a supercapattery delivers a high energy density of 44.1 Wh·kg⁻¹ at 992.6 W kg⁻¹, 20.3 Wh·kg⁻¹ at 12430.0 W kg⁻¹ as well as excellent cycling durability. The 3D honeycomb-like Ni/NG/CMO could be considered as an advanced flexible battery-type material for high capacity and energy density fields.     

Synthesis,characterization, and electrochemical properties of CoMoO4 nanostructures

We report a facile sonochemical approach for the synthesis of cobalt molybdate (CoMoO₄) nanostructures and their application as electrodes for supercapacitors. X-ray diffraction analysis showed the formation of monoclinic CoMoO₄. The surface morphology was investigated using a field-emission scanning electron microscope, which showed the formation of plate-like CoMoO₄ nanostructures. The growth mechanism and formation of the CoMoO₄ nanostructures is discussed. Further, the electrochemical performance of the CoMoO₄ nanostructures was examined using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge–discharge analysis. The CV curves showed the presence of redox pairs and, along with the EIS data (using Nyquist and Bode plots), demonstrated the pseudocapacitance nature of the synthesized CoMoO₄. The galvanostatic studies showed non-symmetric discharge curves, and a maximum specific capacitance of ∼133 F g⁻¹ was obtained at a constant discharge current density (1 mA cm⁻²). The cyclic stability tests demonstrated capacitance retention of about 84% after 1000 cycles, suggesting the potential application of CoMoO₄ in energy-storage devices.     

Ni–Co–S nanosheets supported by CuCo2O4 nanowires for ultra-high capacitance hybrid supercapacitor electrode

Recently, constructing core-shell arrays directly on conductive substrates is proved as a promising strategy for energy storage devices, due to the abundant active sites and fast electrons transport paths. In this work, we design core-shelled CuCo₂O₄@Ni–Co–S arrays directly on Ni foam substrate by the hydrothermal and electrodeposition processes. The core-shelled arrays can possess the large accessible surface area, fast charge transfer kinetics and the synergistic effect from both components, leading to better electrochemical performances. Consequently, core-shell CuCo₂O₄@Ni–Co–S arrays can deliver a high specific capacitance of 12.10 F cm⁻² (corresponding to 2897 F g⁻¹ mass specific capacitance), and good cycle stability with 82.5% capacitance retention after 8000 cycles of charging and discharging at 20 mA cm⁻². In addition, a battery-supercapacitor hybrid device made of CuCo₂O₄@Ni–Co–S and activated carbon displays a high energy density of 0.65 mWh cm⁻² at 32 mW cm⁻² power density, and the capacitance loss less than 20% (~83.6%) after 8000 cycles.     

Yuba-like porous carbon microrods derived from celosia cristata for high-performance supercapacitors and efficient oxygen reduction electrocatalysts

Here, a novel yuba-like porous carbon microrod is prepared via a simple and facile strategy by using the fluffy fibers of celosia cristata petals (FCCP) as the raw material. The optimized carbon microrod (FCCP-CM-900) possesses unique yuba-like structure, high specific surface area (1680 m² g⁻¹) and large pore volume (0.98 cm³ g⁻¹), and effective nitrogen (∼4.52 at.%) and oxygen (∼5.49 at.%) doping, which can enhance the wettability and conductivity (7.9 S cm⁻¹). As the electrode material for supercapacitor, FCCP-CM-900-based supercapacitor presents high specific capacitance (314.5 F g⁻¹ at 0.5 A g⁻¹) in 6.0 M KOH aqueous electrolyte. The FCCP-CM-900-based symmetrical supercapacitor displays high energy density (18.6 Wh kg⁻¹ at 233.4 W kg⁻¹) and outstanding cycling stability (98% capacitance retention after 10,000 cycles) in 1.0 M Na₂SO₄ electrolyte. In addition, served as oxygen reduction electrocatalyst, the FCCP-CM-900 also exhibits excellent catalytic activity, good durability, together with high methanol tolerance in alkaline electrolyte, which makes it a highly efficient air cathode material toward zinc–air cell.     

N/S dual-doped graphene with high defect density for enhanced supercapacitor properties

N/S dual-doped graphene was prepared by one-pot process using graphene oxide as raw material and thiourea and urea as reduction-dopants. The field emission scanning electron microscopy (FESEM), X-ray powder diffraction (XRD), Raman spectroscopy (Raman), nuclear magnetic resonance (NMR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and other means were used to characterize the microstructure and morphology of the samples. The electrochemical properties of the samples were tested by cyclic voltammetry, electrochemical alternating impedance and constant current charge-discharge techniques, and compared with graphene and nitrogen-doped graphene. Results show that the defect density of graphene can be increased more effectively by N/S dual doping than by nitrogen doping, and the contents of doped nitrogen and sulfur have a significant effect on the morphology and performance of the samples. The specific surface area of the best sample reaches 275.8 m² g⁻¹, and its conductivity is 477.6 S m⁻¹. When the window voltage is −1.2-0 V, the best sample shows superior specific capacitance of 386.5 F g⁻¹ and a high energy density of 69.6 Wh kg⁻¹ at a scan rate of 10 mV s⁻¹. At the current density of 10 A g⁻¹, after 5000 constant current charge/discharge cycles, the specific capacitance retention rate is 94.5%, showing excellent cyclic stability.     

Solvothermal synthesis of novel pod-like MnCo2O4.5 microstructures as high-performance electrode materials for supercapacitors

MnCo₂O_4.5 pod-like microstructures were successfully prepared through an initial solvothermal reaction in a mixed solvent containing water and ethanol, and combined with a subsequent calcinations treatment of the precursors in air. The total synthetic process was accomplished without any surfactant or template participation. The MnCo₂O_4.5 pods possessed a specific surface area as high as 73.7 m²/g and a mean pore size of 12.3 nm. The electrochemical performances were evaluated in a typical three-electrode system using 2 M of KOH aqueous electrolyte. The results demonstrated that such MnCo₂O_4.5 pods delivered a specific capacitance of 321 F/g at 1 A/g with a rate capability of 69.5% at 10 A/g. Moreover, the capacitance retention could reach 87% after 4000 cycles at 3 A/g, suggesting the excellent long-term cycling stability. Furthermore, the asymmetric device was fabricated by using MnCo₂O_4.5 porous pods as anode and active carbon as cathode. It could deliver a specific capacitance of 55.3 F g⁻¹ at 1 A g⁻¹ and an energy density of 19.65 W h kg⁻¹ at a power density of 810.64 W kg⁻¹. Such superior electrochemical behaviors indicate that the MnCo₂O_4.5 pods may be served as a promising electrode material for the practical applications of high-performance supercapacitors. The current synthesis is simple and cost-effective, and can be extended to the preparation of other binary metal oxides with excellent electrochemical properties.     

Facile fabrication of comb-like porous NiCo2O4 nanoneedles on Ni foam as an advanced electrode for high-performance supercapacitor

It is very desirable to develop the high-performance supercapacitors to meet the rapidly growing demands for energy-autonomous operation and miniaturization of devices. Herein, comb-like porous NiCo₂O₄ nanoneedles on the three-dimension (3D) nickel foam (NF) have been successfully synthesized through a facile pulsed laser ablation (PLA) approach without any post-treatments and surfactant (denoted as NiCo₂O₄-PLA). The influence of working solution during the fabricated process on the properties of NiCo₂O₄-PLA has been demonstrated in detail in terms of the crystalline structure, specific surface area, morphology, and electrochemical performance. Benefiting from the large specific surface (261.4 m² g⁻¹), abundant pores, and highly conductive scaffold, the NiCo₂O₄-PLA binder-free electrode exhibits an outstanding specific capacitance (1650 F g⁻¹ at a current density of 1 A g⁻¹) and eminent cycling performance (91.78% retention after a 12,000-cycle test at a current density of 10 A g⁻¹) compared with the control samples. The assembled asymmetric device (NiCo₂O₄-PLA//AC-ASCs) delivers the high specific capacitance of 126.9 F g⁻¹ at the current density of 1 A g⁻¹, the large energy density of 56.7 Wh kg⁻¹ at a power density of 756 W kg⁻¹, and the low internal resistance. The attractive results strongly prove that it is an ideal candidate for advanced supercapacitor application.     

CoFe2O4@methyl cellulose core-shell nanostructure and their hybrids with functionalized graphene aerogel for high performance asymmetric supercapacitor

Recently, the use of asymmetric supercapacitors (ASC) has attracted much attention due to their optimum storage of energy and a high range of voltage. Here, we have indicated the design and fabrication of a unique ASC based on metal-spinel core-shell nanocomposite (CoFe₂O₄@MC) as a positive electrode and a p-phenylenediamine (PPDA)-graphene aerogel composite (AP) as a negative electrode in aqueous KOH electrolyte solution. The CoFe₂O₄@MC nanocomposite was prepared by the chemical deposition method. The AP was also effortlessly organized using the hydrothermal method. Considering the incorporation of methylcellulose carbohydrate polymer (MC) into the CoFe₂O₄ nanomaterial and consequently having a porous structure, a specific capacitance of 433.3 F g^?1 was obtained at the current density of 1 A g^?1 with the configuration of three electrodes. The CoFe₂O₄@MC//AP-ASC operates in the voltage range up to 2.3 V and provides a specific capacitance of 99 in 1 A g^?1. It presents an impressive energy density and power density of ~73 W h Kg^?1 and 1056 W kg^?1, respectively which prove its quality. The most important feature seems to be good cycling stability and capacity retention of 89% after 2000 cycles. These splendid outcomes show that CoFe₂O₄@MC nanocomposite possibly seems to be a satisfying choice for the next generation of devices with the capability of energy storage.     

Fabrication of core-shell NiMoO4@MoS2 nanorods for high-performance asymmetric hybrid supercapacitors

In this work, core-shell NiMoO₄@MoS₂ nanorods were successfully fabricated via a facile two-step hydrothermal method. By inheriting the merits of high electrical conductivity from MoS₂ nanosheets and high pseudocapacitive activity from NiMoO₄ nanorods, the hierarchical NiMoO₄@MoS₂ nanocomposite was endowed with improved electrical conductivity, enlarged specific surface area and enriched porosity, consequently enabling fast ion/electron transport and rapid Faradaic reactivity. Benefited from the synergism of NiMoO₄ and MoS₂, the NiMoO₄@MoS₂ electrode was superior to the NiMoO₄ and MoS₂ electrode, achieving specific capacitance of 2246.7 F g⁻¹, as well as showing good rate performance and improved cyclic stability (88.4% capacitance retention after 5000 cycles). The asymmetric supercapacitor device composed of the NiMoO₄@MoS₂ nanorods and hierarchical porous carbon exhibited a high energy density of 47.5 Wh kg⁻¹ at a power density of 0.44 kW kg⁻¹. The device also showed superior long-term cycling stability, retaining 80.2% of initial capacitance after 10 000 cycles. This work provides a simple strategy for scalable synthesis of integrated nanostructures, which holds great promise for the development of advanced supercapacitors.