Electrode Material For Asymmetric Supercapacitors Research Articles

Fe3O4/carbon nanocomposite: Investigation of capacitive & magnetic properties for supercapacitor applications

Fe3O4 nanoparticles with ∼10 nm diameters were synthesized by an extremely low-cost, scalable and relatively biocompatible chemical co-precipitation method. Magnetic measurements revealed that Fe3O4 nanoparticles have bifunctional superparamagnetic and ferromagnetic character with saturation magnetization (Ms) values of 64 and 71 emu g−1 at 298 K and 10 K, respectively. Pseudocapacitive Fe3O4 nanoparticles were then integrated into hazelnut shells - an abundant agricultural biomass - by an energy efficient hydrothermal carbonization method. Presence of magnesium oxide (MgO) ceramic template or its precursor in the hydrothermal reactor allowed simultaneous introduction of pores into the composite structure. Hierarchically micro-mesoporous Fe3O4/C nanocomposite possesses a high specific surface area of 344 m2 g−1. Electrochemical properties of Fe3O4/C nanocomposite were investigated by cyclic voltammetry and galvanostatic charge-discharge measurements in a conventional three-electrode cell. The Fe3O4/C nanocomposite is able to operate in a large negative potential window in 1 M Na2SO4 aqueous electrolyte (−1.2–0 V vs. Ag/AgCl). Synergistic effect of the Fe3O4 and carbon leads to enhanced specific capacitance, rate capability and cyclability making Fe3O4/C nanocomposite a very promising negative electrode material for asymmetric supercapacitors.

High Volumetric Energy Density Asymmetric Supercapacitors Based on Well‐Balanced Graphene and Graphene‐MnO2 Electrodes with Densely Stacked Architectures

The well-matched electrochemical parameters of positive and negative electrodes, such as specific capacitance, rate performance, and cycling stability, are important for obtaining high-performance asymmetric supercapacitors. Herein, a facile and cost-effective strategy is demonstrated for the fabrication of 3D densely stacked graphene (DSG) and graphene-MnO2 (G-MnO2 ) architectures as the electrode materials for asymmetric supercapacitors (ASCs) by using MnO2 -intercalated graphite oxide (GO-MnO2 ) as the precursor. DSG has a stacked graphene structure with continuous ion transport network in-between the sheets, resulting in a high volumetric capacitance of 366 F cm-3 , almost 2.5 times than that of reduced graphene oxide, as well as long cycle life (93% capacitance retention after 10 000 cycles). More importantly, almost similar electrochemical properties, such as specific capacitance, rate performance, and cycling stability, are obtained for DSG as the negative electrode and G-MnO2 as the positive electrode. As a result, the assembled ASC delivers both ultrahigh gravimetric and volumetric energy densities of 62.4 Wh kg-1 and 54.4 Wh L-1 (based on total volume of two electrodes) in 1 m Na2 SO4 aqueous electrolyte, respectively, much higher than most of previously reported ASCs in aqueous electrolytes.

Facile hydrothermal synthesis of NiTe and its application as positive electrode material for asymmetric supercapacitor

Nickel telluride (NiTe) rods are grown on Ni foam substrate by a simple hydrothermal route. The electrochemical properties of NiTe electrode are evaluated by cyclic voltammograms (CV), galvanostatic charge/discharge (GCD) tests. The prepared NiTe electrode shows a specific capacitance of 804 F g−1 at the current density of 1 A g−1 and remarkable cycling stability. In order to improve the energy density and broaden the potential window, an asymmetric supercapacitor containing NiTe as positive electrode and activated carbon (AC) as negative electrode in 3 M KOH electrolyte is assembled. The fabricated asymmetric supercapacitor can work in the voltage range of 0–1.6 V and displays high energy density of 33.6 Wh kg−1 at a power density of 807.1 W kg−1. Additionally, the AC//NiTe asymmetric supercapacitor shows good rate capability and cyclic durability.

Nanostructured Electrode Materials Derived from Metal-Organic Framework Xerogels for High-Energy-Density Asymmetric Supercapacitor.

This work successfully demonstrates metal-organic framework (MOF) derived strategy to prepare nanoporous carbon (NPC) with or without Fe3O4/Fe nanoparticles by the optimization of calcination temperature as highly active electrode materials for asymmetric supercapacitors (ASC). The nanostructured Fe3O4/Fe/C hybrid shows high specific capacitance of 600 F/g at a current density of 1 A/g and excellent capacitance retention up to 500 F/g at 8 A/g. Furthermore, hierarchically NPC with high surface area also obtained from MOF gels displays excellent electrochemical performance of 272 F/g at 2 mV/s. Considering practical applications, aqueous ASC (aASC) was also assembled, which shows high energy density of 17.496 Wh/kg at the power density of 388.8 W/kg. The high energy density and excellent capacity retention of the developed materials show great promise for the practical utilization of these energy storage devices.

Mesoporous Co0.85Se nanosheets supported on Ni foam as a positive electrode material for asymmetric supercapacitor

Mesoporous Co0.85Se nanosheets on Ni foam for high-performance supercapacitors were prepared by a facile one-step hydrothermal method. The as-synthesized Co0.85Se electrodes possess high pseudocapacitive performance with large specific capacitance and excellent cycling stability. The specific capacitance can achieve a maximum of 1378Fg−1 at a current density of 1Ag−1, which can still keep 95.5% of capacitance retention after 1000 cycles. Then, an asymmetric supercapacitor was fabricated by using Co0.85Se nanosheets as positive material and activated carbon (AC) as negative material. The asymmetric configuration can extend voltage window to 1.6V, which lead to a significant increase in the energy density to 39.7Whkg−1 at a power density of 789.6Wkg−1, couples with outstanding cycle stability. The results demonstrate that the mesoporous Co0.85Se nanosheets are promising electrode materials for supercapacitors.

Solvothermal Synthesis of Three-Dimensional Hierarchical CuS Microspheres from a Cu-Based Ionic Liquid Precursor for High-Performance Asymmetric Supercapacitors.

It is meaningful to exploit copper sulfide materials with desired structure as well as potential application due to their cheapness and low toxicity. A low-temperature and facile solvothermal method for preparing three-dimensional (3D) hierarchical covellite (CuS) microspheres from an ionic liquid precursor [Bmim]2Cu2Cl6 (Bmim = 1-butyl-3-methylimidazolium) is reported. The formation of CuS nanostructures was achieved by decomposition of intermediate complex Cu(Tu)3Cl (thiourea = Tu), which produced CuS microspheres with diameters of 2.5-4 μm assembled by nanosheets with thicknesses of 10-15 nm. The ionic liquid, as an "all-in-one" medium, played a key role for the fabrication and self-assembly of CuS nanosheets. The alkylimidazolium rings ([Bmim](+)) were found to adsorb onto the (001) facets of CuS crystals, which inhibited the crystal growth along the [001] direction, while the alkyl chain had influence on the assembly of CuS nanosheets. The CuS microspheres showed enhanced electrochemical performance and high stability for the application in supercapacitors due to intriguing structural design and large specific surface area. When this well-defined CuS electrode was assembled into an asymmetric supercapacitor (ASC) with an activated carbon (AC) electrode, the CuS//AC-ASC demonstrated good cycle performance (∼88% capacitance after 4000 cycles) and high energy density (15.06 W h kg(-1) at a power density of 392.9 W kg(-1)). This work provides new insights into the use of copper sulfide electrode materials for asymmetric supercapacitors and other electrochemical devices.

Na0.35MnO2/CNT Nanocomposite from a Hydrothermal Method as Electrode Material for Aqueous Supercapacitors

AbstractA Na0.35MnO2/CNT nanocomposite is prepared by a simple and low energy consumption hydrothermal method. Its electrochemical performance as an electrode material for asymmetric supercapacitors with aqueous Na2SO4 solution is investigated. In this nanocomposite less than 2 wt‐% of CNTs are intermingled with the Na0.35MnO2 nanowires. Quite obviously the introduced CNTs efficiently improve the rate performance of the composite. When the current density increases from 0.1 to 10 A·g–1, the capacitance decreases only slightly from 163 to 125 F·g–1. When assembled into an asymmetric aqueous supercapacitor using activated carbon as the counter electrode and an aqueous electrolyte solution of 0.5 mol·L–1 Na2SO4, Na0.35MnO2/CNT shows an energy density of 33.5 Wh·kg–1 at a power density of 3 kW·kg–1 based on the weights of the two electrode materials, higher than those for simple Na0.35MnO2, with an energy density of 28.7 Wh·kg–1 at a power density of 3 kW·kg–1 only. The Na0.35MnO2/CNT nanocomposite presents excellent cycling behavior, no capacitance fading after 10000 cycles, even when dissolved oxygen is not removed from the electrolyte solution. The results are very promising for practical applications of this electrode material since sodium is much cheaper than lithium and its natural resources are rich.

Synthesis of Polythiophene and its Carbonaceous Nanofibers as Electrode Materials for Asymmetric Supercapacitors

A highly porous polythiophene (PTh) nanofibers were synthesized by surfactant assisted dilute polymerization method using FeCl3 as oxidant. They were confirmed by XRD and FTIR analysis. The surface morphology of PTh was done by scanning electron microscopy (SEM). The prepared polythiophene nanofibers were subjected to calcination under inert gas atmosphere at 1400oC for 2 hrs to get carbonaceous PTh nanofibers. The asymmetric supercapacitor was assembled using PTh nanofibers as the cathode and carbonaceous PTh nanofibers as the anode in 6M KOH electrolyte. The electrochemical supercapacitor performances were carried out to find out the specific capacitance, energy density and power density of the cell. The above results confirmed that the prepared PTh nanofibers and carbonaceous PTh nanofibers could be used as electrode materials for asymmetric supercapacitor applications. Keywords: Polythiophene, Dilute polymerization method, Carbonaceous material, Asymmetric supercapacitor, Specific capacitances

Ni(OH)2 nanoflakes electrodeposited on Ni foam-supported vertically oriented graphene nanosheets for application in asymmetric supercapacitors

Binderless Ni(OH)2 nanoflakes grown on Ni foam (NF)-supported vertically oriented graphene nanosheets (V-GNs) has been fabricated as a positive electrode material for asymmetric supercapacitor (ASC), coupled with activated carbon (AC) as a counter electrode material. The introduction of V-GNs leads to dense growth of nanocrystalline β-Ni(OH)2 that is confirmed by X-ray diffraction, transmission electron microscopic and scanning electron microscopic analyses. The electrochemical performances of the Ni(OH)2/GNs/NF electrode are characterized by cyclic voltammetry and charge–discharge tests, which exhibit high specific capacitance of 2215Fg−1 at a scan current density of 2.3Ag−1, enhanced cycling stability and high rate capability. The Ni(OH)2/GNs/NF-AC-based ASC can achieve a cell voltage of 1.4V and a specific energy density of 11.11Whkg−1 at 0.5mAcm−2 with a nearly 100% coulombic efficiency at room temperature.

Spherical porous VN and NiOx as electrode materials for asymmetric supercapacitor

In this work, the asymmetric supercapacitor in which spherical porous VN is used as a negative electrode and NiOx as a positive electrode was assembled in 1M KOH aqueous electrolyte. The spherical porous VN negative material has a specific capacitance of 580F/g and the NiOx positive electrode a specific capacitance of 680F/g. The VN/NiOx symmetric supercapacitor shows a sloping voltage profile from 0.5 to 1.45V with excellent reversibility and delivers a specific capacitance of 139F/g and an energy density of 63Wh/kg based on the total weight of the active electrode materials. The VN/NiOx asymmetric supercapacitor shows a good cycling behavior, about 15% specific capacitance decay after 1000 cycles. It also exhibits an excellent rate capability, even at a power density of 2400W/kg, it has a specific energy 26Wh/kg compared with 50Wh/kg at the power density about 365W/kg.

Hierarchical porous nickel oxide and carbon as electrode materials for asymmetric supercapacitor

Asymmetric supercapacitor is constructed using hierarchical porous electrode materials of nickel oxide and carbon with the aim to facilitate ion transport. Hierarchical porous nickel oxide and carbon are prepared by template-directed synthesis. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charging–discharging are used to test the asymmetric supercapacitor and investigate the electrode processes at different supercapacitor voltages. The capacitance, energy density and power density of the asymmetric supercapacitor can be improved by elevating the supercapacitor voltage, and its cycling stability decays at high voltage, but the columbic efficiency stays close to 100%.

A new asymmetric supercapacitor based on λ-MnO 2 and activated carbon electrodes

Lithium-ion intercalated compound λ-MnO 2 was used as positive electrode in asymmetric supercapacitor with activated carbon used as negative electrode in 1 mol L − 1 Li 2SO 4 aqueous electrolyte solution. Phase composition, morphology and particle sizes of λ-MnO 2 were studied by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). Electrochemical capacitive performance of the asymmetric supercapacitor was tested by cyclic voltammetry and galvanostatic charge–discharge tests. The results show that the asymmetric supercapacitor has electrochemical capacitance performance within wide potential range of 0–2.2 V. The specific capacitance is 53 F g − 1 at a constant current density of 10 mA cm − 2 . The energy density is 36 W h kg − 1 with a power density of 314 W kg − 1 . It is obvious that λ-MnO 2 is a potential electrode material for asymmetric supercapacitor.