Electrode Material For Electrochemical Supercapacitors Research Articles

Electrochemical behaviors of graphene–ZnO and graphene–SnO 2 composite films for supercapacitors

Graphene, graphene–ZnO and graphene–SnO 2 films were successfully synthesized and used as electrode materials for electrochemical supercapacitors, respectively. The screen-printing approach was employed to fabricate graphene film on graphite substrate while the ZnO and SnO 2 were deposited on graphene films by ultrasonic spray pyrolysis. The electrochemical performances of these electrodes were comparatively analyzed through electrochemical impedance spectrometry, cyclic voltammetry and chronopotentiometry tests. The results showed that the incorporation of ZnO or SnO 2 improved the capacitive performance of graphene electrode. Graphene–ZnO composite electrode exhibited higher capacitance value (61.7 F/g) and maximum power density (4.8 kW/kg) as compared with graphene–SnO 2 and pure graphene electrodes.

A novel activated mesocarbon microbead(aMCMB)/Mn3O4 composite for electrochemical capacitors in organic electrolyte

Abstract A novel activated mesocarbon microbead(aMCMB)/Mn 3 O 4 composite is successfully prepared for electrochemical capacitors. The morphology and crystal structure of the composite are investigated by scanning electron microscopy and X-ray diffraction. The electrochemical studies indicate that the aMCMB/Mn 3 O 4 composite has ideal capacitive performance in 1.0 mol L −1 LiPF 6 (EC + DMC). A maximum specific capacitance of 178 F g −1 is obtained for the composite via galvanostatic charge–discharge at a current density of 330 mA g −1 , and the specific capacitance of Mn 3 O 4 is estimated to be as high as 445 F g −1 . The aMCMB/Mn 3 O 4 composite material exhibits ideal capacitive behavior indicating a promising electrode material for electrochemical supercapacitors.

Study on the electrochemical behavior of vanadium nitride as a promising supercapacitor material

Vanadium nitride (VN) powder was synthesized by calcining V 2O 5 xerogel in a furnace under an anhydrous NH 3 atmosphere at 400 °C. The structure and surface morphology of the obtained VN powder were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The supercapacitive behavior of VN in 1 M KOH electrolyte was studied by means of cyclic voltammetry (CV), constant current charge–discharge cycling (CD) and electrochemical impedance spectroscopy (EIS). The XRD result indicates that the obtained VN belongs to the cubic crystal system (Fm3m [2 2 5]) with unit-cell parameter 4.15 Å. SEM images show the homogeneous surface of the obtained VN. The CV diagrams illustrate the existence of fast and reversible redox reactions on the surface of VN electrode. The specific capacitance of VN is 161 F g −1 at 30 mV s −1. Furthermore, the specific capacitance remains 70% of the original value when the scan rate increases from 30 to 300 mV s −1. CD experiments show that VN is suitable for CD at high current density, and the slow and irreversible faradic reactions exist during the charge–discharge process of the VN electrode. The experimental results indicate that VN is a promising electrode material for electrochemical supercapacitors.

Inorganic cryogels for energy saving and conversion

Cryogels are usually obtained by freezing and thawing or freeze drying of gels and residues. Essential morphological features of the cryogels are bimodal pore size distribution, nanosize of the primary particles (crystallites) and their low agglomeration. Widely used for a decades in the polymer science and technology, cryogels find now a growing number of applications in the electroceramic materials. Freeze casting technique based on the freeze gelation effect is proved to be useful forming method in the production of complex-shaped SiO2-containing electroceramics. Directed modification of the micromorphology by using solvent exchange schemes allows to obtain SiO2 cryogel monoliths with density ≤ 0.05 g cm−3 and specific surface area 700–800 m2 g−1 suitable for cryogenic thermal insulation of the superconducting devices. Excellent electrocatalytic activity of the macro/mesoporous PtRu/C cryogels in the methanol oxidation reaction makes them perspective anode materials of direct methanol fuel cells. Application of the cryogel-derived starting powders promoted substantial reduction of the sintering temperatures for a number of electroceramic materials. MnO2- and V2O5-based cryogels are efficient cathode materials for secondary lithium batteries with specific capacity up to 300 mAh g−1. Recent studies demonstrated also a feasibility of cryochemical approaches to the synthesis of complex oxide-based nanocrystalline electrode materials for electrochemical supercapacitors with high specific capacity at current densities up to 50 mA cm−2.

Graphene-based electrochemical supercapacitors

Graphenes prepared by three different methods have been investigated as electrode materials in electrochemical supercapacitors. The samples prepared by exfoliation of graphitic oxide and by the transformation of nanodiamond exhibit high specific capacitance in aq. H2SO4, the value reaching up to 117 F/g. By using an ionic liquid, the operating voltage has been extended to 3·5 V (instead of 1 V in the case of aq. H2SO4), the specific capacitance and energy density being 75 F/g and 31·9 Wh kg−1 respectively. This value of the energy density is one of the highest values reported to date. The performance characteristics of the graphenes which are directly related to the quality, in terms of the number of layers and the surface area, are superior to that of single-walled and multi-walled carbon nanotubes.

Potentiodynamical deposition of nanosized manganese oxides as high capacitance electrochemical capacitors

Nanosized manganese oxides powders were potentiodynamically deposition onto the Pb substrates by anodic oxidation in 0.5 mol L−1 MnSO4 and 0.5 mol L−1 H2SO4 mixed solution at 40 °C. The chemical composition of the sample was determined by complex titration with ethylene diamine tetraacetic acid and redox titration. X-ray diffraction, scanning electron microscopy, cyclic voltammetry, and chronopotentiometry were employed to characterize the materials. The highest specific capacitance of the MnOx composite electrode was up to 420 F g−1 in 1.0 mol L−1 Na2SO4 electrolyte at the scan rate 5 mV s−1. The synthesized nanosized manganese oxide exhibited ideal capacitive behavior indicating a promising electrode material for electrochemical supercapacitors.

Potentiodynamical co-deposited manganese oxide/carbon composite for high capacitance electrochemical capacitors

Manganese oxide/carbon composite materials were prepared by introducing the carbon powders into the potentiodynamical anodic co-deposited manganese oxide in 0.5 mol L − 1 MnSO 4 and 0.5 mol L − 1 H 2SO 4 mixed solution at 40 °C. The surface morphology and structure of the composite material were examined by scanning electron microscope and X-ray diffraction. Cyclic voltammetry tests and electrochemical impedance measurements were applied to investigate the performance of the composite electrodes with different ratios of manganese oxide and carbon. These composite materials with rough surface, which consisted of approximately amorphous manganese oxide, were confirmed to possess the ideal capacitive property. The highest specific capacitance of manganese oxide/carbon composite electrode was up to 410 F g − 1 in 1.0 mol L − 1 Na 2SO 4 electrolyte at the scan rate 10 mV s − 1 . The synthesized composite materials exhibited ideal capacitive behavior indicating a promising electrode material for electrochemical supercapacitors.

Electrochemical supercapacitor electrode material based on poly(3,4-ethylenedioxythiophene)/polypyrrole composite

Poly (3,4-ethylenedioxythiophene)/polypyrrole composite electrodes were prepared by electropolymerization of 3,4-ethylenedioxythiophene (EDOT) on the surface of polypyrrole (PPy) modified tantalum electrodes. The morphology observation of PPy and poly(3,4-ethylenedioxythiophene)/polypyrrole composite (PEDOT/PPy) was performed on Field Emission Scanning Electron Microscope (SEM). The electrochemical capacitance properties of the composite were investigated with cyclic voltammetry (CV), galvanostatic charge–discharge and electrochemical impedance spectroscopy (EIS) techniques in the two- or three-electrode cell system. The results show that the PEDOT/h-PPy (PPy with horn-like structure) composite films were characterized with highly porous structure, which leads to their specific capacitance as 230 Fg −1 in 1 M LiClO 4 aqueous solutions and even 290 Fg −1 in 1 M KCl aqueous solutions. Moreover, the composite exhibits a rectangle-like shape of voltammetry characteristics even at scanning rate 100 mV s −1, a linear variation of the voltage with respect to time without a clear ohm-drop phenomenon in galvanostatic charge–discharge process and almost ideal capacitance behavior in low-frequency in 1 M KCl solutions. Furthermore, specific power of the composite would reach 13 kW kg −1 and it had good cycle stability. All of the above imply that the PEDOT/h-PPy composites were an ideal electrode material of supercapacitor.

Highly efficient organic-inorganic poly(3,4-ethylenedioxythiophene)-molybdenum trioxide nanocomposite electrodes for electrochemical supercapacitor

In this paper, we report a highly efficient organic-inorganic nanocomposite electrode with enhanced double layer capacitance, which has been synthesized using 3,4-ethylenedioxythiophene and crystalline molybdenum trioxide (MoO3) in the presence of an external oxidizing agent. The interlayer spacing of MoO3 upon intercalation expands from 6.93to13.46Å and is followed by an exfoliation and restacking process. The resulting nanocomposite is characterized by powder x-ray diffraction, scanning electron microscopy, transmission electron microscopy, x-ray photoelectron spectroscopy, and four probe conductivity measurements. The application potential of this nanocomposite as an electrode material for electrochemical supercapacitors has been investigated, highlighting the unusual enhancement of double layer capacitance of poly(3,4-ethylenedioxythiphene) (PEDOT-MoO3) nanocomposites (∼300Fg−1) compared to that of pristine MoO3 (∼40mFg−1). The improved electrochemical performance is attributed to the intercalation of electronically conducting PEDOT between MoO3 layers with enhanced bidimensionality and an increase in the surface area.

Electrochemical supercapacitor material based on manganese oxide: preparation and characterization

A novel class of electrochemical supercapacitor electrode material has been electrochemically synthesized from a manganese halide complex in water-containing acetonitrile electrolyte at room temperature. This material has been physically and chemically characterized by scanning electron microscopy, X-ray photoelectron microscopy (XPS), FT-Raman microscopy and cyclic voltammetry. XPS and FT-Raman characterization suggest that this material is composed of manganese oxide with a chemical composition of Mn 3O 4 and containing a moderate amount of carbon. Cyclic voltammetric characterization indicates that this material has higher electronic conductivity than usually seen for manganese oxide and that it shows fast kinetics for the charge–discharge process in both aqueous and acetonitrile electrolytes. The material provides a large pseudocapacitance over a potential window of about 1 V in aqueous electrolyte and about 2 V in acetonitrile electrolyte. It is therefore a good candidate as a material for an electrochemical supercapacitor electrode.

Ideal capacitive behavior of hydrous manganese oxide prepared by anodic deposition

Amorphous hydrous manganese oxide (a-MnO 2· nH 2O) was anodically deposited onto a graphite substrate from a MnSO 4·5H 2O solution with pH of 6.4. The specific capacitance of this thick a-MnO 2· nH 2O deposit, measured from both cyclic voltammetry and chronopotentiometry, is about 265–320 F g −1 in a potential window of 1.0 V. The electrochemical reversibility of redox couples at/within the a-MnO 2· nH 2O was significantly influenced by the pH of the test electrolytes. This amorphous hydrous oxide exhibited ideal capacitive behavior (acceptable capacity, high reversibility and high pulse charge–discharge property) between 0 and 1.0 V in 0.1 M Na 2SO 4 indicating a promising electrode material for electrochemical supercapacitors.

Electrochemical Characterization of Polyaniline in Nonaqueous Electrolyte and Its Evaluation as Electrode Material for Electrochemical Supercapacitors

In this study, the performance of a polyaniline (PANI) based supercapacitor where electroactive PANI films were prepared on carbon paper electrodes from a nonaqueous solution with an organic acid as the proton source was investigated. The use of nonaqueous media as electrolyte led to an increase of the electroactivity window from 0.75 V in aqueous media up to 1.0 V. Low frequency capacitance, evaluated by electrochemical impedance spectroscopy, of about 150 F/g is reported. Scanning electron microscopy indicated a highly porous material for deposited charges greater than 1 C/cm2. Constant current charge/discharge cycling of a symmetric supercapacitor based on PANI in nonaqueous medium was performed in a two-electrode cell configuration and a loss of about 60% of the discharge capacity was demonstrated after 1000 cycles. Tetramethylammonium methanesulfonate was also used instead of tetraethylammonium tetrafluoroborate as supporting electrolyte in acetonitrile for the charge/discharge testing of the PANI-PANI capacitor. Energy and power densities of approximately 3.5 Wh/kg and 1300 W/kg, respectively, were developed by this supercapacitor for a cell voltage of 1 V and a discharge time of 20 s. On the other hand, an asymmetrical supercapacitor with polypyrrole and polyaniline used as positive and negative electrodes, respectively, displayed slightly improved performance. Indeed, an energy density of 5 Wh/kg and a power density of 1200 W/kg were reported for discharge time of about 20 s with 1 M as electrolyte. © 2000 The Electrochemical Society. All rights reserved.

Poly(Cyano-Substituted Diheteroareneethylene) as Active Electrode Material for Electrochemical Supercapacitors

A new class of low band gap thiophene polymers prepared from (E)-α-cyanoethylene thiophene derivatives were electrochemically and physically evaluated as active electrode material for electrochemical supercapacitors. The corresponding polymers were prepared by electrochemical polymerization of these monomers from a nonaqueous solution (acetonitrile) containing tetraethylammonium tetrafluoroborate. The electrochemical properties and the stability under cyclic voltammetry of the polymers were found to be strongly dependent on their electronic configuration, especially in the case where the monomer has two different aromatic heterocycles. The range of stable electroactivity of the polymers in organic media spans about 2 V. Since poor stability was observed by cyclic voltammetry for poly-(E)-α-[(2-thienyl)methylene]-2-(3-methylthiophene)acetonitrile and poly-(E)-α-(2-thienylmethylene)-2-furanacetonitrile, only poly-(E)-α-[(2-thienyl)methylene]-2-thiopheneacetonitrile, poly-(E)-α-[(3-methyl-2-thienyl)methylene...

Keggin‐Type Heteropolyacids as Electrode Materials for Electrochemical Supercapacitors

An inexpensive electrochemical capacitor system with an asymmetric configuration is demonstrated. The system includes heteropolyacids and a proton‐exchange polymer membrane. Heteropolyacid electrodes show facile redox processes and host large amounts of easily accessible mobile protons required for charge balance. The proton‐conducting polymer electrolyte provides chemical stability of the heteropolyacids which would otherwise dissolve into the aqueous liquid electrolyte. In this context, /Nafion 117/ is a model system. A very reversible specific capacitance of 112 F/g and an energy density of 36 J/g, based on the active materials only, were measured for the optimized cold‐pressed single cell with an operating voltage of 0.8 V. This approach can be extended to other transition‐metal oxides chemically unstable in aqueous solution that have mixed‐valence redox energies between the highest occupied and lowest unoccupied molecular orbital of the electrolyte. An electronic energy diagram for advanced design considerations is presented.