Electrochemical capacitance of NiO/Ru0.35V0.65O2 asymmetric electrochemical capacitor

A designed asymmetric hybrid electrochemical capacitor was presented where NiO and Ru_0.35V_0.65O₂ as the positive and negative electrode, respectively, both stored charge through reversible faradic pseudocapacitive reactions of the anions (OH⁻) with electroactive materials. And the two electrodes had been individually tested in 1 M KOH aqueous electrolyte to define the adequate balance of the active materials in the hybrid system as well as the working voltage of the capacitor based on them. The electrochemical tests demonstrated that the maximum specific capacitance and energy density of the asymmetric hybrid electrochemical capacitor were 102.6 F g⁻¹ and 41.2 Wh kg⁻¹, respectively, delivered at a current density of 7.5 A cm⁻². And the specific energy density decreased to 23.0 Wh kg⁻¹ when the specific power density increased up to 1416.7 W kg⁻¹. The hybrid electrochemical capacitor also exhibited a good electrochemical stability with 83.5% of the initial capacitance over consecutive 1500 cycle numbers.     

Supercapacitive properties of hybrid films of manganese dioxide and polyaniline based on active carbon in organic electrolyte

This is the first report about supercapacitive performance of hybrid film of manganese dioxide (MnO₂) and polyaniline (PANI) in an organic electrolyte (1.0 M LiClO₄ in acetonitrile). In this work, a high surface area and conductivity of active carbon (AC) electrode is used as a substrate for PANI/MnO₂ film electro-codeposition. The redox properties of the coated PANI/MnO₂ thin film exhibit ideal capacitive behaviour in 1 M LiClO₄/AN. The specific capacitance (SC) of PANI/MnO₂ hybrid film is as high as 1292 F g⁻¹ and maintains about 82% of the initial capacitance after 1500 cycles at a current density of 4.0 mA cm⁻², and the coulombic efficiency (η) is higher than 95%. An asymmetric capacitor has been developed with the PANI/MnO₂/AC positive and pure AC negative electrodes, which is able to deliver a specific energy as high as 61 Wh kg⁻¹ at a specific power of 172 W kg⁻¹ in the range of 0-2.0 V. These results indicate that the organic electrolyte is a promising candidate for PANI/MnO₂ material application in supercapacitors.     

Construction of composite electrodes comprising manganese dioxide nanoparticles distributed in polyaniline-poly(4-styrene sulfonic acid-co-maleic acid) for electrochemical supercapacitor

This work demonstrated a novel and simple route for preparing a composite comprising of manganese oxide (MnO₂) nanoparticles and polyaniline (PANI) doped poly(4-styrene sulfonic acid-co-maleic acid) (PSSMA) by “electrochemical doping-deposition”. The PANI-PSSMA-MnO₂ composite was characterized by scanning electron microscopy (SEM)), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). SEM images revealed a uniform dispersion of MnO₂ nanoparticles in the porous structure of PANI-PSSMA structure. XRD measurements showed the distortion of the crystal structure of β-MnO₂ after deposition of MnO₂ in PANI-PSSMA structure. Thus, the XRD pattern of PANI was predominating. Cyclic voltammetry and chronopotentiometry were employed in 0.5 M Na₂SO₄ to evaluate the capacitor properties. The results showed a significant improvement in the specific capacitance of the composite electrode. The specific capacitance of PANI-PSSMA-MnO₂ (50.4 F g⁻¹) had improvement values of 172% compared to that of PANI (18.5 F g⁻¹). When only the MnO₂ mass was considered, the composite had a specific capacitance of 556 F g⁻¹.     

Graphene-MnO2 and graphene asymmetrical electrochemical capacitor with a high energy density in aqueous electrolyte

The graphene-manganese oxide hybrid material has been prepared by solution-phase assembly of aqueous dispersions of graphene nanosheets and manganese oxide nanosheets at room temperature. The morphology and structure of the obtained material are examined by scanning electron microscopy, transition electron microscopy, X-ray diffraction and N₂ adsorption-desorption. Electrochemical properties are characterized by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. An asymmetric electrochemical capacitor with high energy and power densities based on the graphene-manganese oxide hybrid material as positive electrode and graphene as negative electrode in a neutral aqueous Na₂SO₄ solution as electrolyte is assembled. The asymmetrical electrochemical capacitor could cycle reversibly in a voltage of 0-1.7 V and give an energy density of 10.03 Wh kg⁻¹ even at an average power density of 2.53 kW kg⁻¹. Moreover, the asymmetrical electrochemical capacitor exhibit excellent cycle stability, and the capacitance retention of the asymmetrical electrochemical capacitor is 69% after repeating the galvanostatic charge-discharge test at the constant current density of 2230 mA g⁻¹ for 10,000 cycles.     

Electrochemically synthesized nanocrystalline spinel thin film for high performance supercapacitor

Spinels are not known for their supercapacitive nature. Here, we have explored electrochemically synthesized nanostructured NiCo₂O₄ spinel thin-film electrode for electrochemical supercapacitors. The nanostructured NiCo₂O₄ spinel thin film exhibited a high specific capacitance value of 580 F g⁻¹ and an energy density of 32 Wh kg⁻¹ at the power density of 4 kW kg⁻¹, accompanying with good cyclic stability.     

Enhancement of the energy storage properties of supercapacitors using graphene nanosheets dispersed with metal oxide-loaded carbon nanotubes

Graphene nanosheets (GNs) dispersed with SnO₂ nanoparticles loaded multiwalled carbon nanotubes (SnO₂-MWCNTs) were investigated as electrode materials for supercapacitors. SnO₂-MWCNTs were obtained by a chemical method followed by calcination. GNs/SnO₂-MWCNTs nanocomposites were prepared by ultrasonication of the GNs and SnO₂-MWCNTs. Electrochemical double layer capacitors were fabricated using the composite as the electrode material and aqueous KOH as the electrolyte. Electrochemical performance of the composite electrodes were compared to that of pure GNs electrodes and the results are discussed. Electrochemical measurements show that the maximum specific capacitance, power density and energy density obtained for supercapacitor using GNs/SnO₂-MWCNTs nanocomposite electrodes were respectively 224 F g⁻¹, 17.6 kW kg⁻¹ and 31 Wh kg⁻¹. The fabricated supercapacitor device exhibited excellent cycle life with ∼81% of the initial specific capacitance retained after 6000 cycles. The results suggest that the hybrid composite is a promising supercapacitor electrode material.     

High energy density PbO2/activated carbon asymmetric electrochemical capacitor based on lead dioxide electrode with three-dimensional porous titanium substrate

A PbO₂/AC asymmetric electrochemical capacitor (AEC) with energy density as high as 49.4 Wh kg⁻¹, power density of 433.2 W kg⁻¹ and specific capacitance of 135.2 F g⁻¹ was fabricated with PbO₂ electrodeposited on three-dimensional porous titanium (3D-Ti/PbO₂) and activated carbon. The high electrochemical active surface of 3D-Ti/PbO₂ resulted in high specific capacity making it suitable for use as positive electrode in PbO₂/AC AEC. The fabricated AEC demonstrated good power performance with an energy density conservation of 30 Wh kg⁻¹ at power density of 2078 W kg⁻¹. The fabricated AEC also showed excellent cycling stability with capacitance retention of 99.2% after 1000 cycles.     

Supercapacitor electrodes based on polyaniline-silicon nanoparticle composite

A composite material formed by dispersing ultrasmall silicon nanoparticles in polyaniline has been used as the electrode material for supercapacitors. Electrochemical characterization of the composite indicates that the nanoparticles give rise to double-layer capacitance while polyaniline produces pseudocapacitance. The composite shows significantly improved capacitance compared to that of polyaniline. The enhanced capacitance results in high power (220 kW kg⁻¹) and energy-storage (30 Wh kg⁻¹) capabilities of the composite material. A prototype supercapacitor using the composite as the charge storage material has been constructed. The capacitor showed the enhanced capacitance and good device stability during 1000 charging/discharging cycles.     

The preparation and performance of calcium carbide-derived carbon/polyaniline composite electrode material for supercapacitors

Calcium carbide (CaC₂)-derived carbon (CCDC)/polyaniline (PANI) composite materials are prepared by in situ chemical oxidation polymerization of an aniline solution containing well-dispersed CCDC. The structure and morphology of CCDC/PANI composite are characterized by Fourier infrared spectroscopy (FTIR), scanning electron microscope (SEM), transmission electron microscopy (TEM) and N₂ sorption isotherms. It has been found that PANI was uniformly deposited on the surface and the inner pores of CCDC. The supercapacitive behaviors of the CCDC/PANI composite materials are investigated with cyclic voltammetry (CV), galvanostatic charge/discharge and cycle life measurements. The results show that the CCDC/PANI composite electrodes have higher specific capacitances than the as grown CCDC electrodes and higher stability than the conducting polymers. The capacitance of CCDC/PANI composite electrode is as high as 713.4 F g⁻¹ measured by cyclic voltammetry at 1 mV s⁻¹. Besides, the capacitance retention of coin supercapacitor remained 80.1% after 1000 cycles.     

Preparation and enhanced capacitance of core–shell polypyrrole/polyaniline composite electrode for supercapacitors

Polypyrrole (PPy) nanotubes were synthesized by using the complex of methyl orange (MO)/FeCl₃ as a template. Then the core–shell polypyrrole/polyaniline (PPy/PANI) composite was prepared by in situ chemical oxidation polymerization of aniline on the surface of PPy nanotubes. The morphology and molecular structure were characterized by transmission electron microscopy (TEM), infrared spectroscopy (IR) and X-ray diffraction (XRD). TEM images confirmed that the composite was core–shell nanotubes. The electrochemical properties of the PPy/PANI composite electrode were investigated by cyclic voltammetry (CV), galvanostatic charge–discharge and electrochemical impedance spectroscopy (EIS). The electrochemical experiments showed that the specific capacitance of the PPy/PANI composite was 416 F g⁻¹ in 1 M H₂SO₄ electrolyte and 291 F g⁻¹ in 1 M KCl electrolyte. Furthermore, the composite electrode exhibited a good rate capability and maintained 91% of initial capacity at a current density of 15 mA cm⁻² in 1 M H₂SO₄ electrolyte.     

Preparation of graphene nanosheet/carbon nanotube/polyaniline composite as electrode material for supercapacitors

Graphene nanosheet/carbon nanotube/polyaniline (GNS/CNT/PANI) composite is synthesized via in situ polymerization. GNS/CNT/PANI composite exhibits the specific capacitance of 1035 F g⁻¹ (1 mV s⁻¹) in 6 M of KOH, which is a little lower than GNS/PANI composite (1046 F g⁻¹), but much higher than pure PANI (115 F g⁻¹) and CNT/PANI composite (780 F g⁻¹). Though a small amount of CNTs (1 wt.%) is added into GNS, the cycle stability of GNS/CNT/PANI composite is greatly improved due to the maintenance of highly conductive path as well as mechanical strength of the electrode during doping/dedoping processes. After 1000 cycles, the capacitance decreases only 6% of initial capacitance compared to 52% and 67% for GNS/PANI and CNT/PANI composites.     

Electrodeposition of manganese dioxide in three-dimensional poly(3,4-ethylenedioxythiophene)–poly(styrene sulfonic acid)–polyaniline for supercapacitor

The preparation of composites of precise metal oxides/conducting polymers is important in studies of supercapacitors. In this work, a three-dimensional matrix of poly(3,4-ethylenedioxythiophene)–poly(styrene sulfonic acid)–polyaniline (PEDOT–PSS–PANI) was prepared by interfacial polymerization of ANI into PEDOT–PSS. Conductivity was enhanced by incorporating of PANI into PEDOT–PSS because of the decrease in the distance for electron shuttling along the conjugated polymeric chain. Composite electrodes were prepared by the electrodeposition of manganese dioxide (MnO₂) in a PEDOT–PSS–PANI three-dimensional matrix. The electrodes were characterized by field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry techniques. The results show a significant improvement in the specific capacitance of the composite electrode. For PEDOT–PSS the specific capacitance was of 0.23 F g⁻¹, while PEDOT–PSS–PANI and PEDOT–PSS–PANI–MnO₂ displayed values of 6.7 and 61.5 F g⁻¹, respectively. When only considering the MnO₂ mass, the composite had the specific capacitance of 372 F g⁻¹. The composite also had an excellent cyclic performance.     

High-energy density graphite/AC capacitor in organic electrolyte

A high-energy density hybrid capacitor has been designed in organic electrolyte (1 mol L⁻¹ LiPF₆ in 1:1 ethylene carbonate (EC)/dimethyl carbonate (DMC)) using commercial grades of graphite and activated carbon for negative and positive electrodes, respectively. Different approaches have been explored for assembling the hybrid capacitor in order to achieve an optimum ratio between the energy and power density, while keeping a long cycle-life capability. In the optimized hybrid capacitor, the potential of the positive electrode ranges from 1.5 up to 5 V vs. Li/Li⁺, being extended to the whole stability window of the activated carbon in the organic electrolyte, whereas the potential of the negative electrode remains almost constant at around 0.1 V vs. Li/Li⁺. After balancing carefully the respective masses of the electrodes and appropriately formatting the system, it was found that a voltage of 4.5 V is the optimal value for avoiding a capacitance fading of the hybrid capacitor during cycling. Gravimetric and volumetric energy densities as high as 103.8 Wh kg⁻¹ and 111.8 Wh L⁻¹, respectively, were obtained. The noticeable value of volumetric energy density is 10 times higher than for symmetric or asymmetric capacitors built with the same activated carbon.     

Electrochemical properties of leucoemeraldine, emeraldine, and pernigraniline forms of polyaniline/multi-wall carbon nanotube nanocomposites for supercapacitor applications

We report on the synthesis and electrochemical properties of leucoemeraldine base, emeraldine salt and pernigraniline base forms of polyaniline (PANI) in the form of nanocomposites with MWNTs. The oxidation state of PANI in the composite is controlled by doping and dedoping of the emeraldine salt form of PANI/MWNT composite, which is prepared through chemical polymerization, using oxidizing and reducing agents without changing the morphology of PANI in the composite and is confirmed by ultraviolet-visible spectroscopy (UV-vis) spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. The electrochemical and pseudocapacitive properties of the composites are investigated using cyclic voltammetry and analyzed with respect to the oxidation state of polyaniline. The PANI/MWNT nanocomposites show specific capacitance values of 217 F g⁻¹, 328 F g⁻¹ and 139 F g⁻¹ for leucoemeraldine base, emeraldine salt and pernigraniline base, respectively. Electrochemical impedance spectroscopy is performed to explain the different electrochemical properties of PANI in different oxidation states.     

Hybrid supercapacitor with nano-TiP2O7 as intercalation electrode

Nano-size (≤100 nm) TiP₂O₇ is prepared by the urea assisted combustion synthesis, at 450 and 900 °C. The compound is characterized by powder X-ray diffraction, Rietveld refinement, high resolution transmission electron microscopy and surface area methods. Lithium cycling properties by way of galvanostatic cycling and cyclic voltammetry (CV) showed a reversible and stable capacity of 60 (±3) mAh g⁻¹ (0.5 mole of Li) up to 100 cycles, when cycled at 15 mA g⁻¹ between 2-3.4 V vs. Li. Non-aqueous hybrid supercapacitor, TiP₂O₇ (as anode) and activated carbon (AC) (as cathode) has been studied by galvanostatic cycling and CV in the range, 0-3 V at 31 mA g⁻¹ and exhibited a specific discharge capacitance of 29 (±1) F g⁻¹stable in the range, 100-500 cycles. The Ragone plot shows a deliverable maximum of 13 Wh kg⁻¹ and 371 W kg⁻¹ energy and power density, respectively.     

Ru oxide supercapacitors with high loadings and high power and energy densities

Supercapacitors with very high energy and power densities have been constructed with hydrous ruthenium oxide powder prepared by a sol–gel method and annealed at 110 °C. Novel features of the capacitors, which improve their performances, are the use of a carbon fibre paper support, a Nafion separator, and Nafion as a binder. 1 M sulfuric acid was employed as the electrolyte. The performances of the supercapacitors were characterized by cyclic voltammetry, impedance spectroscopy and constant current discharging. The interfacial capacitance increased linearly with increasing ruthenium oxide loading to at least 50 mg cm⁻² on each electrode. The gravimetric capacitance of the Ru oxide measure by impedance reached 742 F g⁻¹ (9.66 F cm⁻²) at a loading of 13.0 mg cm⁻², and an interfacial capacitance of 34.9 F cm⁻² (682 F g⁻¹) was obtained at 51.2 mg cm⁻². The average effective series resistance was 0.55 Ω, the electronic resistance of the electrodes was negligible, and their ionic resistances were <0.42 Ω. The average power density for full discharge at 1 A cm⁻² for supercapacitors with 10 mg cm⁻² Ru oxide increased by 39% when 5% Nafion binder was added. The maximum average power density for full discharge was 31.5 W g⁻¹ while the maximum energy density was 31.2 Wh kg⁻¹. At a 1 mA discharge rate a specific capacitance of 977 F g⁻¹ of Ru oxide was obtained.     

Electrochemical profile of an asymmetric supercapacitor using carbon-coated LiTi2(PO4)3 and active carbon electrodes

In this work, we reported an asymmetric supercapacitor in which active carbon (AC) was used as a positive electrode and carbon-coated LiTi₂(PO₄)₃ as a negative electrode in 1 M Li₂SO₄ aqueous electrolyte. The LiTi₂(PO₄)₃/AC hybrid supercapacitor showed a sloping voltage profile from 0.3 to 1.5 V, at an average voltage near 0.9 V, and delivered a capacity of 30 mAh g⁻¹ and an energy density of 27 Wh kg⁻¹ based on the total weight of the active electrode materials. It exhibited a desirable profile and maintained over 85% of its initial energy density after 1000 cycles. The hybrid supercapacitor also exhibited an excellent rate capability, even at a power density of 1000 W kg⁻¹, it had a specific energy 15 Wh kg⁻¹ compared with 24 Wh kg⁻¹ at the power density about 200 W kg⁻¹.     

Electrochemical performance of carbon-coated lithium manganese silicate for asymmetric hybrid supercapacitors

Nanoscale carbon-coated Li₂MnSiO₄ powder is prepared using a conventional solid-state method and can be used as the negative electrode in a Li₂MnSiO₄/activated carbon (AC) hybrid supercapacitor. Carbon-coated Li₂MnSiO₄ material presents a well-developed orthorhombic crystal structure with a Pmn2₁ space group, although there is a small impurity of MnO. The maximum specific capacitance of the Li₂MnSiO₄/AC hybrid supercapacitor is 43.2 F g⁻¹ at 1 mA cm⁻² current density. The cell delivers a specific energy as high as 54 Wh kg⁻¹ at a specific power of 150 W kg⁻¹ and also exhibits an excellent cycle performance with more than 99% columbic efficiency and the maintenance of 85% of its initial capacitance after 1000 cycles.     

Dual functions of activated carbon in a positive electrode for MnO2-based hybrid supercapacitor

Utilizing the dual functions of activated carbon (AC) both as a conductive agent and an active substance of a positive electrode, a hybrid supercapacitor (AC-MnO₂&AC) with a composite of manganese dioxide (MnO₂) and activated carbon as the positive electrode (MnO₂&AC) and AC as the negative electrode is fabricated, which integrates approximate symmetric and asymmetric behaviors in the distinct parts of 2 V operating windows. MnO₂ in the positive electrode and AC in the negative electrode together form a pure asymmetric structure, which extends the operating voltage to 2 V due to the compensatory effect of opposite over-potentials. In the range of 0-1.1 V, both AC in the positive and negative electrode assemble as a symmetric structure via a parallel connection which offers more capacitance and less internal resistance. The optimal mass proportions of electrodes are calculated though a mathematical process. In a stable operating window of 2 V, the capacitance of AC-MnO₂&AC can reach 33.2 F g⁻¹. After 2500 cycles, maximum energy density is 18.2 Wh kg⁻¹ with a 4% loss compared to the initial cycle. The power density is 10.1 kW kg⁻¹ with an 8% loss.     

Asymmetric capacitor based on superior porous Ni-Zn-Co oxide/hydroxide and carbon electrodes

Hierarchical porous multi-phase Ni-Zn-Co oxide/hydroxide is synthesized by using metal-organic framework-5 (MOF-5) as the template. Hierarchical porous carbon is obtained by the facile direct decomposition of the MOF-5 framework with phenolic resin. The structures and textures are characterized by X-ray diffraction, high-resolution transmission electron microscopy, scanning electron microscopy, and nitrogen sorption at 77 K. An asymmetric capacitor incorporating the Ni-Zn-Co oxide/hydroxide as the positive electrode and the porous carbon as the negative electrode is fabricated. A maximum energy density of 41.65 Wh kg⁻¹ is obtained, which outperforms many other available asymmetric capacitors. The asymmetric capacitor also shows a good high-rate performance, possessing an energy density of 16.62 Wh kg⁻¹ at the power density of about 2900 W kg⁻¹.