Binder-free activated carbon papers for high-performance electric double-layer capacitors

A binder-free activated carbon paper (ACP) was simply prepared for electric double-layer capacitors by the carbonization of filter paper, followed by heat-air activation at a lower temperature. The electrochemical cells assembled using the as-prepared ACP-470 provides a high specific capacitance of 296.4 F g^?1 at current density of 0.5 A g^?1 and a high rate performance at a current density of 150 A g^?1 with a capacitance of 191.2 F g^?1 and a high cycle ability at 10,000 recycles with 100 % capacitance retention. In addition, the ACP has a lower electrical resistivity and provides an effective energy storage performance with a maximum energy density of 41.2 Wh kg^?1 and a maximum power density of 138.0 kW kg^?1 in a voltage range of 1 V.     

Synthesis of spherical mesoporous carbon for electric double-layer capacitors

Resorcinol and formaldehyde were used as carbon precursors, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer was employed as a soft template, and tetraethylorthosilicate-generated silica was used as hard templates to synthesize spherical mesoporous carbon. The resulting spherical mesoporous carbons were characterized by nitrogen adsorption–desorption isotherms and electron microscopy (SEM and TEM) and used as electrode materials for aqueous electric double-layer capacitors. The average diameters of spherical particles ranged from 2 to 7 μm and the mesopore was ca 2 nm. The highest specific surface area of 1,000 m²/g and mesopore volume of 0.86 cm³/g was obtained. The specific capacitance of 130 F/g was obtained by means of galvanostatic charging/discharging and cycle voltammetry.     

Cobalt and nitrogen atoms co-doped porous carbon for advanced electrical double-layer capacitors

Electrical double-laye r capacitors are widely concerned fo r their high power density,long cycling life and high cycling efficiency.However,their wide application is limited by their low energy density.In this study,we propose a simple yet environmental friendly method to synthesize cobalt and nitrogen atoms co-doped porous carbon(CoAT-NC) material.Cobalt atoms connected with primarily pyridinic nitrogen atoms can be uniformly dispersed in the amorphous carbon matrix,which is benefit for improving electrical conductivity and density of states of the carbon material.Therefore,an enhanced perfo rmance is expected when CoAT-NC is served as electrode in a supercapacitor device.CoAT-NC displays a good gravimetric capacitance of 160 F/g at 0.5 A/g combing with outstanding capacitance retention of 90% at an extremely high current density of 100 A/g in acid electrolyte.Furthermore,a good energy density of30 Wh/kg can be obtained in the organic electrolyte.     

Fluorination effect of activated carbon electrodes on the electrochemical performance of electric double layer capacitors

The surface of phenol-based activated carbon (AC) was fluorinated at room temperature with different F₂:N₂ gas mixtures for use as an electrode material in an electric double-layer capacitor (EDLC). The effect of surface fluorination on EDLC electrochemical performance was investigated. The specific capacitance of the fluorinated AC-based EDLC was measured in a 1 M H₂SO₄ electrolyte, in which it was observed that the specific capacitances increased from 375 and 145 F g⁻¹ to 491 and 212 F g⁻¹ with the scan rates of 2 and 50 mV s⁻¹, respectively, in comparison to those of an unfluorinated AC-based EDLC when the fluorination process was optimized via 0.2 bar partial F₂ gas pressure. This enhancement in capacitance can be attributed to the synergistic effect of increased polarization on the AC surface, specific surface area, and micro and mesopore volumes, all of which were induced by the fluorination process. The observed increase in polarization was derived from a highly electronegative fluorine functional group that emerged due to the fluorination process. The increased surface area and pore volume of the AC was derived from the physical function of the fluorine functional group.     

Redox functionalization of carbon electrodes of electrochemical capacitors

It is shown that the liquid oxidative treatment of microporous active carbon (AC) of the Norit DLC Supra 30 grade by nitric acid in the presence of carbamide results in an increase in the content of hydroxy groups on the AC surface at the practically unchanged content of carboxyl groups. Redox functionalization and appearance of pseudocapacity result in an increase in the carbon electrode capacity by 26%. The surface state of the carbon material is characterized using the infrared spectroscopy and Boehm titrimetry techniques, while the electrochemical characteristics are studied using the method of cyclic voltammetry in 3 M sulfuric acid solution. Studies of degradation of the electrodes of the initial and modified active carbons show that capacity decreases by 3 and 8%, accordingly, after 1 thousand charging–discharge cycles.     

Platinum/carbon black composites as counter electrodes for high-performance dye-sensitized solar cells

Journal of Solid State Electrochemistry - Low-cost counter electrodes for dye-sensitized solar cells (DSSCs) are prepared using platinum/carbon black (Pt/CB) composites via a spin-coating process....     

Hydrous manganese oxide/carbon nanotube composite electrodes for electrochemical capacitors

A novel type of composite electrode based on hydrous manganese oxide and a single-walled carbon nanotube has been prepared and used in electrochemical capacitors. Cyclic voltammetry, galvanostatic charging/discharging tests and electrochemical impedance measurements were applied to investigate the performance of the composite electrodes with different ratios of hydrous manganese oxide and single-walled carbon nanotube. For comparison, the performance of pure hydrous manganese oxide and pure carbon nanotubes was also studied. In this way, the composite electrode with a 6:4 ratio of hydrous manganese oxide to carbon nanotube was found to be the most promising active material for an electrochemical capacitor, which shows both good capacitance and power characteristics.     

Partially reduced graphite oxide as an electrode material for electrochemical double-layer capacitors

Partially reduced graphite oxide was prepared from graphite oxide by using synthetic graphite as precursor. The reduction of graphite oxide with a layer distance of 0.57?nm resulted in a reduction of the layer distance depending on the degree of reduction. Simultaneously the amount of oxygen functionalities in the graphite oxide was reduced, which was corroborated by elemental analysis and EDX. The electrochemical activation of the partially reduced graphite oxide was investigated for tetraethylammonium tetrafluoroborate in acetonitrile and in propylene carbonate. The activation potential depends significantly on the degree of reduction, that is, on the graphene-layer distance and on the solvent used. The activation potential decreased with increasing layer distance for both positive and negative activation. The resulting capacitance after activation was found to be affected by the layer distance, the oxygen functionalities and the used electrolyte. For a layer distance of 0.43?nm and with acetonitrile as the solvent, a differential capacitance of 220?Fg(-1) was achieved for the discharge of the positive electrode near the open-circuit potential and 195?Fg(-1) in a symmetric full-cell assembly.     

Graphitized carbon black in polyethylene as an electrochemical sensor

The electrochemical behaviour of a material obtained by moulding graphitized carbon black and polyethylene at 100–150°C is described. The material can be used as a pellet electrode in voltammetric procedures. As a tubular anode held in a teflon body, the material is valuable as a sensor for high-performance liquid chromatography. Its properties are comparable with those of glassy carbon with better signal-to-noise ratios. It is applied for the determination of several phenols, chlorophenols and hydroquinone in the low mg l^?1 range or less.     

Reed straw derived active carbon/graphene hybrids as sustainable high-performance electrodes for advanced supercapacitors

Reed straw-derived active carbon@graphene (AC@GR) hybrids were prepared by one-step carbonization/activation process using a mixture of reed straw and graphene oxide (GO) as raw materials and ZnCl₂ as activation agent. The as-prepared hybrids exhibit high specific surface area in a range of 1971–2497 m² g^?1, abundant porosity, as well as excellent energy storage capability. The symmetric C//C supercapacitor using the hybrid obtained at 700 °C as electrodes demonstrates superior cycling durability, ca. 90 % retention after 6000 cycles at 2 A g^?1, and a high energy density of 6.12 Wh kg^?1 at a power density of up to 4660 W kg^?1 in 6 M KOH aqueous electrolyte. The excellent capacitive performance is attributed to the synergistic effect of AC and GR.     

The effect of pre-carbonization of mesophase pitch-based activated carbons on their electrochemical performance for electric double-layer capacitors

The activated carbons (ACs) are prepared from mesophase pitch which is pre-carbonized by using potassium hydroxide as an activating agent. Nitrogen adsorption at 77 K is used to characterize the surface area and the porous structure of the ACs. By changing the pre-carbonization temperature from 560 to 750 °C, the arrangement of the ACs’ microcrystallines might be controllable, and the pore size could be adjusted between 1.5 and 2.4 nm. The electrochemical performance of the ACs in organic solvent (1 M Et₄NBF₄ in propylene carbonate) is investigated by voltage sweep cyclic voltammetry and constant current charge–discharge cycling tests. The results show that the ions can transfer rapidly and freely in the pore larger than or equal to 1.85 nm, even when the current density increases to 25 A g⁻¹.     

Effect of oxygen-containing functional groups on the impedance behavior of activated carbon-based electric double-layer capacitors

The surface chemistry of activated carbon was treated with sulfuric acid and hydrogen to analyze the oxygen-containing functional groups on the impedance behavior of electric double-layer capacitors. Based on the electrochemical impedance spectrum (EIS), an equivalent circuit model was proposed considering the kinetic and charge transfer characteristics, and Marquardt fit procedure was applied to the EIS data. The simulated results indicate that the oxidation treatment made the ionic resistance within the pore of carbon electrode decrease, and the ion diffusion coefficients significantly increase, which leads to improvement of power capability of the carbon electrode.     

Activated nitrogen-doped carbons from polyvinyl chloride for high-performance electrochemical capacitors

Activated nitrogen-doped carbons (ANCs) were prepared by carbonization/activation approach using aminated polyvinyl chloride (PVC) as precursor. ANCs exhibit larger porosities and higher specific surface areas than those of their nitrogen-free counterparts for the same KOH/carbon ratio. The specific surface area of ANC-1 is up to 1,398 m² g^?1 even at a low KOH/carbon ratio of 1:1. Fourier transform infrared spectroscopy investigation of the nitrogen-enriched resin precursor indicates the efficient dehydrochlorination of PVC by ethylenediamine at a low temperature. The nitrogen content and the population of nitrogen functionalities strongly depend on the KOH/carbon ratios and decrease drastically after KOH activation as seen from the elemental and X-ray photoelectron spectroscopy analysis. The surface concentration of N-6 and N-Q almost disappears and the dominant nitrogen groups become N-5 after KOH activation. The highest specific capacitance of ANCs is up to 345 F g^?1 at a current density of 50 mA g^?1 in 6 M KOH electrolyte. ANCs also exhibit a good capacitive behavior at a high scan rate of 200 mV s^?1 and an excellent cyclability with a capacitance retention ratio as high as ～93 % at a current density of 2,000 mA g^?1 for 5,000 cycles.     

Co(OH)2-combined carbon-nanotube array electrodes for high-performance micro-electrochemical capacitors

We have investigated binder-free Co(OH)₂-combined carbon-nanotube (CNT) array electrodes using anodized aluminum oxide (AAO) templates for micro-electrochemical capacitors. It is shown that compared to the capacitors fabricated with CNT only electrodes (6.3 F/cm³ at 100 mV/s), those with the Co(OH)₂-combined CNT array electrodes produce much higher capacitance (12.74 F/cm³ at 100 mV/s) together with superior high-rate capacitance. The improved electrochemical behavior is explained in terms of high capacitance of amorphous Co(OH)₂ electrode and the use of CNT arrays as effective current collector.     

Mechanically flexible reduced graphene oxide/carbon composite films for high-performance quasi-solid-state lithium-ion capacitors

Practical applications of diverse flexible wearable electronics require electrochemical energy storage(EES) devices with multiple configurations. Moreover, to fabricate flexible EES devices with high energy density and stability, organic integration from electrode design to device assembly is required. To address these challenges, a free-standing reduced graphene oxide(rGO)/carbon film with a unique sandwich structure has been designed via the assistance of vacuum-assistant filtration for lithiu...     

New ceramic-carbon composites for electrodes for electrochemical capacitors

A new class of composite materials is introduced. Fine powders of silica, titania, Y-modified zirconia, and three types of alumina were pressed and sintered to form porous monoliths with relatively uniform pore structure. Carbon was then deposited in the pores of such monoliths by thermal decomposition of dichloromethane, cyclohexene, and glucose. The structure of the carbon deposit was studied by low-temperature nitrogen adsorption and by thermal analysis. The composite materials were used as electrodes in electrochemical capacitors with 1-ethyl-3-methylimidazolium trifluoromethylsulfonate (a low-temperature ionic liquid) as the electrolyte. High capacitances were observed for glucose-derived materials, which had high specific surface areas.     

Composite electrodes of electrochemical capacitors based on carbon materials with different structure

For composite electrodes based on active carbon DCL Supra 30, ordered mesoporous carbon, and synthetic carbon material Sibunit, the electrical double layer capacitance is studied. The original carbon samples are characterized by the methods of gas adsorption, X-ray diffraction, and transmission electron microscopy. The mesoporous structure of the material synthesized by the template method provides the maximum rate of ion transport in pores and demonstrates an insignificant decrease in the specific capacitance (9.5% in an aqueous electrolyte and 1.1% in an nonaqueous electrolyte) with an increase in the polarizing current.