Performance Of Double Layer Capacitors Research Articles

Peanut shell waste derived porous carbon for high-performance supercapacitors

Low-cost and high-performance porous carbon electrode materials are the key to supercapacitors. Here, we reported the preparation of porous carbon materials by high-temperature carbonization coupled with chemical activators (H3PO4, ZnCl2, KOH) using peanut shell waste. The as-synthesized porous carbon with KOH as the chemical activator (KOH-AC) has the best ideal electric double-layer capacitance performance, outperforming other activator-treated porous carbon. In the three-electrode system, the prepared KOH-AC electrode material showed an ultra-high specific capacitance of 575.7 F g−1 at a current density of 0.5 A g−1, good rate characteristics and excellent electrochemical stability (106.5 % initial capacitance after 10,000 cycles), which exceeded that of most biomass carbon-based materials. In the two-electrode system with 6 M KOH as electrolyte, the symmetrical supercapacitor based on KOH-AC showed a high specific capacitance of 390.9 F g−1 at 0.5 A g−1 current density in the voltage rang of 0–1.3 V, with the maximum energy density of 22.2 Wh kg−1 and power density of 319.97 W kg−1 and excellent cycle stability (93.8 % after 10,000 cycles). In addition, it is also studied that all-solid-state flexible symmetric supercapacitor in PVA/KOH electrolyte shows a high specific capacitance of 432.7 F g−1 at 0.5 A g−1 current density and can provide energy density of 18.2 Wh kg−1 and power density of 275.3 W kg−1. In summary, this work synthesized high-performance porous carbon materials from renewable and sustainable biological wastes, which provided a feasible method for the application of biomass carbon in energy storage.

C/MoS2@Ti3C2Tx composite flexible films for high performance supercapacitors

Two-dimensional (2D) Ti3C2Tx MXene has important potential applications in supercapacitor due to its high electrical conductivity, good hydrophilicity and abundant surface functional groups. It can be prepared into films of flexible electrochemical capacitors without adhesives. However, the self-stacking of Ti3C2Tx nanosheets seriously reduces their capacitance. Here, we developed a novel structure of the flexible material C/MoS2@Ti3C2Tx through facile physical mixing, three-dimensional C/MoS2 nanoflowers were successfully inserted between two-dimensional Ti3C2Tx layers. The self-stacking of MoS2 and Ti3C2Tx attenuates simultaneously. And these two materials form a particle-layer structure. At a current density of 0.5 A/g, the freestanding C/MoS2@Ti3C2Tx film has an excellent specific capacitance of 410 F g−1, which is 2.6 times that of C/MoS2 and 1.9 times that of Ti3C2Tx, respectively. It remains in good condition after 5000 cycles at 10 A/g, demonstrating excellent long-life cycle stability. The improvement of electrochemical performance is attributed to the particle-layer structure, which effectively avoids the re-packing of Ti3C2Tx and greatly reduces the diffusion distance of electrolyte ions. Furthermore, the addition of C/MoS2 nanoflowers has no effect on the bending ability of MXene composite films. And The nano-flower-like structure of C/MoS2 provides high electric double layer capacitance performance. This study provides new ideas for Ti3C2Tx-based films in the field of energy storage and wearable devices.

Ionic Conductivity Enhancement Achieved by Binder in Electrodes and Its Influence in Supercapacitor

AbstractIonic conductivity is a critical factor affecting the electrochemical performance of double layer capacitor. Therefore, additional ion transport channels are introduced by using Nafion as binder in electrode. In this study, carbonized maple as active substance was mixed with binder of Nafion or PVDF to form electrodes. The electrode structures were obtained by scanning electron microscopy and N2 adsorption‐desorption isotherms with the aim of clarifying negligible differences in the microstructure and binding strength of electrodes with different binders. Furthermore, the two electrodes with different binders tested in KOH exhibited similar electrochemical properties. However, in H2SO4 electrolyte, the electrode containing Nafion showed a much higher specific capacitance than that of electrode using PVDF binder. To directly prove the high ionic conductivity of Nafion electrode, concentration battery was constructed using the two electrodes as separators to investigate their liquid junction potential. This study focused on the ionic conduction in electrodes, which could provide suggestions for electrode design, especially for the utilization of commercial supercapacitors.

In-situ growth of CNTs-porous carbon from asphalt with superior double-layer capacitive performance

Carbon materials have been engaged in supercapacitor, but the commercial biomass and coal-based carbon were far from satisfactory due to the hard control of pore structure and inferior electric conductivity. Newly developed carbon materials or composites, such as porous graphene or CNTs based materials were suffering from high cost or hard to balance energy and power densities. Herein, we obtained a CNTs-porous carbon by directly controlling the pyrolysis process of the petroleum asphalt. The composite combined both porosity and the conductive pathways for the migration of ions and electrons. The existence of a little S, N heteroatoms contributed to the infiltration of the aqueous electrolyte. The obtained symmetric supercapacitor demonstrated a superior capacitance of 385.7 F g−1 at the current density of 1 A g−1 with 93.8% capacity retention after 10,000 cycles under 4 A g−1. This material provided an optimistic choice for high-power equipments.

Preparation of activated carbon from unburned carbon in biomass fly ash and its supercapacitor performance

After the fuel undergoes pyrolysis and combustion in a biomass boiler, the fly ash contains some unburned carbon with abundant pores. However, their low porosities and specific surface areas cannot meet the requirements of the activated carbon for commercial supercapacitors, and the activation method to improve their pore structures is the key to enhance their applicability. After the one-step KOH activation treatment of the unburned carbon with the particle sizes > 0.2 mm, the results showed that the activated carbon has the largest specific area (1982 m2/g) at an impregnation ratio of 3.5:1, and the specific capacitance reached 207 F/g at the current density of 1 A/g. The above results indicate that unburned carbon-based activated carbon has a good double layer capacitance performance, providing a reference for the high value-added utilization of biomass fly ash.

Nelumbo nucifera Seed-Derived Nitrogen-Doped Hierarchically Porous Carbons as Electrode Materials for High-Performance Supercapacitors.

Biomass-derived activated carbon materials with hierarchically nanoporous structures containing nitrogen functionalities show excellent electrochemical performances and are explored extensively in energy storage and conversion applications. Here, we report the electrochemical supercapacitance performances of the nitrogen-doped activated carbon materials with an ultrahigh surface area prepared by the potassium hydroxide (KOH) activation of the Nelumbo nucifera (Lotus) seed in an aqueous electrolyte solution (1 M sulfuric acid: H2SO4) in a three-electrode cell. The specific surface areas and pore volumes of Lotus-seed–derived carbon materials carbonized at a different temperatures, from 600 to 1000 °C, are found in the range of 1059.6 to 2489.6 m2 g−1 and 0.819 to 2.384 cm3 g−1, respectively. The carbons are amorphous materials with a partial graphitic structure with a maximum of 3.28 atom% nitrogen content and possess hierarchically micro- and mesoporous structures. The supercapacitor electrode prepared from the best sample showed excellent electrical double-layer capacitor performance, and the electrode achieved a high specific capacitance of ca. 379.2 F g−1 at 1 A g−1 current density. Additionally, the electrode shows a high rate performance, sustaining 65.9% capacitance retention at a high current density of 50 A g−1, followed by an extraordinary long cycle life without any capacitance loss after 10,000 subsequent charging/discharging cycles. The electrochemical results demonstrate that Nelumbo nucifera seed–derived hierarchically porous carbon with nitrogen functionality would have a significant probability as an electrical double-layer capacitor electrode material for the high-performance supercapacitor applications.

Electrochemical investigation of free-standing reduced graphene oxide hydrogel

Free-standing reduced graphene oxide (RGO) hydrogel was synthesized through two-stepped hydrothermal reduction treatment of aqueous graphene oxide (GO) suspension. GO with high interface affinity for overlapping of cross-linking graphene sheets contributes to forming steady-state RGO hydrogel. RGO hydrogel shows higher B band/G band intensity ratio than GO suspension in Raman spectrum analysis, indicating well-restored hexagonal carbon rings with the enhanced crystal structure. Free-standing RGO hydrogel could be directly acted as supercapacitor electrode without using any substrate material. The specific capacitance decreases from 253.9 to 92.3 F g−1 in 1.0 M Na2SO4 electrolyte and from 275.3 to 125.9 F g−1 in 1.0 M KOH electrolyte when the current density increased from 0.3 to 4.0 A g−1, presenting the capacity retention of 36.4% and 45.7% respectively. Free-standing RGO hydrogel presents specific capacitance in alkaline KOH electrolyte rather than neutral Na2SO4 electrolyte. KOH electrolyte with superior ionic diffusion coefficient of hydroxyl ion leads to higher current response and electrical double-layer capacitance performance. The capacitance retention ratio of 97.8% at 4.0 A g−1 in 1.0 M KOH electrolyte after 1000 charge-discharge cycles presents superior cycling stability. Accordingly, free-standing RGO hydrogel applied well as superior supercapacitor electrode presents the promising energy storage application.

A multi-data-driven procedure towards a comprehensive understanding of the activated carbon electrodes performance (using for supercapacitor) employing ANN technique

Biomass resources are intensively used as economical and green-reserve precursor preparation of sustainable carbon materials used in supercapacitors. The synthetic processes of biomass-based precursors (BPs) are the most determinant proceedings for obtaining activated carbons (ACs) used in the electrode of energy storage devices. The AC-based electrode preparation and operational condition parameters can affect the capacitance performance of electrode. In the present work, the potential of Artificial Neural Network (ANN) modeling is assessed in interpreting how activation procedure, structural features, electrode synthesizing procedure, and operational condition can affect the capacitive performance of the carbon-based electrode. Radial Basis Function (RBF) model is established for the estimation of specific capacitance of biomass-based activated carbon (BAC) utilized in the electrode. Moreover, the algorithms used in RBF model performed accurate predictions of the model with the lowest error. Besides, employing the combination of quantitative and qualitative variables could perform a synergistic result. The multi-data could achieve a precise cognizance of materials participating in electrode preparation to obtain higher specific capacitance. The sensitivity analysis showed prominent effects of structural and operational characteristics (e.g. micropore to macropore carbon structure), molarity of electrolyte, binder ratio, and activation agent ratio, on Electric Double-layer capacitor performance.

Green needle coke-derived porous carbon for high-performance symmetric supercapacitor

The synthesis of low-cost and high-performance electrode material is one of the key challenges in the supercapacitor development. Herein, we report to prepare the porous carbon materials by thermal treatment using coal-based green needle coke. The as-synthesized porous carbon thermally treated at 750 °C achieves the best ideal electric double-layer capacitive performance, which is superior to the ones treated at other temperatures. Because of the high conductivity and free ion diffusion pathway possessed in porous carbon, high specific capacitance (274.9 F/g at 1A/g), and ideal coulomb efficiency (98.9% after 1000 circles at 5 A/g) of the sample observes in 3-electrode testing systems. The operational voltage window can be expanded to 0–1.8 V in 1 M Na2SO4 electrolyte for the 2-electrode system. Moreover, a symmetric button-type supercapacitor has assembled using the as-synthesized porous carbon supported on Ni-foam as both the positive and negative electrodes. The device delivers a high capacitance of 147.7 F/g, capacitive retention rate of 75.8% at 12 A/g, and a prominent energy density of 20.51 Wh/kg at power density of 1031.42 W/kg. Notably, the constructed supercapacitor shows outstanding cycling stability with capacity retention of 95.6% and coulombic efficiency of 98.5% after running 5000 cycles at 1 A/g.

Observation of Ion Electrosorption in Metal-Organic Framework Micropores with In Operando Small-Angle Neutron Scattering.

A molecular-level understanding of transport and adsorption mechanisms of electrolyte ions in nanoporous electrodes under applied potentials is essential to control the performance of double-layer capacitors. Here, in operando small-angle neutron scattering (SANS) is used to directly detect ion movements into the nanopores of a conductive metal-organic framework (MOF) electrode under operating conditions. Neutron-scattering data reveals that most of the void space within the MOF is accessible to the solvent. Upon the addition of the electrolyte sodium triflate (NaOTf), the ions are adsorbed on the outer surface of the protrusions to form a 30 Å layer instead of entering the ionophobic pores in the absence of an applied charging potential. The changes in scattering intensity when potentials are applied suggests the ion rearrangement in the micropores following different mechanisms depending on the electrode polarization. These observations shed insights on ion electrosorption in electrode materials.

Enhanced electrochemical double-layer capacitive performance with CO2 plasma treatment on activated carbon prepared from pyrolysis of pistachio shells

This study reports an original approach based on the CO2 plasma treatment on modification of the chemical or physical properties of activated carbon(AC) from the pistachio shells as a waste for application as electrochemical double-layer capacitors(EDLC). In the AC production experiments, impregnation ratio, impregnation pre-treatment temperature, activation temperature and activation time are investigated. In the AC modification experiments with plasma treatment, the effects of plasma gases, plasma power and plasma time are performed. The results of the different conditions indicated that the structural properties of the obtained AC were significantly dependent on the plasma and pyrolysis parameters. The surface properties of the raw AC and plasma-treated AC (PTAC) with X-ray photoelectron spectroscopy (XPS), nitrogen adsorption technique, and scanning electron microscope (SEM) are characterized. Surface area values for the raw AC and PTAC are 768 and 1250 m2 g−1, respectively. A change in the peak positions and an increase in the percentage of oxygen of the AC treated with CO2 plasma were obtained from XPS results. After 15 min of CO2 plasma activation, a significant increase in the capacitance of up to about 141% was obtained as a 118.4 F g −1 compared to 49.98 F g −1 for untreated AC. The results show that the plasma treatment on the specific surface area and surface functional groups of AC has a significant impact.

Fabrication and electrical double-layer capacitance performance of interconnected and independent titania nanotube array

ABSTRACT The interconnected and independent titania nanotube array (TiO2 NTA) grown on titanium metal foil with tunable nanotube diameter and length is fabricated by ultrasonic bath-assisted anodisation process. The electrical double-layer capacitance is highly dependent on the nanotube microstructure, crystal phase and working electrolyte. Anatase TiO2 NTA shows cyclic voltammetry-based current response and capacitance in H2SO4 rather than NaOH electrolyte, which is due to higher electrical conductivity and more effective proton diffusion rather than hydroxyl ion diffusion. Interconnected and independent TiO2 NTA with a diameter of 60, 120, 200nm and a length of 0.62, 1.69, 1.28μm exhibits galvanostatic charge-discharge based capacitance of 0.76, 1.88 and 2.63 mF cm−2 at 0.1mA cm−2 in 1.0M H2SO4 electrolyte. The superior capacitance performance of independent TiO2 NTA is ascribed to more effective ion diffusion in the enlarged independent nanotube channels. TiO2 NTA with a tunable microstructure is accordingly suitable for supercapacitor electrode substrate application.

Pullulan-ionic liquid-based supercapacitor: A novel, smart combination of components for an easy-to-dispose device

Strategies that simultaneously target energy/power performance, sustainable manufacturing processes, valorization of green raw materials, and easy recycling of supercapacitors are urgently needed. Today, efforts have to be devoted not only to improve system performance but also to address the sustainability of materials and devices manufacturing and recyclability. Specifically, pullulan is herein proposed as a novel bio-degradable binder and separator for green supercapacitors. It is processed by electrospinning from aqueous solutions, therefore overcoming issues related to conventional membrane processing by organic solvents. Furthermore, combining the water-soluble, biodegradable pullulan with a hydrophobic ionic liquid electrolyte brings about a novel approach for end-of-life management of devices. The use of pullulan is demonstrated in a supercapacitor with carbon electrodes obtained from pepper-seeds waste and 1-Ethyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide as the electrolyte. The supercapacitor delivers up to 5 kW kg−1 specific power and 27.8 Wh kg−1 specific energy at 3.2 V, that well compare with conventional electrical double-layer capacitor performance with the added value of being eco-friendly and cheap.

Strong metal oxide-support interactions in carbon/hematite nanohybrids activate novel energy storage modes for ionic liquid-based supercapacitors

Strong metal oxide-support interaction is crucial to activate high energy storage modes of carbon-supported hybrid electrodes in ionic liquid-based supercapacitors. Although it is known that conductive supports can influence the electrochemical properties of metal oxides, insights into how metal oxide-support interactions can be exploited to optimize joint energy storage properties are lacking. We report the junction between α-Fe2O3 nanosplotches and phosphorus-doped ordered mesoporous carbon (CMK-3-P) with strong covalent anchoring of the metal oxide. The oxide-carbon interaction in CMK-3-P-Fe2O3 is strengthening the junction and charge transfer between Fe2O3 and CMK-3-P. It enhances energy storage by intensifying the interaction between ionic liquid ions and the surface of the electrode. Density functional theory simulations reveal that the strong metal oxide-support interaction increases the adsorption energy of ionic liquid to −4.77 eV as compared to −3.85 eV for a CMK-3-Fe2O3 hybrid with weaker binding. In spite of the lower specific surface area and apparently similar energy storage mode, the CMK-3-P-Fe2O3 exhibits superior electrical double-layer capacitor performance with a specific capacitance of 179 F g−1 at 2 mV s−1 (0–3.5 V) in comparison to Fe2O3-free CMK-3 and CMK-3-P reference materials. This principle for design of hybrid electrodes can be applicable for future rational design of stable metal oxide-support electrodes for advanced energy storage.

Lithium polyacrylate-polyacrylamide blend as polymer electrolytes for solid-state electrochemical capacitors

A polymer electrolyte was developed by blending lithium (LiPAA) with non-ionic polyacrylamide (PAM). The LiPAA-PAM showed synergic effect and achieved an ionic conductivity of 13.8 ± 2.4 mS cm−1, higher than previously developed neutral pH polymer electrolytes. Chemical and structural characterizations of the LiPAA-PAM films revealed a stable homogeneous amorphous structure. The performance of double layer capacitors using LiPAA-PAM electrolyte system was demonstrated using YP-50F activated carbon electrodes. These solid cells demonstrated wide voltage window (1.5 V), good cycle life (>10,000 cycles), and excellent rate capability (up to 500 mV s−1 in cyclic voltammetry).

Graphene–Carbon Nanotube Aerogel with a Scroll-Interconnected-Sheet Structure as an Advanced Framework for a High-Performance Asymmetric Supercapacitor Electrode

Carbon nanomaterials have received much attention due to their good electrochemical performance as electrode materials and as substrates for pseudocapacitive materials. Herein, the graphene–carbon nanotube aerogel (GCA) has been constructed by direct cryodesiccation from the aqueous dispersion of a graphene oxide–carbon nanotube hybrid, the so-called “sol-cryo” method, followed by high-temperature carbonization. The as-obtained GCA with a unique sheet-scroll conjoined architecture not only displays an excellent electrical double-layer capacitive performance but also performs as an ideal three-dimensional template for the perpendicular immobilization of Ni(OH)2 nanosheets. The capacitance of Ni(OH)2@GCA is 1208 F g–1 at 1 A g–1 with 88% retention after 2000 cycles. The Ni(OH)2@GCA//GCA asymmetric supercapacitor exhibits a high energy density of 30 Wh kg–1 at a power density of 820 W kg–1. In addition, this template-free sol-cryo method possesses simplicity and large-scale availability, which provides a nov...

Effect of De-Ashing Strategies on Pore Structure and Electrochemical Performance of Activated Carbons for Supercapacitors

The ash was removed before or after carbonization of potassium humate to investigate the effect of ash removal methods on pore structure and electrochemical performance of activated carbons for supercapacitors. The activated carbons were prepared by direct carbonization of potassium humate at 700 ℃ for 1 hour under N 2 atmosphere with different de-ashing strategies. It was found that ash removal before carbonization was an effective strategy to reduce the ash content of the corresponding activated carbon. When de-ashing treatment was adopted after carbonization, part of the ash in activated carbon was coated with carbon and could not be removed through acid soaking. Moreover, ash removal before carbonization could better contribute to creating the micropores and the ash removed after carbonization performed as templates to mainly generate mesopores. The activated carbon with ash removed before carbonization as electrodes delivered a specific capacitance of 164.84 F/g at a current density of 50 mA/g, and exhibited typical electric double layer capacitive performance as well as lower leakage current of 15.3 µA. DOI: http://dx.doi.org/10.5755/j01.ms.24.3.18505

Capillarity-driven assembly of single-walled carbon nanotubes onto nickel wires for flexible wire-shaped supercapacitors

The carbon nanomaterials have been incorporated into composite electrode for wire-shaped supercapacitors (WSSs) to promote development of wearable electronics. Coating of carbon nanomaterials directly onto functional fiber is a facile strategy to prepare wire-shaped electrodes. However, it is still a critical challenge to maximize the adhesion of the nanomaterials onto aimed substrate fiber, while still maintaining the high specific area of the nanomaterials. Herein, both carbon nanotubes (CNTs) and graphene were coated onto the surface of nickel wires via capillary effect driven process. It was discovered that the one dimensional morphology of the CNTs not only benefited the adhesion of CNTs on the relatively smooth surface of the nickel metal wire, but also strengthened the infiltration of the electrolyte among the CNTs. On the contrast, the restacking of graphene oxide (GO) sheets retarded the infiltration of the electrolyte, resulting in inferior capacitive performance. The prepared Ni-CNT electrodes showed excellent electrochemical double layer capacitive performance along with the mechanical robustness and high flexibility. The constructed all-solid flexible wire-shaped supercapacitors maintained a high specific capacitance of approximately 30 F/g after 3000 cycles when bent by 45 degree.

High loading carbon nanotubes deposited onto porous nickel yarns by solution imbibition as flexible wire-shaped supercapacitor electrodes

The deposition of active materials directly onto metal wires is a general strategy to prepare wire-shaped electrodes for flexible and wearable energy storage devices. However, it is still a critical challenge to coat active materials onto the aimed metal wires because of their smooth surface and small specific surface area. In this work, high porous nickel yarns (PNYs) was fabricated using commercial nylon yarns as templates through step-wise electroless plating, electroplating and calcination processes. The PNYs are composed of multiplied fibers with hollow tubular structure of 5–10µm in diameter, allowing the imbibition of carbon nanotubes (CNTs) solution by a facile capillary action process. The prepared CNTs/PNY electrodes showed a typical electrochemical double layer capacitive performance and the constructed all-solid flexible wire-shaped symmetric supercapacitors provided a specific capacitance of 4.67F/cm3 with good cycling stability at a current density of 0.6A/cm3.

Mass Production of Monodisperse Carbon Microspheres with Size-Dependent Supercapacitor Performance via Aqueous Self-Catalyzed Polymerization.

A facile, aqueous, self-catalyzed polymerization method has been developed for the mass production of monodisperse phenolic resin and carbon microspheres. The synthesis is mainly based on the self-catalyzed reaction between phenol derivatives and the hydrolysis products of hexamethylenetetramine (HMTA). The obtained phenolic resin spheres have a tunable size of 0.8-6.0 μm, depending on the type of phenol and HMTA/phenol ratio. Treating the phenolic resin with steam at an elevated temperature results in monodisperse carbon microspheres with abundant micropores, high surface area, and rich surface functionality. The resultant carbon spheres exhibit a size-dependent electrical double-layer capacitor performance; the capacitance increases with decreasing particle size. The nitrogen and oxygen codoped carbon spheres with the smallest size (≈600 nm) deliver a high specific capacitance (282 F g-1 at 0.5 A g-1 ), excellent rate capability (170 F g-1 at 20 A g-1 ), and outstanding cycling stability (95.3 % capacitance retention after 10 000 cycles at 5 A g-1 ). This study provides a new avenue for the mass production of monodisperse carbon microspheres.