Electrochemical Double-layer Capacitor Application Research Articles

Compositional dependence of electrochemical properties in biopolymer blend-based solid electrolytes doped with sodium perchlorate for EDLC applications

Biopolymer-based blends of solid electrolytes capable of conducting sodium ions were prepared via solution casting by incorporating sodium carboxymethyl cellulose (NaCMC) and polyvinyl alcohol (PVA) with varying concentrations of sodium perchlorate monohydrate (NaClO4.H2O), which was used as the dopant. The prepared electrolytes were characterized to reveal their structural, vibrational, electrical, and electrochemical properties that make them promising as solid polymer electrolytes (SPEs). X-ray diffraction (XRD) analysis showed that the amorphous nature of the sample increased with the addition of NaClO4.H2O salt concentrations of up to 30 wt.%. The complexation between the polymers and salt was confirmed by Fourier-Transform Infrared (FTIR) analysis. The SPE exhibited an optimal ionic conductivity of (1.90 ± 0.05) ×10−5 S cm−1, which is three orders higher than that of the pristine polymer blend with (5.31 ± 0.61) ×10−8 S cm−1, as determined by electrochemical impedance spectroscopy (EIS) analysis. Scaling studies conducted based on AC conductivity and tangent loss revealed that these measurements could be represented by a single master curve, which suggests that the optimal sample adheres to the time-temperature superposition principle (TTSP). The temperature dependence of Jonscher's exponent indicates that the conduction mechanism can be effectively represented by the Quantum Mechanical Tunneling model (QMT). Both transference number measurement (TNM) and linear sweep voltammetry (LSV) analyses validated the electrolyte's suitability for energy device applications by demonstrating its high ion transference number and electrochemical potential window of 3.93 V. The optimized SPE film was subsequently utilized in an electrochemical double-layer capacitor (EDLC) device to evaluate its performance as both an electrolyte and separator. The supercapacitor exhibited an impressive energy density of 15.18 Wh kg−1 and a power density of 4512.5 W kg−1, along with remarkable stability in terms of cycle life.

Morphological optimization and nitrogen functionalization of vertically oriented CNW for high performance electrical double layer capacitor electrode

The objective of this study is to explore the influence of topographical surface structures and nitrogen doping effects on Carbon Nano Wall (CNW) characteristics in the context of Electrochemical Double-Layer Capacitor (EDLC) electrode applications. Carbon-based materials attract significant technological and industrial interest for EDLC electrode. Among available carbon-based materials, CNW are suitable candidates for EDLC electrodes based on their extremely high surface area and open top edges, which facilitate easy electrolyte circulation. In this study, CNW are synthesized using an electron cyclotron resonance plasma-system. To evaluate the electrochemical performance of synthesized CNW with various surface morphologies, cyclic voltammetry measurements are conducted in three-electrode systems. Elemental analysis is conducted to measure the weight percentages of the synthesized CNW with varying synthesis conditions. It is found that the amount of synthesized CNW and specific capacitance saturate after 15 min of growth, but considerable differences in specific capacitance based on CNW morphology are observed. Further improvements to the specific capacitance of CNW are achieved by introducing a nitrogen plasma post-treatment without any decline in electrochemical characteristics. These encouraging results may motivate additional research on constructing suitable pore distributions for targeting high-power EDLC applications.

Influence of $$\hbox {NH}_{4}$$Br as an ionic source on the structural/electrical properties of dextran-based biopolymer electrolytes and EDLC application

Biopolymer electrolytes (BPEs), consisting of ammonium bromide ( $$\hbox {NH}_{4}\hbox {Br}$$ ) as the ionic provider and dextran (Leuconostoc mesenteroides) as the polymer host, are prepared by the solution cast technique. Interactions of cations from the salt have been confirmed with hydroxyl (OH) and glycosidic linkage (C–O–C) groups of dextran via Fourier transform infrared analysis. Electrolyte with 20 wt% $$\hbox {NH}_{4}\hbox {Br}$$ maximized the ionic conductivity up to ( $$1.67 \pm 0.36)\times 10^{-6}$$ S $$\hbox {cm}^{-1}$$ . The trend of conductivity has been verified by field emission scanning electron microscopy, where the electrolyte surface became rough as the concentration of $$\hbox {NH}_{4}\hbox {Br}$$ exceeded 20 wt%. The contribution of ions as the main charge carrier in the BPE is confirmed by transference number analysis as $$t_{\mathrm{ion}} = 0.92$$ and $$t_{\mathrm{e}} = 0.08$$ . From linear sweep voltammetry, it is found that the highest conducting BPE in this work is electrochemically stable from 0 to 1.62 V. The fabricated electrochemical double-layer capacitor (EDLC) has been tested for 100 charge–discharge cycles and verified by cyclic voltammetry.

A Promising Polymer Blend Electrolytes Based on Chitosan: Methyl Cellulose for EDLC Application with High Specific Capacitance and Energy Density.

In the present work, promising proton conducting solid polymer blend electrolytes (SPBEs) composed of chitosan (CS) and methylcellulose (MC) were prepared for electrochemical double-layer capacitor (EDLC) application with a high specific capacitance and energy density. The change in intensity and the broad nature of the XRD pattern of doped samples compared to pure CS:MC system evidencedthe amorphous character of the electrolyte samples. The morphology of the samples in FESEM images supported the amorphous behavior of the solid electrolyte films. The results of impedance and Bode plotindicate that the bulk resistance decreasedwith increasing salt concentration. The highest DC conductivity was found to be 2.81 × 10−3 S/cm. The electrical equivalent circuit (EEC) model was conducted for selected samples to explain the complete picture of the electrical properties.The performance of EDLC cells was examined at room temperature by electrochemical techniques, such as impedance spectroscopy, cyclic voltammetry (CV) and constant current charge–discharge techniques. It was found that the studied samples exhibit a very good performance as electrolyte for EDLC applications. Ions were found to be the dominant charge carriers in the polymer electrolyte. The ion transference number (tion) was found to be 0.84 while 0.16 for electron transference number (tel). Through investigation of linear sweep voltammetry (LSV), the CS:MC:NH4SCN system was found to be electrochemically stable up to 1.8 V. The CV plot revealed no redox peak, indicating the occurrence of charge double-layer at the surface of activated carbon electrodes. Specific capacitance (Cspe) for the fabricated EDLC was calculated using CV plot and charge–discharge analyses. It was found to be 66.3 F g−1 and 69.9 F g−1 (at thefirst cycle), respectively. Equivalent series resistance (Resr) of the EDLC was also identified, ranging from 50.0 to 150.0 Ω. Finally, energy density (Ed) was stabilized to anaverage of 8.63 Wh kg−1 from the 10th cycle to the 100th cycle. The first cycle obtained power density (Pd) of 1666.6 W kg−1 and then itdropped to 747.0 W kg−1 at the 50th cycle and continued to drop to 555.5 W kg−1 as the EDLC completed 100 cycles.

Conductive Carbon Materials from the Hydrothermal Carbonization of Vineyard Residues for the Application in Electrochemical Double-Layer Capacitors (EDLCs) and Direct Carbon Fuel Cells (DCFCs).

This study investigates the production of bio-based carbon materials for energy storage and conversion devices based on two different vineyard residues (pruning, pomace) and cellulose as a model biomass. Three different char categories were produced via pyrolysis at 900 °C for 2 h (biochars, BC), hydrothermal carbonization (HTC) (at 220, 240 or 260 °C) with different reaction times (60, 120 or 300 min) (hydrochars, HC), or HTC plus pyrolysis (pyrolyzed hydrochars, PHC). Physicochemical, structural, and electrical properties of the chars were assessed by elemental and proximate analysis, gas adsorption surface analysis with N2 and CO2, compression ratio, bulk density, and electrical conductivity (EC) measurements. Thermogravimetric analysis allowed conclusions to be made about the thermochemical conversion processes. Taking into consideration the required material properties for the application in electrochemical double-layer capacitors (EDLC) or in a direct carbon fuel cell (DCFC), the suitability of the obtained materials for each application is discussed. Promising materials with surface areas up to 711 m2 g−1 and presence of microporosity have been produced. It is shown that HTC plus pyrolysis from cellulose and pruning leads to better properties regarding aromatic carbon structures, carbon content (>90 wt.%), EC (up to 179 S m−1), and porosity compared to one-step treatments, resulting in suitable materials for an EDLC application. The one-step pyrolysis process and the resulting chars with lower carbon contents and low EC values between 51 and 56 S m−1 are preferred for DCFC applications. To conclude, biomass potentials can be exploited by producing tailored biomass-derived carbon materials via different carbonization processes for a wide range of applications in the field of energy storage and conversion.

Sengon wood (Paraserianthes falcataria (L.) Nielsen) carbon as supporting material for electrochemical double layer capasitor

A microstructure carbon electrodes was potentially developed into energy storage device, i.e electrochemical double layer capacitor (EDLC) or super capacitor. The structure has a large surface that able to increased the capacitance of electrodes. Sengon Wood Carbon (SWC) was one of microstructure carbon which mainly has honeycomb structure. SWC was prepared hydrothermally along with microwave heating. SWC has 202 m2g−1 of surface area, 14,4 S.cm−1 of conductivity and crystalline carbon peak at 29.55° with honeycomb structure. Mixtures of honeycomb sengon carbon and graphite were casted it into thin layer electrode (TLE). The electrodes are fabricated into EDLC along with aluminum foil, and their performance are tested by using Galvanostatic and capacitance meter. TLE had 2.984 to 3.547 μF/g of capacitance, initial voltage of EDLC ranged from 0.67 to 0.42 V. Capacitance of 3 cm x 4 cm EDLC ranged from 30.6 to 60 μF. Galvanostatic Charge-Discharge (GCD) indicated that SWC suitable for EDLC application.

(Invited) Binary Mixtures of 1-Butyl-1-Methylpyrrolidinium Bis{(trifluoromethyl)Sulfonyl}Imide and Aliphatic Nitrile Solvents As Electrolyte for Electrochemical Double Layer Capacitors

Electrochemical double layer capacitors (EDLCs), also known as supercapacitors, are promising energy storage devices, especially when considering high power applications [1]. EDLCs can be charged and discharged within seconds [1], feature high power (10 kW·kg-1) and an excellent cycle life (>500,000 cycles). All these properties are a result of the energy storage process of EDLCs, which relies on storing energy by charge separation instead of chemical redox reactions, as utilized in battery systems. Upon charging, double layers are forming at the electrode/electrolyte interface consisting of the electrolyte’s ions and electric charges at the electrode surface. In state-of-the-art EDLC systems activated carbons (AC) are used as active materials and tetraethylammonium tetrafluoroborate ([Et4N][BF4]) dissolved in organic solvents like propylene carbonate (PC) or acetonitrile (ACN) are commonly used as the electrolyte [2]. These combinations of materials allow operative voltages up to 2.7 V - 2.8 V and an energy in the order of 5 Wh·kg-1[3]. The energy of EDLCs is dependent on the square of the operative voltage, thus increasing the usable operative voltage has a strong effect on the delivered energy of the device [1]. Due to their high electrochemical stability, ionic liquids (ILs) were thoroughly investigated as electrolytes for EDLCs, as well as, batteries, enabling high operating voltages as high as 3.2 V - 3.5 V for the former [2]. While their unique ionic structure allows the usage of neat ILs as electrolyte in EDLCs, ILs suffer from low conductivity and high viscosity increasing the intrinsic resistance and, as a result, a lower power output of the device. In order to overcome this issue, the usage of blends of ionic liquids and organic solvents has been considered a feasible strategy as they combine high usable voltages, while still retaining good transport properties at the same time. In our recent work the ionic liquid 1-butyl-1-methylpyrrolidinium bis{(trifluoromethyl)sulfonyl}imide ([Pyrr14][TFSI]) was combined with two nitrile-based organic solvents, namely butyronitrile (BTN) and adiponitrile (ADN), and the resulting blends were investing regarding their usage in electrochemical double layer capacitors [4,5]. Firstly, the physicochemical properties were investigated, showing good transport properties for both blends, which are similar to the state-of-the-art combination of [Et4N][BF4] in PC. Secondly, the electrochemical properties for EDLC application were studied in depth revealing a high electrochemical stability with a maximum operative voltage as high as 3.7 V. In full cells these high voltage organic solvent based electrolytes have a good performance in terms of capacitance and an acceptable equivalent series resistance at cut-off voltages of 3.2 and 3.5 V. However, long term stability tests by float testing revealed stability issues when using a maximum voltage of 3.5 V for prolonged time, whereas at 3.2 V no such issues are observed (Fig. 1). Considering the obtained results, the usage of ADN and BTN blends with [Pyrr14][TFSI] in EDLCs appears to be an interesting alternative to state-of-the-art organic solvent based electrolytes, allowing the usage of higher maximum operative voltages while having similar transport properties to 1 mol∙dm-3 [Et4N][BF4] in PC at the same time.

An ether-functionalised cyclic sulfonium based ionic liquid as an electrolyte for electrochemical double layer capacitors

A novel cyclic sulfonium cation-based ionic liquid (IL) with an ether-group appendage and the bis{(trifluoromethyl)sulfonyl}imide anion was synthesised and developed for electrochemical double layer capacitor (EDLC) testing. The synthesis and chemical-physical characterisation of the ether-group containing IL is reported in parallel with a similarly sized alkyl-functionalised sulfonium IL. Results of the chemical-physical measurements demonstrate how important transport properties, i.e. viscosity and conductivity, can be promoted through the introduction of the ether-functionality without impeding thermal, chemical or electrochemical stability of the IL. Although the apparent transport properties are improved relative to the alkyl-functionalised analogue, the ether-functionalised sulfonium cation-based IL exhibits moderately high viscosity, and poorer conductivity, when compared to traditional EDLC electrolytes based on organic solvents (propylene carbonate and acetonitrile). Electrochemical testing of the ether-functionalised sulfonium IL was conducted using activated carbon composite electrodes to inspect the performance of the IL as a solvent-free electrolyte for EDLC application. Good cycling stability was achieved over the studied range and the performance was comparable to other solvent-free, IL-based EDLC systems. Nevertheless, limitations of the attainable performance are primarily the result of sluggish transport properties and a restricted operative voltage of the IL, thus highlighting key aspects of this field which require further attention.

Physical Properties of a New Deep Eutectic Solvent Based on a Sulfonium Ionic Liquid as a Suitable Electrolyte for Electric Double-Layer Capacitors

We present in this study the physical properties of two deep eutectic solvent (DES) mixtures based on solid sulfonium bis[(trifluoromethyl)sulfonyl]imide (S111TFSI) aprotic ionic liquid and two different H-bond donors, formamide (FMD) and trifluoroamide (TFA), according to temperature. First, we investigated their thermal properties by differential scanning calorimetry , and the results revealed the formation of a deep eutectic solvent giving a wide liquid range from −40 to 270 °C for these mixtures which froze at a much lower temperature than either of the individual components. The densities, ionic conductivities, and viscosities of these DESs were measured according to temperature and then discussed by applying Arrhenius or Vogel–Tamman–Fulcher (VTF) equations, as well as the Walden classification. Thanks to their favorable transport properties, both S111TFSI/TFA and S111TFSI/FMD mixtures contribute to the formulation of the electrolytes with 1 mol·L–1 LiTFSI. The performances of these electrolytes were then estimated by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge for activated carbon electrochemical double layer capacitor applications at 80 °C. The results showed that the selected H-bond donors allowed ion dissociation without solvation, increasing micropore accessibility and giving high capacitance values up to 350 F·g–1 in the case of formamide-based DESs. These unusual performances of the activated carbon material are debated with regards to the activation energy barrier to access the microporosity by ions in sulfonium-amides DESs.

Bowl-like carbon sheet for high-rate electrochemical capacitor application

Simultaneously achieve high power and large energy capacity at a high rate is still difficult in the development of electrochemical double layer capacitors. We design a bowl-like carbon sheet (BCS), which is a promising electrode material for high-rate electrochemical double layer capacitor application. These BCSs have interconnected channels and hierarchical porosity for fast ion diffusion and can maintain 105 F g−1 at 100 A g−1. BCSs can maintain a rectangular degree at a high scan voltage of 1 V s−1. BCSs show the tendency of stack on top of each other, and such behavior can increase the bulk density and subsequently increase volumetric capacitance.

Synthesis of carbon fibers with branched nanographene sheets for electrochemical double layer capacitor application.

We demonstrate a one step technique to synthesis the carbon fibers (CNFs) with branched nanographene sheets by the pulsed discharge (PD) plasma chemical vapor deposition (CVD) process. Highly crystalline branched nanographene sheets were directly grown from the surface of the carbon fibers to obtain a three dimensional (3D) nanostructure. The growth process can be explained from the catalyst support growth of the CNFs, and subsequently nucleation and growth of the nanographene sheets from the crystalline surface of the CNF. The deposited nanostructured films with different pulse discharge were used as an electrode for electrochemical double-layer capacitors (EDLC). It is observed that the capacitance is dependent on the morphology of the electrode materials and an optimum capacitance is obtained with the branched nanographene on CNFs.

Double Layer Energy Storage in Graphene - a Study

An alternate energy storage device for high power applications are supercapacitors. They store energy either by pure electrostatic charge accumulation in the electrochemical double layer or as pseudo capacitance from fast reversible oxidation reduction process. However, they have low energy density. The electrodes in the Electrochemical Double Layer Capacitors (EDLC) are made of high surface area carbon. The carbon that can be used range from activated carbon to Graphene, with varying particle size, surface area, pore size and pore distribution. The main emphasis in the development of EDLCs is fabrication of electrodes having high surface area which would enhance the storage density of the EDLC. The EDLCs are assembled with different electrolytes which determine the operational voltage. Solid electrolytes can also be used as electrolyte and have an advantage in that we can avoid electrolyte leaks and are easy to handle. This would improve the reliability. They can also be shaped and sized to suit the application. The perflurosulfonic acid polymer as electrolyte has been used by various groups for EDLC application. The perflurosulfonic acid polymer possesses high ionic conductivity, good thermal stability, adequate mechanical strength and excellent chemical stability. The EDLCs, which are based on high-surface area carbon materials, utilize the capacitance arising from a purely non-Faradaic charge separation at an electrode/electrolyte interface. Carbon is widely used for many practical applications, especially for the adsorption of ions and molecules, as catalyst supports and electrode materials. The chemical characteristics of carbon determine the performance in all these applications. It is now possible to synthesize one-, two-, or three-dimensional (1-, 2-, or 3-D) carbons. Thus, carbon materials are very suitable candidates for super capacitor electrodes. We can overcome some of the problems in activated carbon like varying micro or meso pores, poor ion mobility due to varying pore distribution, low electrical conductivity, by using Graphene. Many forms of Graphene have been used by various groups. Graphene nanoplates (GNP), with narrow mesopore distribution have been effectively used to enhance charge storage performance. It has been found that graphene shows smaller decrease in storage capacity with increasing scan rate.

Spark plasma sintered carbon electrodes for electrical double layer capacitor applications

The spark plasma sintering (SPS) is an emerging process for shaping any type of materials (metals, ceramic, polymers and their composites). The advantage of such a process is to prepare densified ceramic materials in a very short time, while keeping the materials internal porosity. In the present work, we have used the SPS technique to prepare activated carbon-based electrodes for Electrochemical Double Layer Capacitor applications (EDLC). Self-supported 600 and 300 μm-thick electrodes were prepared and characterized using of Electrochemical Impedance Spectroscopy and galvanostatic cycling in a non-aqueous 1.5 M NEt 4BF 4 in acetonitrile electrolyte. Electrochemical performance of these sintered electrodes were found to be in the same range – or even slightly better – than the conventional tape-casted activated carbon electrodes. Although organic liquid electrolyte was used to characterize the electrochemical performance of the sintered electrodes, these results demonstrate that the SPS technique could be worth of interest in the ultimate goal of designing solid-state supercapacitors.

Mesoporous carbons derived from citrates for use in electrochemical capacitors

Two mesoporous carbons were prepared by simple pyrolysis of commercial magnesium or barium citrate and tested as electrode materials for electrochemical double-layer capacitors (EDLCs), denoted MgC and BaC, respectively. The as-prepared carbon materials were characterized by N 2 adsorption, scanning electron microscopy and Fourier transform infrared spectrometry. Nitrogen adsorption measurements demonstrated that the porosity of the prepared carbons was related to the type of metal cation. BaC possesses a typical bimodal pore size distribution (PSD) at 3.8 and about 15 nm, while MgC was between small-size mesoporous and microporous. The carbons were tested as electrode materials using different electrochemical means such as cyclic voltammetry and constant current charge-discharge. Very high specific capacitance (180 F·g −1 for MgC and 171 F·g −1 for BaC) was achieved in an ionic liquid electrolyte. BaC proved to be an excellent electrode material with a high rate performance for EDLC application and exhibited an energy density up to 53.3 Wh·kg −1 and a high maximum specific power density of 20 kW·kg −1 in IL electrolyte. The good capacitive performance of BaC is attributed to its bimodal PSD and hydrophilic surface properties.

Modified carbon materials for high-rate EDLCs application

Porous carbon materials, such as activated carbon and activated carbon aerogel, were modified chemically by using a surfactant sodium oleate to improve their specific capacity for high-rate electrochemical double layer capacitors (EDLCs) application. Main impacting factors have been examined for surface modification of activated carbon. Specific capacity can be improved significantly by the surface modification. The enhancement in specific capacity is mainly attributable to improvement in wettability of carbon materials, resulting in a higher usable surface area and a smaller internal resistance. The effects from surface modification become more marked at higher discharge rates, and a much higher energy density can be achieved for the modified carbon materials. In addition, the modified carbon materials possess comparable cycle stability to the original carbon.

Surface modification of carbonaceous materials for EDLCs application

In this study, carbonaceous materials such as activated carbon and activated carbon aerogel were chemically modified with a surfactant sodium oleate in order to improve their specific capacitance and energy storage in electrochemical double-layer capacitors (EDLCs). Optimal conditions for surface modification of activated carbon have been examined as a surfactant solution concentration of 0.25 wt.% together with a time of 24 h for treatment at 25 °C. Specific capacitance and energy density can be improved significantly by surface modification of carbon materials. The enhancement in specific capacitance and energy density is mainly attributable to improvement in wettability of carbon materials, which results in a higher usable surface area and a smaller internal resistance. The effects from surface modification become more marked at higher discharge rates, at which the internal resistance has a more important impact on the energy delivery. A two times energy density of the original carbon could be achieved for the modified carbon materials at a high discharge rate, which indicates that the modified carbons are more suitable in EDLCs for high current applications. In addition, the modified carbon materials possess excellent cycle stability (the capacity decay was only 4% after 20,000 cycles).

Electrochemical oxidation of multi-walled carbon nanotubes and its application to electrochemical double layer capacitors

The effect of electrochemical oxidation in 0.2 M HNO 3 for multi-walled carbon nanotubes (MWNTs) on the performance of electrochemical double layer capacitors (EDLCs) was studied. Scanning electron microscope and transmission electron microscope images reveal that electrochemical oxidation increases the specific area of MWNTs by cutting off the nanotube tips. Cyclic voltammetry and constant current charging/discharging was used to characterize the behavior of EDLCs of the oxidized-MWNTs in 1.0 M H 2SO 4. The specific capacitance of the oxidized-MWNTs was remarkably improved. The maximum specific capacitance of 335.2 ± 13.1 F g −1 ( n = 3) was obtained for the oxidized-MWNTs with open tips, which is 11 times than that of normal MWNTs (32.7 ± 7.1 F g −1). Electrochemical oxidation is hence an effective way to improve the performances of the MWNTs electrodes in EDLCs application.