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The article gives an overview of energy storage composites, their materials, manufacturing processes, and applications. Carbon- and metal-based nanoparticles and their relevant properties are presented. We focus on multifunctional structural supercapacitors and their components. Thus, we describe the main structural electrolytes and elements of the structural electrodes. We show that the nanoparticles significantly influence the electrochemical properties of the electrode. For example, carbon-based nanoparticles can achieve low energy density but high power density, while the opposite is true for metal-based nanoparticles. We show that when carbon- and metal-based nanoparticles are used together, a positive synergy is created between them, promoting the development of favorable electrochemical properties in the electrodes. Furthermore, we present structural supercapacitors and possible ways to introduce nanoparticles into the system. Finally, we present a summary of the progress achieved so far and the advancements expected in the future, as well as potential areas where structural supercapacitors could be used. [ABSTRACT FROM AUTHOR]

Current research is focused on developing active materials through surface functionalization, porosity, composites, and doping for ultrafast electric double layer capacitors (EDLCs). In this study, deviating from existing strategies focused on active materials, we designed tunable 3D microgrid-patterned (MP) surface morphologies on Ni foams used as current collectors using SUS meshes as rigid stamps during roll pressing. The surface geometries of the MP-Ni foams were controlled to standard mesh scales of 24, 40, and 60 (denoted as 24MP-Ni, 40MP-Ni, and 60MP-Ni, respectively). The three MP-Ni samples with different microgrid sizes presented different surface geometries, such as root-mean-square roughness (Rrms), skewness roughness (Rsk), and width/depth scales of the microgrid patterns. Consequently, 40MP-Ni demonstrated an optimized surface geometry with high Rrms (35.4 μm) and Rsk (−0.19) values, which facilitated deep slurry infiltration and increased its contact area with the active material. Surface optimization of the MP-Ni enabled ultrafast and reversible charge transport kinetics owing to its relaxed electron transfer resistance and robust adhesion to the active material compared with bare Ni foam. EDLC electrodes with 40MP-Ni achieved an ultrafast-rate capability (96.0 F/g at 20 A/g) and ultrafast longevity (101.9% capacity retention after 5000 cycles at 5 A/g) without specific modification of active material. [ABSTRACT FROM AUTHOR]

Developing multifunctional energy storage systems with high specific energy, high specific power and long cycling life has been the one of the most important research directions. Compared to batteries and traditional capacitors, supercapacitors possess more balanced performance with both high specific power and long cycle-life. Nevertheless, regular supercapacitors can only achieve energy storage without harvesting energy and the energy density is still not very high compared to batteries. Therefore, combining high specific energy and high specific power, long cycle-life and even fast self-charging into one cell has been a promising direction for future energy storage devices. The multifunctional hybrid supercapacitors like asymmetric supercapacitors, batteries/supercapacitors hybrid devices and self-charging hybrid supercapacitors have been widely studied recently. Carbon based electrodes are common materials used in all kinds of energy storage devices due to their fabulous electrical and mechanical properties. In this survey, the research progress of all kinds of hybrid supercapacitors using multiple effects and their working mechanisms are briefly reviewed. And their advantages and disadvantages are discussed. The hybrid supercapacitors have great application potential for portable electronics, wearable devices and implantable devices in the future.

Current research is focused on developing active materials through surface functionalization, porosity, composites, and doping for ultrafast electric double layer capacitors (EDLCs). In this study, deviating from existing strategies focused on active materials, we designed tunable 3D microgrid-patterned (MP) surface morphologies on Ni foams used as current collectors using SUS meshes as rigid stamps during roll pressing. The surface geometries of the MP-Ni foams were controlled to standard mesh scales of 24, 40, and 60 (denoted as 24MP-Ni, 40MP-Ni, and 60MP-Ni, respectively). The three MP-Ni samples with different microgrid sizes presented different surface geometries, such as root-mean-square roughness (Rrms), skewness roughness (Rsk), and width/depth scales of the microgrid patterns. Consequently, 40MP-Ni demonstrated an optimized surface geometry with high Rrms (35.4 μm) and Rsk (−0.19) values, which facilitated deep slurry infiltration and increased its contact area with the active material. Surface optimization of the MP-Ni enabled ultrafast and reversible charge transport kinetics owing to its relaxed electron transfer resistance and robust adhesion to the active material compared with bare Ni foam. EDLC electrodes with 40MP-Ni achieved an ultrafast-rate capability (96.0 F/g at 20 A/g) and ultrafast longevity (101.9% capacity retention after 5000 cycles at 5 A/g) without specific modification of active material.

In this work, poly(vinyl acetate) (PVAc)-based gel polymer electrolytes (GPEs) from precursor solutions containing different volume ratios of vinyl acetate monomer and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIMTFSI) at a fixed concentration of 0.1 M lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) were synthesized via ex-situ polymerization. The GPE with 35% (v/v) of BMIMTFSI exhibits the highest ionic conductivity of (1.90 ± 0.32) × 10–4 S cm−1 at ambient temperature, with a glass transition temperature (Tg) of -28.01 °C. Fourier transform infrared (FTIR) study confirms the complexation and interaction between the BMIMTFSI, LiTFSI, and PVAc. X-ray diffraction (XRD) analysis shows a reduction in degree of crystallinity of the polymer matrix upon addition of LiTFSI and BMIMTFSI. Addition of ionic liquid enhances the potential window of the GPEs as shown in linear sweep voltammetry (LSV) study. The specific capacitance of EDLC increases significantly upon addition of BMIMTFSI, along with relatively stable energy and power densities as proven in Galvanostatic Charge–Discharge (GCD) study. [ABSTRACT FROM AUTHOR]

In this study, electric double layer capacitors (EDLC) were fabricated as laminate type by using NaCl aqueous solution, which should be relatively safe electrolyte against environments and biological objects, for the investigation of the performance from a practical point of view. The capacitance value of the cell depended on the kind of activated carbon used as electrodes. The capacitance values of the EDLCs fabricated from the best activated carbon were ca. 38 F g− 1 at 0.36 mA cm− 2 of discharging current value and at 1.2 V of charging voltage. The capacitance value should be equivalent to commercial EDLCs although the charging voltage is smaller. The relationship between the properties related to pores of activated carbon and the capacitance value was examined. The enumerated values obtained from the Dubinin-Astakhov (DA) method for the activated carbons of this study were between 1 and 2, which could indicate that the micropore distribution of the activated carbons used in this study was heterogeneous. The capacitance value was found to be strongly related to the micropore volume calculated by the DA method from the adsorption isotherm of CO2 at 298 K. That is, the micropore volume estimated from the DA method should be used as the indicator for the selection of high-performance activated carbon for electrode of EDLC containing NaCl aqueous solution electrolyte. [ABSTRACT FROM AUTHOR]

Abstract The primary goal of the current study is to improve the specific capacitance of electric double-layer (EDLC) device using biomass (Tribulus Terrestris) derived activated carbon electrodes synthesized by chemical activation method. Furthermore, high surface area carbon electrodes are characterized using X-ray diffraction (XRD), RAMAN spectroscopy, and scanning electron microscopy (SEM) to confirm the morphological structure. Finally, the electrochemical performance of fabricated EDLC proves a good agreement data using Cyclic Voltammetry (CV), Low Impedance Spectroscopy (LIS), and Galvanostatic Charge–Discharge (GCD) analysis showing the high specific capacitance of 115 Fg−1 for the optimized 1:2 activated carbon material.

By adding different biomass（corn cob or pine sawdust） to hypercoal, the activated carbon electrode materials for double electric layer capacitors were prepared. The effect of biomass on the structure and electrochemical performance of hypercoal-based activated carbon was explored. Its structure and composition were characterized by SEM, XRD, FTIR and N2 desorption. Its electrochemical performance was tested by cyclic voltammetry, constant current charge-discharge and AC impedance. In terms of biomass composition, the addition of biomass with high cellulose content is beneficial to the development of mesopore and the pore structure is more perfect. High cellulose and hemicellulose content can effectively reduce the impedance of carbon materials, and make the ion transport between pore structures more rapid. When corn cob was added to hypercoal, the specific capacitance increased by 45% and the charge transfer resistance decreased by 65%. Adding pine sawdust to hypercoal can increase the specific capacitance by 30% and decrease the charge transfer resistance by 35%. It is proved that adding biomass with high cellulose content is more beneficial to improve the structure and electrochemical performance of activated carbon. [ABSTRACT FROM AUTHOR]

The primary goal of the current study is to improve the specific capacitance of electric double-layer (EDLC) device using biomass (Tribulus Terrestris) derived activated carbon electrodes synthesized by chemical activation method. Furthermore, high surface area carbon electrodes are characterized using X-ray diffraction (XRD), RAMAN spectroscopy, and scanning electron microscopy (SEM) to confirm the morphological structure. Finally, the electrochemical performance of fabricated EDLC proves a good agreement data using Cyclic Voltammetry (CV), Low Impedance Spectroscopy (LIS), and Galvanostatic Charge–Discharge (GCD) analysis showing the high specific capacitance of 115 Fg−1 for the optimized 1:2 activated carbon material. [ABSTRACT FROM AUTHOR]

The bind-free carbon cloth-supported electrodes hold the promises for high-performance electrochemical capacitors with high specific capacitance and good cyclic stability. Considering the close connection between their performance and the amount of carbon material loaded on the electrodes, in this work, NiCo2O4 nanowires were firstly grown on the substrate of active carbon cloth to provide the necessary surface area in the longitudinal direction. Then, the quinone-rich nitrogen-doped carbon shell structure was formed around NiCo2O4 nanowires, and the obtained composite was used as electrode for electric double layer capacitor. The results showed that the composite electrode displayed an area-specific capacitance of 1794 mF·cm−2 at the current density of 1 mA·cm−2. The assembled symmetric electric double layer capacitor achieved a high energy density of 6.55 mW·h·cm−3 at a power density of 180 mW·cm−3. The assembled symmetric capacitor exhibited a capacitance retention of 88.96% after 10000 charge/discharge cycles at the current density of 20 mA·cm−2. These results indicated the potentials in the preparation of the carbon electrode materials with high energy density and good cycling stability. [ABSTRACT FROM AUTHOR]

The waste-to-wealth practice has evolved into the circular economy concept, in which every by-product is converted into a usable product, enabling the concept of zero-waste. As a result, research on converting wastes, particularly bio and agricultural wastes, into usable products is prioritized. Activated carbons are one of these products, which are derived through a variety of physical and chemical processes from agricultural and biowaste. These activated carbons have applications in various fields, including energy storage, catalysis, and water purification. However, the quality of this activated carbon is dependent on the bioresource's structure and chemical composition. As a result, many sources to produce activated carbon, including stems, wood, leaves, root, bark, fiber, flower, and seeds, have been identified and are being explored for their potential use as an electrode material for supercapacitors. Out of these sources, fiber from different bioresources shows improved performance as supercapacitor electrodes due to their higher cellulose and lignin contents. In this study, we systematically review various sources of activated carbon and their performance as supercapacitor electrodes. The electrochemical characterization methodologies used to characterize this fiber-based activated carbon are examined critically, and factors influencing its improved/poor performance are collated. Additionally, the most performing fiber-based sources of activated carbon for supercapacitor electrodes are identified, along with a future perspective. [ABSTRACT FROM AUTHOR]

This study aimed to assemble a high-performance electric double-layer capacitor (EDLC) using a hardwood kraft lignin (HKL)-based separator and HKL-based electrodes, which were fabricated from a nonwoven mat of electrospun HKL fibers. The separator was prepared by the thermostabilization of the mat derived from a mixed dope of HKL, hexamethylenetetramine, and polyethylene glycol (1.66/0.50/0.09, w/w) for electrospinning. Although a mat-type HKL-based electrode containing conductive carbon black (CB) has been reported to be suitable for a commercial cellulosic separator, this electrode was found to be unsuitable for the HKL-based separator because of its rough surface and poor contact with the separator interface. Hence, a powder-type electrode with a smooth surface was fabricated by grinding the mat, followed by casting with a carboxymethyl cellulose aqueous solution, and its EDLC possessed high energy (49 Wh kg−1) and power densities (151 kW kg−1). Moreover, to provide a simple process for electrode fabrication, another mat-type electrode was fabricated by adding CB to the mixed dope, followed by electrospinning, carbonization, and steam activation. The resultant EDLC exhibited excellent electrochemical performance with energy (58 Wh kg−1) and power densities (55 kW kg−1). [ABSTRACT FROM AUTHOR]

Lasers offer a versatile means towards the single-step, binder-free synthesis of three-dimensional graphene-like porous networks, providing an enticing alternative over energy intensive, multi-step traditional synthesis protocols creating unwanted waste streams. Here, we report on a novel laser-assisted method for the one-step preparation of the electrode component, not solely the active material, based on the simultaneous synthesis of turbostratic graphene-like structures on a carbon precursor and its transfer/deposition on the selected current collector. The performance of the graphene-based electrodes was electrochemically evaluated for both electric double layer capacitor (EDLC) and zinc-ion hybrid capacitor (ZIC) configurations. The performance of the EDLC devices was found to be superior to that of the current state-of-the-art devices prepared by laser-grown graphene. The ZIC exhibited higher areal energy density than the symmetric devices by one order of magnitude. The devices showed very low equivalent series resistance, good rate performance and high long-term cycling stability. Notably, the EDLC with the KOH electrolyte demonstrated an unexpected ∼20% increase in capacitance during the stability test of 10,000 cycles. This result was attributed to the substantial increase of oxygen content of the graphene electrodes, which act as sites for redox activity. [Display omitted] [ABSTRACT FROM AUTHOR]

• The mechanism of microwave plasma enhanced chemical vapor deposition of vertical carbon nanoflakes (CNFs) on Ti substrate was proposed as function of temperature in plasma chamber. • The resultant CNFs can be applied to assemble supercapacitors with no requirement of post treatment. • Symmetric supercapacitor with GNFs electrodes showed Coulombic efficiency of 99 % for 10,000 life cycles. As energy storage materials are in an urgent demand and carbon-based nanomaterials provided great potential for battery and supercapacitor. This study applied microwave plasma enhanced chemical vapor deposition (MPE-CVD) to deposit 3-dimensional carbon nanoflakes (CNFs) with distinguished surface area to prepare the electrodes for electric double layer capacitors (EDLCs). The vertical growth of CNFs is driven by MPE-CVD using CH 4 as precursor gas. The as-prepared CNFs on titanium plate (CNFs _700 /Ti) was optimized by thickness and mass loading as function of the applied power. Raman spectroscopy and field emission scanning electron microscopy analyzed the properties and surface morphology of carbon. The electrochemical properties of the CNFs _700 /Ti assembled as Swagelok or pouch cell were evaluated by cyclic voltammetry and galvanostatic charge/discharge for potential developments in supercapacitor. An unprecedented rapid growth rate of CNFs, 180 μm/h, was dramatically accelerated due to MPE-CVD procedure, and could be applied as electrode for EDLCs. The mechanism of CNFs growth was elucidated based on the temperature measurements in reactor which relates closely to the CNFs growth rate, proved by thickness and mass loading of CNFs. The clarification of CNFs growth mechanism assists future developments of carbon-based materials in energy storage materials. [Display omitted] [ABSTRACT FROM AUTHOR]

High power density and long cyclic stability are important characteristics that make supercapacitor suitable for many industrial applications. Measurement of equivalent series resistance and capacitance, is a general way to investigate performance of the Electric Double Layer Capacitor (EDLC). In this work, a Panasonic EDLC (10F) was investigated under cyclic degradation and monitored using electrochemical impedance spectroscopy (EIS) characterisation and Randles circuit model. After fitting, it was observed that series resistance was increased up to 80% and parallel capacitance was decreased up to 22%. The EIS data were validated using Kramers‐Kronig Transformation to check causality, linearity, and stability in the system. [ABSTRACT FROM AUTHOR]

This paper reports a facile carbonization method of a biopolymer to synthesize reduced graphene oxide with excellent electrochemical properties for use as a supercapacitor electrode. Oil palm lignin is used as the biopolymer-based graphene precursor, and a carbon dioxide laser is used to carbonize the material via lithography. Using Raman Spectroscopy, the characterization of the resultant graphene (OP-LSG) revealed D, G, and 2D peaks corresponding to multilayer graphene. Scanning Electron Microscopy of OP-LSG revealed three-dimensional particle-like fibrous and porous nanostructures with an enhanced surface area. In a three-electrode setup in ferrocyanide electrolyte, cyclic voltammetry showed the electrode coated with OP-LSG achieving a specific capacitance as high as 108.044 mF/cm² at a scan rate of 0.01 V/s. The galvanostatic charge-discharge of OP-LSG revealed energy and power density values of 15 µWh/cm² and 597 µW/cm² at a scan rate of 0.01 V/s. The OP-LSG electrode retained 97.5% of its initial capacitance after 1000 charge-discharge cycles.

Global energy and environmental issues are driving the development of modern advances in efficient and environmentally friendly energy storage systems. Such systems must meet a range of requirements, which include high energy and power density, long service life, flexibility, industrial scalability, security and reliability. Progressive achievements in the field of energy storage are associated with the development of various kinds of batteries and supercapacitors. Supercapacitors are state-of-the-art energy storage devices with high power density, long lifespan, and the ability to bridge the power/energy gap between conventional capacitors and batteries/fuel cells. However, supercapacitors have limitations associated with low energy density, which can be solved by using various types of current collectors, since current collectors are one of the main massive components of supercapacitors. This review gives a complete understanding of the effect of current collectors on the actual performance and properties of supercapacitors. We reviewed current collectors based on carbon and metal-containing materials, and supercapacitor configurations to identify possible improvements in electrochemical performance in terms of specific capacitance, energy density, power density, service life and variability in their application.

In recent times, there has been a great increase in the demand of flexible micro-supercapacitors for use in many commercial applications. Flexible capacitors have the potential to replace conventional batteries as they can provide competitive energy storage while being much smaller in size and having greater lifetime than average lithium-ion batteries. The most used design for in-plane flexible micro-supercapacitors is the interdigitated design. However, from findings of various recent studies, it is believed that the capacitance of in-plane EDLC micro-supercapacitors can further be improved by changing electrode designs. Different fractal designs have shown great promise to enhance the electrochemical performance of in-plane micro-supercapacitors by maximizing the active surface area and minimizing the energy lost during ion-transport. In this work, we successfully fabricate graphene-based, laser-scribed flexible micro-supercapacitors and study the effects of change in geometry parameters on total capacitance. Four different geometries for electrode were designed i.e., (1) interdigitated design, (2) fractal F1 (Hilbert) design, (3) fractal F2 (Peano) design, and (4) fractal F3 (Moore) design, and were patterned onto the thin layer of graphene oxide using laser scribing technique. Detailed analysis was presented for the change in capacitance using cyclic voltammetry, galvanic charge-discharge, electrochemical impedance spectroscopy and electrostatic simulation using COMSOL Multiphysics. It was found that fractal design micro-supercapacitors give better performance with higher capacitance and energy density values in comparison to conventional design interdigitated micro-supercapacitors. Among all, Fractal F3 design showed the highest capacitance and energy density value in comparison to other devices. It was found that there were two factors affecting the performance of devices, i.e., (1) a higher active surface area for fractal designs as compared to interdigitated designs with the same unit area, and (2) in addition to electric double layer capacitance, there was also electric field being generated on the edges of electrodes, defined as edging effect. Among both factors, the latter was the major enhancer of capacitance in the fractal design devices.

We have reported the synthesis of methyl cellulose-based biopolymer electrolyte incorporated with ionic liquid (IL) 1-ethyl-3-methylimidazolium tricyanomethanide varying from 10 to 100wt% with respect to biopolymer. Detailed studies like polarized optical microscopy (POM), linear sweep voltammetry (LSV), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), dielectric constant, and impedance spectroscopy were analyzed in detail. The maximum ionic conductivity was attained at 60wt%. IL incorporated with MC polymer which shows maximum conductivity value of 1.93 × 10−2 S/cm. Finally, we have fabricated an EDLC and dye-sensitized solar cell (DSSC) using maximum IL-doped MC which shows high specific capacitance value of 38 F/g and efficiency of 0.46% at 1 sun condition, respectively. [ABSTRACT FROM AUTHOR]

The PVA--NH4SCN polymer membranes were prepared by simple solution casting technique by passing ultrasound waves during the preparation. The polymer membranes were subjected to X-ray diffraction analysis and scanning electron microscopy. The X-ray diffraction pattern confirmed the incorporation of a salt into the polymer matrix. The scanning electron microscopy images showed the morphological changes of the polymer membrane. The polymer electrolyte (designated as UPVA20) incorporated with the 20 wt.% of the salt had the highest electrical conductivity in the order of 10-4 S cm-1. It was concluded from the dielectric, tangent and modulus spectra that the UPVA20 membrane was good at its properties. Thus, electric double layer capacitor was constructed with UPVA20 membrane as the separator. The capacitance value of the electric double layer capacitor determined from cyclic voltammetry was found to be 1652 mF g-1. The ultrasound assisted preparation of polymer membranes were good at performance when compared with the polymer membranes of ultrasound unassisted preparation. Among all the polymer electrolytes, UPVA20 polymer membrane had high conductivity, potential stability and capacitance. [ABSTRACT FROM AUTHOR]

The porous activated carbon nanosheet derived from Syzygium oleana leaves biomass was prepared by one-stage integrated pyrolysis through both carbonization and physical activation for supercapacitor electrode as energy storage application. Carbonization was performed in three different temperatures, including 500 °C, 600 °C, and 700 °C. The 1 M potassium hydroxide was selected to produce activated carbon progressively. Importantly, the surface morphology and the samples were characterized by Scanning electron microscopy at a voltage of 15 kV and nitrogen adsorption/desorption at a temperature of 77 K. The results showed a like-flower nanosheets structure decorated by nanofiber increases the surface area of activated carbon from 216 m2 g−1 to 1218 m2 g−1 with tuneable well-confirmed mesopores sizes. Degree of crystallinity and chemical composition also were characterized by using X-ray diffraction and Energy dispersive spectroscopy. Furthermore, electrochemical measurements had the best performances with a high specific capacitance of 188 F g−1 at two-electrode system with a scan rate of 1 mV s−1.

Recently, the single-walled carbon nanotube (SWCNT) has been the focus as a durable electrode with a high rate performance for the electric double layer capacitor (EDLC). However, it has not yet been clarified whether these reported outstanding properties are universal for all SWCNTs. The authors compared various self-standing SWCNT membranes (buckypapers) as the EDLC electrode to evaluate their stability to a floating high-voltage charge. Some SWCNTs exhibited an excellent rate performance even after the floating durability test, but other electrodes were degraded and showed a lower capacitance-retention. This variability in the durability for the SWCNTs can be attributed to the presence of residual metal impurities. Thus, it should be noted that the purity is a significant factor when using SWCNTs as the EDLC electrode, in addition to the nano-structure design from the viewpoint of operation stability.

The purpose of this study was to add the redox capacitance obtained by adding vanadium ions used in the vanadium redox flow battery to the electric double layer capacitance. CV measurement confirmed a square response characteristic of the electric double layer and a redox peak of vanadium. In EIS measurement, the characteristics as a capacitor when vanadium was added were investigated. The performance as a power storage device was measured during constant current charging and discharging, and it was found that a maximum improvement of 39% in discharge energy density was found compared to blank. However, it was confirmed that the redox capacitance addition in discharging was smaller in CV and CDC than that in charging. This irreversibility was attributed to the activated carbon fiber electrode. For comparison, ACF and CF with different internal and surface structures were compared to clarify the mechanism.

A novel gel polymer electrolyte based on chitosan with 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) is prepared with a new procedure and applied to electric double layer capacitors (EDLCs). The chitosan-based gel polymer electrolyte causes less liquid leakage than the previous one. In this electrolyte system, EMImBF4 plays the roles of both a solvent for dissolving chitosan and a charge carrier ion for EDLC application. The present chitosan solution for gel polymer electrolytes shows acidity, and its acidity is raised by increasing the amount of EMImBF4 and the preparation temperature. The electrochemical stability of the electrolyte is decreased as the acidity of its chitosan solution increases. At 25°C, an EDLC cell with the electrolyte containing 70 wt.% EMImBF4 showed good charge-discharge performance and lower electrode/electrolyte interfacial resistance than those of a liquid-phase EMImBF4 system.

Electric Double Layer Capacitor (EDLC) holds the highest share of commercial supercapacitor market. However, it has been proven that current Helmholtz, Gouy-Chapman and Stern models do not provide comprehensive explanation for energy storage mechanism in EDLC. In this work the effects of interdigitated EDLC design on capacitance of flexible laser scribed interdigitated microsupercapacitor (LSG-MSC) are studied. Three design parameters are tested, (1) current collector-electrode interaction, (2) electrode aperture, and (3) distance between parallel electrodes. Noticeable change was observed in the total capacitance upon change in LSG-MSC design which was analyzed in detail using cyclic voltammetry, electrochemical impedance spectroscopy and electrostatic simulation using COMSOL Multiphysics. It was found that in addition to electric double layer capacitance, an electric field was generated between electrodes and between electrode and current collector which led to small electrostatic capacitance between them. This electric field was also found to cause disturbance in double layer formation at the electrode thus causing change in the overall capacitance as the design parameters were varied.

The wide application of electric double layer capacitor (EDLC) is restricted by its low energy density. Such a bottleneck is hopefully tackled via engineering the carbon surface chemistry to kinetically inhibit the electrolyte decomposition and effectively extend the cell voltage of the EDLC. Here, we propose a facile carbon surface passivation strategy by rational functionalization with fluorine-containing functional groups. Evidenced by electrochemical measurements, the fluorinated activated carbon (F-AC) could tolerate a wider voltage window in commercially available organic electrolyte compared with the commercial activated carbon (AC). The theoretical simulation further verifies that the F-AC displays much increased activation energy for the formation of intermediate products, thereby dynamically hindering the electrolyte decomposition on the carbon surface. The F-AC based EDLC exhibits a remarkable voltage expansion from 2.7 V to 3.3 V and excellent cycling stability of 98.3% capacitance retention after 20000 cycles. A high energy density of 43.3 Wh kg−1 is achieved at the power density of 135 W kg−1, which is about 1.5-fold enhancement compared with the AC based counterpart, outperforming most of the reported organic EDLCs. These inspiring results bring fundamental insights into the regulation of voltage window, which will stimulate the design of high-performance energy storage devices. [Display omitted] [ABSTRACT FROM AUTHOR]

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N/S dual-doped carbon materials were synthesized from coffee waste and cysteine for use as porous carbon electrode materials for electric double layer capacitors. The capacitance of the carbon materials was calculated from the experimental results of cyclic voltammetry and galvanostatic charge-discharge tests. The N/S-doped carbon materials obtained from heat-treatment with cysteine exhibited a higher discharge capacitance, 71.3 F/g, than that of the carbon without the cysteine treatment, 43.8 F/g, at 1 A/g. This is because the N/S dual-doped carbons possess a higher wettability than that of the other carbon material, even though the N/S doping with cysteine destroys the porous carbon structure, which reduces the BET surface area of the carbon samples. Elemental analysis was performed to determine the portions of nitrogen and sulfur elements doped into the carbon. From the XPS results, various states of nitrogen and sulfur elements were identified, and SEM/TEM images were obtained to observe their morphologies and porous structures. [ABSTRACT FROM AUTHOR]

This article demonstrates the development of activated carbon fiber electrodes produced from hardwood kraft lignin (HKL) to fabricate electric double layer capacitors (EDLCs) with high energy and power densities using an ionic liquid (IL) electrolyte. A mixture solution of HKL, polyethylene glycol as a sacrificial polymer, and hexamethylenetetramine as a crosslinker in dimethylformamide/acetic acid (6/4) was electrospun, and the obtained fibers were easily thermostabilized, followed by carbonization and steam activation to yield activated carbon fibers (ACFs). The electrochemical performance of EDLCs assembled with the ACFs, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4) as an IL electrolyte and a cellulosic separator was insufficient due to the low conductivity of the electrode. The conductivity of the electrode was improved successfully by spraying conductive carbon black (CB) onto the fibers mat during electrospinning. The CB containing electrodes with improved conductivity gave the resulting EDLCs a higher electrochemical performance, with an energy density of 91.5 Wh kg−1 and a power density of 76.2 kW kg−1. [ABSTRACT FROM AUTHOR]

Coal tar pitch (CTP) with high carbon content and wide source of raw materials was an excellent precursor for the preparation of porous carbons (PCs). CTP was composed of polycyclic aromatic hydrocarbons (PAHs) with complex molecular size and chemical structure, the separation of CTP into several fractions with relatively narrow molecular weight by solvent extraction was of significance for CTP utilization. In this paper, CTP was treated by single-solvent extraction (carbon disulfide, acetone and ethyl acetate), and the six fractions were used as raw materials to prepare PCs as electrode material for electric double layer capacitor. The fractions were well characterized and the effect of mass distribution of different narrow fractions on structure property and electrochemical performance of the PCs was studied. The PCs prepared by carbon disulfide extract, acetone raffinate and ethyl acetate extract, containing more PAHs, exhibited the excellent specific capacitance performance in comparison with its residual components. The remarkable performance might contribute in the enhanced transport of electrolyte ions via the molecular graphene structure of PAHs. Additionally, the PC prepared by carbon disulfide raffinate showed outstanding cycling performance (99.7% at 2 A g−1 after 15,000 cycles) which was related to its unique layered porous structure. [ABSTRACT FROM AUTHOR]

In this work, we report a stepwise formation method of a chitosan/sodium alginate polyelectrolyte complex (CS/SA PEC) membrane. The proposed method aiming at the utilization of the ultrasonic treatment of chitosan and sodium alginate solution allowed us to obtain a highly homogeneous hybrid membrane for electrochemical usage. The CS/SA PEC membrane saturated in a 2 M Li2SO4 aqueous solution was used in electrochemical double layer capacitor (EDLC) cell to study its applicability as quasi-solid electrolyte. Electrochemical characteristic of EDLC cells was determined by electrochemical impedance spectroscopy, cyclic voltammetry and galvanostatic charge/discharge methods. The results show that the EDLC cell with CS/SA PEC quasi-solid electrolyte exhibit a comparable specific capacitance (102 F g-1 for 0-0.8 V) to CS reference (100 F g-1 for 0-0.8 V) and commercial separator (99 F g-1 for 0-0.8 V) cells. Thus, the CS/SA PEC membrane can be considered as an alternative modification for chitosanbased materials of electrochemical purpose. [ABSTRACT FROM AUTHOR]

This paper challenges the fabrication of a thin film energy storage device on a flexible polymer substrate specifically by replacing most commonly used metal foil current collectors with coated current collectors. Mass‐manufacturable spray‐coating technology enables the fabrication of two different half‐cell electric double layer capacitors (EDLC) with a spray‐coated silver paste current collector and a Ni foil current collector. The larger specific capacitances of the half‐cell EDLC with the spray‐coated silver current collector are obtained as 103.86 F/g and 76.8 F/g for scan rates of 10 mV/s and 500 mV/s, respectively. Further, even though the half‐cell EDLC with the spray‐coated current collector is heavier than that with the Ni foil current collector, smaller Warburg impedance and contact resistance are characterized from Nyquist plots. For the applied voltages ranging from −0.5 V to 0.5 V, the spray‐coated thin film energy storage device exhibits a better performance.

With high-end applications of electric double layer capacitors (EDLCs) in fields of vehicle and aerospace, it is a great challenge to construct lightweight and compact EDLCs. Herein, using polyvinyl pyrrolidone (PVP) as soft template and sulfonated pitch (SP) as carbon source, the dense porous carbons (DPCs) with high pore connectivity and high packing density were prepared by intermolecular hydrogen bonding, capillary densification and KOH activation strategies. The PVP plays a crucial role in structure formation of DPCs. Firstly, PVP molecules can induce the structural orientation of SP molecules and then promote the formation of carbon microcrystals and dense structure of DPCs. Secondly, the decomposition of PVP molecules can form numerous connected pores, which greatly increase the connectivity and effective utilization of pores. The optimized 0.3DPC sample simultaneously owns large pore volume (1.06 cm3 g−1) and high density (0.641 g cm−3). Also it contains a few surface O atoms (8.3 at. %). Thus, this sample achieves high C v of 82 F cm−3 at 0.05 A g−1, and good rate capability of 79% in TEABF 4 /PC electrolyte. The cyclic stability of 0.3DPC is up to 94.6% over 10,000 cycles. Likewise, it acquires high E v of 39.1 Wh L−1 at 3.5 V in EMIMBF 4 electrolyte. [ABSTRACT FROM AUTHOR]

The present study reports synthesis and analysis of different characteristics of sodium ion conducting polymer gel electrolytes (PGEs) containing sodium salts with BF 4 −, ClO 4 − and CF 3 SO 3 − anions dissolved in tetraethylene glycol dimethyl ether and immobilized in a copolymer matrix consisting of polymethyl methacrylate and poly(vinylidene fluoride- co -hexafluoropropylene). The PGE containing the NaBF 4 salt could deliver an ionic conductivity of 1.4 × 10−3 S cm−1 at room temperature along with superior dielectric properties as compared to the electrolytes with NaClO 4 and NaCF 3 SO 3 salts. The feasibility of designing sodium-based batteries and EDLCs has been demonstrated using the optimized PGE containing NaBF 4 salt. The prototype sodium‑sulfur (Na S) battery designed by utilizing the optimized PGE, sodium amalgam anode and sulfur cathode provides open circuit voltage of ∼2.4 V and initial discharge capacity of ∼163 mA h g−1 and 126 mA h g−1 at discharge currents of 33 mA g−1 and 66 mA g−1, respectively. This optimized PGE also demonstrate good compatibility with AC electrodes in electric double layer capacitor (EDLC) application and delivered a significant specific capacity ∼64 F g−1 at 0.5 mA cm−2 current. • Effect of different anions BF 4 , ClO 4 and CF 3 SO 3 on the properties of Na+ conducting polymer gel electrolyte is investigated. • Excellent ionic conductivity of 1.48 × 10−3 S cm−1 at room temperature for optimized polymer gel electrolyte. • The prototype Na-S battery shows open circuit voltage of ∼2.4 V and delivers discharge capacity of ∼163 mA h g−1. • The prototype EDLC delivers a significant specific capacity ∼64 F g−1 at 0.5 mA cm−2 current. [ABSTRACT FROM AUTHOR]

Turning trash into treasure, the present work divulges the preparation of onion-like porous carbon derived out of the most malignant invasive weed, the Prosopis juliflora. The pods of the Prosopis juliflora are treated hydrothermally and chemically activated using KOH. The effect of activation temperature on the pore formation is investigated to obtain the desired porous carbon. The prepared porous carbon (J–800) has a significant specific surface area of 967 m2 g−1 with unique morphology of onion-like nanostructures and provided a sensible specific capacitance of 274 F g−1 at 1.3 A g−1 in H 2 SO 4 electrolyte. Further, the performance of the device is effectually enhanced by adding KI as redox additive. Interestingly, the increased cell voltage (1.4 V) and improved cell capacitance of 588 F g−1 is obtained. Ultimately, a superior energy density of 35.7 Wh kg−1 at an enhanced power density of 971 W kg−1 is also obtained in the redox additive based aqueous electrolyte. A detailed investigation of the surface storage mechanism is discussed, and the stability of the prepared supercapacitors is also demonstrated. Thus, the most eradicable eco-threat P. juliflora is successfully reformed into an efficient electrode material for the energy storage application. Unlabelled Image • A unique onion like morphology with hierarchical porous structure demonstrates enriched electrode properties. • The increasing activation temperature shows sensible evolution on the porous texture of carbon. • The enhancement of surface storage properties is attained through the redox-mediated storage mechanism of EDLC. • The onion-like porous carbon on using redox-additive electrolyte displays remarkable energy and power densities. [ABSTRACT FROM AUTHOR]

The capacity of electric double layer capacitor is dependent on specific surface area of electrodes. The purpose of this study is to prepare porous electrode materials using polyacrylonitrile (PAN) and poly (methyl methacrylate) (PMMA) blends by electrospinning and carbonization process. PMMA from PAN/PMMA nanofiber webs were selectively removed by immersing in methylene chloride. Morphology and diameter of fibers were investigated using scanning electron microscope (SEM). Morphology of webs was controlled using various blend ratios of PAN/PMMA and average diameters of fiber webs slightly decreased by increasing the ratio of PMMA after carbonization. Morphologically controlled PAN/PMMA nanofiber webs were used for carbon electrode materials after carbonization. [ABSTRACT FROM AUTHOR]

Highlights • Activated carbons with surface areas over 3000 m2 g−1 can be prepared through simple CO 2 activation. • Micropores develop through two distinctive steps during activation. • The prepared carbons exhibit a high gravimetric capacitance of approximately 80 F g−1. • A carbon with an optimized bimodal pore system exhibited good rate performance. Abstract Activated carbons for electrodes of non-aqueous electric double layer capacitors were prepared from composites of poly(methymethacrylate) particles and phenolic resins. Their surface areas can be increased up to 3000 m2 g−1 through simple CO 2 activation. Through the characterization of pore properties of the resulting carbons, it was found that the activation process appears to be composed of two steps. The pore properties of the activated carbons were optimized to maximize their performances as electrodes for non-aqueous electric double layer capacitor electrodes. [ABSTRACT FROM AUTHOR]

Abstract Hybrid supercapacitors with their improved performance in energy density without altering their power density have been in trend since recent years. The hybrid supercapacitor delivers higher specific capacitance in comparison to the existing electric double layer capacitor (EDLC) and pseudocapacitors. Generally, the asymmetric behavior of hybrid supercapacitors which is the combination of EDLC and pseudocapacitor acts as an enhancer in its respective capacitance values. This asymmetric approach marks a new beginning towards the much-needed pollution free, long lasting and proficient energy-storing performance. Corresponding to their utilization in hybrid electric vehicles and similar sort of power necessity based devices; the research in developing new advanced storage devices finds an enormous and vast future ahead. The most significant factor for the energy efficient applications demands a considerably higher ratio of surface to the volume by incorporation of new materials. This review article gives an overview of recent advances in the development of hybrid supercapacitors, storage mechanism, criteria of formation, components, different electrode and electrolyte materials, electrochemical profile assessment, design fabrication and their applications. Highlights • The current status and the advancement of supercapacitors are discussed in this review. • The principles, classification and the mechanism of energy storage are discussed. • Finally, various applications of supercapacitors have been discussed. [ABSTRACT FROM AUTHOR]

Abstract The question of how to recycle anaerobic digester residue is a critical issue for the anaerobic digestion process of lignocellulosic biomass. In the current study, anaerobic digester residue from a biogas plant for the treatment of cattle manure was utilized to prepare the activated carbon for supercapacitors. The effect of activation temperature on the specific surface area, pore size distribution, and electrochemical performance of activated carbon was investigated. Results show that activated carbon derived from anaerobic digester residue is feasible for supercapacitors. With an increase in activation temperature, the specific surface area of activated carbon first increases and then gradually decreases. Activated carbon obtained at 700 °C shows both high specific capacitance and excellent electrochemical cycle stability. The good capacitive performance confirms that anaerobic digested manure residue can act as an excellent carbonaceous material for high-performance supercapacitors. Highlights • AC derived from anaerobic digester residue was feasible for supercapacitors. • AC achieved specific high surface area and good pore size distribution. • Highest capacitance was 184.91 F g−1 at 1 A g−1 and with 94.80% retention. [ABSTRACT FROM AUTHOR]

Abstract We have newly designed five kinds of polyvalent solute that have two to four quaternary ammonium functional groups in one cation. Their molecular structure is designed to be as compact as possible, with either two or three cationic groups on a linear molecular structure, or three or four cationic moieties on three strands in a star-shape. The prepared solutes have a bis(trifluoromethylsulfonyl)imide anion in common and a flexible molecular structure that can easily adsorb onto the electrode surface of an electric double layer capacitor (EDLC). Since a single polyvalent solute molecule can accumulate more electric charge by adsorption than can a monovalent solute, a high capacitance is possible even at a low solute concentration compared with conventional cells. We evaluated some electrochemical properties of these polyvalent solutes as an electrolyte and their EDLC performance, including initial capacitance, rate characteristics and cycle durability. All the polyvalent solutes had a potential window of 5 V or more, and in particular the divalent salt showed a capacitor performance equivalent to that of the monovalent salt even at half salt concentration in the electrolyte. On the other hand, the trivalent and tetravalent solutes had a lower charge utilization rate compared with a monovalent solute. Graphical abstract Image 1 Highlights • Five kinds of newly designed polyvalent cations were prepared for capacitor use. • All the polyvalent solutes have a wide electrochemical stability. • The divalent solute has the same capacitance as a monovalent, even at half concentration. • The polyvalent electrolytes have high cycle durability. [ABSTRACT FROM AUTHOR]

Activated carbon derived from cellulose with added melamine sulfate, which is known as one of the chemicals having a flame-retardant effect on the cellulose, was produced in order to dope dual hetero elements, such as nitrogen and sulfur, and was used to improve the yields of the carbonization process and carbon dioxide (CO2) activation process. The addition of melamine sulfate resulted in suppression of the BET specific surface area. The Brunauer-Emmett-Teller (BET) specific surface area for the CO2-activated sample with 30 wt.%-added melamine sulfate was 578 m2 g−1. The existence of nitrogen atoms was confirmed in the CO2-activated sample with the added melamine sulfate. However, no peak assigned to the sulfur atom appeared in the x-ray photoelectron spectroscopy spectrum for the sample with the 30 wt.%-added melamine sulfate. In spite of the lower specific surface area of the samples containing the added melamine sulfate, the capacitance values of the carbon material derived from the cellulose with added melamine sulfate were higher than those of the carbon material derived only from cellulose. [ABSTRACT FROM AUTHOR]

Highlights • Electrochemical capacitors provide highly-reversible energy storage. • Specialized meetings held to advance electrochemical capacitor technology. • Perspective view presented on electrochemical capacitor technology. Abstract Electrochemical capacitors, a type of capacitor also known by the product names Supercapacitor or Ultracapacitor, can provide short-term energy storage in a wide range of applications. These capacitors are powerful, have extremely high cycle life, store energy efficiently, and operate with unexcelled reliability. This article discusses highly-reversible energy storage, presents electrochemical capacitor basics, and identifies several resources that may be useful to a researcher who wishes to participate in this technology arena. A perspective on the future of electrochemical capacitor technology is offered. [ABSTRACT FROM AUTHOR]

Nitrogen functionalization of a highly microporous activated carbon (SBET > 3000 m2/g), to be used as electrode of electric double layer capacitor (EDLC), was carried out by different methods based on organic chemistry protocols at low temperature and selective thermal post-treatments under inert atmosphere. The combination of both methods allowed the production of carbon materials with very similar surface area (2400–3000 m2/g) and different surface chemistry. The nitrogen functionalization by chemical methods produce the attachment of 4 at. % N (XPS) by consumption of oxygen functional groups. The thermal treatments rearrange the surface chemistry by decreasing and converting both nitrogen and oxygen moieties. The effect of surface chemistry on the performance of these materials as electrodes for symmetric supercapacitors was analyzed in organic electrolyte (1M TEMABF4/propylene carbonate). The devices showed high gravimetric capacitance (37–40 F/g) and gravimetric energy density (31–37 Wh/kg). The electrochemical stability of the EDLC was evaluated by a floating test under severe conditions of voltage and temperature. The results evidence an improvement of the durability of nitrogen-doped activated carbons modified by chemical treatments due to the decrease of detrimental oxygen functionalities and the generation of nitrogen groups with higher electrochemical stability.