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In this study, a three-dimensional (3D) interconnected porous Ni/SiC skeleton (3D Ni/SiC) was synthesized by binder-free hydrogen bubble template-assisted electrodeposition in an electrolyte containing Ni2+ ions and SiC nanopowders. This 3D Ni/SiC skeleton served as a substrate for directly synthesizing nickel–cobalt layered double hydroxide (LDH) nanosheets via electrodeposition, allowing the formation of a nickel–cobalt LDH nanosheet-decorated 3D Ni/SiC skeleton (NiCo@3D Ni/SiC). The multiscale hierarchical structure of NiCo@3D Ni/SiC was attributed to the synergistic interaction between the pseudocapacitor (3D Ni skeleton and Ni–Co LDH) and electrochemical double-layer capacitor (SiC nanopowders). It provided a large specific surface area to expose numerous active Ni and Co sites for Faradaic redox reactions, resulting in an enhanced pseudocapacitance. The as-fabricated NiCo@3D Ni/SiC structure demonstrated excellent rate capability with a high areal capacitance of 1565 mF cm−2 at a current density of 1 mA cm−2. Additionally, symmetrical supercapacitor devices based on this structure successfully powered commercial light-emitting diodes, indicating the potential of as-fabricated NiCo@3D Ni/SiC in practical energy storage applications. [ABSTRACT FROM AUTHOR]

This study explored the development of hierarchical graphitic carbon structures (HGCs) from harmful inedible seaweed waste harvested in the summer. Elevated sea temperatures during the summer increase the cellulose content of seaweeds, making them unsuitable for consumption. By utilizing seaweed biomass, this study addresses critical marine environmental issues and provides a sustainable solution for promising electrode materials for energy storage devices. The fabrication process involved impregnating seaweed with Ni ions, followed by annealing to create a highly crystalline carbon structure. Subsequent etching produced numerous nano-sized pores and a large surface area (806 m2/g), significantly enhancing the number of electrically active sites. The resulting HGCs exhibited a high capacitance and maintained their capacity even after 10,000 cycles in fast-current systems. This innovative approach not only mitigates the environmental burden of seaweed waste but also offers a sustainable method for converting it into efficient energy storage materials. [ABSTRACT FROM AUTHOR]

This study used a scalable process to fabricate activated carbon (AC) supercapacitor electrodes with cornstarch as a green binder. A vital aspect of this study was comparing its performance with synthetic binders like polyvinylidene fluoride (PVDF) and Nafion. The chemical and physical properties of the AC were characterized using Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), Raman spectroscopy, and Field Emission Scanning Electron Microscopy (FE-SEM). Water contact angle measurements evaluated the hydrophilicity of AC-based electrodes with different binders. Their electrochemical characteristics were studied using open circuit potential (OCP), cyclic voltammetry (CV), galvanic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS) in 1 M NaSO4 electrolyte, and the charge storage mechanism was discussed in detail. The starch binder significantly facilitated the charge storage mechanism by suppressing diffusion limitations compared to other binders. The fabricated symmetric supercapacitor device of starch-based electrodes exhibited the highest Cs of 120 F/g at a specific current of 1 A g-1 with a high energy density of 135 Wh/kg and an exact power density of 750 W/kg. The starch-based supercapacitor device exhibited a capacitance retention of 104 % and 65.5 % at specific currents of 2 A g-1 and 10 A g-1 after 10,000 cycles of charging/discharging, respectively.

The current study aims to develop a unique approach for constructing an asymmetric supercapacitor utilizing a nanocomposite of MgO-carbon as electrode material. The geometrical surface area of the MgO-carbon has shown to be highly porous with different porosities, and the value is 210 m2g−1. This supercapacitor operates with an aqueous electrolyte consisting of 1 M KOH. The findings indicate that the test cell exhibited exceptional electrochemical output within the voltage range of 0 to 1 V. The capacitance of the MgO-carbon cell is measured to be 225 F g−1 at a current density of 2 A g−1. According to research on cycling, the aforementioned cell has demonstrated the ability to maintain 97% of its original capacitance following 20,000 cycles. The findings of this study suggest that the MgO-carbon holds promise as an electrode material for the development of environmentally friendly and cost-effective energy storage devices. This composite exhibit excellent energy and power densities, along with a prolonged cycle life. [ABSTRACT FROM AUTHOR]

The present study reports the synthesis, characterization, and application as energy devices of an ionic liquid blended polymer electrolyte film in which the host polymer polyvinyl alcohol (PVA) is mixed with low viscosity ionic liquid (IL) 1-ethyl-3-methylimidazolium thiocyanate. Various characterization tools have been used further to elaborate electrical, structural, and photoelectrochemical properties. X-ray diffraction (XRD) and polarized optical microscope (POM) affirm the reduction of crystallinity of polymer, while Fourier transform infrared spectroscopy (FTIR) shows complexation and composite nature. Electrochemical impedance spectroscopy shows an enhancement in ionic conductivity by IL doping, where the highest conductivity is achieved at 60 wt% of IL concentration with a conductivity value of 6.21 × 10⁻⁴ S/cm. The ionic transference number (tion) and electrochemical stability measurement show the film's predominantly ionic nature and a reasonable stability window. Using maximum conducting film sandwiched between electrodes, we have successfully fabricated two devices, i.e., an electrical double-layer capacitor (EDLC) and a dye-sensitized solar cell (DSSC). The fabricated EDLC capacitor shows a specific capacitance of 125 F/g, while DSSC shows an efficiency of 1.1 % at one sun condition.

In this study, a three-dimensional (3D) interconnected porous Ni/SiC skeleton (3D Ni/SiC) was synthesized by binder-free hydrogen bubble template-assisted electrodeposition in an electrolyte containing Ni2+ ions and SiC nanopowders. This 3D Ni/SiC skeleton served as a substrate for directly synthesizing nickel–cobalt layered double hydroxide (LDH) nanosheets via electrodeposition, allowing the formation of a nickel–cobalt LDH nanosheet-decorated 3D Ni/SiC skeleton (NiCo@3D Ni/SiC). The multiscale hierarchical structure of NiCo@3D Ni/SiC was attributed to the synergistic interaction between the pseudocapacitor (3D Ni skeleton and Ni–Co LDH) and electrochemical double-layer capacitor (SiC nanopowders). It provided a large specific surface area to expose numerous active Ni and Co sites for Faradaic redox reactions, resulting in an enhanced pseudocapacitance. The as-fabricated NiCo@3D Ni/SiC structure demonstrated excellent rate capability with a high areal capacitance of 1565 mF cm−2 at a current density of 1 mA cm−2. Additionally, symmetrical supercapacitor devices based on this structure successfully powered commercial light-emitting diodes, indicating the potential of as-fabricated NiCo@3D Ni/SiC in practical energy storage applications.

To date, batteries are the most widely used energy storage devices, fulfilling the requirements of different industrial and consumer applications. However, the efficient use of renewable energy sources and the emergence of wearable electronics has created the need for new requirements such as high-speed energy delivery, faster charge–discharge speeds, longer lifetimes, and reusability. This leads to the need for supercapacitors, which can be a good complement to batteries. However, one of their drawbacks is their lower energy storage capability, which has triggered worldwide research efforts to increase their energy density. With the introduction of novel nanostructured materials, hierarchical pore structures, hybrid devices combining these materials, and unconventional electrolytes, significant developments have been reported in the literature. This paper reviews the short history of the evolution of supercapacitors and the fundamental aspects of supercapacitors, positioning them among other energy-storage systems. The main electrochemical measurement methods used to characterize their energy storage features are discussed with a focus on their specific characteristics and limitations. High importance is given to the integral components of the supercapacitor cell, particularly to the electrode materials and the different types of electrolytes that determine the performance of the supercapacitor device (e.g., storage capability, power output, cycling stability). Current directions in the development of electrode materials, including carbonaceous forms, transition metal-based compounds, conducting polymers, and novel materials are discussed. The synergy between the electrode material and the current collector is a key factor, as well as the fine-tuning of the electrode material and electrolyte. [ABSTRACT FROM AUTHOR]

There has been considerable interest in supercapacitors because of their remarkable advantages, including their high power density, rapid charge–discharge rate, and long cycle life. Metal–organic frameworks (MOFs) have been extensively utilized in energy conversion and storage due to their large specific surface area and tunable pore structures. The poor conductivity of MOFs makes them unsatisfactory electrode materials for supercapacitors. This issue was addressed by synthesizing graphene-supported Zn-BTC metal–organic framework materials with different morphologies by combining ultrasonic oscillation with one-step solvothermal synthesis. It was found that the synthesized Zn-BTC material was uniformly anchored on wrinkled graphene nanosheets and that the specific capacitance was 201.3 C g−1 (at 1 A g−1), exceeding the specific capacitance of graphene-supported two-dimensional sheet-like Zn-BTC (152.6 C g−1), graphene-supported three-dimensional spherical Zn-BTC (139.6 C g−1), graphene (108.2 C g−1), and one-dimensional rod-shaped Zn-BTC (63.5 C g−1). Using graphene-supported, rod-shaped Zn-BTC as a basis for symmetric supercapacitors, a maximum energy density of 4.55 Wh kg−1 was achieved at 104.17 W kg−1 with specific capacitance retention of 93.26% after 2000 charge–discharge cycles at a current density of 1 A g−1. [ABSTRACT FROM AUTHOR]

The large oil palm plantation in Malaysia is located in Sabah which is around 700,000 acres of land that produces around 0.7 million tons of agricultural waste. The conversion of agriculture waste to activated carbon (AC) solves the disposal problem in the agricultural industry. The AC plays an important role as an electrode in supercapacitor due to its characteristics such as high porosity and good conductivity. The performance of supercapacitor electrodes was study by using different sizes of AC. The AC from oil palm kernel shell (PKS) was produced by using the low cost of production with a simple modification in a conventional method. The PKS carbonizes in a furnace at 390 oC for 1 hour. It soaks in KOH for chemical activation. The sample is rushed by using agate mortar to get two different sizes which is fine and coarse. The AC is then mixed for the preparation of the electrode labelled as (Sample 1, Sample 2 & Sample 3). Then, the electrode is assembled with filter paper as separator and 1.0 M KOH as electrolyte. The supercapacitor electrode is connected to the circuit to observe the potential of charge-discharge. The result of capacitance for Sample 1 is 26.3mF, specific capacitance 21.58mF/g and energy density 17.22Wh/kg while the Sample 2 of activated carbon is 2672.38mF, 1113.49 mF/g and energy density 52.384Wh/kg and Sample 3 is 2952.5mF, specific capacitance 1230.16mF/g and energy density 226.34Wh/kg. As conclusion, a high-performance capacitor is achieved by using a mixed size of PKS as active material in electrode. Therefore, PKS has large market potential due to the low-cost AC production but promises high performance in Supercapacitor Application.

• Leveraging locally available biomass (Mesua ferrea) as raw material for supercapacitor applications. • N-doped activated carbon was synthesized through pyrolysis at 700 °C and 800 °C. • Prepared electrode material without commercial carbon black, highlighting the efficacy of the biomass-derived carbon. • Achieved a capacitance of 210 f g⁻¹, comparable to commercial activated carbon. • Bio-waste as a viable candidate for future energy utilities. Developing a high energy density supercapacitor is of great challenge due to the low surface area of commercial activated carbon. The present work aims at developing highly porous nitrogen-doped porous carbon from biomass for supercapacitors. Herein, Mesua ferrea (Nahor) shells, a widely available biomass in northeast India, was used to prepare porous carbon. The effect of activation temperature on structural, textural properties, and electrochemical performance is studied. The carbonization temperature highly influenced the pore structure, porosity, surface area, and thereby influencing the electrochemical performance. The porous carbon pyrolyzed at 700 °C delivered a high specific capacitance of 210 F g-1 at 1 A g-1, higher than porous carbon made at higher temperature (27.5 F g-1 at 1 A g-1 for carbon pyrolyzed at 800 °C). The results provide insights that will be of use in the development of high-energy-density capacitors employing biomass-derived porous carbon. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper investigates the effect of the electric double layer capacitor (EDLC) in reducing stress and prolonging the battery lifespan in a hybrid energy storage system (HESS). A 65 F, 16.2 V EDLC supercapacitor was connected in a laboratory experiment to produce its charge/discharge profile at a constant current of 5 and 10 A. The EDLC's Faranda or "two branch model" mathematical parameters were extracted from the experimental charge/discharge profile. The extracted parameters were used as inputs to design the Python/MATLAB/Simulink (PMS)-hybrid model of the EDLC. The charge/discharge profiles of the simulated PMS model of the EDLC were then compared to the charge/discharge profiles derived from the experimental setup of the EDLC and were found to match. The PMS model of the EDLC was then used as a subcomponent in an HESS system modelled in MATLAB/Simulink. Using constant load conditions, the battery's voltage, current, power and state of charge (SOC) were analyzed for a battery energy storage system (BESS) without a supercapacitor and then compared to an HESS system with a supercapacitor in an experimental setup. This process was repeated with the simulated PMS model of the EDLC in MATLAB/Simulink for HESS and without the EDLC for BESS. Finally using a variable load in an experimental setup, the battery's voltage and current were analyzed for a BESS system and compared to an HESS system. All these data show that, in an HESS system with a supercapacitor, there is less stress on the battery with a load applied. This is indicated by the voltage and current values in an HESS system being consistently more stable with respect to time as compared to the BESS system. As a result, in an HESS system, the battery will have a longer lifespan. [ABSTRACT FROM AUTHOR]

Bacterial Cellulose (BC) derived from local market or symbiotic culture of bacteria and yeast (SCOBY) was employed as the polymer matrix for hydroxyl multi-walled carbon nanotube (MWCNT-OH)-based electrochemical double-layer capacitor (EDLC). Chitosan (CS)-sodium iodide (NaI)-glycerol (Gly) electrolyte systems were used as the polymer electrolyte. CS-NaI-Gly electrolyte possesses conductivity, potential stability and ionic transference number of (1.20 ± 0.26) × 10−3 S cm−2, 2.5 V and 0.99, respectively. For the electrodes, MWCNT-OH was observed to be well dispersed in the matrix of BC which was obtained via FESEM analysis. The inclusion of MWCNT-OH reduced the crystallinity of the BC polymeric structure. From EIS measurement, it was verified that the presence of MWCNT-OH decreased the electron transfer resistance of BC-based electrodes. Cyclic voltammetry (CV) showed that the shape of the CV plots changed to a rectangular-like shape plot as more MWCNT were added, thus verifying the capacitive behavior. Various amount of MWCNT-OH was used in the fabrication of the EDLC where it was discovered that more MWCNT-OH leads to a better EDLC performance. The EDLC was tested for 5000 complete charge-discharge cycles. The optimum performance of this low voltage EDLC was obtained with 0.1 g MWCNT where the average specific capacitance was 8.80 F g−1. The maximum power and energy density of the fabricated EDLC were 300 W kg−1 and 1.6 W h kg−1, respectively.

This paper investigates the characterization of an electric double-layer capacitor (EDLC). In this study, the 300 F and 400 F EDLC supercapacitors are connected in a circuit in a laboratory experiment to produce their charge/discharge profiles at a constant current. The acquired charge/discharge profiles were used to determine the mathematical parameters of the EDLCs using the "Faranda model", or "two-branch model", of the EDLC. The parameters extracted from the equivalent circuit model were then used as inputs to a designed Python/MATLAB/Simulink (PMS)-hybrid model of an EDLC. This was simulated to obtain charge/discharge profiles. The resulting experimental- and simulated-charge/discharge profiles of the EDLCs were compared with each other, by superimposing their profiles to determine the accuracy of the PMS model. The PMS model was found to be very accurate. The innovation of this work lies in modeling a supercapacitor, mostly in the Python programming language in combination with a MATLAB/Simulink model. The experimental-charge/discharge profiles obtained were used to calculate the equivalent circuit resistance (ESR) and the capacitance of the EDLCs, which were compared with the existing datasheet values of the EDLCs. The characterization of the EDLC supercapacitor was done to derive a flexible PMS model of the EDLC, which can be used in a microgrid hybrid energy-storage system (HESS) to show the potential of the EDLC in improving battery lifespan. [ABSTRACT FROM AUTHOR]

Activated carbons derived from viscose fibers were prepared using potassium hydroxide, carbon dioxide, or water vapor as activation agents. The produced activated carbon fibers were analyzed via scanning electron microscopy and energy dispersive X-ray spectroscopy, and their porosity (specific surface area, total pore volume, and pore size distribution) was calculated employing physisorption experiments. Activated carbon fibers with a specific surface area of more than 2500 m2 g−1 were obtained by each of the three methods. Afterwards, the suitability of these materials as electrodes for electrochemical double-layer capacitors (supercapacitors) was investigated using cyclic voltammetry, galvanostatic measurements, and electrochemical impedance spectroscopy. By combining CO2 and H2O activation, activated carbon fibers of high purity and excellent electrochemical performance could be obtained. A specific capacitance per electrode of up to 180 F g−1 was found. In addition, an energy density per double-layer capacitor of 42 W h kg−1 was achieved. These results demonstrate the outstanding electrochemical properties of viscose-based activated carbon fibers for use as electrode materials in energy storage devices such as supercapacitors. [ABSTRACT FROM AUTHOR]

ZnO is considered a promising pseudocapacitive material for supercapacitor devices because of its high specific energy density, low cost, non-toxicity, eco-friendliness, and widespread availability. However, its poor electronic and ionic conductivity limits its power density and cycling stability as a supercapacitor device, restricting its use in energy storage systems. Herein we report a novel hybrid nanocomposite electrode material developed by three-dimensional conducting wrapping of ZnO nanoparticles with graphene sheet to significantly improve the supercapacitor efficiency. The wrapping of ZnO nanospheres by graphene sheets creates highly conductive pathways by bridging individual ZnO together, thereby improving the rate and cycling performance of supercapacitors. The fabricated supercapacitor device using this ZnO–RGO hybrid exhibited a high specific capacitance of 1012 F/g at a current density of 1 A/g. Furthermore, the ZnO–RGO hybrid is capable of achieving an outstanding power density of 3534.6 W/kg, an energy density of 50.6 Wh/kg and a Coulombic efficiency of 96.4%. These findings exhibit the potential of the ZnO–RGO hybrid nanocomposites as an electrode in high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

Supercapacitors and batteries are among the most promising electrochemical energy storage technologies available today. Indeed, high demands in energy storage devices require cost-effective fabrication and robust electroactive materials. In this review, we summarized recent progress and challenges made in the development of mostly nanostructured materials as well as fabrication routes for energy storage devices. Indeed, we systematically sorted out the design principles of electrode materials such as lithium-ion, lead-acid, lithium-sulfur, nickel-cadmium, nickel-metal hydride, and sodium-ion for rechargeable batteries electrode and supercapacitors (SCs) electrode materials following by systematic discussions on electric double-layer capacitors, pseudocapacitors, and hybrid SCs behavior. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of the electric double layer capacitor (EDLC) in reducing stress and prolonging the battery lifespan in a hybrid energy storage system (HESS). A 65 F, 16.2 V EDLC supercapacitor was connected in a laboratory experiment to produce its charge/discharge profile at a constant current of 5 and 10 A. The EDLC’s Faranda or “two branch model” mathematical parameters were extracted from the experimental charge/discharge profile. The extracted parameters were used as inputs to design the Python/MATLAB/Simulink (PMS)-hybrid model of the EDLC. The charge/discharge profiles of the simulated PMS model of the EDLC were then compared to the charge/discharge profiles derived from the experimental setup of the EDLC and were found to match. The PMS model of the EDLC was then used as a subcomponent in an HESS system modelled in MATLAB/Simulink. Using constant load conditions, the battery’s voltage, current, power and state of charge (SOC) were analyzed for a battery energy storage system (BESS) without a supercapacitor and then compared to an HESS system with a supercapacitor in an experimental setup. This process was repeated with the simulated PMS model of the EDLC in MATLAB/Simulink for HESS and without the EDLC for BESS. Finally using a variable load in an experimental setup, the battery’s voltage and current were analyzed for a BESS system and compared to an HESS system. All these data show that, in an HESS system with a supercapacitor, there is less stress on the battery with a load applied. This is indicated by the voltage and current values in an HESS system being consistently more stable with respect to time as compared to the BESS system. As a result, in an HESS system, the battery will have a longer lifespan.

Supercapacitors have attracted considerable attention because of their benefits in terms of high power density, rapid charge-discharge rates, and extended cycle life. Metal-organic framework materials (MOFs), known for their exceptionally high surface area and adjustable pore architectures, are extensively employed in the realm of energy conversion and storage. Nevertheless, the inadequate conductivity of MOF materials impedes their desirable electrochemical performances when employed as electrode materials in supercapacitors. We utilized a straightforward solvothermal technique to produce graphene-supported Cu/Mn-BTC metal-organic framework materials. These materials were then used as electrode materials for supercapacitors. Mn-BTC was effectively incorporated onto the surface and into the pores of Cu-BTC via solvothermal treatment. The incorporation of reduced graphene oxide (rGO) greatly increased the conductivity of MOF materials. In the three-electrode testing system, the graphene-supported Cu/Mn-BTC electrode material exhibited a specific capacitance of 362.2 C g−1 at the current density of 1 A g−1. Assembled into a symmetric supercapacitor, the novel material achieved a specific capacitance of 141.46 F g−1 at 1 A g−1, with a maximum energy density of 12.6 Wh kg−1 at a power density of 111.1 W kg−1. After 1000 charge-discharge cycles, the capacitance retention rate was 83.55 %. [Display omitted] • Innovative nanocomposites, i.e. rGO-supported dual metal organic frameworks, have been fabricated. • The novel material exhibits superior specific capacitance, rate capability, and long cycle life. • Symmetric supercapacitor device made up of this electrode material also exhibits better performances for practical application. [ABSTRACT FROM AUTHOR]

This paper investigates the characterization of an electric double-layer capacitor (EDLC). In this study, the 300 F and 400 F EDLC supercapacitors are connected in a circuit in a laboratory experiment to produce their charge/discharge profiles at a constant current. The acquired charge/discharge profiles were used to determine the mathematical parameters of the EDLCs using the “Faranda model”, or “two-branch model”, of the EDLC. The parameters extracted from the equivalent circuit model were then used as inputs to a designed Python/MATLAB/Simulink (PMS)-hybrid model of an EDLC. This was simulated to obtain charge/discharge profiles. The resulting experimental- and simulated-charge/discharge profiles of the EDLCs were compared with each other, by superimposing their profiles to determine the accuracy of the PMS model. The PMS model was found to be very accurate. The innovation of this work lies in modeling a supercapacitor, mostly in the Python programming language in combination with a MATLAB/Simulink model. The experimental-charge/discharge profiles obtained were used to calculate the equivalent circuit resistance (ESR) and the capacitance of the EDLCs, which were compared with the existing datasheet values of the EDLCs. The characterization of the EDLC supercapacitor was done to derive a flexible PMS model of the EDLC, which can be used in a microgrid hybrid energy-storage system (HESS) to show the potential of the EDLC in improving battery lifespan.

Electrodes from hydrothermally synthesized boron-incorporated reduced graphene oxide (B-rGO), Co3O4, and Co3O4/B-rGO nanocomposites are tested in 2 M KOH and NaOH electrolytes for supercapacitor applications. Structural characterization was done by x-ray diffraction and x-ray photoelectron spectroscopy. Cyclic voltammogram of B-rGO indicates partial electrical double-layer capacitance and pseudocapacitive behaviors. Co3O4, shows two reversible redox peaks, indicating diffusion-controlled (battery-like) process. Interestingly, Co3O4/B-rGO possesses both the pseudocapacitive and diffusion-controlled features. The specific capacitance (Csp) from galvanostatic charge/discharge experiments is higher in all the electrodes in KOH than in NaOH. Co3O4/B-rGO shows the highest Csp of 600 F g−1 (270 C g−1) at 0.1 A g−1 and 454 F g−1 (204 C g−1) at 10 A g−1 in KOH. Co3O4/B-rGO-KOH system retains 87.8% capacitance after 2000 cycles, demonstrating very good cyclic stability. Co3O4/B-rGO-KOH system yields, a remarkable, maximum power density of 2250 W kg−1 with an energy density of 12.77 W h kg−1 at 10 A g−1. The better performance in KOH is attributed to the low hydration sphere radius, high ionic conductivity of K+, low diffusive and charge transfer and electrode resistance, estimated from electrochemical impedance spectroscopy. The electrode–electrolyte combination is crucial for the overall performance as a supercapacitor electrode. [ABSTRACT FROM AUTHOR]

We demonstrate that few layer graphene (FLG), formed by high-shear exfoliation into an aqueous suspension, can be successfully employed as an 'active' conductive additive in flexible activated carbon-based aqueous electric double layer capacitor (supercapacitor) electrodes if introduced by a novel 'vacuum infiltration' technique. The effectiveness of the FLG can be optimised by tailoring its size distribution and loading. It is found that best performance is achieved using FLG with the broadest size distribution and, moreover, that the larger size distribution is effective over the broadest range of loading. With optimum size distribution and loading, FLG is shown to outperform a commercial carbon black conductive additive (Timcal C65). Electrodes containing 8 wt% infiltrated FLG have an equivalent series resistance (ESR) of 1. 3 ± 0. 4 Ω , and a specific capacitance of 142. 3 ± 0. 1 F g−1 over a voltage window of 1.2 V, compared with an ESR of 3 ± 1 Ω and a specific capacitance of 96. 81 ± 0. 02 F g−1 for equivalent electrodes produced with an optimal loading of carbon black additive. As a result, the specific energy density of electric double layer capacitors (EDLCs) produced with a vacuum infused FLG additive is demonstrated to be an average of 47 ± 3 % superior to those containing carbon black measured at similar power densities. In contrast to vacuum infiltration, direct mixing of FLG suspension into the electrodes is found to be ineffective, resulting in limited improvement relative to electrodes without conductive additive, the reasons for which are discussed. [Display omitted] • Few-layer graphene (FLG) is added to flexible EDLC electrodes as an active conductive additive. • A novel vacuum infiltration technique is developed to use FLG from an aqueous suspension. • Energy density improves by ≈ 50 % compared with optimal loading of a commercial carbon black. • Performance is governed by both FLG size distribution and loading. • Optimal performance is found for the broadest FLG size distribution. • Direct mixing of aqueous FLG suspension is inferior to vacuum infiltration. [ABSTRACT FROM AUTHOR]

Owing to their low cost, good performance, and high lifetime stability, activated carbons (ACs) with a large surface area rank among the most popular materials deployed in commercially available electrochemical double-layer (EDLC) capacitors. Here, we report a simple two-step synthetic procedure for the preparation of activated carbon from natural flax. Such ACs possess a very high specific surface area (1649 m2 g–1) accompanied by a microporous structure with the size of pores below 2 nm. These features are behind the extraordinary electrochemical performance of flax-derived ACs in terms of their high values of specific capacitance (500 F g–1 at a current density of 0.25 A g–1 in the three-electrode setup and 189 F g–1 at a current density of 0.5 A g–1 in two-electrode setup.), high-rate stability, and outstanding lifetime capability (85% retention after 150,000 charging/discharging cycles recorded at the high current density of 5 A g–1). These findings demonstrate that flax-based ACs have more than competitive potential compared to standard and commercially available activated carbons.

• Graphene balls and their composites are of interest for supercapacitors. • The recent studies were highlighted and discussed for perspective view. • Those materials are expected as promising energy storage system. In recent years, supercapacitors have received considerable research attention for energy storage systems due to their high-power density, fast charge-discharge processes, and long cycle life. The superior performance of supercapacitors is considerably dependent on the electrode materials. Among electrode materials, graphene balls (GBs) and their composites have recently attracted strong interest. They are considered ideal for the fabrication of electrode materials because of their unique characteristics of large specific surface area and superior electric conductivity, which should make them very effective for use in supercapacitors. In particular, GBs and their microstructured composites have recently been proven promising candidates for supercapacitor electrodes. Their unique 3D morphology provides highly porous graphene structures for decoration with active materials. In this perspective, recent studies were highlighted and discussed that focus on GBs and their composites for the potential energy storage devices called supercapacitors, (i.e., electric double layer capacitors and pseudocapacitors). [ABSTRACT FROM AUTHOR]

This study presents novel investigations of sulphur-graphitic nanoplatelet (S-GNP) and sulphur-microwave expanded graphene oxide (S-MWGO) composite electrodes for structural electrochemical double layer capacitors (EDLCs) with liquid organic electrolyte 1 M TEABF 4 (tetraethylammonium tetrafluoroborate) in propylene carbonate (PC). Elucidating the chemical structure of these electrodes, XPS (X-ray photoelectron spectroscopy) and Raman spectroscopy indicated the presence of C S S C links while mixed EDX (energy dispersive X-ray spectroscopy) elemental maps displayed elemental S outlining the edges of nanoplatelets, concluding the presence of S-links between nanoplatelets. While S-linking improved the mechanical properties and ensured structural integrity of the produced monoliths without the need of any binder, it also decreased the specific surface area of the resulting materials. Furthermore, additional sulphur might have been trapped in other forms, amounting to up to 26 wt% sulphur in the composite graphitic and graphene oxide-based electrodes. Three-point bend testing yielded that an S-GNP-MWCNT monolith with 20 wt% S and 0.24 wt% MWCNT exhibited similar mechanical properties to those of a rigid polyurethane foam. The same S-GNP-MWCNT monolith exhibited an average electrode capacitance of 12.2 F g−1 during discharge at 2.2 mA/cm2. An S-MWGO-MWCNT monolith electrode with 9.6 wt% S, 16.4 wt% carbon black and 0.24 wt% MWCNT exhibited an average electrode capacitance of 64.9 F g−1 during discharge at 2.2 mA/cm2 but higher resistance than the S-GNP electrodes. Image 1 • C S S C links in S-GNP and S-MWGO monoliths by XPS, Raman spectroscopy and EDX. • S-GNP-MWCNT monolith with 20 wt% S behaves mechanically as rigid polyurethane foam. • And in EDLC displays electrode capacitance of 12.2 F g−1 at 2.2 mA/cm2 • S-MWGO-MWCNT monolith in EDLC displays electrode capacitance of 64.9 F g−1. [ABSTRACT FROM AUTHOR]

Abstract In this work, a lithium ion capacitor (LIC) based on carbon electrodes prepared from furfuryl alcohol-derived polymers is presented. While furfuryl alcohol is not a new carbon precursor, it has been evaluated in the past mainly for negative electrodes with Li-ion insertion. Here we describe both an activated carbon (AC) and a hard carbon (HC) made from the same furfuryl alcohol-derived polymers, for both electrodes of the LIC. The polymerization technique used to make carbon from the furfuryl alcohol precursor is different from all the methods described earlier, and is flexible enough to make soft, high surface area AC, as well as a denser, low surface area HC. The HC and the HC-based negative electrode used in this study are targeted at a high-energy and high-power LIC application by specifically reducing the carbon particle size to sub-micrometric levels, using a HC with a specific surface area of ∼300 m2 g−1 and keeping the electrode mass loading to <2 mg cm−2. The HC delivers a stable capacity of ∼400 mAh g−1 vs. Li+/Li at C/10, with excellent capacity retention of 50% at 10C (>200 mAh g−1) and 25% at 50C (∼100 mAh g−1). The AC used for the capacitor-type positive electrode was activated to a specific surface area of ∼1670 m2 g−1. For comparison purposes, a symmetric electric double layer capacitor (EDLC) using the same AC, in a 1.5 M Et 4 NBF 4 (acetonitrile) electrolyte, was also fabricated. Overall, the LIC showed considerably higher energy density over its EDLC counterpart, delivering a maximum energy density (based on the total electrode active mass weight) of 150 Wh kg−1 AM at a power density of 150 W kg−1 AM , with a 66% retention of the initial energy at the highly demanding 10,000 W kg−1 AM power peak point. Additionally, long cycle life was measured, with 83% capacitance retention after 10,000 cycles. Graphical abstract Image 1 Highlights • Synthesis of Hard Carbon and Activated Carbon from furfuryl alcohol. • Development of ultrafast performing Hard Carbon (<100 mAh g−1 at 50C). • Fabrication of Lithium Ion Capacitor with mass balance 1:2 (HC:AC). • Fabrication of Lithium Ion Capacitor exceeding 100 Wh Kg−1 AM at 10 KW Kg−1 AM. • Lithium Ion Capacitor with 83% capacity retention after 10,000 cycles. [ABSTRACT FROM AUTHOR]

Supercapacitors have shown great potential as a possible solution to the increasing global demand for next-generation energy storage systems. Charge repositioning is based on physical or chemical mechanisms. There are three types of supercapacitors—the electrochemical double layer, the pseudocapacitor, and a hybrid of both. Each type is further subdivided according to the material used. Herein, a detailed overview of the working mechanism as well as a new method for capacitance enhancement are presented.

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]

In the present work, the cellulose-based materials were manufactured and used as components of electrochemical double layer capacitors (EDLCs). The preparation method of cellulose membranes as well as composite electrodes containing cellulose as a binder was presented. These materials were prepared using for the first time ionic liquid/dimethyl sulfoxide (IL/DMSO) mixture solvent. Obtained components displayed a uniform structure, thermal stability, and good electrochemical properties. The electrochemical performances of these materials were studied in 2-electrode EDLC cells by common electrochemical techniques as cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS). The composite electrodes were investigated in three types of electrolytes: aqueous, organic, and ionic liquids. The cellulose membranes were, however, soaked in an aqueous electrolyte and tested as hydrogel polymer electrolytes. All investigated materials show high efficiency in terms of specific capacity. The studied cellulose-based capacitors exhibited specific capacitance values in the range of 20-22 F g−1, depending on the type of applied electrolyte. [ABSTRACT FROM AUTHOR]

• Successful demonstration of hBN nanosheets via 3-step facile hydrothermal method. • An optimum temperature for ultrathin nanosheet preparation explored here. • Blue shift in resistance value upon stability analysis shows higher specific capacitance. • Coulombic efficiency of 97% was achieved after 2000 charge/discharge cycles. • Enhanced electrochemical performance proves hBN nanosheet as effective electrode. Due to atomically thin layer structure and high surface area, 2D layered materials exhibit promising physical, chemical, thermal, mechanical, electrical, and optical properties suitable for device fabrication, thus rendering hexagonal boron nitride (hBN) the most versatile material, showing diverse applications. However, there are many different methods for its synthesis or exfoliation, among which liquid exfoliation is most explored. In this work, 2D-hBN ultrathin nanosheets have been prepared by hydrothermal method at an optimum temperature. The well-prepared 2D-hBN was characterized by Transmission electron microscope (TEM), X-Ray Diffraction (XRD), and UV–Visible absorption spectroscopy (UV–Vis). Furthermore, the electrochemical studies of the well-prepared nanosheets were characterized using cyclic voltammetry, galvanostatic charge-discharge, and impedance spectroscopic. The specific capacitance of the prepared nanosheet was found to be 83 F/g at 2 mV/s, which is 4 folded values. Proper exfoliation significantly provides thin transparent morphology for 2D-hBN nanosheets with active surface area, contributing to enhanced electrochemical behavior upon cycling. Also, 97% of coulombic efficiency was achieved after performing 2000 charge-discharge cycles, proving that the 2D-hBN material has an exciting electrochemical characteristic despite its higher bandgap. This work infers that as an electrode material, 2D-hBN nanosheets have better prospects in the field of energy storage application. [Display omitted] [ABSTRACT FROM AUTHOR]

Present state-of-the-art graphene-based electrodes for supercapacitors remain far from commercial requirements in terms of high energy density. The realization of high energy supercapacitor electrodes remains challenging, because graphene-based electrode materials are synthesized by the chemical modification of graphene. The modified graphene electrodes have lower electrical conductivity than ideal graphene, and limited electrochemically active surface areas due to restacking, which hinders the access of electrolyte ions, resulting in a low energy density. In order to solve the issue of restacking and low electrical conductivity, we introduce thiol-functionalized, nitrogen-doped, reduced graphene oxide scrolls as the electrode materials for an electric double-layer supercapacitor. The fabricated supercapacitor exhibits a very high energy/power density of 206 Wh/kg (59.74 Wh/L)/496 W/kg at a current density of 0.25 A/g, and a high power/energy density of 32 kW/kg (9.8 kW/L)/9.58 Wh/kg at a current density of 50 A/g; it also operates in a voltage range of 0~4 V with excellent cyclic stability of more than 20,000 cycles. By suitably combining the scroll-based electrode and electrolyte material, this study presents a strategy for electrode design for next-generation energy storage devices with high energy density without compromising the power density.

In this work, we are presenting both lithium and sodium ion capacitors (LIC and NIC) entirely based on electrodes designed from recycled olive pit bio-waste derived carbon materials. On the one hand, olive pits were pyrolized to obtain a low specific surface area semigraphitic hard carbon to be used as the ion intercalation (battery-type) negative electrode. On the other hand, the same hard carbon was chemically activated with KOH to obtain a high specific surface area activated carbon that was further used as the ion-adsorption (capacitor-type) positive electrode. Both electrodes were custom-made to be assembled in a hybrid cell to either build a LIC or NIC in the corresponding Li- and Na-based electrolytes. For comparison purposes, a symmetric EDLC supercapacitor cell using the same activated carbon in 1.5 M Et 4 NBF 4 /acetonitrile electrolyte was also built. Both LIC and NIC systems demonstrate remarkable energy and power density enhancement over its EDLC counterpart while showing good cycle life. This breakthrough offers the possibility to easily fabricate versatile hybrid ion capacitors, covering a wide variety of applications where different requirements are demanded. [ABSTRACT FROM AUTHOR]

Self-powered electrochemical energy storage devices, which store energy upon application of mechanical force, have emerged as a promising technology for the realization of autonomous systems for maintenance-free, independent and multifunctional operations. However, the existing state-of-the-art technology demonstrates slow self-charging due to slow Faradaic reactions and intercalation mechanism. Here, we report a fast self-charging, self-powered electrochemical energy storage device owing to the formation of an electric double layer with fast adsorption and desorption of ions at the carbon nanotube (CNT) electrode upon application of mechanical force. The device charges up to 70 mV from the open-circuit potential, storing a capacitance of 95 μFcm −2 upon application of a mechanical pressure of 70 N at a frequency of 5 Hz. More importantly, it takes less than 10 s to achieve 90% of the increment in the potential (60 mV), which is more than one order of magnitude faster than all of the previously reported self-powered energy storage devices. [ABSTRACT FROM AUTHOR]

Electrochemical capacitor (EC) applications have broadened tremendously since EC energy storage devices were introduced in 1978. Then typical applications operated below 10 V at power levels below 1 W. Today many EC applications operate at voltages approaching 1000 V at power levels above 100 kW. This paper briefly reviews EC energy storage technology, shows representative applications using EC storage, and describes engineering approaches to design EC storage systems. Comparisons are made among storage systems designed to meet the same application power requirement but using different commercial electrochemical capacitor products. [ABSTRACT FROM AUTHOR]

Due to the low double-layer capacitance of activated carbons (<20 μF cm −2 ) and to their low density related to their large micro/meso porosity, the volumetric energy density of commercial supercapacitors remains low. Therefore, the use of pseudocapacitive oxides or nitrides as electrode materials can drastically improve the volumetric performance. However, there is currently a lack of reliable tools to extrapolate the performance of a 1 cm 2 electrode to a real life cell of several thousand farads. In this paper, we provide a calculation tool to extrapolate the cell capacitance and the energy density both from a gravimetric and volumetric point of view in a 399 cm 3 device. The calculation datasheet indicates that in order to improve the volumetric energy density of supercapacitors, it is crucial to lower the electrodes porosity down to 30–40%. Similarly, the use of high-density pseudocapacitive oxides greatly enhances the volumetric energy density of the related devices. Combining both parameters (porosity of 30%, density of 4.5 g cm −3 , active material capacitance of 250 F g −1 ) can lead to a 28000 F device compared to only 3000 F for a commercial cell of the same volume. The design of asymmetric aqueous devices by combining two high-density pseudocapacitive oxides with reasonable specific capacitance (≈100 F g −1 ) is also an interesting way to further improve the cell voltage and subsequently the volumetric energy density. Additionally, the use of aqueous electrolytes enhances the safety of the cells. Finally, the provided spreadsheet will help to envision different associations of pseudocapacitive and/or capacitive materials and to predict their performance when used in real life cells. [ABSTRACT FROM AUTHOR]

In this work, for the first time, we demonstrate a supercapacitive microbial fuel cell which integrates the energy harvesting function of a microbial fuel cell (MFC) with the high-power operation of an internal supercapacitor. The pursued strategies are: (i) the increase of the cell voltage by the use of high potential cathodes like bilirubin oxidase (BOx) or iron–aminoantipyrine (Fe–AAPyr); (ii) the use of an additional capacitive electrode (additional electrode, AdE) which is short-circuited with the MFC cathode and coupled with the MFC anode (MFC-AdE). The high working potential of BOx cathode and the low impedances of the additional capacitive electrode and the MFC anode permitted to achieve up to 19 mW (84.4 W m −2 , 152 W m −3 ), the highest power value ever reported for MFCs. Exploiting the supercapacitive properties of the MFC electrodes allows the system to be simpler, cheaper and more efficient without additional electronics management added with respect to an MFC/external supercapacitor coupling. The use of the AdE makes it possible to decouple energy and power and to achieve recharge times in the order of few seconds making the system appealing for practical applications. [ABSTRACT FROM AUTHOR]