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Porous carbon electrode materials are utilized in supercapacitors with very fast charge/discharge and high stability upon cycling thanks to their electrostatic charge storage mechanism. Further enhancement of the performance of such materials can be achieved by doping them with heteroatoms which alter the kinetics of charge/discharge of the adsorbed species and result in pseudocapacitance phenomena. Here, microporous N-doped activated carbons were synthesized by thermochemical activation process. The structure and composition of the final material were adjusted by tuning the synthesis conditions and the choice of precursor molecules. In particular, N-doped activated carbons with a controlled specific surface area in the range of 270–1380 m2/g have been prepared by KOH-activation of sucrose/ammonium citrate mixture. By adjusting the composition of precursors, N-doping was varied from ca. 1.5 to 7.3 at%. The role of the components and synthesis conditions on the composition and structure of final products has been evaluated. The N-doped activated carbon with optimized structure and composition has demonstrated an outstanding performance as electrode material for aqueous electrolyte supercapacitors. The specific capacitance measured in a 3-electrode cell with 0.75 mg/cm2 loading of optimized activated carbon in 1M H2SO4 changed from 359 F/g at 0.5 A/g charging rate to 243 F/g at 20 A/g. Less than 0.01% of capacitance loss has been detected after 1000 charging/discharging cycles. [ABSTRACT FROM AUTHOR]

This study used a physical activation method to prepare asphalt-pitch-derived activated carbon (Pitch AC) for an electric double-layer capacitor (EDLC) electrode. X-ray diffraction analysis and Raman spectroscopy were used to estimate the change in the crystal structure of Pitch AC with activation time. In addition, the textural properties of Pitch AC were studied by Brunauer-Emmett-Teller (BET), Dubinin-Radushkevich (DR) and non-localized density functional theory (NLDFT) equations with N2/77K isotherm adsorption-desorption curves. The electrochemical performance of the Pitch AC was analyzed using a coin-type EDLC with 1 M SBPBF4/PC via galvanostatic charge/discharge, cyclic voltammetry and electrochemical impedance spectroscopy. The specific surface area and total pore volume were 990–2040 m2/g and 0.42–1.51 cm3/g, respectively. The pore characteristics of the Pitch AC varied according to the activation time and changed from a microporous structure to a micro-mesoporous structure as the activation time increased. The electrochemical performance analysis also found that the specific capacity was increased from 43.6 F/g to 84.5 F/g at 0.1 A/g as activation time increased. In particular, Pitch AC-9 exhibited the best electrochemical performance (rectangular CV curve, reversible GCD, lowest ion charge transfer resistance and Warburg impedance). In addition, Pitch AC-9 was confirmed to have a specific capacitance similar to commercial activated carbon for EDLC (YP-50F). Therefore, it was considered that Pitch AC could replace commercial activated carbon for EDLC because it has excellent pore characteristics and electrochemical performance despite being manufactured through a very low-cost precursor and a simple process (physical activation method). [ABSTRACT FROM AUTHOR]

In this work, the activated carbon (AC) is derived from the waste material of peanut shells. The obtained activated carbon has been synthesized using the chemical activation process via impregnation with NaOH at various proportions (1:2 and 1:3). The structural, morphological, and electrochemical properties of obtained AC are examined by X-ray diffraction (XRD), BET surface analysis, scanning electron microscopy (SEM), and electrochemical techniques. The resulting AC shows the enhancement in specific surface area (SSA) from 584 to 735 m2/g at 1:2 ratio and 826 m2/g at 1:3 ratio after the activation process. The electrodes are fabricated using derived activated carbon for electrochemical characterization. It has been observed through cyclic voltammetry and galvanostatic charge–discharge measurements that 1:3 NaOH-activated samples reveal the maximum value of specific capacitance (263 F/g at 10 mV/s and 290 F/gat 0.2A/g). The sample also conveys the pre-dominant ~ 98% of efficiency from 400 to 1000th cycle with fast and almost constant capacitance. The electrochemical impedance spectroscopy (EIS) result suggests the pure capacitive nature of the sample and indicates the dominating electric double-layer capacitive (EDLC) behavior. The obtained results demonstrate that the peanut shell–derived activated carbon is a potential candidate as an electrode material for supercapacitors. [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.

In this study, the real‐time increase in pressure of the accumulated gases at the electrode/electrolyte interface serves as a safety criterion for four conductive electrolytes comprising acetonitrile (ACN) and organic salts. They include tetrafluoroborate as an anion and cyclic 1,1‐dimethylpyrrolidinium (Pyr11+), spiro‐(1,1′)‐bipyrrolidinium (SBP+), acyclic methyl triethyl ammonium (Et3MeN+) or standard tetraethylammonium (Et4N+) as cations. The main focus lies on the SPBF4/ACN system. While the concentrated Pyr11BF4/ACN exhibits a minimal pressure evolution (≈25 Pa) under ambient conditions at 3.0 V, its electrochemical stability is inferior to SPBF4 at high operating voltage. The electrolytes with acyclic tetrafluoroborate salts (1.0 mol L−1) reveal a 20‐fold increase in pressure due to the weak salt‐ACN interactions and the subsequent high solvent evaporation. The pressure evolution at the interface of activated carbon/electrolyte in electrochemical double layer capacitor (EDLCs) is merely related to the operating voltage and cation nature, viz. Pyr11+ < SBP+ < Et4N+ < Et3MeN+. The fixed specific capacity of 109 F g−1, volumetric capacity of 76 F cm−3, and moderate gas generation (≈190 Pa at 3.0 V, that shifts to ≈400 Pa at 3.4 V) confirm the safe character of the SPBF4/ACN electrolyte for such energy storage devices. [ABSTRACT FROM AUTHOR]

• 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]

Abstract In this study, the real‐time increase in pressure of the accumulated gases at the electrode/electrolyte interface serves as a safety criterion for four conductive electrolytes comprising acetonitrile (ACN) and organic salts. They include tetrafluoroborate as an anion and cyclic 1,1‐dimethylpyrrolidinium (Pyr11+), spiro‐(1,1′)‐bipyrrolidinium (SBP+), acyclic methyl triethyl ammonium (Et3MeN+) or standard tetraethylammonium (Et4N+) as cations. The main focus lies on the SPBF4/ACN system. While the concentrated Pyr11BF4/ACN exhibits a minimal pressure evolution (≈25 Pa) under ambient conditions at 3.0 V, its electrochemical stability is inferior to SPBF4 at high operating voltage. The electrolytes with acyclic tetrafluoroborate salts (1.0 mol L−1) reveal a 20‐fold increase in pressure due to the weak salt‐ACN interactions and the subsequent high solvent evaporation. The pressure evolution at the interface of activated carbon/electrolyte in electrochemical double layer capacitor (EDLCs) is merely related to the operating voltage and cation nature, viz. Pyr11+ < SBP+ < Et4N+ < Et3MeN+. The fixed specific capacity of 109 F g−1, volumetric capacity of 76 F cm−3, and moderate gas generation (≈190 Pa at 3.0 V, that shifts to ≈400 Pa at 3.4 V) confirm the safe character of the SPBF4/ACN electrolyte for such energy storage devices.

Porous carbon electrode materials are utilized in supercapacitors with very fast charge/discharge and high stability upon cycling thanks to their electrostatic charge storage mechanism. Further enhancement of the performance of such materials can be achieved by doping them with heteroatoms which alter the kinetics of charge/discharge of the adsorbed species and result in pseudocapacitance phenomena. Here, microporous N-doped activated carbons were synthesized by thermochemical activation process. The structure and composition of the final material were adjusted by tuning the synthesis conditions and the choice of precursor molecules. In particular, N-doped activated carbons with a controlled specific surface area in the range of 270–1380 m2/g have been prepared by KOH-activation of sucrose/ammonium citrate mixture. By adjusting the composition of precursors, N-doping was varied from ca. 1.5 to 7.3 at%. The role of the components and synthesis conditions on the composition and structure of final products has been evaluated. The N-doped activated carbon with optimized structure and composition has demonstrated an outstanding performance as electrode material for aqueous electrolyte supercapacitors. The specific capacitance measured in a 3-electrode cell with 0.75 mg/cm2 loading of optimized activated carbon in 1M H2SO4 changed from 359 F/g at 0.5 A/g charging rate to 243 F/g at 20 A/g. Less than 0.01% of capacitance loss has been detected after 1000 charging/discharging cycles.

In this work, the electrodes of a microbial desalination cell (MDC) are investigated as the positive and negative electrodes of an internal supercapacitor. The resulting system has been named a supercapacitive microbial desalination cell (SC-MDC). The electrodes are self-polarized by the red-ox reactions and therefore the anode acts as a negative electrode and the cathode as a positive electrode of the internal supercapacitor. In order to overcome cathodic losses, an additional capacitive electrode (AdE) was added and short-circuited with the SC-MDC cathode (SC-MDC-AdE). A total of 7600 discharge/self-recharge cycles (equivalent to 44 h of operation) of SC-MDC-AdE with a desalination chamber filled with an aqueous solution of 30 g L-1 NaCl are reported. The same reactor system was operated with real seawater collected from Pacific Ocean for 88 h (15,100 cycles). Maximum power generated was 1.63 ± 0.04 W m-2 for SC-MDC and 3.01 ± 0.01 W m-2 for SC-MDC-AdE. Solution conductivity in the desalination reactor decreased by ∼50% after 23 h and by more than 60% after 44 h. There was no observable change in the pH during cell operation. Power/current pulses were generated without an external power supply.

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]

Copyright of Revista de la Academia Colombiana de Ciencias Exactas, Físicas y Naturales is the property of Academia Colombiana de Ciencias Exactas, Fisicas y Naturales and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Laser‐induced graphene (LIG) is under the spotlight as a promising material for flexible supercapacitors due to its simple processing and flexibility. However, the poor conductivity and the reduced surface area have prompted research to improve its performance, traditionally introducing a pseudocapacitive behavior. Herein an effective yet easy way is presented to dramatically improve the electric double layer capacitance of LIG electrodes for supercapacitor‐related applications without the occurrence of redox reactions. The strategy simply relies on the exploitation of an LIG network to trap and interconnect activated carbon (AC) particles. In order to optimize the infiltration of AC into LIG porosities, several strategies are tested, both varying the surface wettability of LIG and acting on the impregnation approach. Overall, the best compromise results in the combination of LIG N‐doping by nitric acid incubation with vacuum‐assisted infiltration of an AC‐slurry, allowing a two‐order of magnitude improvement in the specific capacitance up to 20 mF cm−2 in device configuration. [ABSTRACT FROM AUTHOR]

Electric double layer capacitors are energy storage devices with advantages of fast charge-discharge and long life span. Surface modification of activated carbon electrodes is an effective way to improve their performance. For this purpose, deoxofluorination of activated carbon with sulfur tetrafluoride was attempted in this study. Successful introduction of fluorine atom on the surface of activated carbon resulted in the increased capacitance and improved coulombic efficiencies in electrochemical tests for electric double layer capacitors.

Copyright of Electronic Components & Materials is the property of Electronic Components & Materials and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The electric double-layer capacitor (EDLC) has attracted attention by using activated carbon (AC) as an active electrode material with a high power density and high cost-efficiency in industrial applications. The EDLC has been actively developed over the past decade to improve the power density and capacitance. Extensive studies on EDLCs have been conducted to investigate the relation of EDLC capacitance to the physical properties of AC, such as the specific surface area, pore type and size, and electrical conductivity. In this study, EDLC was fabricated with AC, and its capacitance was evaluated with the physical properties of AC. The AC was prepared using petroleum-based pitch synthesized using pyrolysis fuel oil (PFO) with polyethylene terephthalate (PET). The AC based on PFO and PET (PPAC) exhibited high specific surface area and low micropore fraction compared to the PFO-based AC without PET addition (PAC). Furthermore, the reduction of the EDLC capacitance of PPAC was smaller than that of PAC, as the scan rate was increased from 5 to 100 mV s−1. It was determined that the minor reduction of capacitance with an increase in the scan rate resulted from the development of 4 nm-sized mesopores in PPAC. In addition, a comprehensive correlation of EDLC capacitance with various physical properties of ACs, such as specific surface area, pore characteristics, and electrical conductivity, was established. Finally, the optimal properties of AC were thereupon derived to improve the EDLC capacitance.

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.

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]

Abstract Development of biomass based activated carbon materials for electrical double layer capacitor (EDLC) usage has gained attention as a result of requesting efficient and low cost energy storage device production. In this study, pine cone based activated carbons were produced with a combined chemical and physical activation route. ZnCl 2 and CO 2 were used for chemical and physical activation of the material, respectively. Activation parameters are adjusted to give different chemical and textural characteristics. FTIR and Raman spectroscopies were used for functional group identification and structural order characterization, respectively. As a result, efficient active materials for EDLC usage were obtained, with as high as 87 F/g specific capacitance in organic electrolytes. Highlights • Activated carbons were produced using combined chemical and physical activation. • Impregnation ratio was the most important parameter regarding the porosity. • Heat treatment temperature altered the structural evolution of activated carbon. • Resistivity of the active material has a pronounced effect on electrochemical behavior. • CO 2 treated activated carbons showed as high as 87 F/g specific capacitance. [ABSTRACT FROM AUTHOR]

Carbonization and post-activation of polysaccharides (utilized as food residue) created new bio-nanocarbons for the electrode of electric double layer capacitors (EDLC). Large specific capacitance (46.1 F/g, 26.4 F/cm 3 ) and high rate performance was confirmed under optimized conditions of carbonization temperature (600 °C) and supplied amount of sodium hydroxide in NaOH-activation process (250 wt %). The capacitance and rate performance were larger than the reported values, 42.9 F/g, 19.7 F/cm 3 of currently used activated carbon MSP-20. The feature that NaOH is usable as the activation agent, instead of KOH, is advantageous for reducing the cost of EDLC. [ABSTRACT FROM AUTHOR]

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]

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 manuscript are reported the synthesis and physicochemical characterization of low viscosity pyrrolidinium dicyanamide (DCA − ) ionic liquids (ILs). Due to their high ionic conductivity, these fluorine-free, molecular solvent-free ILs are excellent candidates to be employed as electrolytes in electrochemical double layer capacitors (EDLCs). Tests of lab-scale prototypes reported herein show that DCA − -based EDLCs display high power at room temperature as well as high cycling stability. [ABSTRACT FROM AUTHOR]

Lithium oxalyldifluoroborate (LiODFB) has several unique characteristics, such as high ionic conductivity over a wide temperature range and the ability to form and stabilize solid electrolyte interface films on graphite surfaces. A series of binary, room-temperature, molten electrolytes composed of LiODFB and organic compounds with acylamino groups (acetamide, oxazolidinone or OZO) have been synthesized. Fourier-transform infrared (FT-IR) spectroscopy indicates that C O and N–H functional groups undergo blue or red shifts upon addition of LiODFB. The electrolytes have excellent thermal stabilities and electrochemical characteristics that allow them to be promising electrolytes for electrochemical double layer capacitors (EDLCs). Here, we examine 1:5 molar ratio LiODFB and acetamide/OZO ionic liquid (IL) electrolytes in EDLCs. IL compatibility with two types of carbon-based electrodes is investigated theoretically and experimentally. We simulate possible structures and ion diameters for the ILs, which must be compatible with pore sizes of the carbon electrodes. Mesoporous activated carbon AC2, with a pore size similar to the ionic diameter of LiODFB–acetamide, has a specific capacitance of 154.2 Fg −1 at 20 m Ag −1 . Additionally, typical capacitive and reversibility behaviors can be seen in the charge–discharge curves over 0–2 V. Finally, the EDLCs exhibit good charging/discharging performances. [ABSTRACT FROM AUTHOR]

Electrical double layer capacitors (EDLCs) with HyperCoal-derived activated carbons (ACs) as electrodes are reported in this work. The ACs were prepared by the carbonization of HyperCoal at 600°C followed by the activation with KOH and NaOH for 2h between 500 and 800°C to achieve high total pore volume (TPV) and specific surface area (SSA). The porosity of the ACs was characterized with N2 adsorption at 77K. The results show that the ACs prepared with KOH and NaOH activations at 700°C have a SSA of 2594 and 3010m2 g−1 and a TPV of 1.36 and 1.77cm3 g−1, respectively, leading to the highest specific capacitance of 43.1 and 43.9Fg−1, respectively, in a two-electrode EDLC cell with 0.5M tetraethylammonium tetrafluoroborate/propylene carbonate (TEABF4/PC) electrolyte. Activations with CaCO3 and KOH/CaCO3 mixture were also investigated to understand the effect of CaCO3 on the properties of the ACs. CaCO3 significantly inhibited the porosity development during KOH activation and gave ACs with quite low SSA and specific capacitance. The results demonstrated that the alkaline hydroxide activation is an efficient approach to the preparation of ACs from HyperCoal with high-performance for EDLCs. [ABSTRACT FROM AUTHOR]

Abstract: Carbon aerogel (CA) was prepared by a carbonization of resorcinol–formaldehyde (RF) polymer gels, and it was chemically activated with KOH to obtain activated carbon aerogel (ACA) for electrode material for EDLC in organic electrolyte. Coin-type EDLC cells with two symmetrical carbon electrode were assembled using the prepared carbon materials. Electrochemical performance of the carbon electrodes was measured by galvanostatic charge/discharge and cyclic voltammetry methods. Activated carbon aerogel (20.9 F/g) showed much higher specific capacitance than carbon aerogel (7.9 F/g) and commercial activated carbon (8.5 F/g) at a scan rate of 100 mV/s. This indicates that chemical activation with KOH served as an efficient method to improve electrochemical performance of carbon aerogel for EDLC electrode in organic electrolyte. The enhanced electrochemical performance of activated carbon aerogel was attributed to the high effective surface area and the well-developed pore structure with appropriate pore size obtained from activation with KOH. [Copyright &y& Elsevier]

Highlights: [•] The HyperCoal based ACs for EDLCs were prepared by single step direct KOH-activation. [•] The capacitance of ACs not only depends on surface area, but also on pore size distribution. [•] AC-500 shows the capacitance of 46.0Fg−1 and BET surface area of 2540m2 g−1. [•] HyperCoal is an excellent and low-cost candidate for manufacturing ACs for EDLC. [ABSTRACT FROM AUTHOR]

Abstract: Electrochemical double layer capacitor cells were fabricated based on electrodes with activated carbon (AC) coating as the host material, targeting large energy storage. Highly dispersed multiwall carbon nanotubes (MWNTs) were added to form nanocomposite coatings, used as electrodes targeting high-power performance for very low content of MWNTs. 1M tetraethylammonium tetrafluoroborate–propylene carbonate solution was used as organic electrolyte. The resulting cells were characterized using impedance spectroscopy, cyclic voltammetry, and galvanostatic charge–discharge tests. It was concluded that at optimum composition of AC–MWNT coatings both power and energy densities are raised whereas further increase of the MWNT content would increase the power density but decrease the energy density. [Copyright &y& Elsevier]

In the present work we show results related with the influence of the binder type used to elaborate active electrodes made of activated carbon (DLC) for the assembly of supercapacitor cells. A Nafion 5%w solution and/or Kinar Flex (Polyvinylidene fluoride, PVDF) were used as binders at different concentrations, using DLC carbon as the active material to make the electrodes by aerography, and carbon paper as support and current collector. Thickness of the electrodes was controlled by the weight of active material (DLC carbon). Cyclic voltammetry technique was used to investigate the intrinsic capacitive nature of these electrodes, increasing this value from 120 F/g to 245 F/g at 20 mV/s just by improving the type and amount of binder, and the thickness of the electrode. Symmetric 2-electrode cells assembled with binder-free electrodes were electrochemically characterized by galvanostatic cycling, showing capacitance values of 38F/g and a stable behavior during 7000 charge-discharge cycles. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we investigated the role of fluorination in improving the electrochemical properties of activated carbon nanofiber (ACNF) electrodes. The ACNFs were prepared with various textural properties and then fluorinated. The electrochemical properties of the resulting ACNFs were subsequently evaluated to investigate the effect of the fluorination of the prepared ACNFs with various textural properties on the electrochemical properties. The specific capacitances of the ACNF electrodes increased by 15.8–47.3% after fluorination, although the specific surface area and the total pore volume decreased significantly; these results suggest that the introduction of C F functional groups onto the ACNF surface was more important than the induction of changes in the textural properties of the ACNF samples with respect to improving the electrochemical properties of the ACNF electrodes. The retained capacitances of the ACNF electrodes also increased 2–12% after fluorination, although the etching effect of the fluorination significantly collapsed the mesopores; these results suggest that the C F functional groups were electrochemically active even at a high scan rate. [Copyright &y& Elsevier]

Abstract: An electric double-layer capacitor (EDLC) was tested using load tests involving charging/discharging at 60°C for 17h using an electrolyte consisting of a solution of 1moll−1 of tetraethylammonium tetrafluoroborate (TEA·BF4) in sulfolane (SL) in order to examine the deterioration of the properties of the EDLC, including its capacitance. The interactions between the molecules of the electrolyte and the surface of the activated-carbon electrode were investigated by solid-state 13C-MAS-NMR spectroscopy. The molecules (ions) adsorbed on the surfaces of the positive and negative electrodes and the free molecules (ions) in liquid phase were clearly detectable by solid-sate 13C-MAS-NMR. In the blank spectrum, corresponding to the electrode prior to the load test, four pairs of sharp and broad peaks could be observed. Two sharp peaks from the liquid-phase SL appeared at about 24ppm and 52ppm, respectively, and those for the adsorbed molecules on the electrode surface appeared at about 17ppm and 45ppm, respectively, both being shifted to a higher magnetic field by about 7ppm. The peak shapes of the latter two adsorbed molecules were much broader than those in liquid phase, suggesting stronger interaction with the electrode surface and restriction of molecular movement. Two pairs of such sharp and broad peaks could also be observed for the TEA molecule, which contained two types of carbon atoms. The chemical shifts of the peaks of the adsorbed molecules gradually shifted to a lower magnetic field after the load test at higher voltages ranging from 0.7V to 1.3V. Such changes in the chemical shift of adsorbed molecules were intimately related to the weaker adsorption forces acting on the adsorbed molecules, indicating that the electrode surface had been deteriorated by the load test at higher voltages. On the basis of these solid-state 13C-MAS-NMR spectra, the deterioration mechanism of the EDLC electrode at higher temperatures was discussed. [Copyright &y& Elsevier]

Abstract: A facile and green preparation of high surface area activated carbons with mixed microporosity and mesoporosity from durian shell waste is reported in this work. The pore structure and surface chemistry of the parent carbon were modified by the combination of ultrasonication and microwave irradiation techniques. The effects of temperature and time in the ultrasonication treatment and power output and time in the microwave irradiation were studied. The electrochemical performance of carbon electrodes for supercapacitors was tested by cyclic voltammeter (CV) and galvanostatic charge–discharge. The results show that the capacitive energy storage of electrodes is critically dependent on the microporosity and surface chemistry of activated carbons. The highest electrode capacitance in this work was 103.6F/g that prepared from activated carbon modified at an ultrasonication temperature of 323.15K for 10min and microwave power output of 900W for 10min. [Copyright &y& Elsevier]

Abstract: Electrochemical double layer supercapacitor cells were fabricated and tested using composite electrodes of activated carbon with carbon black and poly(3,4-ethylenedioxythiophene) (PEDOT), and an organic electrolyte 1M TEABF4/PC solution. The effect of PEDOT on the performance of the EDLC cells was explored and the cells were characterised by electrochemical impedance spectroscopy (EIS), cyclic voltammetry and galvanostatic charge–discharge. A generalised equivalent circuit model was developed for which numerical simulations were performed to determine the properties and parameters of its components from the EIS data. It was found that the proposed model fitted successfully the data of all tested cells. PEDOT enhanced the electrode and cell capacitance via its pseudo-capacitance effect up to a maximum value for an optimum PEDOT loading and greatly increased the energy density of the cell while the maximum power density has been still maintained at supercapacitor levels. Furthermore, PEDOT replaced PVDF as a binder and harmful solvent release was reduced during electrode processing. Activated carbon–carbon black composite electrodes with PEDOT as binder were found to have specific capacitance superior to that of activated carbon–carbon black electrodes with PVDF binder. [Copyright &y& Elsevier]

Abstract: This study introduces amino-fluorination, a novel chemical modification method for activated carbon (AC), and investigates the surface and electrochemical properties of the resulting AC. The procedure was modified by controlling the surface reaction with concentrated ammonium hydroxide and diluted hydrofluoric acid or diluted ammonium hydroxide and concentrated hydrofluoric acid. Amino-fluorination of AC with concentrated ammonium hydroxide and diluted hydrofluoric acid significantly increased the specific surface area, total pore volume, mesopore volume, and number of N- and F-containing surface functional groups and decreased the number of O-containing surface functional groups. These changes resulted in improving the specific capacity to 417F/g at a scan rate of 10mVs−1 from the specific capacity of raw AC-based EDLCs (241F/g). On the other hand, amino-fluorination of AC with diluted ammonium hydroxide and concentrated hydrofluoric acid increased the specific surface area, total pore volume, mesopore volume, and number of N-, O-, and F-containing surface functional groups. These changes resulted in the highest specific capacitance for the prepared AC-based EDLCs (485F/g), with a 101% increase compared to the raw-AC-based EDLCs. Therefore, the amino-fluorination of AC is a simple and efficient way to enhance the performance of AC-based EDLCs. [Copyright &y& Elsevier]

Abstract: The application of poly(2-methoxyaniline-5-sulfonic acid), PMAS, as a molecular template in a bi-layered co-polymerisation process onto a microporous activated carbon fibre is presented. This process produces a bound, compact molecular layer of PMAS, onto which polyaniline (PAni) or polypyrrole (PPy) is co-polymerized as a thin permeable layer coating the surface of the carbon fibre. The physical porous structure of the coated carbon fibre is examined via multi-point isothermal N2 adsorption at 77K. Surface area and porosity data, calculated using BET and Density Functional Theory (DFT) models, indicates that the majority of the microporosity of the activated carbon fibre is still accessible after polymer deposition. Voltammetry and impedance data, in an aqueous electrolyte (1M H2SO4), is presented to show the enhancement of the capacitance and resistance properties of the composite material and the benefit of these improvements to its use as a supercapacitor electrode material. Formation of the bi-layer carbon fibre composite resulted in an effective increase in capacitance; from 125Fg−1 for the untreated carbon substrate, to as high as 222Fg−1 for the PAMS/PAni treated sample. The latter result represents a 69% improvement in capacitance and is attributed to the additional pseudocapacitive contribution of the ECP and the preservation of double-layer capacitance through the retention of fibre microporosity. Impedance analysis of the PMAS/PAni composite sample estimates the materials’ intrinsic resistance to be R s =3.7Ω and distributed pore resistances (ΩDPR) of 2.8Ω; compared to R s =1.8Ω and ΩDPR =6.4Ω for the untreated carbon substrate. [Copyright &y& Elsevier]

The electric double-layer capacitor (EDLC) has attracted attention by using activated carbon (AC) as an active electrode material with a high power density and high cost-efficiency in industrial applications. The EDLC has been actively developed over the past decade to improve the power density and capacitance. Extensive studies on EDLCs have been conducted to investigate the relation of EDLC capacitance to the physical properties of AC, such as the specific surface area, pore type and size, and electrical conductivity. In this study, EDLC was fabricated with AC, and its capacitance was evaluated with the physical properties of AC. The AC was prepared using petroleum-based pitch synthesized using pyrolysis fuel oil (PFO) with polyethylene terephthalate (PET). The AC based on PFO and PET (PPAC) exhibited high specific surface area and low micropore fraction compared to the PFO-based AC without PET addition (PAC). Furthermore, the reduction of the EDLC capacitance of PPAC was smaller than that of PAC, as the scan rate was increased from 5 to 100 mV s−1. It was determined that the minor reduction of capacitance with an increase in the scan rate resulted from the development of 4 nm-sized mesopores in PPAC. In addition, a comprehensive correlation of EDLC capacitance with various physical properties of ACs, such as specific surface area, pore characteristics, and electrical conductivity, was established. Finally, the optimal properties of AC were thereupon derived to improve the EDLC capacitance. [ABSTRACT FROM AUTHOR]

Abstract: Nano-sized carbon fibers were prepared by using electrospinning, and their electrochemical properties were investigated as a possible electrode material for use as an electric double-layer capacitor (EDLC). To improve the electrode capacitance of EDLC, we implemented a three-step optimization. First, metal catalyst was introduced into the carbon fibers due to the excellent conductivity of metal. Vanadium pentoxide was used because it could be converted to vanadium for improved conductivity as the pore structure develops during the carbonization step. Vanadium catalyst was well dispersed in the carbon fibers, improving the capacitance of the electrode. Second, pore-size development was manipulated to obtain small mesopore sizes ranging from 2 to 5 nm. Through chemical activation, carbon fibers with controlled pore sizes were prepared with a high specific surface and pore volume, and their pore structure was investigated by using a BET apparatus. Finally, polyacrylonitrile was used as a carbon precursor to enrich for nitrogen content in the final product because nitrogen is known to improve electrode capacitance. Ultimately, the electrospun activated carbon fibers containing vanadium show improved functionality in charge/discharge, cyclic voltammetry, and specific capacitance compared with other samples because of an optimal combination of vanadium, nitrogen, and fixed pore structures. [Copyright &y& Elsevier]

Abstract: Mesoporous activated carbon samples were prepared from electrospun PAN-based carbon fibers using physical activation with silica. Textural characterization was performed using nitrogen adsorption at 77 K. The BET specific surface area and pore size distribution of silica activated carbon materials were investigated. According to the increment of silica, BET specific surface area was increased about thirty times and it was found that silica activated carbon materials were highly mesoporous by studying pore surface distribution and pore volume distribution. Surface morphology of silica activated carbon materials were observed by SEM images. The spherical typed carbon materials were investigated. The diameter of spherical typed carbon materials was increased in proportional of the increment of silica. [Copyright &y& Elsevier]

Abstract: Activated and high-energy milled carbons were halide modified via a vapor phase deposition of iodine. The physical and electrochemical properties of carbons iodated under various conditions were investigated. The iodine incorporation induced marked structural and electrochemical modification of activated carbons. These compounds resulted in a unique combination of high volumetric/gravimetric capacity. Specifically, the incorporation of halide leads to a 200–500% increase in volumetric capacity of carbon materials. The resulting improvement is brought about through a modification of the non-Faradaic performance and development of a psuedocapacitive reaction at approximately 3.1V. Both of these reactions have contributed to the higher volumetric capacity and are investigated relative to the synthesis conditions of the compound. [Copyright &y& Elsevier]