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Wood-based activated carbons for supercapacitors with organic electrolyte

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Abstract

The thermocatalytical synthesis conditions required for the activation of wood charcoal with NaOH in terms of the formation of pores in its structure were investigated. The present study was conducted to explore the potential application of activated carbons as electrodes in supercapacitors with organic electrolyte. The total pore volume and micro- and mesopore ratio were controlled by the activation temperature and alkali addition rate. The working characteristics of carbon electrodes (e.g., specific capacity and ohmic losses) in supercapacitors are strongly influenced by the properties of the pores in their structures. Herein, the optimal ratio of raw material to activator and activation temperature are established: an increase in the ratio of NaOH to carbonizate rate by a factor of 2 and setting the synthesis temperature at 700°C positively influence the electrochemical characteristics of supercapacitors and provide them with specific capacities of up to 160 F g

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... Other areas of carbonaceous sorbent application are medicine and pharmaceutics as hemosorbents and enterosorbents. Lately carbonaceous nanomaterials are being applied as electrodes in supercapacitors and as oxygen reduction catalysts in fuel cells [6][7][8]. ...
... Electrode mass was not mentioned in that paper, although it may have had an impact on the performance of the supercapacitor [24]. Generally, higher electrode mass reduced the specific capacitance [10,11], while slower cycling rates increased the capacitance [25]. Based on the lower usable voltage window, aqueous electrolytes revealed generally lower specific energy than organic electrolytes. ...
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Willow bark is a byproduct from forestry and is obtained at an industrial scale. We upcycled this byproduct in a two-step procedure into sustainable electrode materials for symmetrical supercapacitors using organic electrolytes. The procedure employed precarbonization followed by carbonization using different types of KOH activation protocols. The obtained electrode materials had a hierarchically organized pore structure and featured a high specific surface area (>2500 m2 g−1) and pore volume (up to 1.48 cm3 g−1). The assembled supercapacitors exhibited capacitances up to 147 F g−1 in organic electrolytes concomitant with excellent cycling performance over 10,000 cycles at 0.6 A g−1 using coin cells. The best materials exhibited a capacity retention of 75% when changing scan rates from 2 to 100 mV s−1.
... In comparison with the published reported porous carbons electrode materials which were commonly synthesized by chemical activation methods (Table 2) [20,36,40,43,44,46,[54][55][56], the MMC electrode shows the competitive specific capacitance of 195 F g À1 at a discharge current density of 0.1 A g À1 . This result shows the formation uniform system of cellulose aerogels. ...
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Cellulose has been explored as a tentative renewable carbon source to convert into micro- and meso-porous carbon (MMC) via carbonizing cellulose aerogel at a temperature of 700 °C without further activation. The obtained MMC materials based on cellulose possess a specific surface area of 646 m² g⁻¹, a pore volume of 0.4403 m³ g⁻¹, with an optimal pore structure that consists of the micropores in average size of 1.49 nm and the mesopores in the range of 2.25 ∼ 3.32 nm. A two-electrode symmetric supercapacitor based on the MMC materials exhibits a comparable high electrochemical performance with a large capacitance (up to 160 F g⁻¹ at 0.2 A g⁻¹), an high energy density of 17.81 Wh kg⁻¹ at a power density of 180.11W kg⁻¹ in the voltage range of 0 V to 1.8 V. The mesoporous can provide a good channel to further facilitate the electrolyte ion penetrating inner pores, while the microporous can store more electrolyte ions. The above cooperative effect of MMC is the key to the high-performance of the supercapacitors.
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Echinus-like nitrogen-doped carbon with a hierarchical porous structure was synthesized from green larch waste and urea via liquid in situ doping and high-temperature carbonization. Benefitting from a large specific surface area (649 m ² g ⁻¹ ) and hierarchical porous structure, the nitrogen-doped carbon exhibited excellent electrochemical performance for supercapacitors. Remarkably, the echinus-like nitrogen-doped carbon achieved a high specific capacitance of 340 F g ⁻¹ at a current density of 1 A g ⁻¹ in 6 M KOH electrolyte as well as a good performance rate and stability (with a capacitance retention of 98% after 5000 cycles). This capacitance was almost 1.5 times higher than that of undoped carbon due to the contribution of the pseudocapacitance from the nitrogen doping. Larch sawdust is a promising carbon source for fabricating inexpensive, sustainable and high-performance supercapacitor materials.
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The chemical activation of anthracites with hydroxides has been shown to be of interest for the production of activated carbons with a highly microporous structure. In a previous paper, attention was placed on the reactions occurring during the chemical activation of an anthracite by NaOH and KOH. In the present work, the process of chemical activation by hydroxides has been extended to different coal precursors to confirm that such a chemical activation process starts through a solid–solid reaction and continues as a solid–liquid reaction. In such a solid reaction, the reactivity of the solid (precursor) should be a key parameter. The importance of the carbon reactivity on its reaction with hydroxides has been confirmed: the lowest rank coal reacts much easily and has a much lower temperature for the beginning of reaction than the highest rank coal.
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Highly microporous carbon materials with high apparent surface areas (up to 2400 m2·g−1) were obtained by heat treatment of mixtures of demineralized Kraft lignin and sodium hydroxide. The application of a statistical tool, the response surface methodology, was used to determine the optimum operation conditions for preparing activated carbon able to adsorb large quantities of organic compounds. For that purpose, three parameters were varied: temperature of activation, sodium hydroxide and demineralized Kraft lignin percent mass ratio, and nitrogen flow rate. This carbon was tested for the adsorption of methylene blue that is a model compound for the most usual organic pollutant behavior, such as dyes. The adsorption of methylene blue was 93.2 g/100 g activated carbon, and this has a high microporosity and a specific surface area of 2610 m2·g−1. The optimum preparation conditions of this best activated carbon were determined at 755 °C, 22.4 % Kraft lignin, and 200 cm3 N2·min−1.
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Carbon adsorbents (CAs) were made by heat treatment of a mixture of coal char and KOH under the protection of an inert argon flow and the influence of operating conditions on the properties of adsorbents was investigated. Changes in the characteristics of graphitic crystallites during manufacture by X-ray diffraction (XRD) analysis indicated that disappearance of the peak corresponding to 002 faces correlated to high specific surface area. Based on the experimental results, a new model of graphitic crystallites containing hydrogen atoms is proposed to calculate idealized surface area of CAs. With this model, the idealized surface areas of CA can be precisely calculated with the aid of X-ray diffraction. In this way, some experimental problems can be overcome, such as the difficulty to measure specific surface area with N2 adsorption when pore diameters are too small and overestimation when surface areas are too large.
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Chemical activation of carbons is currently a very common method for obtaining activated carbons with very high surface areas. KOH is one of the most effective agents employed for this purpose. However, the reaction mechanism of this kind of activation it is not yet completely elucidated, although some models have been proposed. In this paper, an activated charcoal was obtained from a lignocellulosic material by impregnation with different amounts of KOH. The activation process was studied by X-ray photoelectron spectroscopy and X-ray diffraction. These techniques point to the formation of different potassium compounds at the carbon surface (mainly K2CO3 and different oxides) and show the dependence between surface area development in the carbons and the amount of K2CO3 formed during the activation process.
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Activation of Quercus Agrifolia char with NaOH and KOH using a rotary batch reactor is presented in this work. Several samples of activated carbon showing a very high degree of activation with predominance of microporosity were obtained. Nitrogen and argon were used as gaseous media in the activation procedure. Samples were evaluated using nitrogen adsorption applying BET and DR equation for porosity assessment. The existence of CN− in activated samples suggests the occurrence of not previously reported chemical reactions in this process and could be an indication of the involvement of N2 in the chemical reaction. Following these results, some additional chemical reactions are proposed as part of the reaction mechanism for MeOH-C-N2 system.
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A detailed investigation was conducted about the process of alkali activation of charred rice hulls using NaOH. A carbon-rich precursor was initially prepared from the pyrolysis of rice hulls under N2 atmosphere, part of it being leached with HF to remove silica. The precursor was then mixed with NaOH, heat-treated at activation temperatures from 600 to 800 °C, and part of the product was finally washed with distilled water. Thermogravimetric curves under O2 flux showed a strong reduction in the ash content of the activated samples, indicating the consumption of silica during the activation process. From X-ray diffractometry, 29Si, and 23Na NMR spectroscopy, it was possible to identify the formation of sodium carbonate and silicates in the non-washed samples. After washing, all these compounds were removed and specific surface area measurements indicated a substantial porosity development, with larger surface area values obtained for the samples prepared from the HF-leached precursor. The use of 23Na NMR spectroscopy indicated the retention of sodium in the washed samples, in a chemical environment distinct from carbonates and silicates. The shapes and positions of the observed resonance lines pointed to a disordered environment, associated with oxygenated surface groups within the porous structure of the activated carbons.
Article
Activated carbons (ACs) were prepared by microwave-assisted heat treatment of petroleum coke with KOH as activation agent, and characterized by infrared spectroscopy and nitrogen adsorption technique with the aim of studying the effect of activation time on the properties of ACs for electrodes in electric double layer capacitors (EDLCs). The electrochemical properties of AC electrodes in EDLCs were studied by cyclic voltammetry, constant current charge–discharge and electrochemical impedance spectroscopy. The results show that the specific surface area (SBET) and total pore volume of ACs goes through a maximum as the activation time increases. At 35 min of the activation time, the as-made AC (denoted as AC-35) has a SBET of 2312 m2/g. With AC-35 as the electrode, its specific capacitance in EDLC at a current density of 50 mA/g can reach 342.8 F/g, and remains at 245.6 F/g even after 800 cycles while the energy density of the capacitor remains at 8.0 Wh/kg. The results have demonstrated that the microwave-assisted heat treatment is an efficient approach to the preparation of ACs with high performance for EDLCs.
Article
Direct mixing of an anthracite with hydroxides (KOH or NaOH) and heat treatment up to 730 °C has shown to be a very good activation procedure to obtain activated carbons with very high surface areas and high micropore volumes. The reactions involved during the heat treatment of these hydroxide/anthracite mixtures have been analysed to deep into the fundamental of the knowledge of this chemical activation process, that has not been studied before. For this purpose, the present paper analyses the drying process, the atmosphere during the carbonisation, the chemical state of the activating agents (NaOH, KOH and Na2CO3) and the chemical reactions occurring during the heat treatment which have been followed by FTIR and TPD. The analysis of our results allows us to conclude that steam is a good atmosphere for the carbonisation process, alone or joined with nitrogen, but not as good as pure nitrogen. On the other hand, during the activation process, the presence of CO2 should be avoided because it does not develop porosity. The reactions, and chemical changes, involved during this chemical process are discussed both from a thermodynamical point of view as well as identifying the reaction products (H2 by TPD and Na2CO3 by FTIR). As a result, this paper helps to cover the present lack of understanding of the fundamentals of the reactions of an anthracite with hydroxides which are necessary to understand the activation of the material.
Article
Three Japanese coals with different rank (Ohmine, Miike and Taiheiyo coals) were activated with KOH from 300 to 850 °C. Higher rank coal with lower oxygen content showed a high yield and also a large specific surface area determined by N2 adsorption isotherms. X-ray diffraction (XRD) patterns of the activated carbons were measured to characterize stacking structure of aromatic layers by standardized analysis of coal by XRD method, considering the presence of slit-shaped micropores among the stacking structure. Structural parameters obtained by this method were related to the yield and the surface area in order to discuss the feature of micropores developed during the activation.
Article
New information was obtained on the mechanism of porosity development during chemical activation by KOH and NaOH using various multiwalled nanotubes (MWNTs) of different structural organization. The high purity MWNTs were prepared by acetylene decomposition on a cobalt-based catalyst at different temperatures. The obtained samples ranged from MWNTs with well organised graphitic walls to nanotubes with disorganised layers mixed with some pyrolytic carbon when decreasing synthesis temperature. The results of transmission electron microscopy (TEM) observations were linked with gas adsorption measurements and X-ray diffraction data. They show that NaOH is only effective with disordered materials whereas KOH is effective whatever the structural order. After reaction of the poorly ordered precursor with KOH, the nanotubular morphology is completely destroyed, whereas it is preserved when NaOH is used. However for the more ordered materials, the morphology remains unchanged with both reactants. Effects of activation are only seen with KOH, which generated a large concentration of defects in the nanotubes walls. The differences found between KOH and NaOH during activation are related with an additional intercalation step of metallic K or Na produced during the redox reactions. It is shown that metallic K has the ability to be intercalated in all materials in contrast with Na which can only intercalate in the very disorganised ones. The conclusions obtained from the study on ordered nanotubes were confirmed with an ordered carbon black, demonstrating that the structural organization of the carbon precursor is an important parameter which must be taken into account when alkali reactants are used for the activation.
Book
The declared objective of this book is to provide an introductory review of the various theoretical and practical aspects of adsorption by powders and porous solids with particular reference to materials of technological importance. The primary aim is to meet the needs of students and non-specialists who are new to surface science or who wish to use the advanced techniques now available for the determination of surface area, pore size and surface characterization. In addition, a critical account is given of recent work on the adsorptive properties of activated carbons, oxides, clays and zeolites.
Article
Lignocellulosic materials are good and cheap precursors for the production of activated carbon. In this study, activated carbons were prepared from the pyrolysis of soybean oil cake at 600 and 800 degrees C by chemical activation with K(2)CO(3) and KOH. The influence of temperature and type of chemical reagents on the porosity development was investigated and discussed. K(2)CO(3) was found more effective than KOH as a chemical reagent under identical conditions in terms of both porosity development and yields of the activated carbons. The maximum surface area (1352.86 m(2)g(-1)) was obtained at 800 degrees C with K(2)CO(3) activation which lies in the range of commercial activated carbons. Elemental analyses of the activated carbons indicate insignificant sulphur content for all activated carbons. The ash and sulphur contents of the activated carbons obtained with chemical activation by K(2)CO(3) were lower than those by chemical activation with KOH.
Electrochemical capacitor carbons
  • S M Lipka
  • C R Swartz
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  • Tsyganova
Electrochemical Supercapacitors: Scientific Fundamentals and Technological Applications
  • B Conway
Synthesis and application of carbon sorbents
  • B N Kuznetsov
Synthesis of active carbons from birch wood modified by phosphoric acid and potassium hydroxide
  • S Tsyganova
  • I Korolkova
  • G Bondarenko
  • N Chesnokov
  • B Kuznetsov
Synthesis and application of carbon sorbents Educational
  • Kuznetsov
Activated Carbon Amsterdam
  • Marsh