Relationship between the nanoporous texture of activated carbons and their capacitance properties in different electrolytes (original) (raw)
Related papers
Effect of pore size distribution of coal-based activated carbons on double layer capacitance
Electrochimica Acta, 2005
A series of coal-based activated carbons representing a wide range of mesopore content, from 16.7 to 86.9%, were investigated as an electrode in electric double layer capacitors (EDLCs) in 1 mol l −1 H 2 SO 4 and 6 mol l −1 KOH electrolytic solutions. The activated carbons (ACs) used in this study were produced from chemically modified lignite, subbituminous and bituminous coals by carbonization and subsequent activation with steam. The BET surface area of ACs studied ranged from 340 to 1270 m 2 g −1 . The performance of ACs as EDLC electrodes was characterized using voltammetry, galvanostatic charge/discharge and impedance spectroscopy measurements. For the carbons with surface area up to 1000 m 2 g −1 , the higher BET surface area the higher specific capacitance (F g −1 ) for both electrolytes. The surface capacitance (F cm −2 ) increases also with the mesopore content. The optimum range of mesopore content in terms of the use of ACs studied for EDLCs was found to be between 20 and 50%. A maximum capacitance exceeding 160 F g −1 and a relatively high surface capacitance about 16 F cm −2 measured in H 2 SO 4 solution were achieved for the AC prepared from a sulfonated subbituminous coal. This study shows that the ACs produced from coals exhibit a better performance as an electrode material of EDLC in H 2 SO 4 than in KOH electrolytic solutions. For KOH, the capacitance per unit mesopore surface is slightly lower than that referred to unit micropore surface (9.1 versus 10.1 F cm −2 ). However, in the case of H 2 SO 4 the former capacitance is double and even higher compared with the latter (23.1 versus 9.8 F cm −2 ). On the other hand, the capacitance per micropore surface area is the same in both electrolytes used, about 10.0 F cm −2 .
Effects of thermal treatment of activated carbon on the electrochemical behaviour in supercapacitors
This paper studies the electrochemical behaviour of activated carbons with different oxygen content and investigates the contribution of pseudocapacitance to the global behaviour of the samples. A mesophase-derived activated carbon was further heat treated to 600 or 1000 °C in nitrogen. The changes in texture and surface chemistry induced by the thermal treatment were deeply studied. The electrochemical behaviour of the samples was studied in two- and three-electrode cells. The contribution of pseudocapacitance was evaluated by cyclic voltammetry and by the differences of specific capacitance obtained from galvanostatic tests performed in acidic (H2SO4) and basic (KOH) media. The presence of an extra capacitance due to redox reactions has been proved both in acidic and basic media for the samples with high oxygen content, although its contribution in basic media is significantly lower. The results obtained clearly indicate that the oxygen responsible for CO-evolution participates in...
Vol.:(0112 33456789) Advanced Composites and Hybrid Materials, 2023
Hydrochar (HC), obtained by the hydrothermal carbonization (HTC) of biomass, is an excellent precursor for preparing activated carbon (AC). However, the effects of the intrinsic properties of HC on the microstructure and electrochemical properties of AC are largely unknown. This study investigates the impact of particle size and the degree of aromatization of in-situ HC on the microstructure and electrochemical properties of AC. Our results show that a large particle size and a high degree of aromatization help protect the HC from overactivation by ZnCl 2 , resulting in an large specific surface area (SSA > 2000 m 2 /g) and high mesopore to micropore volume ratio value (V mes /V mic > 0.3) of the AC. Electrochemical performance measurements show a maximum specific capacitance of 218 F/g at 0.5 A/g was achieved in all samples where the AC (AC180-10 h) was prepared by activating HC180-10 h with a large size, a high degree of aromatization, and abundant surface oxygen-containing functional groups. After AC180-10 h was assembled into a supercapacitor, the specific capacitance of AC180-10 h still reached 158 F/g at 0.5 A/g, and it showed excellent cycling stability. This study advances the understanding of the impact of HC particle size and degree of aromatization on AC properties, providing new insights into tailoring HC qualities so that improving improve the properties of AC.
ACS Energy&Fuel, 2022
An anthracitic coal-derived activated porous carbon is proposed as a promising carbon electrode material for supercapacitor (SC) applications. The specific capacitance of this activated carbon SC electrode is related to the characteristics, such as specific surface area, pore size distribution, wettability, and conductivity. In the present work, a series of anthracite-based activated carbons (ABAC) were prepared via a multistage activation process and used as electrode materials for SCs. The multistage activation experiment was developed by exploring different activation temperatures, precursor/activating agent mass ratios, and process treating environments. The electrochemical performance of ABACs was evaluated in a three-electrode testing system. Multiple electrolytes were utilized, such as 1 M sulfuric acid (H 2 SO 4) and 1 and 6 M potassium hydroxide (KOH) solutions. An optimum ABAC electrode was obtained, characterized by its largest wettability and superior conductivity, and achieved excellent electrochemical performance. The three-electrode system exhibited a specific capacitance of 288.52 and 260.30 F/g at 0.5 A/g in the 1 M H 2 SO 4 and 6 M KOH electrolytes, respectively. It was found that moderate multistage activation temperatures are beneficial for the electrolyte uptake which enhances the specific capacitance. The high content of the oxygen functional groups on the activated carbon surface greatly improved its specific capacitance due to the increase in wettability. In the 1 M H 2 SO 4 electrolyte, the working electrode exhibited better performance than in 1 M KOH because the ion diameter in the acidic electrolyte was more suitable for pore diffusion. The concentrated KOH electrolyte leads to an increase in specific capacitance due to increased ions being adsorbed by a certain number of the hydrophilic pores. Moreover, the specific capacitance of the optimum ABAC sample remained at 95.4% of the initial value after 1000 galvanostatic charge−discharge tests at 0.5 A/g, which is superior to the performance of SC grade commercial carbon.
On the relation between texture parameters and double layer capacitance of activated carbons
Journal of the …, 2011
The porous textures of activated carbons and their electrochemical double layer capacitance (DLC) in organic electrolyte, prepared on the basis of spent coffee waste ground, were investigated by using low-temperature nitrogen adsorption and constant electric current cycling methods. A relation between texture parameters and DLC of activated carbon samples based on a modified H. Shis model was established. On the basis of the experimental data the modified model was examined and the main parameters of the relation (DLC per unit of internal (INT C) and per unit external surface area (EXT C)) were calculated. The possibility of linear relationship between the double layer capacity and specific (BET) surface area was discussed.
Electrochemical Capacitance of Activated Carbons Regenerated using Thermal and Chemical Activation
Journal of Electrochemical Science and Technology, 2021
Spent activated carbons (SACs) collected from a water treatment plant were regenerated and then adopted as electrochemical material in capacitors. The SACs used in this study were regenerated via two steps, namely thermal and chemical activation. However, during the activation process, the adsorbates were converted into ashes, which caused pore blockage and decreased specific surface area. The regenerated SACs were washed with acid solutions with different levels of acidity (strong: HCl, mild: H3PO4, and weak: H2O2) to remove the ashes. The regenerated SACs washed with HCl exhibited the highest specific surface area, although their capacitance was not the highest. Conversely, the specific surface area of regenerated SACs washed using H3PO4 was slightly lower than that of HCl, but exhibited higher capacitance and electrochemical stability. Although the strong acid removed the generated ashes in the pores efficiently, it could adversely affect their structural stability, which would l...
Relationship between chemical and physical surface properties of activated carbon
Water Research, 1998
ÐThe relationships between structural (chemical or physical) and more general properties such as the surface electrokinetic potential (zeta potential or isoelectric point) or spreading pressure of water were investigated for three powder activated carbon (PAC) samples (manufactured from woods, coconut shell and coal). The PAC samples were characterized by physical parameter measurements (such as zeta potential, speci®c surface area, spreading pressure) and chemical parameters; surface functional groups and structural mineral elements. Chemical studies show that all PAC samples contain large quantities of mineral ions, mostly calcium, sulfate and phosphate ions. These groups in¯uence surface properties in the same way as do acidic or basic organic surface functional groups. The thermal treatment of activated carbon decreases acidic surface functional groups and this reaction accompanies an increase in the electrokinetic potential. The``grafting'' of a cationic polymer adds positive charge to activated carbon surfaces, but the quantity of surface functional groups is also modi®ed by this process. Adsorption isotherms of water in activated carbon enable us to estimate initial polar adsorption sites. The localised adsorption of water on activated carbon is a function of the number of mineral ions and surface functional groups. Quantitative adsorption of water is related to the microporous volume.