高比表面活活性炭电级的电化学性能研究

选用比表面积为2590m^2/g的石油焦基活性炭作为双电层电容器的炭电极材料,用直流恒流循环实验考察双电层电容器在不同允放电条件下的电化学性能。实验发现,活性炭电极具有良好的循环充放电性能,充放电效率高达97％,远高于普通电池。不同充放电电流有不同的充放电容量,恒流1mA充放电容量大于2mA和5mA时的充放电容量。活性炭的比电容为60F／g,且电化学性能稳定,有良好的应用前景。     

Curvature effects on electric-double-layer capacitance

Understanding the microscopic structure and thermodynamic properties of electrode/electrolyte interfaces is central to the rational design of electric-double-layer capacitors (EDLCs). Whereas practical applications often entail electrodes with complicated pore structures, theoretical studies are mostly restricted to EDLCs of simple geometry such as planar or slit pores ignoring the curvature effects of the electrode surface. Significant gaps exist regarding the EDLC performance and the interfacial structure. Herein the classical density functional theory (CDFT) is used to study the capacitance and interfacial behavior of spherical electric double layers within a coarse-grained model. The capacitive performance is associated with electrode curvature, surface potential, and electrolyte concentration and can be correlated with a regression-tree (RT) model. The combination of CDFT with machine-learning methods provides a promising quantitative framework useful for the computational screening of porous electrodes and novel electrolytes.     

Aging of electrochemical double layer capacitors with acetonitrile-based electrolyte at elevated voltages

Laboratory-scale electrochemical capacitor cells with bound activated carbon electrodes and acetonitrile-based electrolyte were aged at various elevated constant cell voltages between 2.75 V and 4.0 V. During the constant voltage tests, the cell capacitance as well as the capacitance and resistance of each electrode was determined. Following each aging experiment, the cells were analyzed by means of electrochemical impedance spectroscopy, and the individual electrodes were characterized by gas adsorption and X-ray photoelectron spectroscopy. At cell voltages above 3.0 V, the positive electrode ages much faster than the negative. Both the capacitance loss and resistance increase of the cell could be totally attributed to the positive electrode. At cell voltages above 3.5 V also the negative electrode aged significantly. X-ray photoelectron spectroscopy indicated the presence of degradation products on the electrode surface with a much thicker layer on the positive electrode. Simultaneously, a significant decrease in electrode porosity could be detected by gas adsorption.     

Comparison of the characteristics of electric double-layer capacitors with an activated carbon powder and an activated carbon fiber

The characteristics of electric double-layer capacitors (EDLCs) with activated carbon powder (ACP), pulverized activated carbon fiber (ACF), and ACF-cloth have been compared. The BET surface areas of the ACP and ACF were estimated to be 1740 and 1970 m² g⁻¹, respectively. In the pore-size distribution curve of the ACP and ACF, the most dominant pore diameter was 1.8 and 1.1 nm for the ACP and ACF, respectively. Disc- and cloth-type of electrodes were fabricated using ACP and ACF. The electrical resistance of the ACF-disc and ACF-cloth electrodes was four orders of magnitudes lower than that of the ACP-disc electrodes. In accordance with the lower electrical resistance of the ACF-disc and ACF-cloth, the d.c. resistance of the EDLC with the ACF-disc and with ACF-cloth was lower than that of the EDLC with the ACP-disc. The highest specific volume capacitance of 28.3 F cm⁻³ (capacitance / volume of total ACF in the EDLC) was achieved with the ACF-disc. In the cyclic voltammograms of the ACF-disc, the stable electric double-layer charging and discharging behavior was observed.     

Comparison of Pore Structures of Cellulose-Based Activated Carbon Fibers and Their Applications for Electrode Materials

This study presents the first investigation of cellulose-based activated carbon fibers (RACFs) prepared as electrode materials for the electric double-layer capacitor (EDLC) in lieu of activated carbon, to determine its efficacy as a low-cost, environmentally friendly enhancement alternative to nanocarbon materials. The RACFs were prepared by steam activation and their textural properties were studied by Brunauer–Emmett–Teller and non-localized density functional theory equations with N₂/77K adsorption isotherms. The crystallite structure of the RACFs was observed by X-ray diffraction. The RACFs were applied as an electrode material for an EDLC and compared with commercial activated carbon (YP-50F). The electrochemical performance of the EDLC was analyzed using galvanostatic charge/discharge curves, cyclic voltammetry, and electrochemical impedance spectroscopy. The results show that the texture properties of the activated carbon fibers were influenced by the activation time. Crucially, the specific surface area, total pore volume, and mesopore volume ratio of the RACF with a 70-min activation time (RACF-70) were 2150 m²/g, 1.03 cm³/g and 31.1%, respectively. Further, electrochemical performance analysis found that the specific capacitance of RACF-70 increased from 82.6 to 103.6 F/g (at 2 mA/cm²). The overall high specific capacitance and low resistance of the RACFs were probably influenced by the pore structure that developed outstanding impedance properties. The results of this work demonstrate that RACFs have promising application value as performance enhancing EDLC electrode materials.     

The pore texture of zinc electrodes characterized by impedance measurements

Impedance measurements have been applied to the characterization of the pore texture of zinc electrodes used in electrochemical batteries. It is shown that these electrodes are equivalent to cylindrical pore electrodes. The electrode parameters (radius of pore, pore depth and surface density of pores) have been determined from the values of the electrode capacitance, the electrolyte resistance inside the pores and the electrode porosity.     

Superior electric double layer capacitors using ordered mesoporous carbons

This paper reports for the first time superior electric double layer capacitive properties of ordered mesoporous carbon (OMCs) with varying ordered pore symmetries and mesopore structure. Compared to commercially used activated carbon electrode, Maxsorb, these OMC carbons have superior capacitive behavior, power output and high-frequency performance in EDLCs due to the unique structure of their mesopore network, which is more favorable for fast ionic transport than the pore networks in disordered microporous carbons. As evidenced by N₂ sorption, cyclic voltammetry and frequency response measurements, OMC carbons with large mesopores, and especially with 2-D pore symmetry, show superior capacitive behaviors (exhibiting a high capacitance of over 180 F/g even at very high sweep rate of 50 mV/s, as compared to much reduced capacitance of 73 F/g for Maxsorb at the same sweep rate). OMC carbons can provide much higher power density while still maintaining good energy density. OMC carbons demonstrate excellent high-frequency performances due to its higher surface area in pores larger than 3 nm. Such ordered mesoporous carbons (OMCs) offer a great potential in EDLC capacitors, particularly for applications where high power output and good high-frequency capacitive performances are required.     

Contrast structure and EDLC performances of activated spherical carbons with medium and large surface areas

Two spherical carbons of 500 and 3000 m²/g, respectively, activated with NaOH (M500) and KOH (M3000), were examined in relation to their carbon structure and electrochemical behavior to explain their contrast capacitances as EDLC electrode.M500 and M3000 showed capacitances per weight (F/g) and volume (F/ml) of 35 and 35 (M500), 40 and 25 (M3000), respectively. The charge profile of M500 by galvanostat charge indicated that the charge took place rapidly below 1.5 V and then very gradually increased up to the final voltage of 2.7 V in the first charge. Such electrochemical behavior suggests electric field activation of this particular activated carbon at the charge. The charge profile of M3000 was conventional. The structure of M500 suffered a certain marked expansion at the charge, however the 0 0 2 diffractions profile shifted very slightly to a lower angle at the change. Such charge appears reversible while the structure of expansion was more or less irreversible. No expansion was observed with M3000 at the charge to the same voltage.Such a structure allows high efficiency of EDLC due to small pores and electric field activation to induce small pores among the graphitic units. In contrast, M3000 with its larger surface areas of relatively large pores in the graphitic structure showed a larger capacitance per weight. However many useless pores cause lower the capacitance per volume. In addition, large pores lose the efficiency for the formation of an electric double layer per unit surface area of the pore, while the non-graphitic wall of M3000 fails to introduce small pores with a higher capacitance.     

活化温度对无灰煤基活性炭结构及性能的影响

以无灰煤(HPC)为原料,KOH为活化剂,采用直接活化法制备无灰煤基活性炭(HAC),并在不同活化温度下探究HAC孔结构的衍化规律。结果表明:活化温度较低时,活化过程表现为无规则碳的烧失,同时微晶单元参与反应,片层明显减小,主要形成0.5 nm以下的微孔,以开孔作用为主。随活化温度的升高,KOH刻蚀微晶结构加剧,以扩孔作用为主,孔径大于0.5 nm的孔居多,同时发展超微孔和中孔。将HAC作为电极材料应用于水系双电层电容器(EDLC)时,其显示出优异的电化学性能,在电流密度为50 mA/g时的比电容达258.2 F/g,在电流密度为5000 mA/g时的比电容保持率在80%以上。研究还发现,EDLC的比电容随HAC电极中0.5 nm^1.5 nm微孔的增加而增大。     

活性炭电极材料前处理对KOH电解液体系双电层电容器电化学性能的影响

制备了沥青焦基活性炭,将活性炭分别经水洗、酸洗纯化处理以及气流粉碎处理得超细粉末。将处理后的活性炭作为双电层电容器用电极材料,在3mol/LKOH电解液体系中组装成电容器。采用直流充放电、交流阻抗等表征手段,对比评价了各种活性炭前处理方法对电容器电化学性能的影响。结果表明,酸洗后活性炭的比电容增加,气流粉碎后活性炭的高功率充放电性能改善,以酸洗气流粉碎后活性炭为电极的电容器具有良好的能量及功率性能。     

A comparison of the aging of electrochemical double layer capacitors with acetonitrile and propylene carbonate-based electrolytes at elevated voltages

The aging behavior of electrochemical double layer capacitors (EDLCs) based on activated carbon electrodes bound with poly(tetrafluoroethylene) (PTFE) was tested in electrolyte solutions based on acetonitrile (AN) and propylene carbonate (PC) at a constant elevated cell voltage of 3.5 V. The aging was quantified in terms of capacitance loss and resistance increase for the full cell and the individual electrodes. It is shown that the enhanced aging rate of symmetric EDLCs in either solvent at elevated voltages is dominated by the aging of a single electrode, and that the polarity of this limiting electrode depends directly on the solvent. In AN, the positive electrode ages much more rapidly than the negative, while in PC the negative electrode exhibits faster aging than the positive. After aging, the electrodes were investigated by nitrogen adsorption and X-ray photoelectron spectroscopy, revealing significant modifications of the electrode surface and providing clear evidence for the deposition of electrolyte degradation products on the electrodes.     

Electrochemical behavior of metallic and semiconducting single-wall carbon nanotubes for electric double-layer capacitor

Electrochemical behavior of metallic and semiconducting single-wall carbon nanotubes (SWCNTs) separated by agarose gel chromatography was analyzed as electrodes of electric double-layer capacitor (EDLC). Due to the doping of ions to semiconducting SWCNTs, the cyclic voltammogram of semiconducting SWCNTs showed amphoteric behavior, which is analogous to that of dopable conducting polymers. As the potential was increased or decreased from the flat band potential, the capacitance of semiconducting SWCNTs was increased, but that of metallic SWCNTs was slightly increased. The high capacitance of semiconducting SWCNTs at the high potential is beneficial for EDLC due to the possible limitation of capacitance.     

中孔活性炭电极储电影响因素研究

选用树脂基中孔活性炭作为双电层电容器的电极材料 ,通过水蒸气活化提高活性炭的比表面积 .实验发现 ,随着活化时间的延长 ,活性炭收率降低 ,活化 2 h烧失率高达 73.5 % ,比表面积从原来的 761 m2 g增加到 1 480 m2 g.孔结构分析表明 ,随活化时间的延长 ,在 2 nm附近孔容分布强度增强 .活性炭电极的放电时间和比电容随活化时间的延长而增加 ,但增速变缓 ,活化 2 h活性炭的比电容最高为 1 85 .84F/ g,增加了 2 8.9% .     

High power density electric double-layer capacitor based on a porous multi-walled carbon nanotube microsphere as a local electrolyte micro-reservoir

A high rate capability is a primary requirement for an electric double-layer capacitor (EDLC) in practical applications, which is mainly governed by the ionic diffusion rate. Construction of the electrode structure with proper paths for the rapid transport of ions is an efficient method to facilitate the diffusion of ions in the electrode. In this study, we prepared multi-walled carbon nanotube microspheres (MWNTMS) with a stable porous structure via the spray drying method. The MWNTMS act as a local electrolyte micro-reservoir and provide stable ion transport paths in the EDLC electrode, which will facilitate the access of the electrode to the electrolyte and accelerate the diffusion rate of the ions. Using only MWNTMS as active materials, an areal capacitance of 105 mF/cm² at 30 A/g is observed at an areal density of 7.2 mg/cm². When the MWNTMS are combined with reduced graphene oxides (rGO) to form an rGO-MWNTMS hybrid electrode with an areal density of 3.0 mg/cm², a high areal capacitance of 136 mF/cm² at 100 A/g is observed. This rGO-MWNTMS-based EDLC presents a high areal power density of 1540 mW/cm². These favorable results indicate that MWNTMS are promising materials for applications in high power supercapacitors.     

双电层电容器用多孔炭材料的研究与开发

阐述了双电层电容器的工作原理，探讨了多孔炭材料的比表面积、孔径分布、表面官能团、表面石墨微晶取向、体积密度和电导率以及电化学稳定性等微孔结构与物理化学性质对其电容特性的影响，介绍了近年来用作双电层电容器电极的几种新型多孔炭材料的研究进展。     

Graphene nanosheets as electrode material for electric double-layer capacitors

Graphene nanosheets (GNSs) with narrow mesopore distribution around 4 nm were mass-produced from natural graphite via the oxidation and rapid heating processes. The effects of oxidant addition on the morphology, structure and electrochemical performance of GNSs as electrode materials for electric double-layer capacitor (EDLC) were systematically investigated. The electrochemical properties of EDLC were influenced by the specific surface area, pore characteristics, layer stacking and oxygen-containing functional group contents of electrode materials. Deeper oxidation makes graphite possess both higher specific surface area and more graphene edges, which are favorable for the enhancement of capacitive performance of EDLC. The electrodes with freestanding graphene nanosheets prepared by coating method exhibited good rate capability and reversibility at high scan rates (to 250 mV s⁻¹) in electrochemical performances. GNS electrode with specific surface area of 524 m² g⁻¹ maintained a stable specific capacitance of 150 F g⁻¹ under specific current of 0.1 A g⁻¹ for 500 cycles of charge/discharge.     

PAN基凝胶聚合物电解质双电层电容器

为了得到安全、无泄漏、微型、超薄型的双电层电容器,采用内聚合方法制得聚丙烯腈基凝胶聚合物电解质双电层电容器,电解质的增塑剂为碳酸丙烯酯和碳酸乙烯酯,支持电解质为高氯酸锂,电极材料分别为比表面积1000m2/g和2600m2/g的活性炭。采用交流阻抗、循环伏安、恒流充放电、循环寿命等测试方法对内聚合式凝胶聚合物电解质及其组成的双电层电容器的性能进行了测试。结果表明,此种方法制得的双电层电容器的内阻小,比容量较大,其中以比表面积2600m2/g活性炭为电极材料的电容器的双电极比容量达到47.41F/g。     

Exfoliated carbon fibers as an electrode for electric double layer capacitors in a 1 mol/dm H2SO4 electrolyte

Exfoliated carbon fibers (ExCFs) synthesized through the rapid heating of intercalation compounds of carbon fibers were examined as electrodes of electric double layer capacitors (EDLC). The measurement of EDLC was performed using a standard three-electrode cell with 1 mol/dm³ sulfuric acid electrolyte. The capacitance of as-prepared ExCFs reached 117 F/g, even though they had a relativity small surface area of about 330 m²/g. After air activation of ExCFs, the BET surface area increased slightly, but the capacitance of the EDLC increased up to 160 F/g. Capacitance of ExCFs strongly depended on their BET surface area, having a different dependence from that reported on activated carbon fibers.     

Charging/discharging kinetics of poly(3,4-ethylenedioxythiophene) in 1-ethyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)imide ionic liquid under galvanostatic conditions

The constant current charging/discharging experiments of poly(3,4-ethylenedioxythiophene) (PEDOT), modified electrodes in room temperature ionic liquid, for instance 1-ethyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)imide, were performed for two types of cell configurations, three and two-electrode cells. In each case, a linear variation of the voltage with respect to time was observed. The electrochemical responses were analyzed in term of a series combination of a resistance R and a capacitor C. Accordingly, the capacitance of the modified electrodes was determined. One observed a linear variation of the capacitance as a function of the amount of PEDOT. This capacitance described the chemical capacitance of PEDOT that reflected the capability of the system to accept or release additional charge carriers on a given variation of the chemical potential. Also, the electrochemical response during constant current charging/discharging experiments for two-electrode cell in which the same amount of PEDOT was deposited on each electrode showed a type I electrochemical supercapacitor response. This kind of an electrochemical chain allowed us to mimic and to analyze the electrical responses of an electrochemical actuator based on an interpenetrating polymer networks containing PEDOT that was able to work in air.     

Hydrous RuO(2)-Carbon Nanofiber electrodes with high mass and electrode-specific capacitance for efficient energy storage

We demonstrate a new strategy for the fabrication of supercapacitor electrodes possessing high mass and area-specific capacitance for efficient charge storage, which can be extremely useful for the development of light, compact and high performance supercapacitors for a variety of high power demanding applications. High mass and electrode area specific capacitances were attained by using Hydrous Ruthenium Oxide (HRO)-Carbon Nanofiber (CNF) hybrid electrodes prepared by the deposition of HRO (~31% Ru content) on both the outer and inner surfaces of a cylindrical hollow CNF having open tips. Electrochemical studies of the uniformly deposited HRO nanoparticles on the CNF surface showed a mass specific capacitance of 645 F g(-1) and an electrode specific capacitance of 1.29 F cm(-2) with a HRO-CNF material loading of 2 mg cm(-2) in the supercapacitor electrodes. The mass specific capacitance of pure HRO is 301 F g(-1), whereas the mass specific capacitance of HRO in the HRO-CNF electrode is ~1300 F g(-1), which is very close to the theoretical capacitance of HRO. This enhanced charge storage ability, high rate capability, better cyclic stability and low ESR of the HRO-CNF will be useful for the development of high performance supercapacitors.