Characterization of Microporous Activated Carbon Electrodes for Electric Double-layer Capacitors

IntroductionElectric double layer capacitors( EDLCs) witha high power density can be used as memory back-up devices or electric vehicles.EDLCs store energyin the electric double layer by charge accumulationon the interface between the electrode and the elec-trolyte. In order to obtain reasonable energies andpower densities,the more suitable material forEDLCs musthave a high surface area with a signif-icant value of specific double layer capacitance,better pore size distribution and electro…     

Electrochemical behavior of activated carbon electrodes in electric double layer capacitors with tetrametylammonium bis(oxalato)borate electrolyte synthesized by microwave irradiation

The electrochemical behavior of electric double layer capacitors (EDLCs) with tetramethylammonium bis(oxalato)borate electrolyte and electrodes based on various activated carbons (ACs) was studied. Tetraalkylammonium bis(oxalate)borate salts were synthesized by means of microwave (MW) irradiation. The specific conductivities of salt solutions were determined. It was shown that the efficiency of electric double layer capacitors increases with an increase in specific surface area and a decrease in the purity of carbon materials.     

Effect of pore characteristics on electrochemical capacitance of activated carbons

Activated carbons (ACs) for electric double layer capacitors (EDLCs) were fabricated from waste tea leaves, activated with the pore-forming substances ZnCl₂ then, carbonized at high-temperature in N₂ atmosphere. The surface texture and porosity of the ACs were determined using transmission electron micros-copy and N₂ adsorption/desorption studies. The surface area of the 20 wt % ZnCl₂ treated sample was found to be 1029 m²g^?1 and had a distribution of micropores and mesopores. The electrochemical properties of the ACs were evaluated by using cyclic voltammetry and galvanostatic charge-discharge studies. ACs from waste tea leaves exhibited excellent specific capacitance as high as 196 F g^?1 in the 0.1 M Na₂SO₄ neutral electrolyte, with rectangular-like cyclic voltammetry curves at a cell potential of 1.5 V and good cyclability with a capacitance retention of 95% at a high current density of 100 mA g^?1 for 2000 cycles. The results show that the pore texture properties and specific surface area of ACs are dominated by changing carbonization temperature and the amount of activating agent ZnCl₂. The electrochemical performance is influenced mainly by surface area, but the pore size distribution becomes a dominating factor for specific capacitance of a carbon electrode material when the pore structure is in range of micropores/mesopores.     

Correlation of EDLC Capacitance with Physical Properties of Polyethylene Terephthalate Added Pitch-Based Activated Carbon

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.     

A review on the development of a porous carbon-based as modeling materials for electric double layer capacitors

Carbon electrodes are a key factor for electric double layer capacitors (EDLCs). Carbon gels have high porosity with a controllable pore structure by changing synthesis conditions and modifying preparation processing to improve the electrochemical performance of EDLCs. This review summarizes the preparation of carbon gels and their derivatives, the criteria to synthesize high surface area in each process, the development by some carbon forms, and EDLC applications. Porous carbons are also prepared as model materials by concentrating on how pore structure increases electrochemical capacitance, such as electronic and ion resistance, the tortuosity of pore channel, suitable micropore and mesopore sizes, and mesopore size distribution. This review emphasizes the significance of pore structures as the key factor to allow for the design of suitable pore structures that are suitable as the carbon electrode for EDLCs.     

Heteroatom‐Doped Porous Carbon Nanosheets: General Preparation and Enhanced Capacitive Properties

High‐performance electrical double‐layer capacitors (EDLCs) require carbon electrode materials with high specific surface area, short ion‐diffusion pathways, and outstanding electrical conductivity. Herein, a general approach combing the molten‐salt method and chemical activation to prepare N‐doped carbon nanosheets with high surface area (654 m² g^?1) and adjustable porous structure is presented. Owing to their structural features, the N‐doped carbon nanosheets exhibited superior capacitive performance, demonstrated by a maximum capacitance of 243 F g^?1 (area‐normalized capacitance up to 37 μF cm^?2) at a current density of 0.5 A g^?1 in aqueous electrolyte, high rate capability (179 F g^?1 at 20 A g^?1), and excellent cycle stability. This method provides a new route to prepare porous and heteroatom‐doped carbon nanosheets for high‐performance EDLCs, which could also be extended to other polymer precursors and even waste biomass.     

甲烷在活性炭上裂解制氢研究

在连续流动石英固定床反应器上研究了甲烷在活性炭上裂解制氢的反应，并对反应前后活性炭的比表面积以及孔径分布等的变化进行了测定。结果表明，甲烷在五种活性炭上的裂解行为基本相同，反应初期转化率最高，随着反应进行转化率逐渐降低直至一个平稳的状态；降低甲烷分压和增加甲烷与活性炭的接触时间可提高甲烷转化率；温度的升高有利于初始转化率的提高，但不利于活性炭的稳定性；反应后活性炭比表面积、孔容及微孔孔容都明显降低，平均孔径增大，孔径分布向中孔方向迁移，说明甲烷的裂解导致了活性炭孔特别是微孔内的炭沉积以及进一步的孔堵塞。     

Mechanism of adsorption of different humic acid fractions on mesoporous activated carbons with basic surface characteristics

The effects of the humic acid (HA) nature and the activated carbon (AC) surface chemistry on the effectiveness of HA removal were investigated. Brown (BHA) and gray (GHA) humic acid fractions of different structure and physicochemical properties were tested in the adsorption process using mesoporous ACs. The modification of chemical structure and surface properties of AC was achieved by ammonization (AC/N) and hydrogen treatment (AC/H). Both approaches led to a decrease in the oxygen content followed by an increase in the carbon basicity, maintaining the porous texture of AC nearly unaltered. Over twice higher removal degree of BHA and GHA was observed for the modified ACs. The kinetics of adsorption of HA fractions have been discussed using the pseudo-second-order model and the intraparticle diffusion model. All ACs showed a higher adsorption capacity toward BHA compared to GHA, which is mainly attributed to the lower molecular weight of BHA. The shape of the equilibrium isotherms indicates a strong competition between water and HA molecules for adsorption sites of the carbon surface.     

Secondary Activation of Commercial Activated Carbon and its Application in Electric Double Layer Capacitor

The cheap commercial activated carbon (AC) was improved through the secondary activation under steam in the presence of FeCl2 catalyst in the temperature range of 800-950℃ and its application in electric double layer capacitors(EDLCs) with organic electrolyte was studied. The re-acivation of AC results in the increases in both specific capacitance and high rate capability of DELCs. For AC treated under optimized conditions, its discharge specific capacitance increases up to 55.65F/g, an increase of about 33% as compared to the original AC, and the high rate capability was increased significantly.The good performances of EDLC with improved AC were correlated to the increasing mesoporous ratio.     

Effect of surface oxygen functionalities on capacitance of activated carbon in non-aqueous electrolyte

Electric double-layer capacitors (EDLCs) are composed of two activated carbon (AC) electrodes and an electrolyte/separator, in which the ACs contain numbers of surface oxygen functionalities (SOFs). In this work, the effect of SOFs on the EDLC’s capacitance in non-aqueous electrolytes is studied by using a 1.0 m (molality) LiPF₆ 3:7 (wt.) ethylene carbonate-ethyl methyl carbonate electrolyte and a commercial activated carbon. Results show that the SOFs on one hand contribute to Faradic pseudocapacitance, and on the other hand adversely reduce the EDLC’s performances, including the initial reversibility, coulombic efficiency, and capacitance retention. It is found that the AC behaves significantly different in the Li/AC half cells and in the AC/AC full cells and that the SOF’s pseudocapacitance increases with widening the EDLC’s operating voltage. The latter is attributed to the large-voltage hysteresis of the redox of SOFs. In this paper, the AC’s unique behaviors in Li salt electrolyte are presented, and a possible mechanism for the observed behaviors is proposed.     

Comparative study on composition, structure, and adsorption behavior of activated carbons derived from different synthetic waste polymers

The composition, structure, and adsorption behavior of activated carbons (ACs) derived from three different types of waste polymers, i.e., tire rubber (TR), polyvinyl chloride (PVC), and polyethyleneterephtalate (PET), by KOH activation were compared. The AC derived from PET exhibited the largest surface area (2831 m(2)/g) and pore volume (1.68 cm(3)/g) due to the homogenous aromatic composition of PET. The AC derived from PVC exhibited relatively lower surface area (2666 m(2)/g) but more narrowed pore size distribution (2-3 nm). The complex composition and high ash content of tire particles resulted in AC product with significantly lower surface area (398.5 m(2)/g) and heterogeneous pore width. Adsorption data of methylene blue (MB) were fitted well by Langmuir equation, indicating monolayer coverage on the ACs. The high oxygen content of PET-derived AC heavily affected its adsorption to MB and iodine. Due to the remarkable surface area and highly mesoporous structures, ACs based on both PET and PVC exhibited much higher adsorption capacities than that of TR and commercial coal-based AC (F400). This study demonstrates that the properties of ACs are highly dependent on their starting polymers and the potential of converting synthetic polymer waste into effective adsorbents for environmental remediation and cleanup.     

隔膜对双电层电容器和混合型电池-超级电容器的电化学性能的影响

隔膜是双电层电容器和混合型电池-超级电容器等电化学储能器件的重要组成元件.本文采用1 mol?L-1四乙基四氟硼酸铵的丙烯碳酸酯电解液制备了基于活性炭的扣式双电层电容器,并采用1 mol?L-1六氟磷酸锂锂离子电解液制备了(LiNi0.5Co0.2Mn0.3O2+活性炭)/石墨体系的混合型电池-超级电容器.研究了不同类型隔膜的物理化学性能,以及其对双电层电容器和混合型电池-超级电容器的电化学性能的影响.四种隔膜分别是无纺布聚丙烯毡、多孔聚丙烯薄膜、Al2O3涂层的聚丙烯薄膜和纤维素纸隔膜.进行了表面形貌、差示扫描量热、电解液吸液量和表观接触角测试表征.电化学测试表明,采用纤维素隔膜的双电层电容器具有最高的比电容和更优的倍率性能,电容器的自放电性能差别不大.而对于混合型电池-超级电容器,采用聚丙烯薄膜和无纺布聚丙烯毡隔膜器件的比容量比其它器件约高20%,且采用纤维素隔膜的器件自放电率最高.     

Influence of KMnO4 oxidation on the electrochemical performance of pitch-based activated carbons

In this work, activated carbons (ACs) are obtained from petroleum pitch by the combination of a chemical treatment with different potassium permanganate (KMnO₄) amounts, i.e., 0, 0.5, 1.0, and 2.0 g, and a chemical activation with KOH at a constant KOH/pitch ratio of 3/1. The effects of the chemical activating agent on the surface morphology and porosity are evaluated with scanning electron microscopy and N₂ adsorption isotherms at 77 K, respectively. The specific surface area of the pitch-based ACs is increased with increasing the amount of KMnO₄ pre-treatment and showed the highest value of 2,334 m² g^?1 at 2 g of KMnO₄ amount. The electrochemical performance of AC electrodes is examined by cyclic voltammetry and galvanostatic charge/discharge characteristics in 6 M KOH electrolyte. Among the prepared ACs, 2.0 K-ACs possesses a specific capacitance as high as 237 F g^?1 and showed excellent electrochemical performance due to its suitable porous structure and low interface resistance.     

植物基多孔炭材料在超级电容器中的应用

植物基多孔炭具有发达的孔结构、大的表面积、较为成熟的制备工艺、丰富的来源、低廉的价格,是目前商业应用范围最广的超级电容器电极材料。然而在实际应用中仍然存在着质量/体积比容量较低、倍率性能差等问题。本文针对先进电容器件的高能量密度、优异功率性能的要求,首先介绍了近年来发展的植物基多孔炭的制备方法,讨论了植物前驱体的组成和结构对其产物结构的影响以及与其电化学性能之间的构效关系,特别总结了近年来植物基超大比表面积多孔炭、中孔炭、层次化多孔炭的制备方法和电容储能性能。针对大比表面积多孔炭用于超级电容器时的体积性能不佳这一关键问题,本文还总结了提高植物基多孔炭体积电化学性能的方法。最后,对植物基多孔电极材料存在的问题进行了分析与总结,并展望了其研究前景。     

Surface and chemical characteristics of platinum modified activated carbon electrodes and their electrochemical performance

Platinum (Pt) loaded activated carbons (ACs) were synthesized by the thermal decomposition of platinum (II) acetylacetonate (Pt(acac)₂) over chemically activated glucose-based biochar. The effect of Pt loading on surface area, pore characteristics, surface chemistry, chemical structure, and surface morphology were determined by various techniques. XPS studies proved the presence of metallic Pt⁰ on the AC surface. The graphitization degree of Pt loaded ACs were increased with the loaded Pt⁰ amount. The electrochemical performance of the Pt-loaded ACs (Pt@AC) was determined not only by the conventional three-electrode system but also by packaged supercapacitors in CR2032 casings. The capacitive performance of Pt@AC electrodes was investigated via cyclic voltammetry (CV), galvanostatic charge-discharge curves (GCD), and impedance spectroscopy (EIS). It was found that the Pt loading increased the specific capacitance from 51 F/g to 100 F/g. The ESR drop of the packaged cell decreased with the Pt loading due to the fast flow of charge through the conductive pathways. The results showed that the surface chemistry is more dominant than the surface area for determining the capacitive performance of Pt loaded AC-based packaged supercapacitors.     

The preparation and characterization graphene-cross-linked phenol–formaldehyde hybrid carbon xerogels

A new synthesis route based on polycondensation of phenol and formaldehyde cross-linked by graphene oxide (GO) was developed. Wet gel after gelation was converted into an organic xerogel by ambient pressure drying to obtain GO-cross-linked phenol–formaldehyde (PF) organic xerogels (GOCPFOX). Graphene-cross-linked PF carbon xerogels (GCPFCX) were produced by carbonization. The morphology and chemical structure of GOCPFOX and GCPFCX were analyzed. The electrochemical behavior of GCPFCX as an electrode material in electric double-layer capacitors (EDLCs) was investigated. Results show that the high mechanical strength of GO increased the gel skeleton strength; thus, organic xerogels exhibit very low drying shrinkage. Scanning electron micrographs indicated that addition of GO altered the gel structure. Thus, when GO was added into the PF solution, the PF molecular chains were anchored on the surface of GO by chemical and physical interaction. The GCPFCX-10 sample achieved the highest specific surface area, mesoporous volume, and specific capacity with 378 m²/g, 0.56 cm³/g, and 116 F/g, respectively. Hence, GCPFCX is a potential material for EDLCs owing to its low production cost and ability to avoid supercritical drying.     

Graphitized carbon from wastepaper as electrodes for high-performance electric double-layer capacitors

Graphitized carbon electrode material was prepared from wastepaper by graphitization in molten sodium metal. X-ray diffraction and Raman spectroscopy were used to investigate the structural change of resulted carbons, both of which well proved the formation of graphite structure. Graphitized carbons have surface area that is nearly 26 times larger than initial carbonized paper and exhibit better electrochemical performances. The electrochemical performances of graphitized carbons were investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge methods. The cyclic voltammetry results show a maximum specific capacitance of 194 F g^?1. Therefore, wastepaper can be a promising electrode material for high-performance electric double-layer capacitors (EDLCs).     

Nanosize catalysts based on carbon materials promoted by cobalt tetra(<Emphasis Type="Italic">para</Emphasis>-methoxyphenyl) porphyrin pyropolymer for oxygen electroreduction

We present the results of electrochemical and structural investigations of several carbon materials: carbon blacks AD 100 and XC 72, ultradisperse diamond (UDD), multiwalled nanotubes (MWNT), various types of filament-like carbon materials (CFC series), and similar carbon materials promoted with cobalt tetra(para-methoxyphenyl) porphyrin (CoTMPhP) pyropolymer (PP). The electrochemical studies were performed at room temperature in 0.5 M H₂SO₄ by using a rotating disk electrode (RDE), a rotating ring-disk electrode (RRDE) (a thin layer of test material was applied onto the disk electrode), and a floating electrode. Structural characterization of initial and promoted carbon materials involved the determination of specific surface area by the BET method and by the polarization capacitance from cyclic voltammograms, and the particle morphology and dimensions by the transmission electron microscopy (TEM) method. The study of kinetics and mechanism of oxygen electroreduction on carbon materials promoted with CoTMPhP PP showed that the catalysts based on carbon materials of CFC and UDD series possess high specific activity in this reaction and high selectivity with respect to oxygen reduction to water. These catalysts are superior to the catalysts, in which carbon blacks AD 100 and XC 72 are used as the supports, in the specific activity.     

水蒸汽活化活性炭及其负载乙炔氢氯化铋基催化剂

以水蒸汽活化的两种活性炭为载体,采用等体积浸渍法制备了一系列Bi/AC催化剂,考察了其乙炔氢氯化反应的催化性能。分别通过氮气吸附脱附实验(BET),扫描电子显微镜(SEM),傅里叶变换红外(FTIR),透射电子显微镜(TEM),X射线粉末衍射(XRD),X射线光电子能谱(XPS)和热重分析(TGA)对活性炭和催化剂进行表征。结果表明：（1）水蒸汽活化重整了活性炭的孔径和孔道,尤其是介孔材质活性炭,增加了其比表面积,形成了新的微孔结构。（2）积碳是Bi/AC催化剂失活的主要原因,水蒸汽活化抑制了积碳,并增加了BiOCl的结晶度和分散性,提高了乙炔氢氯化反应的催化性能。     

活性炭孔径和比表面积对TiO2/AC光催化性能的影响

采用“同步物理-化学活化法”二次活化商品活性炭, 制备不同孔径和比表面积的系列活性炭(AC)载体, 以偏钛酸为钛源, 利用均匀沉淀法制备TiO2负载型光催化剂(TiO2/AC), 用氮吸附、XRD、SEM等方法表征, 研究活性炭的孔径和比表面积对TiO2/AC性能的影响; 并通过降解水溶液中的亚甲基蓝(MB)研究TiO2/AC光催化氧化特性, 考察催化剂投加量、不同MB浓度等因素对光催化氧化的影响. 结果表明, 负载的TiO2粒子粒径为12-20 nm, 活性炭的比表面积大、平均孔径大有利于TiO2的均匀分散, 阻止TiO2晶粒生长, 有利于充分发挥TiO2小尺度效应; 另外, 活性炭吸附和TiO2光解的协同效应使TiO2/AC光催化剂对MB降解的效率显著提高. 动力学研究表明, TiO2/AC光催化降解MB反应符合表观一级动力学特征.