超级电容器炭电极材料孔结构对其性能的影响

采用无瓶颈的系列酚醛树脂活性炭为电极材料，用氮吸附和恒流充、放电，以及交流阻抗法，研究孔径和孔表面积等孔结构对其性能的影响.结果表明，活性炭电极材料双电层电容与微孔(孔宽度< 2.0 nm)表面和外孔(孔宽度 >2.0 nm)表面都有关系，但主要取决于微孔表面双电层电容.微孔表面比电容为21.4 μF•cm－2，外孔表面比电容< 10 μF•cm－2.外孔表面比电容较低可能是由于空间电荷层的影响.微孔孔径较大的炭材料具有高比电容和良好的高倍率放电的特性.     

电解液离子与炭电极双电层电容的关系

以酚醛树脂基纳米孔玻态炭(NPGC)为电极, 通过微分电容伏安曲线的测试, 研究了水相体系电解液离子与多孔炭电极双电层电容的关系. 结果表明, 稀溶液中, 多孔炭电极的微分电容曲线在零电荷点(PZC)处呈现凹点, 电容降低, 双电层电容受扩散层的影响显著；若孔径小, 离子内扩散阻力大, 电容下降更为迅速, 扩散层对双电层电容的影响增大. 而增大炭材料的孔径或电解液浓度, 可明显减弱甚至消除扩散层对电容的影响. 炭电极的单位面积微分电容高, 仅表明孔表面利用率高, 如欲获得高的电容量, 还要有大的比表面积. 离子水化对炭电极的电容产生不利影响, 选用大离子和增大炭材料的孔径, 可有效降低离子水化对炭电极电容性能的影响.     

酚醛基活性炭纤维孔结构及其电化学性能研究

利用水蒸汽活化法制备了酚醛基活性炭纤维(ACF-H2O), 对其比表面积、孔结构与在LiClO4/PC(聚碳酸丙烯酯)有机电解液中的电容性能之间的关系进行了探讨. 用N2(77 K)吸附法测定活性炭纤维的孔结构和比表面积, 用恒流充放电法和交流阻抗技术测量双电层电容器(EDLC)的电容量及内部阻抗. 研究表明, 在LiClO4/PC有机电解液中, ACF-H2O电极的可用孔径(d)应在0.7 nm以上. 随着活化时间的延长, ACF-H2O的孔容和比表面不断增大, 但微孔(0.7 nm ＜ d ＜ 2.0 nm)和中孔(d ＞ 2.0 nm)率变化很小, 活化过程中孔的延伸和拓宽同步进行, 但过度活化则造成孔壁塌陷, 孔容和比表面迅速下降. 因此, 除活化过度的样品外, 电容量随比表面积呈线性增长, 最高达到109. 6 F•g-1. 但中孔和微孔的孔表面对电容的贡献不同, 其单位面积电容分别为8.44 μF•cm-2和4.29 μF•cm-2, 中孔具有更高的表面利用率. ACF-H2O电极的电容量、阻抗特性和孔结构密切相关. 随着孔径的增大, 时间常数减小, 电解液离子更易于向孔内快速迁移, 阻抗降低, 电极具有更好的充放电倍率特性. 因此, 提高孔径和比表面积, 减少超微孔(d ＜ 0.7 nm), 是提高 EDLC能量密度和功率密度的重要途径. 然而仅采用水蒸汽活化, 只能在小中孔以下的孔径范围内进行调孔, ACF-H2O电极电容性能的提高受限.     

Impedimetric characterization of the changes produced in the electrode–solution interface by bacterial attachment

This paper describes a new method for measuring the attachment of bacteria, specifically Escherichia coli on platinum electrodes using impedance spectroscopy. Impedance spectroscopy measurements showed that the double layer capacitance of the electrode was very sensitive both to the concentration of bacteria in the solution and to the attachment time. Impedance measurements of E. coli were compared with classical measurements of bacterial attachment on identical electrodes such as staining/microscopy and bacterial removal by sonication and plating onto agar. The relationship between the measured impedance of the electrode during attachment and the biophysical processes involved is discussed.     

Activated carbon derived from marine Posidonia Oceanica for electric energy storage

In this paper, the synthesis and characterization of activated carbon from marine Posidonia Oceanica were studied. The activated carbon was prepared by a simple process namely pyrolysis under inert atmosphere. The activated carbon can be used as electrodes for supercapacitor devices. X-ray diffraction result revealed a polycrystalline graphitic structure. While scanning electron microscope investigation showed a layered structure with micropores. The EDS analysis showed that the activated carbon contains the carbon element in high atomic percentage. Electrochemical impedance spectroscopy revealed a capacitive behavior (electrostatic phenomena). The specific capacity per unit area of the electrochemical double layer of activated carbon electrode in sulfuric acid electrolyte was 3.16 F cm⁻². Cyclic voltammetry and galvanostatic chronopotentiometry demonstrated that the electrode has excellent electrochemical reversibility. It has been found that the surface capacitance was strongly related to the specific surface area and pore size.     

High temperature all solid state supercapacitor based on multi-walled carbon nanotubes and poly[2,5 benzimidazole]

Supercapacitor containing multi-walled carbon nanotubes (MWCNT) as the electrode material and phosphoric acid-doped poly[2,5 benzimidazole] (ABPBI) as the solid electrolyte and separator membrane has been investigated in a wide temperature range. Supercapacitors with different solid electrolyte concentrations have been fabricated and evaluated for their electrochemical performance. Specific capacitance of supercapacitors at room temperature was found to increase after the first heating cycle. Supercapacitor containing 10?wt.% of solid electrolyte in the electrode shows higher specific capacitance than the supercapacitor with liquid electrolyte. Cyclic voltammetry analysis of supercapacitors indicates high rate capability. The linear increase in the specific capacitance with temperature implies that capacitance is predominantly due to electric double layer. Electrochemical impedance analysis indicates that the mass capacitance and Warburg parameter increase with temperature, while solution resistance and leakage resistance decrease with temperature. The complex capacitance of the supercapacitors shows that both real and loss capacitances increase with temperature. The phase angle of supercapacitors is found to be around 85.2?±?1° at room temperature and it decreases with temperature. Galvanostatic charge–discharge cycling exhibits almost constant specific capacitance of 28?F?g^?1 at room temperature. However, it increases sharply and then attains stable value of 52?F?g^?1 during cycling at 100?°C. The increase in specific capacitance has been attributed to increase in surface area of the carbon nanotube (CNT), due to activation by phosphoric acid and diffusion of free phosphoric acid into the central canal of MWCNT.     

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.     

Influence of the semiconducting properties of a current collector on the electric double layer formation on porous carbon

The electrochemical behavior of polyacrylonitrile-based activated carbon cloth combined with a stainless steel current collector was examined using ac impedance spectroscopy. H(2)SO(4), KOH, and KNO(3) were employed as the electrolytes. The data presented in the impedance complex plane exhibit a semicircle at high frequencies followed by a vertical line at low frequencies. The high frequency data were found to be characteristic of the space charge region of the semiconducting oxide layer on the stainless steel, while the low frequency data depicted the double layer formation on the porous carbon. The double layer capacitance was found to decrease with the space charge resistance, which was potential dependent and a major contribution to the overall resistance of the carbon/stainless steel electrode. The electrolyte type affected the potential window employed in energy storage and thus the semiconducting behavior of the oxide layer. Both the n- and p-type semiconductors in depletion condition appeared within the potential window applied for the H(2)SO(4) electrolyte, and this caused the presence of a peak capacitance. Only the n-type depletion condition was found in the KNO(3) and KOH electrolytes with the p-type oxide situated in accumulation at the potentials applied, and thus, the capacitance was larger at more negative potentials.     

Influence of chemical composition of electrode material on the differential capacitance characteristics of the ionic liquid | electrode interface

The electrical double layer structure at polycrystalline metal | ionic liquid interface has been studied using cyclic voltammetry, electrochemical impedance spectroscopy and in situ infrared methods. Polycrystalline Bi(PC), Pb(PC), Au(PC) and Pt(PC) electrodes have been prepared using ultra-high vacuum magnetron sputtering method. Noticeable dependence of differential capacitance on the electrode potential has been observed. For all electrodes, a wide well-expressed minimum in capacitance, potential (C, E) curve has been shown. For graphene, C(0001), carbide-derived carbon and Bi(PC) U-shaped curves and for Pb(PC), Au(PC) and Pt(PC) M-shaped C, E curves have been measured. Dependence of the C, E curve shape on the electrode chemical composition has been explained by the different position of the image plane of surface charge, dependent on the electronic characteristics of the electrodes under study.     

粉末多孔镍电极电化学阻抗谱及其数学模型

镍电极反应动力学在大多情况下是受固态质子扩散过程控制的，以此为出发点建立了具有明确物理意义的镍电极电阻抗谱（ＥＩＳ）的数学模型，并以该模型为基础，讨论了一些模型参数如双电层电容Ｃｄ１，质子扩散系数Ｄ及活性物质粒子半径ｒ０等改变，电极的不同荷电状态及多孔镍电极中的传质过程对镍电阻阻抗谱的影响，理论模型较好地解释了一些实验结果。     

Computer simulation of negative electrode operation in lithium—ion battery: Galvanostatic discharge,porous electrode model and film model

Computer simulation of the structure and methods of operation (galvanostatic discharge) of the negative electrode of a lithium-ion battery is performed. Two possible models of the active anode layer were compared. 1. The model of porous active layer (mixture of active substance grains with grains of electrolyte). Here, the electrochemical process occurs within a porous active layer. 2. The film model (constant-thickness layer) of pure active substance (intercalating agent) grains without admixture of grains of electrolyte. In this case, the electrochemical reaction occurs only on the planar active electrode layer/interelectrode space interface. In both cases, the optimum working parameters of anode active layers were calculated: porous active layer thickness (in the film model, this was the calculation parameter), duration of full anode discharge, specific electric capacitance and finite difference between the intercalating agent/electrolyte potentials at the active anode layer/interelectrode space interface. It is found that each of these two models has its advantages and faults. Specific electric capacitance C cannot exceed the values of the order of magnitude of 10 C/cm² when a porous active layer is used. Whereas in the film model, much higher values of C may be obtained: tens and even hundreds of C/cm². On the other hand, in the case of anode discharge, the reasonable discharge current density value, its maximum value, at which practically full recovery of lithium atoms from active intercalating agent grains is still possible, proves to be by orders of magnitude higher in the case of an anode with a porous active layer, as compared with a film-type anode. Thus, in the case of development of electrode active layers of lithium-ion batteries, there is a possibility of choosing from two variants. There is the variant of an active film-type layer providing high capacitance values, but low discharge current density. Or there is another variant: a porous active layer with limited capacitance but then much higher values of discharge current density.     

Proposed model for quantification of dissolution—and evolution of a steel-CO2 solution interface by the transmission line approach

The corrosion mechanisms occurring at the homogeneous porous layer was determined assuming that the pores had a cylindrical geometry, and that the initial interface of a carbon steel-CO₂ solution behaved as a transmission line (TL). TL modeling quantitatively assessed the impedance distribution and the mesoporous layer formation and evolution at the interface, while describing the physical characteristics of the mesoporous FeCO₃ layer at the base and wall within the initial pore. The TL helped to characterize four stages during the interfacial evolution: active, active-porous layer, mixed layer, and the reactive stages. Using TLs helped to quantify the dissolution process and distinguish the mechanisms with good agreement between calculated magnitudes and experimental data.     

Preparation of activated carbon from Turbinaria turbinata seaweeds and its use as supercapacitor electrode materials

Turbinaria turbinata brown seaweeds were tested as carbon electrode material in symmetric, electrochemical supercapacitors. The electrochemical properties of the carbon materials were characterised for their application as supercapacitors using cyclic voltammetry, galvanostatic charge/discharge method and electrochemical impedance spectroscopic analyses. Our initial results showed that the optimal behaviour was obtained for the sample prepared by pyrolysis at 800 °C. The average surface area of the carbon was 812 m²/g. Electrochemical tests with an organic electrolyte gave the following interesting results: a capacitance of 74.5 F/g, a specific series resistance of 0.5 Ω cm² and an ionic resistivity of 1.3 Ω cm². These results show the promising capacitive properties of carbon derived from seaweeds and their application in electrochemical supercapacitors.     

Adsorption of long-chain aliphatic amines—components of corrosion inhibitors

Adsorption of certain long-chain aliphatic amines with 6–18 carbon atoms is studied on a stationary mercury drop electrode using the impedance method. It is found that adsorption of amines with C₆–C₁₂ results in the formation of an adsorption layer with the limiting capacitance of about 5 μF/cm². In the case of amines with C₁₄–C₁₆, the limiting capacitance is approximately 0.5–0.7 μF/cm². The most probable reason for such abrupt decrease in the adsorption layer capacitance is the formation of condensed layers of adsorbate molecules at the electrode surface. The adsorption parameters are calculated for hexylamine. The surface activity is estimated for amines with 10–14 carbon atoms in their chains.     

Determination of diffusion coefficient of lithium in substituted LiMn1.95Cr0.05O4 spinel using impedance technique

Electrodiffusion properties of chromium-substituted lithium-manganese spinel Li _x Mn_1.95Cr_0.05O₄ intended for application as a cathodic material for lithium-ion batteries is studied. The studies are carried out at 25°C using the electrochemical impedance spectroscopy technique in alkyl-carbonate electrolyte. In the analysis of impedance spectra, the apparatus of electric equivalent circuits was employed to determine surface layer resistances, double electric layer capacitance, differential intercalation capacity, chemical diffusion coefficient D of lithium, and other electrode characteristics. The issues of substantiating the choice of electric equivalent circuits and correct interpretation of their elements are discussed; dependences of the calculated model parameters on the electrode potential (lithium concentration in the electrode) are analyzed. The chemical diffusion coefficient of Li⁺ in Li _x Mn_1.95Cr_0.05O₄ found on the basis of the impedance spectra is in the range of 10^?9 to 10^?12 cm²/s under electrode potential variation in the range of 3.5–4.5 V (vs. Li/Li⁺) with a pronounced minimum of D in the middle of this range. Repeated cycling of the electrode is accompanied by a gradual increase in resistance of the solid-electrolyte interphase (SEI).     

Mesoporous graphitic carbon nanodisks fabricated via catalytic carbonization of coordination polymers

Mesoporous graphitic carbon nanodisks with hierarchical porous structure, facilely fabricated by catalytic carbonization of iron-based coordination polymer nanodisks, exhibit high capacitance even at high scan rates as electrode materials for electrochemical double layer capacitors.     

Hierarchical porous nanofibers of carbon@nickel oxide nanoparticles derived from polymer/block copolymer system

The triblock copolymer (PAA-b-PAN-b-PAA) is prepared by reversible addition-fragmentation chain-transfer polymerization, and then blended with polymer (PAN) and metal hydroxide (Ni(OH)₂) as a precursor for heat-treatment. A composite material of hierarchical porous nanofibers and nickel oxide nanoparticles (HPCF@NiO) is prepared by electrospinning combined with high-temperature carbonization. The effects of the ratio of PAA and PAA-b-PAN-b-PAA on the internal structure of nanofibers and their electrochemical properties as positive electrode materials are investigated. The experimental results show that when the ratio of PAA to PAA-b-PAN-b-PAA is 1.3 to 0.4, it has good pore structure and excellent electrochemical performance. At the current density of 1 A/g, the specific capacitance is 188.7 F/g and the potential window is −1 V to 0.37 V. The asymmetric supercapacitor assembled with activated carbon as the negative electrode materials has a specific capacitance of 21.2 F/g in 2 mol/L KOH and a capacitance retention of 85.7% after 12,500 cycles at different current density.     

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.     

An all-solid-state polymeric membrane Pb-selective electrode with bimodal pore C60 as solid contact

An all-solid-state polymeric membrane Pb²⁺ ion-selective electrode (Pb²⁺-ISE) based on bimodal pore C₆₀ (BP-C₆₀) as solid contact has been developed. A BP-C₆₀ film can be readily formed on the surface of a glassy carbon electrode by electrochemical deposition. Cyclic voltammetry and electrochemical impedance spectroscopy have been employed to characterize the BP-C₆₀ film. The large double layer capacitance and fast charge-transfer capability make BP-C₆₀ favorable to be used as solid contact for developing all-solid-state ISEs. The all-solid-state BP-C₆₀-based Pb²⁺-ISE shows a Nernstian response in the range from 1.0 × 10⁻⁹ to 1.0 × 10⁻³ M with a detection limit of 5.0 × 10⁻¹⁰ M. The membrane electrode not only displays an excellent potential stability with the absence of a water layer between the ion-selective membrane and the underlying BP-C₆₀ solid contact, but also is insensitive to interferences from O₂, CO₂ and light. The proposed solid-contact Pb²⁺-ISE has been applied to determine Pb²⁺ in real water samples and the results agree well with those obtained by anodic stripping voltammetry.     

Cupressus arizonica fruit essential oil: A novel green inhibitor for acid corrosion of carbon steel

Natural-based corrosion inhibitors have gained great research interest thanks to their low cost and higher performance. The Cupressus arizonica fruit essential oil (CAFEO) has a higher extraction yield than leaves; however, it has less antibacterial and antifungal activities. The three main components in the CAFEO were α-pinene (51.07%), myrcene (17.92%), and limonene (9.66%). Essential oils with a higher percentage of α-pinene were found to have outstanding corrosion inhibition properties. Therefore, herein, the CAFEO was investigated as a green corrosion inhibitor for carbon steel (CS) in 1.0 mol/L HCl using electrochemical, i.e., potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS), and scanning electron microscope (SEM) techniques. The experimental results revealed that CAFEO successfully inhibited the carbon steel corrosion in 1.0 mol/L HCl solution. Results from PDP indicated that the inhibitor had a mixed-type effect with a predominance cathodic character. EIS data showed that the charge transfer resistance of the CS electrode increased from 20.9 Ω cm² in blank solution to 294.5 Ω cm² in HCl solution inhibited with 0.5 g/L of CAFEO at 298 K, leading to a significant decrease in the double layer capacitance values and an inhibition efficiency (η%) of 93%. The high temperatures showed a negative effect on the corrosion inhibition efficiency of the tested inhibitor. At 323 K, the η% of CAFEO decreased to 77%. Besides, SEM images showed that the inhibitor formed a protective barrier against acid attack, preventing carbon steel from corrosion. Theoretical calculations by Density Functional Theory (DFT) were performed to investigate the reactivity of the three main components of CAFEO.