Adsorption of K^+ from an aqueous phase onto an activated carbon used as an electric double-layer capacitor electrode

The adsorption capacity and absorption rate for electrolyte onto activated carbon are important parameters used to characterize activated carbon electric double-layer capacitor electrodes. In this paper the pore structure of typical commercial activated carbons, and various Mn-doped activated carbons prepared on a laboratory scale, are described. The pore structure was character-ized by N2 adsorption/desorption isotherms. Isotherms for K+ adsorption onto these activated carbons from the aqueous phase were also obtained. The experimental, equilibrium K+ adsorption data were fitted to the Langmuir, Freundlich or Temkin equations. Adsorption of K+ onto the activated carbons was measured and plotted as a function of time. The adsorption kinetic data were modeled by either pseudo-first or pseudo-second order equations. The Elvoich equation, a liquid film diffusion and an intra-particle diffusion model were used to fit the kinetic data. The results indicate that the adsorption of K+ onto activated carbon is influenced by many factors including pore size distribution, specific surface area and the surface chemistry of the activated carbons. The Temkin equation best describes the equilibrium adsorption data. The pseudo-second order model exactly describes the whole adsorption process, which is controlled by both liquid film and intra-particle diffusion.

Porous monoliths of 3D graphene for electric double-layer supercapacitors

For delivering the nanoscaled extraordinary characteristics in macroscopical bulk,it is essential to integrate two-dimensional nanosheets into threedimensional(3D)porous monoliths,alternatively called as 3D architectures,3D networks,or aerogels.The intersupported structure of porous monolithic 3D graphene(3DG)can prevent aggregation or restacking of graphene individuals,and the interconnected sp^(2) network of 3DG not only can provide the highway for the transport of electron/phonon but also can present continual cavities/channels for mass transfer.This review summarizes the synthesis methodology of 3DG porous monoliths and highlights the application for electric double-layer capacitors.Present challenges and future prospects about the manufacture and application of 3DG are also discussed.

Carbon aerogels for electric double-layer capacitors

In this study, carbon aerogels were derived via the pyrolysis of resorcinol-formaldehyde (RF) aerogels, which were cost-effectively manufactured from RF wet gels by an ambient drying technique instead of conventional supercritical drying. By varying the R/C ratio (molar ratio of resorcinol to catalyst), mesoporous carbon aerogels with high specific surface area were prepared successfully and further investigated as electrode materials for electric double-layer capacitors (EDLCs). The textural properties of carbon aerogels obtained were characterized by nitrogen adsorption/desorption analysis and SEM. The electrochemical performances of carbon aerogels were investigated by impedance spectroscopy, galvanostatic charge/discharge and cyclic voltammetry methods. The results show that BET surface area and specific capacitance increase with R/C ratio, the maximum values of 727 m2·g-1 and 132 F·g-1 are achieved at R/C ratio will of 300. Increasing R/C ratio increase the average pore size of carbon aerogel electrode, which has improved the rate capability. Furthermore, EDLC with carbon aerogel electrodes has an excellent stability at large discharge current and long cycle life.

Design of Supercapacitor Electrodes Using Molecular Dynamics Simulations

Electric double-layer capacitors(EDLCs) are advanced electrochemical devices for energy storage and have attracted strong interest due to their outstanding properties. Rational optimization of electrode–electrolyte interactions is of vital importance to enhance device performance for practical applications. Molecular dynamics(MD) simulations could provide theoretical guidelines for the optimal design of electrodes and the improvement of capacitive performances, e.g., energy density and power density. Here we discuss recent MD simulation studies on energy storage performance of electrode materials containing porous to nanostructures. The energy storage properties are related to the electrode structures, including electrode geometry and electrode modifications. Altering electrode geometry, i.e., pore size and surface topography,can influence EDL capacitance. We critically examine different types of electrode modifications, such as altering the arrangement of carbon atoms, doping heteroatoms and defects, which can change the quantum capacitance. The enhancement of power density can be achieved by the intensified ion dynamics and shortened ion pathway.Rational control of the electrode morphology helps improve the ion dynamics by decreasing the ion diffusion pathway. Tuning the surface properties(e.g., the affinity between the electrode and the ions) can affect the ionpacking phenomena. Our critical analysis helps enhance the energy and power densities of EDLCs by modulating the corresponding electrode structures and surface properties.

Raman probing carbon&aqueous electrolytes interfaces and molecular dynamics simulations towards understanding electrochemical properties under polarization conditions in supercapacitors

Raman probing of carbon electrode and electrolyte under dynamic conditions is performed here using different aqueous electrolytes to elucidate the fundamental events occurring in electrochemical supercapacitor during charge–discharge processes.The areal capacitance ranges from 1.54 to 2.31μF cm^(-2)μm and it is determined using different techniques.These findings indicate that the Helmholtz capacitance governs the overall charge-storage process instead of the space charge(quantum)capacitance commonly verified for HOPG electrodes in the range of~3 to 7μF cm^(-2).Molecular dynamics simulations are employed to elucidate the origin of the reversible Raman spectral changes during the charge–discharge processes.A correlation is verified between the reversible Raman shift and the surface excesses of the different ionic species.A theoretical framework is presented to relate the effect of the applied potential on the Raman shift and its correlation with the surface ionic charge.It is proposed that the Raman shift is governed by the interaction of solvated cations with graphite promoted by polarization conditions.It is the first time that a comparative study on different aqueous electrolyte p H and cation ion size has been performed tracking the Raman spectra change under dynamic polarization conditions and contrasting with comprehensive electrochemistry and dynamic molecular simulations studies.This study shines lights onto the charge-storage mechanism with evidence of Kohn anomaly reduction in the carbon electrode during the reversible adsorption/desorption and insertion/extraction of ionic species.

Specializing liquid electrolytes and carbon-based materials in EDLCs for low-temperature applications

Electric double-layer capacitors(EDLCs) are emerging technologies to meet the ever-increasing demand for sustainable energy storage devices and systems in the 21 st Century owing to their advantages such as long lifetime, fast charging speed and environmentally-friendly nature, which play a critical part in satisfying the demand of electronic devices and systems. Although it is generally accepted that EDLCs are suitable for working at low temperatures down to-40℃, there is a lack of comprehensive review to summarize the quantified performance of EDLCs when they are subjected to low-temperature environments. The rapid and growing demand for high-performance EDLCs for auxiliary power systems in the aeronautic and aerospace industries has triggered the urge to extend their operating temperature range,especially at temperatures below-40℃. This article presents an overview of EDLC’s performance and their challenges at extremely low temperatures including the capability of storing a considerable amount of electrical energy and maintaining long-term stability. The selection of electrolytes and electrode materials is crucial to the performance of EDLCs operating at a desired low-temperature range. Strategies to improve EDLC’s performance at extremely low temperatures are discussed, followed by the future perspectives to motivate more future studies to be conducted in this area.

Analysis of Hybrid Rechargeable Energy Storage Systems in Series Plug-In Hybrid Electric Vehicles Based on Simulations

In this paper, an extended analysis of the performance of different hybrid Rechargeable Energy Storage Systems (RESS) for use in Plug-in Hybrid Electric Vehicle (PHEV) with a series drivetrain topology is analyzed, based on simulations with three different driving cycles. The investigated hybrid energy storage topologies are an energy optimized lithium-ion battery (HE) in combination with an Electrical Double-Layer Capacitor (EDLC) system, in combination with a power optimized lithium-ion battery (HP) system or in combination with a Lithium-ion Capacitor (LiCap) system, that act as a Peak Power System. From the simulation results it was observed that hybridization of the HE lithium-ion based energy storage system resulted from the three topologies in an increased overall energy efficiency of the RESS, in an extended all electric range of the PHEV and in a reduced average current through the HE battery. The lowest consumption during the three driving cycles was obtained for the HE-LiCap topology, where fuel savings of respectively 6.0%, 10.3% and 6.8% compared with the battery stand-alone system were achieved. The largest extension of the range was achieved for the HE-HP configuration (17% based on FTP-75 driving cycle). HP batteries however have a large internal resistance in comparison to EDLC and LiCap systems, which resulted in a reduced overall energy efficiency of the hybrid RESS. Additionally, it was observed that the HP and LiCap systems both offer significant benefits for the integration of a peak power system in the drivetrain of a Plug-in Hybrid Electric Vehicle due to their low volume and weight in comparison to that of the EDLC system.

Cobalt and nitrogen atoms co-doped porous carbon for advanced electrical double-layer capacitors

Electrical double-layer capacitors are widely concerned for their high power density,long cycling life and high cycling efficiency.However,their wide application is limited by their low energy density.In this study,we propose a simple yet environmental friendly method to synthesize cobalt and nitrogen atoms co-doped porous carbon(CoAT-NC) material.Cobalt atoms connected with primarily pyridinic nitrogen atoms can be uniformly dispersed in the amorphous carbon matrix,which is benefit for improving electrical conductivity and density of states of the carbon material.Therefore,an enhanced perfo rmance is expected when CoAT-NC is served as electrode in a supercapacitor device.CoAT-NC displays a good gravimetric capacitance of 160 F/g at 0.5 A/g combing with outstanding capacitance retention of 90% at an extremely high current density of 100 A/g in acid electrolyte.Furthermore,a good energy density of 30 Wh/kg can be obtained in the organic electrolyte.

Relationship between space charge and effective pore size of nanoporous electrode in electric double-layer capacitor

The space-charge distributions of electric double-layer capacitors （EDLCs）, which are energy storage devices, were examined with the pulsed electroacoustic （PEA） method. It was found that the experimental results could be influenced by the reflection and penetration of sound waves when the space-charge dis- tributions of EDLCs were measured with the PEA method. This is because EDLCs have a five-layer structure consisting of three materials （aluminum, cellulose, and activated carbon）. We calculated the reflection wave components that influenced the charge density through the acoustic impedance and the relative permittivity of the materials. In this way, we found that the changes in the space-charge distributions of EDLCs and their charge characteristics corresponded closely. We determined that measuring the space- charge distributions with the PEA method was effective for evaluating the charge accumulation of EDLCs. In this study, a polarized electrode was prepared for use in EDLCs. The ratio of the surface area to the average pore diameter of the polarized electrode was measured with the nitrogen adsorption method at 77 K. The relationship between the ratio of the surface area to the average pore size and the space-charge distributions of EDLCs is also discussed in this paper.

High Density 3D Carbon Tube Nanoarray Electrode Boosting the Capacitance of Filter Capacitor

Electric double-layer capacitors(EDLCs)with fast frequency response are regarded as small-scale alternatives to the commercial bulky aluminum electrolytic capacitors.Creating carbon-based nanoarray electrodes with precise alignment and smooth ion channels is crucial for enhancing EDLCs’performance.However,controlling the density of macropore-dominated nanoarray electrodes poses challenges in boosting the capacitance of line-filtering EDLCs.Herein,a simple technique to finely adjust the vertical-pore diameter and inter-spacing in three-dimensional nanoporous anodic aluminum oxide(3D-AAO)template is achieved,and 3D compactly arranged carbon tube(3D-CACT)nanoarrays are created as electrodes for symmetrical EDLCs using nanoporous 3D-AAO template-assisted chemical vapor deposition of carbon.The 3D-CACT electrodes demonstrate a high surface area of 253.0 m^(2) g^(−1),a D/G band intensity ratio of 0.94,and a C/O atomic ratio of 8.As a result,the high-density 3D-CT nanoarray-based sandwich-type EDLCs demonstrate a record high specific areal capacitance of 3.23 mF cm^(-2) at 120 Hz and exceptional fast frequency response due to the vertically aligned and highly ordered nanoarray of closely packed CT units.The 3D-CT nanoarray electrode-based EDLCs could serve as line filters in integrated circuits,aiding power system miniaturization.

Effect of ball-milling technology on pore structure and electrochemical properties of activated carbon

The effects of particle size of activated carbon （AC） on its wettability, electrode coating technology and electric chemical performance were studied to assemble nonaqueous electric double layer capacitors （EDLCs） for high power requirements. The results show that the specific surface area and total pore volume of AC decrease from 2 137 m^2/g to 1 683 m^2/g, and 0.95 cm^3/g to 0.78 cm^3/g, respectively, if it is ball-milled for 8 h. The pore size distributions are similar in the range of 0.7 nm to 3.5 nm for different ball-milling time. There exists oxidation on the surface of AC during the ball-milling process and the ratios of O-C=O oxygen compositions increase whereas those of C-O, C=O decrease. The peeling strength of AC coated on current collector is almost inverse proportion with the particle size of AC as well as the resistance of EDLCs, and its capacitance decreases about 6%.

粘结剂对块状极板碳纳米管双电层电容器性能影响研究

碳纳米管具有良好的导电性和合适的双电层形成区，适于制作双电层电容器极板． 不同粘结剂的使用会影响电容器的性能，分别选用酚醛树脂和聚四氟乙烯（ＰＴＦＥ）作为碳纳米 管极板的粘结剂，在有机电解质溶液中，研究其电容性能与比表面积和极板结构的关系，从而 找出合适的碳纳米管极板粘结剂．

以食糖热裂解碳作为电极的双电层电容器的性能

A new precusor of activated carbon material--sugar was pyrolyzed under many different conditions. Experiments were carried out to search for optimal pyrolyzing conditions. It was found that sugar should be carbonized at 700 ℃ and activated with potassium hydroxide at 800 ℃. The activated carbon prepared from pyrolytic treatment of sugar is therefore potential candidates as electrode material of electric double layer capacitor.

新型复合电化学电容器的研究

在单体碳/碳型双电层电容器的电极中分别添加一定量具有高容量性质的活性物质,构成正、负复合电极,活性物质经激活后即可在两极存储电能。该新型复合电容器与原碳/碳型双电层电容器相比,具有更高的稳定工作电压以及较高的单电极比容量,可有效改善双电层电容器的比能量及安全性能。根据所加活性物质比例及所选工作电压之不同,比能量可增加45%～70%。经不同电流密度恒流充放电试验,复合电容器的功率密度、充放电效率及循环寿命等性能良好,高容量活性物质的添加对双电层电容器较高的自放电现象具有一定的抑制作用。

超级电容器用炭材料的研究进展

综述了活性炭(AC)、活性炭纤维(ACF)、炭气凝胶、碳纳米管(CNTs)和模板炭等5种用于超级电容器的炭材料的性能和不足,展望了炭材料应用于超级电容器的发展方向。

微网系统中超级电容充电性能研究(英文)

为了考察超级电容微网储能性能,以典型超级电容实际产品为对象,针对恒电压、恒电流以及恒功率3种充电模式,研究充电时间及储能效率问题.提出了各种充电模式的数值计算方法,并利用严格的数学推导讨论了不同充电模式的效率问题.同时通过一个独立PV/EDLC系统验证了计算的准确性.最后研究分析了不同充电模式的充电速度与能量损失的权衡问题.研究结果表明:与传统的恒电压和恒电流充电方式相比,恒定功率充电方式更适用于微网系统.混合充电方式在实际应用中会更高效节能,但需根据实际具体要求合理处理不同充电模式的组合比例.

双电层电容器活性炭电极的优化

通过物理方法对双电层电容器用活性炭电极进行改性实验,探讨了活性炭电极的结构(比表面积、孔径分布、孔容)和性能(比电容、充放电特性)的优化问题.改性后活性炭电极BET比表面积从1739.77m2·g-1增至2215.40m2·g-1,其中微孔比表面积增幅22%,中孔比表面积增幅35%,孔容积也有20%～30%的增幅量,孔径分布更为合理.优化的活性炭电极结构改善了电极材料的电化学特性,比电容量可达424F·g-1,增幅10%.

煤基活性炭用作双电层电容器电极材料

以云南小发路煤矿产无烟煤为原料,KOH为活化剂制取双电层电容器用高比表面积活性炭电极材料。系统考察了活化剂用量、活化时间和活化温度对活性炭电容特性的影响。研究结果表明,在mKOH/m无烟煤=4、升温速度为4℃/min、活化温度为750℃及保温时间为1h的工艺条件下,可制得双电极比电容达69.7F/g的无烟煤基高比表面积活性炭,由它组装的模拟双电层电容器具有良好的充放电性能和循环性能。

双电层电容器用酚醛树脂基活性炭的制备

以酚醛树脂为原料,KOH为活化剂制备双电层电容器用高比表面积活性炭电极材料。考察了工艺因素对活性炭比电容的影响,探讨了酚醛树脂基高比表面积活性炭作双电层电容器电极的电化学特性。结果表明,在固化温度为150℃、炭化温度为700℃,ζ(碱/炭)为4,活化温度为800℃时,制得的高比表面积活性炭双电极比电容可达74.2 F/g。