Characterisation of activated nanoporous carbon for supercapacitor electrode materials

Commercial nanoporous carbon RP-20 was activated with water vapor in the temperature range from 950 °C to 1150 °C. The XRD analysis was carried out on nanoporous carbon powder samples to investigate the structural changes (graphitisation) in modified carbon that occurred at activation temperatures T ? 1150 °C. The first-order Raman spectra showed the absorption peak at 1582 cm⁻¹ and the disorder (D) peak at 1350 cm⁻¹. The low-temperature N₂ adsorption experiments were performed at −196 °C and a specific surface area up to 2240 m²g⁻¹ for carbon activated at T = 1050 °C was measured. The cell capacitance for two electrode activated nanoporous carbon system advanced up to 60 F g⁻¹ giving the specific capacitance ∼240 F g⁻¹ to one electrode nanoporous carbon ∣1.2 M (C₂H₅)₃CH₃NBF₄ + acetonitrile solution interface. A very wide region of ideal polarisability for two electrode system (∼3.2 V) was achieved. The low frequency limiting specific capacitance very weakly increases with the rise of specific area explained by the mass transfer limitations in the nanoporous carbon electrodes. The electrochemical characteristics obtained show that some of these materials under discussion can be used for compilation of high energy density and power density non-aqueous electrolyte supercapacitors with higher power densities than aqueous supercapacitors.     

Synthesis of nanocast ordered mesoporous carbons and their application as electrode materials for supercapacitor

Various nanocast ordered mesoporous carbons (OMCs) were synthesized using mesoporous silicas such as SBA-15, SBA-16, KIT-6, SBA-3 and MCM-48 as templates via nanocasting pathway. The structures of OMCs were analyzed by X-ray diffraction, transmission electron microscope and nitrogen sorption technique. These OMCs with well-defined pore structure were used as model electrode materials for investigating the influence of pore structure on their double layer capacitances. The cyclic voltammetry and galvanostatic charge/discharge measurements were conducted to estimate the capacitive behaviour of OMCs. The results show that the mesopore structures of OMCs play an important role in improving surface utilization for the formation of electrical double layer. OMCs synthesized from SBA-15 and SBA-16 show great advantage over others because their micropores are being easy accessible through the mesopores, thus allowing rapid electrolyte ion diffusion. To achieve a higher specific capacitance (μF cm⁻²), the optimized amount ratio between micropore and mesopore needs to be controlled. In addition, great impact of the electrode disc thickness on the capacitive performance was demonstrated by a series of careful measurements.     

Hierarchical porous carbons with controlled micropores and mesopores for supercapacitor electrode materials

Various porous carbons were prepared by CO₂ activation of ordered mesoporous carbons and used as electrode materials for supercapacitor. The structures were characterized by using X-ray diffraction, transmission electron microscopy and nitrogen sorption at 77 K. The effects of CO₂ treatment on their pore structures were discussed. Compared to the pristine mesoporous carbons, the samples subjected to CO₂ treatment exhibited remarkable improvement in textural properties. The electrochemical measurement in 6 M KOH electrolyte showed that CO₂ activation leads to better capacitive performances. The carbon CS15A6, which was obtained after CO₂ treatment for 6 h at 950 °C using CMK-3 as the precursor, showed the best electrochemical behavior with a specific gravimetric capacitance of 223 F/g and volumetric capacitance of 54 F/cm³ at a scan rate of 2 mV/s and 73% retained ratio at 50 mV/s. The good capacitive behavior of CS15A6 may be attributed to the hierarchical pore structure (abundant micropores and interconnected mesopores with the size of 3-4 nm), high surface area (2749 m²/g), large pore volume (2.09 cm³/g), as well as well-balanced microporosity and mesoporosity.     

State of hydrogen electrochemically stored using nanoporous carbons as negative electrode materials in an aqueous medium

Nanoporous carbons were used as negative electrode material in aqueous KOH medium to store hydrogen by electrodecomposition of water at atmospheric pressure. The storage capacity by this process is approximately one order of magnitude higher than in the gas phase at ambient conditions. By considering the particularities of the electrochemical characteristics, this paper gives information on the mechanism and on the kind of bond between hydrogen and the carbon host. For most experiments, a self-standing porous carbon cloth electrode has been used in order to avoid any side effect which could be due to additives. After galvanostatic hydrogen charging, the carbon material was analyzed by galvanostatic discharge and temperature-programmed desorption in order to determine the nature of the carbon-hydrogen bond and the amount of hydrogen sorbed. The activation energy for hydrogen desorption was estimated to be 110 kJ/mol, that confirms a weak chemical character of the hydrogen-carbon bond. Although the bond is stronger than in the case of physisorption, the fraction of hydrogen irreversibly trapped is low compared to the reversible fraction. Finally, we show that the reversible capacity can be significantly enhanced by increasing the temperature to 60 °C during the electrochemical reduction of water. The well-defined plateau during the oxidation step demonstrates high potentialities of this technique for electrochemical energy storage in nanoporous carbons using an aqueous medium.     

Feasibility of bamboo-based activated carbons for an electrochemical supercapacitor electrode

This study focused on the preparation and electrochemical properties of bamboo-based activated carbons (ACs) through carbonization and subsequent activation with steam and non-aqueous electrolyte solutions. The specific surface areas and the capacitances of samples ranged from 445 to 1,025 m²/g and from 5 to 60 F/g, respectively, depending on the activation conditions. The sample activated at 900 ‡C for 60 min under our experimental conditions exhibited the highest capacitance and the largest specific surface area.     

Synthesis of nanoporous carbons from mixtures of coal tar pitch and furfural and their application as electrode materials

Synthetic nanoporous carbons are prepared by polymerization of mixtures containing coal tar pitch and furfural in different proportions, followed by carbonization of obtained solid product and steam activation of the carbonizate. The chemical composition of the initial mixture significantly affects the physicochemical properties (surface area, pore structure, electro resistance and amount of oxygen-containing groups on the surface) of the obtained materials. The incorporation of oxygen in the precursor mixture by means of furfural, has a strong influence in the synthetic step; increasing the furfural content facilitates the formation of a solid product characterized by a large oxygen content. Moreover, the solid product is more reactive towards activation as the furfural content increases, giving rise to nanoporous carbons with large surface areas and unique chemical features (high density of oxygen functionalities of basic nature). These nanoporous carbons have been investigated as electrodes in electrochemical applications.     

Photoluminescence of nanoporous carbons: Opening a new application route for old materials

Photoluminescence of oxygen, sulfur, and nitrogen containing nanoporous carbons was detected in the visible range. This behavior was linked to the presence of sulfones, sulfoxides, sulfonic acids and nitrogen moiety, which act as chromophores in the carbon pore system. They absorb radiation close to visible range and electrons are transferred to the graphitic domains of carbon matrices, which are in the vicinity of these groups. This process results in photoluminescence, which was observed in spite of the strong light absorbing nature of carbons. These features of nanoporous carbons can open the new route for their applications as sensors and drug delivery carries.     

超级电容器电极材料研究最新进展

超级电容器是一种介于传统电容器与化学电源之间的新型储能元件,它具有充电时间短、循环寿命长、功率密度大、能量密度高、适用温度范围宽和经济环保等优势,目前在很多领域都受到广泛关注。本文概述了超级电容器电极材料的研究情况,包括碳基材料、金属氧化物材料及导电聚合物材料等。     

浅谈超级电容器电极材料的研究进展

介绍了碳材料、金属氧化物和导电聚合物及其复合材料等超级电容器电极材料的研究现状,并指出其发展方向是制备性能优异的复合材料和实现材料纳米化。     

Ferroelectric metal organic framework (MOF)

Multiferroic metal organic frameworks (MOFs) with magnetic ordering and ferroelectric ordering coexisting have recently drawn considerable interest for their amazing applications in the field of magnetoelectric multifunctional materials. Based on the Landau theory and related characterizations, this comment in detail discusses the second-order ferroelectric phase transition of ABO₃ perovskite-type MOFs, including Curie–Weiss constants, symmetry breaking, spontaneous polarization, dielectric hysteresis loop, and so on. Eventually, the author gives a prospect about the development of ferroelectric MOFs. This mini-account will be of guiding significance for the design and synthesis of metal organic framework functional materials with specific multiferroic properties.     

Nanostructured manganese dioxides: Synthesis and properties as supercapacitor electrode materials

Low-cost layered manganese oxides with the rancieite structural type were prepared by reduction of KMnO₄ or NaMnO₄ in acidic aqueous medium, followed or not by successive proton- and alkali-ion-exchange reactions. Samples were characterized by X-ray diffraction, energy dispersive X-ray analysis, BET surface area measurements, thermal analyses and X-ray photoelectron spectroscopy. As a result of successive exchange steps, compounds with high surface area (reaching 200 m² g⁻¹) can be obtained, and in the case of syntheses made with KMnO_4, the α-MnO₂ phase is formed. Capacitive properties of the synthesized materials were studied using potentiodynamic cycling in K₂SO₄. Correlations between the electrochemical and the physicochemical properties of the samples were investigated. The interesting conclusion is that the morphology and the size of the particles influence directly the capacitance, and that among the samples presenting the best morphology, the compounds derived from K-containing rancieite-type compounds (and containing α-MnO₂) present a better cycleability.     

Synthesis of nanoporous carbons/metal nanoparticles composite through direct carbonization of a MOF for catalytic reduction of 4-nitrophenol

Journal of Porous Materials - A facile and effective synthetic route has been utilized to synthesize nanoporous carbons (NPCs)/cobalt nanoparticles (CoNPs) composites by direct carbonization of a...     

石油焦基多孔炭电极材料的制备及调控

以石油焦为原料,氢氧化钾为活化剂,采用化学活化法制得中孔丰富、比表面积高的多孔炭。通过硝酸铁溶液浸渍,再经高温热处理,或在高温过程中通入CO2,对多孔炭进行孔结构深度调控。将所制多孔炭用作电化学电容器电极材料,通过恒流充放电、循环伏安测试其电化学性能,采用氮气吸附法测定多孔炭的比表面积及孔径分布。结果表明:KOH与石油焦质量比为3∶1,活化温度850℃,活化时间90 min时,可以制得比表面积为2 738 m2/g,总孔容为1.51 cm3/g,中孔率为43.2%的多孔炭,在电流密度为100 mA/g时,该电极在6 mol/L KOH电解液中的比电容值高达256.6 F/g。多孔炭经金属盐溶液浸渍并经CO2二次活化后,中孔率由43.2%提高至70.7%,尽管因比表面积的下降造成了电极比电容值的下降,但由于中孔率的提高,电极的充放电速率明显加快。     

Polyaniline/multi-walled carbon nanotube composites with core-shell structures as supercapacitor electrode materials

Composites with core-shell structures consisting of polyaniline and carbon nanotubes were prepared via in situ polymerization of aniline monomers by using multi-walled carbon nanotubes with minimized defects as templates. The strong interaction in such conjugated systems greatly improves the charge-transfer reaction between polyaniline and the carbon nanotube. Influences of the thickness of the polyaniline layer on the surface of the carbon nanotubes on the electrochemical properties of the resulting composites are discussed. The highest specific capacitance of 560 F/g was achieved by using a composite with 66 wt% polyaniline content as the supercapacitor electrode. Additionally, enhancement of the capacity retention was observed, with the composite losing only 29.1% of the maximum capacity after 700 cycles, and then remaining stable.     

四氧化三钴超级电容器电极材料的制备与研究

电极材料是决定电化学电容器性能的一个主要方面,研究与开发高性能的电极材料是人们的研究重点之一.碳电极材料比电容较小;钌等贵重金属氧化物电极材料比电容量虽然很高,但昂贵的价格限制了其实际应用.因此价格低廉、环境友好、同样具有较高氧化还原电容的过渡金属氧化物成为目前超级电容器的研究热点之一.以硝酸钴为原料,以柠檬酸为模板水热合成了前驱体,200 ℃热处理后得到了四氧化三钴.循环伏安、恒流放电等电化学测试表明,200 ℃所得四氧化三钴电极在6 mol/L氢氧化钾溶液中和-0.1～0.5 V (vs. SCE) 电位范围内,具有较好的循环稳定性能,单电极比电容达到442 F/g.为开发高性能的超级电容器电极材料提供了参考.     

碳包覆金属氧化物作为超级电容器电极材料的研究进展

综述了碳包覆金属氧化物作为超级电容器电极材料的最新研究进展。详细介绍了贵重金属氧化物（如RuO2）和廉价金属氧化物（如Fe3O4、SnO2、TiO2、MnO2等）在超级电容器电极材料领域内的应用现状和存在的问题,指出了碳包覆廉价金属氧化物所形成的核/壳结构很好地解决了金属氧化物易溶于电解液、充放电体积易膨胀等问题,展望了其作为超级电容器电极材料在消费电子、航空航天、国防科技等领域中的应用前景。