Effect of surface area and heteroatom of porous carbon materials on electrochemical capacitance in aqueous and organic electrolytes

A series of porous carbon materials with wide range of specific surface areas and different heteroatom contents had been prepared using polyaniline as carbon precursor and KOH as an activating agent. Effect of surface area and heteroatom of porous carbon materials on specific capacitance was investigated thoroughly in two typical aqueous KOH and organic 1-butyl-3- methylimidazolium tetrafluoroborate/acetonitirle electrolytes. The different trends of capacitance performance were observed in these two electrolytes. Electrochemical analyses suggested that the presence of faradaic interactions on heteroatom-enriched carbon materials in organic environment is less significant than that observed in aqueous electrolytes. Thus, in aqueous electrolyte, a balance between surface area and heteroatom content of activated porous carbon would be found to develop a supercapacitor with high energy density. In organic electrolyte, the capacitance performance of porous carbon is strongly dependent on the surface area. The results may be useful for the design of porous carbon-based supercapacitor with the desired capacitive performance in aqueous and organic electrolytes.     

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.     

The effect of pre-carbonization of mesophase pitch-based activated carbons on their electrochemical performance for electric double-layer capacitors

The activated carbons (ACs) are prepared from mesophase pitch which is pre-carbonized by using potassium hydroxide as an activating agent. Nitrogen adsorption at 77 K is used to characterize the surface area and the porous structure of the ACs. By changing the pre-carbonization temperature from 560 to 750 °C, the arrangement of the ACs’ microcrystallines might be controllable, and the pore size could be adjusted between 1.5 and 2.4 nm. The electrochemical performance of the ACs in organic solvent (1 M Et₄NBF₄ in propylene carbonate) is investigated by voltage sweep cyclic voltammetry and constant current charge–discharge cycling tests. The results show that the ions can transfer rapidly and freely in the pore larger than or equal to 1.85 nm, even when the current density increases to 25 A g⁻¹.     

Double-layer capacitance of waste coffee ground activated carbons in an organic electrolyte

Using ZnCl₂ activation we prepared a series of carbon electrodes from waste coffee grounds to study the effect of mesopores on double-layer capacitance in a tetraethyl ammonium tetrafluoroborate/acetonitrile electrolyte. The activated carbon with the largest mesopore volume achieved an energy density of 34 Wh kg^?1 at low current loads, and significantly retained an energy density of 16.5 Wh kg^?1 and specific capacitance of more than 100 F g^?1 at fast charge–discharge rates (20 A g^?1). The effect of mesopores on capacitance at fast charge–discharge rates is discussed.     

Hybrid electrochemical capacitors in aqueous electrolytes: Challenges and prospects

In an internal hybrid capacitor, at least one electrode displays battery-like charge/discharge and the other electrode stores charge reversibly at the electric double-layer (EDL). Recently, a plethora of hybrid cells in aqueous electrolytes have been proposed by coupling an EDL electrode with a battery electrode, the latter made from a variety of redox-active/redox-mediator species either dissolved in the electrolyte or adsorbed/immobilized in nanoporous electrodes. This review presents current opinions, discusses challenges, and supplies recommendation about the hybrid cells with aqueous electrolytes and carbon electrodes.     

Impact of synthesis conditions on surface chemistry and structure of carbide-derived carbons

Carbide-derived carbons produced by chlorination of titanium carbide at 600, 800, or 1100 °C were subjected to a post-treatment at 600 °C in Ar, H₂, or NH₃ atmosphere. Experimental results suggest that the chlorination temperature influences the ordering of carbon in a manner that impacts specific surface area and porosity. Higher chlorination temperatures lead to higher total pore volume and increased ordering, but lower microporosity. The effect of post-treatments on surface chemistry is pronounced only for samples chlorinated at 600 °C; post-treatments in Ar are shown to be less effective for chlorine removal than those performed in H₂ or NH₃. Post-treatments in Ar result in a lower total pore volume compared to the ones in H₂ or NH₃ for the same chlorination temperature. Samples chlorinated at higher temperatures contained less oxygen functionalities than samples chlorinated at 600 °C, and showed correspondingly less desorption of H₂O, possibly due to diminished uptake of ambient water.     

Synchrotron-induced photoemission of GaAs electrodes after electrochemical treatment in aqueous electrolytes

Electrochemically-induced oxidation and reduction reactions of UHV-cleaved GaAs(110) surfaces have been studied after emersion under potential control using high resolution synchrotron-induced photoelectron spectroscopy. High quality spectra of the As and Ga core 3d lines and the valence band region have been obtained. The spectra of the anodic oxide show strong emission of bulk-like Ga(2)O(3) and some As(2)O(3) with the admixture of suboxides and hydroxides. Ga(2)O(3) and As(2)O(3) are cathodically reduced leaving the GaAs surface covered mostly with elemental As, some As-H and remnants of Ga-suboxides and -hydroxides.     

氧化石墨烯/聚苯胺复合材料的制备及电化学电容性能的研究

以对苯二胺为引发剂,用苯胺和氧化石墨烯(GO)为原料,采用化学原位聚合法制备了氧化石墨烯/聚苯胺(GP)复合材料,不添加任何表面活性剂和模板剂。采用傅里叶变换红外(FTIR)光谱、X射线粉末衍射(XRD)、扫描电镜(SEM)和透射电镜(TEM)对复合材料进行了物性表征,并对其电化学性能进行了测试。结果显示,复合材料保持了氧化石墨烯的基本形貌,聚苯胺纤维分布在氧化石墨烯层间及所形成的褶皱上。二者形成的二元纳米复合材料,发挥良好的协同作用,电化学性能得到了改善。当电流密度为0.5A·g-1时,复合材料的比电容可以达到623F·g-1,远大于石墨烯和聚苯胺单体的比电容。     

Insights on electrochemical properties of gel polymer electrolytes based on methylmethacrylate

This paper explains some properties of gel polymer electrolytes, which are mostly used in lithium ion batteries. An emphasis is laid on the internal structure and its influence on the mobility of ions in the substance. The ions are solvated and located randomly in the liquid base of the gel, and their movement is predominantly determined by the Stokes law for liquid electrolytes. Polymethylmethacrylate gel is used as a model substance here. This report is based on the experience of the authors and their associates.     

Correlation in the properties of aqueous single films and foam containing a nonionic surfactant and organic/inorganic electrolytes

Correlation of the behavior of foam from aqueous solutions of C(10)E(8) + TPeAB mixtures with the properties of the single foam films is sought through a theoretical analysis based on experimental data. The state in the adsorption layer on the air/solution interface has been determined from the surface tension experimental data by applying the Frumkin adsorption isotherm for mixed surfactants. Diverse parameters of the adsorption layer have been calculated. Values of the surface potential, estimated from the electrostatic disjoining pressure in the films, are found to be in good agreement with those calculated through the Grahame equation for the air/water interface. The energy of interaction (attraction) in the mixed adsorption layers is determined. The behavior of a foam body produced from solutions of the same composition, is also investigated in two independent ways using the stationary foam column and the foam life-time (decay rate) methods. Both techniques gave similar results with respect to foam stability.     

Effects of activation conditions on the electrochemical capacitance of activated carbon nanotubes

The effects of different activation conditions (including KOH/CNTs ratio, activation temperature, activation time and nitrogen flow rate) on the electrochemical capacitance of activated carbon nanotubes (CNTs) have been investigated. All the four factors can affect the activated CNTs’ electrochemical capacitance. And the effects on the activated CNTs’ electrochemical capacitance carried out by virtue of their effects on activated CNTs’ BET specific surface area and graphitized degree.     

Experimental strategy for characterization of essential dynamical variables in oscillatory systems: effect of double-layer capacitance on the stability of electrochemical oscillators

An experimentally accessible algorithm for changing the time scale associated with a dynamical variable is proposed. In general, a differential controller can be applied to (a) identify the essential species in oscillatory systems and (b) explore their role in the feedback loops. Here, we report on classifying electrochemical oscillators by changing the time scale over which the electrode potential varies; the type of different electrochemical oscillators is identified based on whether the controlled modification of pseudo-capacitance induces or suppresses current oscillations.     

Corrosion properties of nickel coatings obtained from aqueous and nonaqueous electrolytes

Nickel was deposited on a copper substrate from aqueous and nonaqueous ethanol electrolytes. X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy and chronovoltametry, scanning electron microscopy, and atomic force microscopy were used to study the effect of the solvent on the surface and corrosion properties of the Ni coatings formed. Unifom and relatively smooth Ni films were obtained as measured with microscopy techniques. The formation of a passive film in acidic, alkaline, and neutral chloride-containing media was confirmed with X-ray photoelectron spectroscopy. The water-based nickel-plating electrolyte makes it possible to deposit coatings with higher corrosion resistance as compared with coatings deposited from ethanol electrolyte in NaOH and NaCl media. The proposed mechanism of corrosion in a 0.5 M H₂SO₄ solution involves cycles of active-passive surface behavior due to its passivation by corrosion products.