Carbide-derived Carbon Materials Research Articles

Supercapacitors Based on Activated Silicon Carbide-Derived Carbon Materials and Ionic Liquid

Cyclic voltammetry, constant current charge/discharge, electrochemical impedance spectroscopy and constant power discharging methods have been applied to establish the electrochemical characteristics of electric double–layer capacitor (EDLC) consisting of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) and micro/mesoporous carbon electrodes prepared from silicon carbide derived carbon (SiC-CDC) that have been additionally activated with carbon dioxide (CO2). The electrochemical characteristics for EDLCs (region of ideal polarizability, characteristic time constant, specific series and parallel capacitances) are significantly dependent on the CO2 activation extent of the SiC-CDC materials. The calculated coulombic efficiency values for CO2 activated systems vary within the range from 97 to 99.8% (calculated using integrated charge density values). The energy efficiencies from 82 to 86.5% show that the CO2 activated SiC-CDC powders are much more suitable for various power and energy storage applications compared to untreated SiC-CDC. From impedance spectroscopy the highest capacitance value of 170 F g−1 at 3.6 V has been established for SiC-CDC with the largest activation burn–off extent of carbon from SiC-CDC. The Ragone plots for the carbon materials synthesized show noticeable influence of the CO2 activation extent on the stored specific energy and specific power values delivered.

Producing high quality carbide-derived carbon from low quality byproducts stemming from SiC production

The utilization of carbide-derived carbons (CDCs) in a wide range of applications is obstructed due to relatively high production costs. In this study a possibility to reduce the costs of CDC synthesis by employing low quality SiC byproducts stemming from the ESK process is presented. While the crystallinity and impurity content differs for the different precursor qualities, the resulting CDC materials possess similar textural characteristics and carbon microstructures. Evaluation of intrinsic kinetic data reveals that the low grade precursors react faster during reactive extraction and can be best described by a power law approach. The CDC materials were further investigated with respect to their performance as electrode materials in Electric Double Layer Capacitors (EDLC). All SiC-CDCs display a comparable and excellent specific capacitance of approx. 115Fg−1. The results are demonstrating the promising utilization of CDC materials synthesized from low valuable SiC feedstock.

Carbon Dioxide Activated SiC-CDC: Attractive Material for Supercapacitor Electrodes

Nanostructured carbide-derived carbons (CDC) were synthesized from SiC powders (SiC-CDC) via gas phase chlorination at temperature 1000 ºC [1]. Thereafter the CDCs were additionally activated by CO2 treatment method, resulting in nearly two-fold increase in specific surface area. The results of X-ray diffraction, high-resolution transmission electron microscopy (Figs. 1a and b) and Raman spectroscopy showed that the synthesized CDC materials are mainly amorphous, however containing small graphitic crystallites. The low-temperature N2 sorption experiments (Fig. 1c) were performed and the specific micropore surface areas from 1100 m2 g-1 up to 2270 m2 g-1 were obtained, depending on the extent of CO2 activation. The energy and power density characteristics of the supercapacitors based on 1 M (C2H5)3CH3NBF4 solution in acetonitrile and SiC-CDC as an electrode material were investigated using the cyclic voltammetry, electrochemical impedance spectroscopy, galvanostatic charge/discharge and constant power discharge methods. The cycling efficiency, i.e., the so–called round trip efficiency (RTE) has been calculated as a ratio of charge released and accumulated during discharging and charging of the supercapacitors. The calculated RTE values for all CO2 activated systems remained within the range from 98 to 99 %, showing that the CO2 activated SiC-CDC powders are promising materials for various energy storage applications. The specific capacitance values (C m), calculated from the Nyquist plots at ac frequency ƒ = 1 mHz depend on the SiC-CDC material used and C m values are very high for CO2 treated systems if compared with untreated SiC-CDC. C m values obtained from Nyquist plots are somewhat higher, but nevertheless in a good agreement with the values obtained using CV and CC methods. C m values for additionally CO2 treated SiC-CDC are comparable with data obtained for other CDC materials (TiC-CDC, VC-CDC, WC-CDC) studied. The maximum C m values (125 - 130 F g-1) have been calculated for mainly microporous SiC-CDC 1000 ºC activated with CO2 at 950 ºC for 8 h, however having well developed mesopores inside 2 – 4 nm region (Fig. 1c). The Ragone plots (Fig. 1d) calculated to the total material weight of two electrodes for the supercapacitors based on different SiC-CDC electrodes have been obtained from the constant power tests within the cell potential range from 3.0 V to 1.5 V. The mass fraction of active carbon material per electrode is 0.9, taken into account the PTFE binder and Al current collector. Very good performance has been established for SiC-CDC 1000 ºC, additionally activated at 900 °C during 8 h. The activation time 16 h at T = 950 ºC seems to be too long and therefore we have established different activation times for SiC-CDC additionally CO2 activated supercapacitors if various activation temperatures have been used. This conclusion is in a good agreement with N2 sorption data as well as our data published before [2,3]. Thus, differently from TiC-CDC the additional CO2 activation step has enormous influence on power densities of supercapacitor cells completed.

Huge enhancement of energy storage capacity and power density of supercapacitors based on the carbon dioxide activated microporous SiC-CDC

Nanostructured carbide-derived carbons (CDC) were synthesized from SiC powders (SiC-CDC) via gas phase chlorination within the temperature range from 1000°C to 1100°C. Thereafter the CDCs were additionally activated by CO2 treatment method, resulting in nearly two-fold increase in specific surface area. The results of X-ray diffraction, high-resolution transmission electron microscopy and Raman spectroscopy showed that the synthesized CDC materials are mainly amorphous, however containing small graphitic crystallites. The low-temperature N2 sorption experiments were performed and the specific micropore surface areas from 1100m2g−1 up to 2270m2g−1 were obtained, depending on the extent of CO2 activation. The energy and power density characteristics of the supercapacitors based on 1M (C2H5)3CH3NBF4 solution in acetonitrile and SiC-CDC as an electrode material were investigated using the cyclic voltammetry, electrochemical impedance spectroscopy, galvanostatic charge/discharge and constant power discharge methods. The electrochemical data indicated two-times increase in specific capacitance. Most importantly, the activation of SiC-CDC with CO2 significantly increases the performance (energy density, power density, etc.) of the supercapacitors especially at higher potential scan rates and at higher power loads.

Experimentelle Analyse der Mikrostrukturbildung am Einzelpartikel und Mikrotropfen

© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Chem. Ing. Tech. 2014, 86, No. 9, 1541–1567 Classical approaches to combine mesoporosity with a high graphitization are mainly using softor hardtemplating techniques [1]. However, drawbacks are the limited degree of graphitization obtained and the functionalization/impurity of the materials. In contrary, carbidederived carbon (CDC) is a high-purity carbon originating from the reactive extraction of carbides [2]. The applied extraction conditions and the choice of the precursor allow for tuning of material properties [2]. Nevertheless, for CDC materials, there is a lack of combining mesoporosity with a graphitic character without further treatments. The reactive extraction of titanium carbide with chlorine above 1200 °C as a one-step process was studied, resulting in high-purity graphitic and mesoporous carbons. The mean pore size increases from 0.71 nm at 500 °C to 3.70 nm at 1400 °C. Below 1000 °C X-ray amorphous carbons result whereas at 1200 °C graphite reflexes start to get observable. Further TEM and Raman studies proof the higher graphitic order. In line with the increasing graphitic character, cyclic voltammetric measurements reveal an enhanced electrochemical stability.

Novel micromesoporous carbon materials synthesized from tantalum hafnium carbide and tungsten titanium carbide

Nanostructured carbide-derived carbons (CDC) were synthesized from Ta4HfC5 and WTiC2 powders via gas phase chlorination within the temperature range from 800 to 1100°C. The results of X-ray diffraction, high-resolution transmission electron microscopy and Raman spectroscopy showed that the synthesized CDC materials are mainly amorphous, containing relatively small graphitic crystallites. The scanning electron microscopy data revealed the breaking down of the initial carbide particles into smaller ones. The low-temperature N2 sorption experiments were performed and the specific micropore surface areas up to 1950m2g−1 and 1880m2g−1 were obtained for Ta4HfC5-CDC and WTiC2-CDC, respectively. The energy-related properties of the supercapacitors based on 1M (C2H5)3CH3NBF4 solution in acetonitrile and Ta4HfC5-CDC or WTiC2-CDC as an electrode material were investigated using the cyclic voltammetry, electrochemical impedance spectroscopy, galvanostatic charge/discharge and constant power charge/discharge methods. The Ragone plots (using the total material weight or volume of two electrodes) for the supercapacitors based on the Ta4HfC5-CDC and WTiC2-CDC electrodes have been calculated from constant power tests within the potential range from 3.0 to 1.5V, demonstrating the high gravimetric (28Whkg−1) and volumetric (18Whdm−3) energy densities at high power density (10kWkg−1 and 15kWdm−3, respectively).

Electrochemical and Physical Characterization of Pt Activated Micromesoporous Vanadium Carbide Derived Carbon Electrodes in Sulfuric Acid Solution

Micromesoporous carbide derived carbon (CDC) powders synthesized from vanadium carbide (VC) at 900°C and 1100°C using high-temperature chlorination method were used as catalyst supports for Pt nanoclusters modified electrodes. The specific surface area of unmodified C(VC)900°C and C(VC)1100°C powders were 1348 and 236 m2 g−1, respectively, and for modified Pt-C(VC)900°C and Pt-C(VC)1100°C powders 513 to 89 m2 g−1, respectively. Analysis of X-ray diffraction, X-ray fluorescence, X-ray photoelectron spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and high-resolution transmission electron microscopy data confirm that CDC based catalysts are free from residuals of raw materials, chlorine and, chloride ions contamination and show that the materials with highly porous structure have been formed. It was established that the Pt nanoclusters have been deposited uniformly into/onto CDC. Cyclic voltammetry and rotating disk electrode data show that high cathodic current density −70 A m−2 has been achieved for 0.5 M H2SO4 aqueous solution. The high kinetic current density values, noticeably depending on the material porosity studied, have been obtained for Pt-nanocluster|CDC materials.

Carbide‐Derived Carbon Monoliths with Hierarchical Pore Architectures

Porous carbon materials are crucial components in catalysis, gas storage, electronics, and biochemistry. A hierarchical pore architecture in these materials is essential to achieve high surface areas combined with advanced mass transport kinetics. Widely used approaches for the generation of microor mesopores are activation and nanocasting. In contrast, macroporous carbon materials are primarily obtained by carbonization of polymeric precursor gels or replication of larger templates. A relatively new class of microand mesoporous carbon material with tunable porosity are carbide-derived carbon materials (CDCs). High-temperature chlorination of carbides leads to selective removal of metalor semi-metal atoms and allows control over the pore size of the resulting CDCs in a subngstrcm range by changing synthesis conditions or the carbide precursor. These materials have been studied for applications in gas storage and as electrode materials in supercapacitors because of their high specific surface areas. Recently, metal etching from pyrolyzed pre-ceramic components (polysilsesquioxanes or polysilazanes) was found to be a useful route towards carbide-derived carbon materials with enhanced porosity and gas-storage properties. A significant step towards ultrahigh specific surface area combined with a hierarchical mesoporous–microporous system was achieved using nanocasting of silica templates (SBA-15 or KIT-6) with polycarbosilane precursors and subsequent chlorine treatment of the resulting ordered mesoporous silicon carbides. These ordered mesoporous CDCs offer specific surface areas as high as 2800 mg 1 and total pore volumes of up to 2 cmg . Their mesostructure can be easily controlled by changing the silica hard template, resulting in excellent performance in protein adsorption, gas storage, and as electrodes for supercapacitors. However, such carbon materials are available only as nonstructured micrometer-sized powders and cannot be shaped into films without the addition of binders or the use of high mechanical stress, leading to structural deformation. Chlorine treatment of mechanically mixed Si/SiC precursors was found to be a useful route towards monolithic CDC with a hierarchical pore system. The presence of a free metal phase in the precursor system provides the opportunity to introduce a secondary macroporosity of 3 mm sized channels with a volume of 0.23 cmg 1 along with the microporous carbide-derived carbon material system. The introduction of large transport pores in polymerbased CDCs might be an alternative way to form materials that combine high surface areas with efficient fluid transport. The current literature describes a variety of routes for the production of highly macroporous ceramics from precursor polymers with controllable cell and window sizes. In particular, direct blowing of polycarbosilanes was found to be a useful approach for the generation of silicon carbide foams that might be suitable materials for the production of hierarchical CDCs. In the following, we describe a novel synthesis route for monolithic carbide-derived carbon materials, including micro-, meso-, and macroporous structures with extremely high specific surface area. They can be obtained by hightemperature chlorination of macroporous polymer-derived silicon carbide (SiC-PolyHIPE). A soft-templating approach starting from a high internal phase emulsion (HIPE) was used with an external oil phase consisting of liquid polycarbosilane SMP-10 and the cross-linker paradivinylbenzene. Using Span-80 as surfactant to stabilize the internal water phase, the application of oxidic or carbon hard templates and the corresponding template removal under harsh conditions is no longer necessary. After cross-linking the polymer chains, the resulting PolyHIPEs were pyrolyzed to silicon carbides at maximum temperatures of 700, 800, and 1000 8C and subsequently converted into CDCs by chlorine treatment at the maximum pyrolysis temperature (Supporting [*] M. Oschatz, L. Borchardt, Dr. I. Senkovska, N. Klein, Dr. R. Frind, Prof. Dr. S. Kaskel Department of Inorganic Chemistry Dresden University of Technology Bergstrasse 66, 01062 Dresden (Germany) E-mail: stefan.kaskel@chemie.tu-dresden.de

In-situ thermal activation of carbide-derived carbon

Microporous carbons attract high interest due to their application as a medium for gas storage, catalyst support or electrode material in lithium ion batteries or supercapacitors. Carbide-derived carbons (CDC) produced by halogenation of carbides exhibit a narrow pore size distribution and a tunable pore and microstructure by choosing the appropriate carbide precursor and chlorination temperature. However, the pore volume is limited by the amount of metal in the carbide structure, and the variation of pore size by varying the process conditions is not possible for all carbides. With an in-situ thermal activation in CO 2 parallel to the chlorination, the porosity of the CDC materials can be further increased. This improved carbide-derived carbon process also allows producing novel pore structures which vary in the meso- to micropore ratio from the outside to the center of the particle. Thereby also the boarder case of shell-like carbon structures showing different pore size distributions in the shells can be produced. For this in-situ activation and chlorination of carbides the influence of the processing, the concentration of CO 2 and activation time on the pore structure of CDC was studied.

Processing of carbide-derived carbons with enhanced porosity by activation with carbon dioxide

Carbide-derived carbon (CDC) materials were synthesized by high temperature chlorination of biomorphic TiC and SiC ceramic structures. CDC allows the control over the pore size by choosing an appropriate carbide precursor as well as the reaction temperature. However, the pore volume is limited by the fraction of metal in the carbide structure. Since activation procedures such as treatment in CO 2 significantly increase the porosity of the carbon structure it is applied to pyrolyzed paper preforms and CDC materials. The activation procedure raises the specific surface area (SSA BET) and the pore volume of the carbon-based materials. The effect of variation of activation conditions like temperature, time and flow rate of CO 2 on the resulting pore structure is investigated. SSA BET up to 2300 m 2 g −1 and pore volumina of about 1.3 cm 3 g −1 are obtained. Activation times up to 6 h increase the micropore volume whereas longer activation times result in a decreased micropore volume by simultaneous transformation into mesopores. Activated CDCs from biomorphic ceramics are structured materials compared to powders described mainly in the literature.

Oxygen reduction on carbon nanomaterial-modified glassy carbon electrodes in alkaline solution

Electroreduction of oxygen in alkaline solution on glassy carbon (GC) electrodes modified with different carbon nanomaterials has been studied. Electrochemical experiments were carried out in 0.1 M KOH employing the rotating disk electrode and rotating ring-disk electrode methods. The GC disk electrodes were modified with carbon nanomaterials using polytetrafluoroethylene as a binder. Four different carbon nanomaterials were used: multiwalled carbon nanotubes, carbon black powder, and two carbide-derived carbons (CDC). For the first time, the electrocatalytic behavior of CDC materials toward oxygen reduction is explored. Electrochemical characterization of the materials showed that all the carbon nanomaterial-modified GC electrodes are highly active for the reduction of oxygen in alkaline solutions.

Carbide-derived-carbons with hierarchical porosity from a preceramic polymer

Synthesis of carbon by extraction of metals from carbides has been successfully used to produce a variety of micro-porous carbide-derived carbons (CDCs) with narrow pore size distributions and tunable sorption properties. This approach is of limited use when larger mesopores are targeted, however, because the relevant synthesis conditions yield broad pore size distributions. Here we demonstrate the porosity control in the 3–10 nm range by employing preceramic polymer-derived silicon carbonitride (SiCN) precursors. Polymer pyrolysis in the temperature range 600–1400 °C prior to chlorine etching yields disordered or graphitic CDC materials with surface area in the range 800–2400 m 2 g −1. In the hierarchical pore structure formed by etching SiCN ceramics, the mesopores originate from etching silicon nitride (Si 3N 4) nano-sized crystals or amorphous Si–N domains, while the micropores come from SiC domains. The etching of polymer-derived ceramics allows synthesis of porous materials with a very high specific surface area and a large volume of mesopores with well controlled size, which are suitable for applications as sorbents for proteins or large drug molecules, and supports for metal catalyst nanoparticles.

Micro- and Mesoporous Carbide-Derived Carbon Materials and Polymer Membranes for Supercapacitors

Several nanoscale fine-tuned micro- and mesoporous carbon powders C(Mo2C) produced by reacting Mo2C with Cl2 at various temperatures were studied and characterized using XRD and Raman spectroscopy methods and compared with low temperature N2 adsorption/desorption measurements data. Supercapacitors based on two ideally polarizable nanoporous carbon electrodes and different mesoporous commercially available separators in acetonitrile (AN) as the solvent for the 1.0 M (C2H5)3CH3NBF4 electrolyte have been completed and tested by cyclic voltammetry and electrochemical impedance methods.

Micro- and Mesoporous Carbide-Derived Carbon Materials and Polymer Membranes for Supercapacitors

not Available.

A Universal Model for Nanoporous Carbon Supercapacitors Applicable to Diverse Pore Regimes, Carbon Materials, and Electrolytes

Supercapacitors, commonly called electric double-layer capacitors (EDLCs), are emerging as a novel type of energy-storage device with the potential to substitute batteries in applications that require high power densities. In response to the latest experimental breakthrough in nanoporous carbon supercapacitors, we propose a heuristic theoretical model that takes pore curvature into account as a replacement for the EDLC model, which is based on a traditional parallel-plate capacitor. When the pore size is in the mesopore regime (2-50 nm), counterions enter mesoporous carbon materials and approach the pore wall to form an electric double-cylinder capacitor (EDCC); in the micropore regime (<2 nm), solvated/desolvated counterions line up along the pore axis to form an electric wire-in-cylinder capacitor (EWCC). In the macropore regime (>50 nm) at which pores are large enough so that pore curvature is no longer significant, the EDCC model can be reduced naturally to the EDLC model. We present density functional theory calculations and detailed analyses of available experimental data in various pore regimes, which show the significant effects of pore curvature on the supercapacitor properties of nanoporous carbon materials. It is shown that the EDCC/EWCC model is universal for carbon supercapacitors with diverse carbon materials, including activated carbon materials, template carbon materials, and novel carbide-derived carbon materials, and with diverse electrolytes, including organic electrolytes, such as tetraethylammonium tetrafluoroborate (TEABF(4)) and tetraethylammonium methylsulfonate (TEAMS) in acetonitrile, aqueous H(2)SO(4) and KOH electrolytes, and even an ionic liquid electrolyte, such as 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI). The EDCC/EWCC model allows the supercapacitor properties to be correlated with pore size, specific surface area, Debye length, electrolyte concentration and dielectric constant, and solute ion size It may lend support for the systematic optimization of the properties of carbon supercapacitors through experiments. On the basis of the insight obtained from the new model, we also discuss the effects of the kinetic solvation/desolvation process, multimodal (versus unimodal) pore size distribution, and exohedral (versus endohedral) capacitors on the electrochemical properties of supercapacitors.

The effect of graphitization catalyst on the structure and porosity of SiC derived carbons

A number of carbide-derived carbon (CDC) samples were synthesized through the reaction between α-SiC and gaseous chlorine at temperatures 900, 1000 and 1100 °C and by varying the amount of catalyst. The chlorides of Co(II), Ni(II) and Fe(III) were used as catalytic additives in a range of concentration of 0.1–5 wt%. The structural differences of the obtained carbons were studied by low-temperature nitrogen adsorption, X-ray diffraction and Raman spectroscopy. Results showed that porosity, specific surface area and graphitization degree of the CDC materials is a function of chlorination temperature and catalyst concentration, which agrees with previous results. It was shown that the catalytic graphitization only weakly influences the L a value of the crystallites, which according to the Raman scattering is ∼4–5 nm in both the highly disordered SiC derived carbons and in fully graphitic carbons made from SiC containing 15 wt% of surface-contacted Co–Ni–Fe catalyst. The surface area of the CDC materials can be controlled in the range of 300–1350 m 2 g −1, depending on the amount of catalysts used.

Electrical double-layer characteristics of novel carbide-derived carbon materials

A variety of nanoporous carbide-derived carbon materials possessing improved pore size distributions were synthesised from a mixture of titanium carbide and titanium dioxide. It was observed that TiO 2 caused partial oxidation of the carbon particles created during high-temperature chlorination of the TiC/TiO 2 mixture. The resulting carbon powder is characterised by narrow pore size distribution with a peak pore size of around 8 Å and a noticeably smaller amount of pores below 6–7 Å compared to the carbon derived from pure TiC. Electrochemical and electrical double-layer characteristics of novel carbon materials in the acetonitrile solution of triethylmethylammonium tetrafluoroborate were obtained by using cyclic voltammetry and constant current methods. Carbon electrode materials of this study were tested over the temperature range from −10 °C to +60 °C. Results of this study affirmed a great potential of the synthesised advanced carbide-derived carbon, whose specific double-layer capacitance reaches approximately 90 F cm −3 and 125 F g −1.

Electrochemical characteristics of nanoporous carbide-derived carbon materials in non-aqueous electrolyte solutions

Electrochemical characteristics for the 1 M (C 2H 5) 3CH 3NBF 4 + acetonitrile (AN)|carbide-derived carbon nanoporous (prepared from TiC, α-SiC, Mo 2C, Al 4C 3 and B 4C) interface have been established by cyclic voltammetry and electrochemical impedance spectroscopy. The gas adsorption measurements have been used for the obtaining the specific surface area, pore size distribution, nanopore volume and other characteristics, dependent on the precursor carbide used (nanopores are pores in the range of 2 nm and below – i.e. micropores according to IUPAC classification). The region of ideal polarizability, values of series and parallel capacitances, parallel resistance and capacitance and other characteristics dependent on the precursor carbide have been established.