Synthesis of nanoporous carbide-derived carbon by chlorination of titanium silicon carbide

Synthesis of nanoporous carbide-derived carbon, CDC, by extraction of titanium and silicon from Ti₃SiC₂ by chlorine is discussed in this work. Thermodynamic simulations using a Gibbs free energy minimization program provided general guidelines to the experimental design. Raman spectroscopy, X-ray diffraction, and electron microscopy studies showed that the structure of CDC depends on the chlorination temperature. The low temperature synthesis resulted in an amorphous CDC structure. Noticeable graphite formation starts above 800 °C and well ordered graphite ribbons of 1-3 nm in thickness form at 1200 °C. The macroscopic volume and shape of Ti₃SiC₂ preform were preserved during the transformation. However, the chlorination resulted in the formation of cracks between the former grains of the polycrystalline Ti₃SiC₂ preform. These cracks are believed to be caused by a contraction in the direction perpendicular to the basal planes of Ti₃SiC₂. The synthesized nanoporous carbon demonstrated excellent sorption properties. Energy dispersive X-ray spectroscopy studies showed that Ti₃SiC₂ material chlorinated at 400 °C is capable of trapping over 40 wt.% of Cl₂.     

Growth mechanism of carbon nanotubes in methane diffusion flames

Straight and bamboo-like carbon nanotubes were synthesized in a methane diffusion flame using a Ni-Cr-Fe wire as a substrate. The catalyst particles were nickel and iron oxides formed on the wire surface inside the flame. When the wire was oxidized using nitric acid more nanotubes could be produced. Most nanotubes grew by a base growth mode. The formation of bamboo-like nanotubes was related to the shape of the catalyst particles. A segregation growth mechanism of bamboo-like nanotubes is proposed.     

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 CO₂ 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 CO₂ and activation time on the pore structure of CDC was studied.     

Molybdenum carbide-derived carbon for hydrogen storage

Physisorption of hydrogen in microporous molybdenum carbide (Mo₂C)-derived carbons has been studied as a function of synthesis conditions. Changes in local structure induced by varying the chlorination temperature afford controllable variations in average pore size and specific surface area. Optimal hydrogen storage capacity of 4.3 wt%, measured at −196 °C and 35 bar pressure, is obtained from a sample chlorinated at 660 °C for 3 h. This optimum correlates with the largest fraction of total pore volume having average pore sizes in the 0.6–0.8 nm range.     

Flexible supercapacitor-like actuator with carbide-derived carbon electrodes

Soft and flexible electric driven transducers based on carbide-derived carbon (CDC), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF₄), polyvinylidenefluoride-co-hexafluoropropylene (PVdF(HFP)) are proposed, and electroactive performances of these materials are reported. By its nature, the synthesized device has two features when voltage is applied. Firstly, it is a bending-type electrochemical actuator. Besides the external change of shape, this device is also an electrochemical capacitor, providing opportunity to store a considerable amount of charge. Laminated actuators can work in open air at low voltages (1–3 V). Their operating frequency is between 5 × 10⁻³ – 1 × 10¹ Hz (it is from 5 millihertz to 200 hertz) and 10 Hz and the maximum strain calculated from transducer displacement is 0.6%. The gravimetric capacitance of CDC in actuator electrodes was found to be 119 F g⁻¹ at 1 mV s⁻¹ sweep rate of the applied triangle voltage. The effects of synthesis temperature of CDC and associated changes in the porosity and surface area on the actuator displacement are discussed. The results of this study demonstrated a great potential of CDC as an active material for actuator electrodes, especially in these applications where the performance of the actuator has to be standardized and highly predictable.     

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 TiO₂ caused partial oxidation of the carbon particles created during high-temperature chlorination of the TiC/TiO₂ 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.     

碳化物衍生碳及其在吸附领域中的应用研究进展

碳化物衍生碳（CDC）是近年来开发的一种具有纳米结构的新型多孔碳材料。该材料是将碳化物前体通过物理（如热分解等）或化学（如卤化等）过程,由表及里逐层刻蚀掉非碳原子得到的,可以实现原子水平上的调控。本文介绍了CDC的制备工艺、性质（孔和形貌）及其在吸附领域中的应用。结果表明,可以通过控制刻蚀温度、碳化物前体、后处理等合成条件实现CDC比表面积大范围可调、孔径及孔径分布等微观结构精确可控,得到从无定形碳到高度有序的石墨、碳纳米管或石墨烯等多种结构。最后指出了解制备过程-结构-性质之间的关系有利于精确调控CDC以满足特定应用的要求。     

Transition metal loaded silicon carbide-derived carbons with enhanced catalytic properties

Carbide-derived carbons (CDC) with incorporated transition metal nanoparticles (～2.5 nm) were prepared using a microemulsion approach. Time-consuming post synthesis functionalization of the carbon support material can thus be avoided and nanoparticle sizes can be controlled by changing the microemulsion composition. This synthesis strategy is a technique for the preparation of highly porous carbon materials with a catalytically active component. In particular we investigated the integration of ruthenium, palladium, and platinum in a concentration ranging from 4.45 to 12 wt.%. It was found that the transition metal has a considerable influence on sorption properties of resulting nanoparticle-CDC composite materials. Depending on the used metal salt additive the surface area and the pore volume ranges from 1480 m²/g and 1.25 cm³/g for Pt to 2480 m²/g and 2.0 cm³/g for Ru doped carbons. Moreover, members of this material class show impressive properties as heterogeneous catalysts. The liquid phase oxidation of tetralin and the partial oxidation of methane were studied, and electrochemical applications were also investigated. Primarily Pt doped CDCs are highly active in the oxygen reduction reaction, which is of great importance in present day fuel cell research.     

Nanostructured carbide-derived carbon synthesized by chlorination of tungsten carbide

Nanostructured carbide-derived carbons were synthesized from α-tungsten carbide (WC-CDC) powder via gas phase chlorination within the temperature range from 700 to 1100 °C. Analysis of X-ray diffraction results showed that WC-CDC are mainly amorphous consisting of relatively small graphitic crystallites and the apparent crystallite size along the a- and c-directions of graphite structure L_a ≈ 4 nm and L_c ≈ 1.5 nm were calculated. The first-order Raman spectra showed the graphite-like absorption peak at ∼1590 cm⁻¹ and the disorder-induced peak at ∼1350 cm⁻¹. The low-temperature N₂ sorption experiments were performed and a specific micropore surface area up to 1550 m² g⁻¹ and total pore volume up to 0.89 cm³ g⁻¹ were obtained for WC-CDC synthesized at T = 1100 °C. High-resolution transmission electron microscopy and electron energy loss spectroscopy studies revealed that WC-CDC prepared at 800 °C correspond to the highly disordered carbon material but WC-CDC prepared at 1100 °C showed partial graphitization.     

CH4和CO2在活性炭微球内扩散系数的测定

活性炭微球是一种储存及净化天然气的新型碳材料.采用高精度的重力分析仪(IGA-003, HIDEN)对天然气主要成分CH₄和CO₂杂质在活性炭微球材料内的扩散性质进行了研究.运用Fick扩散模型关联得到了CH₄及CO₂在活性炭微球内的扩散系数.研究结果表明,CH₄与CO₂在活性炭微球内的扩散属于晶体扩散,二者的扩散系数处于10^-13m²·s^-1数量级上.同时,CH₄与CO₂在介孔活性炭微球内的扩散速率均随着温度的增加而增加,随着体系平衡压力的增加而减小,而且CH₄的扩散速率要略大于CO₂的扩散速率.研究结果可用于活性炭微球吸附剂应用中传质性质的计算.     

A carbide-derived carbon laminate used as a mechanoelectrical sensor

The mechanoelectrical effects attained through the enforced transfer of an ionic liquid through an electric double-layer capacitor-like laminate are described. The core component of the laminate is carbide-derived carbon, supported and separated by poly(vinylidene fluoride co-hexafluoropropylene). The different lateral sizes of the cations and anions of the ionic liquid electrolyte cause their different mobilities in the porous carbon structure. The judicious matching of the porosity of the carbon with the particular ionic liquid allows the formation of a diffusion potential solely by mechanical strain. Bending of this sheet-like laminate generates voltage and current; hence, it can be used as a motion sensor or as an energy harvesting unit.     

Tunable and selective formation of micropores and mesopores in carbide-derived carbon

Pore structure of carbide-derived carbon (CDC) was tunable by chlorination of Ti(C_1−xA_x) solid–solution carbides (A = O or N). High-energy ball milling method was used to synthesize various nanocrystalline Ti(C_1−xA_x) phases. We were able to obtain specific dimension of pore volumes in the range of micropore (<2 nm) or mesopore size (2–50 nm), depending on the compositions of the precursors. The substitutional atoms and their contents effectively modify the characteristics of pores i.e., pore size, volume and their distributions. The micropore volume density, total pore volume density and specific surface area (SSA) of Ti(C_0.7O_0.3) CDCs were found 1.55 cm³/g, 1.72 cm³/g and 3100 m²/g, respectively. In contrast, Ti(C_0.5N_0.5) CDCs showed enhancement of mesopore formation with 3.34 cm³/g, 3.45 cm³/g and 522 m²/g for mesopore volume density, total pore volume density and SSA, respectively.     

Carbon dioxide activated carbide-derived carbon monoliths as high performance adsorbents

Carbide-derived carbon (CDC) monoliths (DUT-38) with a distinctive macropore network are physically activated using carbon dioxide as oxidizing agent. This procedure is carried out in a temperature range between 850 and 975 °C with durations ranging from 2 to 6 h. Resulting materials show significantly increased specific surface areas as high as 3100 m²/g and total (micro/meso) pore volumes of more than 1.9 cm³/g. The methane (214 mg/g at 80 bar/25 °C), hydrogen (55.6 mg/g at 40 bar/−196 °C), and n-butane (860 mg/g at 77 vol.%/25 °C) storage capacities of the activated CDCs are significantly higher as compared to the non-activated reference material. Moreover, carbon dioxide activation is a suitable method for the removal of metal chlorides and chlorine residuals adsorbed in the pores of CDC after high temperature chlorination. The activation does not influence the hydrophobic surface properties of the CDCs as determined by water adsorption experiments. The macropore network and the monolithic shape of the starting materials can be fully preserved during the activation procedure. n-Butane breakthrough studies demonstrate the materials applicability as an efficient hydrophobic filter material by combining excellent materials transport with some of the highest capacity values that have ever been reported for CDCs.     

Hydrogen production from catalytic decomposition of methane over ordered mesoporous carbons (CMK-3) and carbide-derived carbon (DUT-19)

This paper presents a thermogravimetric analysis of catalytic methane decomposition using ordered mesoporous carbon nanorods (CMK-3) and ordered mesoporous carbide-derived carbon (DUT-19) as catalysts. X-ray diffraction and N₂ physisorption analyses were performed for both fresh catalysts. Threshold temperatures for methane decomposition with DUT-19 and CMK-3 were estimated by three different methods found in literature. Carbon formation rate and carbon weight gain as a function of time at various temperatures and methane partial pressures were studied, and the kinetics of CMK-3 and DUT-19 as catalysts for methane decomposition were investigated. Arrhenius energy values of 187 kJ/mol for CMK-3 and 196 kJ/mol for DUT-19 with a reaction order of 0.5 were obtained for both catalysts. Results show that carbon deposition on the catalyst during the reaction lead to catalyst deactivation with significant surface modification. Scanning electron microscope studies of fresh and deactivated catalyst samples show the blocking of catalyst pores and the formation of agglomerates on the outer surface of the catalyst during the course of reaction. DUT-19 catalytically outperforms CMK-3 because of a lower threshold temperature, higher surface area, and higher pore volume. These results show that ordered mesoporous carbons are promising catalysts for methane decomposition.     

Novel actuators based on polypyrrole/carbide-derived carbon hybrid materials

Polypyrrole (PPy) hybrid films incorporated with porous carbide-derived carbon (CDC) particles are synthesized through a novel one-step electrochemical synthesis process that provides a simple and efficient alternative for current tape-casting and inkjet printing technologies to make conducting polymer–CDC-based electroactive composites. The resulting porous, robust and electrically conductive hybrid layer was used to fabricate electroactive polymer actuators both as perpendicularly expanding actuators and as bending trilayer actuators. Raman and FTIR spectroscopy confirm successful incorporation of CDC in the PPy matrix. Cyclic voltammograms confirm slightly higher charging/discharging currents of the PPyCDC hybrid. This indicates the successful coupling of CDC in order to increase electric double-layer capacitance in the hybrid films. The maximum steady state electromechanical diametrical strain is 13% for hybrid material which is in the same order of magnitude as for PPy and 10× more than previously reported CDC films made with non-conducting polymer binders. Furthermore, the expanding actuators made from hybrid material are more efficient than non-modified PPy actuators, having doubled the amount of swelling per injected charge. This improvement is very important since the low energy efficiency is a major shortcoming for ionic electroactive polymers. The high pseudocapacitance makes these new hybrid materials also interesting for energy storage applications.     

An advanced method to manufacture hierarchically structured carbide-derived carbon monoliths

The preparation of carbide-derived carbon (CDC) monoliths with a hierarchically structure in the nm and μm range is presented. Basis is the manufacturing of porous cellular SiC ceramics based on a biomorphous approach with μm porosity and subsequent conformal conversion to CDC by reactive extraction with chlorine. The SiC ceramics can be sintered at low temperatures and short times (1500 °C, 2 h) compared to classical preparation methods. The SiC ceramics show a macro pore volume (1–10 μm channel size) of 0.56 ml g⁻¹, which corresponds to 1.5 ml g⁻¹ in the resulting CDC. The final carbon material exhibits an additional nano pore volume of 0.525 ml g⁻¹ with a mean slit pore size of 0.86 nm. Mechanical stabilities of the highly porous CDC are excellent (bending strength 2.1 ± 0.2 MPa, corrected Weibull modulus 8.7, characteristic strength 2.2 MPa and Youngs modulus 10.0 ± 0.5 GPa). The reactive extraction of the carbide monoliths shows very high reaction rates, approx. two dimensions faster (95×) compared to non-porous samples. Thus the manufacturing of the structured carbide and CDC can be performed at lower costs.     

Impact of carbon nanotube additives on carbide-derived carbon-based electroactive polymer actuators

The effects of single-walled carbon nanotubes (SWCNTs) on the properties of carbide-derived carbon (CDC)-based electroactive polymer (EAP) actuators were studied. SWCNTs were used as an additive to increase the mesoporosity and electrical conductivity of the electrodes, and also to support the CDC matrix. EAP actuators with various ratios of SWCNTs to CDC in the electrodes were fabricated and their electromechanical and electrochemical characteristics were examined. The addition of SWCNTs to CDC-based electrodes significantly increased the bending strain and stress (bending force) of the actuators. The actuator assembled with electrodes containing SWCNTs and CDC in the ratio 50/50 (wt.%/wt.%) showed the highest strain output among the samples at lower frequencies (<0.1 Hz). The increase in maximum strain was more than twice that of pure CDC-based EAPs (0.85% vs. 0.35% at an applied voltage of ±2 V). Also, the high frequency (5–50 Hz) response of the combined SWCNT/CDC-based actuators was considerably improved.     

Effect of transition metal catalysts on the microstructure of carbide-derived carbon

Carbon materials with different microstructure can be produced by a carbide-derived carbon (CDC) approach varying the carbide precursor and the reaction conditions for the selective etching of the metal. CDC was produced using biomorphic TiC and SiC ceramics derived from paper preforms by a chemical vapor infiltration and reaction technique. In this work the effect of transition metal salt catalysts such as Ru(III), Fe(II), Fe(III) or Ru(III)/Fe(III) on the chlorination process at temperatures in the range 600-1200 °C as well as on the microstructure of the resulting carbon was investigated. The produced CDC was characterized by its degree of order and pore structure using Raman spectroscopy, high resolution transmission electron microscopy and low temperature nitrogen adsorption. A higher etching rate as well as a higher degree of order at lower reaction temperatures was observed if a catalytically active metal was present during the chlorination process. This effect was mostly pronounced in the case of a Ru(III)/Fe(III) bimetallic catalyst. The higher degree of order of the carbon is associated with an increased amount of mesopores and with a decrease in specific surface area. Therefore, the CDC processing in the presence of catalysts offers another way to produce ordered carbon structures at lower temperatures.     

Nanoscale fine-tuning of porosity of carbide-derived carbon prepared from molybdenum carbide

Micro- and mesoporous carbide-derived carbon (CDC) was synthesised from molybdenum carbide (Mo₂C) powder by gas phase chlorination in the temperature range from 400 to 1200 °C. Analysis of XRD results show that C(Mo₂C), chlorinated at 1200 °C, consist mainly on graphitic crystallites of mean size, L_a = 9 nm and L_c = 7.5 nm. The first-order Raman spectra showed the graphite-like absorption peak at ∼1587 cm⁻¹ and the disorder-induced (D) peak at ∼1348 cm⁻¹. The low-temperature N₂ adsorption experiments were performed and a specific surface area up to 1855 m² g⁻¹ and total pore volume up to 1.399 cm³ g⁻¹ were obtained. Sorption measurements showed the presence of both micro- and mesopores after chlorination at 400-900 °C and only mesopores after chlorination at 1000°-1200 °C. Stepwise formation of micro- and mesopores was achieved and the peak pore size can be shifted from 0.8 nm up to 4 nm by increasing the chlorination temperature.