Silicon Carbide-derived Carbon Research Articles

Steam activation of silicon carbide-derived porous carbon and its use as a capacitor electrode

Steam activation of silicon carbide-derived porous carbon and its use as a capacitor electrode

Nitrogen and sulphur co-doped carbon-based composites as electrocatalysts for the anion-exchange membrane fuel cell cathode

Nitrogen and sulphur co-doped nanocarbon composites based on silicon carbide-derived carbon (SiCDC), carbon nanotubes (CNT) and/or mesoporous carbon (MPC) are prepared for oxygen reduction reaction (ORR) and anion-exchange membrane fuel cell (AEMFC) studies. Thiosemicarbazide is used as nitrogen and sulphur doping agent. The rotating ring-disc electrode (RRDE) measurements exhibit good electrocatalytic activity towards the ORR for all the prepared catalysts in alkaline solution. Obtained materials are rich in pyridinic-N and consist of thiophene-S, which could improve the ORR performance due to the synergistic effect of N and S. Textural properties, including specific surface area (SSA) and porosity parameters are different amongst the three studied N,S-doped nanocomposite materials, which also affect the outcome of AEMFC test results. In AEMFC testing using Aemion+ (AF2-HLE8-10-X, 10 μm) anion-exchange membrane, N,S-SiCDC/MPC (with SSAdft = 952 m2 g−1) shows the highest performance with the peak power density (Pmax) of 379 mW cm–2. This result is comparable with the performance of Pt/C catalyst in AEMFC (Pmax = 347 mW cm–2), making N,S-doped nanocomposite materials promising cathode catalyst for AEMFCs.

Adsorptive separation of Xe/Kr using nanoporous carbons in the presence of I2 and CH3I

• Better Xe/Kr separation performance achieved in CNTs than amorphous carbons. • The presence of I 2 and CH 3 I excludes the adsorption of Xe/Kr completely. • Adequate adsorption of CH 3 I and high CH 3 I/I 2 selectivity in (6, 6) CNT. • High adsorption of I 2 and high I 2 /CH 3 I selectivity in (15, 15) CNT. • Enhanced amorphization reduces the adsorption kinetics significantly. Grand canonical Monte Carlo (GCMC) and molecular dynamic (MD) simulations were systematically conducted to reveal the influence of volatile radionuclides, I 2 and CH 3 I, on the adsorption of Xe/Kr/N 2 mixtures in well-shaped carbon nanotubes (CNTs), stratified activated carbon fiber (ACF-15) and completely disordered silicon carbide derived carbon (SiC-DC). In the absence of radioactive impurities, the (6, 6) CNT with a pore size of 0.81 nm achieves adequately high adsorption of Xe (0.37 mol/kg) and Xe/Kr selectivity (45.3), presenting significantly superior performance than other CNTs and amorphous carbons. Albeit enhancing the amorphization of nanoporous carbons hardly impacts the sorption capacity, it hinders the adsorption kinetics dramatically by introducing the energy barriers to diffusion. However, when either I 2 or CH 3 I presents in the gas phase, the adsorptions of Xe and Kr are severely excluded in nanoporous carbons due to the dominant adsorption of I 2 and CH 3 I. For the Xe/Kr/N 2 /I 2 /CH 3 I mixture, the intense competitive adsorption occurs between I 2 and CH 3 I in nanoporous carbons. It is found while the (6, 6) CNT demonstrates the greatest potential on separating CH 3 I from the quinary mixture, the (15, 15) CNT achieves the best performance on separating I 2 among the carbon structures considered.

Optimal Performance of Nanoporous Carbons on Adsorptive Separation of CO2 from Flue Gas

We adopted grand canonical Monte Carlo (GCMC) simulations to comprehensively investigate the adsorption of CO2/N2 mixtures of different compositions in well-shaped single-walled carbon nanotubes (CNTs), stratified activated carbon fiber (ACF-15), and completely disordered silicon carbide-derived carbon (SiC-DC) at different temperatures. It was found that reducing the pore size initially enhances the adsorption and selectivity of CO2 for enhanced adsorbate–adsorbent interactions, which, however, eventually reduces the selectivity for the enhanced entropic effect. It was also revealed that formation of a cylindrical pore could dramatically enhance the potential field, emphasizing that the morphology of the carbons could have a significant impact on the adsorptive separation performance. While increasing the temperature reduces the separation performance, the enhanced mole fraction of CO2 after multistage separation facilitates the subsequent flue gas separation procedure. A performance coefficient was adopted to comprehensively measure the separation performance of nanoporous carbons on the separation of CO2 from CO2/N2 mixtures with varying compositions and at different temperatures. Among the CNTs considered, either the (6, 6) or the (7, 7) CNT achieves the best separation performance for specific working conditions, associated with the performance coefficient being around 1 order of magnitude higher than the counterparts of ACF-15 and SiC-DC.

Silicon carbide-derived carbon electrocatalysts dual doped with nitrogen and phosphorus for the oxygen reduction reaction in an alkaline medium

In this study, two compounds (melamine phosphate and hexachlorocyclotriphosphazene) were used as nitrogen and phosphorus precursors to dope silicon carbide-derived carbon (SiCDC) with nitrogen and phosphorus moieties. The successful heteroatom doping was confirmed by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy/energy-dispersive X-ray (SEM-EDX) analysis. The resulting N,P-doped SiCDC exhibited high oxygen reduction reaction (ORR) performance in alkaline conditions in terms of onset and half-wave potential, slightly surpassing the ORR activity of solely N-doped SiCDC. Since N2 physisorption showed that the porosity parameters and specific surface area of N,P-doped SiCDC (in which melamine phosphate was used as a N and P precursor) were rather similar to that of N-doped SiCDC, the improvement in the ORR activity of N,P-doped SiCDC could be attributed to the new ORR-active sites produced by the introduction of nitrogen and phosphorus moieties into the SiCDC.

Non-precious metal cathodes for anion exchange membrane fuel cells from ball-milled iron and nitrogen doped carbide-derived carbons

Iron and nitrogen doping of carbon materials is one of the promising pathways towards replacing Pt/C in polymer electrolyte fuel cell cathodes. Here, we show a synthesis method to produce highly active non-precious metal catalysts and study the effect of synthesis parameters on the oxygen reduction reaction (ORR) activity in high-pH conditions. The electrocatalysts are prepared by functionalizing silicon carbide-derived carbon (SiCDC) with 1,10-phenanthroline, iron(II)acetate and, optionally polyvinylpyrrolidone, by ball-milling with ZrO2 in dry or wet conditions, followed by pyrolysis at 800 °C. The catalysts are characterized by scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, N2 physisorption and inductively coupled plasma mass spectrometry. By optimizing the ball-milling conditions, we achieved a reduction in the size of SiCDC grains from >1 μm to 200 nm without negatively affecting the high BET area of catalysts derived from SiCDC. This resulted in increased ORR activity in both rotating disk electrode and anion exchange membrane fuel cell (AEMFC) environments, and improved mass-transport properties of the cathode layer in fuel cell. The ORR activity at 0.9 V in AEMFC of the optimized iron and nitrogen-doped SiCDC reaches 52 mA cm−2, exceeding that of a Pt/C cathode at 36.5 mA cm−2.

The Effect of Ball-Milling on the Oxygen Reduction Reaction Activity of Iron and Nitrogen Co-Doped Carbide-Derived Carbon Catalysts in Acid Media

Storing renewable energy to complete the energy cycle is a crucial challenge in the movement from a fossil fuel-based economy to a circular one. In the hydrogen cycle, stored hydrogen is converted back to usable energy in a fuel cell. The biggest issue in proton exchange membrane fuel cells (PEMFC) is the replacement of noble metal catalysts with a non-precious metal catalysts (NPMC). Iron and nitrogen doped nanocarbon materials are among the most promising alternatives.In our previous works on iron and nitrogen doped carbide-derived carbons (CDC) we discovered that ball-milling of CDCs has a crucial effect on their porosity and the final activity of the catalyst.1,2 In this work,3 we study the effect of ball-milling conditions and compositions of catalyst precursors comprising a silicon carbide-derived carbon (SiCDC) on the properties of the final catalysts, most importantly their activity toward the oxygen reduction reaction (ORR). Ball-milling rates from 100 to 800 rpm were investigated with 400 rpm proving to be the optimum value. The effect of 1,10-phenanthroline-to-iron ratio in the precursor mixture was also studied, with a 12-1 molar ratio leading to the highest activity. Finally, ZnCl2 addition to the precursor mixture was explored as a pore former during pyrolysis. A ZnCl2-to-CDC mass ratio of 1 resulted in the highest ORR activity. 57Fe Mössbauer spectroscopy confirmed that most of the iron was atomically dispersed as Fe-Nx moieties (Figure 1, left). The most active catalyst showed a kinetic current density of 4.6 mA cm-2 at 0.8 V in rotating disk electrode tests and a current density of 18.6 mA cm-2 at 0.8 V in a single-cell proton exchange membrane fuel cell (Figure 1, right). References Ratso, N.R. Sahraie, M.T Sougrati, M. Käärik, M. Kook, R. Saar, P. Paiste, Q. Jia, J. Leis, S. Mukerjee, F. Jaouen, and K. Tammeveski, J. Mater. Chem. A, 6, 14663–14674 (2018).Ratso, M. Käärik, M. Kook, P. Paiste, J. Aruväli, S. Vlassov, V. Kisand, J. Leis, A. M. Kannan, and K. Tammeveski, Int. J. Hydrogen Energy, 44, 12636–12648 (2019).Ratso, M. T. Sougrati, M. Käärik, M. Merisalu, M. Rähn, V. Kisand, A. Kikas, P. Paiste, J. Leis, V. Sammelselg, F. Jaouen, and K. Tammeveski, ACS Appl. Energy Mater., 2, 7952–7962 (2019). Figure 1

Toward High‐Performance Capacitive Potassium‐Ion Storage: A Superior Anode Material from Silicon Carbide‐Derived Carbon with a Well‐Developed Pore Structure

AbstractPotassium‐ion battery (PIB) using a carbon‐based anode is an ideal device for electrochemical energy storage. However, the large atomic size of potassium ions inevitably leads to huge volume expansion and the collapse of anodes, resulting in the severe capacity fading during the long‐term cycling. Herein, silicon carbide‐derived carbon (SiC‐CDC) with a controllable pore structure is synthesized with a concise etching approach. It exhibits a maximum capacity of 284.8 mA h g−1 at a current density of 0.1 A g−1 after 200 cycles as well as a highly reversible capacity of 197.3 mA h g−1 at a current density of 1.0 A g−1 even after 1000 cycles. A mixed mechanism of the potassium storage is proposed for this prominent performance. The interconnected pore structure with a high proportion of mesopore volume provides abundant active sites for the adsorption of potassium ions, a shortened electrolyte penetration path, and enlarged accumulation space for potassium ions, eventually leading to facilitated capacitive potassium storage inside this SiC‐CDC electrode. This work provides fundamental theories of designing pore structures for boosting capacitive potassium storage and unveils CDC‐based materials as the prospective anodes for high‐performance PIBs.

Rice-husk-based Silicon-carbide-derived Carbon as an Electrode Material for Electric Double-layer Capacitors

Silicon-carbide-derived carbon (SiC-CDC) was prepared by heat treatment and chlorination of rice husk charcoal. Its specific surface area and micropore peak size were 1060 m2g−1 and ∼0.75 nm, while those of a α-SiC-CDC, fabricated by chlorination of α-SiC, were 1350 m2g−1 and ∼0.60 nm, respectively. These SiC-CDCs exhibited excellent surface-area-normalized capacitance as capacitor electrodes. The internal resistance of the rice husk-based SiC-CDC was significantly lower than that of the α-SiC-CDC and comparable to that of commercial activated carbon.

Effect of the CO2 activation parameters on the pore structure of silicon carbide-derived carbons

A silicon carbide derived carbon (SiC-DC) with a high specific surface area (SSA) fabricated by chlorination of a silicon carbide derived from polysiloxane was activated by CO2. The effect of activation temperature and time on the microstructure of the activated samples was investigated by N2 sorption, XRD, SEM and TEM. Results showed that CO2 activation effectively changed the pore structure of the SiC-DC and had little impact on carbon crystallinity. The activated samples retained the morphology of the SiC powder or the non-activated SiC-DC. The SSA, total pore volume (Vtot) and micropore volume of the activated SiC-DCs all increased and the yield decreased with increasing activation temperature or time. The SSA and Vtot increased by 46.5 % (from 1 316.8 to 1 929.0 m2g−1) and 86.4 % (from 0.560 to 1.044 cm3g−1), respectively after the SiC-DC was activated at 950 °C for 2 h, mainly as a result of the increased micropore volume.

Electrosynthesis of SiC derived porous carbon nanospheres for supercapacitors

Porous silicon carbide derived carbon (SiC-CDC) nanospheres have been successfully synthesized by electrochemical extraction of Si atoms from SiC nanospheres precursor in molten CaCl2. The electrochemical etching process was conducted at 900 °C and 3.2 V. The results show that the obtained product is porous SiC-CDC nanospheres, which contain amorphous carbon and a small amount of ordered graphite phase. The specific surface area of the produced SiC-CDC was determined to be 881 m2/g. The specific capacitance of the SiC-CDC is 176 F/g and possesses excellent cycling stability (97.8% retention of the initial capacitance after 1000 cycles) at a current density of 1000 mA/g.

Steam and Carbon Dioxide Co-Activated Silicon Carbide-Derived Carbons for High Power Density Electrical Double Layer Capacitors

Different mico-mesoporous silicon carbide-derived carbons (SiC-CDC) were synthesized via gas phase chlorination at 1100°C and thereafter activated at 900°C and 1000°C with H2O steam using Ar and CO2 as the carrier gases. The physical characterization data show that these materials are mainly amorphous, the structure does not change remarkably during the activation process and the surface chemistry of the differently activated and treated materials remains the same and there are no functional groups at the SiC-CDC surface. N2, Ar and CO2 sorption measurements indicate an increase in the specific surface area and pore size distribution with increasing the activation temperature, whereas the influence of the carrier gas during synthesis is minimal. Although the specific surface areas and pore size distributions differed, the electrochemical parameters in 1 M (C2H5)3CH3NBF4 acetonitrile solution for all SiC-CDC materials were similar - specific gravimetric capacitances 130 ± 18 F g−1 and volumetric capacitance 67 ± 14 F cm−3 were calculated. Absolute phase angle values from −85° to −88° at low frequencies and very high energy and power densities 22 Wh kg−1 at 20 kW kg−1 and 12 Wh dm−3 at 10 kW dm−3 have been achieved.

Designed synthesis of SiC nanowire-derived carbon with dual-scale nanostructures for supercapacitor applications

A simple approach has been designed for the synthesis of mesoporous silicon carbide-derived carbon nanowires (SiC-CDC NWs) for supercapacitor applications.

Synthesis of Silicon Carbide-Derived Carbon as an Electrode of a Microbial Fuel Cell and an Adsorbent of Aqueous Cr(VI)

Micron-sized nonporous silicon carbide (SiC) powder of the spent heating elements of a graphite furnace were used as the common precursor of two different forms of carbide-derived carbon (CDC) synthesized by chlorination at different temperatures: (1) graphitic and (2) amorphous Si-CDCs. Whereas the former material having high electroconductivity was used as an efficient electrode of a microbial fuel cell (MFC), the latter material having high specific surface area was used as an efficient adsorbent for aqueous hexavalent chromium (Cr(VI)). The MFCs generated a significantly high maximum power density of ∼1570 ± 30 mW/m2 and open circuit potential of ∼460 ± 5 mV. The adsorbents exhibited a significantly large adsorption capacity of ∼95 ± 5 mg/g. This study has developed for the first time two types of Si-CDCs having different physicochemical characteristics, from the common SiC precursor via the facile route of different temperature conditions, for bioelectricity generation and environmental remediation a...

Silicon Carbide-Derived Carbon Coated Graphitized Mesocarbon Microbead Composites for Anode of Lithium-Ion Battery

Unique silicon carbide-derived carbon (SiC-CDC) and graphitized mesocarbon microbead (GMCMB) composites (GMCMB@SiC-CDC) were prepared by solid reaction of GMCMB and silicon and following etching reaction with chlorine. The microstructure of SiC-CDC was characterized as mainly amorphous carbon combined with some short and curved sheets of graphite. N2 adsorption/desorption isotherms and pore size distributions proved the composites presented both an enormous amount micropores centered at around 0.5~0.6 nm and a few mesopores (2~50 nm). The GMCMB@SiC-CDC composites showed higher specific surface area and pore volume, especially the microporous surface area and volume. The composites as the anode materials manifested much higher charge specific capacities of 877.6 mAh·g-1 at the first cycle compared with pure GMCMB of 359.6 mAh·g-1, which was probable that Li ions could insert into not only carbon layers but also micropores. The GMCMB@SiC-CDC composites presented better discharge specific capacities at higher charge/discharge rates. The component and electrochemical performances of the composites can be optimized through changing the molar ratio of GMCMB/Si to control the corresponding proportion of SiC-CDC and GMCMB.

Bioinspired carbide-derived carbons with hierarchical pore structure for the adsorptive removal of mercury from aqueous solution.

Biosilica of the diatom species Thalassiosira pseudonana is used as hard template for the synthesis of silicon carbide-derived carbons. The typical species-specific macroporous structure is retained during the nanocasting-chlorine treatment process and the resulting materials exhibit very high specific surface areas up to 2300 m2 g-1. Bioinspired carbons show very high capacities in mercury adsorption from aqueous solution compared to reference materials.

Computational investigation on CO2 adsorption in titanium carbide-derived carbons with residual titanium

We develop a new approach for modeling titanium carbide derived-carbon (TiC-CDC) systems with residual titanium by the generation of modified atomistic structures based on a silicon carbide derived-carbon (SiC-CDC) model and the application of weighted combinations of these structures. In our approach, the original SiC-CDC structure is modified by (i) removing carbon, (ii) adding carbon and (iii) adding titanium. The new atomic scale carbide-derived carbon (CDC) structures are investigated using classical molecular dynamics simulations, and their pure CO2 adsorption isotherms are calculated using grand canonical Monte Carlo simulations. The system of TiC-CDC with residual titanium is modeled as weighted combinations of pure carbon CDC structures, CDC structures with titanium and a TiC crystalline structure. Our modeling is able to produce both structural properties and adsorption isotherms in accordance with experimental data. The fraction of different models in the systems successfully reflects the structural differences in various experimental TiC-CDC samples. The modeling also suggests that in partially etched TiC-CDC systems, the titanium that may be accessible to CO2 gas at the transitional interface may provide significant interaction sites for CO2 and may lead to more efficient overall gas adsorption.

Fluorination-Induced Changes in Hydrophobicity of Silicon Carbide-Derived Nanoporous Carbon

We report the effect of fluorine doping on hydrophobicity of microporous silicon carbide-derived carbon (SiCDC), exploring water vapor adsorption in virgin and fluorinated samples experimentally and using semiempirical isotherm models. The surface chemistry of the virgin carbon and samples fluorinated to three different levels is characterized by X-ray photoelectron spectroscopy and 19F nuclear magnetic resonance analysis techniques. Besides having different textural features such as surface area and pore size distribution, the virgin and fluorinated SiCDCs show different surface chemistries in terms of the nature and quantity of the C–F bonds. The comparison of the characterization results of the samples and model parameters is used as the methodology to understand the water adsorption mechanism in virgin and fluorinated SiCDCs. We demonstrate that with increasing fluorination level the hydrophobic character of the low and medium fluorinated SiCDC samples remains almost constant while the highly fluorine...

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.

Synthesis and characteristics of chloroform-treated silicon carbide-derived carbon layers

The pores reduced for CDC layers synthesized using (d–f) bubbled chloroform compared to that of (a–c) chlorine gas.