Nanoporous Carbide-derived Carbon Research Articles

Molecular insights on optimizing nanoporous carbon-based supercapacitors with various electrolytes

Molecular dynamics (MD) simulations using the constant potential method (CPM) can provide nanoscale insight to explain and optimize supercapacitor charging dynamics and charge storage. We report CPM MD operando simulations for charging of nanoporous carbide-derived carbon supercapacitors with four distinct electrolytes, including ionic liquid (IL), mixed IL-solvent, and solvent-in-salt electrolytes. Instead of employing a coarse-grained model, we used an all-atom model for the electrolytes, allowing us to uncover the essential effects of solvents on the charging mechanism. We find that the water-in-salt electrolyte, lithium bis(trifluoromethanesulfonyl)imide / water, leads to the greatest charge storage among the studied combinations and exhibits a significantly higher integral and differential capacitance on the negative electrode, associated with a strong cation-driven charging mechanism. Our simulations also demonstrate the varying contributions of the different electrode regions to supercapacitor performance, with an especially high local capacitance (up to ∼250 F/g) within the interfacial region of the electrodes. These molecular insights provide important guidance for optimizing supercapacitor performance by carefully tuning electrode nanostructure and electrolyte composition.

Effects of Local Graphitization on the Charging Mechanisms of Capacitive Microporous Carbon Supercapacitor Electrodes Application

Electrochemical double layer capacitors (EDLCs) store the charge by reversible adsorption of ions at the electrode/electrolyte interface. The optimization of EDLC performance needs to push further our basic understanding of the ion fluxes that occur during the charging/discharging process. Microporous carbon has been widely used as supercapacitor electrode material thanks to their tunable porosity and high specific surface area. However, most of the porous carbon materials have complex carbon structures, so that the mechanism is still poorly understood.Using electrochemical quartz crystal microbalance technique (EQCM) technique, we studied the charge storage mechanisms of two nanoporous carbide-derived carbon (TiC-CDC) electrodes, namely CDC-800 synthesized at 800℃ and CDC-1100 synthesized at 1100℃. These two carbons have a similar porosity but the CDC-1100 sample shows more graphitic carbon microstructure. We found that a counter-ion adsorption process mainly controls the charging mechanism of CDC-800 (“V” shape m vs Q plot), while an expanded ion-exchange and counter-ion adsorption process is obtained for CDC-1100 (“U” shape). We show here that the local carbon structure affects the charging mechanism of electrical double layer capacitance, and a strong interaction between the anions and graphitic carbons explains these different behaviors. Our results provide more insights into the fundamental understanding of the carbon/electrolyte interface and the charge of the electrical double layer capacitance.Figure 1. Electrode mass change versus charge during the polarization of CDC-800 (a) and CDC-1100 (b) coated Au electrodes in 2M EMI-TFSI/ACN electrolyte at the scan rate of 10 mV·s−1. Figure 1

The Performance of Fibrous CDC Electrodes in Aqueous and Non-Aqueous Electrolytes

The aim of this study was to investigate the electrochemical behaviour of aqueous electrolytes on thin-layer (20 µm) nanoporous carbide-derived carbon (CDC) composite fibrous directly electrospun electrodes without further carbonisation. There have been previously investigated fibrous electrodes, which are produced by applying different post-treatment processes, however this makes the production of fibrous electrodes more expensive, complex and time consuming. Furthermore, in the present study high specific capacitance was achieved with directly electrospun nanoporous CDC-based fibrous electrodes in different neutral aqueous electrolytes. The benefit of fibrous electrodes is the advanced mechanical properties compared to the existing commercial electrode technologies based on pressure-rolled or slurry-cast powder mix electrodes. Such improved mechanical properties are preferred in more demanding applications, such as in the space industry. Electrospinning technology also allows for larger electrode production capacities without increased production costs. In addition to the influence of aqueous electrolyte chemical composition, the salt concentration effects and cycle stability with respect to organic electrolytes are investigated. Cyclic voltammetry (CV) measurements on electrospun electrodes showed the highest capacitance for asymmetrical cells with an aqueous 1 M NaNO3-H2O electrolyte. High CV capacitance was correlated with constant current charge–discharge (CC) data, for which a specific capacitance of 191 F g−1 for the positively charged electrode and 311 F g−1 for the negatively charged electrode was achieved. The investigation of electrolyte salt concentration on fibrous electrodes revealed the typical capacitance dependence on ionic conductivity with a peak capacitance at medium concentration levels. The cycle-life measurements of selected two-electrode test cells with aqueous and non-aqueous electrolytes revealed good stability of the electrospun electrodes.

Blue Energy and Desalination with Nanoporous Carbon Electrodes: Capacitance from Molecular Simulations to Continuous Models

Capacitive mixing (CapMix) and capacitive deionization (CDI) are currently developed as alternatives to membrane-based processes to harvest blue energy—from salinity gradients between river and sea water— and to desalinate water—using charge-discharge cycles of capacitors. Nanoporous electrodes increase the contact area with the electrolyte and hence, in principle, also the performance of the process. However, models to design and optimize devices should be used with caution when the size of the pores becomes comparable to that of ions and water molecules. Here, we address this issue by simulating realistic capacitors based on aqueous electrolytes and nanoporous carbide-derived carbon (CDC) electrodes, accounting for both their complex structure and their polarization by the electrolyte under applied voltage. We compute the capacitance for two salt concentrations and validate our simulations by comparison with cyclic voltammetry experiments. We discuss the predictions of Debye-Huckel and Poisson-Boltzmann theories, as well as modified Donnan models, and we show that the latter can be parametrized using the molecular simulation results at high concentration. This then allows us to extrapolate the capacitance and salt adsorption capacity at lower concentrations, which cannot be simulated, finding a reasonable agreement with the experimental capacitance. We analyze the solvation of ions and their confinement within the electrodes—microscopic properties that are much more difficult to obtain experimentally than the electrochemical response but very important to understand the mechanisms at play. We finally discuss the implications of our findings for CapMix and CDI, both from the modeling point of view and from the use of CDCs in these contexts.

Characterisation of steam-treated nanoporous carbide-derived carbon of TiC origin: structure and enhanced electrochemical performance

Modifications of pore size distribution and structural order of nanoporous carbide-derived carbon (CDC) materials with variety of surface areas and pore sizes were investigated using physical activation by etching with water vapour. Variable etching duration was used to explore the activation impact on the pore size distribution and the adsorption behaviour of TiC-derived carbon. A distribution of micro- and mesopores, modified during physical activation, was studied using N2 and CO2 adsorption. Notable impact of preceding carbon structure on the activation product was revealed by the results of scanning electron microscopy, powder X-ray diffraction and Raman spectroscopy. An infrared spectroscopy, energy dispersive spectroscopy and X-ray photoelectron spectroscopy confirmed that water-induced etching of CDC followed by high-temperature treatment in inert gas atmosphere does not change notably the total amount of surface oxygen, however, leads to the changes in a composition of oxygen containing functional groups in post-activated carbon. The electrochemical evaluation was performed in triethylmethylammonium tetrafluoroborate/acetonitrile electrolyte to elaborate the structure-electrochemical properties relationships on post-activated nanoporous CDC materials. It was observed that the degree of improvement in double-layer capacitance achievable with a steam-treatment significantly depends on the preceding properties of CDC prior treatment, whereby the highest capacitance, ~ 160 Fg−1, was reached for the steam-treated TiC-derived CDC made at 800 °C, which clearly is a very promising material for the electrical double-layer capacitor.

High Performance Micro-Supercapacitors Integrated on Both Silicon Chips and Flexible Polyimide Substrate

Modern microelectronic systems, such as electronic papers, smart clothes, sensors or biomedical devices, demand new energy storage devices to achieve their tasks (1, 2). While batteries suffer from limited power capabilities and cyclability, owing to the faradic mechanisms involved during energy delivery and harvesting, electrochemical double layer supercapacitors (or so called EDLCs) can handle fast charge and discharge over 1,000,000 cycles (3). Indeed, EDLCs store energy via reversible adsorption of ions from an electrolyte at the surface of high-surface-area carbons, or by fast redox reactions occurring at the surface of metal oxide or polymer electrodes (4). However, standard electrode preparation, consisting in mixing the active material with a polymer binder, is not compatible with micro-fabrication processes. Therefore, high performance micro-supercapacitors have to be prepared using non wet processing routes. In this work, nanoporous carbide-derived carbon (CDC) films were integrated onto silicon chips by removing under chlorine atmosphere the metallic atoms of a thin film titanium carbide (TiC) precursor sputtered on silicon wafers (5). The TiC precursor could be patterned through reactive ion etching, thus leading to interdigitated on-chip CDC-based micro-supercapacitors after partial chlorination. The as-prepared devices provided capacitance values up to 410 F.cm-3 (205 mF.cm-2) in 1M H2SO4 with more than 50% of the initial capacitance preserved for 0.9 s discharge time (6). Full chlorination could lead, in certain conditions, to self-supported CDC films of several mm², which were transferred on PET. The flexible CDC electrode delivered 240 mF.cm-2 in sulfuric acid (6). A second strategy consisted in the preparation of flexible micro-supercapacitors via laser-writing of commercial RuO2 on polyimide substrate. Indeed, laser-writing provides facile and scalable engineering with low cost (7), as less than 1 mg.cm-2 of active material are needed in micro-electrodes. Thus, RuO2 interdigitated electrodes were obtained from laser-writing of a precursor mixture of commercial RuO2.xH2O powder and HAuCl4.3H2O salt, spin-coated onto KaptonTM. Laser-writing led to current collector-free and mechanically stable flexible interdigitated RuO2 electrodes. Capacitance values of ~ 30 mF.cm-2 were recorded at 20 mV.s-1 in 1M H2SO4 for the flexible device. This work open the way for the design of high performance micro-devices at large scale. 1. S. Zhai, H. E. Karahan, L. Wei, Q. Qian, A. T. Harris, A. I. Minett, S. Ramakrishna, A. K. Ng, and Y. Chen, Textile energy storage: Structural design concepts, material selection and future perspectives. Energy Storage Mater. 3, 123–139 (2016). 2. J. R. Miller, Valuing reversible energy storage. Science. 335, 1312–1313 (2012). 3. P. Simon and Y. Gogotsi, Materials for electrochemical capacitors. Nat. Mater. 7, 845–854 (2008). 4. T. Brousse, D. Belanger, and J. W. Long, To Be or Not To Be Pseudocapacitive? J. Electrochem. Soc. 162, A5185–A5189 (2015). 5. J. Chmiola, C. Largeot, P. L. Taberna, P. Simon, and Y. Gogotsi, Monolithic Carbide-Derived Carbon Films for Micro-Supercapacitors. Science. 328, 480–483 (2010). 6. P. Huang, C. Lethien, S. Pinaud, K. Brousse, R. Laloo, V. Turq, M. Respaud, A. Demortière, B. Daffos, P. L. Taberna, B. Chaudret, Y. Gogotsi, and P. Simon, On-chip and freestanding elastic carbon films for micro-supercapacitors. Science. 351, 691–695 (2016). 7. M. F. El-Kady and R. B. Kaner, Direct laser writing of graphene electronics. ACS Nano. 8, 8725–8729 (2014).

A Ni/CeO2–CDC-SiC Catalyst with Improved Coke Resistance in CO2 Reforming of Methane

A nanocomposite Ni/CeO2–CDC-SiC catalyst which consists of highly dispersed Ni nanoparticles contacting intimately with CeO2 nanoparticles on a nanoporous carbide-derived carbon (CDC) layer over SiC support has been successfully designed for carbon dioxide (CO2) reforming of methane. In comparison with the Ni/CDC-SiC catalyst, the ceria-promoted Ni/CDC-SiC catalyst possessed enhanced activity and improved stability. The catalysts were systematically characterized with N2 sorption, X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectrometry elemental mapping, thermogravimetric/differential thermal analysis, temperature-programmed reduction, and X-ray photoelectron spectroscopy measurements. It was found that, after introducing CeO2 promoter, the specific surface area was increased, and a smaller Ni particle size was obtained. The smaller Ni particle size led to an enhanced reforming activity. The presence of abundant Ni–CeO2 interfaces on the CeO2-promoted catalyst accelerated...

Niobium carbide nanofibers as a versatile precursor for high power supercapacitor and high energy battery electrodes

Electrospun niobium carbide/carbon nanofibers are a facile precursor to derive highly nanoporous carbide-derived carbon for supercapacitor applications, or niobium pentoxide/carbon for battery electrodes.

Carbide-derived carbon as active interlayer of polypyrrole tri-layer linear actuator

Electro-chemo-mechanical deformations (ECMD) of electrochemically prepared tri-layer polypyrrole (PPy) linear actuators with active nanoporous carbide-derived carbon (CDC) based actuating interlayers were studied under isotonic (constant length) and isometric (constant force) conditions and compared with those of single-layer CDC and PPy linear actuators. The goal of this study was to combine two active materials with different electroactive and mechanical properties for obtaining improved tri-layer PPy linear actuators. CDC linear actuators were used as electrode materials for the electrochemical deposition of PPy. SEM images showed the PPy and polymeric CDC layers could be clearly distinguished. The CDC, CDC–PPy and PPy linear actuators were cycled in aqueous electrolyte in the voltage range of ±0.8V. The CDC–PPy actuators had improved mechanical and electro-chemo-mechanical properties, compared to the free-standing CDC and PPy linear actuators. The Raman spectra did not show any signs of degradation of either CDC or PPy layers during actuation.

Nanoporous carbide-derived carbon based actuators modified with gold foil: Prospect for fast response and low voltage applications

Carbide-derived nanoporous carbon (CDC) based polymeric actuators have been designed and fabricated in combination with gold foil. The gold-foil-modified actuators exhibited high frequency response and required remarkably low operating voltage (as low as ±0.25 V). Hot-pressed additional gold layer (thickness 100 nm) ensures better conductivity of polymer supported CDC electrodes, while maintaining the elasticity of actuator. Electrochemical impedance measurements confirmed that relaxation time constant of gold-foil-modified actuator decreased more than one order of magnitude, thus allowing faster charge/discharge cycles. Gold-foil-modified actuators obtained the strain level of 2.2% when rectangular voltage ±2 V was applied with frequency 0.5 Hz. However, frequency dependent actuation analyses revealed back-relaxation effect of gold-foil-modified actuators below 0.1 Hz. In case of uncovered CDC actuators aforementioned effect was not observed.

Nanoporous Carbide-derived Carbon for Bio-applications

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Porosity control in nanoporous carbide-derived carbon by oxidation in air and carbon dioxide

Carbide-derived carbons (CDC) allow a precise control over the pore size through the selection of the carbide precursor and varying of the synthesis conditions. However, their pore volume is limited by the carbide stoichiometry. While activation of carbons derived from various organic precursors has been widely studied, this process may similarly be able to increase the pore volume and specific surface area of CDC. Oxidation of carbide-derived carbon in air and CO 2 at different temperatures and times allows for significant increase in pore volume and specific surface area as well as control over average pore size with subnanometer accuracy. The effect of activation and associated changes in the pore volume and surface area on the hydrogen uptake are also discussed.

Influence of Mesoporous Separator Properties on the Parameters of Electrical Double-Layer Capacitor Single Cells

The specific surface area, pore size distribution function, micropore and mesopore volume, and area values have been obtained by gas adsorption/absorption method for various separator materials prepared from polypropylene, cellulose, and poly(vinylidene fluoride). Electrical double-layer capacitors (EDLCs) based on the two identical ideally polarizable nanoporous carbide-derived carbon electrodes and different mesoporous separator materials in acetonitrile solution have been tested by cyclic voltammetry and electrochemical impedance methods. The limits of ideal polarizability, low-frequency limiting capacitance and series resistance, time constant, complex power components, and electrolyte conductivity in the separator matrix have been obtained and discussed. The model of Srinivasan and Weidner [ J. Electrochem. Soc. , 146 , 1650 (1999)] has been modified by introducing into it the very high-frequency constant phase and charge-transfer resistance elements. The applicability limits of the modified model have been tested. Noticeable influence of separator chemical composition, thickness, specific surface area, and pore size distribution on the characteristics of the EDLC single cells have been found.

Synthesis, characterization and energy-related applications of carbide-derived carbons obtained by the chlorination of boron carbide

A nanoporous carbide-derived carbon (CDC) was synthesized by chlorination of boron carbide powder using hydrogen chloride as the reactive gas. The structure and texture of the CDCs were characterized by X-ray diffraction, high-resolution transmission electron microcopy and nitrogen adsorption at 77 K, which confirmed a structural and textural dependence on chlorination temperature and reaction time. The CDC technique to produce porous carbons is very attractive because it can obtain carbons with desired structure and porosity and the CDCs produced here show great potential for energy-related applications. Used as hydrogen storage materials, the hydrogen uptake capacity could reach 1.06 wt.% at 77K and 1 bar. When tested as electrodes for supercapacitors, specific surface capacitance value up to 0.403 F m −2 and a capacitance retention ratio up to 86% (at a voltage scan rate of 50 mV s −1) could be obtained.

Synthesis and characterisation of nanoporous carbide-derived carbon by chlorination of vanadium carbide

Nanoporous carbide-derived carbon (CDC) was synthesised from vanadium carbide (VC) powder via gas phase chlorination in the temperature range from 500 to 1100 °C. The XRD analysis of nanoporous carbon powder samples was carried out to investigate the structural changes (graphitisation) of nanoporous carbons synthesised. The first-order Raman spectra showed the absorption peak at ∼1582 cm −1 and the disorder-induced (D) peak at ∼1345 cm −1. The low-temperature N 2 adsorption experiments were performed and a specific surface area up to 1305 m 2 g −1 and total pore volume up to 0.66 cm 3 g −1 were obtained.

Characterization of Activated Nanoporous Carbon as Electrical Double Layer Capacitor Electrode Materials

Thermodynamical and electrochemical characteristics for the non-aqueous electrolyte | nanoporous carbide-derived carbon (CDC), activated carbon cloth (ACC) or commercial activated nanoporous carbon RP-20 (from Kuraray Chemical Co.) interface have been established by XRD, Raman spectroscopy, BET, 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 nanoporous carbon used (nanopores are pores in the range of 2 nm and below - i.e. micropores according to IUPAC classification).

Bactericidal activity of chlorine‐loaded carbide‐derived carbon against Escherichia coli and Bacillus anthracis

The authors investigated the bactericidal activity of high-chlorine-content nanoporous carbide-derived carbon (CDC) against the Gram-positive, spore-forming bacterium Bacillus anthracis and the common Gram-negative enteric bacterium Escherichia coli. Chlorine-loaded nanoporous CDC produced by thermochemical etching of metals and metalloids by chlorination of carbides can retain up to 40 wt % of chlorine. Etching temperature and the structure and composition of carbides allow tuning the porosity of CDC. The CDC chlorine content depends on the synthesis temperature, pore size, and metal carbide used during preparation. It was observed that chlorine-loaded CDC killed up to 100% of exposed E. coli and B. anthracis spores and vegetative cells in a dose and time-dependent manner. CDC containing higher concentrations of chlorine killed bacteria to a greater extent and faster than did CDC containing lesser concentrations of chlorine. The results suggest that chlorine-loaded CDC can be used in several commercial, defense, and industrial activities and processes to kill bacteria.

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.

Electrical double layer characteristics of nanoporous carbon derived from titanium carbide

Electrochemical parameters of the nanoporous carbide-derived carbon|organic electrolyte have been studied by cyclic voltammetry and electrochemical impedance spectroscopy. The gas adsorption measurements have been used for evaluating the specific surface area, pore size distribution and porosity as the essential parameters influencing the double layer performance of carbon. The region of ideal polarizability, values of series and parallel resistance, capacitance and other important electrical double layer parameters were established. It was shown that specific capacitance of typical nanoporous carbon derived from titanium carbide is in the range of 70–90 F cm −3 or 100–130 F g −1 and it depends on the synthesis conditions. The influence of the electrolyte solvent to the capacitance was insignificant, although acetonitrile was advantageous with respect of smaller viscosity.

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 Ti 3SiC 2 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 Ti 3SiC 2 preform were preserved during the transformation. However, the chlorination resulted in the formation of cracks between the former grains of the polycrystalline Ti 3SiC 2 preform. These cracks are believed to be caused by a contraction in the direction perpendicular to the basal planes of Ti 3SiC 2. The synthesized nanoporous carbon demonstrated excellent sorption properties. Energy dispersive X-ray spectroscopy studies showed that Ti 3SiC 2 material chlorinated at 400 °C is capable of trapping over 40 wt.% of Cl 2.