The Experts below are selected from a list of 1539 Experts worldwide ranked by ideXlab platform

Yury Gogotsi - One of the best experts on this subject based on the ideXlab platform.

  • Designing Pseudocapacitance for Nb2O5/Carbide-Derived Carbon Electrodes and Hybrid Devices
    Langmuir : the ACS journal of surfaces and colloids, 2017
    Co-Authors: Chun-han Lai, Yury Gogotsi, David S. Ashby, Melissa Moz, Laurent Pilon, Bruce Dunn
    Abstract:

    Composite structures for electrochemical energy storage are prepared on the basis of using the high-rate lithium ion insertion properties of Nb2O5. The Nb2O5 is anchored on reduced graphene oxide (rGO) by hydrothermal synthesis to improve the charge-transfer properties, and by controlling the surface charge, the resulting Nb2O5-rGO particles are attached to a high-surface-area Carbide-Derived Carbon scaffold without blocking its exfoliated layers. The electrochemical results are analyzed using a recently published multiscale physics model that provides significant insights regarding charge storage kinetics. In particular, the composite electrode exhibits surface-confined charge storage at potentials of 2.2 V. A hybrid device composed of the composite electrode with activated Carbon as the positive electrode demonstrates increased energy density at power densities comparable to an activated c...

  • High capacitance of coarse-grained carbide derived Carbon electrodes
    Journal of Power Sources, 2016
    Co-Authors: Boris Dyatkin, Patrice Simon, Oleksiy Gogotsi, Bohdan Malinovskiy, Yuliya Zozulya, Yury Gogotsi
    Abstract:

    We report exceptional electrochemical properties of supercapacitor electrodes composed of large, granular Carbide-Derived Carbon (CDC) particles. Using a titanium carbide (TiC) precursor, we synthesized 70–250 μm sized particles with high surface area and a narrow pore size distribution. Electrochemical cycling of these coarse-grained powders defied conventional wisdom that a small particle size is strictly required for supercapacitor electrodes and allowed high charge storage densities, rapid transport, and good rate handling ability. The material showcased capacitance above 100 F g−1 at sweep rates as high as 250 mV s−1 in organic electrolyte. 250–1000 micron thick dense CDC films with up to 80 mg cm−2 loading showed superior areal capacitances. The material significantly outperformed its activated Carbon counterpart in organic electrolytes and ionic liquids. Furthermore, large internal/external surface ratio of coarse-grained Carbons allowed the resulting electrodes to maintain high electrochemical stability up to 3.1 V in ionic liquid electrolyte. In addition to presenting novel insights into the electrosorption process, these coarse-grained Carbons offer a pathway to low-cost, high-performance implementation of supercapacitors in automotive and grid-storage applications.

  • Graphene-like carbide derived Carbon for high-power supercapacitors
    Nano Energy, 2015
    Co-Authors: Pengcheng Gao, Yury Gogotsi, Pierre-louis Taberna, Patrice Simon, Carlos R. Pérez, Wan-yu Tsai, Barbara Daffos, Frédéric Favier
    Abstract:

    Abstract Two graphene-like carbide derived Carbons (CDC-Gs) were produced by chlorination of SiC nanosheets obtained by magnesio-thermal reduction at moderate temperature of silica/graphene oxide nanocomposites. These CDC-Gs were evaluated as supercapacitor electrode materials in an organic electrolyte. Starting from a low SiO2/GO ratio in the precursor, the resulting CDC-G nanosheets are composed of a few layers of graphite, partially coated with microporous CDC. In contrast, a high SiO2/GO ratio leads to micropores generated on the basal plane of individual Carbon nanosheets. The latter CDC-G shows a remarkable high power capability with 76 % of retention of the initial capacity at scan rates up to 3 V s−1. Notably, the equivalent series resistance (ESR) and time constant of the cell were found to be extremely low at 0.45 Ω·cm2 and 0.4 s, respectively, thanks to the unique 2D open surface and enhanced access to micropores. These features were attributed to the unique nanostructure of the microporous graphene.

  • Synthesis and electrochemical properties of niobium pentoxide deposited on layered Carbide-Derived Carbon
    Journal of Power Sources, 2015
    Co-Authors: Chuanfang Zhang, Maria R Lukatskaya, Boris Dyatkin, Wenming Qiao, Donghui Long, Bruce Dunn, Ryan Maloney, Majid Beidaghi, Emilie Perre, Yury Gogotsi
    Abstract:

    Abstract Herein we report on the hydrothermal synthesis of niobium pentoxide on Carbide-Derived Carbon (Nb2O5/CDC) with a layered structure. The presence of phenylphosphonic acid guides the deposition during preparation, leading to the formation of amorphous Nb2O5 particles which are 4–10 nm in diameter and homogeneously distributed on the CDC framework. Electrochemical testing of the Nb2O5/CDC electrode indicated that the highest capacitance and Coulombic efficiency occurred using an electrolyte comprised of 1 M lithium perchlorate in ethylene Carbonate/dimethyl Carbonate. Subsequent heat treatment of Nb2O5/CDC in CO2 environment led to crystallization of the Nb2O5, allowing reversible Li+ intercalation/de-intercalation. For sweep rates corresponding to charging and discharging in under 3 min, a volumetric charge of 180 C cm−3 and Coulombic efficiency of 99.2% were attained.

  • Capacitance, charge dynamics, and electrolyte-surface interactions in functionalized Carbide-Derived Carbon electrodes
    Progress in Natural Science: Materials International, 2015
    Co-Authors: Boris Dyatkin, Eugene Mamontov, Kevin M. Cook, Yury Gogotsi
    Abstract:

    Abstract This study analyzed the dynamics of ionic liquid electrolyte inside of defunctionalized, hydrogenated, and aminated pores of Carbide-Derived Carbon supercapacitor electrodes. The approach tailors surface functionalities and tunes nanoporous structures to decouple the influence of pore wall composition on capacitance, ionic resistance, and long-term cyclability. Quasi-elastic neutron scattering probes the self-diffusion properties and electrode-ion interactions of electrolyte molecules confined in functionalized pores. Room-temperature ionic liquid interactions in confined pores are strongest when the hydrogen-containing groups are present on the surface. This property translates into higher capacitance and greater ion transport through pores during electrochemical cycling. Unlike hydrogenated pores, aminated pores do not favorably interact with ionic liquid ions and, subsequently, are outperformed by defunctionalized surfaces.

Bastian J. M. Etzold - One of the best experts on this subject based on the ideXlab platform.

  • Improving control of Carbide-Derived Carbon microstructure by immobilization of a transition-metal catalyst within the shell of carbide/Carbon core-shell structures.
    Beilstein journal of nanotechnology, 2019
    Co-Authors: Teguh Ariyanto, Andreas M. Kern, Jan Glaesel, Guirong Zhang, Bastian J. M. Etzold
    Abstract:

    Carbon materials for electrical energy devices, such as battery electrodes or fuel-cell catalysts, require the combination of the contradicting properties of graphitic microstructure and porosity. The usage of graphitization catalysts during the synthesis of Carbide-Derived Carbon materials results in materials that combine the required properties, but controlling the microstructure during synthesis remains a challenge. In this work, the controllability of the synthesis route is enhanced by immobilizing the transition-metal graphitization catalyst on a porous Carbon shell covering the carbide precursor prior to conversion of the carbide core to Carbon. The catalyst loading was varied and the influence on the final material properties was characterized by using physisorption analysis with nitrogen as well as Carbon dioxide, X-ray diffraction, temperature-programmed oxidation (TPO), Raman spectroscopy, SEM and TEM. The results showed that this improved route allows one to greatly vary the crystallinity and pore structure of the resulting Carbide-Derived Carbon materials. In this sense, the content of graphitic Carbon could be varied from 10-90 wt % as estimated from TPO measurements and resulting in a specific surface area ranging from 1500 to 300 m2·g-1.

  • improving control of carbide derived Carbon microstructure by immobilization of a transition metal catalyst within the shell of carbide Carbon core shell structures
    Beilstein Journal of Nanotechnology, 2019
    Co-Authors: Teguh Ariyanto, Andreas M. Kern, Jan Glaesel, Guirong Zhang, Bastian J. M. Etzold
    Abstract:

    : Carbon materials for electrical energy devices, such as battery electrodes or fuel-cell catalysts, require the combination of the contradicting properties of graphitic microstructure and porosity. The usage of graphitization catalysts during the synthesis of Carbide-Derived Carbon materials results in materials that combine the required properties, but controlling the microstructure during synthesis remains a challenge. In this work, the controllability of the synthesis route is enhanced by immobilizing the transition-metal graphitization catalyst on a porous Carbon shell covering the carbide precursor prior to conversion of the carbide core to Carbon. The catalyst loading was varied and the influence on the final material properties was characterized by using physisorption analysis with nitrogen as well as Carbon dioxide, X-ray diffraction, temperature-programmed oxidation (TPO), Raman spectroscopy, SEM and TEM. The results showed that this improved route allows one to greatly vary the crystallinity and pore structure of the resulting Carbide-Derived Carbon materials. In this sense, the content of graphitic Carbon could be varied from 10-90 wt % as estimated from TPO measurements and resulting in a specific surface area ranging from 1500 to 300 m2·g-1.

  • Molecular Modeling of Microporous Structures of Carbide-Derived Carbon-Based Supercapacitors
    The Journal of Physical Chemistry C, 2017
    Co-Authors: Sabine Schweizer, Bastian J. M. Etzold, Robert H. Meißner, Marc Amkreutz, Karsten Thiel, Peter Schiffels, Johannes Landwehr, Jörg-rüdiger Hill
    Abstract:

    Microporous Carbide-Derived Carbons are an important structural class for various technological applications. We present two possible strategies based on molecular dynamics simulations for modeling microporous amorphous Carbon. In addition, we have investigated the influence of the precursor structure and simulation parameters on the porosity of the final model structure. We observed a minor influence of the precursor structure on the porosity and found that the structural properties such as pore size and hybridization in the modeled Carbon structures agree well with experimental findings. Moreover, CO2 adsorption isotherms have been simulated using Monte Carlo simulations for comparsion with experimental data. In this context, we have also considered partially oxidized Carbon structures for which an increased uptake of CO2 was observed.

  • vanadium pentoxide carbide derived Carbon core shell hybrid particles for high performance electrochemical energy storage
    Journal of Materials Chemistry, 2016
    Co-Authors: Bastian J. M. Etzold, Teguh Ariyanto, Marco Zeiger, Benjamin Kruner, Nicolas J Peter, Simon Fleischmann, Volker Presser
    Abstract:

    A novel, two step synthesis is presented combining the formation of Carbide-Derived Carbon (CDC) and redox-active vanadium pentoxide (V2O5) in a core–shell manner using solely vanadium carbide (VC) as the precursor. In a first step, the outer part of VC particles is transformed to nanoporous CDC owing to the in situ formation of chlorine gas from NiCl2 at 700 °C. In a second step, the remaining VC core is calcined in synthetic air to obtain V2O5/CDC core–shell particles. Materials characterization by means of electron microscopy, Raman spectroscopy, and X-ray diffraction clearly demonstrates the partial transformation from VC to CDC, as well as the successive oxidation to V2O5/CDC core–shell particles. Electrochemical performance was tested in organic 1 M LiClO4 in acetonitrile using half- and asymmetric full-cell configuration. High specific capacities of 420 mA h g−1 (normalized to V2O5) and 310 mA h g−1 (normalized to V2O5/CDC) were achieved. The unique nanotextured core–shell architecture enables high power retention with ultrafast charging and discharging, achieving more than 100 mA h g−1 at 5 A g−1 (rate of 12C). Asymmetric cell design with CDC on the positive polarization side leads to a high specific energy of up to 80 W h kg−1 with a superior retention of more than 80% over 10 000 cycles and an overall energy efficiency of up to 80% at low rates.

  • Thermal and Electrical Conductivity of Amorphous and Graphitized Carbide‐Derived Carbon Monoliths
    Chemical Engineering & Technology, 2016
    Co-Authors: Andreas M. Kern, Bodo Zierath, Joachim Haertlé, Tobias Fey, Bastian J. M. Etzold
    Abstract:

    The influence of graphitization and composition of Carbide-Derived Carbon (CDC) monoliths on the electrical and thermal conductivity was investigated. Carbon monoliths with varying porosities were synthesized employing biomorphous macroporous TiC and SiC as precursors. Graphitization was carried out in situ during high-temperature chlorination with and without addition of nickel, iron, and cobalt chloride to the carbide. The graphitized monoliths showed improved properties. The results demonstrate that despite graphitic Carbon also glass-like Carbon, stemming from the carbide synthesis, increases the thermal and electrical conductivity significantly.

Gleb Yushin - One of the best experts on this subject based on the ideXlab platform.

  • review of nanostructured Carbon materials for electrochemical capacitor applications advantages and limitations of activated Carbon carbide derived Carbon zeolite templated Carbon Carbon aerogels Carbon nanotubes onion like Carbon and graphene
    Wiley Interdisciplinary Reviews: Energy and Environment, 2014
    Co-Authors: Wentian Gu, Gleb Yushin
    Abstract:

    Electric double layer capacitors, also called supercapacitors, ultracapacitors, and electrochemical capacitors, are gaining increasing popularity in high power energy storage applications. Novel Carbon materials with high surface area, high electrical conductivity, as well as a range of shapes, sizes and pore size distributions are being constantly developed and tested as potential supercapacitor electrodes. This article provides an overview of the electrochemical studies on activated Carbon, carbide derived Carbon, zeolite-templated Carbon, Carbon aerogel, Carbon nanotube, onion-like Carbon, and graphene. We discuss the key performance advantages and limitations of various nanostructured Carbon materials and provide an overview of the current understanding of the structure–property relationships related to the transport and adsorption of electrolyte ions on their surfaces, specific and volumetric capacitance, self-discharge, cycle life, electrolyte stability, and others. We discuss the impact of microstructural defects, pore size distribution, pore tortuosity, chemistry and functional groups on the Carbon surface, nanoscale curvature, and Carbon-electrolyte interfacial energy. Finally, we review state-of-the art commercial large scale applications of supercapacitors, including their use in smart grids and distributed energy storage, hybrid electric and electric vehicles, energy efficient industrial equipment, ships, wind power stations, uninterruptible power supplies, power backup, and consumer devices. © 2013 John Wiley & Sons, Ltd.

  • Micro‐ and Mesoporous Carbide‐Derived Carbon–Selenium Cathodes for High‐Performance Lithium Selenium Batteries
    Advanced Energy Materials, 2014
    Co-Authors: Jung Tae Lee, Martin Oschatz, Stefan Kaskel, Hyea Kim, Dong-chan Lee, Huan-ting Lin, Bogdan Zdyrko, Won Il Cho, Gleb Yushin
    Abstract:

    Nanocomposites of selenium (Se) and ordered mesoporous silicon Carbide-Derived Carbon (OM-SiC-CDC) are prepared for the first time and studied as cathodes for lithium-selenium (Li-Se) batteries. The higher concentration of Li salt in the electrolytes greatly improves Se utilization and cell cycle stability. Se-CDC shows significantly better performance characteristics than Se-activated Carbon nanocomposites with similar physical properties. Se-CDC also exhibits better rate performance and cycle stability compared to similarly produced sulfur (S)–CDC for Li/S batteries.

  • sulfur infiltrated micro and mesoporous silicon carbide derived Carbon cathode for high performance lithium sulfur batteries
    Advanced Materials, 2013
    Co-Authors: Youyang Zhao, Lars Borchardt, Martin Oschatz, Stefan Kaskel, Soeren Thieme, Alexandre Magasinski, Gleb Yushin
    Abstract:

    Lithium ion batteries (LiBs) are commercially successful and widely used in various portable electronic devices as well as automobiles. However, the needs for high energy and power density with longer cycle life cannot be fulfi lled by the current state-of-art LiBs. It is inevitable to explore alternative electrode materials with higher gravimetric and volumetric capacities. [ 1 , 2 ] Sulfur (S) is considered to be one of the most probable candidates for the next generation cathodes due to its high theoretical gravimetric capacity of 1672 mA h g − 1 , low cost and its abundance in nature. [ 3 , 4‐10 ] Although this capacity is an order of magnitude higher than that of existing commercial electrode materials, S cathodes still have several challenges to be overcome for commercialization. The key problems include dissolution of polysulfi des (the reaction intermediates during discharge such as Li 2 S 8 or Li 2 S 4 ) and precipitation of electrically insulating Li 2 S 2 and/or Li 2 S onto the surface of both electrodes. [ 6 , 11 ] Both phenomena restrict the cell performance by lowering the active mass and increasing cell resistance during prolonged operation. The dissolution and re-precipitation of polysulfi des (shuttle mechanism) additionally results in overcharge and low Coulombic effi ciency. [ 5 , 6 ] Highly undesirable dissolution and re-deposition of polysulfi des can be suppressed via several strategies. First, the electrolyte can be modifi ed to reduce the solubility of polysulfi des. The addition of Li 2 S 8 into organic electrolyte [ 7 ] has shown to somewhat alleviate the dissolution of sulfur. Unfortunately, however, Li 2 S 8 can be similarly reduced on the Li anode to Li 2 S 2 and Li 2 S, thus offering only limited and temporary benefi ts. Higher temperature operation [ 10 ] as well as using LiNO 3 additive in organic electrolyte [ 9 ] has been shown to advantageously change the properties of solid electrolyte interface (SEI) on Li anodes, reducing the degree of continuous Li 2 S precipitation on the Li surface and thus minimizing the shuttle mechanism. Alternatively, solid electrolytes (e.g. polymer) can similarly repress or possibly eliminate the shuttle mechanism. [ 4 , 12 ] The challenges with the solid electrolytes are related to the active material (S) volume changes upon insertion/extraction of Li, which are diffi cult to accommodate if the electrolyte deformability is insuffi cient. In order to increase the electrical conductivity of sulfur electrode, it can be mixed with or better confi ned within electrically conductive materials such as Carbon or conductive polymer. This approach improves the utilization of S, which is in close contact with the electrically conductive media. [ 2 , 3 , 6 , 11 , 13 ] More importantly, these S confi nement hosts can synergistically suppress the active material dissolution. In this case, the physical properties of porous hosts become signifi cant. The size and shape of pores as well as the pore-size distribution and specifi c surface area have a major impact on the composite cathode’s electrochemical performance and thus can be optimized for achieving high capacity, fast rate capability and stable cycling performance. Smaller pore size leads to stronger interactions between the polysulfi des and the pore walls due to the overlap of the adsorbate-adsorbent interaction potentials from both sides of the pore. [ 14 ] In case when interaction strength between the Carbon pore walls and polysulfi des is higher than that between the pore walls and electrolyte solvent molecules, smaller pores shall increase the energy barrier and reduce the driving force of the polysulfi des diffusion into the electrolyte, thereby decreasing the S cathode dissolution. Pores that are too small, however, may negatively impact the Li diffusion and the rate capability of the cell. Carbide derived Carbons (CDCs) are synthesized by a selective removal of non-Carbon species such as metals or semimetals via physical or chemical processes (most commonly by chlorination) from various carbide precursors. [ 15 , 16 ] The micropore size of many CDCs is very uniform and precisely controllable up to angstrom level due to the highly uniform distribution of Carbon atoms within such precursors and continuous extraction of large metal chloride molecules from CDC during their formation. [ 15 ] The use of CDC for S nanoconfi nement can be greatly advantageous because of the precise tuning of the pore-size distribution possible by both selecting

  • hierarchical micro and mesoporous carbide derived Carbon as a high performance electrode material in supercapacitors
    Small, 2011
    Co-Authors: Lars Borchardt, Martin Oschatz, Stefan Kaskel, Emanuel Kockrick, Marcus Rose, Yair Korenblit, Gleb Yushin
    Abstract:

    Ordered mesoporous Carbide-Derived Carbon (OM-CDC) materials produced by nanocasting of ordered mesoporous silica templates are characterized by a bimodal pore size distribution with a high ratio of micropores. The micropores result in outstanding adsorption capacities and the well-defined mesopores facilitate enhanced kinetics in adsorption processes. Here, for the first time, a systematic study is presented, in which the effects of synthesis temperature on the electrochemical performance of these materials in supercapacitors based on a 1 M aqueous solution of sulfuric acid and 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid are reported. Cyclic voltammetry shows the specific capacitance of the OM-CDC materials exceeds 200 F g(-1) in the aqueous electrolyte and 185 F g(-1) in the ionic liquid, when measured in a symmetric configuration in voltage ranges of up to 0.6 and 2 V, respectively. The ordered mesoporous channels in the produced OM-CDC materials serve as ion-highways and allow for very fast ionic transport into the bulk of the OM-CDC particles. At room temperature the enhanced ion transport leads to 75% and 90% of the capacitance retention at current densities in excess of similar to 10 A g(-1) in ionic liquid and aqueous electrolytes, respectively. The supercapacitors based on 250-300 mu m OM-CDC electrodes demonstrate an operating frequency of up to 7 Hz in aqueous electrolyte. The combination of high specific capacitance and outstanding rate capabilities of the OM-CDC materials is unmatched by state-of-the art activated Carbons and strictly microporous CDC materials.

  • a cubic ordered mesoporous carbide derived Carbon for gas and energy storage applications
    Carbon, 2010
    Co-Authors: Martin Oschatz, Lars Borchardt, Gleb Yushin, Emanuel Kockrick, Marcus Rose, Nicole Klein, Irena Senkovska, Thomas Freudenberg, Yair Korenblit, Stefan Kaskel
    Abstract:

    A hierarchical and highly porous Carbide-Derived Carbon (CDC) was obtained by nanocasting of pre-ceramic precursors into cubic ordered silica (KIT-6) and subsequent chlorination. Resulting CDC replica materials show high methane and n-butane uptake and excellent performance as electrode materials in supercapacitors.

Stefan Kaskel - One of the best experts on this subject based on the ideXlab platform.

  • Micro‐ and Mesoporous Carbide‐Derived Carbon–Selenium Cathodes for High‐Performance Lithium Selenium Batteries
    Advanced Energy Materials, 2014
    Co-Authors: Jung Tae Lee, Martin Oschatz, Stefan Kaskel, Hyea Kim, Dong-chan Lee, Huan-ting Lin, Bogdan Zdyrko, Won Il Cho, Gleb Yushin
    Abstract:

    Nanocomposites of selenium (Se) and ordered mesoporous silicon Carbide-Derived Carbon (OM-SiC-CDC) are prepared for the first time and studied as cathodes for lithium-selenium (Li-Se) batteries. The higher concentration of Li salt in the electrolytes greatly improves Se utilization and cell cycle stability. Se-CDC shows significantly better performance characteristics than Se-activated Carbon nanocomposites with similar physical properties. Se-CDC also exhibits better rate performance and cycle stability compared to similarly produced sulfur (S)–CDC for Li/S batteries.

  • direct synthesis of carbide derived Carbon monoliths with hierarchical pore design by hard templating
    Journal of Materials Chemistry, 2014
    Co-Authors: Winfried Nickel, Philipp Adelhelm, M. Von Der Lehr, Bernd M. Smarsly, Martin Oschatz, Matthias Leistner, Guangping Hao, Philipp Muller, Stefan Kaskel
    Abstract:

    Carbide-Derived Carbon Monoliths (CDC-Ms) containing a multimodal arrangement with high volumes of micro- meso- and macropores are prepared by direct nanocasting of silica monoliths with polycarbosilane precursors. CDC-Ms show well-defined pore structures along with specific surface areas of more than 2600 m2 g−1 and overall pore volumes as high as 3.14 cm3 g−1. They exhibit advanced gas filtration properties compared to purely microporous materials due to enhanced storage capacities and kinetics as demonstrated by thermal response measurements based on InfraSORP technology.

  • Evolution of porosity in Carbide-Derived Carbon aerogels
    J. Mater. Chem. A, 2014
    Co-Authors: Martin Oschatz, Lars Borchardt, Winfried Nickel, Matthias Leistner, Matthias Thommes, Katie A. Cychosz, Marion Adam, Giovanni Mondin, Patrick Strubel, Stefan Kaskel
    Abstract:

    Carbide-Derived Carbon (CDC) aerogel monoliths with very high porosity are synthesized starting from polymeric precursors. Cross-linking by platinum-catalyzed hydrosilylation of polycarbosilanes followed by supercritical drying yields preceramic aerogels. After ceramic conversion and silicon extraction in hot chlorine gas, hierarchically porous Carbon materials with specific surface areas as high as 2122 m2 g−1 and outstanding total pore volumes close to 9 cm3 g−1 are obtained. Their pore structure is controllable by the applied synthesis temperature as shown by combined nitrogen (−196 °C) and Carbon dioxide (0 °C) measurements coupled with electron microscopic methods. The combination of large micropore volumes and the aerogel-type pore system leads to advanced adsorption properties due to a combination of large storage capacities and effective materials transport in comparison with purely microporous reference materials as shown by thermal response measurements.

  • Titanium Carbide and Carbide‐Derived Carbon Composite Nanofibers by Electrospinning of Ti‐Resin Precursor
    Chemie Ingenieur Technik, 2013
    Co-Authors: Jan Märtin, Lars Borchardt, Martin Oschatz, Giovanni Mondin, Stefan Kaskel
    Abstract:

    TiO2/C and TiC/C composite nanofibers were produced by electrospinning of resin/TiCl4 precursor solution. The resulting ceramic fiber webs were porous and showed surface areas as high as 523 m2g–1. They were further converted to Carbide-Derived Carbon (CDC) fibers under full retention of the fiber-like shape and flexibility. These CDC membranes showed a hierarchical pore structure and specific surface as high as 1378 m2g–1. Applications in the area of high temperature filtration, catalyst support and energy storage are conceivable.

  • sulfur infiltrated micro and mesoporous silicon carbide derived Carbon cathode for high performance lithium sulfur batteries
    Advanced Materials, 2013
    Co-Authors: Youyang Zhao, Lars Borchardt, Martin Oschatz, Stefan Kaskel, Soeren Thieme, Alexandre Magasinski, Gleb Yushin
    Abstract:

    Lithium ion batteries (LiBs) are commercially successful and widely used in various portable electronic devices as well as automobiles. However, the needs for high energy and power density with longer cycle life cannot be fulfi lled by the current state-of-art LiBs. It is inevitable to explore alternative electrode materials with higher gravimetric and volumetric capacities. [ 1 , 2 ] Sulfur (S) is considered to be one of the most probable candidates for the next generation cathodes due to its high theoretical gravimetric capacity of 1672 mA h g − 1 , low cost and its abundance in nature. [ 3 , 4‐10 ] Although this capacity is an order of magnitude higher than that of existing commercial electrode materials, S cathodes still have several challenges to be overcome for commercialization. The key problems include dissolution of polysulfi des (the reaction intermediates during discharge such as Li 2 S 8 or Li 2 S 4 ) and precipitation of electrically insulating Li 2 S 2 and/or Li 2 S onto the surface of both electrodes. [ 6 , 11 ] Both phenomena restrict the cell performance by lowering the active mass and increasing cell resistance during prolonged operation. The dissolution and re-precipitation of polysulfi des (shuttle mechanism) additionally results in overcharge and low Coulombic effi ciency. [ 5 , 6 ] Highly undesirable dissolution and re-deposition of polysulfi des can be suppressed via several strategies. First, the electrolyte can be modifi ed to reduce the solubility of polysulfi des. The addition of Li 2 S 8 into organic electrolyte [ 7 ] has shown to somewhat alleviate the dissolution of sulfur. Unfortunately, however, Li 2 S 8 can be similarly reduced on the Li anode to Li 2 S 2 and Li 2 S, thus offering only limited and temporary benefi ts. Higher temperature operation [ 10 ] as well as using LiNO 3 additive in organic electrolyte [ 9 ] has been shown to advantageously change the properties of solid electrolyte interface (SEI) on Li anodes, reducing the degree of continuous Li 2 S precipitation on the Li surface and thus minimizing the shuttle mechanism. Alternatively, solid electrolytes (e.g. polymer) can similarly repress or possibly eliminate the shuttle mechanism. [ 4 , 12 ] The challenges with the solid electrolytes are related to the active material (S) volume changes upon insertion/extraction of Li, which are diffi cult to accommodate if the electrolyte deformability is insuffi cient. In order to increase the electrical conductivity of sulfur electrode, it can be mixed with or better confi ned within electrically conductive materials such as Carbon or conductive polymer. This approach improves the utilization of S, which is in close contact with the electrically conductive media. [ 2 , 3 , 6 , 11 , 13 ] More importantly, these S confi nement hosts can synergistically suppress the active material dissolution. In this case, the physical properties of porous hosts become signifi cant. The size and shape of pores as well as the pore-size distribution and specifi c surface area have a major impact on the composite cathode’s electrochemical performance and thus can be optimized for achieving high capacity, fast rate capability and stable cycling performance. Smaller pore size leads to stronger interactions between the polysulfi des and the pore walls due to the overlap of the adsorbate-adsorbent interaction potentials from both sides of the pore. [ 14 ] In case when interaction strength between the Carbon pore walls and polysulfi des is higher than that between the pore walls and electrolyte solvent molecules, smaller pores shall increase the energy barrier and reduce the driving force of the polysulfi des diffusion into the electrolyte, thereby decreasing the S cathode dissolution. Pores that are too small, however, may negatively impact the Li diffusion and the rate capability of the cell. Carbide derived Carbons (CDCs) are synthesized by a selective removal of non-Carbon species such as metals or semimetals via physical or chemical processes (most commonly by chlorination) from various carbide precursors. [ 15 , 16 ] The micropore size of many CDCs is very uniform and precisely controllable up to angstrom level due to the highly uniform distribution of Carbon atoms within such precursors and continuous extraction of large metal chloride molecules from CDC during their formation. [ 15 ] The use of CDC for S nanoconfi nement can be greatly advantageous because of the precise tuning of the pore-size distribution possible by both selecting

Enn Lust - One of the best experts on this subject based on the ideXlab platform.

  • Specific Performance of Electrical Double–Layer Capacitors Based on Different Separator Materials and Non–Aqueous Electrolytes
    ECS Transactions, 2013
    Co-Authors: K. Tõnurist, Thomas Thomberg, Alar Jänes, Enn Lust
    Abstract:

    Influence of the separator material characteristics on the performance of electrical double–layer capacitors (EDLCs), based on the two identical ideally polarizable microporous titanium carbide–derived Carbon electrodes in 1 M (C2H5)3CH3NBF4 acetonitrile solution or in room temperature ionic liquid (1–ethyl–3–methylimidazolium tetrafluoroborate), has been tested by cyclic voltammetry, constant power and electrochemical impedance spectroscopy methods. Self–made separator materials have been prepared from poly(vinylidene fluoride) solutions in N,N–dimethylacetamide or N,N–dimethylformamide and acetone mixture (8:2 mass ratio) by using the electrospinning method. Noticeable influence of the separator porosity and chemical composition on the limits of ideal polarizability, specific capacitance, equivalent series resistance, specific energy and power of the EDLCs has been obtained and discussed.

  • Comparative Study of Using Chlorine and Hydrogen Chloride for Synthesis of Titanium Carbide Derived Carbon
    ECS Transactions, 2013
    Co-Authors: Indrek Tallo, Thomas Thomberg, Alar Jänes, Enn Lust
    Abstract:

    For the synthesis of carbide derived Carbons molecular chlorine is dominantly used, but hydrogen chloride is also mentioned as a reagent. There is however no thorough investigation whether the resulting Carbon is comparable or distinct using different gases for halogenation of carbides. Different titanium carbide derived Carbon powders were synthesized from titanium carbide within the temperature range from 700 to 1100°C either using molecular chlorine or hydrogen chloride as reactants. High-resolution transmission electron microscopy, X-ray diffraction and Raman spectroscopy analysis were carried out to investigate the structure of the synthesized materials. The electrochemical characteristics of the supercapacitors based on the synthesized Carbon electrode materials have been tested using cyclic voltammetry, constant power and electrochemical impedance methods. Based on experimental results, titanium carbide derived Carbon materials synthesized by using molecular chlorine can be considered superior over those materials that have been synthesized using hydrogen chloride.

  • Specific performance of electrical double layer capacitors based on different separator materials in room temperature ionic liquid
    Electrochemistry Communications, 2012
    Co-Authors: K. Tõnurist, Thomas Thomberg, Alar Jänes, Ilmar Kink, Enn Lust
    Abstract:

    Abstract Influence of the separator material characteristics on the performance of electrical double layer capacitors (EDLCs), based on the two identical ideally polarizable microporous titanium carbide‐derived Carbon electrodes in room temperature ionic liquid (1‐ethyl‐3‐methylimidazolium tetrafluoroborate), has been tested by cyclic voltammetry, constant power and electrochemical impedance spectroscopy methods. Self‐made separator materials have been prepared from poly(vinylidene fluoride) solutions in N,N‐dimethylacetamide or N,N‐dimethylformamide and acetone mixture (8:2 mass ratio) by using the electrospinning method. Noticeable influence of the separator porosity and chemical composition on the limits of ideal polarizability, specific capacitance, equivalent series resistance, phase angle, specific energy and power of the EDLCs has been obtained and discussed.

  • Impact of Carbon nanotube additives on Carbide-Derived Carbon-based electroactive polymer actuators
    Carbon, 2012
    Co-Authors: Viljar Palmre, Alar Jänes, Enn Lust, Janno Torop, Mati Arulepp, Takushi Sugino, Kinji Asaka, Alvo Aabloo
    Abstract:

    Abstract 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 (

  • Nanostructured Carbide-Derived Carbon synthesized by chlorination of tungsten carbide
    Carbon, 2011
    Co-Authors: Indrek Tallo, Thomas Thomberg, Alar Jänes, Kyösti Kontturi, Enn Lust
    Abstract:

    Abstract 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 La ≈ 4 nm and Lc ≈ 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.