T. Thomberg

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Supercapacitors based on carbide-derived carbons synthesised using HCl and Cl2 as reactants

Journal of Solid State Electrochemistry, 2012

ABSTRACT Micro- and mesoporous carbide-derived carbons (CDCs) were synthesised from TiC powder vi... more ABSTRACT Micro- and mesoporous carbide-derived carbons (CDCs) were synthesised from TiC powder via a gas-phase reaction using HCl and Cl2 within the temperature range of 700–1,100 °C. Analysis of X-ray diffraction results show that TiC-CDCs consist mainly of graphitic crystallites. The first-order Raman spectra showed the graphite-like absorption peaks at ~1,577 cm−1 and the disorder-induced peaks at ~1,338 cm−1. The low-temperature N2 sorption experiments were performed, and specific surface areas up to 1,214 and 1,544 m2 g−1 were obtained for TiC-CDC (HCl) synthesised at T = 800 °C and TiC-CDC (Cl2) synthesised at T = 900 °C, respectively. For the TiC-CDC powders synthesised, a bimodal pore size distribution has been established with the first maximum in the region up to 1.5 nm and the second maximum from 2 to 4 nm. The energy-related properties of supercapacitors based on 1 M (C2H5)3CH3NBF4 in acetonitrile and TiC-CDC (Cl2) and TiC-CDC (HCl) as electrode materials were also investigated by cyclic voltammetry, impedance spectroscopy, galvanostatic charge/discharge and constant power methods. The specific energy, calculated at U = 3.0 V, are maximal for TiC-CDC (Cl2 800 °C) and TiC-CDC (HCl 900 °C), which are 43.1 and 31.1 W h kg−1, respectively. The specific power, calculated at cell potential U = 3.0 V, are maximal for TiC-CDC (Cl2 1,000 °C) and TiC-CDC (HCl 1,000 °C), which are 805.2 and 847.5 kW kg−1, respectively. The Ragone plots for CDCs prepared by using Cl2 or HCl are quite similar, and at high power loads, the TiC-CDC material synthesised using Cl2 at 900 °C, i.e. the material with optimal pore structure, delivers the highest power at constant energy.

D-Glucose Derived Nanospheric Hard Carbon Electrodes for Room-Temperature Sodium-Ion Batteries

by Ronald Väli, T. Thomberg, and Enn Lust

Electrochemical performance of nanospheric glucose derived hard carbon based electrodes, speciall... more Electrochemical performance of nanospheric glucose derived hard carbon based electrodes, specially derived from D-glucose via hydrothermal carbonization and subsequent pyrolysis at 1100◦C, has been studied in 1 M NaClO4 propylene carbonate electrolyte. High Na+
electroreduction and Na oxidation peaks were observed in cyclic voltammograms. Galvanostatic charge/discharge measurements demonstrated high speciﬁc capacity, over 300 mAh g−1 for the ﬁrst cycle. After 200thcycle, a speciﬁc capacity of 160 mAh g−1(at 50 mA g−1 cycling rate) has been calculated for the nanospheric hard carbon based half-cells. Raman spectroscopy, inductively coupled plasma mass spectrometry and energy-dispersive X-ray spectroscopy data indicated accumulation (adsorption/absorption) of Na onto/into the electrochemically polarized porous nanospheric hard carbon material. Impedance data demonstrated that electrode potential has a noticeable inﬂuence on the total polarization, and charge transfer resistance as well as on the mass transfer characteristics at the carbon | (1 M NaClO4 + propylene carbonate) electrolyte interface.

Different Carbide Derived Nanoporous Carbon Supports and Electroreduction of Oxygen

by H. Kurig and T. Thomberg

ECS Transactions, 2015

ABSTRACT Using rotating disc electrode technique, the oxygen reduction reaction in 0.1M KOH was s... more ABSTRACT Using rotating disc electrode technique, the oxygen reduction reaction in 0.1M KOH was studied at various micromesoporous carbide derived carbon powders, synthesized from various binary metal carbides. The catalytic activity and mechanism noticeable depends on the hierarchical structure of the nanoporous carbon electrode. The activation with CO2 increases the differential volume of pores and proportion of mesopores in carbon matrix. It was shown that the partially graphitized carbon C(Mo2C) with a large number of edge plane sites has higher electrocatalytic activity toward oxygen reduction in alkaline media compared with other amorphous or partly graphitized carbons studied. The corresponding relative catalytic activity of catalysts increases in the following order: C(WTiC2) &lt; Vulcan &lt; C(TiC) &lt; C(TiC)-A1 ≤ C(TiC)-A2 &lt; C(Mo2C)-A &lt; C(Mo2C).

High power density supercapacitors based on the carbon dioxide activated d-glucose derived carbon electrodes and 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid

by T. Thomberg and Alar Jänes

Journal of Power Sources, 2015

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Editorial Board

by T. Thomberg and K. Tõnurist

Stabilization of flavylium dye by incorporation into Fe-containing mesoporous silicate Y. Kohno, M. Senga, M. Shibata, K. Yoda, R. Matsushima, Y. Tomita, Y. Maeda and K. Kobayashi............. 77 Analysis of bentonite specific surface area by kinetic model during activation process in presence of...

by T. Thomberg and Alar Jänes

Advanced nanostructured carbon materials for electrical double layer capacitors

by Alar Jänes, H. Kurig, and T. Thomberg

Journal of Physics: Conference Series, 2007

Thermodynamical and electrochemical characteristics for the non-aqueous electrolyte | nanostructu... more Thermodynamical and electrochemical characteristics for the non-aqueous electrolyte | nanostructured 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 measurement data have been used for the obtaining the specific surface area, pore size distribution, nanopore volume and other characteristics, dependent on the nanostructured carbon used (nanopores are pores in the range of 2 nm and below -i.e. micropores according to IUPAC classification).

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

by T. Thomberg, K. Tõnurist, and Alar Jänes

Journal of The Electrochemical Society, 2009

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Energy and power performance of vanadium carbide derived carbon electrode materials for supercapacitors

by T. Thomberg and Alar Jänes

Journal of Electroanalytical Chemistry, 2009

Electrochemical characteristics of the electrical double layer capacitor based on the nanoporous ... more

The kinetics of electroreduction of peroxodisulfate ions on single crystal cadmium and bismuth electrodes

by T. Thomberg and K. Lust

Journal of Electroanalytical Chemistry, 2005

The electroreduction of the peroxodisulfate anions on the electrochemically polished (EP) Cd(0 0 ... more The electroreduction of the peroxodisulfate anions on the electrochemically polished (EP) Cd(0 0 0 1), Bi(1 1 1) and Bið0 1 1Þ planes has been studied by cyclic voltammetry, rotating disc electrode and impedance methods. The rate constant values of the heterogeneous electroreduction reaction of the S 2 O 2À 8 anion on the EP Cd(0 0 0 1) and Bi(h k l) planes dependent on electrode polarisation and base electrolyte concentration have been calculated. The values of apparent transfer coefficient a app corrected for the double layer effect (a app 6 0.15) only very weakly depend on the electrode potential and base electrolyte concentration. The very low values of the apparent charge transfer coefficient for S 2 O 2À 8 electroreduction show that the activationless charge transfer mechanism is valid for EP Cd(0 0 0 1) and EP Bi(h k l) electrodes in various surface inactive base electrolyte solutions. This conclusion is in a good agreement with the theoretical models for the high hydrogen overvoltage metals based on the diabatic charge transfer mechanism from the metal to an ion [R.R. Nazmutdinov,

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Impedance spectroscopy data for anions electroreduction kinetics at Cd(0001) plane electrode

Journal of Electroanalytical Chemistry, 2006

Kinetics of electroreduction of peroxodisulfate anions on electrochemically polished single cryst... more Kinetics of electroreduction of peroxodisulfate anions on electrochemically polished single crystal Cd(0 0 0 1) electrode has been studied using impedance spectroscopy. The influence of the electrode potential, the electrolyte as well as reactant concentrations on the kinetic parameters has been established. The fitting analysis of results demonstrates the influence of adsorption of the base electrolyte as well as reactant components (Na + or ion complex at more negative electrode potentials and S 2 O 2À 8 or reaction intermediates at less negative surface charge densities) on the electroreduction rate of the S 2 O 2À 8 anions.

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Application of multistep electrospinning method for preparation of electrical double-layer capacitor half-cells

by Alar Jänes, H. Kurig, T. Thomberg, and K. Tõnurist

Electrochimica Acta, 2014

Electrical double-layer capacitor Micromesoporous carbon Specific energy and power a b s t r a c ... more Electrical double-layer capacitor Micromesoporous carbon Specific energy and power a b s t r a c t Electrochemical characteristics of the two identical electrospun micromesoporous carbon electrodes and polymer membrane based half-cells, prepared using the electrospinning method, have been studied in 1 M triethylmethylammonium tetrafluoroborate solution in acetonitrile, using cyclic voltammetry, constant current charge/discharge, constant power discharge and electrochemical impedance spectroscopy methods. The novel electrical double-layer capacitor (EDLC) half-cell preparation method consisted of two steps, at first the nanowire polymer separator layer has been prepared by electrospinning method using poly(vinylidene fluoride) (PVDF) solution in N,N − dimethylformamide and acetone mixture. Thereafter, the electrode material layer has been directly electrospun onto the separator layer from the mixture of carbon (90% commercial RP-20 carbon + 10% few layered graphene) and PVDF solution in N,N − dimethylformamide + acetone mixture. Applying the novel composite electrode preparation method we are able to prepare composite electrodes for EDLC with lower density and thickness than using the widely used traditional roll-pressing method. The wide region of ideal polarizability, high specific capacitance, low equivalent series resistance, short characteristic time constant and high specific energy and specific power values for the completed EDLC have been obtained and discussed.

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Influence of separator properties on electrochemical performance of electrical double-layer capacitors

by T. Thomberg and Alar Jänes

Journal of Electroanalytical Chemistry, 2013

ABSTRACT Influence of separator material characteristics on the high and low frequency series and... more ABSTRACT Influence of separator material characteristics on the high and low frequency series and parallel resistance, low and high frequency capacitance, characteristic time constant, energy and power densities of the 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, has been tested by cyclic voltammetry and electrochemical impedance spectroscopy methods. Self-made separator materials have been prepared from 20% or 25% poly(vinylidene fluoride) solutions in N,N-dimethylacetamide or N,N-dimethylformamide and acetone mixture (8:2 mass ratio) by using the electrospinning method at different electric field strengths and polymer solution feed rates. Separator material total porosity, pore size distribution and specific surface area, calculated using mercury porosimetry data, noticeably depend on electrospinning conditions and mercury pressure applied, explained by the compressibility of materials under study. It was established that the separator material structure (total porosity, specific surface area), chemical composition and thickness determines the high frequency series and low frequency parallel resistance, characteristic time constant and power density values of the EDLC. However, the limits of ideal polarizability, low frequency capacitance and the specific energy only weakly depend on the separator material properties used in EDLC cells.

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