Thomas Thomberg

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 1 M (C 2 H 5 ) 3 CH 3 NBF 4 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.

Electroreduction of peroxodisulfate anion at a Cd(0001) single-crystal plane electrode

Electroreduction of peroxodisulfate anion on electrochemically polished face Bi(111) in aqueous NaF solution with different additions of Na2S2O8 is studied by rotating-disc voltammetry. The S2O 8 2- electroreduction rate depends on the electrode potential and base-electrolyte concentration, i.e. on the diffuse layer thickness. The kinetic current densities atE = const are obtained by the Koutecky-Levich method and used for the determination of the apparent rate constants of electroreduction of S2O 8 2- . The charge number of the reacting S2O 8 2- species is obtained; it depends on the surface-inactive electrolyte concentration and the electrode potential. The ψ0 potential values at the outer Helmholtz plane, obtained for various NaF + H2O systems according to Gouy-Chapman-Stern-Grahame (GCSG) model, are used for constructing corrected Tafel plots (CTP), which are linear atE- ψ0 < -0.9 V (SCE). The charge transfer coefficient oc for electrochemically polished Bi(111) somewhat decreases with the concentration of the base electrolyte (0.22 ≤α ≤0.27), but the value of α is practically independent of the S2O 8 2- concentration in solution if cNaF = const. However, CTP noticeably depend onc NaF.

Advanced nanostructured carbon materials for electrical double layer capacitors

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).

Replacing Chlorine with Hydrogen Chloride as a Possible Reactant for Synthesis of Titanium Carbide Derived Carbon Powders for High-Technology Devices

Micro- and mesoporous carbide-derived carbons were synthesized from titanium carbide (TiC) powder via gas phase reaction by using different reactants (Cl2 and HCl) within the temperature range from 700 to 1100 °C. Analysis of XRD results show that TiC-derived carbons (TiC-CDC) consist mainly of graphitic crystallites. The first-order Raman spectra showed the graphite-like absorption peaks at ~1577 cm1 and the disorder-induced peaks at ~1338 cm-1. The energy-related properties of supercapacitors based on 1 M (C2H5)3CH3NBF4 in acetonitrile and carbide-derived carbons (TiC-CDC (Cl2) and TiC-CDC (HCl)) as electrode materials were also investigated using cyclic voltammetry, electrochemical impedance spectroscopy, galvanostatic charge/discharge and constant power methods. The Ragone plots for carbide-derived carbons prepared by using different reactants (Cl2, HCl) are quite similar and at high power loads TiC-CDC (Cl2) material synthesized at 900 °C, i.e. materials with optimal porous structure, deliver higher power at constant energy.