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Shun KOYAMA, Tatsuya KIKUCHI, Masatoshi SAKAIRI, Hideaki TAKAHASHI, Sh ...
2007 Volume 75 Issue 8 Pages
573-575
Published: August 05, 2007
Released on J-STAGE: March 20, 2012
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Formation of Nb
2O
5 films on aluminum was attempted by sol-gel coating, using NbCl
5 as a precursor. The structure and the dielectric properties of anodic oxide films formed on aluminum by sol-gel coating and the subsequent anodizing were examined. Anodic oxide film formed by this process was composed of an inner Al
2O
3 layer and an outer Nb
2O
5 layer. The capacitance of the anodic oxide films formed on Nb
2O
5-coated specimens was at most 34% higher than that of anodic oxide films on aluminum without coating.
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Shinsuke OHKI, Daisuke HOSHINO, Kenta TATE, Kazuhiro TACHIBANA, Michio ...
2007 Volume 75 Issue 8 Pages
576-578
Published: August 05, 2007
Released on J-STAGE: March 20, 2012
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A new concept was proposed as the energy storage rubber to develop the batteries involving electrode materials in rubber matrix. The cathode active material (LiMn
2O
4) and conductive carbon were mixed with rubber material to give flexible electrode. Some rubber materials were tested for this purpose, and the acrylic rubber matrix cathode gave the good charge/discharge cycle. The initial discharge capacity was 123 mAh/g, which value corresponded to that obtained in electrolyte solution.
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Shinji NOHARA, Takuya MIURA, Chiaki IWAKURA, Hiroshi INOUE
2007 Volume 75 Issue 8 Pages
579-581
Published: August 05, 2007
Released on J-STAGE: March 20, 2012
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An acidic polymer hydrogel electrolyte was successfully prepared from 4 M H
2SO
4 aqueous solution, poly(vinyl alcohol) and glutaraldehyde. The polymer hydrogel electrolyte showed higher ionic conductivity than that prepared from 1 M H
2SO
4 aqueous solution in our previous study. An electric double layer capacitor (EDLC) cell assembled using the polymer hydrogel electrolyte exhibited higher discharge capacitance in the wide range of current density than that using the hydrogel electrolyte with 1 M H
2SO
4 aqueous solution.
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Vinay GUPTA, Norio MIURA
2007 Volume 75 Issue 8 Pages
582-585
Published: August 05, 2007
Released on J-STAGE: March 20, 2012
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The amorphous cobalt-nickel oxide nano-rods (diameter: 20∼30 nm, length: 100∼150 nm) were potentiodynamically deposited onto a stainless-steel electrode. Their structure and surface morphology were investigated by means of X-ray diffraction analysis and scanning electron microscopy. Their capacitive characteristics were evaluated in 1 M KOH electrolyte by using cyclic voltammetry and constant current charge-discharge methods. It was found that the capacitive characteristics of deposited cobalt-nickel oxide were strongly influenced by the deposition condition. A high specific capacitance value of ∼370 F/g and a specific power of 29 kW/kg were obtained when cobalt-nickel oxide was deposited in the aqueous solution of 0.15 M NiCl
2·6H
2O+0.05 M CoCl
2·6H
2O in potentiodynamic conditions. In comparison, the specific capacitance values for the deposited cobalt oxide and nickel oxide were 184 F/g and 118 F/g, respectively. The cycle-life test showed that the specific capacitance of cobalt-nickel oxide was highly stable even after 100,000 cycles, indicating its high potential for supercapacitor applications.
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Yuichi HONDA, Masayuki TAKESHIGE, Hideki SHIOZAKI, Takaharu KITAMURA, ...
2007 Volume 75 Issue 8 Pages
586-588
Published: August 05, 2007
Released on J-STAGE: March 20, 2012
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A vertically aligned multi-walled carbon nanotube (MWCNT) electrode and a disordered MWCNT electrode are prepared to compare their structural differences and such capacitive performances as frequency response. The frequency response of a capacitor assembled with aligned MWCNT electrodes and a conventional PC-based electrolyte is much superior to a corresponding capacitor with disordered MWCNT electrodes. Such a merit of aligned MWCNT electrodes is observed even for an ionic liquid electrolyte system with high viscosity, diethylmethyl (2-methoxyethyl) ammonium tetrafluoroborate (DEMEBF
4). The obtained results demonstrate that the aligned MWCNT electrode has ideal ion-accessible structure with excellent electron pathways that provide a high-rate capability regardless of electrolytes.
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Yasutake FUKUDA, Rie TANAKA, Masashi ISHIKAWA
2007 Volume 75 Issue 8 Pages
589-591
Published: August 05, 2007
Released on J-STAGE: March 20, 2012
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Origins of cathodic stability of an ionic liquid electrolyte, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF
4) containing lithium tetrafluoroborate (LiBF
4), are investigated mainly by applying electrochemical impedance spectroscopy for a glassy-carbon electrode interface. Its Helmholtz layer capacitance in the EMIBF
4 electrolyte containing Li
+ becomes much higher than that in neat EMIBF
4 with increasing cathodic polarization. On the basis of such analyses as well as our hypotheses, a reasonable mechanism for the stabilizing effect induced by the Li salt addition is discussed.
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Shigeaki YAMAZAKI, Keigo OBATA, Yoshiaki OKUHAMA, Yoshiharu MATSUDA, M ...
2007 Volume 75 Issue 8 Pages
592-594
Published: August 05, 2007
Released on J-STAGE: March 20, 2012
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A novel electrode composed of activated carbon and DNA together with fluorinated binder has been prepared for an electric double layer capacitor (EDLC) with aqueous electrolytes. The DNA-loaded electrodes improve the rate capability and discharge capacitance of EDLC containing aqueous, neutral salt electrolytes. In contrast, the DNA-composite electrodes have a poor effect on the capacitance enhancement in acidic or basic electrolytes. The enhancement of discharge capacitance is significant especially at high-rate cycling in neutral salt electrolytes, because the presence of DNA reduces the internal resistance of an electrode and hence improves its rate capability.
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Minato EGASHIRA, Tomoya UNO, Nobuko YOSHIMOTO, Masayuki MORITA
2007 Volume 75 Issue 8 Pages
595-597
Published: August 05, 2007
Released on J-STAGE: March 20, 2012
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The pseudo-capacitance of ruthenium oxide electrode has been compared in organic solvent electrolytes having different solutes, tetrafluoroborate salts with tetraethylammonium and ethylmethylimidazolium cations, and various solvents using cyclic voltammetry. Some kinds of solvents such as acetonitrile promote substantial capacitance of ruthenium oxide in imidazolium-based electrolyte salt over tetraethylammonium-based one, while propylene carbonate exhibited no such difference between these two electrolyte systems. The pseudo-capacitance of ruthenium oxide in imidazolium-based electrolyte is stable over cycles under limited anodic potential range of 0.5 V vs. Ag. The contamination of
ca. 1000 ppm of water induces further substantial capacitance only for imidazolium-based electrolyte.
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Akinori MUTO, Yoshiki SASADA, Thallada BHASKAR, Yusaku SAKATA
2007 Volume 75 Issue 8 Pages
598-600
Published: August 05, 2007
Released on J-STAGE: March 20, 2012
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The effect of the addition of surfactants to an aqueous electrolyte on discharge property of the capacitor was investigated. Dodecylbenzene sulphonate surfactant drastically improved the specific capacitance of electric double layer capacitor (EDLC) electrode. The addition of surfactants promoted the electrolyte to access the interior portion of micropores. EDLC effective area was increased and subsequently specific capacitance was also increased. However, the specific capacitance depended on chemical structure and concentration of the surfactants added. The adsorbed surfactants interfered with mobillity of ions. This is another factor for decreasing the specific capacitance.
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Kenji MACHIDA, Shunzo SUEMATSU, Kenji TAMAMITSU
2007 Volume 75 Issue 8 Pages
601-603
Published: August 05, 2007
Released on J-STAGE: March 20, 2012
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A nanocomposite material based on polyfluorene (PF) loaded with a carbon black, namely Ketjen Black (KB), was investigated electrochemically as a cathode material for high-energy electrochemical capacitors. The nanocomposite was prepared by a chemical oxidation of fluorene monomer dissolved in the KB suspension. From TEM observation, thin PF films with 5-15 nm in thickness were loaded onto the surface of the aggregated KB particles. The nanocomposite based capacitor electrode exhibited high specific capacitance of 160 F g
−1 (260 F g
−1 per PF mass) in an electrolyte of 1 M tetraethylammonium tetrafluoroborate/propylene carbonate. More importantly, the charge was found to be stored at high potential ranged from 0.4 to 1.0 V vs. Ag/Ag
+, which is higher than the redox potentials for conventional conducting polymers.
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Koichi UI, Kazuma OKURA, Nobuyuki KOURA, Satoru TSUMEDA, Kenji TAMAMIT ...
2007 Volume 75 Issue 8 Pages
604-606
Published: August 05, 2007
Released on J-STAGE: March 20, 2012
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A co-deposited film consisting of activated carbon (AC) and ketjenblack powder (KB) particles was prepared using the electrophoretic deposition (EPD) method and utilized as the electrode for a capacitor cell. As a result of evaluating various organic solvents as the dispersion solvent for the EPD bath, it was found that the best deposition condition was obtained using acetonitrile (AN). However, there was the problem that the co-deposited film consisting of AC and KB particles had a poor adhesion. The co-deposited film fabricated by adding polyvinylidine difluoride (PVdF) as a binder to the bath was able to be used as the electrode for a capacitor cell. The specific capacitance per unit weight of the electrode was almost equal to that of the commercial sheet electrode.
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Noritoshi NANBU, Keita SUZUKI, Nobuyoshi YAGI, Michimasa SUGAHARA, Mas ...
2007 Volume 75 Issue 8 Pages
607-610
Published: August 05, 2007
Released on J-STAGE: March 20, 2012
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The use of partially fluorinated compounds as alternative solvents can improve the performance of electric double layer capacitors (EDLCs). Electrolytic conductivity of fluoroethylene carbonate (FEC) is slightly lower than that of propylene carbonate (PC), which is commonly used as a solvent for EDLCs. However, the capacitance of a coin cell is higher than that obtained for PC.
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Keita SUZUKI, Masanori SHIN-YA, Yoshiya ONO, Takamitsu MATSUMOTO, Nori ...
2007 Volume 75 Issue 8 Pages
611-614
Published: August 05, 2007
Released on J-STAGE: March 20, 2012
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Propylene carbonate (PC), which shows high viscosity, is commonly used as a solvent for electric double-layer capacitors (EDLCs). The use of acetonitrile (AN) as an alternative solvent improves the performance of the EDLCs. Partial fluorination of organic solvents often increases their polarity. We focus our attention on the use of fluoroacetonitorile (FAN) as an alternative solvent for the EDLCs. Although electrolytic conductivity of FAN is slightly lower than that of AN, the capacitance of a model cell is higher than those obtained for AN and PC.
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Noritoshi NANBU, Keita SUZUKI, Takahito EBINA, Hiroyuki UNO, Yukio SAS ...
2007 Volume 75 Issue 8 Pages
615-618
Published: August 05, 2007
Released on J-STAGE: March 20, 2012
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The use of an asymmetric borate anion, difluoro(oxalato)borate (DFOB
−), improves the solubility of the tetramethylammonium salt in propylene carbonate (PC) and the capacitances of electric double-layer capacitors (EDLCs). Electric conductivity of the PC solution containing tetramethylammonium difluoro(oxalato)borate (TMADFOB) was slightly lower than that obtained for tetraethylammonium tetrafluoroborate (TEABF
4), but higher than those obtained for tetramethylammonium bis(oxalato)borate (TMABOB) and tetraethylammonium bis(oxalato)borate (TEABOB). The gravimetric capacitances of measurement cells increased with decreasing the ion sizes of the electrolytes. The PC solution containing TMADFOB afforded the highest gravimetric capacitance.
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Soshi SHIRAISHI, Takayuki MIYAUCHI, Rei SASAKI, Naoya NISHINA, Asao OY ...
2007 Volume 75 Issue 8 Pages
619-621
Published: August 05, 2007
Released on J-STAGE: March 20, 2012
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The double layer capacitance of an activated carbon nanofiber (ACNF) with a 100∼200 nm fiber-diameter, prepared by the polymer blend spinning technique, was investigated using 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF
4) as the electrolyte. The conventional activated carbon fiber (ACF) with the fiber-diameter of ∼10 µm and narrow micropores (∼0.7 nm pore-width) showed a significant irreversible adsorption of EMIm
+ cation in EMImBF
4, however, the ACNF effectively suppress the irreversibility even with the pore structure comparable to the conventional ACF. This suggests the effect of the short pass length on the ion adsorbing/desorbing process. The decreased capacitance by the cycling in EMImBF
4 was recovered by the addition of propylene carbonate as an organic solvent to the electrolyte. This means that the irreversible adsorbed ions can be desorbed using propylene carbonate.
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Kaoru UENO, Larry DOMINEY, Robert S. ALWITT
2007 Volume 75 Issue 8 Pages
622-627
Published: August 05, 2007
Released on J-STAGE: March 20, 2012
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The capacitance recovery of Ta capacitor using poly(3,4-ethylenedioxythiophene) (PEDOT) was evaluated. Capacitance recovery is defined as the ratio of the capacitance of Ta/oxide/PEDOT/Ag to that of Ta/oxide measured in aqueous electrolyte solution. The capacitance recovery was strongly dependent on the oxide formation voltage. From the analysis of this dependence we found an additional capacitance in series with the oxide capacitance which was independent of oxide formation voltage, and was present at the oxide/PEDOT interface. This additional capacitance was postulated by the presence of a depletion layer and poor contact because of the presence of polymerization byproduct at the oxide/PEDOT interface. However, the phenomenon of the additional series capacitance did not match well with the depletion layer capacitance calculated from semiconductor theory assumption.
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Tetsuya SUKIZAKI, Shuhei FUKUDA, Taishi YAMAGUCHI, Kenta FUJII, Ryo KA ...
2007 Volume 75 Issue 8 Pages
628-634
Published: August 05, 2007
Released on J-STAGE: March 20, 2012
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5-Azonia-spiro[4.4]nonane tetrafluoroborate [(CH
2)
4N(CH
2)
4]
+BF
4− is dissolved in dimethyl carbonate (DMC) to yield two liquid phases, DMC and salt-rich DMC solutions. The molecular structure of the [(CH
2)
4N(CH
2)
4]
+ ion in the crystalline state and in the salt-rich DMC solution was studied by means of Raman spectroscopy at 298 K and theoretical DFT calculations. The [(CH
2)
4N(CH
2)
4]
+ ion involves two pyrrolidinium (CH
2)
4N rings bridged through the N atom, and each pyrrolidinium ring involves various types of conformation. Theoretical DFT calculations for the [(CH
2)
4N(CH
2)
4]
+ ion show that the distorted
envelope-envelope conformers of the type
E1-E1 and
E1-E3 give relatively small energies. Observed Raman spectra of [(CH
2)
4N(CH
2)
4]
+BF
4− crystals and the salt-rich DMC solution were satisfactorily explained in terms of the favorable presence of the sole
envelope-envelope conformer of the type
E1-E1.
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Sang-Wook WOO, Kaoru DOKKO, Hiroyuki NAKANO, Kiyoshi KANAMURA
2007 Volume 75 Issue 8 Pages
635-640
Published: August 05, 2007
Released on J-STAGE: March 20, 2012
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Bimodal porous carbons consisting of interconnected macropores and spherical mesopores, were prepared by colloidal crystal templating method. The template was prepared by evaporation process of suspensions containing monodisperse poly[styrene-(
co-2-hydroxyethyl methacrylate)] (PSHEMA) latex and colloidal silica in water. The carbonization of PSHEMA at 1000°C under inert atmosphere provided very thin carbon layer on the colloidal silica in the template, and the macropore corresponding to the PSHEMA particle size were formed simultaneously. After this procedure, bimodal porous carbons were obtained by removing the silica particles with hydrofluoric acid. Three kinds of bimodal porous carbons were prepared using PSHEMA latex of 450 nm and colloidal silica with three different average diameters of 10∼20 nm, 40∼50 nm, and 70∼100 nm, respectively. Bimodal porous structure was observed with a field emission-scanning electron microscope. Nitrogen adsorption/desorption measurements revealed that the prepared samples involved macropore and mesopore with small amount of micropore. The bimodal porous carbons were electrochemically evaluated as a negative electrode of lithium-ion capacitor in ethylene carbonate and diethyl carbonate containing 1 mol dm
−3 LiClO
4. The bimodal porous carbon prepared using silica of 10∼20 nm showed a large capacitance of 360 F g
−1 at a high current density of 7.4 A g
−1.
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Masayuki MORITA, Naoki OHSUMI, Nobuko YOSHIMOTO, Minato EGASHIRA
2007 Volume 75 Issue 8 Pages
641-644
Published: August 05, 2007
Released on J-STAGE: March 20, 2012
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Novel non-aqueous proton (H
+)-conducting polymeric gel systems have bee proposed for utilization as quasi-solid electrolytes in electrochemical capacitors. The gel systems consist of poly(vinylidenedifluoride) (PVdF) or poly(vinylidenedifluoride-co-hexafluoropropylene) (PVdF-HFP) matrix polymer swollen with dimethylformamide (DMF) solutions containing phosphoric acid (H
3PO
4) or trifluoromethanesulfonic acid (CF
3SO
3H). High ionic conductivity of 4.5 mS cm
−1 was obtained at 60°C for a PVdF-HFP-based polymeric gel containing 85 mass% of 0.5 M CF
3SO
3H/DMF with sufficient mechanical stability over the temperature range of 20–60°C. Redox process of hydrous ruthenium oxide, RuO
2·
xH
2O, gave high pseudo-capacitance in the PVdF-HFP-based polymeric gel. The pseudo capacitance behavior was somewhat influenced by the composition of electrode/electrolyte interface. The discharge capacitance of
ca. 350 F g
−1 (with respect to the mass of the oxide) was obtained for PVdF-HFP-based gel using RuO
2·
xH
2O electrode prepared by a “wet process”.
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Wataru SUGIMOTO, Toshiaki OHTA, Katsunori YOKOSHIMA, Yoshio TAKASU
2007 Volume 75 Issue 8 Pages
645-648
Published: August 05, 2007
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The effect of the H
2SO
4 concentration and cell temperature towards the pseudocapacitive behavior of layered ruthenic acid hydrate, H
0.2RuO
2.1·
nH
2O, was examined. The increase in H
2SO
4 concentration resulted in a drastic decrease in the redox pair observed at 0.65 V vs. RHE, while the increase in cell temperature had little effect on this redox pair. The redox pair centered at ∼0.85 V vs. RHE was less dependent on the H
2SO
4 concentration and the charge associated with this peak increased with increasing cell temperature. It is suggested that the redox peak observed at ∼0.65 V vs. RHE is related to the adsorption of SO
42− ions on the outer surface of the microsized particles. The redox pair observed at ∼0.85 V vs. RHE is attributed to the penetration of protons or hydrated protons. The effect of cell temperature was negligible for nanoparticulate RuO
2·
xH
2O, which indicates the difference in the charge storage mechanism of layered H
0.2RuO
2.1·
nH
2O and nanoparticulate RuO
2·
xH
2O.
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Masayuki ITAGAKI, Satoshi SUZUKI, Isao SHITANDA, Kunihiro WATANABE
2007 Volume 75 Issue 8 Pages
649-655
Published: August 05, 2007
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The electrochemical impedance
Z and complex capacitance
C for typical equivalent circuits were summarized systematically in order to support the frequency domain analysis of electric double layer capacitance (EDLC). In the present paper, the impedance and the complex capacitance were calculated in the case that the electrochemical response of porous electrode was presented by a transmission line model (TLM). The loci of
Z and
C on the complex were divided into the lumped constant and distributed constant ranges in low and high frequency ranges, respectively. The complex capacitance plot was superior to obtain the capacitance of porous electrode than the impedance plot.
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Noritoshi NANBU, Satoko ITO, Yukio SASAKI
2007 Volume 75 Issue 8 Pages
656-663
Published: August 05, 2007
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Tetraethylammonium bis(oxalato)borate (TEABOB), which is free from halogens, has the potential for use in electric double-layer capacitors (EDLCs). We have used a transmission-line network of finite length as the equivalent circuit of the average pore of an activated carbon electrode and derived the theoretical equation for a constant-current (CC) charge. We evaluated the performance of EDLCs by comparing the theoretical and the experimental charge curves. A 2025-type coin cell using TEABOB showed double-layer capacitance comparable to that obtained for tetraethylammonium tetrafluoroborate (TEABF
4). A very small distance between activated carbon electrodes in the EDLC may compensate for low ionic mobility of TEABOB in the bulk of the solution. The degree of ionic dissociation of TEABOB in the pores of the activated carbon electrode may not be appreciably lower than predicted from the bulk properties of the solution.
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