The influence of addition (5 wt%) of 1-ethyl-3-methylimidazolium iodide (EMImI) in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF 4 ) on the melting point, bulk conductivity and electrochemical properties of the room temperature ionic liquid (RTIL) mixture as an electrolyte in electrical double layer capacitor (EDLC) has been studied using cyclic voltammetry, electrochemical impedance spectroscopy, constant current charge-discharge and constant power discharge methods. Electrodes were prepared of the D-glucose derived activated carbon powder, which was prepared by hydrothermal carbonization method followed by additional pyrolysis and carbon dioxide activation steps. The specific conductivity reduced from 13.6 mS cm −1 to 12.8 mS cm −1 and the melting point increased from 17 • C to 19.5 • C by adding 5 wt% of EMImI into EMImBF 4 . However, noticeable increase in specific capacitance (245 F g −1 at 1.0 V), specific energy (36.7 Wh kg −1 ) and specific power and minor increase in characteristic relaxation time constant (from 1.45 s to 1.48 s) values has been established for EDLCs using the mixture of RTIL as an electrolyte. The EDLC based on EMImBF 4 + 5 wt% EMImI demonstrated nearly 50% higher stored charge values than EDLCs without EMImI addition.
The influence of the electrode potential on the Bi͑111͒ ͉ 1-ethyl-3-methylimidazolium tetrafluoroborate interface has been studied by cyclic voltammetry and electrochemical impedance. The weak deviation of the system from capacitive behavior for the ideally flat electrode has been established within the moderate electrode potential region from Ϫ0.9 to Ϫ0.1 V vs Ag ͉ AgCl in 1-ethyl-3-methylimidazolium tetrafluoroborate. The parallel faradaic processes are possible outside the potential region from Ϫ0.9 to Ϫ0.1 V. The results obtained for the Bi͑111͒ ͉ 1-ethyl-3-methylimidazolium tetrafluoroborate interface have been compared with those for gold, mercury, and glassy carbon electrodes.Recent research activity of room-temperature ionic liquids ͑RTILs͒, initiated by their potential applications in various modern electrochemical power systems, created interest in the interface between ionic liquids and metal 1-12 as well as carbon, including nanoporous carbon electrodes. [13][14][15] Despite the extensive discussions about whether the electrical double layer ͑edl͒ at the metal ͉ RTIL interface is fundamentally different from or similar to that extensively studied at the metal ͉ electrolyte solution interface, 11,12,[15][16][17][18] our knowledge of the metal ͉ RTIL interface is still sketchy because there is no systematic impedance and capacitance characteristics for edl in single-crystal electrodes. Detailed theoretical papers have been written by Kornyshev et al.;11,12,18 however, the verification of these models needs a detailed systematic analysis of experimental data not existing at present.The electrical double layer capacitor ͑EDLC͒ characteristics 13-15,19-27 have been discussed and it has been established that, due to the limited solubility of salts ͑from 1.5 to 1.8 M͒, a decrease in electrolyte conductivity takes place, caused by the adsorption of a large amount of ions at the electrodes with a high specific surface area. However, there are some possibilities to increase the concentration of ions by using RTILs ͑with molar concentration 4-6 M͒ in EDLCs instead of the traditional electrolyte solution. [19][20][21][22][23][24][25][26][27] There are only few publications devoted to edl capacitance and impedance measurements on the geometrically flat, well-defined electrodes in RTILs. 28-31 Surprisingly low series capacitance ͑C s ͒ values ͑from 1 to 8 F cm −2 ͒ have been calculated for various metal electrodes, which is not easy to explain theoretically. 11,12,[16][17][18] Such low values of C s probably indicate surface blocking of the electrode surface by the irreversible adsorption of contaminants. The adsorption/ desorption kinetics of RTIL ions has not been studied systematically; 31 however, the kinetics of probable electrostatic adsorption with partial charge transfer and distribution of ions near the electrode surface, over screening, and lattice saturation effects 11,18 are extremely important for engineering the high power density supercapacitors. [13][14][15][19][20][21][22][23][24][25][26][27] Anoth...
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