Supercapacitors Based on Mixture of Room Temperature Ionic Liquids Containing Specifically Adsorbed Iodide Anions
In the present studies 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) was chosen due to high bulk conductivity (k=13.6 mS cm-1). To increase the capacitance, EMImI was added because the noticeable increase in capacitance had been established within the potential region of I- ion specific adsorption for Bi(111)„ EMImBF4+ EMImI interface . The electrochemical characteristics of this RTIL mixture have been characterized by cyclic voltammetry, electrochemical impedance spectroscopy, constant current charge/discharge and constant power discharge methods. Carbon used in these studies was synthesized from D-glucose by the hydrothermal carbonization method followed by additional pyrolysis and carbon dioxide activation steps (GDAC - D-glucose derived activated carbon) as described by Thomberg et al. .
Capacitance peaks in cyclic voltammetry curves (Fig. A) for EMImBF4 + EMImI mixture within the cell potential region from 0.8 to 1.2 V were established differently from the data for pure EMImBF4 and about 50% higher discharging charge Q values have been calculated at lower cell potential scan rate v≤10 mV s-1 in comparison with pure EMImBF4. According to the experimental energy and power relationships data, i. e Ragone plots (Fig. B), the addition of EMImI into EMImBF4increases noticeably the specific energy and specific power values of EDLC.
This work was supported by European Regional Development Fund Project 3.2.0501.10–0015 and Estonian Center of Excellence in Research Project 3.2.0101–0030 “High-technology Materials for Sustainable Development”.
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