Study of faradaic impedance at the carbon electrode/ ionic liquid electrolyte interface on the performance of EDL-capacitor
CESEP'17 || 28 October 2017
ABSTRACT: Unlike an electric double-layer capacitor (EDLC), which only relies on the reversible adsorption of electrolyte ions, pseudocapacitors store energy mainly via reversible electrochemical redox reactions between the electrodes and electrolyte ions. The electrochemical behavior of the electrolyte components and functional groups on the carbon electrode is provided by electrochemical impedance spectroscopy measurements. Figure 1-A shows the Nyquist plots for spectra taken in the frequency range from 100 kHz to 100 mHz at different potentials for the negative electrode (Fig.1-A1). Each impedance spectrum consists inductive loop at medium frequency region, which represent a reaction involving one adsorbed intermediate. The measurement of the charge transfer resistance (Rct) and inductive resistance (RL) give important information on the charging/discharging mechanism of EDL-capacitor. As seen in Fig. 1-A, expansion of the electrochemical window has a significant effect on the impedance spectra of 1-ethyl-3-methyimidazolium cation (EtMeImm+). With rise of potential in the negative side, Rct gradually decreases when start to increase below -0.95V vs Ag/Ag+. However, the RL becomes larger, indicating the one electron redox reaction, as follows: the C2 carbon between the two nitrogen atoms in imidazolium cation is the most electron deficient atom going to electrochemical reduction with hydrogen elimination to produce the radical species with further dimerization causing carbon pore blockage (Rct ^). Study of triethylammonium cation (Et3NH+) showed a rapid redox reaction with fast hydrogen radical adsorption to the carbon surface (Fig. 1-B). Impedance spectra for triethylammonium cation with 860 ppm of water content (Fig. 1-B1) reflects hydrogen gas evolution or adsorption into carbon pores (potential-dependent) as a result of hydrogen radical reaction with water what is expected in smaller RL and confirmed by collapsing spectrum curve in a low frequency region. Additionally, the inductive-loop study helped to understand what processes have the biggest affect on the self-discharge rate.
Activated carbon for a powerful sound absorbing technology
REF. LI120416/02/005 || 14 September 2016
Activated carbon can adsorb and desorb gas or liquid molecules in pores. It turns out that the use of carbon plays a significant role in sound absorbing. It can be used in acoustic panels, noise absorbers and barriers and sound deadening materials for vehicles and buildings. In this work, we have examined various meso- and macro-porous activated carbons (pristine and modified) and their sound absorption behavior at different frequency ranges.
Study of carbon-MoS2 composite materials used as negative electrode in electrochemical capacitor
REF.LI070117/02/001 || 14 September 2016
The intercalation pseudocapacitance for slightly expanded layer structure of molybdenum disulfide (MoS2) in non-aqueous electrolyte contains NaI, KI or KBr were study. In order to fully utilize the redox-additives, an asymmetric capacitor is the one of solutions, where Faradaic processes exist simultaneously on both electrode...
Modified flexible fish scales as a potential separator / membrane for electrochemical devices
REF.LI210515/02/003 || 14 September 2016
In this study, we present modification of fish scales use for membrane/seperator in electrochemical capacitors or batteries.
A sulfur doped activated carbon as cathode for electrochemical capacitor application
REF.LI160916/02/002 || 14 September 2016
In most cases during operating of supercapacitor, negative electrode impacts the final electrochemical performance of whole cell. In this work, we present a potential S-carbon material for negative electrode.