Ionic Liquid Electrode Research Articles

Characteristics of Capacitors Based on Ionic Liquids: From Dielectric Polymers to Redox-Active Adsorbed Species

The development of novel devices for energy recuperation and storage systems is of paramount importance for the realization of an energetically sustainable society. Capacitors play a huge role in mentioned complexes, being assumed as versatile devices for power applications. Ionic liquids (IL) have been tabbed as “designer electrolytes”, thus offering a multitude of unique and advantageous properties, such as negligible vapour pressure, high electrochemical and temperature stability, good ionic conductivity and the ability to modify the salt for novel applications. The presentation reviews the recent developments regarding the use of ILs as electrolytes for capacitors, starting from the formation of the electrical double layer (EDL) and ending up with some unique applications of ILs. Capacitor technology is fundamentally based on the formation of the EDL and the storage of charge within the EDL. It is thus important to understand the probable mechanism of charge storage and the formation of the EDL in ILs at different electrode surfaces. Experiments with highly oriented pyrolytic graphite, carbide derived carbons and bismuth electrodes in ILs have shown that the systems are indeed ideally polarizable [1], thus ideally suited for capacitor applications. It has been shown that the value of double layer capacitance in ILs is of the same order of magnitude as that for organic electrolyte based systems and the capacitance-potential curve of carbon electrodes shares the same principal V-shape as those seen for aqueous and organic electrolyte solutions. Although many theoretical studies have been published about the subject, the agreement between experimental and theoretical results is limited. One of the most widely studied IL applications as electrolytes are AC/AC supercapacitors (SC). SCs based on ILs have been shown to possess higher energy density, owing to their wider electrochemical window, but lower power density due to higher viscosity and lower ionic conductivity than more conventional organic electrolyte based SCs[2]. Although extremely wide electrochemical stability has been suggested for many ILs, this has not been realized in SCs, allowing only slightly higher voltage than commercial SCs. This has been explained by IL decomposition at extreme potentials confirmed by both infrared and photoelectron spectroscopy studies[1,3]. Because of this, SCs based on ILs are not competitive in the mainstream, however, serving many alternative applications in high or low temperature systems that require higher security with regards to failure. In order to increase the energy density of SCs based on ILs, the addition of redox species or redox-active organic compounds has been explored. The specific adsorption and subsequent oxidation of halide species has been tested for both bismuth and carbon electrodes. It has been shown that redox and surface active ions can significantly increase the gravimetric capacitance of the system with the drawback of limiting the applied potential range . Small additions of organic solvents to IL has been shown to increase the power density of SCs with negligible effect on the voltage limit and gravimetric capacitance, while the addition of specifically adsorbing organic compounds to ILs has been observed to produce systems with properties similar to those for dielectric capacitors [5]. The electrochemical breakdown of ILs can also be advantageous with regards to specific capacitor applications. It has been shown that some nitrile group-containing anions have the tendency to electropolymerize at high positive potentials, forming thick dielectric layers on the electrode surface [6]. This process has been applied in order to produce dielectric capacitors based porous carbon electrodes with high surface area and has been shown to possess extremely high energy density compared to that of traditional electrolytic capacitors based on electro-oxidized aluminium and tantalum electrodes [6]. Aknowledgements This work was supported by the Estonian Ministry of Education and Research (projects no. IUT 20-13, PUT55 and PUT1107), and Estonian Centres of Excellence (projects no. TK117T and TK141).

Modeling the charge transfer at the electrode-ionic liquid interface in dielectric spectroscopy measurements

The phenomena occurring at the interface between the electrodes and a liquid with ionic conductivity is manifested specifically in the spectrum of the dielectric permittivity. The theoretical model of the electrode polarization (charge space polarization) is met in the dielectric spectroscopy measurements in which electrodes are conductors (allow transfer of electric charge) and the adsorption-desorption of ions occurs on their surface. A pair of ions with equal and opposite charge is considered. The ions are produced by the association-dissociation of neutral molecules. We propose general boundary conditions (BCs) with charge transfer current which contains the adsorption-desorption parameters. The BCs and the basic equations of the Poisson-Nernst-Planck model, i.e. transport equations of charge carriers and Poisson equation, are re-formulated through new variables. The mathematical problem is solved analytically. The results allow finding a criterion for choosing a general and simple admittance expression, thus using a unified approach for different cases. We show that the small signal approximation is no longer needed, at least for modern dielectric spectroscopy equipment. The ions can be point-like or may have finite dimensions. For the last case a model of Stern compact layer with charge transfer is proposed, which allows to calculate the compact layer impedance. Finally we obtain the equivalent admittance of the physical system composed from metal electrodes and ionic liquid in the presence of the Stern layer and the space charge polarization. The limitations of the model are given by the hypothesis of “flat band” and the non-selective adsorption of ions.

Oxide-coated silicon nanowire array capacitor electrodes in room temperature ionic liquid

Improved performance of Si nanowire arrays for capacitor electrodes in ionic liquid [Bmim][NTf2], is obtained by spin-on-doping the nanowires followed by hot, concentrated nitric acid oxidation. n- and p-type Si nanowire arrays are fabricated via a 2-step metal-assisted chemical etch process to increase the effective surface area. Spin-on-doping increases the doping density of the nanowires, enhancing the current by a factor of more than 3. The well-controlled HNO3 oxidation defines a thin, dense oxide layer on the Si nanowires increasing chemical stability, both expanding the electrochemical window and increasing the current further by a factor >2. Specific capacitances of 238μFcm−2 (∼0.4Fg−1, 159mFcm−3) and 404μFcm−2 (∼0.7Fg−1, 269mFcm−3) are obtained for n- and p-type Si nanowire arrays, respectively.

Poly(bisphenol) Polymers as Passivating Agents for Carbon Electrodes in Ionic Liquids

Poly(bisphenol) polymers are identified as a new class of passivating agents for carbon electrodes in ionic liquids. They are inert and can readily be deposited as thin, conformal films by electropolymerization. Unlike conventional poly(monophenol) polymers, a single voltammetric scan is sufficient to accomplish their deposition. This is seen, for example, in the cases of poly(bisphenol A) and poly(bisphenol P). In each case, the thickness of the electropolymerized films is determined by the quantum tunneling distance of the faradaic electrons. Thus, film growth terminates when the faradaic electrons can no longer transit the film at a measurable rate. At that point, all the faradaic reactions cease, while the capacitive charging processes continue unabated. Experimentally, film thicknesses are observed in the range 4–30 nm. A challenging test for the poly(bisphenol) polymers is to coat them onto arrays of microelectrodes (RAM electrodes). Normally, microelectrodes are difficult to coat by electropolymeri...

Rationale for the implementation of reference electrodes in ionic liquids.

A thorough investigation of the reference electrodes for electrochemical measurements is presented in three ionic liquids (ILs), namely 1-butyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide [BMIM][Tf2N], 1-octyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide [OMIM][Tf2N] and 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide [BMPyrr][Tf2N]. The influence of technical aspects such as internal resistance, scan rate and concentration of the active species on cyclic voltammetry has been investigated using three quasi-reference electrodes (QREs) (AgCl, Pt, and Pd) and three reference electrodes (REs) (Fc(+)/Fc/Pt, Ag(+)/Ag, and Cl(-)/AgCl/Ag). The results show that the internal resistance has to be taken dynamically into account during any cyclic voltammetry experiment. Quasi-reference electrodes can be used only for qualitative electrochemical studies. Reference electrodes based on Ag(+)/Ag or Fc(+)/Fc dissolved in an IL have a stable potential over 15 h and thus can be used to perform reliable electrochemical experiments in ionic liquids and to get quantitative information such as potentials.

Electrochemical performance of hard carbon negative electrodes for ionic liquid-based sodium ion batteries over a wide temperature range

Sodium ion batteries (SIBs) have been attracting much attention as promising next-generation energy storage devices for large-scale applications. The major safety issue with SIBs, which arises from the flammability and volatility of conventional organic solvent-based electrolytes, is resolved by adopting an ionic liquid (IL) electrolyte. However, there are only a few reports on the study of negative electrodes in ILs. Here, we report the electrochemical performance of a hard carbon (HC) negative electrode in Na[FSA]-[C3C1pyrr][FSA] (FSA=bis(fluorosulfonyl)amide, C3C1pyrr=N-methyl-N-propylpyrrolidinium) IL over a wide temperature range of −10°C to 90°C. High-temperature operation, which is realized for the first time by using an IL, can take full advantage of the high capacity of HC even at a very high discharge rate of 1000mA (g-HC)−1: the discharge capacity is 230mAh (g-HC)−1 at 90°C and 25mAh (g-HC)−1 at 25°C. Moreover, surprisingly stable cycleability is observed for the HC electrode at 90°C, i.e. a capacity retention ratio of 84% after 500 cycles. Finally, a high full-cell voltage of 2.8V and stable full-cell operation with Coulombic efficiency higher than 99% are achieved for the first time when using NaCrO2 as the positive electrode at 90°C.

Electrochemical performance of potentiodynamically deposited polyaniline electrodes in ionic liquid

Present work reports electropolymerization of aniline onto stainless steel substrate using room temperature ionic liquid N-methyl-2-pyrrolidonium hydrogensulfate [NMP][HSO4] by potentiodynamic electrodeposition method. To study the effect of electropolymerization cycle number on the electrochemical performance, the number of scans is varied from 1st to 5th cycle. X-ray photoelectron spectroscopy is used for the phase identification of polyaniline (PANI) films. Scanning electrochemical microscopy (SECM) was used to study the electrochemical activity of PANI films. The highest specific capacitance of 581 Fg−1 and energy density of 96.6 whkg−1 are obtained for the sample, deposited using four cycle.

On the influence of polarization effects in predicting the interfacial structure and capacitance of graphene-like electrodes in ionic liquids.

The electric double layer (CD) and electrode quantum (CQ) capacitances of graphene-based supercapacitors are investigated using a combined molecular dynamics and density functional theory approach. In particular, we compare an approach that includes electronic polarization to one that is polarization-free by evaluating both CD and CQ using [EMIM][BF4] ionic liquid as a model electrolyte. Our results indicate that the inclusion of polarization effects can yield higher CD values-in this study by up to 40% around ±2 V-which we attribute primarily to the presence of charge smearing at the electrode-electrolyte interface. On the other hand, we find that the polarization-induced distortion of the electronic structure of graphene does not noticeably alter the predicted CQ. Our analysis suggests that an accurate description of the spatial charge distribution at the graphene interface due to polarization is necessary to improve our predictive capabilities, though more notably for CD. However, the conventional polarization-free approximation can serve as an efficient tool to study trends associated with both the CQ and CD at the interface of various graphene-like materials.

Facile electrochemical polymerization of 2-(thiophen-2-yl)furan and the enhanced capacitance properties of its polymer in acetonitrile electrolyte containing boron trifluoride diethyl etherate

ABSTRACT In this study, a new simple hybrid poly(2-(thiophen-2-yl)furan) (PTFu) was easily electrodeposited by direct anodic oxidation of 2-(thiophen-2-yl)furan in acetonitrile solution containing 0.1 M lithium perchlorate (LiClO 4 ). The oxidation onset potential of 2-(thiophen-2-yl)furan monomer in this medium was measured to be 0.90 V, which was lower than those of thiophene (1.47 V) and furan (1.28 V). The structure and morphology of PTFu were characterized by Ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and thermal analysis. The electrochemical capacitance properties of PTFu electrode in three electrolytes were also investigated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscope techniques. The electrochemical results showed that the specific capacitance of PTFu electrode was enhanced to 392.0 F g −1 from 249.4 F g −1 at 5 A g −1 and the cycling stability was also enhanced to 67.0% retention from 25.5% retention after 500 cycles when the equivalent boron trifluoride diethyl etherate (BFEE) was added into the acetonitrile electrolyte. Furthermore, the PTFu electrode in ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF 6 ) showed a lower specific capacitance value (209.4 F g −1 at 5 A g −1 ) and an improved stability (67.6% retention after 600 cycles). These results indicated that the conducting polymers based on furan should be a promising electrode material for supercapacitor applications when the electrolyte based-BFEE is used.

Hexagonal Si-IV Silicon Phase Instead Amorphous Silicon after Electrochemical Lithiation/Delithiation of Silicon in Ionic Liquids?

The amorphisation of the lithiated crystalline silicon after the extraction of lithium in LiPF6/carbonates mixture based electrolyte has been demonstrated by the work of Obrovac and Christiansen [1] ten years ago.Within this work, we focus on the structural changes of the crystalline nanosilicon (nSi, 30-50nm) during electrochemical cycling in ionic liquid (IL) based electrolytes. By means of Raman Spectroscopy and X-Rays Diffraction we investigate the nSi electrodes after 1 cycle of lithium insertion/extraction in 0.8 M LiTFSI in 1-Methyl-1-propylpyrrolidiniumbis (trifluoromethylsulfonyl) imide (P13TFSI) and 1-Methyl-1-propylpiperidiniumbis (trifluoromethylsulfonyl) imide (PP13TFSI). For comparison, nSi electrode is also cycled in conventional LP30 electrolyte. The electrodes consist of 85 wt-% of nSi, 5 wt-% carbon black and 10 wt-% of CMC, the electrode is loading about 0.2 mg*cm-2, insertion/extraction current is 180 mA*g-1.During the first lithium insertion/extraction similar electrochemical behavior is observed in all electrolytes (Fig.1). Nevertheless, during extended cycling the capacity fade is much faster in ionic liquids with respect to LP30. The Raman spectra (Fig. 2) taken after lithium extraction in LP30 show clearly the broad band of amorphous silicon between 430 – 500 cm-1. In contrary no amorphous silicon is found after lithium extraction from nSi electrode in ionic liquids. Instead, the band located at ~ 506 cm-1 is registered in reproducible manner. The sample heating effect leading to the silicon phase transformation and peak of the shift can be excluded as low power of the laser was applied (less than 3 mW) and no significant difference was registered in three subsequent measurements. This shift has already been observed for lithiated silicon, however it has not been commented [2]. On the other hand, very detailed Raman spectroscopy investigation of the phase evolution of crystalline cubic silicon Si-I evolution under stress by means of Vickers indentation has been performed [3] [4]. In the center of the indent, amorphisation of the silicon leading to the broad Raman band at ~480 cm-1 was observed, while a pileup at the border of the indent was assigned to hexagonal silicon Si-IV, appearing as a band at 500-510 cm-1in Raman spectra. Direct phase transition of Si -I to Si-IV requires a high level of a shear deformation. Since the same shift of the Raman peak is observed in our electrochemical experiments of lithiation/delithiation of crystalline cubic nSi, it could be intuitively assumed that hexagonal silicon Si-IV is formed in ionic after cycling in ionic liquids. The XRD measurements confirm Raman Spectroscopy findings. The investigation, if the observed structural differences are the reason of the faster capacity fading of silicon electrode in ILs, is in progress.Is it possible that silicon is exposed to high shear deformation when cycled in ILs? Is it related to the insertion/reaction of TFSI anion which takes place at 0.8 – 1V? Within this work we try at least partially answer these questions. To our best knowledge the basic characteristic of silicon behavior in ILs has never been addressed in electrochemical setups in such context. Therefore, taking into account the interest of the scientific community towards application of silicon anodes as well as ionic liquids electrolytes, we consider this basic study of high importance.Fig. 1 Lithium insertion - extraction curves into nSi electrode recorded in LP30, P13TFSI and PP13TFSI, 180 mAg-1 Fig. 2 Raman Spectra of the nSi electrodes, pristine and after one cycle (Fig.1).[1] M.N. Obrovac, L. Christensen, Electrochemical and Solid-State Letters, 7 (2004) A93-A96.[2] H. Li, X. Huang, L. Chen, G. Zhou, Z. Zhang, D. Yu, Y.J. Mo, N. Pei, Solid State Ionics, 135 (2000) 181-191.[3] A. Kailer, Y.G. Gogotsi, K.G. Nickel, Journal of Applied Physics, 81 (1997) 3057-3063.[4] T. Wermelinger, R. Spolenak, Journal of Raman Spectroscopy, 40 (2009) 679-686.

Three-Dimensional Graphitized Carbon Nanovesicles for High-Performance Supercapacitors Based on Ionic Liquids

Three-dimensional nanoporous carbon with interconnected vesicle-like pores (1.5-4.2 nm) has been prepared through a low-cost, template-free approach from petroleum coke precursor by KOH activation. It is found that the thin pore walls are highly graphitized and consist of only three to four layers of graphene, which endows the material with an unusually high specific surface area (2933 m(2) g(-1) ) and good conductivity. With such unique structural characteristics, if used as supercapacitor electrodes in ionic liquid (IL) electrolytes, the graphitized carbon nanovesicle (GCNV) material displays superior performance, such as high energy densities up to 145.9 Wh kg(-1) and a high combined energy-power delivery, and an energy density of 97.6 Wh kg(-1) can be charged in 47 s at 60 °C. This demonstrates that the energy output of the GCNV-based supercapacitors is comparable to that of batteries, and the power output is one order of magnitude higher. Moreover, the synergistic effect of the GCNVs and the IL electrolyte on the extraordinary performance of the GCNV supercapacitors has been analyzed and discussed.

Electrochemical Intercalation/Deintercalation of Cations Into/From Graphite Electrode in Ionic Liquid

not Available.

Investigation on capacitive behaviors of porous Ni electrodes in ionic liquids

We previously reported some findings on the applicability of porous Ni materials to the electrodes of electric double layer capacitors (EDLCs) [1]. It was found that the porous Ni material prepared via alkali-leaching of Ni–Al alloys and dry process without heating and air-contact provides pseudocapacitance as well as electric double-layer (EDL) capacitance in organic electrolyte solution, TEA·BF4/PC. The pseudocapacitance is ascribed to the electrochemically active surface and bulk state of the porous Ni with low crystallinity. In TEA·BF4/PC, porous Ni materials were found to provide lower volumetric total capacitance than the values of the commercial activated carbons, due to the large difference of specific surface areas (i.e., porous Ni: 43m2/g, the activated carbons examined: 1508–2164m2/g). However, a significant point was the high value of EDL capacitance normalized by the surface areas (CSA), i.e., 10.2μF/cm2, which was beyond 3.6–6.6μF/cm2 of the activated carbons. In this study, the volumetric total capacitance and CSA of porous Ni materials have been further enhanced by using ionic liquids as electrolytes. The volumetric total capacitance has reached 67.4F/cm3 (three-electrode evaluation) in EMIm·BF4 ionic liquid, which approaches 79.3F/cm3 of a high-capacitance-type activated carbon, MSP-20. The total capacitance is affected by the class of ionic liquids due to the difference of the viscosity and conductivity, whereas the pure EDL capacitance is dependent on the ion sizes rather than the physical properties of ionic liquids. Furthermore, the difference of either anions or cations affects the capacitive behaviors in both positive and negative electrodes. Significantly, the CSA value of porous Ni electrodes has increased from 10.2μF/cm2 in TEA·BF4/PC to 16.6μF/cm2 in EMIm·BF4, which is much higher than 7.0μF/cm2 of MSP-20. Furthermore, the electrochemical stabilization of porous Ni materials has been achieved by heat treatment under vacuum, resulting in an excellent cycle performance caused by the exclusion of pseudocapacitance. More noteworthy is that the high CSA can be retained even after the stabilization. The results of this study further emphasize the potential of porous Ni materials as EDLC electrodes.

Charge–discharge behavior of graphite negative electrodes in bis(fluorosulfonyl)imide-based ionic liquid and structural aspects of their electrode/electrolyte interfaces

We evaluated the charge–discharge behavior of four types of graphite electrode, including raw synthetic graphite (SG), shaped natural graphite (NG), soft carbon-coated natural graphite (SCNG), and hard carbon-coated natural graphite (HCNG), in a 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMImFSI) ionic liquid. Based on the charge–discharge curves for the first cycle in LiTFSI/EMImFSI, capacity loss arising from an irreversible reaction on the graphite anodes was clearly observed for the cells consisting of SG and SCNG, whereas the capacity loss for the cells containing NG and HCNG was relatively low. The coulombic efficiency during cell cycling also confirmed that the charge–discharge behavior of graphite in LiTFSI/EMImFSI is strongly affected by the surface structure of the graphite and that basal-plane-oriented graphite, such as NG and HCNG, can reduce the primary charge capacity loss. The advantages of the stable charge–discharge behavior provided by FSI-based ionic liquids for lithium ion batteries are also discussed based on the application of voltammetric and electrochemical impedance techniques to model carbon electrodes in ionic liquids. Based on these analyses, a mechanism involving a double-layer-based interface (not a solid electrolyte interface (SEI)) is proposed to stabilize the surface of graphite negative electrodes.

Impact of Lithium Salt Addition to Ionic Liquid Electrolytes for High-performance Electric Double-layer Capacitors

The charge-discharge behavior of electric double-layer capacitors (EDLCs) composed of several ionic liquids and their lithium solutions were evaluated. The model EDLC cell with a Li+-containing ionic liquid electrolyte, LiTFSI/EMImFSI (LiTFSI = lithium bis(trifluoromethylsulfonyl)imide, EMImFSI = 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide), exhibited a higher discharge capacitance than the cell containing EMImFSI, whereas the discharge capacitance of the cell with LiTFSI/EMImTFSI was lower than that of the cell containing EMImTFSI. In addition, the cells composed of EMImBF4-based electrolytes displayed similar charge-discharge characteristics irrespective of the presence of the corresponding lithium salts. The distinctive results for the EDLCs with lithium-containing ionic liquid electrolytes are also discussed based on the application of the electrochemical impedance technique to model carbon electrodes in ionic liquids. According to the obtained differential capacitance of the model glassy carbon electrode in each ionic liquid electrolyte, the electric double-layer (compact layer) structure at the electrode/electrolyte interface depends on the component anion species of the ionic liquid and the co-existence of the anion and Li+.

Oxygen reduction voltammetry on platinum macrodisk and screen-printed electrodes in ionic liquids: Reaction of the electrogenerated superoxide species with compounds used in the paste of Pt screen-printed electrodes?

Screen-printed electrodes (SPEs) are widely investigated as simple, three-electrode planar surfaces for electrochemical sensing applications, and may be ideal for gas sensing purposes when combined with non-volatile room temperature ionic liquids (RTILs). In this report the suitability of SPEs with RTIL solvents has been investigated for oxygen detection. Oxygen reduction has been studied on commercially available platinum SPEs in eight RTILs. Cyclic voltammetric wave shapes were found to be significantly different on Pt SPE surfaces compared to conventional solid Pt macroelectrodes, suggesting a possible reaction of the electrogenerated superoxide with the compounds that make up the ink/paste of the SPE surface. The only RTIL that did not show such drastically different voltammetry was one that contained a pyrrolidinium cation, suggesting a more chemically stable solvent environment compared to the other imidazolium and phosphonium cations studied. The analytical utility was then studied on four SPE surfaces (carbon, gold, platinum and silver) in two RTILs (one with a pyrrolidinium and one with an imidazolium cation) and linear responses were observed between current and % concentration in the range 10–100% O2. This suggests that SPEs may indeed be suitable for oxygen sensing in some RTILs, but significantly more pre-treatment of the surface is required to obtain reliable results. However, the reaction of superoxide with the SPE ink, together with a noticeable deterioration of the signal over time, suggests that this type of sensing platform may only be suitable for “single-use” oxygen sensing applications.

Electrochemical Behavior of Lithium Metal Electrodes in Ionic Liquid Based Electrolytes

not Available.

PTFE bound activated carbon—A quasi-reference electrode for ionic liquids

Commonly used reference electrodes in ionic liquids are either Ag and Pt wires or even newly developed systems of second order mainly based on the Ag/Ag+ couple. However, the reference potentials may change while changing the ionic liquid and a universal reference scale has not been found yet. In this publication we report on the performance of activated carbon (AC) as quasi-reference electrode for the use in pure ionic liquid (IL) electrolytes. Ferrocene was used as a redox couple in the ionic liquids [EMIM][BF4], [EMIM][TFSI], [EMIM][FAP] and [Pyr13][TFSI]. It is shown that all of them exhibit a half-wave potential of 190mV±10mV indicating that AC may be a good candidate as a quasi-reference in IL.

Exploring the electrochemical behavior of screen printed graphite electrodes in a room temperature ionic liquid

Screen printed graphite electrodes (SPGEs) have been characterized in the room temperature ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate [C6MIM][PF6] by studying pertinent electrochemical parameters of the electroactive species ferrocene (Fc), 1,4-benzoquinone (BQ), 1,4-diphenyl-9,10-anthraquinone (AQ), tetracyclone (TC) and benzophenone-3 (BZ-3). Diffusion coefficients and kinetics calculations together with Digisim simulations for comparison were performed. Additionally, the reductive cyclovoltammograms of organic carbonyl containing BQ, AQ, TC and BZ-3 derivatives provided valuable information and comparison of the electrochemical reduction of the CO functional group in model molecules of different size, solubility and π-aryl aromaticity. Finally, potentialities for the electroanalytical measurement of BZ-3 at SPGEs via the room temperature ionic liquid [C6MIM][PF6] have been evaluated.

Characterization of pulse-driven gas-liquid interfacial discharge plasmas and application to synthesis of gold nanoparticle-DNA encapsulated carbon nanotubes

Gas-liquid interfacial discharge plasmas are generated between ionic liquid and stainless steel electrodes, where a pulse power source is used to operate the discharges. The temporal evolution of the plasma is investigated as well as the spatial distribution of the plasma. The positive pulse discharge plasma can not be detected by a double Langmuir probe, which is attributed to the fast diffusion of the plasma toward the chamber wall due to its high positive potential. On the other hand, the negative pulse discharge plasma parameters can be measured and the density decreases with increasing the distance away from the ionic liquid electrode. The plasma is mostly an after-glow discharge plasma since the plasma density gradually decreases after the discharge in a long period. In addition, we synthesize gold nanoparticle-DNA encapsulated single-walled carbon nanotubes by superimposing a DC voltage to the pulse voltage.