Showing papers on "Supporting electrolyte published in 2010"

Influence of Nonaqueous Solvents on the Electrochemistry of Oxygen in the Rechargeable Lithium−Air Battery

Abstract: A fundamental study of the influence of solvents on the oxygen reduction reaction (ORR) in nonaqueous electrolytes has been carried out for elucidating the mechanism of the oxygen electrode processes in the rechargeable Li−air battery. Using either tetrabutylammonium hexafluorophosphate (TBAPF6) or lithium hexafluorophosphate (LiPF6) electrolyte solutions in four different solvents, namely, dimethyl sulfoxide (DMSO), acetonitrile (MeCN), dimethoxyethane (DME), and tetraethylene glycol dimethyl ether (TEGDME), possessing a range of donor numbers (DN), we have determined that the solvent and the supporting electrolyte cations in the solution act in concert to influence the nature of reduction products and their rechargeability. In solutions containing TBA+, O2 reduction is a highly reversible one-electron process involving the O2/O2− couple. On the other hand, in Li+-containing electrolytes relevant to the Li−air battery, O2 reduction proceeds in a stepwise fashion to form O2−, O22−, and O2− as products. Th...

Organometallic Electrochemistry Based on Electrolytes Containing Weakly-Coordinating Fluoroarylborate Anions

Abstract: Electrochemistry is a powerful tool for the study of oxidative electron-transfer reactions (anodic processes). Since the 1960s, the electrolytes of choice for nonaqueous electrochemistry were relatively small (heptaatomic or smaller) inorganic anions, such as perchlorate, tetrafluoroborate, or hexafluorophosphate. Owing to the similar size-to-charge ratios of these "traditional" anions, structural alterations of the electrolyte anion are not particularly valuable in effecting changes in the corresponding redox reactions. Systematic variations of supporting electrolytes were largely restricted to cathodic processes, in which interactions of anions produced in the reactions are altered by changes in electrolyte cations. A typical ladder involves going from a weakly ion-pairing tetraalkylammonium cation, [N(C(n)H(2n+1))(4)](+), with n > or = 4, to more strongly ion-pairing counterparts with n < 4, and culminating in very strongly ion-pairing alkali metal ions. A new generation of supporting electrolyte salts that incorporate a weakly coordinating anion (WCA) expands anodic applications by providing a dramatically different medium in which to generate positively charged electrolysis products. A chain of electrolyte anions is now available for the control of anodic reactions, beginning with weakly ion-pairing WCAs, progressing through the traditional anions, and culminating in halide ions. Although the electrochemical properties of a number of different WCAs have been reported, the most systematic work involves fluoro- or trifluoromethyl-substituted tetraphenylborate anions (fluoroarylborate anions). In this Account, we focus on tetrakis(perfluorophenyl)borate, [B(C(6)F(5))(4)](-), which has a significantly more positive anodic window than tetrakis[(3,5-bis(trifluoromethyl)phenyl)]borate, [BArF(24)](-), making it suitable in a larger range of anodic oxidations. These WCAs also have a characteristic of specific importance to organometallic redox processes. Many electron-deficient organometallic compounds are subject to nucleophilic attack by the traditional family of electrolyte anions. With a view to testing the scope of the much less nucleophililic WCAs in providing a benign electrolyte anion for the generation of organometallic cation radicals, we carried out a series of studies on transition metal sandwich and half-sandwich compounds. The model compounds were chosen both for their fundamental importance and because their radical cations had been neither isolated nor spectrally characterized, despite many previous electrochemical investigations with traditional anions. The oxidation of prototypical organometallic compounds, such as the sandwich-structured ruthenocene and the piano-stool structured Cr(eta(6)-C(6)H(6))(CO)(3), Mn(eta(5)-C(5)H(5))(CO)(3), Re(eta(5)-C(5)H(5))(CO)(3), and Co(eta(5)-C(5)H(5))(CO)(2), gave the first definitive in situ characterization of their radical cations. In several cases, the kinetic stabilization of the anodic products allowed the identification of dimers or unique dimer radicals having weak metal-metal bonds and provided new preparative options for organometallic systems. In terms of thermodynamic effects, the lower ion-pairing abilities of WCAs and their good solubility in a broad range of solvents, including those of lower polarity, permitted a systematic study that yielded an integrated model of how to use solvent-electrolyte combinations to manipulate the E(1/2) differences of compounds undergoing multiple electron-transfer reactions. Although the efficacy of WCA-based electrolytes in organometallic anodic chemistry is now established, WCAs might further expand applications of organic redox chemistry. Other WCAs, including those derived from carboranes and fluorinated alkoxyaluminates, merit additional studies.

Enhanced electrocatalysis of the oxygen reduction reaction based on patterning of platinum surfaces with cyanide.

Abstract: The slow rate of the oxygen reduction reaction in the phosphoric acid fuel cell is the main factor limiting its wide application. Here, we present an approach that can be used for the rational design of cathode catalysts with potential use in phosphoric acid fuel cells, or in any environments containing strongly adsorbing tetrahedral anions. This approach is based on molecular patterning of platinum surfaces with cyanide adsorbates that can efficiently block the sites for adsorption of spectator anions while the oxygen reduction reaction proceeds unhindered. We also demonstrate that, depending on the supporting electrolyte anions and cations, on the same CN-covered Pt(111) surface, the oxygen reduction reaction activities can range from a 25-fold increase to a 50-fold decrease. This behaviour is discussed in the light of the role of covalent and non-covalent interactions in controlling the ensemble of platinum active sites required for high turn over rates of the oxygen reduction reaction.

Major Effect of Electropolymerization Solvent on Morphology and Electrochromic Properties of PEDOT Films

Abstract: Although significant efforts were devoted to improving the properties of conductive polymers, the effects of solvent and supporting electrolytes on the morphology and electrochromic features of electropolymerized materials have been scantly investigated. In this work, the effects of the polymerization conditions, such as the solvents and supporting electrolytes, on the morphological structure and electrochromic properties of PEDOT films were systematically studied. Surprisingly, we find a very significant solvent effect and a small supporting electrolyte effect. We show that morphological properties also strongly correlate with electrochromic properties. Films prepared in propylene carbonate have a smoother structure than those prepared in acetonitrile and this leads to superior electrochromic properties, such as an exceptionally high contrast ratio (71%), transparency in the doped state (80%), and coloration efficiency (193 cm2/C) for the films prepared in propylene carbonate. Significant differences bet...

Electrocoagulation process applied to wastewater containing dyes from textile industry

Abstract: In the present work, electrocoagulation was applied for the colour removal of solutions containing Direct red 81. Experiments were performed for synthetic solutions in batch mode. The study focuses on the effect of following operational parameters: electrolysis time, current density, initial pH, inter-electrode distance, initial dye concentration and type of supporting electrolyte. The obtained results showed that decolouration optimal conditions are the following: initial pH of about 6, current density of 1.875 mA/cm2, inter-electrode distance of 1.5 cm and finally the use of NaCl as supporting electrolyte. In best conditions, high decolouration efficiency was obtained, reaching more than 98% of colour removal. Fourier transform infrared spectroscopy (FTIR) analysis was used to characterize the residual EC by-product with and without the presence of dye.

Ethanol, Acetaldehyde and Acetic Acid Adsorption/Electrooxidation on a Pt Thin Film Electrode under Continuous Electrolyte Flow: An in Situ ATR-FTIRS Flow Cell Study

Abstract: The interaction of ethanol and its oxidative C2 derivatives acetaldehyde and acetic acid with a Pt thin film electrode in 0.5 M H2SO4 solution was investigated by in situ Fourier transform infrared spectroscopy in an attenuated total reflection configuration (ATR-FTIRS). Time-resolved spectro-electrochemical measurements were carried out under well-defined mass transport to/from the electrode in a thin-layer flow cell setup, allowing to in situ monitor the electrode∣electrolyte interface and the formation/removal of adsorbed species in both potentiodynamic and potentiostatic mode. Spectro-electrochemical transients at constant electrode potentials upon electrolyte exchange were employed to identify adsorbed species and their temporal evolution, followed by subsequent stripping of the resulting adsorbates in the supporting electrolyte. Adsorption transient and stripping measurements performed at different constant potentials lead to the following conclusions. (i) Ethanol does not adsorb on Pt at potential ...

Effects of electrolyte on the electrocatalytic activities of RuO2/Ti and Sb–SnO2/Ti anodes for water treatment

Abstract: The study of high efficiency electrochemical water treatment systems is of great importance in contributing to a sustainable water supply. In this study, we prepared RuO2/Ti and Sb–SnO2/Ti electrodes and investigated their electrocatalytic activities for the oxidation of water and three model substrates (methylene blue, acid orange 7, and 4-chlorophenol) in two supporting electrolytes: NaCl vs. Na2SO4. Irrespective of the electrolyte, the particulate RuO2/Ti anode was found to oxidize water at ca. 0.8 V lower potential ranges with significantly higher currents than the cracked-mud type of Sb–SnO2/Ti, indicating that the latter is more suitable for substrate oxidation. In the system of Sb–SnO2/Ti anode–stainless steel cathode couple, the degradation rates of all the substrates were highly enhanced in NaCl, whereas their complete oxidation (i.e., CO2 evolution) occurred more markedly in Na2SO4. Additional detailed experimental results indicated that the relative superiority of Sb–SnO2/Ti over RuO2/Ti for treating the model substrates depended greatly on the employed supporting electrolytes, and that the superiority particularly vanished when NaCl was used as the electrolyte. Using this electrolyte, active chlorine species-mediated indirect reactions seemed to occur at both anodes, while in the Na2SO4 electrolyte, the surface-specific reaction occurred. Finally, surface analysis and diverse electrochemical experiments were performed to compare both anodes in a more quantitative way and to investigate the effect of the electrolytes on the electrocatalytic activities of the anodes.

Electrocatalytical Oxidation of Nitrite and Its Determination Based on Au@Fe3O4 Nanoparticles

Abstract: A promising electrochemical nitrite sensor was fabricated by immobilizing Au@Fe3O4 nanoparticles on the surface of l-cysteine modified glassy carbon electrode, which was characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy and cyclic voltammetry. The proposed sensor exhibited excellent electrocatalytic activity toward nitrite oxidation. The kinetic parameters of the electrode reaction process were calculated, (1 – a)na was 0.38 and the heterogeneous electron transfer coefficient (k) was 0.13 cm s � 1 .T he detection conditions such as supporting electrolyte and pH value were optimized. Under the optimized conditions, the linear range for the determination of nitrite was 3.6 � 10 � 6 to 1.0 � 10 � 2 M with a detection limit of 8.2 � 10 � 7 M( S/ N ¼ 3). Moreover, the as-prepared electrode displayed good stability, repeatability and selectivity for promising practical applications.

Voltammetric method for determining the trace moisture content of organic solvents based on hydrogen-bonding interactions with quinones.

Abstract: Voltammetry experiments were performed on the natural quinone, vitamin K1 (VK1), in a range of organic solvents of varying dielectric constant that are commonly used for electrochemical measurements [dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), acetonitrile (MeCN), propionitrile (EtCN), butyronitrile (PrCN), 1,2-dichloroethane (DCE), dichloromethane (DCM), and 1,1,2,2-tetrachloroethane (TCE)]. The water content of the solvents was accurately measured using Karl Fischer (KF) coulometric titrations, and the voltammetric data were used to estimate the degree of hydrogen-bonding interactions between the reduced forms of VK1 and variable levels of water, thereby allowing a ranking of water−substrate interactions in the different solvents. The voltammetric data were analyzed based on interactions that occur between reduced forms of VK1 and the water, the solvent, and the supporting electrolyte. Calibration data were obtained that are independent of the nature of the reference electrode and allow the ...

Voltammetric Ion-Selective Electrodes for the Selective Determination of Cations and Anions

Abstract: A general theory has been developed for voltammetric ion sensing of cations and anions based on the use of an electrode coated with a membrane containing an electroactive species, an ionophore, and a supporting electrolyte dissolved in a plasticizer. In experimental studies, a membrane coated electrode is fabricated by the drop coating method. In one configuration, a glassy carbon electrode is coated with a poly(vinyl chloride) based membrane, which contains the electroactive species, ionophore, plasticizer and supporting electrolyte. In the case of a cation sensor, ionophore facilitated transfer of the target cation from the aqueous solution to the membrane phase occurs during the course of the reduction of the electroactive species present in the membrane in order to maintain charge neutrality. The formal potential is calculated from the cyclic voltammogram as the average of the reduction and oxidation peak potentials and depends on the identity and concentration of the ion present in the aqueous solution phase. A plot of the formal potential versus the logarithm of the concentration exhibits a close to Nernstian slope of RT/F millivolts per decade change in concentration when the concentration of K(+) and Na(+) is varied over the concentration range of 0.1 mM to 1 M when K(+) or Na(+) ionophores are used in the membrane. The slope is close to RT/2F millivolts for a Ca(2+) voltammetric ion-selective electrode fabricated using a Ca(2+) ionophore. The sensor measurement time is only a few seconds. Voltammetric sensors for K(+), Na(+), and Ca(2+) constructed in this manner exhibit the sensitivity and selectivity required for determination of these ions in environmentally and biologically important matrixes. Analogous principles apply to the fabrication of anion voltammetric sensors.

Electrochemical reduction of quinones: interfacing experiment and theory for defining effective radii of redox moieties.

Abstract: Using cyclic voltammetry, we examined the dependence of the reduction potentials of six quinones on the concentration of the supporting electrolyte. An increase in the electrolyte concentration, resulting in an increase in the solution polarity, caused positive shifts of the reduction potentials. We ascribed the observed changes in the potentials to the dependence of the solvation energy of the quinones and their anions on the media polarity. Analysis of the reduction potentials, using the Born solvation energy equation, yielded unfeasibly small values for the effective radii of the quinone species, that is, the experimentally obtained effective radii were up to 4-fold smaller than the radii of the solvation cavities that we calculated for the quinones. The nonspherical shapes of the quinones, along with the uneven charge density distribution in their anions, encompassed the underlying reasons for the discrepancies between the obtained experimental and theoretical values for the radii of these redox speci...