Showing papers on "Supporting electrolyte published in 1994"
TL;DR: In this article, the authors studied a catalytic decomposition of methanol on low Miller index platinum surfaces, Pt(111), Pt(110), and Pt(100) in perchloric, sulfuric, and phosphoric acids at room temperature.
Abstract: We have studied a catalytic decomposition of methanol on low Miller index platinum surfaces, Pt(111), Pt(110), and Pt(100) in perchloric, sulfuric, and phosphoric acids at room temperature. The instantaneous methanol oxidation current is unaffected by the methanolic CO formation (surface poisoning) and depends on platinum surface structure and composition of supporting electrolyte with respect to the anions. The highest oxidation current, 156 mA-cm[sup [minus]2], is observed with the Pt(110) electrode in perchloric acid solution at 0.200 V vs Ag/AgCl reference. In terms of turnover, this current translates to 163 molecules-(Pt site)[sup [minus]1][center dot]s[sup [minus]1], a high rate exceeding previous expectations in methanol electrode kinetics. Overall, the oxidation current changes by 3 orders of magnitude between the extreme cases examined in this study. Breaking up the total effect into individual components shows that the surface geometry and anionic effects are roughly comparable. Therefore, we have an evidence that anion-platinum interactions are as important in determining the methanol oxidation rate as is the surface geometry of the Pt catalyst. 52 refs., 13 figs., 4 tabs.
388 citations
TL;DR: In this article, the ion transfer reactions at single microhole interfaces were studied using only pure water as the aqueous phase electrolyte resulting in a significantly increased potential window and the organic phase supporting electrolyte concentrations were reduced to micromolar levels.
108 citations
TL;DR: In this paper, it was found that morphology of the polyaniline deposit depends greatly upon the anion present in the solution and the structure of the deposit influences the conductivity, being higher for a dense deposit from oxyacid solutions and three orders of magnitude lower in case of a deposit from hydrochloric acid solution.
Abstract: Electrochemical synthesis of polyaniline (PANI) was carried out under cyclovoltammetric conditions using H2SO4, HCl, HNO3, and HClO4 as supporting electrolytes. The observed different rate of PANI deposit growth depending on the acid in the solution has been explained on the grounds of a different degree of specific adsorption for particular anion. It has been found that morphology of the deposit depends greatly upon the anion present in the solution. Thus, PANI synthesized from the solution of oxyacids results in a dense sponge-like structure while PANI from the hydrochloric acid solution results in a spaghetti-like structure. The structure of the deposit influences the conductivity, being higher for a dense deposit from oxyacid solutions and three orders of magnitude lower in case of a deposit from hydrochloric acid solution. © 1994 John Wiley & Sons, Inc.
86 citations
TL;DR: Amperometry in stirred solution has been used for the systematic evaluation of modified screen-printed carbon electrodes (SPCEs) with a view to developing a reagentless biosensor for uric acid, suggesting that the process is diffusion-controlled and not governed by the kinetics of the enzyme.
Abstract: Amperometry in stirred solution has been used for the systematic evaluation of modified screen-printed carbon electrodes (SPCEs) with a view to developing a reagentless biosensor for uric acid. The developed system consists of a base cobalt phthalocyanine (CoPC) electrode tailored to the electrocatalytic oxidation of H2O2 by means of a cellulose acetate (CA)–uricase bilayer. Uricase was immobilized by drop-coating the enzyme onto the CA membrane covering the CoPC-SPCE. The device exploits the near-universal H2O2-generating propensity of oxidases, the permselectivity of the CA film towards H2O2 and the electrocatalytic oxidation of this product at the CoPC-SPCE. The electrochemical oxidation of the resulting Co+ species was used as the analytical signal, facilitating the application of a greatly reduced operating potential when compared with that required for direct oxidation of H2O2 at unmodified electrodes. The time required to achieve 95% of the steady-state current (t95iSS) was 44 s [relative standard deviation = 7.5%(n= 10)]. Amperometric calibrations were linear over the range from 13 × 10–6 to 1 × 10–3 mol dm–3, with the former representing the limit of detection. The CA membrane extended the linear range of the biosensor by over two orders of magnitude, when apparent Michaelis–Menten constants (Km′) of immobilized and free enzymes are compared. This suggests that the process is diffusion-controlled and not governed by the kinetics of the enzyme. The precision of electrode fabrication was determined by cyclic voltammetry to be 4.9%(n= 6). Successive amperometric calibrations (n= 7) over 7 d using a single sensor revealed only a 14.0% diminution in sensitivity from the original response. Sensor stability and the dependence of the steady-state current on the pH, ionic strength and temperature of the supporting electrolyte were studied and the results are presented. The functioning of the biosensor is indifferent to a wide range of potential interferences studied in a synthetic sample and results correlate favourably with those of a standard hospital method.
81 citations
TL;DR: In this article, the point of zero charge (pzc) has been measured by potentiometric titration using KNO3 as a supporting electrolyte, regardless of the source, the same pzc at 8.1 ± 0.1.
75 citations
TL;DR: In this article, the authors show that the wave height in the absence of electrolyte exceeds that with electrolyte present by a factor of 2, as expected for one-electron reduction of a singly charged reactant.
Abstract: Weak acids such as acetic, ascorbic, and salicylic acids are easily reduced at platinum microelectrodes in the absence of the supporting electrolyte. The current is mass transport controlled, and the reduction of proton is preceded by dissociation of the acid in the reaction layer. Since these acids are only slightly dissociated, transport should not be enhanced by migration and the heights of their voltammetric wave should be nearly independent of supporting electrolyte concentration. However, transport-limited currents diminish by 50% when a small amount of a supporting electrolyte is added to the solution. Thus the wave height in the absence of electrolyte exceeds that with electrolyte present by a factor of 2, as expected for one-electron reduction of a singly charged reactant
73 citations
TL;DR: In this paper, the steady-state faradaic current for H+ reduction on a 18 mu m diameter Pt microdisc located within few micrometres of the PANI film while cycling the potential of the film through different oxidation states was measured.
58 citations
54 citations
TL;DR: In this article, the authors investigated the oxygen reduction reaction and the transport of the reactant through the membrane at Pt/proton exchange membrane interfaces immersed in H2SO4 + H3PO4 mixtures using cyclic voltammetry, rotating disk electrode techniques and potential-step chronoamperometry.
47 citations
TL;DR: In this paper, the authors performed experiments with thin layer cells of polyaniline containing a supporting electrolyte such as LiC10 4 dissolved in polyethylene oxide (PEO) or polyvinyl alcohol (PVA).
Abstract: Polyaniline is currently considered to have good device potential [1-5]. One of the devices for which polyaniline is seriously considered is the electrochromic display. A number of studies on the electrochromism (EC) of polyaniline covering various aspects, such as the mechanism of the colour change [6-8] and the effect of cell parameters on the switching time [9], have been done, but these and similar studies have generally been conducted in liquid media in electrochemical cells. In practical devices it is preferable to employ solid materials in order to minimize the problems of sealing in hazardous liquids. Furthermore, EC devices are usually required to have a thin layer configuration. With these considerations in mind, we have performed experiments with thin layer cells of polyaniline containing a supporting electrolyte such as LiC10 4 dissolved in polyethylene oxide (PEO) or polyvinyl alcohol (PVA). We have also studied cells containing urea dissolved in glycerol as the medium. We report the performance of such cells in this letter. A polymeric electrolyte such as PEO was chosen because the amorphous nature of PEO leads to good ionic conductivity and redox stability up to +3 V [10]. In addition, the combination of PEO/ LiC104 is known to be a very fast ionic conductor, with the Li ÷ being the mobile species [11]. Recently, reports have also appeared which describe solid state electrochromic cells of methylene blue using polyacrylamide [12] and gels of polymethyl methacrylate in electrochromic cells of WO3 [13]. The composition of the electrochromic cells used in this study is given in Table I. We have studied the effects of the medium on the various parameters such as switching time, cycle lifetime and applied voltage on the electrochromic display. The current transients for the switching reaction of polyaniline were analysed to understand the influence of mass transport on the switching reaction in polyaniline. Cells for electrochromic studies were constructed as follows. Polyaniline (nominal thickness 1 #m) was coated with indium tin oxide (ITO) plate by application of alternating voltage ( -0 .1 V to 1 V) in HC1 medium containing 0.1 M aniline. The film was dried and dip coated with the appropriate electrolyte then covered with another plate of ITO. The whole assembly was then sealed with wax to exclude air. The schematic of such an electrochromic cell is shown in Fig. 1. Electrical contacts were made using alligator clips after ensuring that there was minimal contact resistance. The cell was mounted on a stand in an optical bench and illuminated at 632 nm with a tungsten-halogen lamp (Oriel Corp., USA) through a monochromator (Oriel). The transmitted light was monitored by an Si photodiode (Oriel). The diode
37 citations
TL;DR: In this paper, a polycrystalline Au electrode, obtained by electroplating of gold, has been studied in 0.1 M HClO4 using cyclic voltammetry and radiotracer technique.
TL;DR: In this article, the transport of hydrogen counterions was studied in solutions of the strong polymer acid poly(styrenesulfonic acid) (PSSA) by voltammetric measurements at Pt disc microelectrodes.
Abstract: The transport of hydrogen counterions was studied in solutions of the strong polymer acid poly(styrenesulfonic acid) (PSSA) by voltammetric measurements at Pt disc microelectrodes. Use of voltammetric microelectrodes makes measurement possible in the absence of supporting electrolyte. Very strong interactions between counterion and polyion were observed under these conditions. Results obtained for polyacid solutions were compared with results for simple strong acids. The experimentally determined limiting value (with no electrolyte) of D/D 0 was 0.345, where D and D 0 are diffusion coefficients of counterion with and without PSSA
24 Jul 1994
TL;DR: In this paper, an insoluble black powder was obtained from carbyne (polyyne) with a broad absorption at 2100 cm−1 due to a polyyne structure and broad absorptions ranged from 1700 to 1000 cm− 1 due to the mixed structure of carbon-carbon double bond and other bonds.
Abstract: Diiodoacetylene was electrolyzed at −2.0 V (vs. SCE) with a platinum cathode in dimethyl formamide containing a supporting electrolyte in the presence of a nickel complex, giving an insoluble black powder. Infrared spectrum of this product was similar to those of carbyne (polyyne) reported previously. A broad absorption at 2100 cm−1 due to a polyyne structure and broad absorptions ranged from 1700 to 1000 cm−1 due to a mixed structure of carbon-carbon double bond and other bonds were observed. The absorption at 2100 cm−1 reduced on a heat treatment under anaerobic conditions or on exposure to air. The electrical conductivity of pellet samples prepared from the black powder under a pressure of 600 kgf cm−2 was about 3 × 10−5 S cm−1.
TL;DR: In this paper, the authors studied the kinetics of sulphur(IV) oxidation by ozone in an aqueous solution, using the stopped flow method, in various supporting electrolytes (NaClO4, NaCl, NH4ClO 4, Na2SO4), and showed that ozone reaction becomes faster than hydrogen peroxide reaction above −log [H+] = 4.70.
Abstract: The kinetics of sulphur(IV) oxidation by ozone in an aqueous solution were studied in various supporting electrolytes (NaClO4, NaCl, NH4ClO4, Na2SO4), using the stopped flow method. The rate data in perchlorate medium (chosen as reference electrolyte) are empirically correlated by the following expression: r = −d[O3]/dt = k [O3] [S(IV)] [H+]−1/2. For each supporting electrolyte studied, the rate constant varies linearly with the ionic strength. The value of the rate constant is extrapolated to zero ionic strength (1.65 × 104 mol−0.5 L0.5 s−1). The rate constants are shown to be higher mainly when ammonium chloride and sodium sulphate are added to the solution. The effect of temperature is studied between 13 ° and 28 °C. The reaction rate is unaffected by the trace presence of metal ion (Mn2+, Fe2+, Cu2+, Fe3+, Cr3+). The rate of oxidation of dissolved SO2 by O3, in water droplets under atmospheric conditions (presence of [H2O2] = 4.31 × 10−5 mol L−1 and [O3] = 1.17 × 10−9 mol L−1), is calculated as a function of [H+] and compared to the oxidation by H2O2. At zero ionic strength the ozone reaction becomes faster than hydrogen peroxide reaction above −log [H+] = 4.70. This effect appears at higher H+ concentration when the ionic strength increases (−log [H+] = 3 in 4 mol L−1 NaCl or 2 mol L−1 Na2SO4).
TL;DR: In this paper, the electrochemical behavior of indole-3-acetic acid (IAA) with a silicone OV-17 modified carbon paste electrode was explored for the determination of this compound in plant tissues.
Abstract: The electrochemical behavior of indole-3-acetic acid (IAA) with a silicone OV-17 modified carbon paste electrode was explored for the determination of this compound in plant tssues. Under optimum conditions, the procedure gave a linear concentration range up to 0.6 μg mL−1 detection of 0.053 μ mL−1 containing the preconcentration solution 0.08M Hac/Ac− buffer (pH4) and 0.4 M phosphate buffer (pH12) as a supporting electrolyte in the measurement cell. The accumulation time was 10 minutes and the sweep potentials were carried mV s−1 with a pulse amplitude (ΔE) of 100 mV. This method is available for the determination of IAA in plant tissues.
TL;DR: In this paper, the experimental behavior under linear sweep and cyclic voltammetry at low scan rates of the reduction of Pb 2+ and Cd 2+ at solid and mercury microelectrodes is reported in the presence and in the absence of supporting electrolyte.
TL;DR: In this paper, the relative ability of certain azoles in inhibiting the corrosion of copper was evaluated using pure carbon paste and chemically modified carbon paste electrodes in support electrolytes containing both Cu(I) and the particular azole.
TL;DR: In this paper, the adsorption behavior of Mn, Co, Ni, and Zn onto a synthetic akageneite (β-FeOOH) sample from different background electrolyte solutions, such as KNO3, NaCl, and major ion seawater, has been studied.
TL;DR: The photoelectrochemical reduction of p -bromo-nitrobenzene in acetonitrile solution, containing tetrabutylammonium perchlorate as supporting electrolyte, was studied using a platinum channel electrode as mentioned in this paper.
TL;DR: In this paper, Taylor dispersion and differential refractometry are used to measure the tracer diffusion coefficients of FeEDTA2, NiEDTA 2, CuEDTA, ZnEDTA and LaEDTA complexes in 0.01, 0.05 and 0.10 mol dm-3 aqueous NaCI solutions at 25 °C.
Abstract: Taylor dispersion and differential refractometry are used to measure the tracer diffusion coefficients of FeEDTA2–, NiEDTA2–, CuEDTA2–, ZnEDTA2– and LaEDTA– complexes in 0.01, 0.05 and 0.10 mol dm–3 aqueous NaCI solutions at 25 °C. A comparison is made with the tracer diffusion coefficients of Fe2+, Ni2+, Cu2+, Zn2+, La3+ and H2EDTA2– ions, which are also measured. The limiting mobilities of the species are estimated by extrapolating the tracer diffusion coefficients to zero ionic strength. Detecting the dispersed samples by differential refractometry allows the diffusion coefficient of supporting electrolyte and the cross-diffusion coefficient between the supporting and tracer electrolytes to be determined in addition to the tracer diffusion coefficient. Radiochemical labels are not required.
Patent•
02 Sep 1994TL;DR: In this paper, photoelectrochemical oxidation and dissolution of silicon (Si) is performed in the absence of water and oxygen, producing a spatially selective etch rate of greater than 4 μm/min.
Abstract: The photoelectrochemical oxidation and dissolution of silicon (Si) is performed in the absence of water and oxygen. Etch rates and photocurrents in an anhydrous HF-acetonitrile (MeCN) solution are directly proportional to light intensity up to at least 600 mW/cm2, producing a spatially selective etch rate of greater than 4 μm/min. Four electron transfer reactions per silicon molecule occur with a quantum yield greater than 3.3 due to electron injection from high energy reaction intermediates. Further, the electrochemical oxidation of p-doped silicon in HF-MeCN results in the formation of porous silicon which electroluminescence in an aqueous solution. In an aprotic electrolyte, where tetrabutylammonium tetrafluoroborate (TBAFB) is used as both the supporting electrolyte and source of fluoride in MeCN, photo-induced etching of n-doped silicon occurs at quantum efficiency of 1.9. This indicates that the oxidation and dissolution mechanism of Si in MeCN can occur without protons.
TL;DR: In this article, the cobalt hexacyanoferrate was immobilized onto a silica gel surface, chemically modified with tin(IV) oxide, and the formal potential of the attached electroactive species was dependent on the supporting electrolyte used.
TL;DR: In this article, a gold-mesh optically-transparent thinlayer electrode (OTTLE) was used for the spectroelectrochemical investigation of the azomethazine and transition-metal chromophores.
Abstract: The Schiff base nickel(II) complexes of N,N′-bis(salicylaldehyde)–o-phenylenediamine and N,N-bis(2-hydroxy-1-naphthaldehyde)–o-phenylenediamine provide an opportunity for the spectroelectrochemical investigation of the azomethazine and transition-metal chromophores using a gold-mesh optically-transparent thinlayer electrode (OTTLE) in protic solvents. Cyclic voltammetry of these compounds showed a well ordered electrochemical behaviour with reductions in both the metal and ligand. All complexes showed two well defined electrode couples, NiI/NiII and NiII/NiIII. The dependence of the electrochemical parameters on the solvent, supporting electrolyte, scan rate and the nature of the ligands is discussed. Application of the OTTLE cell technique to the study of the redox chemistry of the nickel(II) pigments tested proved efficient for the spectral and electrochemical characterization of the various oxidation states. The spectropotenotiostatic experiments provided redox potentials, n values, close to those obtained by controlled potential coulometry and in agreement with those values predicted from the bulk cyclic voltammetry. The estimated standard electrode potential (E0) values agreed well with those obtained by Nernstian analysis, and facilitated the acquisition of E and n values, which are not readily obtained by conventional techniques. This was possible even for quasireversible reactions where the peak separation does not yield accurate n values. Exhaustive electrolysis of the small volume of solution in the OTTLE ensured the quantitative generation of a particular redox state without interference from extraneous redox reactions. The effect of an additional aromatic ring is to provide an additional redox couple. The electrochemical and spectral behaviours were in good agreement, which suggests that the phenomenon of colour fading in the complex and electrochemical changes produce similar trends.
TL;DR: The results obtained agree quite well with theoretical expectations and indicate that the potential shifts found are mainly conditioned by both charge and concentration of the counterion from the supporting electrolyte and by the ratio of the ion-exchange equilibrium constants for the two redox partners involved.
TL;DR: In this article, an ultrasensitive voltammetric procedure for the determination of molybdenum was proposed, where the adsorptive collection of 2-(2′-thiazolylazo)-p-cresok (TAC), coupled with the catalytic current of the adorbed complex, yield an ultrasound-sensitive voltammetry procedure.
Abstract: The adsorptive collection of the molybdenum (VI) complex of 2-(2′-thiazolylazo)-p-cresok (TAC), coupled with the catalytic current of the adsorbed complex, yield an ultrasensitive voltammetric procedure for the determination of molybdenum. Optimal experimental conditions were found with the use of a stirred acetate buffer (pH 2.9) supporting electrolyte, a TAC concetration of 1.0 × 10−5 M, and a concentration of 0.1 M potassium nitrate. In addition, a preconcentration potential of −0.13 V (vs. Ag/AgCl), equilibrium time of 30 seconds, and an anodic scan rate of 200 mV/s from −0. 93 to −0. 20 was used. A catalytic effect was observed when nitrate was present. The response was found to be linear over a concentration range of 0.0 to12.0 μg L−1 Mo (VI). For a preconcentration time of 3 minutes, the detection limit was found to be 11 pM. Possible interferences by anions and other trace metals were investigated. The interference by copper may be masked by CDTA, and sequential determination with molybdenum is possible. The merits of the procedure are demonstrated in the analysis of sea and mineral water.
TL;DR: In this paper, a polarized platinum tube is used for aqueous solution containing supporting electrolyte and a small concentration of an electroactive analyte to flow under a gravitational head, and the analyte concentration is accurately calculable, when the applied voltage and head are optimized, from the measured flow rate of the solution and the steady-state electric current.
Abstract: An aqueous solution containing supporting electrolyte and a small concentration of an electroactive analyte is allowed to flow, under a gravitational head, through a polarized platinum tube. The tube is narrow enough that, during their few seconds of residence time within the tube, virtually all the analyte molecules are able to diffuse to the tube wall and be electrolytically destroyed. The analyte concentration is accurately calculable, when the applied voltage and head are optimized, from the measured flow rate of the solution and the steady-state electric current, the latter being background-corrected by subtracting the current under no-flow conditions. Though the detailed theory is complicated, the principles of the method and its experimental realization are straightforward.
TL;DR: In this paper, a sensitive method for the determination of vitamin K3 using cathodic stripping voltammetry is presented using sodium sulfate as the supporting electrolyte at pH 1.70-1.85, a reductive peak (−0.64 V vs SCE) is observed.
TL;DR: In this article, a 2-vinylthiophene (2-VTh) was polymerized at a potential of 2.75 V vs Ag/Ag + in acetonitrile solvent using tetrabutylammonium tetrafluoroborate as supporting electrolyte.
Abstract: We have polymerized 2-vinylthiophene (2-VTh) anodically at a potential of 2.75 V vs Ag/Ag + in acetonitrile solvent using tetrabutylammonium tetrafluoroborate as supporting electrolyte. Two products result: a semiconducting (10 -4 S/cm), dark coating on the electrode (polymer C) and a nonconducting precipitate from the anolyte solution (polymer B). Polymer B is spectroscopically similar to poly(2-vinylthiophene) (PVTh) produced by bulk, benzoyl peroxide-initiated polymerization of 2-VTh (polymer A) except that it has a lower molecular weight (1.5×10 3 vs 1.9×10 4 for polymer A by SEC using polystyrene as standard)
TL;DR: In this paper, cyclic voltammetry and chronoamperometry were used to study the oxidation process for ferrocene in chloroform at Pt, Au and GC electrodes using Bu 4 NClO 4 (TBAP) as supporting electrolyte.
TL;DR: In this paper, the authors used three Pt electrodes including a Pt disc microelectrode as indicator electrode, and water gave well defined anodic voltammetric waves in acetone.
Abstract: Using three Pt electrodes including a Pt disc microelectrode as indicator electrode, water gives well defined anodic voltammetric waves in acetone. The height of the water wave is linearly proportional to the water concentration. The wave is located at about +3.0 V versus the Pt quasi-reference electrode. As perchlorate ion is oxidized in the same potential range, it is necessary to control strictly the concentration of the supporting electrolyte (LiClO4) in the determination of water. As little as 0.1 mmol l–1 of the supporting electrolyte provides measurable waves. Voltammetry is shown to be a suitable method for determining water in acetone from millimolar to molar concentrations, and water in various substances that can be dissolved in acetone such as fats or insoluble substances such as salts. The method might be particularly useful for the in situ determination of water during voltammetric experiments in acetone.