Electrode In Aqueous Solution Research Articles

Direct Growth of ZnO Whiskers Bridging between Micron-Gap Electrodes in Aqueous Solution

Zinc oxide (ZnO) whiskers were directly synthesized onto the interdigital structured electrodes with 10μm gap through an aqueous solution process. X-ray diffraction (XRD) patterns, photoluminescence of the whiskers at room temperature and field emission-scanning electron microscope (FE-SEM) images showed that the main products were wurtzite ZnO whiskers like hexagonal columns. The whiskers obtained have more than 10μm long and several μm wide. A few whiskers which were strongly bridging the electrodes could be selectively left by applying ultrasonic waves for several ten minutes. Photoconductivity of the whiskers at 390nm was clearly seen with 5V bias. The same characters of whiskers are kept over a long period of time, more than 2months.

Three‐Phase Interlines Electrochemically Driven into Insulator Compounds: A Penetration Model and Its Verification by Electroreduction of Solid AgCl

A dynamic three-phase interline model has been developed for the reduction of a solid insulating metal compound to the metal in a suitable electrolyte, focusing on the electrochemically driven penetration of the process (or the three-phase interlines) into the insulator. Consideration is given to the effects of electrochemical, concentration and ohmic polarizations in the reduction-generated porous metal layer on top of the solid compound. Under potentiostatic conditions, reduction in the depth direction (penetration) becomes progressively slower as a result of the rising ohmic and concentration polarizations, whilst the electrochemical polarization exerts a declining effect. The quantitative equations established here also provide simple methods for the determination of some kinetic parameters of the reduction process, including rho (total resistivity) and D(R) (diffusion coefficient). The model has been experimentally verified by electrochemical reduction of solid AgCl with two novel metal|AgCl cylinder electrodes in aqueous solutions.

Simultaneous Detection of Peracetic Acid and Hydrogen Peroxide by Amperometry at Pt and Au Electrodes

AbstractBased on preliminary voltammetric investigations at both Pt and Au electrodes in aqueous solutions buffered at different pH values in the range 0–10, two possible profitable triple‐pulse amperometric approaches were developed for determining simultaneously peroxyacetic acid (PAA) and hydrogen peroxide present in the same samples. At both surfaces a pulsed waveform applied at rotating‐disc electrodes was adopted to take advantage on one hand of the optimized signal reproducibility achieved by this potential multistep antifouling approach and on the other hand of the constant thickness of the diffusion layer, which is necessary when the recording of time‐independent currents is desired. At a rotating‐disc Pt electrode an anodic selective signal was indeed recorded for H2O2 alone, while PAA contents could be inferred only from the difference of convenient signals, since at all pHs explored its sole cathodic reaction could be observed at potentials coincident with those proper for the reduction of H2O2 too. The same pulse approach at Au electrodes instead provided totally independent signals for the two analytes considered, thus proving to be suitable for their independent detection. In fact, H2O2 alone undergoes anodic oxidation also at this surface, while the reduction of PAA occurs at potentials less cathodic than those required for H2O2. At both electrodes, the best results turned out to be achieved at pH 0 in terms of both precision (±2–4%) and detection limits (0.2–0.3 mM), as well as of linear range which extended for about three orders of magnitude. The kinetics of the equilibrium involving the generation of H2O2 from the reaction of PAA with water was also evaluated, since it was suspected of making unreliable the proposed amperometric approaches.

Measurement and Analysis of Gas Bubbles near a Reference Electrode in Aqueous Solutions

Bubble size distributions (BSDs) near a reference electrode (RE) in aqueous glycerol solutions of an electrolyte NaCl have been investigated under various gas superficial velocities (Us). BSD and voltage reading of the solution were measured by using a high-speed digital camera and a pH/voltage meter, respectively. The results show that bubble size (b) increases with liquid viscosity (μc) and Us. Self-similarity is seen and can be described by the log-normal form of the continuous number frequency distribution. The result shows that b controls the voltage reading in each solution. As b increases, the voltage increases because of gas bubbles interrupting their electrolyte paths in the solutions. An analysis of bubble rising velocity reveals that Stokes' Law should be used cautiously to describe the system. The fundamental equation for bubble formation was developed via Newton's second law of motion and shown to be the function of three dimensionless groupsWeber number, Bond number, and Capillary number. Af...

Thermodynamic studies of dodecylpyridinium ion binding to humic acid and effect of solution parameters on their binding

Thermodynamic information of dodecylpyridinium ions (C 12Py +) binding to Aso humic acid (AHA) has been investigated by using potentiometric titration method with surfactant-ion-selective membrane electrodes in aqueous solution of pH 9.18. No significant change in binding has been observed with changing the temperature in C 12Py +–AHA system. The enthalpy of C 12Py + ions binding with AHA is slightly negative. The solution parameters, such as pH and ionic strength affect the binding. The binding strength is most pronounced at pH 9.18 since the functional groups of AHA are fully ionized and the degree of dissociation ( α) is unity at around pH 9.18. The binding strength decreases with increasing ionic strength due to the ion-screening effect. The sensitivity of binding to electrolyte concentration is higher in AHA system than that in Aso fulvic acid (AFA) system. The hydrodynamic diameters of C 12Py +–AHA and C 12Py +–AFA aggregates was measured as a probe of their molecular interaction by dynamic light scattering (DLS) microscopy. In both AHA and AFA systems, the hydrodynamic diameters increase with increasing surfactant concentration. DLS measurements also give the similar results of lower sensitivity of binding to electrolyte concentration in AFA system. AHA concentration does not interfere the binding strength within the concentration range of 0.2–1.5 g dm −3.

Salient features of the electrical double layer structure on mechanically renewed gold-silver electrodes in aqueous solutions of a surface-inactive electrolyte

The behavior of electrodes, which are made of binary Au-Ag alloys (Ag content 1–15 at %) and renewed by mechanical cutting in aqueous solutions of sodium fluoride, is studied with the aid of cyclic voltammetry and impedance methods. It is established that, in the region of potentials corresponding to ideal polarizability, the differential capacitance of the electrical double layer rapidly changes with time elapsed after the renewal of the surface of the electrodes. The change in the capacitance is brought about by the exit of silver atoms into a surface layer. The implication is that silver is the surface-active component in these alloys. The rate of the surface segregation of silver atoms depends on the electrode potential. The segregation rate substantially increases upon going into the region that corresponds to positive charges of the silver electrode surface and to the beginning of adsorption of atomic oxygen on the electrode. Based on phenomenological models, a method for processing capacitance curves is realized, which links experimentally observed time effects to variations that occur in the surface composition, and assumptions concerning the mechanism of relaxation processes that are responsible for the observed time effects are put forth. Explicit data on the effect, which is exerted by mechanical renewal on the composition of the surface layer of Au-Ag alloys at different distances from the interface with a vacuum, are obtained with the aid of an x-ray photoelectron spectroscopy method. It is established that the surface layer (∼0.5 nm) is enriched by silver atoms as compared with the alloy’s bulk.

Amperometric Detection of Cysteine at an In3+ Stabilized Indium Hexacyanoferrate Modified Electrode

AbstractThis research focuses on the stabilization of indium hexacyanoferrate (InHCF) modified electrode in aqueous solution and the amperometric detection of cysteine (Cys). It was found that the stability of the InHCF modified electrode in the aqueous solution could be improved upon adding In3+ in the solution. EQCM experiments verified that such an In3+ addition greatly inhibited an oxidized InHCF thin film's dissociation and thus considerably stabilizes the InHCF modified electrode. The amperometric detection was performed by the application of a static potential at 1.2 V, with the sampling time at 30 s. The sampled current was linearly dependent on [Cys] when [Cys] was ranged from 100 μM to 1 mM. The sampled current approached a plateau gradually with the increase in the concentration of cysteine. The trend of calibration curve at the InHCF modified electrode generally follows the Michaelis–Menten type kinetics, and Km and vmax were calculated to be 3.86 mM and 30.2 μA, respectively, from the Lineweaver–Burke plot. In addition, the amperometric detection was reversible and reproducible with relative standard deviations of 2.79%.

Voltammetric determination of methidathion insecticide

An electroanalytical method has been developed for the determination of methidathion by squarewave voltammetry on a Nafion®-coated glassy carbon electrode in aqueous solutions with 0.05 M acetate buffer as a supporting electrolyte. The best voltammetric conditions were found to be pH 4.0, a preconcentration potential of 0.45 V, and a preconcentration time of 60 s. The experimental parameters, such as pH, film thickness, preconcentration potential, preconcentration time, and square-wave voltammetric parameters, were optimized. Using this method, the calibration curve is linear in the range 5 × 10−8−7 × 10−7 M with a detection limit (S/N = 3) of 30 nM.

Raman Study on Pt/C Electrode in Aqueous Solution

not Available.

Zero resistance ammeter of metallic alloys in aqueous solutions

In the present work, the corrosion current density of a low carbon steel, a pure aluminum, a stainless steel, a copper–nickel alloy were obtained in 1 M NaOH, 1 M KCl, 1 M NaCl, 1 M H 2SO 4 solutions, respectively. The obtained corrosion data from the optical interferometry technique, as a zero resistance Ammeter were compared with corrosion data obtained on the same alloys, in the specified solutions, from an electronic zero resistance-Ammeter as well as from the linear polarization method. The comparison among the three techniques indicates that there is a contrast in the results among the investigated alloys. In general, the results of the optical interferometry were found to fall in between the corrosion values of the zero resistance ammeter and the linear polarization method, because the technique works based on the electromagnetic principle, in the absence of electronic noise. As a result, the optical interferometry can be considered as a useful zero resistance-Ammeter for measuring the corrosion current density of metallic electrodes in aqueous solutions, at the open circuit potential of the electrodes in the aqueous solutions.

Study of electrochemical instabilities of PEMFC electrodes in aqueous solution by means of membrane inlet mass spectrometry

Abstract Electrochemical stability of electrodes based on C and Pt/C materials is studied in aqueous solution by means of the membrane inlet mass spectrometry technique (MIMS). This technique is based on mass spectrometry detection using a semipermeable membrane for the inlet of gases dissolved in liquid solutions. MIMS is applied to the study of gas evolving reactions taking place at electrodes made from platinum nanoparticles supported on carbon (Pt/C), and immersed in 0.5 M H2SO4 solution. Potentiodynamic experiments under MIMS detection show the formation of carbon oxidation products like CO2, CO and HCOOH. The oxidation of carbon is accelerated in the presence of Pt eletrocatalyst. Instability of a Pt/C electrode starts at 0.35 VNHE, close to the C/CO2 thermodynamic potential, reflected by the detection of CO2 evolution. Partial oxygen reduction to hydrogen peroxide produces carbon corrosion at even lower potentials due to chemical reactivity. The corrosion rate is in the order of 10 - 9 A cm C - 2 (related to total carbon area) at room temperature. The results are of interest for stability studies on proton exchange membrane fuel cell (PEMFC) electrodes.

Cathodic electrochemiluminescence of lucigenin at disposable oxide-coated aluminum electrodes

Electrogenerated chemiluminescence (ECL) of lucigenin is induced at oxide-coated aluminum electrodes in aqueous solution by cathodic pulse polarization. This ECL can be enhanced by the presence of coreactants such as peroxodisulfalte. The present method is based on the injection of hot electrons into the aqueous electrolyte solution, which probably results in the generation of hydrated electrons as reducing mediators. The successive one-electron redox reactions result in the excited states of lucigenin or its fragmentation products. The method can detect lucigenin over several orders of magnitude of concentration with detection limit below nanomolar concentration level. In addition, the relatively long lifetime of the ECL of lucigenin makes time-resolved detection possible. This study suggests that the derivatives of lucigenin can be utilized as electrochemiluminescent labels in aqueous solution in bioaffinity assays at thin insulating film-coated cathodes. The cathodic ECL reaction mechanisms are discussed.

Effect of calcination temperature on electrocatalytic activities of Ti/IrO 2 electrodes in methanol aqueous solutions

The electrochemical activity of thermo-decomposed Ti/IrO 2 electrodes in aqueous solution containing methanol compound has been studied, emphasizing on the influence of calcination temperature. Scanning electron microscopy (SEM) images showed that the typical cracked morphology of oxide coatings disappears gradually as the preparation temperature increases, leading to the decrease in the amount of electrochemically active sites as measured by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in organics-free aqueous solution. With the exception of samples prepared at high temperatures (e.g. 600 °C), same change tendency of electro-activity with temperature was also found in methanol aqueous solutions, in which activity was observed to decrease as compared with that in blank solution. Three possible explanations for this phenomenon (i.e. active dissolution of oxide coatings, organics adsorption and dimerization/polymerization on electrode surface, respectively) were discussed, where the former two were believed to be more reasonable considering the CH 3OH small molecular chosen in this system. However, none of these three mechanisms could explain the abnormal activation behavior observed at electrodes prepared at 600 °C in CH 3OH solution. XRD pattern showed the fact that when sintering temperature went up to 600 °C IrO 2 would decompose into metallic iridium component. The existence of metallic iridium might facilitate the organics oxidation as stated in previous literatures, which leads to the exceptional activation of oxide surface by methanol component. A simple reaction mechanism for electrodes in methanol aqueous solutions was proposed and used to interpret the negative shift in startness potential of the oxygen evolution reaction (OER). Organics oxidation seems to facilitate the OER and vice versa. The latter statement has been reported by other workers.

Thermodynamic studies of dodecylpyridinium ion binding to fulvic acid

The binding of dodecylpyridinium ions (C12Py+) with Aso fulvic acid (AFA) has been studied from the thermodynamic point of view by using potentiometric titration method with surfactant-ion-selective membrane electrodes in aqueous solution of pH 9.18 and at the ionic strength of 0.03moldm−3. The cooperative binding of C12Py+ with AFA is the endothermic process driven by the positive entropy resulting possibly from the dehydration of hydrophobically hydrated water molecules around the hydrocarbon chains of the bound C12Py+ ions. The binding is obviously pH dependent and is most pronounced at pH 9.18. Different binding modes are observed at two pH regions, i.e., cooperative binding at pH>7 and non-cooperative binding at pH<7. The effect of ionic strength is also important in binding phenomenon. As the ionic strength decreases, the C12Py+ binding with AFA is enhanced, probably due to the lowering of screening effect of counterions. The sensitivity of binding to ionic strength is larger at high pH than that at low pH in AFA system.

Electrochemical degradation of Amaranth aqueous solution on ACF

The degradation of Amaranth, a kind of azo dye, has been studied under galvanostatic model with activated carbon fiber (ACF) electrode in aqueous solution with electrochemical method. The ACF was used as anode and cathode, respectively for the decolorization process. The onset oxidation potential and reduction potential for Amaranth on ACF were respectively ascertained at 0.6 and −0.4 V. During the range of −1.1 to 0.50 mA cm −2, the decolorization was clarified into three processes as electroreduction, adsorption and electrooxidation. There were little contributions to the color and COD removals for the process of adsorption. The color removal can be up to 99% when the current density was 0.50 mA cm −2. The maximum COD removal was 52% for the process of electrooxidation. Hundred percent color removal was obtained when the current density of −1.0 mA cm −2 was applied. The maximum COD removal was 62% for the electroreduction. The COD removal results from the adsorption of products for the decolorization process of electrooxidation or electroreduction.

Electroless deposition of vanadium–Schiff base complex onto carbon nanotubes modified glassy carbon electrode: Application to the low potential detection of iodate, periodate, bromate and nitrite

The multiwall carbon nanotubes (MWCNTs) were used as an immobilization matrix to incorporate vanadium-Schiff base complex as electron transfer mediator onto a glassy carbon electrode surface. First, the preheated glassy carbon was subjected to abrasive immobilization of MWCNTs by gently rubbing the electrode surface on a filter paper supporting the carbon nanotubes. Second, the electrode surface was modified with casting 100 μL of V-complex solution (0.01 M in ACN). The cyclic voltammograms of the modified electrode in aqueous solution is shown a pair of well defined, stable and nearly reversible redox system of (V(IV)/V(V)) couple with surface confined characteristics. Combination of unique electronic and electrocatalytic properties of MWCNTs and vanadium–Schiff base complex, results in a remarkable synergistic augmentation on the response. The electrochemical behavior and stability of the modified electrode in aqueous solution at pH range 1–7 was characterized by cyclic voltammetry. The apparent electron transfer rate constant ( K s) and transfer coefficient ( α) were determined by cyclic voltammetry and they were about 7 s −1 and 0.55, respectively. The modified electrodes showed excellent catalytic activity toward reduction of BrO 3 - , IO 4 - , IO 3 - and NO 2 - at unusually positive potential in acidic solution. The electrochemical reversibility, stability and catalytic activity of modified electrode prepared with incorporation of V-complex into CNTs film was compared with the film of adsorbed complex on the surface of preanodized GC electrodes. The modified electrode shows inherent stability at wide pH range, fast response time, high sensitivity, low detection limit and especially remarkable positive potential reduction of oxoanions that decreasing the effect of interferences in analysis. This modified electrode can be used as an amperometric detector for monitoring oxoanions in chromatography or flow injection systems.

Refining adsorption parameters of n-butyl alcohol at the interface of mercury electrode with aqueous NaF and Na2SO4 solutions by correcting the adsorbate concentration

As an adjunct to the regression analysis of differential capacitance curves, which allows refining the adsorption parameters, a program, which takes into account possible errors in volume concentrations of organic substances, is developed. Using this procedure, the earlier data on the differential capacitance of a mercury electrode in aqueous solutions of normal butanol (1-BuOH) containing either 0.1 M NaF or 0.05 and 0.5 M Na2SO4 as the supporting electrolyte are analyzed. This allows obtaining the most accurate values of adsorption parameters for the systems mentioned above within the framework of the model of two parallel capacitors and the Frumkin isotherm. It is shown that, when a linear dependence of the intermolecular interaction parameter on the electrode potential is taken into account, the standard deviation of experimental capacitance values from those calculated using the mentioned model is 6.8–8.8%, which points to very high accuracy of this phenomenological model.

Electroanalytical Determination of Carbaryl in Natural Waters on Boron Doped Diamond Electrode

AbstractThe anodic voltammetric behavior of carbaryl on a boron‐doped diamond electrode in aqueous solution is reported. The results, obtained by square‐wave voltammetry at 0.1 mol L−1 Na2SO4 and pH 6.0, allow the development of a method to determine carbaryl, without any previous step of extraction, clean‐up, preconcentration or derivatization, in the range 2.5–30.0×10−6 mol L−1, with a detection limit of 8.2±0.2 μg L−1 in pure water. The analytical sensitivity of this electrochemical method diminished slightly, from 3.07 mA mmol−1 L to 2.90 mA mmol−1L, when the electrolyte was prepared with water samples collected from two polluted points in an urban creek. In these conditions, the recovery efficiencies obtained were around 104%. The effect of other pesticides (fenthion and 4‐nitrophenol) was evaluated and found to exert a negligible influence on carbaryl determination. The square‐wave voltammetric data obtained for carbaryl were typical of an irreversible electrode process with mass transport control. The combination of square‐wave voltammetry and diamond electrodes is an interesting and desirable alternative for analytical determinations.

Electrochemical Response of Cobalt(II) in the Presence of Ammonia

AbstractThe electrochemical oxidation of cobalt(II) at gold, boron‐doped diamond, basal and edge plane pyrolytic graphite, and highly oriented pyrolytic graphite electrodes in aqueous solutions containing NH3 has been studied using cyclic voltammetry, with subsequent chemical and electrochemical processes explained in detail. Furthermore, the electro‐reduction of [Co(NH3)6]3+ in the presence of different electrolytes has also been studied to obtain a better understanding of the oxidation pathway of the Co(II)‐ammine complexes. In aqueous solution the mechanism can be described by the following scheme:

New Analysis of Data on the Differential Capacitance of a Mercury Electrode during the Adsorption of tert-Butanol

A regression analysis of data on the differential capacitance of a mercury electrode in aqueous solutions of tert-butanol, which were published previously, is performed. It is shown that, in contradistinction to an analogous analysis of electrocapillary curves (ECC), in order to describe the adsorption of this compound in the framework of a model of two parallel capacitors, it is necessary to take into account the linear dependence of the parameter of an intermolecular interaction on the electrode potential. It is established on the basis of modeling calculations that, in order to obtain the same result in the case of a regression analysis of ECC, the relative accuracy of measurements of the interfacial tension must be two orders of magnitude the relative accuracy of measurements of the differential capacitance.