Simultaneous determination of paracetamol and ascorbic acid using tetraoctylammonium bromide capped gold nanoparticles immobilized on 1,6-hexanedithiol modified Au electrode

Tetraoctylammonium bromide stabilized gold nanoparticles (TOAB-AuNPs) attached to 1,6-hexanedithiol (HDT) modified Au electrode was used for the simultaneous determination of paracetamol (PA) and ascorbic acid (AA) at physiological pH. The attachment of TOAB-AuNPs on HDT modified Au surface was confirmed by attenuated total reflectance (ATR)-FT-IR spectroscopy and atomic force microscope (AFM). The ATR-FT-IR spectrum of TOAB-AuNPs attached to the HDT monolayer showed a characteristic stretching modes corresponding to -CH₂ and -CH₃ of TOAB, confirming the immobilization of AuNPs with surface-protecting TOAB ions on the surface of the AuNPs after being attached to HDT modified Au electrode. AFM image showed that the immobilized AuNPs were spherical in shape and densely packed to a film of ca. 7 nm thickness. Interestingly, TOAB-AuNPs modified electrode shifted the oxidation potential of PA towards less positive potential by 70 mV and enhanced its oxidation current twice when compared to bare Au electrode. In addition, the AuNPs modified electrode separated the oxidation potentials of AA and PA by 210 mV, whereas bare Au electrode failed to resolve them. The amperometry current of PA was increased linearly from 1.50 × 10⁻⁷ to 1.34 × 10⁻⁵ M with a correlation coefficient of 0.9981 and the lowest detection limit was found to be 2.6 nM (S/N = 3). The present method was successfully used to determine the concentration of PA in human blood plasma and commercial drugs.     

Protoporphyrin-modified gold surfaces for the selective monitoring of catecholamines

Protoporphyrin IX (PPIX) was immobilized on Au surfaces for the electrochemical oxidation of dopamine (DA) and epinephrine (EP). Two procedures for the immobilization were employed. One class of modified electrodes was prepared by immobilizing the PPIX into polypyrrole (PPy) films synthesized by anodic electropolymerization. The other procedure involved the immobilization of PPIX on an electrode modified by a 11-mercaptoundecanoic acid (MUA) self-assembled monolayer (SAM). The modified surfaces were characterized by cyclic voltammetry (CV).The efficiency of these modified surfaces for the electrochemical oxidation of DA and EP was investigated and compared. The peak potential for the oxidation of each analyte at the different electrode surfaces was determined by square-wave voltammetry (SWV).The dependence of the sensitivity of the electrodes for the detection of the catecholamines on the applied potential was also measured. The SAM-based electrodes showed better selectivity for detecting DA in the potential range between 0.2 and 0.4 V versus Pt (QRE). However, higher sensitivity and linearity were observed for the film-based electrodes.     

Voltammetric behavior study of folic acid at phosphomolybdic-polypyrrole film modified electrode

The electrochemical behavior of folic acid at the Keggin-type phosphomolybdate (PMo₁₂) doped polypyrrole (PPy) film modified glassy carbon electrode (PMo₁₂-PPy/GCE) was studied. PMo₁₂ doped PPy modified electrodes were achieved during the electrochemical preparation of the polymer films in aqueous solution. The redox behavior of the modified electrode was described by cyclic voltammetry. The electrochemical behavior of folic acid at PMo₁₂-PPy/GCE was studied by 0.5 order differential voltammetry. Numerous factors affecting the reduction peak currents of folic acid at PMo₁₂-PPy/GCE were optimized to maximize the sensitivity. The results showed that folic acid had high inhibitory activity toward the reduction of modified electrode in 0.01 M H₂SO₄. The reduction peak currents were directly proportional to the concentration of folic acid from 1.0 × 10⁻⁸ to 1 × 10⁻⁷ M with correlation coefficient of 0.9976, a detection limit of 1.0 × 10⁻¹⁰ M of folic acid was estimated. From the inhibitory effect of folic acid on PMo₁₂-PPy/GCE, the apparent formation constant of folic acid with the modified film was estimated. This modified electrode showed excellent sensitivity and stability for the determination of folic acid. The response mechanism of folic acid at PMo₁₂-PPy/GCE was discussed in detail.     

Influence of the surface area of the support on the activity of gold catalysts for CO oxidation

In the preparation of 1% Au/TiO₂ catalysts supported on either Degussa P-25 or anatase (90 m² g⁻¹) by deposition–precipitation, the gold content passes through a maximum at about the isoelectric point (pH 6), but maximum specific rates occur at pH 8–9 because the Au particle size becomes smaller as the pH is further increased. The gold uptake increases with the surface area of the support (anatase, rutile, P-25) and is complete above 200 m² g⁻¹; adsorption of the gold precursor at pH 9 is shown to be equilibrium-limited. Highest activities are found with supports of 50 m² g⁻¹. Catalysts made with high-area anatase (240 or 305 m² g⁻¹) are least active but show least deactivation.With Au/SnO₂ catalysts, gold uptake does not depend on the area of the support, and is highest at pH 7–8; very active catalysts (T₅₀ = 230–238 K) are obtained using SnO₂ of 47 m² g⁻¹. Storing a catalyst at 258 K for 1 week dramatically improves its stability. Results for Au/CeO₂ and Au/ZrO₂ catalysts confirm that moderate support areas give the most active catalysts, and suggest that surface area is often more important than chemical composition.     

In situ fabricated iodine-adlayer assisted selective electrooxidation of uric acid in alkaline media

This work presents the electrooxidation of uric acid (UA) at an iodine-adlayer-modified gold, Au (I|Au (poly)) electrode in 0.1 M NaOH solution using cyclic voltammetric, amperometric and open-circuit potential measurement techniques. A tremendous enhancement of the electrode activity towards the electrooxidation of UA was achieved by virtue of the simple modification of the Au (poly) electrode surface with a neutral iodine-adlayer, fabricated in situ through the spontaneous oxidative chemisorption of iodide present in the sample solution. The cyclic voltammetric peak current increases remarkably for the oxidation of UA and the peak potential shifts by 365 mV to the negative direction of potential compared to the bare Au (poly) electrode. Oxidation of ascorbic acid (AA) at the I|Au (poly) electrode takes place at the same potential as that at the bare electrode, but the peak current intensity is almost twice at the bare Au (poly) electrode as compared to the modified one. In the mixture of the AA and UA, the cyclic voltammetric signals corresponding to the oxidations of AA and UA were resolved by 340 mV. The electrode response in the mixture was highly reproducible because of the inhibition of adsorption of oxidation products and UA.     

Monodispersed gold nanoparticles supported on γ-Al2O3 for enhancement of low-temperature catalytic oxidation of CO

Monodispersed nano-Au/γ-Al₂O₃ catalysts for low-temperature oxidation of CO have been prepared via a modified colloidal deposition route, which involves the deposition of dodecanethiolate self-assembled monolayer (SAM)-protected gold nanoparticles (C₁₂ nano-Au) in hexane on γ-Al₂O₃ at room temperature. The diameter of the gold nanoparticles deposited on the support is 2.5 ± 0.8 nm after thermal treatment, and their valence states comprise both the metallic and oxidized states. It is found that the thermal treatment temperature affects significantly the catalytic activity of the catalysts in the processing steps. The catalyst treated at 190 °C exhibits considerably higher activity as compared to catalysts treated at 165 and 250 °C. A 2.0-wt.% nano-Au/γ-Al₂O₃ catalyst treated at 190 °C for 15 h maintains the catalytic activity at nearly 100% CO oxidation for at least 800 h at 15 °C, at least 600 h at 0 °C, and even longer than 450 h at −5 °C. Evidently, the catalysts obtained using this preparation route show high catalytic activity, particularly at low temperatures, and a good long-term stability.     

Iron(III) protoporphyrin IX—single-wall carbon nanotubes modified electrodes for hydrogen peroxide and nitrite detection

Iron(III) protoporphyrin IX (Fe(III)P), adsorbed either on single-walled carbon nanotubes (SWCNT) or on hydroxyl-functionalized SWCNT (SWCNT-OH), was incorporated within a Nafion matrix immobilized on the surface of a graphite electrode. From cyclic voltammetric measurements, performed under different experimental conditions (pH and potential scan rate), it was established that the Fe(III)P/Fe(II)P redox couple involves 1e⁻/1H⁺. The heterogeneous electron transfer process occurred faster when Fe(III)P was adsorbed on SWCNT-OH (11 s⁻¹) than on SWCNT (4.9 s⁻¹). Both the SWCNT-Fe(III)P- and SWCNT-OH-Fe(III)P-modified graphite electrodes exhibit electrocatalytic activity for H₂O₂ and nitrite reduction. The modified electrodes sensitivities were found varying in the following sequences: S_{SWCNT-OH-Fe(III)P} = 2.45 mA/M ≈ S_{SWCNT-Fe(III)P} = 2.95 mA/M > S_Fe(III)P = 1.34 mA/M for H₂O₂, and S_{SWCNT-Fe(III)P} = 3.54 mA/M > S_Fe(III)P = 1.44 mA/M > S_{SWCNT-OH-Fe(III)P} = 0.81 mA/M for NO₂⁻.     

Study on the influence of anionic and cationic surfactant on Au-colloid modified electrode function by cyclic voltammetry and electrochemical impedance techniques

The influence of different surfactants on Au-colloid modified electrode function has been investigated by using cyclic voltammetry and electrochemical impedance techniques. Colloidal Au was self-assembled onto the gold electrode through the thiol-groups of 1,6-hexanedithiol (HDT) monolayer. It was found that some HDT molecules stood on the gold electrode and some molecules lay on the electrode by using the quartz crystal microbalance (QCM). A cathodic peak at about 0.486 V (vs. SCE) was observed at the bare gold electrode and the Au-colloid modified electrode. Cyclic voltammetry was used to investigate the influence of different surfactants on the cathodic peak of Au-colloid modified electrode. Electrochemical impedance technique was also used to study the electron transfer ability of the redox probe on Au-colloid modified electrode after being immersed in different surfactants. The results showed that anionic surfactant and cationic surfactant exhibit different behaviors, the reason of which was discussed.     

Electrochemical formation of Au2Na alloy and the characteristics of (Au2Na+Au) reference electrode in a LiF–NaF–KF eutectic melt

A cyclic voltammogram at a Au electrode in a LiF–NaF–KF eutectic melt at 773 K showed a cathodic peak at 0.45 V (vs. K⁺/K). XRD analysis of the electrode confirmed that the cathodic peak corresponded to the formation of Au₂Na alloy phase. The equilibrium potential of the reaction: 2Au+Na⁺+e⁻Au₂Na was determined to be 0.535 V at 773 K by open-circuit potentiometry at the Au–Na alloy electrode. The thermodynamic properties including the standard Gibbs free energy of formation were estimated for Au₂Na alloy at 773–860 K. The (Au₂Na+Au) electrode was proved to have excellent characteristics as a reference electrode in terms of reproducibility, stability and reversibility.     

Magnetron sputtering of gold nanoparticles onto WO3 and activated carbon

In this paper we describe the production and investigation of two supported gold catalyst systems prepared by magnetron sputtering: Au on WO₃ and Au on activated carbon. The magnetron sputtering technique entails using an argon plasma to sputter a high purity gold target producing a flux of gold atoms which are deposited onto a constantly tumbling support material. This technique offers a number of advantages over conventional chemical preparation methods. One advantage is the ability to create gold nanoparticles (diameters <3 nm) on unusual support materials, such as WO₃ and carbon, which are generally not accessible using the ubiquitous deposition-precipitation technique. We present data demonstrating the formation of catalytic gold nanoparticles with average diameters of 1.7 nm (Au/C) and 2.1 nm (Au/WO₃), as well as a substantial number of single atom species on the Au/C sample. Prototypical carbon monoxide oxidation (Au/WO₃) and glycerol oxidation (Au/C) reactions were performed in order to gauge the activity of these catalysts. The WO₃ supported catalyst exhibits substantial catalytic activity from room temperature to 135 °C (0.0018–0.082 mol CO/mol Au s) with an activation energy near 23 kJ/mol. The activity of the Au/C catalyst was compared to a Au/C catalyst prepared from a poly(vinyl alcohol) (PVA) sol. The smaller catalysts prepared by sputtering are more active than the large gold particles prepared using the PVA sol, however the larger gold nanoparticles are substantially more selective towards the production of intermediate products from the oxidation of glycerol.     

Preparation and characterization of heteropolyacid/mesoporous carbon catalyst for the vapor-phase 2-propanol conversion reaction

H₃PMo₁₂O₄₀ catalyst was chemically immobilized on the surface modified CMK-3 (SM-CMK-3) support as a charge compensating component, by taking advantage of the overall negative charge of [PMo₁₂O₄₀]³⁻. The supported H₃PMo₁₂O₄₀/SM-CMK-3 catalyst was characterized to have high surface area (≈1000 m²/g) and relatively large pore volume (0.83 cm³/g). The H₃PMo₁₂O₄₀/SM-CMK-3 catalyst was applied to the vapor-phase 2-propanol conversion reaction. The H₃PMo₁₂O₄₀/SM-CMK-3 catalyst exhibited higher 2-propanol conversion than the unsupported H₃PMo₁₂O₄₀ and the impregnated H₃PMo₁₂O₄₀ on CMK-3. Furthermore, the PMo₁₂/SM-CMK-3 catalyst showed the enhanced oxidation activity (acetone formation) and the suppressed acid catalytic activity (propylene formation) compared to the other two catalysts. It is believed that [PMo₁₂O₄₀]³⁻ species were chemically and finely immobilized on the SM-CMK-3 support as charge matching species, and thus, the PMo₁₂/SM-CMK-3 catalyst showed an excellent oxidation activity.     

A comparative study of TiO2 supported noble metal catalysts for the oxidation of formaldehyde at room temperature

The TiO₂ supported noble metal (Au, Rh, Pd and Pt) catalysts were prepared by impregnation method and characterized by means of X-ray diffraction (XRD) and BET. These catalysts were tested for the catalytic oxidation of formaldehyde (HCHO). It was found that the order of activity was Pt/TiO₂  Rh/TiO₂ > Pd/TiO₂ > Au/TiO₂  TiO₂. HCHO could be completely oxidized into CO₂ and H₂O over Pt/TiO₂ in a gas hourly space velocity (GHSV) of 50,000 h⁻¹ even at room temperature. In contrast, the other catalysts were much less effective for HCHO oxidation at the same reaction conditions. HCHO conversion to CO₂ was only 20% over the Rh/TiO₂ at 20 °C. The Pd/TiO₂ and Au/TiO₂ showed no activities for HCHO oxidation at 20 °C. The different activities of the noble metals for HCHO oxidation were studied with respect to the behavior of adsorbed species on the catalysts surface at room temperature using in situ DRIFTS. The results show that the activities of the TiO₂ supported Pt, Rh, Pd and Au catalysts for HCHO oxidation are closely related to their capacities for the formation of formate species and the formate decomposition into CO species. Based on in situ DRIFTS studies, a simplified reaction scheme of HCHO oxidation was also proposed.     

Effective Au-Au-Clx/Fe(OH)y catalysts containing Cl for selective CO oxidations at lower temperatures

Supported Au catalysts Au-Au⁺-Cl_x/Fe(OH)_y (x < 4, y ≤ 3) and Au-Cl_x/Fe₂O₃ prepared with co-precipitation without any washing to remove Cl⁻ and without calcining or calcined at 400 °C were studied. It was found that the presence of Cl⁻ had little impact on the activity over the unwashed and uncalcined catalysts; however, the activity for CO oxidation would be greatly reduced only after Au-Au⁺-Cl_x/Fe(OH)_y was further calcined at elevated temperatures, such as 400 °C. XPS investigation showed that Au in catalyst without calcining was composed of Au and Au⁺, while after calcined at 400 °C it reduced to Au⁰ completely. It also showed that catalysts precipitated at 70 °C could form more Au⁺ species than that precipitated at room temperatures. Results of XRD and TEM characterizations indicated that without calcining not only the Au nano-particles but also the supports were highly dispersed, while calcined at 400 °C, the Au nano-particles aggregated and the supports changed to lump sinter. Results of UV–vis observation showed that the Fe(NO₃)₃ and HAuCl₄ hydrolyzed partially to form Fe(OH)₃ and [AuCl_x(OH)_4−x]⁻ (x = 1–3), respectively, at 70 °C, and such pre-partially hydrolyzed iron and gold species and the possible interaction between them during the hydrolysis may be favorable for the formation of more active precursor and to avoid the formation of Au–Cl bonds. Results of computer simulation showed that the reaction molecular of CO or O₂ were more easily adsorbed on Au⁺ and Au⁰, but was very difficultly absorbed on Au⁻. It also indicated that when Cl⁻ was adsorbed on Au⁰, the Au atom would mostly take a negative electric charge, which would restrain the adsorption of the reaction molecular severely and restrain the subsequent reactions while when Cl⁻ was adsorbed on Au⁺ there only a little of the Au atom take negative electric charge, which resulting a little impact on the activity.     

Photoelectrochemical treatment of the dye reactive red 198 using DSA electrodes

The study of the oxidation of the dye reactive red 198 on Ti/Ru_0.3Ti_0.7O₂ electrode is presented. Three different techniques were employed: photocatalytic (interaction of UV radiation and electrode surface), electrochemical (application of a constant current) and photoelectrochemical (simultaneous application of a constant current and UV radiation). The effect of temperature (20–45 °C) and current density (5–89 mA cm⁻²) were investigated. No significant temperature effect was observed for the three techniques used. It was observed that at low current densities (5–30 mA cm⁻²) the photoelectrochemical (PhEC) rate of colour and TOC removal is simply the sum of the photocatalytic (PC) and electrochemical (EC) rates. However, as the current density increases, the rate of PhEC removal is much greater. This phenomenon is interpreted as being due to the increased production of O₂, which goes on to interact with the UV radiation and cause the oxidation of the dye.     

Electrochemistry and electrochromism of a poly(cyclopentadithiophene) derivative with a viologen pendant

N-Methyl-N′-(6-4H-cyclopenta[2,1-b:3,4-b′]dithiophene-4-ylhexyl)-4,4′-bipyridinium dihexafluorophosphate (CPDT-V²⁺-Me) was synthesized. The monomer was electropolymerized on a glassy carbon or an ITO electrode in a potentiodynamic mode to form the corresponding polymer P(CPDT-V²⁺-Me) on the electrodes. During the electropolymerization, two redox peaks of the viologen (V) moiety increased up to several cycles and then decreased while the redox peak of P(CPDT) moiety still increased. Especially, a new oxidative peak a in the range of ca. −0.4 and 0 V versus Ag/Ag⁺ appeared and increased up to several cycles. Peak a almost disappeared after the redox peaks of the viologen moiety almost disappeared. As a result of cyclic voltammetric study, it was shown that peak a originated from the oxidation of reduced viologen moiety via P(CPDT)-mediated electron transfer mechanism. We also found that the electroactivity of viologen moiety in P(CPDT-V²⁺-Me) decreased significantly when the potential was scanned to the second viologen redox (V⁰/V√⁺). In practical applications, the polymer can be used in the potential range from the first viologen redox to P(CPDT) redox. The polymer turned into highly transparent P(CPDT⁺-V²⁺-Me), blue P(CPDT-V²⁺-Me), dark violet P(CPDT-V√⁺-Me), and violet P(CPDT-V⁰-Me) approximately at 0.8, −0.4, −0.8, and −1.7 V versus Ag/Ag⁺, respectively.     

Electrochemical characterization of 8-hydroxyquinoline-5-sulphonate/aluminium(III) aqueous solutions

8-Hydroxyquinoline-5-sulphonate/Al(III) aqueous solutions were studied both by potentiometric titrations and voltammetric measurements, in order to obtain the number, the stoichiometry and the stability constants of the complexes formed at equilibrium, and to evaluate the redox and (electro)kinetic properties of the free ligand and of the metal/ligand complexes. The complexes formed in 0.2 m (Na)Cl aqueous solution (stability log beta values ± standard deviation) are AlL⁺ (8.95 ± 0.05), AlL₂⁻ (17.43 ± 0.03) and AlL₃³⁻ (24.58 ± 0.05), where “L” denotes the free ligand in the completely deprotonated form (L²⁻, pK_a1 = 3.910 ± 0.008, pK_a2 = 8.319 ± 0.004). AlL₃³⁻ is the predominant Al(III) species in a very wide range of pH, metal and ligand concentrations and metal-to-ligand ratios. The free ligand shows an oxidation wave at 0.62 V versus SCE. The proposed oxidation mechanism includes a first reversible one-electron oxidation of the ligand, followed by a coupling reaction and by a second reversible one-electron oxidation, and finally by a decomposition reaction. The addition of Al(III) lowers the intensity of the oxidation wave due to the formation of the redox-inactive complex AlL₃³⁻. A residual low signal was attributed to the free ligand produced by the complex dissociation, AlL₃³⁻ = AlL₂⁻ + L²⁻. All the kinetic parameters involved in the ligand oxidation and in the complex disruption were calculated on the basis of the agreement between experimental and simulated linear sweep and cyclic voltammetries. Correctness of the mechanisms proposed was further confirmed “a posteriori” by the agreement between potentiometric and linear sweep voltammetric results. The low residual signal observed in the presence of fully formed complex was attributed to the free ligand produced by the complex dissociation, having a kinetic constant estimated 0.2 s⁻¹.     

Application of thionine-nafion supported on multi-walled carbon nanotube for preparation of a modified electrode in simultaneous voltammetric detection of dopamine and ascorbic acid

A modified carbon-paste electrode (CPE) is prepared by incorporating thionine-nafion supported on multi-walled carbon nanotube (MWCNT). The electrochemical behavior of dopamine (DA) and ascorbic acid (AA) on the surface of the modified electrode is investigated by cyclic voltammetry (CV). The results show that thionine effectively immobilized in the matrix of the paste by using an appropriate mixture of nafion/MWCNT under the ultrasonic condition. On the other hand, presence of nafion enhances the stability of the thionine supported by MWCNT in the composite electrode and improves the reproducibility of the surface of the modified electrode under renewing process by polishing. The results of cyclic and differential pulse voltammetric investigations show that the modified electrode possesses an efficient electrocatalytic activity for the electrochemical oxidation of DA and AA and a peak potential separation nearly 379 mV is resulted for two compounds. The prepared modified electrode does not show any considerable response toward the electro-oxidation of sulfhydryl compounds, such as, cysteine, penicillamine and glutathione, revealing a good selectivity for voltammetric response to AA and DA in clinical and pharmaceutical preparations. The effective electrocatalytic property, excellent peak resolution and ability for masking the voltammetric responses of the other biologically reducing agents, make the modified electrode suitable for simultaneous and sensitive voltammetric detection of sub-micromolar amounts of AA and DA.     

Electrocatalytic oxidation and simultaneous determination of uric acid and ascorbic acid on the gold nanoparticles-modified glassy carbon electrode

A new gold nanoparticles-modified electrode (GNP/LC/GCE) was fabricated by self-assembling gold nanoparticles to the surface of the l-cysteine-modified glassy carbon electrode. The modified electrode showed an excellent character for electrocatalytic oxidization of uric acid (UA) and ascorbic acid (AA) with a 0.306 V separation of both peaks, while the bare GC electrode only gave an overlapped and broad oxidation peak. The anodic currents of UA and AA on the modified electrode were 6- and 2.5-fold to that of the bare GCE, respectively. Using differential pulse voltammetry (DPV), a highly selective and simultaneous determination of UA and AA has been explored at the modified electrode. DPV peak currents of UA and AA increased linearly with their concentration at the range of 6.0 × 10⁻⁷ to 8.5 × 10⁻⁴ mol L⁻¹ and 8.0 × 10⁻⁶ to 5.5 × 10⁻³ mol L⁻¹, respectively. The proposed method was applied for the detection of UA and AA in human urine with satisfactory result.     

Kinetics of hydrogen oxidation reaction on Nafion-coated Pt/C electrodes under high overpotentials

The influences of the Nafion film thickness and Pt loading on the kinetics of the hydrogen oxidation reaction on Nafion-coated 20 wt% Pt/C electrodes immersed in 0.5 M H₂SO₄ were investigated using a rotating disk electrode configuration. The coating of a Nafion film (8 μm) had a negligible effect on the electrochemical surface area of an electrode. The kinetic parameters were estimated at an overpotential of 0.4 V; the values obtained were shown to vary with the method of data treatment. The diffusional resistance for H₂ in the Nafion film was negligible when the film was thinner than 0.2 μm. The permeability of H₂ in the Nafion film ranged from 2.4 × 10⁻⁵ to 4.8 × 10⁻⁵ mM cm²/s. The error analysis demonstrated that the apparent kinetic current estimated was resulted from experimental errors, instead of resulting from a chemical process as proposed by some previous investigators.     

Time resolved impedance spectroscopy as a probe of electrochemical kinetics: The ferro/ferricyanide redox reaction in the presence of anion adsorption on thin film gold

In this work, we use the time resolved technique of Fourier transform electrochemical impedance spectroscopy (FT-EIS) for quantitative kinetic analyses of Faradaic and nonfardaic, as well as heterogeneous and adsorption reactions. As a model system, we investigate the Fe(CN)₆^3−/4− redox reaction on a thin film Au electrode in the presence of nonfaradaically adsorbing ClO₄⁻ or Cl⁻ in neutral electrolytes. The redox process indicates a predominantly Faradaic outer sphere reaction, with nearly negligible adsorption of reactants on Au. dc voltage dependent kinetic parameters for both the anion and redox reactions are obtained by FT-EIS in real time during cyclic voltammetry. Equilibrium values of reaction rate constants, adsorption resistances and pseudocapacitances for the redox couple are also obtained. The theoretical background and working principles of these measurements are discussed, and the experimental findings are compared with previously published data.