Apparent Charge Transfer Coefficient Research Articles

A brief study on the kinetic of the voltammetric behavior of the modified carbon paste electrode with NiO nanoparticles towards loratadine as a carboxylate-amidic drug compound

A carbon paste electrode (CPE) was modified by NiO nanoparticles (NPs). NiO NPs were synthesized by the sol-gel method and characterized by XRD and SEM-EDX techniques. The non-calcined NiO NPs and the calcined one at 200 °C showed an amorphous phase. The calcined sample’s grain size was estimated at 36 and 42 nm by applying the Scherer and Williamson-Hall equations, respectively. Cyclic voltammogram (CV) of the NiO-CPE showed an irreversible response with a peak separation of 320 mV in 0.1 M NaOH. The peak current was improved by the addition of loratadine (Lor). The apparent charge transfer coefficients of αa and αc were 0.56 and 0.32, and the rate-constant values (ks) were 0.068 and 0.01 s−1 for the anodic and cathodic directions from the CV results, respectively. The diffusion coefficient (D) was estimated 1.48 × 10−8 cm2 s−1 for the Lor analyte. The modified electrode had a geometric surface area of about 0.0314 cm2 and the effective one of about 0.2 cm2.

Identification of Mechanistic Subtleties that Apply to Voltammetric Studies at Boron-Doped Diamond Electrodes

The α-[S2W18O62]4–/5– and α-[S2W18O62]5–/6– polyoxometalate (POM) reduction processes at boron-doped diamond (BDD) disk electrodes in acetonitrile (0.50 M [n-Bu4N][PF6]) have been investigated using large-amplitude Fourier transformed alternating current (FTAC) voltammetry. The origins of subtle differences in experimental data and simulated data modeled assuming the Butler–Volmer relationship with ion-paring implicitly included, planar diffusion and a uniform surface are considered. Parameters estimated are the apparent heterogeneous electron-transfer kinetics (kapp0′), apparent formal reversible potential (Eapp0′), and apparent charge transfer coefficient (αapp′). The electrode kinetic parameters, in contrast to theoretical predictions of the model employed, are dependent on frequency, POM concentration, and the data analysis method. Reasons for nonconformance to the model include the adsorption of POM on graphite-like sp2-bonded carbon impurities, limitations in the availability of charge carriers in BDD, and the method of incorporating ion pairing when slow electrode kinetics apply. Masking of the sp2 carbon-rich (edge) region of the BDD disk provided FTAC voltammetric data that complied much more closely with the simulated data. Nevertheless, data analysis still produces a concentration dependence in the estimated kapp0′ values, which is considered in terms of the assumption of an infinite number of charge carriers. Conclusions derived from this study are likely to be generally applicable to electrode kinetic investigations at BDD electrodes.

Immobilization of functionalized iron(II) clathrochelates with terminal (poly)aromatic group(s) on carbonaceous materials and their detailed cyclic voltammetry study

The detailed cyclic voltammetry (CV) study of the iron(II) clathrochelates with one, two or six terminal (poly)aromatic group(s) in a wide range of scan rate of the potential using glassy carbon (GC) and Pt working electrodes was performed. Their CVs contain the single one-electron quasireversible Fe2+/+ reduction wave in the cathodic potential range and one or two oxidation waves in the anodic range, assigned to a metal-centered Fe2+/3+ process and to oxidation of their polyaromatic terminal group(s). The potentials of both the reduction Fe2+/+ and oxidation Fe2+/3+ processes are shifted in the cathodic range as compared with their halogenoclathrochelate precursors and the values of shifts are substantially affected by a material of the working electrode; the electrochemical characteristics of the metal-centered waves suggest their diffusion-controlled character. Plots of the current peaks versus υ1/2 for the second anodic waves suggest a more complex diffusion – kinetic controlled character of these oxidations; for the dipyrenyl-terminated cage complex, the plots of the peak potentials versus lnυ allowed to obtain the corresponding average values of the apparent charge transfer coefficient α for both these electrodes, which are evidenced a very slow rate and irreversible character of this redox process. CVs of the hexafunctionalized clathrochelates contain an additional peak between the first and second (or after the second) anodic oxidation waves, an intensity of which linearly depends on a scan rate; the shapes of these CVs and the presence of an additional oxidation wave or plateau suggest their strong adsorption. The quantitative data about the physical adsorption of the iron(II) clathrochelate on activated carbon (AC) and reduced graphene oxide (RGO) were obtained. Using UV–vis spectral method; the Langmuir adsorption isotherms were used to calculate the corresponding adsorption equilibrium constants K. The observed changes of a free Gibbs energy are characteristic of the processes of physical adsorption via the stacking and Van-der-Waals interactions. Their limiting adsorption on AC decreases with increase in the number of the polyaromatic group(s) per a molecule from approximately 3·10−4 to 5.65·10−5 mol l−1, whereas in the case of RGO as an adsorbent that increases from 2.57·10−4 to 3.16·10−1 mol l−1. Values of K for AC also decrease with their number, while in the case of RGO as a substrate, its maximal value was observed for the difunctionalized iron(II) cage complex. Therefore, the physical adsorption of these clathrochelates is a structure-dependent process, which is strongly affected by the number of the functionalizing substituents at a cage framework. The value of K is determined by energy of the supramolecular binding of an adsorbate to an adsorbent. In the case of the diphenanttheryl-terminated iron(II) cage complex, its supramolecular binding with a surface of AC is stronger, thus suggesting a higher adsorption energy, while the hexafunctionalized cage complex forms the more strong supramolecular assemblies on a surface of RGO. This effect is explained by the presence of wedge-shaped pores in a macrostructure of RGO, both the size and the form of which is favorable for the physical adsorption of bulky molecules of the hexaphenanthrenyl-terminated macrobicyclic complex, while the size and the form of mesopores of AC are favorable for that of the difunctionalized iron(II) clathrochelate.

H3PO3 electrochemical behaviour on a bulk Pt electrode: adsorption and oxidation kinetics

Polybenzimidazole-type polymer doped with H3PO4 is commonly used as the proton-conductive phase in high-temperature proton-exchange membrane fuel cells. However, H3PO4 is not stable during fuel cell operation and undergoes reduction by hydrogen on a Pt surface to phosphorus compounds in a lower oxidation state, such as H3PO3. In this work the kinetics of H3PO3 oxidation on Pt electrode was studied, including an investigation of H4P2O6 as a possible oxidation intermediate. H3PO3 adsorption in hydrogen underpotential deposition region was described by a triple Langmuir isotherm corresponding to adsorption on specific Pt crystalline planes. Co-adsorption of hydrogen as well as SO42−, HSO4− ions decreased the total amount of adsorbed H3PO3. The determined apparent charge transfer coefficients of H3PO3 anodic oxidation on a metallic Pt surface were found to be concentration and temperature-dependent, indicating that the nature of the anodic process is complex. From chronopotentiometric measurements of H3PO3 and H4P2O6 oxidation on a preoxidised Pt surface it was concluded that, while H3PO3 is oxidised by means of a chemical reaction with PtOx, H4P2O6 undegoes anodic oxidation on the PtOx surface. According to voltammetry and bulk electrolysis experiments H4P2O6 is not formed as an intermediate product during electrochemical oxidation of H3PO3 on a metallic Pt surface.

Unraveling the Nonideal Recombination Kinetics in Cobalt Complex Based Dye Sensitized Solar Cells: Impacts of Electron Lifetime and the Distribution of Electron Density

Kinetics of the recombination at TiO2/dye/electrolyte interfaces is vital to establish reliable strategy for reducing energy loss in dye sensitized solar cell (DSCs). The semilogarithmic plots of open circuit voltage–light intensity indicate that the DSCs exhibit different recombination behaviors in high and low voltage regions. Even so, the average orders of recombination reaction in the two regions are both found to be expressed as the summation of the apparent charge transfer coefficient and the averaged density distribution parameter. This statement is based upon the fact that the “steady-state” electron lifetimes in cobalt complex based DSCs are well interpreted by using the Butler–Volmer model. Combining the results of electron lifetime, the order of recombination reaction, and density distribution, we addressed that the dominant pathway of recombination in cobalt complex based DSCs is via the trapping states rather than the conduction band. In addition, the variation of the Fermi level in TiO2 film...

Modeling dendrite growth during lithium electrodeposition at sub-ambient temperature

Increased propensity for dendritic lithium electrodeposition during sub-ambient temperature operation has been widely reported in lithium battery systems, yet is not fully understood. In the present paper, a mathematical model is developed to quantify the dendritic growth rate during lithium electrodeposition at sub-ambient temperature. This model builds on a diffusion–reaction framework presented recently by Akolkar [J. Power Sources 232 (2013) 23–28]. Using a steady-state diffusion model with a concentration-dependent diffusion coefficient, the lithium-ion concentration depletion in the stagnant Nernst diffusion boundary layer near the lithium surface is modeled. A surface electrochemical reaction model is then employed to correlate the lithium concentration depletion to the dendrite growth rate. Temperature effects on the lithium-ion transport and its electrochemical surface reaction are incorporated in the model via an Arrhenius-type temperature-dependence of the diffusion coefficient and the apparent charge transfer coefficient. It is shown that lowering the system temperature has the effect of increasing the lithium-ion diffusion resistance and decreasing the surface film thickness – conditions favorable for the formation of dendrites during lithium electrodeposition.

Electrochemical impedance spectroscopy study of the oxygen evolution reaction on a gas-evolving anode composed of lead dioxide microfibers

The oxygen evolution reaction (OER) during the electrolysis of electrolyte-free water on a gas-evolving anode composed of lead dioxide microfibers (MF-β-PbO2) was studied in a solid polymer electrolyte cell using the electrochemical impedance spectroscopy (EIS) technique. EIS spectra were recorded as a function of the overpotential for the OER. Impedance spectra characterized by two time constants distributed in the low and high frequency domains indicated that both the charge transfer and adsorption of reaction intermediates affect the electrode kinetics. In addition, it was verified that morphological aspects do not comprise the main cause for the time constant observed in the high frequency domain. In trying to interpret the EIS findings, a transfer function was derived for the electrode mechanism of Pavlov and Monahov in order to permit the evaluation of the adsorption pseudocapacitance, the double-layer capacitance and the charge transfer and adsorption resistances. It was verified that the adsorption pseudocapacitance is potential-dependent while the double-layer capacitance is almost potential-independent. It was also verified that the adsorption resistance decreases exponentially upon increasing the overpotential, exhibiting Tafel-like behavior. The apparent charge transfer coefficient, the exchange current density and the kinetic rate constant were evaluated from the impedance data.

Influência das condições de resfriamento sobre as propriedades superficiais e eletroquímicas de anodos dimensionalmente estáveis

Surface and electrochemical properties of the dimensionally stable anode Ti/(Ru0.3Ti0.7)O2 were studied as a function of the annealing temperature using different conditions in order to perform the cooling process of the oxide films (conventional thermal shock and the slow cooling processes). It was found that surface and electrochemical properties for the oxygen evolution reaction are both affected through the cooling process, being the electrode prepared at 400 oC using the slow cooling process the less susceptible to wear. The Tafel slope obtained in the high overpotential domain was analysed in light of the apparent charge transfer coefficient.

Influence of lead dioxide electrodes morphology on kinetics and current efficiency of oxygen-ozone evolution reactions

AbstractInfluence of electrode morphology on electrochemical properties of lead dioxide electrodes (β-PbO2) for oxygen-ozone evolution reactions in acid medium was investigated using scanning electronic microscopy (SEM), cyclic voltammetry (CV), polarization curves (PC), and determination of the current efficiency (Φ). Experimental findings revealed that application of high electrodeposition current densities furnishes more rough β-PbO2 films. Surface characteristics were verified by SEM images and the analysis of interfacial pseudo-capacitances and morphology factor (φ). Kinetic study of the overall electrode process (O2 + O3) based on the analysis of the Tafel slope revealed that the electrode morphology and electrolyte composition considerably affect the electrode kinetics. In most cases, the existence of two Tafel slopes distributed in the low and high overpotential domains was observed. Abnormal Tafel slopes (b ≠ 120 mV) obtained for the primary water discharge step during water electrolysis were interpreted considering the apparent charge transfer coefficient (α apa). Optimum conditions for the ozone production were obtained for the less rough β-PbO2 electrode immersed in a sulfuric acid solution (1.0 mol dm−3) containing KPF6 (30 × 10−3 mol dm−3), where the current efficiency of 15 mass % for the ozone production was obtained.

Electrocatalytic dechlorination of a PCB congener at a palladized granular-graphite-packed electrode: Reaction equilibrium and mechanism

Our previous study on the electrocatalytic dechlorination of 2-chlorobiphenyl at a Pd-loaded granular graphite-packed electrode demonstrated that the process did not follow the first-order kinetics. The rate constant varied with the applied potential at the beginning, but later became irrelevant to the potential. The electrocatalytic kinetic was investigated in this study, in which several experiments were conducted to dechlorinate 2-chlorobiphenyl using a Pd-loaded granular graphite-packed electrode at different potentials and in methanol–water solutions. Analysis of the experimental results reveals that the electrocatalytic process had reached equilibrium in these experiments. The apparent equilibrium constants, as well as the rate constants for the overall forward and backward reactions, were related to the applied potential. These relationships follow the Tafel equation, but the apparent charge transfer coefficients are very small values. The potential dependence of the overall rate constants suggests a reaction mechanism in which the electrocatalytic reaction is the rate-determining step. The influence of methanol on (together with the potential dependence of) the overall rate constants and the apparent equilibrium constant suggests a Langmuir–Hinshelwood mechanism.

Impact of Nonuniform Potential in SOFC Composite Cathodes on the Determination of Electrochemical Kinetic Parameters: A Numerical Analysis

Engineering of porous solid oxide fuel cell (SOFC) composite cathodes comprising a mixture of electrocatalyst and ionic conductor requires the knowledge of electrochemical kinetic parameters such as the reaction order and the charge-transfer coefficients. Conventional dc techniques are commonly employed in electrochemical measurements for composite cathodes. The results are often analyzed in terms of the low-or high-field approximations of the Butler–Volmer equation, which is based on the assumption that no potential or overpotential gradients exist within the electrode. In this study, numerical simulation of lanthanum strontium manganate–yttria-stabilized zirconia composite cathode was performed with an assumed oxygen reduction reaction mechanism and corresponding electrochemical kinetic parameters. The simulation results indicated that for composite cathodes significant gradients in the overpotential exist. The apparent reaction order and apparent charge-transfer coefficients, derived on the basis of nominal overpotential and net current, the two quantities that are typically accessible experimentally, were significantly different than the actual kinetic parameters used in the simulation. The extent of the variation between the actual and apparent electrochemical kinetics parameters was found to be dependent on the thickness and microstructure of the composite cathode. Simulation of conventional cathodes, which had no potential gradients within the bulk of the cathode, showed no errors.

Effect of Albumin on Underpotential Lead Deposition and Stripping on Ag‐RDE

AbstractThe effects of adsorption of bovine serum albumin (BSA) on the electrodeposition and stripping of Pb‐adatoms at a Ag‐RDE in acetate buffer solutions have been studied. The adsorbed BSA molecules have been found to inhibit the lead adsorption process. A decrease in the apparent charge transfer coefficient α for Pb‐adatom desorption from 0.39 to 0.34 in the presence of adsorbed BSA molecules has been attributed to the electric field screening by multiply charged BSA in the adsorption film, since no major lateral interactions between Pb and BSA have been observed. The kinetics of BSA adsorption on a Ag‐RDE was followed by Pb‐adatom probe technique in the range of low BSA coverage, 0<θBSA<0.4. The adsorption (k1) and desorption (k−1) rate constants were determined as follows: k1=2.42×10−4 cm/s, k−1=1.12×10−14 mol cm−2 s−1. The equilibrium constant for BSA adsorption on Ag electrode from 3×10−8 M BSA solution, also determined from the Pb‐adatom probe method, was: Kads=2.17×107 L/mol and the corresponding Gibbs free energy of adsorption: ΔG°ads=−9.99 kcal/mol (−41.85 kJ/mol). The formation of BSA films on Ag electrodes has been confirmed by EQCN mass transients and AFM imaging. It follows from these experiments that BSA molecules adsorb in horizontal orientation and form a film on Ag with 4 nm thickness.

The kinetics of electroreduction of peroxodisulfate ions on single crystal cadmium and bismuth electrodes

The electroreduction of the peroxodisulfate anions on the electrochemically polished (EP) Cd(0 0 0 1), Bi(1 1 1) and Bi ( 0 1 1 ¯ ) planes has been studied by cyclic voltammetry, rotating disc electrode and impedance methods. The rate constant values of the heterogeneous electroreduction reaction of the S 2 O 8 2 - anion on the EP Cd(0 0 0 1) and Bi( h k l) planes dependent on electrode polarisation and base electrolyte concentration have been calculated. The values of apparent transfer coefficient α app corrected for the double layer effect ( α app ⩽ 0.15) only very weakly depend on the electrode potential and base electrolyte concentration. The very low values of the apparent charge transfer coefficient for S 2 O 8 2 - electroreduction show that the activationless charge transfer mechanism is valid for EP Cd(0 0 0 1) and EP Bi( h k l) electrodes in various surface inactive base electrolyte solutions. This conclusion is in a good agreement with the theoretical models for the high hydrogen overvoltage metals based on the diabatic charge transfer mechanism from the metal to an ion [R.R. Nazmutdinov, D.V. Gluhov, O.A. Petrii, G.A. Tsirlina, G.N. Botikova, J. Electroanal. Chem. 552 (2003) 261].

Nanogravimetric study of templated copper deposition in ion-channels of self-assembled glutathione films on gold piezoelectrodes

The ionic permeation and discharge processes at a controllable-gate ion-channel electrode were investigated. The ionically transmissible films were formed on Au piezoelectrodes by surface modification performed using self-assembled monolayers (SAM) of glutathione (GS) molecules adsorbed onto gold. The gating state of a AuSG film was controlled by utilizing uncomplexed Cu 2+ ions acting as the controller cations through their interactions with terminal carboxylic groups of AuSG, which results in a conformational transition leading to the film ion-channel opening. The open-gate conformation of AuSG is stabilized by lowering the solution pH. Under these conditions, we were able to record Cu 2+ ion transport and discharge at a Au substrate surface accessible through the open ion gates. We have found that despite of a very limited space of this access, in the first stage of the Cu 0 deposition process, a Cu-upd on Au is formed, with LSV peak potential E p = 0.385 V versus Ag/AgCl, though the rate of upd formation is lower than that for a upd on an unmodified Au, as evidenced by the decrease in the Cu deposited mass and the deposition charge. The value of the apparent charge transfer coefficient α app is also smaller ( α app = 0.36 compared to 0.52 for bare Au). The 3D nucleation and growth of copper nanocrystals was observed using the potential step i– t and m– t transients. The size of Cu 0 nuclei at the beginning of their overlapping process was in the range of d = 2–3 nm, which is larger than the ion-channel height ( h ≈ 1.22 nm) determined for the open-gate conformation of AuSG. We found no dynamic film instabilities associated with fast potential step programs.

The kinetics of electroreduction of peroxodisulfate anion on electrochemically polished Cd(0 0 0 1) plane

The electroreduction of the peroxodisulfate anion on the electrochemically polished (EP) Cd(0 0 0 1) plane has been studied by cyclic voltammetry and rotating disc electrode methods. The rate constant of the heterogeneous electroreduction reaction of the S 2O 8 2− anion on the EP Cd(0 0 0 1) plane dependent on electrode polarisation and base electrolyte concentration has been established. The values of apparent transfer coefficient α app corrected for the double layer effect, noticeably lower than 0.5 for the EP Cd(0 0 0 1) plane, only very weakly depend on the electrode potential but noticeably on the electrolyte concentration, decreasing with the base electrolyte concentration. The very low values of the apparent charge transfer coefficient show that the activationless charge transfer mechanism is probably valid for EP Cd(0 0 0 1) | NaF+ Na 2 S 2 O 8 aqueous solution interface in a good agreement with the theoretical models for the high hydrogen overvoltage metals based on the diabatic charge transfer mechanism from the metal to an ion.

Simple kinetic models of ion transfer across an interface between two immiscible electrolyte solutions.: A comparison with experimental data

The Nernst–Planck equation is used to examine the kinetic behavior of three simple models of ion transfer, which all assume that the potential of mean force acting on the ion can be obtained as a superposition of the solvation potential and the electrical double layer potential. A comparison is made with the experimental kinetic data for 21 ion transfer reactions at the water/nitrobenzene interface. It is shown that only the models which account in an explicit way for the effect of the electrical double layer can provide a plausible description of experimental behavior. In particular, the absence of a correlation between the apparent standard rate constant or the apparent charge transfer coefficient and the standard Gibbs energy of ion transfer across the water/nitrobenzene interface can be due to the mutual compensation of the effect of electrical double layer and the effect of the difference in solvation energy on the ion transfer rate. It is concluded that a double layer correction is necessary to obtain true kinetic parameters of ion transfer across the interface.

Rate Constant for Ion Transfer in Inhomogeneous Media at the Interface of Immiscible Electrolytes

An expression for the impedance due to ion transfer across the interface of immiscible electrolyte solutions (ITIES) is derived, assuming a continuous change of the ionic resolvation energy across an interfacial layer. The model is analogous to the Goldman constant field approximation. The result is practically identical to the one obtained assuming an activated step occurs during the transfer, i.e., the classical Butler−Volmer relationship, so that the standard rate constant k0 in the Butler−Volmer theory is replaced by the quantity D/δ, where D is the average diffusion coefficient of the transferring ion inside the interfacial layer and δ is the thickness of the interfacial layer. At potentials close to the standard transfer potential, the apparent charge-transfer coefficient α takes the value of 1/2. Combination of the charge-transfer impedance and an inner layer capacitance in parallel gives a complete semicircle in an impedance plot, characteristic of a parallel RC circuit.

Electrode polarization at the Au, O 2(g)/Fe implanted yttria-stabilized zirconia interface

Ion implantation has been applied to modify the surface properties of yttria-stabilized zirconia (YSZ). A three-electrode cell was used for measuring steady state current-overpotential curves and for determining the electrode impedance. An increase of the equilibrium exchange current density at the Au, O 2(g)/yttria stabilized zirconia interface with a factor 10–50 has been observed after the implantation of 15 kV 56Fe up to a dose of 8 × 10 16 at.cm −2. This increase results from a broadening of the active surface area due to an increase in the electronic conductivity of the Fe implanted YSZ surface and from an increase of the fraction of coverage of the adsorbed oxygen molecules. The double layer capacitance of the Au, O 2,g/YSZ interface increases with a factor 10–100 after the Fe implantation. This is most likely due to the variable oxidation state of the implanted Fe ions, thus providing an additional way for charge accumulation. In comparison with the not implanted Au, O 2,g/YSZ interface no changes in the rate-determining steps of the oxygen exchange mechanism occur after Fe implantation. Similar apparent charge-transfer coefficients have been determined. A slight decrease in the oxygen partial pressure dependence of I o is observed. The experimental results can still be explained with a reaction model where the charge-transfer process is in competition with the surface diffusion of molecular adsorbed oxygen species along the noble metal-solid electrolyte interface. At cathodic and anodic overpotentials inductive effects appear at low frequencies in the impedance diagram. The inductive effects result from a charge-transfer mechanism where a step-wise transfer of electrons to adsorbed oxygen species takes place.

Effect of adsorbed neutral and ionic phenyl-substituted arsenic compounds on ion-transfer and electron-transfer reactions

The effect of adsorbed triphenyl arsine oxide, tetraphenylarsonium and methyl-triphenylarsonium cations on the kinetics of representative ion-transfer (ITR) and electron-transfer (ETR) reactions, viz. the reduction of Cd 2+ and CrO 2− 4 ions respectively, has been studied by the dc polarographic method. The dependence of the apparent rate constants and the apparent charge-transfer coefficients on the surfactant concentration was employed for the elucidation of the reaction mechanism. Finally, an attempt was made to determine the nature of the electronic transitions.

Determination of the kinetics of facilitated ion transfer reactions across the micro interface between two immiscible electrolyte solutions

The transfer of K+ from water to dichloroethane assisted by dibenzo-18-crown-6 has been studied at a liquid–liquid interface supported at the tip to a micropipette. The apparent electrochemical rate constant and apparent charge-transfer coefficient have been determined by analysis of the quasireversible steady-state wave observed. A kinetic model is proposed and the true electrochmical rate constant for the complexation reaction is thereby calculated.