Simulation Of Cyclic Voltammograms Research Articles

Potential program invariant representation of diffusion-adsorption related voltammograms and impedance spectra

A theory is presented by which voltammograms, and dynamic electrochemical impedance spectroscopy (dEIS) measurements of diffusion-hindered adsorption processes can be analyzed. By the proposed procedure, from a set of voltammograms, taken at varied scan-rates, parameters of the kinetics and isotherm of the adsorption can be calculated. These are scan-rate independent functions of potential. The theory also comprises the analysis of the high frequency impedance spectra of the same system, which have been measured during dynamic conditions, i.e., during potential scans. The properties of the analysis are illustrated by transformation of simulated cyclic voltammograms. The presented theory is a synthesis of previous ones on diffusion-controlled charge transfer and on adsorption. The theory supports the determination of rate coefficients as a function of electrode potential from fast dEIS measurements.

Establishing zone regions in cyclic voltammetry using unsupervised machine learning

Cyclic voltammetry is widely used to establish mechanistic details associated with electrode processes. Commonly, an experienced electrochemist manually seeks to identify key feature maps to create zones of parameters present in simulated cyclic voltammograms that mimic features observed experimentally over a range of scan rates and concentrations. In this study, as an alternative to this tedious approach, an automated K-means time series clustering algorithm is applied as a form of unsupervised machine learning to sort and classify voltammetric information. In order to establish advantages and limitations of the K-means clustering approach, extensive simulations of six commonly encountered electrochemical reaction mechanisms using a wide range of parameters have been undertaken to generate zone regions relevant to each example. The K-means time series clustering together with a dynamic time warping metric successfully sort the simulated data into logical groups based on the features present.

Effects of Voltage-Dependence of the Constant Phase Element and Ohmic Parameters in the Modeling and Simulation of Cyclic Voltammograms

Although the constant phase element (CPE) parameters have been found to vary with DC bias voltage in electrochemical impedance spectroscopy measurement, to date, the CPE parameters are assumed to be constant within the voltage window in cyclic voltammetry (CV) simulation. This leads to failure in predicting the voltammetric response of a double layer in some cases. In this study, the voltage-dependent CPE and ohmic parameters are used to simulate the capacitive current. The results show good agreement with the experimental measurements of commercial electrical double layer capacitors. The model is extended to predict the response of a system involving both Faradaic and capacitive currents by combining the conventional physicochemical transport model with circuit analysis to include effects of the resistances and CPE. To accurately predict the entire CV responses, a modified Randles circuit with an additional resistance connected in series with the CPE is proposed to be an equivalent circuit of the system. Furthermore, the closed-form analytical solution of the time-domain response of CPE under CV conditions is also derived and presented to gain better understanding of the CPE response. Using the derived equation, CV can serve as an alternative approach for determining the CPE parameters.

Theoretical Analysis of a Surface Catalytic Mechanism Associated with Reversible Chemical Reaction Under Conditions of Cyclic Staircase Voltammetry

AbstractIn this work, we present theoretical results in cyclic staircase voltammetry of a surface catalytic mechanism that features reversible chemical step, the so‐called “surface catalytic ECrev’ mechanism”. We consider specific surface regenerative mechanism, in which both of the electro‐inactive substrates are present in large excess in electrochemical cell from the beginning of the experiment. The chemical reversibility brings at this mechanism more complexity in respect to the features of well‐elaborated surface catalytic EC’ mechanism coupled with chemically irreversible regenerative reaction. As we present plenty of simulated cyclic voltammograms, we also propose methods to get insight to kinetics and thermodynamics parameters relevant to chemical regenerative step. The elaboreted results can be important in analysing the kinetics and thermodynamics of many drug‐drug and drug‐DNA interactions, for example. In addition, with the results elaborated in this work we can access relevant information about the chemistry of important lipophilic enzymes studied in protein‐film voltammetry set up.

Ab Initio Cyclic Voltammetry on Cu(111), Cu(100) and Cu(110) in Acidic, Neutral and Alkaline Solutions.

Electrochemical reactions depend on the electrochemical interface between the electrode surfaces and the electrolytes. To control and advance electrochemical reactions there is a need to develop realistic simulation models of the electrochemical interface to understand the interface from an atomistic point-of-view. Here we present a method for obtaining thermodynamic realistic interface structures, a procedure we use to derive specific coverages and to obtain ab initio simulated cyclic voltammograms. As a case study, the method and procedure is applied in a matrix study of three Cu facets in three different electrolytes. The results have been validated by direct comparison to experimental cyclic voltammograms. The alkaline (NaOH) cyclic voltammograms are described by H* and OH*, while in neutral medium (KHCO3 ) the CO species are dominating and in acidic (KCl) the Cl* species prevail. An almost one-to-one mapping is observed from simulation to experiments giving an atomistic understanding of the interface structure of the Cu facets. Atomistic understanding of the interface at relevant eletrolyte conditions will further allow realistic modelling of electrochemical reactions of importance for future eletrocatalytic studies.

Electrochemistry of vanadium redox couples on nitrogen-doped carbon

The redox reaction of vanadium ions (V2+↔3+↔4+↔5+) on well-developed nitrogen-doped ordered mesoporous carbon (NOMC) was extensively investigated in different electrolyte solutions by electrochemical methods. It is found that both the electronic structure modulated by nitrogen doping and the enriched electrochemically active functional groups on NOMC favor the three electrochemical transitions between the adjacent couples, viz. V2+↔3+↔4+↔5+, as compared with Vulcan XC72 carbon black. Salient findings are as follows. First, the transition of V3+↔2+ is the same on the two distinctly different carbons, which indicates that this reaction is an outer-sphere charge transfer reaction. The concomitant hydrogen evolution reaction makes NOMC unsuitable to be used as a negative electrode material in flow batteries. Second, the transition of V5+↔4+ shows a quasi-reversible behavior, indicating that NOMC can be used as a positive electrode material. Simulation of cyclic voltammogram (CV) reveals that the standard rate constant and the adsorption equilibrium constant are (7.0 ± 0.9)*10−3 cm s−1 and 0.70 ± 0.09 (both V4+ and V5+), respectively. Third, the transition of V4+↔3+ is recognized in the CV curve, which proceeds in a quasi-reversible reaction. The preceding adsorption of the symmetrical ions (V3+) is found to play a key role in determining the kinetics. Finally, for the two latter transitions, the content of dopant nitrogen yields a negligible effect on the electrochemical activity, excluding the possibility of its direct involvement in electrocatalysis. The above findings not only reveal the applicability of the nitrogen-doped carbon to be used as an electrode material in flow batteries, but also offer an in-depth understanding of the reaction mechanism of vanadium redox couples.

A green strategy for the synthesis of sulfone derivatives of p-methylaminophenol: Kinetic evaluation and antibacterial susceptibility

This is one of the few examples in which the diverse products have been synthesized just by changing the applied potential. The synthesis of sulfonyl derivatives of p-methylaminophenol were carried out by reaction of the electrogenerated p-methylquinoneimine with sulfinic acids. Various types of mono (MSP), bis (BSP) and tris (TSP) sulfonyl p-methyl aminophenols were obtained by changing the electrode potential, in one pot under green conditions. The mono sulfonyl-p-(methylamino)phenol derivatives (MSP) were assessed for their in vitro antibacterial activity against the gram positive (Staphylococcus aureus) and gram negative (Escherichia coli) strains. It was found that the tested compounds were more active against Staphylococcus aureus than Escherichia coli. We also found that the antimicrobial activity of MSP derivatives to vary in the order MSP4 (R = CH3) > MSP1 (R = p-tolyl) ≈ MSP2 (R = phenyl) > MSP3 (R = p-ClC6H4). Moreover, the observed homogeneous rate constants (kobs) of the reaction of p-methyl quinoneimine with sulfinic acids were estimated in various pH values, based on the EC and ECEC mechanisms, by comparing the simulated cyclic voltammograms with the experimental ones.

Mechanism of the Br−/Br2 Redox Reaction on Platinum and Glassy Carbon Electrodes in Nitrobenzene by Cyclic Voltammetry

We report the determination of a complete mechanism for the Br−/Br2 reaction in nitrobenzene using simulations of cyclic voltammograms at platinum and glassy carbon macroelectrodes and platinum ultramicroelectrodes at varying scan rates (0.02–500V/s) and concentrations of Br−, Br3−, and Br2 (2.5–20mM). As in other nonaqueous solvents and ionic liquids, we observe two consecutive redox processes at lower and higher potentials that we assign to the Br−/Br3− and Br3−/Br2 redox reactions, respectively. A complete reaction mechanism, including the elementary steps of each process, was fit to the voltammetric data using DigiElch® simulation software. The model proposed here is different from previous models of halide reactions in nonaqueous solvents in three ways. First, it proposes the direct oxidation and reduction of Br3−, whereas previous models describe the reduction and oxidation of X3− as a CE process, with the dissociation of X3− into X− and X2 occurring first. Second, it is able to accurately match data at a wide range of scan rates and concentrations without the use of unrealistically large homogeneous rate constants. Finally, it can match data at platinum and glassy carbon electrodes by simply changing the apparent heterogeneous kinetics of the electron transfer reactions.

Computational Study of Fluorinated Diglyoxime-Iron Complexes: Tuning the Electrocatalytic Pathways for Hydrogen Evolution.

The ability to tune the properties of hydrogen-evolving molecular electrocatalysts is important for developing alternative energy sources. Fluorinated diglyoxime-iron complexes have been shown to evolve hydrogen at moderate overpotentials. Herein two such complexes, [(dAr(F)gBF2)2Fe(py)2], denoted A, and [(dAr(F)g2H-BF2)Fe(py)2], denoted B [dAr(F)g = bis(pentafluorophenyl-glyoximato); py = pyridine], are investigated with density functional theory calculations. B differs from A in that one BF2 bridge is replaced by a proton bridge of the form O-H-O. According to the calculations, the catalytic pathway for A involves two consecutive reduction steps, followed by protonation of an Fe(0) species to generate the active Fe(II)-hydride species. B is found to proceed via two parallel pathways, where one pathway is similar to that for A, and the additional pathway arises from protonation of the O-H-O bridge, followed by spontaneous reduction to an Fe(0) intermediate and intramolecular proton transfer from the ligand to the metal center or protonation by external acid to form the same active Fe(II)-hydride species. Simulated cyclic voltammograms (CVs) based on these mechanisms are in qualitative agreement with experimental CVs. The two parallel pathways identified for B arise from an equilibrium between the protonated and unprotonated ligand and result in two catalytic peaks in the CVs. The calculations predict that the relative probabilities for the two pathways, and therefore the relative magnitudes of the catalytic peaks, could be tuned by altering the pK(a) of the acid or the substituents on the ligands of the electrocatalyst. The ability to control the catalytic pathways through acid strength or ligand substituents is critical for designing more effective catalysts for energy conversion processes.

Does bromine atom-free radical (Br·) undergo a chemical reaction before dimerization to dibromine (Br2)? An electrochemical investigation

The important question, does bromine atom free radical, Br·, undergo a chemical reaction with a substrate before it dimerizes to dibromine Br2, is investigated through electrochemical oxidation of bromide ion Br−. Cyclic voltammetry and spectrophotometry were used as electro-oxidation and monitoring devices. Simulation of cyclic voltammogram was used to obtain information about the mechanism of electro-oxidation process as well as reaction with substrates. It is shown that the primary electro-oxidation product (PEOP) of Br−, Br· (bromine atom-free radical), reacts with chemicals like chloroform, glycine, cytosine, etc. It can also dimerize, for example in acetonitrile. Reactions of PEOP Br· with substrate chloroform, acetone, DNA components adenine, cytosine, thymine and amino acid glycine were studied and their kinetics are reported here.

Voltammetric behavior of 1- and 4-[S₂V(V)W₁₇O₆₂]⁵⁻ in acidified acetonitrile.

Data derived from a voltammetric and spectroscopic study of the V(V/IV) couple associated with the initial reduction of the Wells-Dawson-type mono vanadium-substituted polyoxometalates, 1- and 4-[S2V(V)W17O62](5-) in CH3CN as a function of CF3SO3H acid concentration have been obtained. (51)V NMR (V(V) component) and EPR (V(IV) component) spectra were measured in CH3CN in the presence and absence of an acid. These data showed a small fraction of the 1-isomer in the 4-[S2V(V)W17O62](5-) sample and that protonation could occur at both redox levels for both isomers. On the basis of the mechanism postulated from the voltammetric and spectroscopic data, simulations of cyclic voltammograms were undertaken for the reduction of the isomerically pure 1-[S2V(V)W17O62](5-) isomer over a wide acid concentration range, and the results were compared with experimental data. Cyclic voltammograms of the V(V/IV) couple derived from the reduction of 1- and 4-[X2V(V)W17O62](7-) (X = P, As) were also obtained in CH3CN and the results were compared with those for 1- and 4-[S2V(V)W17O62](5-). Reversible potentials for the V(V/IV) couple are dependent on the anion charge of the polyoxometalate. Analysis of cyclic voltammograms obtained for 1- and 4-[S2V(V)W17O62](5-) in acetonitrile, acetone, dimethyl sulfoxide, dimethyl formamide and nitromethane showed that these V(V/IV) reversible potentials are also dependent on the acceptor numbers and the polarity index (E(T)(N)) values of the organic solvents.

Electrochemical oxidation of catecholamines in the presence of aromatic amines: interplay between inter- and intramolecular nucleophilic addition

The reactions of electrochemically generated o-quinones from oxidation of catecholamines with aniline derivatives have been studied using cyclic voltammetry. There is a close and pH-dependent interplay between intra and intermolecular Michael addition reactions of side chain amine group of catecholamines and anilines toward the electrochemically generated o-quinone. The pH dependence of reactions has been studied and the condition for domination of each reaction was obtained. The observed homogeneous rate constants of reactions were estimated by digital simulation of cyclic voltammograms for each pathway. The reactivities and the rate constants of Michael addition of anilines depend on the electron-withdrawing character of their substituent, which have been studied quantitatively.

Estimation of diffusion coefficients from voltammetric signals by support vector and gaussian process regression.

BackgroundSupport vector regression (SVR) and Gaussian process regression (GPR) were used for the analysis of electroanalytical experimental data to estimate diffusion coefficients.ResultsFor simulated cyclic voltammograms based on the EC, Eqr, and EqrC mechanisms these regression algorithms in combination with nonlinear kernel/covariance functions yielded diffusion coefficients with higher accuracy as compared to the standard approach of calculating diffusion coefficients relying on the Nicholson-Shain equation. The level of accuracy achieved by SVR and GPR is virtually independent of the rate constants governing the respective reaction steps. Further, the reduction of high-dimensional voltammetric signals by manual selection of typical voltammetric peak features decreased the performance of both regression algorithms compared to a reduction by downsampling or principal component analysis. After training on simulated data sets, diffusion coefficients were estimated by the regression algorithms for experimental data comprising voltammetric signals for three organometallic complexes.ConclusionsEstimated diffusion coefficients closely matched the values determined by the parameter fitting method, but reduced the required computational time considerably for one of the reaction mechanisms. The automated processing of voltammograms according to the regression algorithms yields better results than the conventional analysis of peak-related data.

Structure and Spectroelectrochemical Response of Arene–Ruthenium and Arene–Osmium Complexes with Potentially Hemilabile Noninnocent Ligands

Nine of the compounds [M(L2–)(p-cymene)] (M = Ru, Os, L2– = 4,6-di-tert-butyl-N-aryl-o-amidophenolate) were prepared and structurally characterized (Ru complexes) as coordinatively unsaturated, formally 16 valence electron species. On L2–-ligand based oxidation to EPR-active iminosemiquinone radical complexes, the compounds seek to bind a donor atom (if available) from the N-aryl substituent, as structurally certified for thioether and selenoether functions, or from the donor solvent. Simulated cyclic voltammograms and spectroelectrochemistry at ambient and low temperatures in combination with DFT results confirm a square scheme behavior (ECEC mechanism) involving the Ln ligand as the main electron transfer site and the metal with fractional (δ) oxidation as the center for redox-activated coordination. Attempts to crystallize [Ru(Cym)(QSMe)](PF6) produced single crystals of [RuIII(QSMe•–)2](PF6) after apparent dissociation of the arene ligand.

Predicting the Electrochemical Behavior of Lithium Nitrite in Acetonitrile with Quantum Chemical Methods

Electrolyte stability is an essential prerequisite for the successful development of a rechargeable organic electrolyte Li-O2 battery. Lithium nitrate (LiNO3) salt was employed in our previous work because it was capable of stabilizing a solid-electrolyte interphase on the Li anode. The byproduct of this process is lithium nitrite (LiNO2), the fate of which in a Li-O2 battery is unknown. In this work, we employ density functional theory and coupled-cluster calculations combined with an implicit solvation model for neutral molecules and a mixed cluster/continuum model for single ions to understand the chemical and electrochemical behavior of LiNO2 in acetonitrile (AN). The redox potentials of oxygenated nitrogen compounds predicted in this study are in excellent agreement with the experimental results (the average accuracy is 0.10 V). Theoretical calculations suggest that the reaction between the nitrite ion and its first oxidation product, nitrogen dioxide (NO2), in AN solution proceeds via the initial formation of a trans-ONO-NO2 dimer that is subject to autoionization and the subsequent reaction of produced nitrosyl ion (NO(+)) with NO2(-). Good agreement between experimental and simulated cyclic voltammograms for electrochemical oxidation of LiNO2 in AN provides support to the proposed mechanism of coupled electrochemical and chemical reactions. The results suggest a possible mechanism of regeneration of LiNO3 in electrolyte in the presence of oxygen, which is uniquely possible under charging conditions in a Li-O2 battery.

Electrochemical reduction of phthalide at carbon cathodes in dimethylformamide: Effects of supporting electrolyte and gas chromatographic injector-port chemistry on the product distribution

Abstract Cyclic voltammetry and controlled-potential (bulk) electrolysis have been used to investigate the direct reduction of phthalide at carbon electrodes in dimethylformamide (DMF) containing 0.10 M tetramethylammonium perchlorate (TMAP) or tetra- n -butylammonium perchlorate (TBAP). Cyclic voltammograms recorded with a glassy carbon electrode exhibit a single cathodic peak and a corresponding anodic peak that arise, respectively, from one-electron reduction of phthalide to generate a radical-anion intermediate and from reoxidation of the intermediate. At a scan rate of 100 mV s −1 , quasi-reversible behavior is observed (due to ring-opening of the radical-anion), whereas fully reversible behavior is seen at 5 V s −1 or higher. Digital simulation of cyclic voltammograms indicates that the lifetime of the radical-anion is 3.5 s. Bulk electrolysis of phthalide at a reticulated vitreous carbon cathode affords products that depend on the procedure used to analyze the catholyte. Direct injection of catholyte into a gas chromatograph shows phthalide and a 2-methylbenzoate ester bearing an alkyl moiety from the supporting-electrolyte cation. However, if the catholyte is partitioned between diethyl ether and aqueous hydrochloric acid before gas chromatographic analysis, phthalide and 2-methylbenzoic acid are observed. Thermally induced reactions that occur in the injector port of the gas chromatograph are responsible for the formation of the 2-methylbenzoate ester as well as for the phthalide found in all electrolyzed solutions.

Voltammetric analysis of the possibility of derivatization of levodopa in the presence of aniline derivatives

Electrochemical oxidation of levodopa (LD) as one of the most well-known neurotransmitters has been studied in the presence of some aniline derivatives. The electron transfer of LD is followed by two competitive reactions in the presence of these amines. The reactions are the Michael additions of side chain amine group of LD and/or aromatic amines to electrochemically generated o-quinone. There are two ECE mechanisms for both pathways and the competition between these inter and intramolecular reactions drastically depends on the pH of the medium. The pH dependence of reactions has been studied and the observed homogeneous rate constants of the reactions were estimated by digital simulation of cyclic voltammograms. The effect of aniline substituents was also studied with regard to their reactivities toward o-quinone of LD and the competitive reactions. Based on the obtained results, the products of intermolecular reactions are electroactive diphenylamine derivatives and their half-wave potentials depend on the nature of the aniline substituent.

Global Analysis for the measurement of electrochemical parameters with cylindrical electrodes

Global Analysis is applied to simulated cyclic voltammograms obtained at electrodes with cylindrical geometry to calculate the characteristic transport, kinetic and thermodynamic parameters that describe the electron transfer process. The capacity to directly analyze for various electron transfer models is also demonstrated and the results indicate that the accuracy in obtaining the important transport, kinetic and thermodynamic parameters is excellent.

Facile determination of formal transfer potentials for hydrophilic alkali metal ions at water|ionic liquid microinterfaces

The formal transfer potentials of hydrophilic alkali metal ions Li(+), Na(+), K(+), Rb(+), and Cs(+) were determined at water|room temperature ionic liquid (w|RTIL) interfaces. A working curve for an interface held at the tip of a micropipette (25 μm in diameter) was developed through simulated cyclic voltammograms (CVs) via finite element analysis with Comsol Multiphysics software. This methodology takes advantage of the symmetric diffusion regime experienced at the w|RTIL micropipette interface between two immiscible electrolytic solutions (micro-ITIES) which generates peak-shaped waves in the forward and reverse scans similar to those in CVs obtained at large (centimeter scale) ITIES. Through the simulation a profile of IT was generated in order to construct the working curve from which, in conjunction with experimentally obtained CVs, the formal transfer potentials were extrapolated. The unique characteristics of diffusion at an interface utilizing a pulled capillary make this approach possible. Additionally, within the simulation the geometry can be tailored to approximate closely the actual physical and experimental conditions. In this way the formal transfer potentials of Li(+), Na(+), K(+), Rb(+), and Cs(+) were found to be 0.565, 0.548, 0.521, 0.531, and 518 V, respectively, at the interface between water and our extremely hydrophobic ionic liquid, trihexyltetradecylphosphonium tetrakis(pentafluorophenyl)borate. The implications of these constants towards the evaluation of metal ion extractions will also be discussed.

Experimental and Digital Simulation Studies of the Electrochemical Oxidation of the Metal Anion [CpW(CO)2(IMes)]−and the 17-Electron Metal Radical CpW(CO)2(IMes)•. Kinetics and Thermodynamics of Capture and Release of MeCN by a Metal Radical and a Metal Cation

The electrochemistry of [CpW(CO)2(IMes)]−[K(18-crown-6)]+ (Cp = η5-C5H5, IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), CpW(CO)2(IMes)•, and [CpW(CO)2(IMes)(MeCN)]+PF6– were studied by cyclic voltammetry in MeCN (0.2 M nBu4N+PF6–). The tungsten anion [CpW(CO)2(IMes)]− showed a fully reversible one-electron oxidation with E1/2 = −1.65 V vs Cp2Fe+/0. Oxidation of the resultant 17-electron radical CpW(CO)2(IMes)•was irreversible at all scan rates, affording the 18-electron solvent adduct [CpW(CO)2(IMes)(MeCN)]+. Reduction of [CpW(CO)2(IMes)(MeCN)]+ proceeded with loss of coordinated MeCN and was followed by a second reduction to generate [CpW(CO)2(IMes)]−. Simultaneous digital simulation of voltammograms of [CpW(CO)2(IMes)]− and CpW(CO)2(IMes)• over a range of scan rates and concentrations gave estimates for E° of −0.49 V for the [CpW(CO)2(IMes)]+/• couple and −1.92 V for the [CpW(CO)2(IMes)(MeCN)]+/• couple. The neutral 19-electron radical complex CpW(CO)2(IMes)(MeCN)• is a stronger reducing agent (by 1.42 V) than the unsolvated 17-electron radical CpW(CO)2(IMes)•. Binding of MeCN by the unsolvated 16-electron cation [CpW(CO)2(IMes)]+ is exergonic with Keq = 1.2 × 1011 M–1 for [CpW(CO)2(IMes)]+ + MeCN ⇌ [CpW(CO)2(IMes)(MeCN)]+. Expulsion of the MeCN ligand from the 19-electron complex CpW(CO)2(IMes)(MeCN)• is also exergonic, with Keq = 1.2 × 1013 M for CpW(CO)2(IMes)(MeCN)• ⇌ CpW(CO)2(IMes)• + MeCN. Experimental and simulated cyclic voltammograms also account for the chemical reduction of the metal cation [CpW(CO)2(IMes)(MeCN)]+ by the metal anion [CpW(CO)2(IMes)]−, which ultimately produces two equivalents of the metal-centered radical CpW(CO)2(IMes)•.