Ángela Molina

Conditions of applicability of the superposition principle in potential multipulse techniques: implications in the study of microelectrodes

Abstract In this article we establish the necessary mathematical conditions for the superposition principle to be applicable to obtaining the faradaic response to a multipulse sequence on plane and spherical electrodes (whether increasing with time or not) and on cylindrical electrodes. These conditions have been partially established by some authors, but to date have not been derived in a rigorous and general form. The general expressions derived in this paper for the current I j corresponding to any pulse j are much simpler than those obtained previously in the literature for some specific cases and can easily be used in practice. To illustrate this, we apply these solutions to staircase and square-wave voltammetry. The effect of the size of the electrode on the final solution is also analysed.

Recent Advances in Voltammetry.

Recent progress in the theory and practice of voltammetry is surveyed and evaluated. The transformation over the last decade of the level of modelling and simulation of experiments has realised major advances such that electrochemical techniques can be fully developed and applied to real chemical problems of distinct complexity. This review focuses on the topic areas of: multistep electrochemical processes, voltammetry in ionic liquids, the development and interpretation of theories of electron transfer (Butler–Volmer and Marcus–Hush), advances in voltammetric pulse techniques, stochastic random walk models of diffusion, the influence of migration under conditions of low support, voltammetry at rough and porous electrodes, and nanoparticle electrochemistry. The review of the latter field encompasses both the study of nanoparticle-modified electrodes, including stripping voltammetry and the new technique of ‘nano-impacts’.

D.c. polarography: Current-potential curves for electrode processes involving a preceding first-order chemical reaction

Abstract An explicit equation, which is valid without any limitation in the magnitude of rate constant of the chemical reaction involved, is derived in a rigorous way, for the d.c. polarographic instantaneous (and average) current-potential curves with a c.e. mechanism accompanied by nernstian behaviour. On the basis of these equations, the range of validity of the steady state approximation is discussed.

General analytical solution for a catalytic mechanism in potential step techniques at hemispherical microelectrodes : Applications to chronoamperometry, cyclic staircase voltammetry and cyclic linear sweep voltammetry

An easy, general analytical solution, applicable to any multipotential step technique for a catalytic process in planar and spherical electrodes (including ultramicrohemispheres), is presented. The solution has been deduced rigorously using the mathematical method described by Molina (A. Molina, J. Electroanal. Chem. 443 (1998) 163) based on the application of the superposition principle. In this paper it has been applied to multistep chronoamperometry, cyclic staircase voltammetry (CSCV) and cyclic linear sweep voltammetry (CLSV) by analysing the influence of the electrode radius and the equilibrium and rate chemical constants over the different I/t and I/E responses. Different voltammetric steady states (kinetic, microgeometrical and geometrical-kinetic) can be distinguished and methods for calculating the kinetic parameters of the chemical reaction are also proposed. In the case of an irreversible chemical reaction in linear sweep voltammetry our results are in agreement with those recently deduced by Diao and Zhang (G. Diao, Z. Zhang, J. Electroanal. Chem. 429 (1997) 67).

Derivative and Differential Voltammetry and Reciprocal Derivative Chronopotentiometry Identical Behavior Verification for Electrode Reversible Processes

In the present paper, we carry out the experimental verification of the analogy between the responses obtained in derivative and differential voltammetric techniques and those corresponding to a new modality of the reciprocal derivative chronopotentiometric techniques using a programmed current of the form I(t) = I 0 t u with u ≥ - 1/2. Identical information can be obtained from derivative voltammetry and reciprocal derivative chronopotentiometry although the experimental application of the latter is simpler and signals obtained are less noise influenced due to the use of programmed current. In order to show the above mentioned analogy in the case of reversible electrode processes, we have carried out an experimental study of the systems Fe(C 2 O 4 ) 3 3 in 0.2 M K 2 C 2 O 4 (pH 4.49) at a static mercury drop electrode and ferrocene in CH 3 CN/0.25 M PF 6 NBu 4 at a Pt electrode.

Differential pulse voltammetry for ion transfer at liquid membranes with two polarized interfaces.

A simple analytical expression for the response of the double-pulse technique differential pulse voltammetry (DPV) corresponding to ion transfer processes in systems with two liquid/liquid polarizable interfaces has been deduced. This expression predicts lower and wider curves than those obtained with a membrane system with a single polarizable interface. Moreover, the peak potential of these systems is shifted 13 mV from the half-wave membrane potential. We have applied this expression to study the ion transfer of drugs with different pharmacological activities (verapamil, clomipramine, tacrine, and imipramine), at a solvent polymeric membrane ion sensor.

Pulse Voltammetry in Physical Electrochemistry and Electroanalysis

Introduction.- Single Potential Step Voltammetry.- Double and Triple Potential Step Techniques.- Multipotential Step Voltammetry.- Linear and Cyclic Sweep Voltammetry.

General solutions for the I/t response for reversible processes in the presence of product in a multipotential step experiment at planar and spherical electrodes whose areas increase with any power of time

Abstract General explicit expressions are presented for the current I p corresponding to the p th step of any sequence of potential steps E 1 , E 2 ,…, E p , when both oxidised and reduced species are present initially. These equations are applicable to reversible processes at planar and spherical electrodes whose areas increase with any power of time ( A ( t )= A 0 t z , z =0 for planar and spherical static electrodes and microelectrodes, and z =2/3 for the DME). For an SMDE we have also considered those situations in which the diffusion coefficient values of both species are not equal and the reaction product is amalgamated initially into the electrode. As an example of the application of these equations, we have analysed the influence of the presence of the reaction product in multistep chronoamperometry for an SMDE and also when microhemispheres are used by considering that the diffusion coefficients are equal and the product is soluble in the electrolytic solution. All equations are applicable to any single, double or multipotential step techniques and also to linear sweep and cyclic voltammetry and polarography.

Theory for cyclic reciprocal derivative chronopotentiometry with power and exponential programmed currents applied to electrodes coated with reversible electroactive molecular films

Theoretical expressions corresponding to the responses of adsorbed redox molecules exhibiting reversible charge transfer in cyclic reciprocal derivative chronopotentiometry with programmed currents of the form I(t) ( 1) i 1 I0t i and I(t)(1) i 1I0 e vti are presented. The effects of the interfacial potential distribution are considered in both cases by using the Smith and White model (Anal. Chem. 64 (1992) 2398). These equations become those previously deduced by Honeychurch (J. Electroanal. Chem. 445 (1998) 63) in reciprocal derivative chronopotentiometry with constant current on making u 0a ndv 0. The total analogy between the reciprocal derivative chronopotentiograms (dt i 1 :dE versus E or d e vti :dE versus E curves) and the cyclic voltammograms (I:E curves) is proved.

Study of multistep electrode processes in double potential step techniques at spherical electrodes

Analytical solutions for reversible multistep electrode processes in double potential step techniques at spherical electrodes of any size, including plane electrodes and ultra-microelectrodes, are derived. These solutions are valid when the diffusion coefficients of all species are equal, and they are applicable for any number of the species initially present in the solution, for any values of the formal potentials of the different steps and for any duration of the two potential steps. In differential pulse voltammetry (DPV) and in additive differential pulse voltammetry (ADPV) the effects of the applied potential and of the electrode sphericity on the current are found to be separable and, therefore, the position of the peaks and the cross potentials are not dependent on the size of the electrode. The convenience of using ADPV in determining the formal potentials when some electrochemical steps are not completely separated is shown. It is also demonstrated that the reproportionation/disproportionation homogeneous reactions have no effect either on the surface concentrations nor on the currents in any multipotential step technique under the conditions considered here.