Manuela López-Tenés

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.

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.

Application of the superposition principle to the study of CEC, CE, EC and catalytic mechanisms in cyclic chronopotentiometry. Part III

In this paper we have obtained the general analytical equations corresponding to the response of complicated charge transfer processes with coupled homogeneous chemical reactions in cyclic chronopotentiometry by applying the superposition principle. The analysis of different cycles of this response can be used to obtain accurate and contrasted values of kinetic parameters in each complex reaction scheme analysed. These parameters are of great interest for the chemist and the biochemist. These equations are also applicable to cyclic derivative chronopotentiometry which is a very useful method since the response is obtained with peaks in a similar way to cyclic voltammetry but its mathematical treatment is simpler.

Chronopotentiometry with a potential-exponential current-time function at the DME with a preceding blank period: Application to the study of higher order electrochemical reactions

Abstract The general theory for higher order electrochemical reactions with a current-time function of the form I ( t ) = I o t u e wt applied to a DME after a blank period t 1 , is presented. The existence intervals for the transition times, depending on the relative sign of the exponents u and w , are discussed. Methods for determining the forward reaction order and the kinetic parameters for irreversible processes are proposed. The expressions corresponding to the expanding plane electrode, the static mercury dropping electrode and the stationary plane electrode can also be deduced as particular cases of the equations obtained here.

Study of an EE mechanism using double potential step techniques

An analytical solution corresponding to the double potential step problem for a reversible EE mechanism is presented. This solution is applicable to any double pulse technique without restrictions on the duration of the first and second potential steps and is valid when several species are initially present in the solution. The influence of the duration of the two pulses on the characteristic of the current � /potential curves on differential and reverse double pulse techniques in static and dynamic electrodes is also discussed. # 2002 Elsevier Science B.V. All rights reserved.

Reversible multistep electrode processes. Consideration of the bulk presence of intermediate species and of the values of the diffusion coefficients in voltammetry

Analytical solutions for reversible multistep electrode processes in voltammetry with constant potential at planar electrodes whose areas increase with an arbitrary power of time and at spherical electrodes are presented. These solutions are valid when several or all species are initially present and, in the case of planar electrodes, when their diffusion coefficients are not necessarily equal. Interesting consequences and simplifications that clarify the experimental study of any multistep process can be deduced from these solutions.

Chronopotentiometry with several types of programmed current at most usual electrodes: General study of systems with coupled first-order chemical reactions

Abstract The general equations corresponding to CEC and catalytic processes when current-time functions of the forms I ( t ) = I 0 t u e wt and I ( t ) = I 0 ( t 1 + t ) v are applied to a DME were deduced taking into account the electrode sphericity and using a blank period t 1 . From these expressions we deduce as particular cases those corresponding to other types of electrodes (for example expanding plane electrode, static mercury dropping electrode and stationary plane electrode), other well-known current-time functions (power current, exponential current and step current), other reaction schemes (CE, EC and E mechanisms) and those cases in which the blank period is zero. Moreover, methods for determining heterogeneous and homogeneous kinetic parameters are proposed in each reaction scheme.

Reversible surface two-electron transfer reactions in square wave voltcoulommetry: application to the study of the reduction of polyoxometalate [PMo12O40]3- immobilized at a boron doped diamond electrode.

Reversible surface two-electrons transfer reactions (stepwise processes) are analyzed using square wave voltcoulommetry (SWVC), which is a variety of square wave techniques based on the measurement of the transferred charge. Such reversible surface redox processes are exhibited by many two-redox center and multicenter biomolecules (proteins, enzymes, ...) and inorganic molecules like polyoxometalates (POMs), which have very interesting applications, mainly as electrocatalysts. Because of the stationary character of the response obtained, the key parameters that govern the cooperativity degree of the two reversible electron transfers (ETs) are the difference between their formal potentials, ΔE(0), and the square wave amplitude, |E(SW)|, whose combined effect sets the two peaks → one peak transition in the response. Working curves based on the variation of the peak parameters (peak potentials, half-peak widths, and peak heights) with ΔE(0) and |E(SW)| are given, from which the formal potentials and the total surface excess can be accurately determined. SWVC has been applied to the study of the reduction of polyoxometalate [PMo12O40](3-) adsorbed at a boron doped diamond electrode (BDD), for which three stable and well-defined reversible charge peaks, corresponding to three cooperative EE processes, are obtained in the interval (0.6, -0.2) V by using low square wave frequencies. From the analysis of these peaks, the values of the total surface excess and the formal potentials of the six ETs have been obtained in aqueous media for two electrolytes: HClO4 and LiClO4.

Study of an EE mechanism in additive differential pulse techniques

Additive differential pulse techniques are applied to the study of a reversible EE mechanism. Analytical solutions are obtained in additive differential normal pulse voltammetry (ADNPV) and in additive differential pulse voltammetry (ADPV). The usefulness of these techniques in obtaining accurate simultaneous determinations of the formal potentials of both electrochemical steps when they are not completely separated is discussed and also applied to the study of the reduction of pyrazine in aqueous acid media. Excellent agreement between experimental results and theoretical predictions has been found.

Derivation of a general theory for reversible multistep electrode processes in voltammetry with constant potential at spherical electrodes

The rigorous theory for a reversible multistep electrode process in voltammetry with constant potential at spherical electrodes is derived. The expressions for the surface concentrations, the concentration profiles of species participating in the different steps and the current as a function of time have been deduced. These expressions are valid for any number of steps in which the initial species is oxidized/reduced, whatever the relative values of the formal potentials of the different steps and for any electrode radius value, including plane electrodes and ultra-microelectrodes.