Marién M. Moreno

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.

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.

Reciprocal Derivative Chronopotentiometry with Programmed Current: Influence of the Reversibility

The behavior of the system Cd 2/Cd(Hg) in the absence and presence of an aliphatic alcohol in noncomplexing media is analyzed in reciprocal derivative and double derivative chronopotentiometry with programmed current (RDCP and RDDCP, respectively). These electrochemical methods have been compared with derivative and double derivative voltammetry (DV and DDV, respectively). When the above system behaves as non reversible, it is not possible to establish a total analogy between chronopotentiometric and voltammetric responses, contrary to the case of a reversible process. The peaks obtained in RDCP are better resolved than those obtained in DVand the different operational principles of RDCP compared to those of DV can reduce its susceptibility to ohmic drop effects. Moreover, RDCP and RDDCP are very versatile in the determination of kinetic parameters of electrode processes since, by varying the current amplitude and/or the power of time u in the programmed current, it is easy to influence the reversibility of the process.

Additive differential pulse voltammetry, instead of double differential pulse voltammetry

A new electrochemical double pulse potential technique called additive differential pulse voltammetry (ADPV) is proposed. This technique is inspired by the original idea of Birke et al. [Anal. Chem. 53 (1981) 852] of recording two differential pulse (DP) voltammograms and it consists of plotting the sum of these two signals versus the first pulse potential, although in this paper the proposal is to obtain the ADPV signal through just one experiment. ADPV behaves in an identical way to the triple-pulse technique double differential pulse voltammetry (DDPV) for reversible processes when diffusion coefficients are equal for spherical electrodes and for any value of diffusion coefficients in planar electrodes. In the case of reversible electrode processes with amalgamation of reaction product or other more complex processes, ADPV is more advantageous than DDPV. This is due, among other reasons, to the fact that, under these conditions, a double potential step is much simpler to analyse than a triple potential step.

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.