Application of a Power Time Current to the Study of a Catalytic Mechanism in Chronopotentiometry and Reciprocal Derivative Chronopotentiometry. Advantages of a Cyclic Stationary Response

Abstract

This paper develops the theory for a pseudo-first order catalytic mechanism in chronopotentiometry with a power time current, I(t) ¼ I 0 t u (u ! À 1/2), applied to a spherical electrode of any size, and the advantages of the use of small electrodes and ultramicroelectrodes are discussed. The advantages of using a cyclic power time current to reach a stationary response suitable for characterizing a catalytic mechanism easily and accurately are reported. The reciprocal derivative (dt/dE À E) curves, which present peaks quantitatively related to the kinetic parameters of the chemical reaction, have been obtained from the potential-time responses. The influence of the homogeneous kinetic, the electrode radius and the power of time current in the achievement of a stationary response is analyzed. Methods for determining thermodynamic and kinetic parameters of the chemical reaction are proposed.

Theoretical and Experimental Study of the Homogeneous Catalytic Oxidation of Nicotinamide Adenine Dinucleotide (NADH) at Spherical Gold Electrodes Using Linear Sweep Voltammetry and Chronopotentiometry

“…Under steady state conditions, the general I À E curve for the process given in Scheme 2 is valid for any voltammetric or chronopotentiometric technique, in agreement with [6,9,10,15]. Thus, to obtain this expression we must impose the condition (k 1 þ k 2 )t ) 1, in such a way that for a spherical electrode of radius r 0 we obtain (see Appendix and [9, 10, 15 -17]):…”

“…Thus, for the former case (k D !1 , Eq. A3), we obtain the derivative curve given in Equation 19 of [9], whereas for irreversible processes (k D ( 1), the following expression is obtained (see Appendix):…”

“…k ox and k red are the electrochemical rate constants of oxidation and reduction heterogeneous processes, respectively. k 1 ' and k 2 ' are the chemical rate constants for the forward and backward catalytic step from which, by assuming an excess of species Z and Y in solution, we can define the corresponding pseudo-first order rate constants, This mechanism has been previously studied in voltammetry [14,15] and also in chronopotentiometry with different programmed currents [6,7,9,10] by considering that the charge transfer step is reversible. The solution corresponding to the above mechanism with non reversible electrochemical step when programmed currents of the form I(t) ¼ I 0 t u or I(t) ¼ I 0 e wt are applied to an spherical electrode of any radius r 0 , is given in Appendix.…”

“…Reciprocal derivative chronopotentiometry (RDCP) with programmed currents is a very useful technique for characterizing electrochemical steady state conditions [7,9,10,21]. This technique is based on the plotting of the dI/dE À E curves obtained from the experimental I À E ones, with I being the programmed current applied and E the measured potential.…”

“…Moreover, from the peak parameters it is possible to obtain quantitative information of the process under study in a very easy way [7,9,10,21].…”