Chronopotentiometry of systems involving follow-up chemical reactions: Application of convolution and finite difference procedures

Abstract

Distortion of polarization curves by double layer charging severely limits the standard application of chronopotentiometry to mechanism and rate constant analysis of systems involving fast follow-up chemical reactions. A procedure is proposed to overcome these difficulties in the case of irreversible electrochemical-chemical processes (pure kinetic conditions). It starts with the extraction of the faradaic component, i f, of the imposed current and the computation of its convolution integral, I, with the function ( πt) −1/2. The i f- E and I-E are then simultaneously treated by a logarithmic analysis the form of which depends upon the expected mechanism. The efficiency of the method in mechanism and rate determination is illustrated experimentally on the example of the electrohydrodimerization of p-methylbenzylidene malononitrile for which discrimination between 32 possible limiting mechanisms has to be carried out. The same reaction is also used to test another type of analysis to be applied to partially reversible systems. Data processing then combines finite difference approach and convolution. It amounts to fitting the formal kinetics with the experimental data automatically in a small size computer avoiding tedious manual fitting with a priori calculated working curves. It is shown that the rate constants can be thus determined with a good accuracy even from single-step experiments.