The surface catalytic mechanism: a comparative study with square-wave and staircase cyclic voltammetry

Abstract

A pseudo-first-order catalytic mechanism in which both reactant and product of a redox reaction are strongly immobilized on an electrode surface is theoretically analysed under conditions of square-wave (SWV) and staircase cyclic voltammetry (SCV). A mathematical procedure is developed under diffusionless conditions. The relationships between the properties of the voltammetric response and both the kinetic parameters of the redox reaction and the parameters of the excitation signal are studied. The phenomenon of the quasi-reversible maximum is discussed. A comparative study between SWV and SCV is presented and the limitations and advantages of both techniques, from analytical and kinetic points of view, are discussed. The theoretical predictions are experimentally confirmed by the redox reaction of azobenzene in the presence of hydrogen peroxide as an oxidizing agent.

Catalytic mechanism in successive two-step protein-film voltammetry—Theoretical study in square-wave voltammetry

“…In addition to the kinetic parameters γ, K 1 and K 2 , the features of the calculated SW voltammograms of the protein-film EEC′ mechanisms depend also on the number of exchanged electrons in both steps n 1 and n 2 , the electron transfer coefficients α 1 and α 2 (for the sake of simplicity, it is assumed in the model that n = n 1 = n 2 = 1, and α = α 1 = α 2 = 0.5), the temperature T, and the potential modulation parameters (frequency-f, amplitude-E sw , and potential step ΔE). Similarly as by the simple surface EC′ mechanism [14,16,17,20,22,23,25,32], the features of the calculated SW voltammograms obtained for this specific surface EEC′ system strongly depend on the magnitude of the chemical (or catalytic) rate constant. Besides the rate of the catalytic reaction and kinetics of both electron transfer steps, the features of the theoretical SWV voltammograms of the surface EEC′ mechanism are strongly affected by one "virtual" thermodynamic parameter (E f ) defined as a potential difference in the standard redox potentials between both electron transfer steps, i.e.…”

“…Expectedly, the features of the first electrochemical step are not affected by the catalytic parameter γ. Under such circumstances, the behavior of the second electrochemical step of the protein-film EEC′ mechanism is equivalent to that of a simple surface catalytic EC′ reaction described elsewhere [17,25,32]. This holds true only if the kinetics of the first electrochemical step by the EEC′ mechanism is big enough in order to supply initial electroactive .…”

“…From an analytical point of view, this feature is quite an important advantage of the SWV over the other voltammetric techniques, because the parameters of the net-SW voltammograms get easily measurable even at very pronounced catalytic effects. This is not the case by catalytic mechanism studied with other voltammetric techniques [32]. More detailed elaboration of the effects of catalytic parameter γ to the features of calculated SW voltammograms can be found elsewhere [17,25,32].…”

“…This is not the case by catalytic mechanism studied with other voltammetric techniques [32]. More detailed elaboration of the effects of catalytic parameter γ to the features of calculated SW voltammograms can be found elsewhere [17,25,32].…”

“…The redox transformations of the aforementioned proteins can only be described by theoretical models considering successive two-step electron transfer. In the last few years, we started theoretical considerations of various redox mechanisms relevant to protein-film voltammetry, and we published scores of theoretical and experimental works in the past decade [17,21,22,25,[27][28][29][30][31][32][33][34]. In this paper we consider the surface catalytic mechanism that follows the two-step surface EE (electron-electron) redox reaction, which can be described by the following reaction scheme: The common designation of this complex protein-film redox mechanism in the electrochemical terminology is a surface EEC′, or surface EECat [13,14].…”