Square-wave voltammetry for ECE mechanisms

Abstract

on other chemical reactions and especially on the luminescence of single pulses are necessary to elucidate the details of the chemical processes occurring during bubble nucleation and disto intensities below 3 W/cm2. Chemical effects at intensities of some IO W/cm2 have been observed by various authors, mainly by using transducers with a horn. It is not yet known quantitatively how the chemical yield responds to pulsing at these high intensities. Only two investigations at higher intensities have yet been carried out which showed that the time interval between pulses also determines the efficiency of the pulses under these condition^.^^^' .4cknowledgment. The authors thank Dr. Eberhard Janata for supported by Deutsche Forschungsgemeinschaft and Fonds der appearance in ultrasonic fields. The present studies were limited construction of the electronic equipment. This work wasIndustrie.The theory of square-wave voltammetry is extended to include the ECE mechanism in which an intermediate chemical step occurs between sequential electrode reactions. Exemplary calculations show how the thermodynamic and kinetic parameters of this mechanism affect the shapes of square-wave voltammograms. The theory is used with a nonlinear least-squares technique to obtain first-order rate constants for the chemical step of the reduction of p-nitrosophenol. This procedure discriminates against several experimental artifacts and does not require the usual separate determination of a normalization current. The rate constants obtained for the intermediate chemical step are 0.46 s-l at 25 "C, 2.40 s-' at 50 "C, and 17.3 s-I at 80 "C (12% uncertainty at 95% confidence) in good agreement with previous studies.

Surface ECE mechanism in protein film voltammetry—a theoretical study under conditions of square-wave voltammetry

“…This situation is commonly observed for electroactive molecules that can exist as more than one isomer; for example, cis and trans isomers of transition metal complexes, but it is also frequently met by some proteins and other important biomolecules [7,[13][14][15][16][17][18][19]. The features of the SW voltammetric responses in such scenario will significantly depend on the value of the chemical kinetic parameter l, but they will be also affected by the values of the electron transfer kinetic parameters K 1 and K 2 of the two reduction steps.…”

“…If we consider a surface electron transferchemical reaction (EC) mechanism for example, and if the product of the first electron step can be converted chemically to another electroactive specie, then we assign these reactions to follow the surface electron transfer-chemical reactionelectron transfer (ECE) mechanistic pathway. Although this reaction mechanism is quite complex, it is a widespread pathway of many proteins [7] and other important compounds in organic electrochemistry [1,7,[13][14][15][16][17][18][19]. For example, the product of the first electron transfer step can undergo protonation, elimination, substitution, or reorganization reaction to give second electroactive specie [1,[13][14][15][16][17][18][19].…”

“…Although this reaction mechanism is quite complex, it is a widespread pathway of many proteins [7] and other important compounds in organic electrochemistry [1,7,[13][14][15][16][17][18][19]. For example, the product of the first electron transfer step can undergo protonation, elimination, substitution, or reorganization reaction to give second electroactive specie [1,[13][14][15][16][17][18][19]. As the most familiar among the voltammetric techniques, the cyclic voltammetry is commonly used for characterization of electrochemically active systems following the ECE pathway [7, 13-16, 18, 19].…”

“…The numerical solutions in this work are adapted to the conditions of SWV. It is worth to mention that the initial theoretical considerations of an ECE mechanism under conditions of SWV, by redox reactions taking place from dissolved state, have been given by O'Dea et al [17].…”

Theoretical study of a surface electrode reaction preceded by a homogeneous chemical reaction under conditions of square-wave voltammetry

“…The SWV is capable to discriminate the charging current as well as to provide an insight into both half-electrode reactions, making this technique particularly suitable for studying the electrode mechanism [27][28][29][30][31][32][33][34][35]. Several electrode mechanisms involving chemical reactions under semi-infinite diffusion mass transfer in SWV have been studied by Osteryoung and OÕDea [2,4] and others [16][17][18][19][20]22,23]. Beside the diffusion controlled electrode reactions, significant attention has also been paid to the diffusionless electrode reactions, e.g., the surface electrode reactions [3,13,14,21,[24][25][26][28][29][30][31][32][33][34][35].…”