Quasireversible maximum

Marchiando et al. employed both the quasireversible maximum and splitting of the net S W peak for a complete kinetic and thermodynamic characterization of alter-... 

From the definition of cOint follows that the quasireversible maximum can be also determined by varying the frequency, while keeping 0 constant. In analogy to (2.105), it is obvious that the critical frequency, associated with the position of the maximum, depends on the interaction product a. The relationship between the critical frequency and the interaction product is given by the following equation ... 

This equation is of particular importance since it enables estimation of both the interaction product a and the standard rate constant sur, provided the relative surface coverage is known. For this, the quasireversible maximum is to be determined by varying the frequency for various values of the surface coverage 0. Plotting ln(/)... 

Fig. 2.62 The quasireversible maximum of azobenzene recorded in 1 mol/L HNO3. All other conditions are the same as for Fig. 2.61 (reprinted from [86] Croat Chem Acta 73 305)...

The physical meaning of the kinetic parameter m is identical as for surface electrode reaction (Chap. 2.5.1). The electrochemical reversibility is primarily controlled by 03 (Fig. 2.71). The reaction is totally irreversible for log(m) < —3 and electrochemically reversible for log(fo) > 1. Between these intervals, the reaction appears quasireversible, attributed with a quasireversible maximum. Though the absolute net peak current value depends on the adsorption parameter. Fig. 2.71 reveals that the quasireversible interval, together with the position of the maximum, is independent of the adsorption strength. Similar to the surface reactions, the position of the maximum varies with the electron transfer coefficient and the amphtude of the potential modrrlation [92]. 

The charge transfer kinetics of azobenzene at the mercury electrode is slower than that of methylene blue, thus the frequency interval provided by modem instra-mentation (10 < //Hz < 2000) allows variation of the electrochemical reversibility of the electrode reaction over a wide range [79]. The quasireversible maxima measured by the reduction of azobenzene in media at different pH ate shown in Fig. 2.47 in the previous Sect. 2.5.1. The position of the quasireversible maximum depends on pH hence the estimated standard rate constant obeys the following dependence A sur = (62-12pH) S- for pH < 4. These results confirm the quasite-versible maximum can be experimentally observed for a single electrode reaction by varying the frequency, as predicted by analysis in Fig. 2.75. 

The latter equation is valid for Asw = 20 mV and Ofc = 0.5 [134]. Note that the sensitivity of the quasireversible maximum to the concentration of the ligand can serve as a qualitative diagnostic criterion for the reaction mechaiusm of a second order. 

For a given adsorption constant, the observed electrochemical reversibility depends on the kinetic parameter defined as (O = Xy, or (o =. This reveals that the inherent properties of reaction (2.208) are very close to surface electrode reactions elaborated in Sect. 2.5. The quasireversible maximum is strongly pronounced, being represented by a sharp parabolic dependence of vs. m. The important feature of the maximum is its sensitivity to the adsorption constant, defined by the following equation ... 

Due to the similarity with surface electrode processes, a quasireversible reaction in thin-film voltammetry exhibits a quasireversible maximum and splitting of the net peak. The reasons causing these voltammetric features are the same as for surface... 

As the electrochemical reaction is confined to the boundaries of the thin film, the voltammetric response exhibits a quasireversible maximum. The position of the quasireversible maximum on the log frequency axis depends on the kinetics of the overall reaction at the thin-film electrode, i.e., reflecting the coupled electron-ion transfer (4.3). Analyzing the evolution of the quasireversible maximum measured with different redox probes and various transferring ions, it has been demonstrated... 

Figures 4.11 and 4.12 show the quasireversible maxima corresponding to the transfer of anions and cations, respectively. The position of the maximum depends on the nature of the transferring ion, confirming that the overall process is controlled by the ion transfer kinetics. For each transferring ion, the evolution of the quasireversible maximum was analyzed by varying. In all cases, the position of the...

Quasireversible maximum — is a feature of the square-wave voltammetric response (see - square-wave voltammetry) of a kinetically controlled - electrode reaction in which at least one component of the - redox couple is immobilized on the - electrode surface [i] and kinetically controlled electrode reaction occurring in a restricted diffusion space [ii] (see - thin-film electrode and... 

Fig. 2.43 Quasireversible maximum. Alfp as a function of log(m). Conditions of the simulations are the same as for Fig. 2.41...

Beside the quasireversible maximum, the splitting of the net peak is the second intriguing feature of a surface electrode reaction [84]. The splitting emerges by... 

---