Cyclic heterogeneous charge transfer

The solid line of Figure 23.1 gives the calculated trace for Equation 23.1 with a moderate heterogeneous charge-transfer rate (a quasi-reversible E system). The circles give the calculated response on the basis of Equations 23.2-23.4, in which the initial product B reacts rapidly to give X, which is oxidized on the return sweep. The anodic wave therefore arises from the electroactive decomposition product (X) of B. The cathodic (forward) scan is therefore an EC process and the reverse scan an E process, so that the overall cyclic mechanism might be referred to as EC,E (Eq. 23.2-23.4). 

Initially, the simple case of a irreversible first-order chemical reaction step (Cin-ev) following a reversible heterogeneous charge transfer process (Erev) is considered. The reaction scheme for this type of process is given in Eq. II. 1.21 and simulated cyclic voltammograms for the ErevCirrev reaction sequence are shown in Fig. II.1.21a. 

As noted above, cyclic voltammetry is a powerful tool for the investigation of processes combining solution-phase reactions and heterogeneous charge transfer at the electrode surface. However, this technique can also be applied to systems with additional phase boundaries. For example, multi-phase processes in thin films covering an electrode surface (Fig. II. 1.24a), particulate solids, bacteria, or microdroplets attached to the electrode surface (Fig. II. 1.24b), or micro-emulsion systems... 

Figure 6-4 The relationship of the reversibility factor f, and the heterogeneous charge transfer constant k°. The concentrations of the electroactive species in the electrode surface were evaluated at the peaks of cyclic voltammogram by digital simulation with E° = — 1.529 V, a = 0.78, and D = 1.8 x 10 cmVs at — 30°C. The reversibility factor /, was calculated through Equation (1). (a) 300mV/s, = 590s (b) 50mV/s,...

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