Electrochemical processes steady-state voltammograms

Cyclic voltammetry is a widely used electrochemical technique, which allows the investigation of the transient reactions occurring on the electrode surface when the potential applied to the electrode is varied linearly and repetitively at a constant sweep rate between two given suitable limits. The steady-state current-potential curves or voltammograms provide direct information as to the adsorption-desorption processes and allow estimating the catalytic properties of the electrode surface. 

In short, SECM is a scanning probe technique similar to STM or atomic force microscopy (AFM). A tip current arises due to an electrochemical reaction (faradaic process) at an ultra-microelectrode (UME) tip (see Chapter 6). The tip generally consists of a Pt wire of diameter between 1 and 25 pm that is sealed in a glass capillary and polished to get a flat electrode surface. A typical voltammogram recorded on a UME is shown in Figure 9.28b. It is a sigmoidal, steady-state current-potential curve without any hysteresis. 

Figure II. 1.4 compares the characteristic features of (a) a steady-state process, (b) a potential step experiment, and (c) a cyclic voltammogram. The steady-state experiment is independent of time and gives a sigmoidally shaped response. Most important is the extent to which the concentration profile penetrates into the solution phase. For a steady-state process, there is no time dependence and the diffusion layer thickness, <5, remains constant. In a chronoamperometric or potential step experiment, the diffusion layer thickness continuously moves into the solution phase. During the initial course of a cyclic voltammetric experiment, the diffusion layer also moves into the solution phase. However, this is of course followed by a second change in concentration generated after the reversal of the scan direction. The diffusion layer thickness for an electrochemically reversible process at the time when the peak occurs is a useful benchmark and...

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