Potentiostats probe positioning

The scanning electrochemical microscopy (SECM) technique introduced in recent years by Allen Bard is another area where the smallness of the electrode is essential [38]. The principle in SECM is a mobile UME inserted in an electrolyte solution. The UME is normally operated in a potentiostatic manner in an unstirred solution so that the current recorded is controlled solely by the spherical diffusion of the probed substance to the UME. The current can be quantified from Eqs. 48, 49, or 89 as long as the electrode is positioned far from other interfaces. However, if a solid body is present in the electrolyte solution, the diffusion of the substance to the UME is altered. For instance, when the position of the UME is lowered in the z direction, that is, towards the surface of the object, the diffusion will be partially blocked and the current decreases. By monitoring of the current while the electrode is moved in the x-y plane, the topology of the object can be graphed. The spatial resolution is about 0.25 pm. In one investigation carried out by Bard et al, the... 

Conventional electrochemical experiments at the ITIES are based on a four-electrode configuration with a reference and an auxiliary electrodes positioned in each liquid phase (16,17). A four-electrode potentiostat is used to apply a voltage between the reference electrodes and to measure the current flowing between auxiliary electrodes. The interfacial charge transfer is assumed to be rate limiting, and the whole potential drop occurs mostly within a thin interfacial layer. However, the ITIES in such an experiment is not microscopically probed directly, and the nature of CT reaction (i.e., ET vs. IT) typically remains uncertain. 

Potentiostatic setups control the potential drop between electrode and electrolyte. This requires a probe to measure the potential of the electrolyte, the so-called reference electrode. The probe tip, the sensing point, is positioned somewhere in the electrolyte. This is illustrated in Fig. 1, showing the equivalent circuit of a common electrochemical cell. 

Fig. 15.4 Left. A very instructive way for calibrating the Kelvin probe is by positioning it over an electrolyte-covered surface potentiostatically polarised to different potentials. A typical calibration curve is shown on the right. As can be seen, there is a linear relation between measured Kelvin probe signal and the applied electrode potential. Once the correct functioning of an SKP set-up has been checked this way, it is sufficient to calibrate the offset value (here it is about 4(K) mV) with just one measurement vs. a reference. This is usually done by positioning the SKP over a small Cu beaker filled with CUSO4 solution of well-known concentration (usually saturated) and referencing the SKP signal to the corresponding Cu/Cu potential [31]...

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