Limiting-current plateau, defined

With a well-defined polarographic wave where the limiting current plateau is parallel to the residual current curve, the measurement of the diffusion current is relatively simple. In the exact procedure, illustrated in Fig. 16.6(a), the actual... 

The ohmic contribution to the overpotential can be minimized by suitable placement of the reference electrode, but the surface overpotential cannot be reduced similarly. In making limiting-current measurements, the surface overpotential, or rather its rate of increase with current density, should be low enough to permit observation of a long, clearly defined limiting-current plateau. 

In limiting-current measurements, the counterelectrode is sometimes used as a reference electrode. In that case, the surface overpotential of the counterelectrode contributes to the recorded overpotential that is, the potential of the reference electrode is now current dependent. Unless precautions are taken (e.g., the area of the counterelectrode is much larger than that of the working electrode), a properly defined limiting-current plateau may not be obtained. 

In the first region, the current is completely independent of rotation rate of the electrode and increases exponentially, which means that in this region the current (or reaction rate) is mainly controlled by electron transfer and not by transport phenomena. This allows a study of the kinetics and the mechanism of the electron-transfer reaction of the oxidation of dithionite. The third region shows a well-defined limiting-current plateau. This indicates that in this region, electron transfer is so fast that the overall reaction rate is controlled by transport only. This is confirmed by a linear relationship between limiting-current and square root of the rotation rate of the electrode. In this region, it is not possible to study the kinetics and the mechanism, but such conditions are suitable for electroanalytical purposes and sensor development (see sections 6.5 and 6.7). 

Two, a region of rising current response defined by the Nernst equation, if the system is reversible. Third, a limiting current plateau that is independent of potential. 

As shown above, potentiodynamic generation of limiting currents is more rapid and, therefore, preferable in principle to the galvanodynamic technique. However, during a linear decrease of potential to the limiting-current condition, the current density initially rises more rapidly than when a current ramp is used. Therefore, in the case of copper deposition at the cathode, a linear potential ramp tends to yield a rougher deposit and a less well-defined plateau than a linear current ramp (see Section III,F). 

While initial attempts of quantification of i-Az traces obtained in (single) molecule conductance studies suffered from rather poorly defined data selection strategies and limited current ranges [64, 116], most of the leading groups in the field focus now on the construction of all-data point conductance and plateau length... 

Within this working range, the presence of a reactive sample will give rise to a cui-rent/potential (// ) curve (Fig. 4.3). This curve is unique for a particular sample/elu-ent/electrode combination. It is characterized by a half-wave potential and by a "diffusion current plateau. The half-wave potential (the potential half way up to the diffusion current plateau) is defined as the potential needed to induce electrolysis of the electroactive species. As the potential is increased, the electrolysis current also increases because more ions migrate to the electrode and become oxidized (or reduced). The electrolysis current eventually forms a plateau in the HE curve because, ultimately, the amount of current is limited by the rate of diffusion of ions to the electrode surface. In normal operation, the electrochemical detector potential is set at the smallest potential possible that is still on the diffusion current plateau. The detector should be on the plateau for consistent performance, but at the lowest potential to lessen the chance of side reactions. 

Voltammograms obtained by the RDE technique are of common shape (Figure 8.32). They contain a well-defined plateau of limiting current that is observed over a wide region of cathodic potentials (-1.2 limiting current density (ij ) depends on solution composition, and... 

Co(II) complexes are reduced at more negative potentials simultaneously with hydrogen evolution. Therefore, cathodic voltammograms obtained in Co(II) and malic acid solutions contain poorly defined plateau of limiting current density (fn ) [136]. The rate of this partial process grows at an increase in cathodic polarization. Besides, decreases at an increase in the ligand concentration. If an... 

The complex time dependence of the diffusion process to an inlaid disk electrode is described by Eqs. (5.10) and (5.11), which are defined in terms of the dimensionless time parameter 0. It follows that under a specific set of experimental conditions, a unique ratio of Vd / will apply and this ratio can be defined as a single parameter, p. In order to obtain the convolved current, M(t), an initial estimate for p must be inputted into the convolution algorithm. If c is known and Ml can be obtained from the limiting convolved current plateau, then it is possible to iteratively refine p based on Eq. (5.7) for a known value of Tq ... 

Manipulation of these equations or of those pertaining to the q formulation for various limiting values of the two dimensionless parameters defining the zone diagram allows derivation of the expressions of the plateau currents given in Table 4.1. With the two-step reaction scheme discussed in Section 4.3.6, a similar procedure may be used to obtain the various expressions of the plateau currents given in Table 4.2. 

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