Current interruption technique

Pelenc.Y. Review of the main current interruption techniques Voltas Limited, Switchgear Division, India. 

The latter equals IRwc where RWc is the ohmic resistance between the working and counter electrode. Experimentally it is rather easy to measure the riohmic.wc term using the current interruption technique as shown in Figure 4.9. Upon current interruption the ohmic overpotential r 0i,mjCtwc vanishes within less than 1 ps and the remaining part of the overpotential which vanishes much slower is t w+T c (Eq. 4.9). 

Figure 4.9. Use of the current interruption technique to measure the ohmic overpotential, r ohmic,wc> between the working (W) and counter (C) electrode.

Moreover, in the case of electrochemical kinetics and corrosion studies, some current should flow through the system and the IR drop is unavoidable and can be estimated using the current interruption technique [3]. 

The current interruption technique [59] can be simply and accurately described with reference to the circuit in figure 11 and using the Laplace transform [65] to examine its behaviour over the time interval [0, t]. 

Figure 11. Circuit scheme illustrating the current interruption technique for the ohmic drop evaluation.

Currently, the current interruption technique can be employed following two distinct procedures. One is based on the high-speed sampling of the voltage signal [66] and... 

A very interesting application of the classical current interruption technique has been reported by Lorenz and Eichkom [67], who showed that by adopting the galvanostatic configuration it is possible to evaluate the importance of the ohmic drop realistically, point by point, and obtain polarization curves with a trend very close to the ideal one. In fact, it can be experimentally demonstrated that the value of R, is not constant but is influenced by the mass transfer when the current flowing in the electrolytic cell is sufficiently high. In other words, it cannot be excluded a priori that the quantity R, depends on the electrode overvoltage. 

Our laboratory experience, however, has shown that, when measurements are performed axlopting the galvanostatic mode, the use of alternating current is a very satisfactory means of determining the value of the resistance R, accurately. In fact, unlike the direct current interruption technique, the AC technique can be utilized for a very large class of electrochemical systems. 

Current Interruption Technique. As discussed in the previous section, proper choice and positioning of the Luggin probe will minimize the contribution of the ohmic drop to the measured electrode potential. One can also correct the measured electrode... 

Fig, 7.3 - Steady state /-17 characteristic for a Pt cathode in 5 mol dm H2SO4. The data are corrected for IR drop using a current interruption technique. 

Fig. 11.13 — Measurement of the uncompensated resistance using the current interruption technique (a) /-/ function applied, (b) E-t response.

In order to capture the dynamic nature, and electrical characteristics of a fuel cell, methods like chronoamperometry or current interruption techniques are an option. The method is able to separate the contributions of ohmic and non-ohmic processes and capture the dynamic voltage response during a few steps in the current. A generic plot of the expected voltage and corresponding current step signal is shown in Fig. 21.21. 

The current interrupt technique is the most widely used method of ohmic drop and ohmic resistance evaluation of various electrochemical systems including fuel cells. The principle behind the current interrupt method is the performance of the voltage response of the fuel cell for a given step change of current flow. 

The ohmic overpotential can be measured via ac impedance spectroscopy or via the current interruption technique in conjunction with a recording oscilloscope and is proportional to the cell current 1. It is due to the ohmic resistance of the electrodes, of the solid electrolyte Rj, and the electrode-electrolyte contact resistance R. ... 

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