Two-Electrode Method Ref

This method employs the basic principles previously described for the EIS method but with the use of two identical working electrodes. The method does not use an auxiliary electrode nor a reference electrode. With reference to Fig. 6.21, the two working electrodes (A and B), ideally, are identical in all aspects—geometry, chemical composition, microstructure, surface condition, etc. The method involves application of a low-amplitude (e.g., 20 mV) AC potential across the two electrodes, at a very low frequency (If) and at a very high frequency (hf), and measurement of the impedance of the system at each frequency, Z lf and Z hf. The assumed equivalent electrical circuit for the system also is indicated in Fig. 6.21. This circuit assumes that the simplest equivalent electrical circuit, as shown in Fig. 6.18, is applicable to each of the electrodes in the two-electrode method. In this case, Rs is the solution resistance (normalized with respect to specimen area, for example, ohms-m2) between the two electrodes. With reference to Fig. 6.21 (and also with reference to the previous discussion of the EIS method), it is seen that  

Once Rp is determined, icorr is evaluated with the polarization-resistance (or Stem-Geary) equation, Eq 6.28. The two-electrode method is a relatively simple and fast method for evaluating when compared with the standard polarization-resistance and electrochemical-impedance methods. 

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