Lugin capillary

Figure 6.16. Three-compartment three-electrode electrochemical cell RE, reference electrode LC, Lugin capillary TE, test electrode GF, glass frit CE, counterelectrode.

Another important question is the importance of correcting for the uncompensated Ohmic resistance in experiments of the ORR. This problem is not new, but it is often disregarded. It was elaborated by van der Vliet et al. [68] who showed that if one omits to correct measured current for IR drop erroneous values of specific activity and E a is obtained. This is a consequence of the fact that no matter how close Lugin capillary is to the working electrode, it is difficult to reduce electrolyte resistance below 10 Q. For measured ORR current of approx. 1 mA this would shift electrode potential by 10 mV. For ORR Tafel slope of 120 mV dec", this potential shift induces approx. 25% underestimated ORR activity (expressed as A,esa or 7k,mass a d corrected for mass transfer) and also incorrect value of Tafel slope. For these purposes, positive feed-back scheme is proposed [52]. 

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