J. Electroanal. Chem., 124 (1981 ) 309 309 Elsevier Sequoia S.A., L a u s a n n e - - P r i n t e d in The N e t h e r l a n d s

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iR CORRECTION APPLIED TO CHLORINE EVOLUTION ON PLATINUM

L.F .G. W I L L I A M S and R.J . T A Y L O R

Materials Research Laboratories, Department of Defence, P.O. Box 50, Ascot Vale, Vic- toria 3032 (Australia)

(Rece ived 10 th N o v e m b e r 1980)

In our paper on computer-controlled iR correction [ 1 ] it was intended to reproduce the conditions under which Tafel region had been reported for chlorine evolution on platinum after the data had been subjected to regres- sion analysis to correct for the iR drop [2]. Owing to a lack of experimental information a cleaned platinum electrode was immersed in a NaC1 solution and a polarization curve obtained without any pre-oxidation.

Recently, using a rotating platinum disc we were able to reproduce the Tafel region on oxidized electrodes [3] with no effect due to rotation. The E vs. i data were corrected for iR using the regression analysis method and a value of 194.2 -+ 0.2 mV was obtained, compared with 168.9 + 3.6 mV previously reported [ 2]. We therefore accept that our electrode was partially oxidized and that the effect which we attr ibuted to stirring was most likely due to oxidation of the platinum electrode.

However, we are more emphatic that erroneous results can be obtained by the regression analysis method [ 2 ]. Recalculation using the regression analysis method [2] of two sets of E vs. i data on partially oxidized electrodes have resulted in acceptable fits with apparent Tafel slopes of 35.41 + 0.01 and 52.47 + 0.03 mV, and Ru values of 5.44 + 0.08 and 4.8 + 0.2 ~2 respectively. These fits are quite good and give the impression that there is a Tafel region.

The computerized iR correction method, however, gave an Ru of 0.36 ~2 and no Tafel region. On these partially oxidized electrodes we are in agreement that a Tafel region would not be expected and so due to some fortuitous fit of the E vs. i data, the regression analysis method has resulted in a Tafel region.

In principle, therefore, it is better to measure iR directly and avoid having to make assumptions which may seem to be verified by a fortuitous fit of the regressional analysis method [ 2].

R E F E R E N C E S

1 L.F.G. Williams and R.J. Taylor, J. Electroanal. Chem., 108 (1980) 293. 2 M. Hayes, A.T. Kuhn and W. Patefield, J. Power Sources, 2 (1978) 121. 3 A.T. Kuhn and P.M. Wright, J. Eleetroanal. Chem., 38 (1972) 291.

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