  The chronoamperometric measurements performed with rotating ring-disc
electrode become a one of the standard techniques for the diffusion coefficient
determination. However, the theoretical estimation of the transit time on which
the technique is based is not strictly connected to the apparent time interval
measured in the experiments. Therefore, we employed numerical simulation of
RRDE in order to predict possible error of the diffusion coefficient estimation
in respect to the disc electrode conditions. According to the results the
obtained estimation can vary up to two times depending on the disk electrode
potential. On the other hand, even an intense disk passivation process leading
to the peak-like shape of the ring current transient does not affect
significantly the apparent transit time and the diffusion coefficient
estimation. Additionally, it was showed, that the presence of a linear segment
in the disk current transient indicates that the time it took to cover most of
the disk electrode with the passivation film is close to the RRDE
characteristic time.
