Impact of alignment defects of rotating disk electrode on transport properties

The rotating disc electrode (RDE) is by far the most popular of the hydrodynamic electrodes, in which the transport of electroactive species is enhanced by a controlled flow; one of the reasons of this success is its resilience, as the rate of transport of actual RDEs are close to the theoretical predictions. However, if this is true for defect-free electrodes, little is known about the effect of defects on the transport properties of actual RDEs. In this paper, we use state-of-the-art finite volumes computational fluid dynamics simulations to investigate the transport properties of a defect-free cylindrical RDE, and of three RDEs presenting defects that commonly arise from imperfect construction, handling or even just ageing. We show that, while the transport toward the defect-free cylindrical RDE can be considered homogeneous, this is not the case for the other electrodes. We found that the presence of defects has only a minor effect on the average rate of mass-transport of the electrodes, which is what matters for analytical purposes, but that they significantly increase the heterogeneity of mass transport. This heterogeneity can have a significant impact in the context of kinetic studies, especially those in which the response is non-linear with respect to the concentration, like the study of immobilized enzymes using protein film voltammetry.