Mass Transfer to Point Electrodes on the Surface of a Rotating Disk

A zeroth order perturbation solution is presented for the rate of laminar mass transfer to three types of point electrodes embedded in the surface of an insulating rotating disk—those sensitive to radial, tangential, and local velocity components. It is shown that the diffusion current density on the point electrode increases with decreasing geometrical parameter defined as the ratio of the electrode size to the radial location of the electrode on the disk surface. With a properly chosen geometrical parameter, it is possible to obtain a current density ten times greater than that on the disk electrode at a given rotational speed. From the electroanalytical point of view, this offers experimental advantages in the study of fast surface reactions. An experimental setup for studying the transfer characteristics of such electrodes is described. A diffusion‐controlled redox reaction is used for the measurement. The results indicate that the "local" and the "tangential" electrodes give reasonable agreement with the theory prediction. However, data from the "radial" electrode scatter randomly around the predicted values. This failure of the radial electrode to behave properly appears to be consistent with thin‐ring experiments reported in the literature.