PARTIALLY BLOCKED SURFACE STUDIED BY THE ELECTROHYDRODYNAMIC IMPEDANCE

The mass transport to a partially blocked surface on a rotating disc e lectrode when its angular velocity is submitted to small sinusoidal os cillations around a mean value has been analysed. From the quantitativ e treatment of the response of a single active site embedded in an oth erwise conducting surface, it was inferred that the high frequency res ponse of a partially blocked surface with active sites of the same siz e can be estimated. The response contains two time constants and its f requency analysis can provide the average size site and the active fra ction of the interface. These predictions were compared with an experi mental investigation using a photolithographic model of a partially bl ocked electrode. Good agreement between theory and experiment was obta ined when the high frequency response was corrected for kinetic effect s due to the finite rate of the chosen redox reaction and double-layer charging.