This paper reports on the electrochemical processes at the surface of conducting materials such as aluminium in a thin-layer cell usually employed for electrokinetic measurements. The cell contains one or more planar Al wafers in contact with an electrolyte solution, which is subjected to an external electric field parallel to the surfaces of the wafers. Beyond a certain threshold value of the magnitude of the field, the current through the cell increases more than proportionally with the field strength. This is due to faradaic processes occurring at the two ends of the conducting substrates, i.e. reduction at the positive side of the electric field in the solution and oxidation at the negative side. In the case of Al wafers, anodic dissolution of the metal takes place and the progression of the 'corroding' edge can be followed visually. The overall electrolytic process, corresponding with the distributed current along the surface of the wafer, could be explained and modeled on the basis of the conventionally measured Butler-Volmer characteristics of the monopolar Al electrode. .