EXPERIMENTAL INVESTIGATION OF THE CURRENT DISTRIBUTION ON A RECESSED ROTATING-DISK ELECTRODE

The design of a recessed rotating disk electrode is described. Its current distribution and mass-transfer characteristics are compared to those of a rotating-disk electrode without recess. The ohmic resistance of the recessed-disk electrode was found to vary linearly with aspect ratio (recess depth/electrode radius). For aspect ratios greater than 0.5, the deviation of the current density at the edge of the electrode from the average current density was less than 10% under conditions of primary current distribution. The mass-transfer-limited current varied linearly with the square root of rotation rate up to an aspect ratio of 1.0, but the absolute values of the current decreased with increasing aspect ratio. The mass-transfer-limited thickness distribution on plated Cu samples was measured at aspect ratios of 0.1, 0.5, and 1.0. The thickness was uniform near the center of the electrode but decreased rapidly near the edge. The radius at which the thickness began to decrease approached the edge of the electrode as the aspect ratio decreased.