Rotating Disk Electrode Voltammetry Using Small Sample Volumes

Since the early work of Riddiford (1, 2) which demonstrated that deviation from the Levich equation occurred for certain electrode shapes at low rotation speeds, users of the rotating disk electrode (RDE) have been concerned about disk electrode mantle geometries. The usual practical electrode is a compromise between theoretical requirements and convenience of fabrication. In addition, it was originally anticipated, based on theoretical considerations, that it would also be necessary to use electrolysis cells whose dimensions are large compared to those of the disk electrode. The study of Prater and Adams (3), however, failed to show the existence of any significant effect on current in going from a 100-ml beaker to a 9-liter vessel while Gregory and Riddiford (4) found that a 5-cm disk operated satisfactorily in vessels only 11 cm or larger in diameter. Furthermore, we have observed, as other workers have (3, 4), that the position of a rotating disk electrode in a cell has little or no effect on the observed current. For example, it makes little difference in the disk current whether the end of the electrode is just below the solution surface, just above the cell bottom, well centered in the cell, or next to one of the cell walls.