Uncompensated Resistance. 2. The Effect of Reference Electrode Nonideality

A finite-element simulation study has been made of the effect upon the uncompensated resistance, U, of the size of a reference electrode positioned at various distances above the center of an inlaid-disk working electrode. The idealized reference electrode is treated as a conducting circular disk embedded in a cylindrical insulator. Two effects are encountered, in addition to the expected diminution in U as the reference electrode approaches the working electrode. A "backwater effect", reducing U, arises from the avoidance of the Luggin probe by the current lines. A "short-circuiting" effect, enhancing U, arises if those current lines pass through the reference electrode on their way to the counter electrode. Two detrimental effects of the intrusion of a finite-sized reference electrode into the vicinity of the working electrode--a reduction in the total current and the perturbation of the current density distribution-are also briefly examined. It is demonstrated that U may be reduced indefinitely by decreasing the working-to-reference gap, but, the Luggin probe must have a diameter of one-fourth or less of that of the working electrode if significant shielding is to be avoided.