Macroscopic Space Charge in a Potassium Chloride Solution during Electrolysis

Abstract

The macroscopic space charge and potential distributions were determined in a uniform column of 0.0024 N KCl solution during electrolysis by the methods used by Reed and Schriever. The platinum electrodes were 8×8 cm in area and spaced 40 cm apart; their constant potential difference was 8000 mv. For the first time, all four space-charge regions were observed in one column of solution directly experimentally. The maximum negative space charge in the cathode region, 45×10−5 statcoulomb/cm3 at x=0.6 cm, and the maximum positive space charge in the anode region, 40×10−5 statcoulomb/cm3 at x=37.7 cm, both fell within the range of such space charges observed by Reed and Schriever. The potential gradient between x=10 cm and x=35 cm had the constant value of 13.75 mv/mm. Thus, Ohm's law was obeyed in this region. The mean gradient in the first mm next to the cathode was 1130 mv/mm; that in the last mm next to the anode was 1200 mv/mm. The total fall of potential in these two one-mm layers was thus 29.1 percent of the total fall of potential between the electrodes. For Zn(C2H3O2)2 and CuSO4 the falls in these two layers were respectively only 1 and 1.06 percent of the total; the greatest value observed by Reed and Schriever was 22.5 percent of the total for NiSO4. It is pointed out that the shapes of the potential distribution curves cannot be explained by phenomena which occur only at, and very near, the electrodes.