Electrode current distribution in a hypochlorite cell

Abstract

Electrochemical production of gases, e.g. C12, H2 and 02, is generally carried out in vertical electrolysers with a narrow electrode gap. The evolution of gas bubbles, on one hand, speeds up the mass transport; on the other it increases the solution resistance and also the cell potential. The gas void fraction in the cell increases with increasing height and, consequently, the current density is expected to decrease with increasing height. Insight into the effects of various parameters on the current distribution and the ohmic resistance in the cell is of the utmost importance in understanding the electrochemical processes at gas-evolving electrodes. An example of the described phenomena is the on-site production of hypochlorite by means of a vertical cell. Experiments were carried out with a working electrode consisting of 20 equal segments and an undivided counter electrode. It has been found that the current distribution over the anode is affected by various electrolysis parameters. The current density, j, decreased linearly with increasing distance, h, from the leading edge of the electode.The absolute value of the slope of the I/h straight line increased with increasing average current density and temperature, and with decreasing velocity of the solution, NaC1 concentration and interelectrode gap.

Behaviour of a tall vertical gas-evolving cell. Part I: Distribution of void fraction and of ohmic resistance

“…The parallel-plate electrochemical cell and the flow circuit have been described in [6]. The solution is pumped from a solution reservoir overflow-vessel upwards through the inter-electrode gap.…”

Behaviour of a tall vertical gas-evolving cell Part II: Distribution of current

“…The experimental set-up for a rectangular vertical cell has been described previously [5,6] between successive segments and a one-plate electrode 0.020m in width and 0.50m in height. Experiments were carried out with two combinations of electrodes, namely, one with two segmented electrodes, both 0.01 m in width and the other combination with a segmented electrode and one-plate electrode, both 0.02 m in width.…”

“…Characteristics of GEEST-1 are given in [3][4][5][6] and those of GEEST-2 in [5]. The main difference between the two systems is the chargeability of segment pairs.…”

“…The experimental procedure with GEEST-1 is described in [5,6] and that with GEEST-2 in [5]. Unless otherwise mentioned GEEST-2 was used.…”

“…Results for the distribution in a gas-evolving diaphragm cell have been published by Bongenaar-Schlenter et al [3,4] and those in a hypochlorite electrolyser by Czarnetzki et aL [5,6]. Further research has shown that, particularly at low current densities corresponding to low voidages, the reliability of the results is very sensitive to variations in the width of the inter-electrode gap.…”