Influence of Gas Void Fraction on Electrode Performance in Industrial Alkaline Water Electrolysis

Abstract

Listen

Translate article

In alkaline water electrolysis cells with an electrolyte gap between the electrodes, the cell's internal resistance increases when the gas void fraction in the electrolyte rises (Figure 1 a). Bongenaar-Schlentner et al. [1] were able to show this in their work already in 1985. As laboratory cells are usually significantly lower in height than industrial cells and the flow velocities [2] are typically higher than during technical operation, the influence of the gas void fraction within the cell has been paid little attention to date.Cell heights of more than 1 m with a zero-gap arrangement are currently used in the industry [3, 4]. The influence of the gas void fraction on the efficiency in this cell configuration needs further experimental investigations, as the gas evolves in the void of the cell and does not necessarily affect the area in between them. However, it can be expected that the gas void fraction and the bubble size distribution impair the wetting of the electrode, the detachment of gas bubbles, the mass transport to the electrode and the wetting of the separator, to name just a few of the possible effects.To emulate these effects in a real industrial-scale cell, different gas void fractions were generated in a lab-scale cell through gas addition corresponding to the gas flow rate of the industrial-scale cell at variable heights (Figure 1 b). To evaluate the influence on the current density, chronoamperometry was applied. The inlet temperature and electrolyte flow rate were varied within industrially relevant operating conditions, and the effect of different cell internals was studied.It was observed that the influence of the additional gas is considerable, decreasing the local cell current up to 20 % at high gas void fractions. The results obtained were compared with those of a pilot plant with full-size cells, showing significant electrode utilization differences over the cell height.This experimental investigation is a good starting point for further investigations on the effect of the gas-void fraction on the electrode performance and can lead to improved cell designs.