Influence and use of gas bubbles for the reduction of stray currents in industrial alkaline water electrolysis

Alkaline Water Electrolysis (AWE) is a key technology for green hydrogen production. It is named after the highly conductive alkaline electrolyte, typically ~30 wt.% KOH solution, that is pumped through the electrolysis cells during operation. In industrial applications, many individual cells are electrically connected in series to form a "stack". Because the electrolyte is conductive, a short circuit occurs and some current bypasses the cells through the manifold, known as a stray, leakage or shunt current. This current has several undesirable effects: a reduction in current efficiency, a maldistribution of load across the cells and corrosion due to electrochemical reactions outside of the electrolysis cells [1].One approach to increase the resistance and lower stray currents in the electrolyte is to introduce gas bubbles into the distribution tubes, decreasing the area of the conductive liquid. This occurs naturally at the outlet of the stack, where the produced gas and the electrolyte leave the cells mixed. It is usually assumed that this significantly increases the resistance, especially when a plug flow or annular flow regime is reached. However, no experimental studies have been carried out to quantify this resistance increase. In this work, resistance in circular tubes at different gas and liquid flow velocities is measured at industrial AWE conditions. Furthermore, the transfer of this concept to the feed distribution via the addition of gas bubbles to the electrolyte is evaluated.[1] A. T. Kuhn, J. S. Booth, J Appl Electrochem. 1980, 10 (2), 233–237. DOI: https://doi.org/10.1007/BF00726091.[2] L. Chen, Y. S. Tian, T. G. Karayiannis, International Journal of Heat and Mass Transfer. 2006, 49 (21–22), 4220–4230. DOI: https://doi.org/10.1016/j.ijheatmasstransfer.2006.03.025.