Electrolyte

The ion-conducting medium between the electrodes.

In alkaline electrolysers this is a liquid solution of potassium hydroxide, typically in the range of twenty to thirty per cent by mass, circulated through the stack. In PEM and AEM systems the role is played by a solid polymer membrane and the circulating fluid is water.

Liquid electrolyte concentration and conductivity are operational variables with a direct effect on cell voltage. They drift through water consumption, carbonation from carbon dioxide ingress, and contamination from feedwater or from the plant itself.

Because the liquid circulates through every cell, contamination introduced anywhere reaches the whole stack. This makes electrolyte quality one of the few genuinely fast-acting condition variables, and one worth monitoring upstream rather than inferring from cell behaviour after the fact.