Hydrogen and oxygen are generated at the electrodes of an electrolyser in dissolved form. When the solubility is exceeded, the electrolyte supersaturates with dissolved gas, and bubbles nucleate at the surface. They grow by taking up dissolved gas until they are large enough that buoyancy or interactions with the flow or other bubbles cause them to leave.
After departure, modellers usually assume that the bubbles maintain their departure size. However, by analysing videos from the open literature, we found that they continue to grow as they rise.
This means that some distance from the electrode, the electrolyte is still supersaturated. This is important to know and model accurately because it can cause increased transport of hydrogen towards the oxygen side or oxygen towards the hydrogen side, potentially leading to explosive mixture conditions.