  In this study, we examine the effects of bubble collisions and coalescence on
electrolysis performance using micro-electrodes in a 0.5 M H2SO4. We observe
that the addition of electrolytes such as HClO4, despite increasing
conductivity, significantly reduces energy conversion efficiency by inhibiting
bubble coalescence. A phase diagram illustrates the trade-off between improved
conductivity and inhibition of coalescence with varying concentrations of
supporting electrolytes (HClO4 or Na2SO4) at different electrolysis current.
Contrary to conventional understanding, we find that larger bubbles resulting
from coalescence enhance efficiency. This can be attributed to the early
release of smaller bubbles, approximately 10 micron in size, facilitated by the
coalescence of the surface microbubble and the just-detached large bubble.
Additionally, the merge of two bubbles, at a critical velocity of ~2 m/s,
enhances agitation at the electrode surface that significantly improves
electrolyte transport within the stagnant layer. These findings challenge
conventional perspectives on bubble detachment size and suggest innovative
approaches to optimize energy consumption in electrolysis, especially in
systems where the bubble coalescence is inhibited, such as alkaline water
electrolysis and the chlor-alkali industry.
