Electrostatic interaction induced bubble coalescence in saturated electrolytes

Coalescence of (produced) gas bubbles in an electrolyzer plays a crucial role in the subsequent dynamics and removal of these bubbles, leading to a specific efficiency of the electrolyzer. One of the parameters influencing this bubble coalescence is the restructuring of interfacial charge due the the electrolyte being saturated with the produced gas. In this work, we investigate the coalescence of two simultaneously growing gas bubbles, positioned next to each other, in a saturated electrolyte. We particularly focus on the effect of the approach velocity (towards each other) of these bubbles, resulting in an atypical film (between the two gas bubbles) thinning dynamics prior to the coalescence. The thin film dynamics is observed to be dependent on the redistribution of charges on either interface (of the thin film) due to reactions occurring in presence of the saturating gas in the surrounding. The resulting electrostatic interaction governs the timescale of gas bubble coalescence below a threshold approach velocity. Above this approach velocity, the coalescence dynamics is governed by the capillary timescale of the drainage of the thin film. The observation is further supported by the coalescence behavior at various pH values of the electrolyte, since these pH values contribute to different degrees of electrostatic charge redistribution at the interface.