## 3 Results and Discussion
### Bubble Growth and Departure Regimes  
Bubble growth and departure regimes were investigated further through high-speed camera footage. At a potential of 1.9 V, bubble nucleation failed to occur. Starting from 2.0 V and up to 2.3 V, nucleation sites are visible in the reflection of the surface. At higher potentials, the nucleation site density increases together with the size of the bubbles, obscuring the identification of individual microbubbles. For low potentials ranging from 2.0 to 2.6 V at increments of 0.1 V, a single snapshot is presented at each potential. At 2.0 V, only three nucleation sites are active, while the bubble departure diameter varies between individual nucleation sites. Bubbles detaching from  
Figure 10: High-speed video recording evaluated for average bubble departure frequency at the applied potentials ranging from 2.5 to 3.5 V. No data are shown for \(U\leq\) 2.8 V, as the bubble departure frequency could not be reliably determined due to the microbubble emission regime. Figure 9: High-speed video recording evaluated for average bubble departure diameter at the applied potentials ranging from 2.5 to 3.5 V.  
the nucleation site on the left are considerably larger compared to the bubbles from the remaining nucleation sites, as evident in Figure 11. The repeatability of the bubble departure period and departure diameter is more consistent on that particular side, indicating more favorable conditions for nucleation, which can be attributed to local surface chemical and/or topographical properties. By increasing the voltage above 2.0 V, more nucleation sites become active, making it increasingly difficult to track individual microbubble growth. The bubble departure diameters increase with applied potential. Some bubble coalescence might be present above 2.4 V, but it is not as clear as with voltages above 2.7 V.  
At a potential of 2.7 V, bubbles start to coalesce, as presented in Figure 12. At this potential, despite prevailing coalescence, several non-coalesced bubbles still depart from the surface. Occasionally, large bubbles with a diameter of up to \(\sim\)60% of the electrode diameter form, with an example presented at 0.131 s, denoted by a red arrow. Figure 11: Comparison of bubble sizes during electrolysis at a platinum microelectrode at set potentials ranging from 2.0 to 2.6 V. The diameter and location of the electrode are denoted by a red line. Figure 12: Snapshots of the electrolysis process on the microelectrode at a potential of 2.7 V at different time frames. The diameter and location of the electrode are denoted by a red line. At 2.8 V, the diameter of coalesced bubbles increases significantly compared to those observed at 2.7 V, as shown in Figure 13. Microbubbles are rarely visible, with most bubbles having a departure diameter of approximately 50 \(\upmu\)m. The occurrence of larger single bubbles with a departure diameter of 100 \(\upmu\)m or more is rare (an example is shown in Figure 13 at 0.581 s). The coalesced bubble with a diameter equal to or larger than the electrode prevents other bubbles from departing simultaneously and represents the total hydrogen generated during the bubble growth period. At 2.9 V, a single large coalesced bubble predominantly departs from the electrode surface. In Figure 14, the growth of such a bubble is captured at different time frames. Immediately after the previous bubble detachment at the 0.000 s mark, several micro bubbles start to individually form on the surface and eventually coalesce into larger bubbles. At 0.023 s, three coalesced bubbles are observed. Figure 14: Growth of a single coalesced hydrogen bubble at a potential of 2.9 V.  
Figure 13: Snapshots of the electrolysis process on the microelectrode at a potential of 2.8 V at different time frames. The diameter and location of the electrode are denoted by a red line.