## 3 Results and Discussion  
### Temporal Dynamics of the Electrical Current Density  
First, the temporal changes in the electrical current were studied to determine how the electrical potential influences the bubble evolution cycle. Figure 2 shows the electrical current density achieved on the microelectrode at low applied potentials (below 3.0 V). The potential of 2.0 V was the lowest potential at which stable emergence of bubbles during the whole measurement period was observed. At potentials below 2.0 V, bubbles start to emerge at the beginning of the measurement and stop emerging after a few seconds, depending on the applied potential. At increasing electrical potentials, the periodic growth and departure of small bubbles start to affect the temporal dynamics of the electrical current, which is evident as ripples in the recorded current density in Figure 2 (e.g., at 2.9 V). Figure 3 shows the temporal dynamics of the electrical current density on the microelectrode at six electrical potentials. At low voltages (\(U\) < 3.2 V), solitary bubbles are generated at a high frequency, resulting in high-frequency fluctuations in the current density. These indistinct peaks of current density led to a high standard deviation (up to 200%) of the nominal average bubble departure diameter. However, at higher potentials (\(U\geq\) 3.3 V), a clear bubble evolution cycle appears due to strong coalescence of the small bubbles on the electrode surface. The resulting larger bubble only departs the surface when its size is sufficient for the buoyancy to overcome the pinning forces [25; 29; 43]. At \(U\) = 3.2 V, a transition between the two regimes was observed approx. 25 s after the start of the measurement. Above 3.2 V, the standard deviation of the determined bubble frequency is below 7% of the average value. Figure 3: Temporal evolution of the electric current during measurements at electric potentials between 3.0 and 3.5 V. The left image shows the full recording (200 s), while the middle image is the zoomed-in region showing the last 10 s of the measurement, and the right image shows the size of the bubbles at detachment at specified potentials. Figure 2: Electrical current density at low electrical potentials, where bubbles do not merge into a single coalesced bubble. In all measurements, 95% of the electrical current density drop towards the final value was found to occur within the first 50 s of the measurement. As the bubble growth was recorded and evaluated within the last 20 s of the measurement (i.e., after 150 s), steady state conditions can safely be assumed. Figure 4 provides a side-by-side comparison of bubble generation regimes as snapshots from the high-speed videos, clearly showing small, mostly uncoalesced bubbles departing the microelectrode surface at lower electrical potentials and the emergence of a large, coalesced bubble at increased electrical potentials. During each measurement, the electrical current density decreased asymptotically. In general, a lower normalized reduction in the electrical current density was observed at higher potentials, except for the transition region at potentials of 3.2 and 3.3 V, where the reduction was notably higher. As observed in Figure 3, the first part of the measurement at these potentials represents the emission of microbubbles with limited coalescence, while a notable reduction in the electrical current density occurs when the coalescence regime with the emission of a large coalesced bubble is established. This trend is clearly observable at 3.2 V, whereas at 3.3 V it is not obvious due to the rapid establishment of the bubble coalescence regime within the first 2 s of the measurement. The ratio between the first and the last peak in the measured electrical current density at different potentials is presented in Figure 5, providing a quick evaluation of the total decrease in electrical current density over the measurement period.