Thermocapillary convection during hydrogen evolution at microelectrodes

Oscillating Hydrogen Bubbles at Pt Microelectrodes

“…There has been speculation as to whether electrostatic attraction, the solutal Marangoni effect [16], or coalescence, as recently proposed in [27], is behind the physics of the reattachment. While the solutal Marangoni effect due to the concentration dependence of surface tension can be ruled out based on recent works [28,29], the role of electrostatic interactions and coalescence remains unclear.…”

“…It was reported in [29] that a thermocapillary Marangoni flow exists at electrogenerated bubble interfaces on microelectrodes. Hence the bubble experiences Marangoni force given by the integration of thermocapillary stress over the interface [29],…”

“…As the solution pH is below the isoelectric point, the hydrogenwater interface is expected to be positively charged [43] due to the specific adsorption of protons at the interface and therefore F e acts downward (−y direction). It was shown in [29] that also the Marangoni force experienced by the bubble acts against buoyancy. Therefore, at the moment of detachment, the force equilibrium at the bubble is given by F e þ F M ¼ F b .…”

“…Therefore we solve for the temperature and flow distribution in the cell for the domain shown in Fig. 3(a) by the methodology described in [29]. As the Pt electrode carries significant heat away from the fluid, the counter and working electrodes as well as the surrounding glass cuvette were included in the computation domain.…”

“…We further assume in the following that a quasiconstant thermocapillary Marangoni force exists during the fast bubble oscillations (f ∼ 100 Hz). As the temperature at the interface is determined by convection (Pe ≫ 1) [29], this approximation is justified by the separation of the timescales of oscillation (2=f ∼ 5 ms) and Marangoni convection [R=j⃗ uj ∼ 0.5 mm=ð10 mm=sÞ ¼ 50 ms]. Hence, the electric force remains as the primary driving force for the oscillations.…”