Dynamics of Single Hydrogen Bubbles at a Platinum Microelectrode

Abstract

Bubble dynamics, including the formation, growth, and detachment, of single H2 bubbles was studied at a platinum microelectrode during the electrolysis of 1 M H2SO4 electrolyte. The bubbles were visualized through a microscope by a high-speed camera. Electrochemical measurements were conducted in parallel to measure the transient current. The periodic current oscillations, resulting from the periodic formation and detachment of single bubbles, allow the bubble lifetime and size to be predicted from the transient current. A comparison of the bubble volume calculated from the current and from the recorded bubble image shows a gas evolution efficiency increasing continuously with the growth of the bubble until it reaches 100%. Two different substrates, glass and epoxy, were used to embed the Pt wire. While nearly no difference was found with respect to the growth law for the bubble radius, the contact angle differs strongly for the two types of cell. Data provided for the contact point evolution further complete the image of single hydrogen bubble growth. Finally, the velocity field driven by the detached bubble was measured by means of PIV, and the effects of the convection on the subsequent bubble were evaluated.

On the Electrolyte Convection around a Hydrogen Bubble Evolving at a Microelectrode under the Influence of a Magnetic Field

“…The detachment of the preceding bubble is immediately followed by the formation of much smaller bubbles which coalesce rapidly to one larger bubble already on the electrode. 27 The absolute value of the current is the highest in the beginning of the bubble evolution process and decreases as the bubble grows. This is due to a reduction of the active electrode area, leading to a change of the current distribution and an increase of the resistance.…”

“…Electrochemical setup.-A cuboid glass cuvette (Hellma, 45 × 10 × 10 mm 3 [H × W × D]) with a 3-electrode setup 27 was used to periodically generate single H 2 bubbles in a 1 M H 2 SO 4 solution (Fig. 1).…”

“…• were assumed according to the data of Yang et al, 27 which were obtained for the same electrochemical cell. This yields a covered electrode radius of about 22.7 μm and 20.5 μm, respectively.…”

“…Therefore, researchers have chosen nano- 26 or microelectrodes (diameter ∼ O(100 μm)) to pin the bubbles at a certain position. [27][28][29][30] In contrast to the case of large working electrodes, experimental 29,28 and numerical 31 investigations at microelectrodes point to a stabilizing effect of the magnetic field on the bubbles. Indeed, with increasing Lorentz force, the growth rate of the bubbles became smaller and the bubbles remained attached longer on the electrode before they detached.…”

“…The bubble growth dynamics and the bubble-induced velocity field in the absence of a magnetic field has already been studied thoroughly by Yang et al 27 for the same electrochemical cell that was used here. Thus, the focus of the current investigation lies on the effects of the magnetic field and the generated Lorentz forces, which were varied by operating the cell under different potentials and applying a permanent magnet.…”