Dynamics of Oxygen Bubbles at Microelectrodes
The dynamics of oxygen bubbles at electrodes during hydrogen production by electrolysis is an important field of research, as it influences the efficiency of hydrogen production. In the electrolysis of water, electricity is used to split water into hydrogen and oxygen. This process causes gas bubbles to form at the electrodes, which can interfere with the production process by reducing the contact area between the electrode and the electrolyte. In the project “Dynamics of oxygen bubbles at microelectrodes,” the research group led by Kerstin Eckert at the Helmholtz Center Dresden-Rossendorf is investigating how the bubbles form and dissolve again during electrolysis.
Schematic representation of the forces acting on a growing O₂ bubble
Project Presentation
by A.Babich, G.Mutschke, A.Bashkatov, H.Rox, M.Eftekhari, X.Yang, K.Eckert
This project investigates the mechanisms that control the growth and detachment of oxygen bubbles on microelectrodes in an acidic electrolyte. Particular focus is placed on a newly discovered regime in which there is an abrupt switch between regimes with high and very low current density. We were able to show [1] that the current density correlates with microconvection around the bubble and that there is a permanent switch between fast thermocapillary and slower solutocapillary convection. This is caused by the interactions of temperature and concentration gradients along the bubble surface, which drive local Marangoni convection and modulate bubble behavior. The aim is to elucidate the interaction of these convective flows in order to find optimization approaches for more efficient electrolysis cells.
Schlieren images of a growing O₂ bubble (sg: slow growth, fg: fast growth mode) [1]
How is it researched?
The investigation is carried out using potentiostatic electrolysis on platinum microelectrodes at varying potentials and sulfuric acid concentrations, with high-speed shadowgraphy being used for the quantitative determination of bubble radius, contact angle, and contact line movement. In addition, micro-particle tracking velocimetry (µ-PTV) is used to record the resulting Marangoni vortex structures and flow velocities at the bubble surface, while schlieren imaging enables precise refractive index and temperature field measurements at the bubble base and along the gas-liquid interface [2]. In addition, parabolic flight experiments under microgravity were conducted during the 39th DLR campaign to investigate the influence of absent buoyancy forces on bubble dynamics in isolation.
What is the benefit for society?
A deeper understanding of thermal and solute Marangoni convection at the gas-liquid interface enables targeted control of bubble detachment and minimizes the blockage of active catalytic sites on the electrodes due to bubble adhesion. This reduces bubble-induced overvoltages, thereby increasing the energy efficiency of hydrogen production and enabling a reduction in operating costs. At the system level, optimized mass transfer rates enable higher current densities and more stable operating windows for the electrolysers.
[1] A Babich et al., Solutal Marangoni convection at growing oxygen bubbles during water electrolysis, Phys. Review Research 7 (2025)
[2] A Babich et al., Oxygen versus hydrogen bubble dynamics during water electrolysis at micro-electrodes, PRX Energy 4 (2025)