Research Project

Experimental Investigation of Forces Action in Electrolytic Bubbles Nucleated on Microelectrodes for Loss Mitigation in Water Electrolysis

Water electrolysis (WE) is a promising pathway to produce green hydrogen and decarbonize entire industrial sectors [1, 2]. During electrolysis, water is split into its molecular components, hydrogen and oxygen, by applying a voltage between two electrodes. Both products of this reaction are gaseous at ambient condition and will therefore form electrolytical gas bubbles in liquid electrolytes. These gas bubbles then attach to the electrodes blocking water from reaching the electrode and decreasing the active surface area usable for further chemical reactions reducing the overall efficiency of the WE cell [2, 3, 4]. A detailed investigation into the forces acting on freshly nucleated bubbles can give further insight into ideal electrolytes employed, optimal surface morphology, electrode sizes etc. and help formulate rational design strategies for WE systems.

Water splitting basics

Water electrolysis is an electrochemical redox reaction breaking up the bonds of water by using electrical energy. The reaction occurs in an electrolyzer con taining an anode and a cathode, separated by an electrolyte. Oxidation and reduction occur at their respective electrodes, while the electrolyte enables ionic transport and blocks electron transfer. In acidic environments the half-reactions are 

Cathodic (Reduction): 2H+ +2e^- → H₂ (1)

Anodic (Oxidation): H₂O → ½ O₂ +2H⁺ +2e^- (2)

Overall: H₂O → ½ O₂ +H₂ (3)

Marangoni Force

In addition to buoyancy and surface interaction forces acting on the gas bubbles, the Marangoni Force has recently gained increasing attention in electrolytic gas evolution. The Marangoni Force is a resulting from a gradient in surface tension, where the fluid will flow from areas with high surface tension to those with low surface tension and create a restoring force [5, 6]. The surface tension of a gas-liquid interphase is dependent on several factors, including temperature (T) and ion concentration (C) around the gas bubble. Consequently, a gradient in T or C will cause a surface tension gradient and create such a force. A temperature gradient will be created by the joule heating of a gas evolving electrode which creates a heat source at the electrode. Since surface tension of an interphase always decreases with temperature the thermal Marangoni force will force the bubble towards the electrode [5, 6]. The solutal Marangoni Force, however, can be manipulated to act in different directions, depending on the electrolytes and the half reaction that is regarded. Different electrolytes have a different response to an increase in ion concentration with respect to their surface tension, while the ion gradient at the anode and at the cathode is flipped in sign, since hydrogen ions are consumed at the cathode and generated at the anode [5, 7].

Experimental Setup

The experiments aim to provide insights into the bubble nucleation, departure and growth at micro electrodes for anodic and cathodic compartments, while measuring the pH, temperature and velocity profiles in situ. Platinum micro disc-electrodes will be forged into two glass cuvettes separated by a proton con ducting membrane. Each of the cuvettes will be filled with acidic electrolytes and fluorescent nanoparticles. A sheet laser at the centerline of the disc elec trode will illuminate the nanoparticles. A high-speed camera will record the nanoparticles’ emission spectra, which are sensitive to temperature and pH. Therefore, a two-dimensional concentration and temperature field can be mea sured. The velocity field can calculated by tracking location the emission of the particles and will not require additional equipment. These direct measurements of temperature, pH and velocity fields can then be related back to Marangoni Forces acting at the micro bubble and the bubble dynamics.

References

[1] International Energy Agency. Global Hydrogen Review 2025. Tech. rep. Li cence: CC BY 4.0. Paris: International Energy Agency, 2025. url: https: //www.iea.org/reports/global-hydrogen-review-2025.

[2] Raffaello Cozzolino and Gino Bella. “A review of Electrolyzer-based sys tems providing grid ancillary services: Current status, market, challenges and future directions”. In: Frontiers in Energy Research 12 (Feb. 2024). doi: 10.3389/fenrg.2024.1358333. 

[3] Lingao Deng et al. “Bubble evolution dynamics in Alkaline Water Electrol ysis”. In: eScience 5.4 (July 2025), p. 100353. doi: 10.1016/j.esci.2024. 100353. 

[4] Lizhen Wuetal. “Bubble dynamics matters at high-rate water electrolysis”. In: Nature Communications 17.1 (Feb. 2026). doi: 10.1038/s41467-026 69052-5. 

[5] Sunghak Park et al. “Solutal marangoni effect determines bubble dynamics during electrocatalytic hydrogen evolution”. In: Nature Chemistry 15.11 (Aug. 2023), pp. 1532–1540. doi: 10.1038/s41557-023-01294-y. 

[6] Syed Sahil Hossain et al. “The thermocapillary effect on gas bubbles grow ing on electrodes of different sizes”. In: Electrochimica Acta 353 (Sept. 2020), p. 136461. doi: 10.1016/j.electacta.2020.136461. 

[7] A.M. Meulenbroek, N.G. Deen, and A.W. Vreman. “Marangoni forces on electrolytic bubbles on Microelectrodes”. In: Electrochimica Acta 497 (Sept. 2024), p. 144510. doi: 10.1016/j.electacta.2024.144510.