In a paradigm-shifting study published in the journal eScience, researchers have discovered that larger bubbles leaving electrodes during water electrolysis can actually improve efficiency, contrary to decades of conventional wisdom that favored small, fast-departing bubbles. The findings, reported by a team from East China University of Science and Technology and Southern University of Science and Technology, suggest that bubble coalescence acts as a self-cleaning mechanism that enhances the hydrogen evolution reaction (HER) under high-current conditions.
The research, available online in July 2026, addresses a critical bottleneck in green hydrogen production. Electrolysis, a key method for producing green hydrogen, is hampered by bubbles that form on electrode surfaces, blocking active sites and hindering ion transport. Traditional strategies have focused on making bubbles detach quickly and at smaller sizes through surface engineering or external fields. However, at high current densities, bubble-bubble interactions become dominant, and the team's investigation revealed that promoting coalescence can lead to significant efficiency gains.
Using a three-electrode electrolytic cell with a platinum disk electrode, the researchers employed electrochemical measurements, high-speed imaging, and numerical simulations to study the effect of electrolyte composition on bubble behavior. In sulfuric acid, bubbles coalesced readily, but adding perchloric acid or sodium sulfate suppressed coalescence, leading to smaller departing bubbles. Surprisingly, these smaller bubbles did not improve performance. At -40 mA, adding perchloric acid reduced bubble size but caused about a 20% drop in HER efficiency; at -60 mA, the performance gap reached approximately 30%.
The mechanistic analysis revealed that a just-detached bubble can linger above the electrode, continuously merging with surface-anchored microbubbles. This late departure pulls away microbubbles smaller than 10 μm, freeing active sites before they become blocked. Additionally, coalescence generates local flows exceeding 1 m/s, which disrupt the stagnant interfacial layer and enhance heat and mass transfer. In alkaline media, where coalescence is naturally suppressed, the addition of hydrophobic polystyrene microparticles promoted coalescence and improved efficiency by 2–6%.
The authors argue that the key question in bubble management should shift from how to make bubbles smaller to how bubbles interact after formation. Bubble coalescence, they say, acts like a self-driven cleaning and mixing process at the electrode surface, removing microbubbles early, reopening reaction sites, and bringing fresh electrolyte into a region where transport is usually slow. This explains why larger departing bubbles can signal better performance under high-current conditions.
These findings, detailed in the article with DOI: 10.1016/j.esci.2025.100472, suggest new design principles for gas-evolving electrochemical systems. In acidic systems, electrodes or flow fields could be designed to increase beneficial bubble collisions. In alkaline water electrolysis, seawater electrolysis, and chlor-alkali processes, where coalescence is often inhibited, electrolyte additives or particle-assisted strategies may restore beneficial merging. The study, funded by the National Natural Science Foundation of China and other organizations, points to broader applications in industrial electrolysis, where surface bubble removal and interfacial transport remain major limits. By treating coalescence as a controllable tool, future devices may reduce energy loss without relying solely on catalyst or electrode-surface improvements.
