A new study published in the journal eScience reveals that promoting bubble coalescence on electrodes during water electrolysis can significantly improve hydrogen production efficiency, challenging decades of research that focused on making bubbles smaller and faster to detach. The findings, reported by researchers from East China University of Science and Technology and Southern University of Science and Technology, suggest that under high-current conditions, larger departing bubbles—formed through coalescence—can enhance the hydrogen evolution reaction (HER) by clearing tiny bubbles from the electrode surface and stirring the nearby liquid.
The research, available online at https://doi.org/10.1016/j.esci.2025.100472, demonstrates that in acidic electrolytes, systems that promoted coalescence achieved up to 30% higher HER efficiency compared to those where coalescence was suppressed. In alkaline media, adding hydrophobic polystyrene microparticles to encourage coalescence improved efficiency by 2–6%. This challenges the prevailing assumption that smaller, quick-departing bubbles are always better.
The study's mechanistic analysis shows that when bubbles coalesce, they form larger bubbles that linger above the electrode. These larger bubbles continuously merge with surface-anchored microbubbles, pulling them away at sizes below 10 micrometers—freeing active sites before they become blocked. Additionally, coalescence generates local liquid flows exceeding 1 meter per second, breaking up the stagnant interfacial layer and improving heat and mass transfer.
“This work shifts the key question in bubble management,” the authors state. Instead of asking only how to make bubbles smaller, future electrolysis design should consider how bubbles interact after formation. Bubble coalescence acts like a self-driven cleaning and mixing process at the electrode surface, removing microbubbles early, reopening reaction sites, and bringing fresh electrolyte into regions where transport is usually slow.
The implications for the green hydrogen industry are substantial. Green hydrogen is expected to play a critical role in decarbonizing chemical manufacturing, transportation, steelmaking, and other hard-to-electrify sectors. However, electrolysis efficiency has been limited by bubble accumulation on electrodes, which blocks catalytic sites and hinders ion transport. Conventional strategies have focused on surface design, wettability control, and external fields to make bubbles detach earlier and at smaller sizes. But at high current densities, bubble–bubble interactions dominate, and this study suggests that leveraging coalescence could be a more effective approach.
The findings point to new design principles for gas-evolving electrochemical systems. In acidic systems, where bubbles already merge easily, electrodes or flow fields could be engineered to increase beneficial bubble collisions. In alkaline water electrolysis, seawater electrolysis, and chlor-alkali processes, where coalescence is often suppressed, electrolyte additives or particle-assisted strategies could restore beneficial merging.
This research also has broader applications in industrial electrolysis, where surface bubble removal and interfacial transport remain major bottlenecks. By treating coalescence as a controllable tool, future devices may reduce energy loss without relying solely on catalyst or electrode-surface improvements. The study was funded by the National Natural Science Foundation of China, the Shanghai Pilot Program for Basic Research, the Special Project for Peak Carbon Dioxide Emissions-Carbon Neutrality from the Shanghai Municipal Science and Technology Commission, and the Guangdong Basic and Applied Basic Research Foundation.
