A new study challenges decades of assumptions in water electrolysis research by showing that larger bubbles, formed through coalescence, can actually enhance the hydrogen evolution reaction (HER) under high-current conditions. The findings, published in eScience, reveal that promoting bubble coalescence can improve HER efficiency by up to 30% compared to systems that inhibit coalescence, offering a fresh perspective on reducing energy losses in hydrogen production.
Green hydrogen is increasingly seen as a key to decarbonizing hard-to-electrify sectors like chemical manufacturing, transportation, and steelmaking. However, the efficiency of electrolysis is hampered by bubbles that form on electrode surfaces, which can block active sites and impede ion transport. Traditional strategies have focused on making bubbles detach earlier and at smaller sizes through surface engineering or external fields. But at high current densities, bubble-bubble interactions become dominant, and the new study suggests that coalescence can actually be beneficial.
The research team, from East China University of Science and Technology and Southern University of Science and Technology, conducted experiments using a three-electrode electrolytic cell with a platinum disk electrode. They manipulated electrolyte composition to control bubble coalescence in both acidic and alkaline media. 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; instead, HER efficiency dropped by about 20% at -40 mA and up to 30% at -60 mA when coalescence was inhibited.
The mechanistic analysis revealed that when bubbles coalesce, they pull away tiny microbubbles (<10 μm) from the electrode surface, freeing active sites and generating localized flows exceeding 1 m/s. These flows disrupt the stagnant interfacial layer, enhancing heat and mass transfer. In alkaline media, where coalescence is naturally suppressed, the addition of hydrophobic polystyrene (PS) microparticles promoted coalescence and improved efficiency by 2–6%.
This study shifts the paradigm from simply making bubbles smaller to understanding how bubble interactions affect performance. Coalescence acts as a self-driven cleaning and mixing process at the electrode surface, which is why larger departing bubbles can signal better performance under high-current conditions. The authors suggest that future electrolyzer designs could incorporate strategies to promote beneficial bubble collisions, such as electrode or flow field modifications in acidic systems, or electrolyte additives in alkaline and seawater electrolysis.
The findings have significant implications for industrial electrolysis, where surface bubble removal and interfacial transport are major bottlenecks. By treating coalescence as a controllable tool, it may be possible to reduce energy losses without relying solely on catalyst improvements. The study was funded by the National Natural Science Foundation of China and other grants, and it is available online with DOI: 10.1016/j.esci.2025.100472.
