A recent study published in eScience challenges the long-held belief that smaller, faster-departing bubbles are always better for water electrolysis. The research, conducted by teams from East China University of Science and Technology and Southern University of Science and Technology, demonstrates that under high-current operation, bubbles that merge and leave the electrode later can actually improve the hydrogen evolution reaction (HER). This finding could have significant implications for the production of green hydrogen, a key component in decarbonizing industries such as chemical manufacturing, transportation, and steelmaking.
Water electrolysis efficiency is often hampered by bubbles that form on electrode surfaces, covering catalytic sites and impeding ion transport. Traditional strategies have focused on making bubbles detach earlier and at smaller sizes through surface design and external fields. However, at high current densities, bubble-bubble interactions become dominant, and the new study shows that promoting bubble coalescence can lead to energy savings.
The team, led by researchers at the two universities, used a three-electrode electrolytic cell with a platinum disk electrode, along with high-speed imaging and numerical simulations. They found that in sulfuric acid, bubbles readily coalesced, but adding perchloric acid or sodium sulfate suppressed coalescence, resulting in smaller bubble departure sizes. Surprisingly, these smaller bubbles did not improve performance; in fact, at −40 mA, HER efficiency dropped by about 20%, and at −60 mA, the gap reached about 30%.
The mechanistic analysis revealed that when bubbles coalesce, they create local flows exceeding 1 m/s, which stir the liquid near the electrode and help remove tiny microbubbles that would otherwise block active sites. This self-driven cleaning and mixing process frees up catalytic sites and enhances heat and mass transfer. In alkaline media, where coalescence is naturally suppressed, adding hydrophobic polystyrene microparticles promoted coalescence and improved efficiency by 2–6%.
The authors suggest that future electrolysis design should focus on how bubbles interact after formation, rather than solely on making them smaller. “Bubble coalescence can act like a self-driven cleaning and mixing process at the electrode surface,” they said. This new design principle could lead to more efficient gas-evolving electrochemical systems, including alkaline water electrolysis, seawater electrolysis, and chlor-alkali processes.
The study, with DOI 10.1016/j.esci.2025.100472, is part of eScience, a journal indexed in SCIE and ranked first in electrochemistry with an impact factor of 52.9. The research was funded by the National Natural Science Foundation of China and other grants. As the world seeks to scale up green hydrogen production, this research offers a new avenue for improving efficiency without relying solely on catalyst or electrode-surface improvements.
