Promoting Bubble Coalescence Could Boost Green Hydrogen Production Efficiency

In the quest to make green hydrogen production more efficient, a new study suggests that the behavior of bubbles on electrode surfaces—long considered a nuisance—may hold the key to significant performance gains. Published in the journal eScience (DOI: 10.1016/j.esci.2025.100472), the research challenges the conventional wisdom that smaller, faster-departing bubbles are always better in water electrolysis.

Water electrolysis, which splits water into hydrogen and oxygen, is a cornerstone of green hydrogen production. However, the process is hampered by bubbles that form on electrodes, blocking active sites and impeding ion transport. Traditional strategies have focused on making bubbles detach quickly and at smaller sizes through surface engineering or external fields. But at high current densities, bubble-bubble interactions become dominant, and the new findings indicate that encouraging bubbles to merge can actually improve efficiency.

The research team, from East China University of Science and Technology and Southern University of Science and Technology, conducted experiments in both acidic and alkaline electrolysis. They manipulated electrolyte composition to control bubble coalescence. In sulfuric acid, bubbles coalesced readily, but adding perchloric acid or sodium sulfate suppressed coalescence, resulting in smaller bubbles. Surprisingly, these smaller bubbles led to reduced hydrogen evolution reaction (HER) efficiency—by about 20% at −40 mA and up to 30% at −60 mA compared to systems where coalescence was promoted.

The mechanism behind this counterintuitive result lies in the dynamics of bubble departure. When bubbles coalesce, they form larger bubbles that detach later, but their departure creates a suction effect that pulls away tiny microbubbles stuck to the electrode, clearing active sites. Additionally, coalescence generates localized fluid flows exceeding 1 m/s, which disrupt the stagnant boundary layer near the electrode, enhancing heat and mass transfer. This self-driven cleaning and mixing process, the authors note, explains why larger departing bubbles can signal better performance.

In alkaline media, where coalescence is naturally suppressed, the team introduced hydrophobic polystyrene microparticles to promote coalescence, resulting in a 2–6% improvement in efficiency. This suggests a new design principle: instead of solely focusing on making bubbles smaller, engineers should consider how to promote beneficial bubble interactions.

The findings have broad implications for industrial electrolysis, including alkaline water electrolysis, seawater electrolysis, and chlor-alkali processes, where bubble management is critical. By viewing coalescence as a controllable tool, future devices could reduce energy losses without relying solely on catalyst or electrode-surface innovations. The research was supported by the National Natural Science Foundation of China and other funding bodies, and the full article is available at the original source URL.