Larger bubbles may boost water electrolysis efficiency

A new study finds that, under high current, letting bubbles merge before they leave an electrode can improve hydrogen production rather than hurt it. The work suggests a new way to cut energy losses in green hydrogen and other industrial electrolysis systems.

Why it matters: - Water electrolysis is a core route to green hydrogen, which could help decarbonize chemical manufacturing, transportation, steelmaking and other hard-to-electrify industries. - Bubble formation on electrode surfaces remains a major source of efficiency loss because bubbles block active sites and slow ion, heat and mass transfer. - The study suggests a shift in design strategy: in some systems, promoting bubble coalescence can improve hydrogen evolution reaction performance instead of suppressing it.

What happened: - Researchers from East China University of Science and Technology and Southern University of Science and Technology reported the findings in eScience. - The article was available online in July 2026. - The paper examines how electrolyte composition affects bubble coalescence, bubble departure and hydrogen evolution reaction performance in acidic and alkaline water electrolysis. - The source DOI is the published paper.

The details: - The team used a three-electrode electrolytic cell with a platinum disk electrode, electrochemical measurements, high-speed imaging and numerical simulations. - In sulfuric acid, bubbles coalesced readily. - Adding perchloric acid or sodium sulfate suppressed coalescence and made departing bubbles smaller. - Smaller bubbles did not improve performance. - At -40 mA, adding perchloric acid reduced bubble size and cut hydrogen evolution reaction efficiency by about 20%. - At -60 mA, the performance gap widened to about 30%. - A just-detached bubble can linger above the electrode and merge with surface-anchored microbubbles. - That later departure can pull microbubbles away at sizes below 10 μm, clearing blocked active sites. - Coalescence also generates local flows above 1 m/s, which disrupt the stagnant interfacial layer and improve heat and mass transfer. - In alkaline media, where coalescence is naturally suppressed, adding hydrophobic polystyrene microparticles promoted coalescence and improved efficiency by 2% to 6%.

Between the lines: - The study challenges a long-running assumption in electrolysis research that smaller, faster-detaching bubbles are always better. - The key variable is not bubble size alone. It is how bubbles interact after they form. - Coalescence appears to work like a self-cleaning and mixing mechanism at the electrode surface. - That matters most at high current densities, where bubble-bubble interactions become frequent and transport limits become more severe.

What's next: - In acidic systems, electrode surfaces or flow fields could be designed to encourage useful bubble collisions. - In alkaline water electrolysis, seawater electrolysis and chlor-alkali processes, electrolyte additives or particle-assisted strategies may help restore beneficial bubble merging. - The broader goal is to reduce energy loss in industrial electrolysis without relying only on catalyst improvements or surface engineering.

The bottom line: - Larger departing bubbles are not automatically a problem. - Under the right conditions, bubble coalescence can clear active sites, stir the electrode interface and improve hydrogen production efficiency.