Bigger Bubbles Boost Hydrogen Production Efficiency in Electrolysis

A groundbreaking study challenges the long-held belief that smaller, faster-departing bubbles are always better in water electrolysis. Researchers from East China University of Science and Technology and Southern University of Science and Technology discovered that, under high-current conditions, bubbles that coalesce and leave the electrode later can actually improve the hydrogen evolution reaction (HER) efficiency by up to 30%. The key insight is that larger departing bubbles are not beneficial because of their size but because their coalescence helps clear tiny stuck bubbles and stirs the nearby liquid, enhancing mass and heat transfer. This finding, published in eScience, offers a new approach to reducing energy losses in hydrogen production.

The team conducted experiments in both acidic and alkaline media, using electrochemical measurements, high-speed imaging, and numerical simulations. In sulfuric acid, where bubbles naturally coalesce, adding perchloric acid or sodium sulfate suppressed coalescence and reduced bubble size, but unexpectedly led to a 20-30% drop in HER efficiency. Mechanistic analysis revealed that coalescence promotes the removal of microbubbles (below 10 μm) and generates local flows exceeding 1 m/s, breaking up the stagnant interfacial layer. In alkaline media, where coalescence is naturally suppressed, introducing hydrophobic polystyrene microparticles enhanced coalescence and improved efficiency by 2-6%.

These findings suggest a paradigm shift in bubble management: instead of solely focusing on making bubbles smaller, engineers should consider how bubble interactions can be harnessed. The study proposes that coalescence acts as a self-driven cleaning and mixing process, reopening reaction sites and bringing fresh electrolyte to the electrode. This principle could be applied to improve efficiency in alkaline water electrolysis, seawater electrolysis, and chlor-alkali processes, where coalescence is often inhibited. By treating bubble coalescence as a controllable tool, future electrolysis devices may achieve significant energy savings without relying solely on catalyst or surface modifications.