A new study published in eScience challenges the long-held assumption that smaller, faster-departing bubbles are always better for water electrolysis. Researchers from East China University of Science and Technology and Southern University of Science and Technology found that under high-current conditions, bubbles that merge and leave the electrode later can actually improve the hydrogen evolution reaction (HER) efficiency by up to 30%.
The findings, reported in the journal eScience (DOI:10.1016/j.esci.2025.100472), are significant because green hydrogen is expected to play a crucial role in decarbonizing industries such as chemical manufacturing, transportation, and steelmaking. However, electrolysis efficiency is often hampered by bubbles that cover catalytic sites and impede ion transport. Traditional strategies have focused on making bubbles detach earlier and at smaller sizes through surface design or external fields. But this study suggests that bubble–bubble interactions, particularly coalescence, can be harnessed to improve performance.
The research team conducted experiments in both acidic and alkaline water electrolysis using a platinum disk electrode. They found that in sulfuric acid, bubbles readily coalesced, but when perchloric acid or sodium sulfate was added, coalescence was suppressed, leading to smaller bubble departure sizes. Surprisingly, these smaller bubbles did not improve performance. At −40 mA, adding perchloric acid reduced bubble size but caused about a 20% drop in HER efficiency, and at −60 mA, the performance gap reached around 30%.
Mechanistic analysis revealed that larger departing bubbles are beneficial because their coalescence clears tiny microbubbles stuck to the electrode surface, freeing active sites before they become blocked. Additionally, coalescence generates local fluid flows exceeding 1 m/s, which disrupts the stagnant interfacial layer 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 argue that this work shifts the key question in bubble management from how to make bubbles smaller to how bubbles interact after formation. Bubble coalescence acts like a self-driven cleaning and mixing process at the electrode surface, removing microbubbles early and bringing fresh electrolyte into a region where transport is typically slow. This explains why larger departing bubbles can signal better performance under high-current operation.
These insights suggest a new design principle for gas-evolving electrochemical systems. In acidic systems, where bubbles already merge easily, electrodes or flow fields could be engineered to increase useful bubble collisions. In alkaline water electrolysis, seawater electrolysis, and chlor-alkali processes, where coalescence is often inhibited, electrolyte additives or particle-assisted strategies may help restore beneficial merging. The study points to broader applications in industrial electrolysis, offering a potential path to reduce energy loss without relying solely on catalyst or electrode-surface improvements.
The research was funded by the National Natural Science Foundation of China, the Shanghai Pilot Program for Basic Research, the Special Project for Peak Carbon Dioxide Emissions-Carbon Neutrality from the Shanghai Municipal Science and Technology Commission, and the Guangdong Basic and Applied Basic Research Foundation. The original source can be accessed at https://doi.org/10.1016/j.esci.2025.100472.
