Nanobubble formation observed during water electrolysis

Water electrolysis is a critical technology for producing hydrogen and is expected to play an important role in decarbonizing the global economy. With the manufacturing capacity of hydrogen expected to increase to approximately 130 gigawatts a year by 2030 (just one gigawatt equals 100 million LED bulbs), water electrolysis must perform at peak efficiency.

As water electrolyzers scale to higher operating current densities (the amount of electric current traveling across the electrode), gas bubbles formed on the electrode surface can be a source of degradation and failure if they are not effectively removed. While gas bubbles are a necessary byproduct of water electrolysis, these attached gases reduce the electrode’s active area.

To better understand the mechanics of gas bubble formation during water electrolysis, researchers from PLS’s Materials Science Division and Engineering’s Materials Engineering Division used grazing incidence small-angle x-ray scattering (GISAXS) at Argonne National Laboratory’s Advanced Photon Source to make in-situ observations of nanobubble formation on the electrode’s surface.

Time-resolved GISAXS measurements show that while individual nanobubbles quickly coalesce and grow into micron-scale bubbles (one micron equals 1,000 nanometers), they also cover the electrode surface throughout the entire electrolysis process, measuring an average of two nanometers in diameter regardless of the current density.

The research team combined their experimental analyses with theoretical simulations (continuum and molecular dynamics), finding that the accumulation of high levels of supersaturated hydrogen near the surface during electrolysis are the driving force for nanobubble formation on the electrode surface and influence the bubble size.

“The data from this study gives us a clearer picture of the earliest stages of gas bubble formation, and my hope is that these findings can be used to build better models and design better electrolyzers for high-current density operations,” said Jonathan “Jack” Davis (ENG).

The bubbles observed by the researchers are some of the smallest bubbles that have ever been detected on an electrode surface. Up until this point, the presence of such a clear population of 1–2 nanometer nanobubbles, alongside much larger micron-sized bubbles, have not been a phenomenon considered in the current literature.

Altogether, this study suggests a significant portion of the electrode surface is covered by nanobubbles, due to high levels of supersaturation, opening the door to future strategies—i.e., encouraging the coalescence and subsequent departure of these nanobubbles—that would help electrolyzers operating at scale to maintain stable performance.

This work is supported by LLNL’s Laboratory Directed Research and Development Program (22-ERD-050).

[J.A. Hammons, S.Y. Kang, T.J. Ferron, F. Aydin, T.Y. Lin, K.Seung, P. Chow, Y. Xiao, J.T. Davis,  Nanobubble Formation and Coverage during High Current Density Alkaline Water Electrolysis, American Chemical Society (2024), doi: 10.1021/acs.nanolett.4c03657.]

–Physical and Life Sciences Communications Team