MIT cracks decades-old bubble mystery to build better electrodes, electrolyzers

A research team has found a new way to design electrode surfaces that can minimize the formation of bubbles in electrochemical processes that use electrodes to produce chemical products.

The research team, which includes members from the MIT, University of Chicago, and Argonne National Laboratory, shows how the bubble formation process works and how it affects the performance of the electrodes.

Previously, it was thought that the blockages created by the bubbles could reduce the performance of electrodes by 10 to 25 percent. The new research has come up with an explanation for the decades-long misunderstanding about the interference.

The findings of the research team

For several years, it had been thought that the entire area of the electrode shadowed by each bubble would be effectively inactivated. However, the research team found that only the area where the bubble actually contacts the surface is affected.

This is a much smaller area than previously thought of, and the new insights could lead to new ways of patterning the surfaces to minimize the contact area and improve overall efficiency of the electrode.

Moreover, the research team has also made available an open-source, AI-based software tool that other scientists can use “to automatically recognize and quantify bubbles formed on a given surface, as a first step toward controlling the electrode material’s properties.”

Gas-evolving electrodes, most often the ones with catalytic surfaces that boost chemical reactions , are used in a number of processes. These include ‘green’ hydrogen production, carbon capture to reduce greenhouse gas emissions, aluminum production, and the chlor-alkali process for manufacturing common chemical products.

Designing better electrodes and electrolyzers

The chlor-alkali process accounts for 2 percent of all US electricity usage; aluminum production accounts for 3 percent of global electricity; and carbon capture and hydrogen production are likely to grow rapidly in the coming years.

As the world strives to meet greenhouse gas emission reduction targets, the new findings have a significant impact, according to professor of mechanical engineering at MIT Kripa Varanasi.

“Our work demonstrates that engineering the contact and growth of bubbles on electrodes can have dramatic effects on how bubbles form and how they leave the surface,” Varanasi says.

“The knowledge that the area under bubbles can be significantly active ushers in a new set of design rules for high-performance electrodes to avoid the deleterious effects of bubbles.”

Testing the research findings

To test the findings of the result, the team of researchers built various versions of electrode surfaces with patterns of dots that nucleated and trapped bubbles at different sizes and spacings.

With these new set of electrodes, the team succeeded in showing that surfaces with widely spaced dots promoted large bubble sizes but only tiny areas of surface contact, which helped to make clear the difference between the expected and actual effects of bubble coverage.

Graduate student Simon Rufer, who also worked on the research, stated that developing the software to detect and quantify bubble formation was important for the whole process.

Using the software, the team was able to collect “really significant amounts of data about the bubbles on a surface, where they are, how big they are, how fast they’re growing.”

In short, it means that electrode designers should now seek to minimize bubble contact area rather than simply bubble coverage, which can be achieved by controlling the morphology and chemistry of the electrodes.

Varanasi said, “The insights from this work could inspire new electrode architectures that not only reduce the usage of precious materials, but also improve the overall electrolyzer performance.”

The findings were published in the journal Nanoscale .

Abstract

The adverse effects of electrochemical bubbles on the performance of gas-evolving electrodes are well known, but studies on the degree of adhered bubble-caused inactivation, and how inactivation changes during bubble evolution are limited. We study electrode inactivation caused by oxygen evolution while using surface engineering to control bubble formation. We find that the inactivation of the entire projected area, as is currently believed, is a poor approximation which leads to non-physical results. Using a machine learning-based image-based bubble detection method to analyze large quantities of experimental data, we show that bubble impacts are small for surface engineered electrodes which promote high bubble projected areas while maintaining low direct bubble contact. We thus propose a simple methodology for more accurately estimating the true extent of bubble inactivation, which is closer to the area which is directly in contact with the bubbles.