Industrial electrochemical processes that utilize electrodes for generating fuels and chemical products face challenges due to bubble formation. These bubbles can obstruct parts of the electrode surface, significantly diminishing the active reaction area and leading to performance drops of 10 to 25 percent. However, recent research has shed light on a long-standing misconception about this interference.
Traditionally, it was believed that the entire area of an electrode shadowed by a bubble was rendered inactive. New findings indicate that only a smaller portion—approximately the area where the bubble directly touches the surface—is actually inhibited from participating in electrochemical activity. This revelation could pave the way for innovative designs in electrode surfaces, aimed at minimizing these inefficiencies commonly encountered in electrochemical systems.
The comprehensive findings are detailed in a paper published in the journal Nanoscale by MIT graduate Jack Lake, along with a collaborative team including graduate student Simon Rufer and professor Kripa Varanasi. The research effort also included scientists from the University of Chicago and Argonne National Laboratory. Notably, the team developed an AI-driven open-source software tool, which enables engineers and scientists to automatically identify and quantify bubble formation on any given surface, marking a vital step towards optimizing electrode properties.
Gas-evolving electrodes, typically featuring catalytic surfaces, are critical to a variety of processes such as the production of “green” hydrogen—which eliminates fossil fuel dependency—carbon capture initiatives aimed at reducing greenhouse gas emissions, aluminum production, and the chlor-alkali process, a key method in manufacturing essential chemical products.
These processes are highly prevalent; for instance, the chlor-alkali production process is responsible for approximately 2 percent of all electricity consumption in the U.S., while aluminum processing accounts for 3 percent of global electricity use. Given the current global efforts to meet ambitious greenhouse gas reduction targets, the potential impact of these new findings is substantial, as noted by Varanasi.
“Our research underscores that controlling how bubbles interact with electrodes can significantly influence their formation and ejection,” Varanasi states. “Recognizing that the area beneath bubbles can still function actively introduces a fresh set of design principles for crafting high-performance electrodes that mitigate the adverse effects of bubble interference.”
Rufer adds, “Previous literature erroneously indicated that both the contact area and the entire area under a bubble were inert. Our research establishes a critical distinction that alters electrode development strategies, minimizing performance losses.”
To validate their findings, the research team constructed various electrode surfaces featuring patterned dots that encouraged bubble formation at specific sizes and spacings. This approach illustrated that surfaces designed with greater dot spacing resulted in larger bubbles but with minimal contact area, highlighting the gap between expected and actual bubble impacts.
The necessity of developing this software for detecting and quantifying bubble formation was crucial for their methodology. Rufer explains, “We aimed to gather extensive data from various electrodes, reactions, and bubble types, each exhibiting unique characteristics. Crafting software capable of managing different materials under varying light conditions while reliably tracking bubble behavior was a complex challenge, with machine learning being essential in this process.”
Leveraging this tool, the team amassed significant datasets on bubble dynamics—documenting their locations, sizes, growth rates, and more. The software is currently available for free via a GitHub repository, facilitating access for researchers worldwide.
By correlating visual bubble data with electrical performance measurements, the researchers successfully debunked previously accepted theories, demonstrating that it is the direct contact area that is affected. Video evidence substantiated their claims, showing new bubbles developing right beneath larger ones.
The researchers established a robust methodology applicable to any electrode or catalyst surface to characterize bubble impact. They quantified bubble passivation using a new performance metric termed BECSA (Bubble-induced Electrochemically Active Surface Area), which contrasts with the conventional ECSA (Electrochemically Active Surface Area) metric used historically. Varanasi noted, “We defined the BECSA metric in earlier work but lacked an effective estimation method until this study.”
The understanding that submerged areas of bubbles can retain significant activity inspires novel electrode design principles. Electrodes should prioritize minimizing the bubble contact area over mere bubble coverage, achievable through engineering surface morphology and chemistry. By optimizing surfaces to control bubble dynamics, efficiency in these processes can be enhanced, leading to lower energy consumption and reduced material costs. This is particularly significant for electrodes coated with costly metals like platinum or iridium; the insights gleaned from this research could guide the development of electrodes that minimize material losses due to bubble blockage.
Varanasi explains, “The insights derived from this research could ignite the development of new electrode architectures that not only reduce the consumption of precious materials but also enhance electrolyzer performance, ultimately yielding substantial environmental benefits.”
The research team comprised Jim James, Nathan Pruyne, Aristana Scourtas, Marcus Schwarting, Aadit Ambalkar, Ian Foster, and Ben Blaiszik from the University of Chicago and Argonne National Laboratory, with the study backed by the U.S. Department of Energy under the ARPA-E program.
Photo credit & article inspired by: Massachusetts Institute of Technology
