2D x-ray imaging technique reveals hidden processes in CO2 electrolyzers

Electrochemical devices that convert CO2 into useful chemicals are a promising route toward sustainable industrial production, yet their long-term stability remains a major challenge. A new study by researchers from Technical University of Denmark (DTU), Ecole Polytechnique Fédérale de Lausanne (EPFL), and the European Synchrotron Radiation Facility (ESRF) introduces a powerful in-operando two-dimensional X-ray diffraction imaging techniques that allows researchers to watch, in real time, what happens inside a membrane–electrode assembly (MEA)-based CO2 electrolyzer.

The team published their research in Carbon Future on September 9, 2025.

Using high-energy synchrotron X-rays and a serpentine scanning method, the researchers were able to map salt formation and water movement across different regions of the electrolyzer with micrometer resolution. They discovered that salt precipitation occurs preferentially at the gas-flow channels region, rather than under the solid “land” region of the flow field plate.

“Until now, most characterization techniques could only provide averaged signals across the whole device, making it nearly impossible to resolve where specific failures occur,” said Dr. Xu. “Our new imaging method reveals a two-dimensional cross-section of the electrolyzer in action, allowing us to pinpoint where salts form and how they migrate. This is a game-changer for diagnosing why these systems lose efficiency over time.”

Salt buildup inside CO2 electrolyzers is one of the key obstacles to scaling the technology. When salts accumulate within the porous gas diffusion layer, they block CO2 transport pathways, leading to reduced efficiency and shorter device lifetimes. By visualizing the precise regions where salts initiate and grow, this new technique provides crucial information for designing more durable electrolyzers.

According to Prof. Seger, “The surprising result was that salt forms more extensively in the channel regions, where gas transport is easier. Faster CO2 supply in these areas actually accelerates local reactions that produce bicarbonate, driving salt formation. This insight helps explain why degradation does not always follow the patterns we expect.”

The study further showed that salts tend to migrate toward the junction between the channel and land areas, likely driven by water vapor and gas bubble movements. This migration could lead to uneven performance across the device. By modeling diffusion pathways based on the X-ray images, the team confirmed that CO2 has longer transport paths under the land regions, whereas channel regions provide shorter diffusion lengths, enhancing reactions but also accelerating salt growth.

Beyond CO2 electrolysis, the researchers believe their 2D X-ray imaging platform could be widely applied to other electrochemical energy systems, including water electrolyzers and fuel cells. “This combination of advanced X-ray techniques gives us a window into buried electrochemical interfaces that are otherwise inaccessible,” added co-author Dr. Jakub Drnec of ESRF. “It opens the door to studying how catalysts, membranes, and ions behave dynamically under real operating conditions, the critical information for device optimization.”

Looking ahead, the team plans to expand the method to faster time and space resolution, enabling even more detailed visualization of rapid changes inside operating devices. The ultimate goal is to provide a toolbox for guiding the design of stable, industrial-scale CO2 electrolyzers capable of producing carbon-neutral fuels and chemicals.

About Carbon Future

Carbon Future is an open access, peer-reviewed and international interdisciplinary journal sponsored by Tsinghua University and published by Tsinghua University Press. It serves as a platform for researchers, scientists, and industry professionals to share their findings and insights on carbon-related materials and processes, including catalysis, energy storage and conversion, as well as low carbon emission process and engineering. It features cutting-edge research articles, insightful reviews, perspectives, highlights, and news and views. The article publishing charge is covered by the Tsinghua University Press.

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