Researchers in California and Estonia have developed a custom microscope system to watch carbon dioxide transform directly into graphite inside a 500-degree-Celsius molten salt bath. Published in Nature Communications, the real-time observations reveal a two-step reaction pathway driven by peroxide, opening a potential path to produce battery materials without mining.
Scientists have found a way to pull carbon dioxide right out of the air and lock it into solid carbon, sidestepping traditional extraction methods for one of modern life’s most important materials. Graphite is best known as the core ingredient in pencils, but it also serves an indispensable role in smartphones, laptops, electric vehicles, and grid-scale power systems. Nearly all of the global supply currently relies on mining and processing, with the United States importing the vast majority of what it consumes.
A collaborative team spanning the US Department of Energy’s Lawrence Berkeley National Laboratory, UC Berkeley, and Estonia’s National Institute of Chemical Physics and Biophysics has demonstrated an alternative. By feeding captured carbon dioxide into a pool of extremely hot molten salts charged with electricity, the team successfully converted the waste gas into solid carbon structures.
Operando Raman Microscopy Inside a 500-Degree Molten Salt Bath
For decades, researchers have studied molten-salt electrolysis—a process that uses electrical current and liquid salts heated to about 932 degrees Fahrenheit—to turn carbon dioxide into solid carbon. Exactly what happened at the molecular level during the harsh reaction, however, remained a persistent mystery because the extreme environment is notoriously difficult to probe directly.
The research team solved this visibility problem by building a custom microscope system connected to a confocal Raman microscope. Led by chemical physicist Sander Ratso of UC Berkeley, the team monitored the transformation in real time while detecting the vibrational modes of molecular bonds.
The setup gave researchers unprecedented detail on how carbon evolves during electrolysis, revealing a two-step reaction pathway. Using Raman spectroscopy to observe the reaction in action, the team noticed bands of light indicating the appearance of carbon-adsorbed peroxide as carbon gradually deposited.
While scientists had theoretically proposed peroxide as an intermediate step as early as 1999, the new microscopy setup provided the first direct empirical proof.
Cathode Selection and the Search for Battery-Grade Graphite
The team discovered that while the core chemistry remains consistent across different setups, the specific shape of the deposited carbon changes depending on the cathode material used.
- Pure nickel: Produced carbon in the form of nanotubes and platelet-like shapes.
- Inconel 600 alloy: Yielded almost exclusively carbon platelets.
- Gold electrode: Resulted in amorphous carbon clumps.
- Tungsten cathode: Produced more amorphous carbon alongside carbon nano-onions.
This tunability gives scientists greater control over the final carbon structure, moving the process closer to engineering materials specifically tailored for high-value industrial applications.
While a few commercial entities already use molten-salt electrolysis on an industrial scale to produce tons of carbon products, those operations rely heavily on ex situ trial-and-error. Manufacturers typically synthesize a material, examine its structure, alter a variable, and check the reactor output again. That trial-and-error approach makes property improvements expensive and time-consuming.
According to Ratso, who is a co-founder of one such company, real-time monitoring via operando Raman spectroscopy could make manufacturing significantly more efficient by revealing synthesis dynamics as they occur.
Funding, Supply Chain Pressures, and Next Steps
The project received support through the Minerals for Energy Storage Synthesis (MINES) program, which is funded by the Department of Energy’s Basic Energy Sciences program. Researchers emphasize that scaling the technology remains a primary hurdle before it can supply industrial quantities of graphite to domestic battery supply chains.
Beyond graphite manufacturing, the custom microscopy technique introduces a reliable way to study chemical reactions inside harsh, corrosive molten salts that have historically been difficult to probe directly. The next phase of research focuses on identifying optimal combinations of molten salts, electrode materials, temperatures, and electrical voltages to produce graphite reliably, alongside moving the technology from a lab demonstration to industrial output.
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