Real-time view of CO2-to-graphite conversion could cut battery supply chain emissions

Researchers have for the first time observed in real time how CO2 from ambient air is converted into graphite via molten salt electrolysis, a process that could yield low-emission battery materials.

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A team led by chemophysicist Sander Ratso at the University of California has achieved the first real-time observation of CO2 being filtered from ambient air and converted into solid carbon structures through molten salt electrolysis. The findings, published in Nature Communications, could pave the way for low-cost, low-emission production of graphite for batteries, addressing both supply chain and climate concerns.

In molten salt electrolysis, salts are heated to extreme temperatures, and an electric current, applied via electrodes, binds CO2 from the air and converts it into usable graphite. The team tracked the process at a constant temperature of 500 degrees Celsius using Operando Raman spectroscopy, a technique that analyzes scattered light patterns to identify materials. They observed a peroxide ion rising in parallel with carbon deposition, confirming a two-step reaction pathway in which carbon deposits gradually while the peroxide ion acts as a necessary intermediate.

Ratso described the process as akin to a closed oven into which the team has now installed a window, allowing them to see inside. He called the technology "Eine der wichtigsten Schlüsseltechnologien, um die CO₂-Belastung spürbar zu senken" — one of the most important key technologies for noticeably reducing CO2 emissions. Ratso also conducts research at the National Institute of Chemical Physics and Biophysics in Tallinn, Estonia.

Theoretical work had suggested since 1999 that peroxide could drive the conversion of CO2 to solid carbon, but it had not been proven until now, thanks to new measurement methods. The team also found that the cathode material influences the carbon structure: pure nickel produced carbon nanotubes and platelet-like forms, gold produced amorphous carbon lumps, Inconel 600 (a nickel-chromium-iron alloy) produced almost exclusively platelets, and tungsten produced amorphous carbon and carbon nano-onions.

Geoscientist Mike Whittaker from Lawrence Berkeley National Laboratory in California sees the results as a massive gain for the synthesis of critical battery materials. He suggests that if electrolysis could run at low temperatures with cheaper salts, enough graphite could be generated to significantly relieve global battery supply chains. Some specialized companies already use this technology industrially to produce carbon products ranging from a few kilograms to several tons.

However, conventional production of pure carbon for batteries and fuel cells emits massive CO2-equivalents, and molten salt electrolysis is extremely energy-intensive, requiring constant high temperatures to keep the salt liquid. Ratso notes that critical materials could be produced with a negative CO2 balance only if the process is fully coupled with renewable energy.

Experts agree that CO2 capture and storage technologies alone will not solve global climate problems. Direct air capture, a form of CO2 removal that extracts CO2 from ambient air, can store the separated CO2 underground or convert it into products. The U.S. Department of Energy has launched the Carbon Negative Shot initiative, aiming to capture CO2 from the atmosphere and store it at a scale of 1 billion tons for less than $100 per net metric ton of CO2-equivalent. The DOE supports direct air capture research through several offices and programs, and participates in the U.S. Carbon Cycle Science Program, a multi-agency effort to coordinate carbon cycle science.