| By Mary Bailey
Researchers at the U.S. Department of Energy‘s Lawrence Berkeley National Laboratory (Berkeley Lab; Berkeley, California), UC Berkeley (Berkeley, California), and Estonia’s National Institute of Chemical Physics and Biophysics (Tallinn, Estonia) have shown a promising way to convert waste carbon pulled from the air into graphite, opening up a potential alternative to mining. The work was published in the journal Nature Communications.
Researchers built a custom microscope setup to watch a process known as molten-salt electrolysis, which uses electricity and hot liquid salts to turn carbon dioxide into solid carbon. For the first time, researchers were able to watch the process in real time inside the corrosive, 500°C molten salts while the system was running.
The observations answered a decades-old question about how the reaction actually occurs at the molecular level, revealing an unexpected two-step process. The researchers also found that the basic chemical reaction remained the same even when they changed the materials used for the electrodes and molten salts. Because different materials produce different carbon structures, scientists should be able to tune the process to make valuable carbon products, with an end goal of making battery-grade graphite.
A close-up shows the inner experimental set-up to study how carbon dioxide transforms into solid carbon in molten-salt electrolysis. Gray electrodes provide the electricity and serve as the site of chemical reactions with a salt sample (center). (Credit: Sander Ratso/National Institute of Chemical Physics and Biophysics)
“This is a major win in a larger effort of synthesizing critical materials and battery materials using molten salts,” said Mike Whittaker, a Berkeley Lab (Berkeley, California) scientist who worked on the project. “If you could run this process at low temperatures with really cheap salts, you could have it in a lot of places, and you could generate enough graphite that you could feed into battery supply chains.”
The team’s approach demonstrates a powerful new way to study chemistry inside molten salts, an environment that has been historically difficult to probe directly because of its harsh conditions. The next step is determining the optimal combinations of molten salts, electrode materials, temperatures, and voltages to make graphite and other carbon materials. Researchers will also need to scale up the approach to produce industrially useful amounts.
This work was part of the MINerals for Energy Storage Synthesis (MINES) program funded by the Department of Energy’s Basic Energy Sciences program.
