A new catalytic process has been used to convert carbon dioxide into solid carbon nanofibers, The created material has a wide range of unique properties and many potential long-term uses. The process, a joint venture between the U.S. Department of Energy and Brookhaven National Laboratory, utilizes electrochemical and thermochemical reactions, reactions that run at relatively low temperatures (400 degrees Celsius) and ambient pressure.
The process could successfully lock carbon away to offset or even achieve negative carbon emissions. Carbon nanotubes and nanofibers have many useful properties, including strength and thermal and electrical conductivity.
According to lead researcher Professor Jingguang Chen: “You can put the carbon nanofibers into cement to strengthen the cement. That would lock the carbon away in concrete for at least 50 years, potentially longer. By then, the world should be shifted to primarily renewable energy sources that don’t emit carbon.”
The process addresses concerns with other carbon dioxide conversions as many produce carbon-based chemicals or fuels that are used right away, which simply releases carbon dioxide right back into the atmosphere.
The reaction occurs in two stages and each requires a different type of catalyst. The two work together sequentially. The first is an electrocatalyst made of palladium supported on carbon. Electrocatalysts drive chemical reactions using an electric current. In the presence of flowing electrons and protons, the catalyst splits both carbon dioxide and water into carbon monoxide and hydrogen.
The second requires a heat-activated thermocatalyst made of an iron-cobalt alloy. This catalyst operates at temperatures around 400 degrees Celsius, significantly milder than a direct carbon dioxide conversion would require. Both catalysts are recyclable.
The use of electrocatalysis and thermocatalysis is referred to as a tandem process. The most complex part of the research was determining which catalysts to use and with understanding their properties. This required extensive computational modeling studies, physical and chemical characterization, X-ray Absorption and Scattering and Inner-Shell Spectroscopy (ISS) beamlines together with microscopic imaging.
This enabled the researchers to determine the active sites on the catalysts and subsequently to understand how these sites bond with the reaction intermediates. From this, the researchers came to understand how the catalysts change physically and chemically during the reactions.
Subsequent analysis has revealed the morphologies, crystal structures, and elemental distributions within the carbon nanofibers, enabling the resultant product to be put to specific use.
The process also produces hydrogen gas, which is a promising alternative fuel that, when used, creates zero emissions.
The research appears in the journal Nature Catalysis, titled “CO2 fixation into carbon nanofibres using electrochemical–thermochemical tandem catalysis.”
