Institute of Science Tokyo achieves continuous and large-scale synthesis of carbon black from CO with high electrical conductivity at low temperatures

A research group led by Professor Tomohiro Nozaki and Doctoral Researcher Xiaozhong Chen of the Department of Mechanical Engineering, School of Engineering, Institute of Science Tokyo, announced that they have succeeded in the continuous and large-scale production of carbon black, which exhibits a high electrical conductivity, by activating carbon monoxide (CO) in nonequilibrium plasma and reacting it with an iron catalyst. This feat was achieved based on the fact that it is possible to increase the electron temperature of nonequilibrium plasma alone to tens of thousands of degrees Celsius to induce chemical reactions while maintaining the temperature of the reaction field at a low level. The synthesized carbon material is characterized by a high electrical conductivity and expected to be used as an electrochemical-device electrode material that is seen to be promising in low-carbon technologies such as fuel cells and secondary batteries. The results of this research were published in the international journal ACS Energy Letters on November 26.

This technology of chemically decomposing CO₂ and recycling it as a solid carbon material (carbon black) is attracting attention as one of the promising low-carbon technologies. The first step of converting CO₂ into CO is an endothermic reaction, which requires heat energy to be supplied at relatively high temperatures.

Meanwhile, the next step of converting CO into carbon is an exothermic reaction. From an equilibrium point of view, the yield of carbon black is expected to increase when the reaction temperature is lowered. Therefore, the realization of a nonthermal catalytic reaction that maintains high rates even at low temperatures and produces carbon black with a high degree of graphitization was desired.

In 2022, the research group showed that the vibrational excitation of CO enhances its reaction with lattice oxygen, constituting a catalytic effect. In this study, the researchers employed this reaction for the synthesis of carbon black. Using a plasma fluidized-bed reactor with an inexpensive iron catalyst as the fluidized medium, they succeeded in the large-scale continuous synthesis of carbon black with high electrical conductivity from CO at a low temperature of about 600℃. Moreover, it was confirmed that the plasma characteristics (e.g., voltage-current characteristics), CO consumption rate, and catalytic activity remained almost unchanged after about 11 hours of continuous synthesis.

The developed method shows the characteristics of a carbon manufacturing technology with a low CO₂ emission and the potential to fully electrify the carbon-black synthesis process by effectively utilizing heat generated from the plasma. It is estimated that if this power is supplied from a low-carbon power source (renewable energy), CO₂ emissions can be reduced to about one-tenth that generated by a technique of synthesizing general furnace black (carbon black synthesized by a high-temperature process (1,000℃ or higher) using partial combustion of hydrocarbons).

Nozaki said, "Plasma catalyst technology not only enables the realization of nonthermal reactions that cannot be handled by thermochemical reactions but also has the practical advantage of high connectivity with renewable energy. We succeeded in developing a new technology to convert carbon dioxide into high value-added carbon material by taking advantage of these features. The objective of this study was not only to make effective use of carbon dioxide but also to contribute to the early realization of a low-carbon society by promoting the electrification of chemical processes using renewable energy sources."

Journal Information
Publication: ACS Energy Letters
Title: Plasma-Catalyzed Sustainable Nanostructured Carbon Synthesis: Advancing Chemical-Looping CO₂ Fixation
DOI: 10.1021/acsenergylett.4c02660