Carbon dioxide (CO 2 ) is a major greenhouse gas emitted through various types of human activities. In an effort to decrease humanity’s carbon footprint, scientists and policymakers across the globe are continuously trying to explore new methods for reducing atmospheric CO 2 emissions and converting them into useful forms. In this regard, the electrochemical method of reducing CO 2 to other carbonaceous forms like carbon monoxide, alcohols and hydrocarbon has gained considerable attention.
Against this backdrop, environmental researchers from Doshisha University, Japan led by Prof. Takuya Goto recently published a study in Electrochimica Acta on 10 July 2023 that demonstrated one such method for converting CO 2 into multi-walled carbon nanotubes (MWCNT) using molten salts through sustainable electrochemistry. Their study was made available online on 22 April 2023, and included contributions from Dr. Yuta Suzuki from the Harris Science Research Institute and Mr. Tsubasa Takeda from the Department of Science of Environment and Mathematical Modeling.
Using a sustainable electrochemical technique, the research team facilitated the conversion of CO 2 into MWCNT using LiCl-KCl melt. The molten salts were saturated with CO 2 gas and semi-immersed nickel (Ni) substrate was used as electrode. The supplied CO 2 was electrochemically converted to solid carbon at the end of the procedure. This green conversion occurred via a reduction reaction at the Ni electrode/LiCl-KCl melt/CO 2 interface.
“The electrochemical reduction of CO 2 on a Ni electrode in LiCl-KCl melt at 723 K was studied. Under high polarization, a super meniscus was formed at the three-phase interface of the Ni electrode/LiCl-KCl melt/CO 2 gas, where the direct electrochemical reduction of CO 2 to solid carbon progressed. Solid carbon was obtained in the wetted area of the Ni electrode as well as in the bulk molten salt via the electrochemical technique,” remarks Prof. Goto.
Subsequent characterization of the electrode-deposited carbon using electron microscopy techniques and elemental analysis revealed that the obtained carbonaceous material consisted of MWCNTs, commercially viable nanostructures, that were 30 – 50 nm in diameter. The team then varied the applied voltage and extended the reaction time, recording noticeable changes in the MWCNTs. The height of the generated MWCNTs increased after the electrolysis time was increased from 10 min to 180 min. “We studied the dependence of applied potential and electrolytic time on the morphology and crystallinity of the electrodeposited carbon. Based on our experimental results, we proposed a model for the formation of the MWCNTs on the Ni electrode,” highlights Prof. Goto.
The proposed model for the generation of MWCNTs from CO 2 is described in three stages. The first stage involves the reduction of CO 2 to carbon atoms at the Ni/LiCl-KCl melt/CO 2 interface. During the second stage, the electrodeposited carbon atoms form Ni-C compounds (like NiC) on the surface of Ni electrode. Finally, when solubility limit of carbon in Ni-C compounds is reached, the cylindrical-shaped MWCNTs grow from the edge of the Ni-C compounds generated during the second stage.
In summary, the study identifies a novel process for sustainably converting CO 2 into commercially useful carbonaceous materials. Moreover, the employed electrochemical process is environment friendly owing to the non-usage of fossil fuel. In addition, the use of high-temperature molten salts is unique because it enables the direct conversion of CO 2 gas into MWCNTs.
“Our results indicate that CO 2 can be converted into carbonaceous functional materials. By combining non-consumable oxygen-evolving anodes, this technique can contribute to the development of a carbon recycling technology that will not only solve global environmental problems but also play an important in carbon pricing economies. The material production process, which does not use fossil fuels, will help realize a sustainable society in the near future,” concludes an optimistic Prof. Goto.
We certainly hope his visions will be realized soon!
About Professor Takuya Goto from Doshisha University, Japan
Prof. Takuya Goto serves as a Professor at the Department of Science of Environment and Mathematical Modeling, Graduate School of Science and Engineering at Doshisha University, Japan. He obtained his Ph.D. in energy science from Kyoto University, Japan. Prof. Goto has over 80 publications to his credit. His laboratory primarily conducts research in the area of energy science, nuclear engineering, inorganic chemistry, and electrochemistry.
Media contact:
Organization for Research Initiatives & Development
Doshisha University
Kyotanabe, Kyoto 610-0394, JAPAN
E-mail： jt-ura@mail.doshisha.ac.jp
Electrochimica Acta
10.1016/j.electacta.2023.142464
Experimental study
Not applicable
Direct Electrochemical Formation of Carbonaceous Material from CO2 in LiCl-KCl Melt
10-Jul-2023
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper