Carbon dioxide (CO2) is a significant greenhouse gas emitted through various human activities, and efforts are being made by scientists and policymakers worldwide to reduce its impact on the environment. One promising approach involves electrochemical methods for converting CO2 into useful forms such as carbon monoxide, alcohols, and hydrocarbons. Recently, a team of environmental researchers from Doshisha University in Japan, led by Prof. Takuya Goto, published a study in Electrochimica Acta showcasing a sustainable electrochemical technique to convert CO2 into multi-walled carbon nanotubes (MWCNT) using molten salts.
In their study, the researchers utilized a LiCl-KCl melt and employed a semi-immersed nickel (Ni) substrate as an electrode to facilitate the conversion of CO2 into MWCNT. By saturating the molten salts with CO2 gas and applying electrochemical reduction at the Ni electrode/LiCl-KCl melt/CO2 interface, the supplied CO2 was transformed into solid carbon. The team achieved a “green” conversion, producing MWCNTs via this approach.
The carbonaceous material obtained from electrode-deposition was thoroughly characterized using electron microscopy techniques and elemental analysis. The analysis revealed that the material consisted of commercially valuable MWCNTs with diameters ranging from 30 to 50 nm. The researchers experimented with varying the applied voltage and extending the reaction time, observing notable changes in the MWCNTs. Increasing the electrolysis time from 10 minutes to 180 minutes led to an increase in the height of the generated MWCNTs.
Based on their experimental findings, the research team proposed a model for the formation of MWCNTs on the Ni electrode. The model encompasses three stages: CO2 reduction to carbon atoms at the Ni/LiCl-KCl melt/CO2 interface, the formation of Ni-C compounds (such as NiC) from the electrodeposited carbon atoms on the Ni electrode’s surface during the second stage, and the subsequent growth of cylindrical MWCNTs from the edge of the Ni-C compounds once the solubility limit of carbon in Ni-C compounds is reached.
To summarize, this study presents a novel and sustainable process for converting CO2 into commercially valuable carbonaceous materials. The electrochemical technique employed is environmentally friendly since it does not rely on fossil fuels. Furthermore, the use of high-temperature molten salts is noteworthy as it enables the direct conversion of CO2 gas into MWCNTs.
The results of this study have significant implications, suggesting that CO2 can be converted into functional carbonaceous materials. By combining this technique with non-consumable oxygen-evolving anodes, it has the potential to contribute to the development of carbon recycling technology, addressing global environmental challenges and playing a crucial role in carbon pricing economies. Moreover, the production process, which avoids the use of fossil fuels, aligns with the goal of achieving a sustainable society in the near future, as emphasized by Prof. Goto.