Effect of Fe/N-doped carbon nanotube (CNT) wall thickness on CO₂ conversion: A DFT study

Many researches on CO₂ adsorption using carbon nanotubes (CNTs) have been actively studied, but experimental and theoretical studies on CO₂ conversion are still in demand. In particular, the effect of CNT wall thickness on CO₂ conversion is not yet established clearly. This study employed two different-walled CNT catalysts doped with iron and nitrogen, single-walled CNT (Fe-N-SWCNT) and double-walled CNT (Fe-N-DWCNT). The structural and electrical properties of these CNTs and their influences on CO₂ conversion were characterized and compared using density functional theory (DFT) calculations. As a result, Fe-N-DWCNT was shown to improve catalyst stability with higher formation energy and adsorption energy for CO₂ adsorption than Fe-N-SWCNT. Also, the CO₂ molecules were found to be highly delocalized and strongly hybridized with Fe-N-DWCNT, leading to more active charge transfer in the catalyst. These findings demonstrate the potential of selective CO₂ conversion, as wall thickness differences can lead to different electrical properties of CNTs by showing that the larger the thicknesses, the lower the energy barrier required for CO₂ conversion. Specifically, Fe-N-DWCNT is easier to convert CO₂ to HCOOH than Fe-N-SWCNT at lower overpotential (0.15 V) obtained with limiting potentials and free energies calculated by understanding the possible reaction pathways in the proton-electron transfer process. Therefore, these results support the hypothesis that the wall thickness of CNT influences CO₂ conversion by showing that the double-walled heterogeneous CNT (Fe-N-DWCNT) is a potential catalyst to selectively produce HCOOH from CO₂ conversion.

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Published in: Sustainable Materials and Technologies
License: http://creativecommons.org/licenses/by/4.0/
See article on publisher's website: https://dx.doi.org/10.1016/j.susmat.2020.e00224