Abstract 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.

中文翻译：

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Fe/N 掺杂碳纳米管 (CNT) 壁厚对 CO2 转化的影响：DFT 研究

摘要 许多利用碳纳米管（CNTs）吸附CO2的研究已经得到积极研究，但仍需要对CO2转化进行实验和理论研究。特别是，CNT 壁厚对 CO2 转化的影响尚未明确。本研究采用两种不同壁的碳纳米管催化剂，分别掺杂铁和氮，单壁碳纳米管（Fe-N-SWCNT）和双壁碳纳米管（Fe-N-DWCNT）。使用密度泛函理论 (DFT) 计算对这些碳纳米管的结构和电学特性及其对 CO2 转化的影响进行了表征和比较。结果表明，与 Fe-N-SWCNT 相比，Fe-N-DWCNT 具有更高的 CO2 吸附形成能和吸附能，从而提高了催化剂的稳定性。此外，发现 CO2 分子高度离域并与 Fe-N-DWCNT 强烈杂交，导致催化剂中更活跃的电荷转移。这些发现证明了选择性 CO2 转化的潜力，因为壁厚差异会导致 CNT 的不同电性能，因为厚度越大，CO2 转化所需的能量势垒越低。具体而言，Fe-N-DWCNT 在较低的过电位 (0.15 V) 下比 Fe-N-SWCNT 更容易将 CO2 转化为 HCOOH，通过了解质子 - 电子转移过程中可能的反应途径计算出极限电位和自由能。因此，这些结果通过表明双壁多相碳纳米管（Fe-N-DWCNT）是从 CO2 转化中选择性产生 HCOOH 的潜在催化剂，支持了 CNT 的壁厚影响 CO2 转化的假设。