Boosting CO-based synthesis of single-walled carbon nanotubes with hydrogen

Aerosol (floating catalyst) chemical vapor deposition method based on CO disproportionation (the Boudouard reaction) is one of the most promising techniques for the synthesis of single-walled carbon nanotubes (SWCNTs), especially in the form of thin films. However, despite its advantages (i.e., high quality of nanotubes, absence of double- or multi-walled nanotubes, and high controllability of the process), synthesis based on CO disproportionation fails to provide high-yield production. In this work, we examined the effect of hydrogen, admixed to the CO atmosphere as a growth promoter, on the synthesis and properties of SWCNTs. Using optical spectroscopy techniques, conductivity tests, TEM and SEM analysis, and thermodynamic calculations, we revealed hydrogen affects both catalyst activation and nanotube growth. We found a positive H₂ effect in two different temperature regimes: the yield increased by a factor of ∼15 at a low temperature (880 °C), which, after doping, led to one of the lowest ratios of the equivalent sheet resistance (R₉₀) and yield (i) and SWCNT lengthening by a factor of 2.4 leading to a 3-fold decrease in an R₉₀ coupled with a noticeable increase in the yield at a high temperature (1000 °C) (ii). We believe the presented results are fruitful for the fundamental understanding of the mechanism for nanotube growth and practical opportunity to fine-tune the production rate of SWCNT films.