The relationship between the growth rate and the lifetime in carbon nanotube synthesis

Abstract

We report an inverse relationship between the carbon nanotube (CNT) growth rate and the catalyst lifetime by investigating the dependence of growth kinetics for ∼330 CNT forests on the carbon feedstock, carbon concentration, and growth temperature. We found that the increased growth temperature led to increased CNT growth rate and shortened catalyst lifetime for all carbon feedstocks, following an inverse relationship of a fairly constant maximum height. For the increased carbon concentration, the carbon feedstocks fell into two groups where ethylene/butane showed an increased/decreased growth rate and a decreased/increased lifetime indicating different rate-limiting growth processes. In addition, this inverse relationship held true for different types of CNTs synthesized by various chemical vapor deposition techniques and continuously spanned a 1000-times range in both the growth rate and catalyst lifetime, indicating the generality and fundamental nature of this behavior originating from the growth mechanism of CNTs itself. These results suggest that it would be fundamentally difficult to achieve a fast growth with a long lifetime.

Investigation of growth dynamics of carbon nanotubes

“…All studies dedicated to the investigation of the dependence of the growth rate of nanotubes on temperature reported that the rate increased nonlinearly with temperature [42,82,154–155 160–162 164,166–168 174–175 177–180 183,187–204]. For example, the authors of [200] found that the growth rate of nanotubes increased exponentially from 1.6 to 28 µm/min (by a factor of 18) while increasing the growth temperature from 800 to 1100 °C in the thermal CVD process using Fe as catalyst and C 2 H 2 as carbon source.…”

“…In recent reports [168,177], it was demonstrated that varying the concentration of gaseous carbon precursor in the reacting gas mixture may lead to changes of the activation energy of the nanotube growth due to switching between different growth rate-limiting processes. The authors of [177] performed the growth of MWCNTs by the laser-assisted CVD method using C 2 H 4 as carbon source (Ar and H 2 were used as gas carriers) and Fe catalyst at temperatures of 600–1000 °C.…”

“…Varying the concentration of C 2 H 4 allowed changing the activation energy between the values of 0.25 eV, which was assigned to the adsorption of gaseous carbon source on the catalyst particle, 0.36 eV, which corresponded to the mass diffusion of the carbon source, 0.57 eV, which was assigned to the dissociation of the carbon precursor to carbon, and 0.76 eV, which corresponded to the surface diffusion of carbon on the catalyst particle. In [168], the SWCNTs were grown by the water-assisted thermal CVD method using C 2 H 4 or C 4 H 10 as carbon source (in the mixture with He and H 2 O) and Fe catalyst at 725–825 °C. When C 2 H 4 was used, the activation energy of the nanotube growth decreased from 2.8 to 1.0 eV with increasing the carbon concentration in the reacting gas mixture from 3 to 10%.…”

“…In [159], it was shown that an increase of the C 2 H 4 pressure in the water-assisted thermal CVD synthesis of SWCNTs on Fe catalyst led to a gradual decrease of the lifetime of the catalyst. The authors of [168] demonstrated that the lifetime evolution with changing precursor pressure depended on the used carbon feedstock. An increase in the C 2 H 4 and C 4 H 10 pressures in the thermal CVD synthesis with Fe catalyst caused a decrease and increase of the lifetime, respectively, and it pointed out different rate-limiting processes of the nanotube growth.…”

A super-growth method for single-walled carbon nanotube synthesis

“…In later research, it was clarified that for the single-walled CNTs to grow vertically at millimeter-scale height, there was a sweet spot for the size and spacing of the catalyst [11] (Fig. 10).…”