Influence of Mo on the Fe:Mo:C nanocatalyst thermodynamics for single-walled carbon nanotube growth

Abstract

We explore the role of Mo in Fe:Mo nanocatalyst thermodynamics for low-temperature chemical-vapor deposition growth of single-walled carbon nanotubes (SWCNTs). By using the size-pressure approximation and ab initio modeling, we prove that for both Fe-rich ($\ensuremath{\sim}80%$ Fe or more) and Mo-rich ($\ensuremath{\sim}50%$ Mo or more) Fe:Mo clusters, the presence of carbon in the cluster causes nucleation of ${\text{Mo}}_{2}\text{C}$. This enhances the activity of the particle since it releases Fe, which is initially bound in a stable Fe:Mo phase, so that it can catalyze SWCNT growth. Furthermore, the presence of small concentrations of Mo reduces the lower size limit of low-temperature steady-state growth from $\ensuremath{\sim}0.58\text{ }\text{nm}$ for pure Fe particles to $\ensuremath{\sim}0.52\text{ }\text{nm}$. Our ab initio-thermodynamic modeling explains experimental results and establishes a direction to search for better catalysts.