High-Throughput Experimentation for Selective Growth of Small-Diameter Single-Wall Carbon Nanotubes Using Ru-Promoted Co Catalysts

Small-diameter single-wall carbon nanotubes (SWCNTs) are desirable in a variety of applications requiring electronic band gaps greater than 1 eV. Here, we utilize the Autonomous Research System (ARES)an automated, high throughput, laser-induced chemical vapor deposition system with in situ Raman spectral feedbackto study the role of Ru promotion of Co catalysts in the growth of small-diameter SWCNTs. By performing over 200 growth experiments in ARES with different feedstocks and extensive multiexcitation Raman spectroscopic characterization, we demonstrate that the Ru-promoted Co catalyst nearly doubles the selectivity of small-diameter SWCNTs (diameters below 1 nm) at 750 °C in comparison to Co. At higher temperatures between 800 and 850 °C, Ru stabilizes Co catalyst nanoparticles and increases the selectivity of small-diameter SWCNTs by almost a factor of three. Results reveal that SWCNT diameters are not only dependent on catalyst properties but also on the type of feedstock as selectivity toward small-diameter SWCNTs decreases in the following order: ethylene > acetylene > FTS-GP (Fischer-Tropsch synthesis gaseous product mixture). Density functional theory calculations with 13 and 55 atom Co_xRu_y clusters (ranging from 0 to 22% Ru content) reveal increases in cluster cohesive energies (E_C) with Ru content, irrespective of the exact location of Ru atoms in the clusters. As these findings are indicative of increases in melting temperature and reduction in atom mobility with Ru content, they are consistent with the presence of ∼10% Ru in our Co catalyst, increasing sintering resistance, stability of small nanoparticles, and the observed high selectivity toward small-diameter SWCNTs.