Evaluation of the role of Au in improving catalytic activity of Ni nanoparticles for the formation of one-dimensional carbon nanostructures

Renu Sharma, See Wee Chee, Andrew Herzing, Ryan Miranda, Peter Rez

Research output: Contribution to journalArticlepeer-review

57 Scopus citations


In situ dynamic imaging, using an environmental transmission electron microscope, was employed to evaluate the catalytic activity of Au/SiO 2, Ni/SiO2, and Au - Ni/SiO2 nanoparticles for the formation of one-dimensional (1-D) carbon nanostructures such as carbon nanofibers (CNFs) and nanotubes (CNTs). While pure-Au thin-film samples were inactive for carbon deposition at 520 °C in 0.4 Pa of C2H 2, multiwalled CNTs formed from Ni thin films samples under these conditions. The number of nanoparticles active for CNF and CNT formation increased for thin films containing 0.1 mol fraction and 0.2 mol fraction of Au but decreased as the overall Au content in thin flims was increased above 0.5 mol fraction. Multiwalled CNTs formed with a root growth mechanism for pure Ni samples, while with the addition of 0.1 mol fraction or 0.2 mol fraction of Au, CNFs were formed via a tip growth mechanism at 520 °C. Single-walled CNTs formed at temperatures above 600 °C in samples doped with less than 0.2 mol fraction of Au. Ex situ analysis via high-resolution scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS) revealed that catalytically active particles exhibit a heterogeneous distribution of Au and Ni, where only a small fraction of the overall Au content was found in the portion of each particle actively involved in the nucleation of graphitic layers. Instead, the majority of the Au was found to be segregated to an inactive capping structure at one the end of the particles. Using density-functional theory calculations, we show that the activation energy for bulk diffusion of carbon in Ni reduces from ≈1.62 eV for pure Ni to 0.07 eV with the addition of small amounts (≈0.06 mol fraction) of Au. This suggests that the enhancement of C diffusion through the bulk of the particles may be responsible for improving the number of particles active for nucleating the 1-D carbon nanostructures and thereby the yield.

Original languageEnglish (US)
Pages (from-to)2464-2471
Number of pages8
JournalNano Letters
Issue number6
StatePublished - Jun 8 2011


  • Au-doped Ni catalyst
  • acetylene
  • carbon nanofibers and carbon nanotubes
  • catalytic chemical vapor deposition
  • environmental scanning/transmission electron microscope (ESTEM)
  • in situ dynamic imaging

ASJC Scopus subject areas

  • Bioengineering
  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanical Engineering


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