First-principles based kinetic modeling of effect of hydrogen on growth of carbon nanotubes

We investigate the influence of hydrogen on carbon nanotube (CNT) growth in thermal catalytic chemical vapor deposition. Kinetic calculations of gas-phase transformations of hydrocarbons show that hydrogen interacts with gaseous carbon precursors, resulting in modification of the carbon supply rate to the catalyst particle. A surface-kinetic model of CNT growth is developed to study adsorption and decomposition kinetics of precursors on Ni catalyst particles. The detailed surface kinetics of carbon precursors and transport of carbon atoms through the catalyst particle are described in the framework of the surface/bulk site formalism, with the parameters of the reactions determined on the basis of first-principles calculations for Ni (1 1 1) and (1 1 3) surfaces. Using this model, different regimes of CNT growth, with and without hydrogen in the system, are analyzed. Hydrogen is shown to enhance desorption of hydrocarbons, leading to a decrease of the surface coverage and effective carbon supply rate.