Hydrogen adsorption on a single Si and SiO2 molecule, doped within C(6,6) and C(10,0)carbon nanotubes (CNTs), is studied using first-principles calculations based on density functional theory. Two orientations of the H2 molecule, inside the nanotubes, are compared. Our calculations revealed a rather weak hydrogen binding energy inside both types of pristine CNTs e namely, -0.51 eV/H2 and -0.38 eV/H2 for C(6,6) and C(10,0)nanotubes, respectively. When a single Si atom is doped in the interior surface of either type of CNTs, it tends to decouple from the wall and to drift towards the nanotube's axis. ASi atom can bind two hydrogen atoms more strongly (-1.4 eV/H2 and -1.13 eV/H2 on Si within metallic and semiconducting CNTs, respectively) than just a pristine CNT would do. A SiO2 molecule binds the hydrogen atoms even stronger, along with formation of water molecule within the metallic CNT. The corresponding binding energy of -1.73 eV/H2 for the C(6,6) is found to be the highest one among the configurations considered. Based on our resuls, we believe that intrinsically Si and SiO2-doped CNTs can be considered as plausible candidates for enhancing the hydrogen adsorption properties.

Keywords