First-principles study of H2 adsorption on the pristine and oxidized (8,0) carbon nanotube

The effect of oxygen, hydrogen, and (oxygen + hydrogen) molecules adsorption on the structural and electrical properties of (8,0) carbon nanotube (CNT) are investigated through density functional theory. The obtained results indicate endothermical chemisorption of O2 on the nanotube surface with a large binding energy of about 598 meV and a significant charge transfer of about 0.43 e per molecule. It is discussed that the O2 chemisorption creates hole carries in the (8,0) carbon nanotube and thus increases the work function of the system. In the case of hydrogen molecule, a weak physisorption on the surface of CNT (∼−5 meV) is identified. The adsorption of H2 on CNT is also accompanied by hole doping and increment of the work function of the CNT, while the charge transfer between CNT and H2 is negligible. The band offsets in the H2-CNT junction are calculated to examine and describe the observed hole doping in this system. The effect of oxygenation of CNT on hydrogen adsorption is also investigated and the most favorable adsorption configuration is found and the related adsorption energy is calculated. It is argued that the oxygenation of CNT enhances the physisorption of hydrogen molecules. It is shown that hydrogen molecule adsorption on the oxidized CNT cancels hole doping and hence decreases the work function of the system.