Enhancement of hydrogen physisorption on single-walled carbon nanotubes resulting from defects created by carbon bombardment

The defect effect on hydrogen adsorption on single-walled carbon nanotubes (SWNTs) has been studied by using extensive molecular dynamics simulations and density functional theory (DFT) calculations. It indicates that the defects created on the exterior wall of the SWNTs by bombarding the tube wall with carbon atoms and C₂ dimers at a collision energy of 200.3em0exeV can enhance the hydrogen adsorption potential of the SWNTs substantially. The average adsorption energy for a H₂ molecule adsorbed on the exterior wall of a defected (10,10) SWNT is ~1500.3em0exmeV, while that for a H₂ molecule adsorbed on the exterior wall of a perfect (10,10) SWNT is ~1040.3em0exmeV. The H₂ sticking coefficient is very sensitive to temperature, and has a maximum value around 700.3em0exto0.3em0ex900.3em0exK. The electron density contours, the local density of states, and the electron transfers obtained from the DFT calculations clearly indicate that the H₂ molecules are all physisorbed on the SWNTs. At temperatures above 2000.3em0exK, most of the H₂ molecules adsorbed on the perfect SWNT are soon desorbed, but the H₂ molecules can still remain on the defected SWNTs at 3000.3em0exK. The detailed processes of H₂ molecules adsorbing on and desorbing from the (10,10) SWNTs are demonstrated.