A DFT study of H2 adsorption on functionalized carbon nanotubes

Hydrogen storage on carbon nanotubes (CNTs) is a key research issue, attracting a lot of interest around the world. Unfortunately, pristine CNTs present very low hydrogen adsorption capacities. Here, the molecular hydrogen adsorption on CNTs functionalized with −NH2, −OH, −BH2 groups was investigated by means of density functional calculations. In contrary to −BH2 group, the −NH2 and −OH functional groups induce an electric dipole moment on the H2 molecule, resulting in more efficient binding of H2 to the functionalized CNTs. The H2 binding affinity is improved from about 0.72 kJ/mol (on the pristine (8, 0) CNT surface) to about 6.47–7.17 kJ/mol on the −NH2 and −OH functionalized CNTs. Additionally, the chemical functionalization leads to a dramatic HOMO–LUMO energy gap opening and also significant increase of the work function of the CNT. This will raise the potential barrier of the electron emission from the tube surface, making the field emission difficult.