DFT studies of Hydrogen adsorption and dissociation on MgO nanotubes

We studied the adsorption of atomic and molecular hydrogen on an Mg12O12 nanotube with a different coverage by means of density functional calculations. We found that (1) an H atom prefers to be adsorbed on the top of an O atom of the tube surface rather than Mg atom; (2) 1, 2 addition of two H atoms to terminal Mg and O atoms is energetically more favorable than the addition to central atoms; (3) HOMO-LUMO energy gap of the tube dramatically decreases upon hydrogen adsorption only on oxygen atoms, transferring the intrinsic semiconductor tube to an extrinsic n-type semiconductor; (4) saturating the open end atoms with 12H atoms has no significant effect on the electronic properties of the tube; (5) upon adsorption of H on O atoms, the work function of the tube is considerably decreased, facilitating the field electron emission from the tube surface.