Reaction and incorporation of H2 molecules inside single-wall carbon nanotubes through multivacancy defects

The interaction of H2 molecules with multivacancy defects in single-wall carbon nanotubes (CNTs) and their subsequent incorporation inside are investigated by density-functional theory calculations and molecular dynamic simulations. We examine the stability of multivacancies (nV) in (8,8) CNT, with n the number of missing atoms (n=2-16). We find that 16V has the limit size where defect reconstruction is unlikely, preserving the unsaturated border. After hydrogenation, the border is passivated leaving an inert pore of about 6 Å in diameter. We verify that the incorporation and release of H2 molecules through this nanopore occurs barrierless and its stability in contact with a H2 gas for both exohedral and endohedral adsorptions is preserved at high temperatures. We also find endohedral binding energies of 0.14-0.21 eV/ H2 at room temperature, which are close to those estimated optimal for a reversible adsorption-desorption process, suggesting that nanoporous CNTs as produced by electron irradiation in a hydrogen atmosphere could be an effective H2 storage medium, allowing the access to the CNT inner space.