Hydrogenated double wall carbon nanotubes

Herein, we investigate the chemisorption of hydrogen on double wall carbon nanotubes (DWCNT) employing density functional theory and periodic boundary conditions. In agreement with recent investigations based on Lennard-Jones potentials, we found that the $(n,m)@(n+9,m)$ combination is favored for tubes with small diameters. The C–H binding energies determined for the (16,0) single wall carbon nanotubes (SWCNT) are nearly identical to those computed for the (7,0)@(16,0) and (8,0)@(16,0) DWCNTs. For both of the latter we found that interlayer interaction modifies the band structure of the inner tube. In the case of hydrogenated DWCNTs, the electronic structure of the inner tube experiences very small changes at high coverages (50%). However, at lower hydrogen coverages (3%–25%) changes are observed in the electronic structure of the inner tube. In agreement with recent experimental results we conclude that, for heavily functionalized DWCNTs, the electronic properties of the inner tube remain unchanged. For zigzag SWCNTs, the band gap becomes larger upon increase in hydrogen coverage; at 50% of coverage the hydrogenated (16,0) SWCNT has a band gap of 3.38 eV. Finally, based on the fact that high coverages significantly elongate C–H bond distances, we propose that the hydrogenation coverage may be determined measuring the C–H vibrational modes.