Migration mechanism for atomic hydrogen in porous carbon materials

To explain the fast kinetics of H in porous carbon, we propose that the migration relies on H hopping from a carbon nanotube (CNT) to another. Using density functional theory, we have found that the barrier for H hopping becomes smaller than that for diffusion along a tube for certain CNT separations, decreasing to less than 0.5 eV for separations of similar to 3.1 angstrom. Such significant reduction occurs irrespective of radius, chirality, registry, and orientation of the two CNTs: the diffusion is thus facilitated by the porous nature of the material itself. The mechanism proposed is applicable for any porous carbon-based nanomaterials. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4718351]