The graphite was porous and consisted of granules and voids. The 1 to 10μm granules were further composed of graphitic micro-crystallites (5 to 10nm), which were separated by micro-voids. The kinetic Monte Carlo was used to study the diffusion of hydrogen in a typical granule of graphite. Molecular dynamics was used to obtain the jump attempt frequency and the migration energy of interstitial graphite which were input to the kinetic Monte Carlo scheme. A consistent parameterization of molecular dynamics within kinetic Monte Carlo was presented. The diffusion exhibited a non-Arrhenius behavior, which could be explained in terms of two different types of jump process within the graphite crystal. The porous granule structure was constructed by using statistical distributions for the crystallite dimensions and for crystallite orientations at a given porosity. The hydrogen trapping at intercrystallite micro-voids was modelled by assuming that a fraction of the hydrogen atom flux transiting through the micro-void was trapped.

Modeling of the Diffusion of Hydrogen in Porous Graphite. Warrier, M., Schneider, R., Salonen, E., Nordlund, K.: Physica Scripta T, 2004, 108, 85-9