Kinetic Monte Carlo methods were used to study the diffusion of hydrogen in a typical graphite granule. Molecular dynamics was used to obtain the jump attempt frequency and migration energy for interstitial graphite as input for the kinetic Monte Carlo method. A consistent parameterization of molecular dynamics within the kinetic Monte Carlo method was presented. The diffusion exhibited a non-Arrhenius behavior which could be explained by two different types of jump process within the graphite crystal. The porous granule structure was constructed using statistical distributions for the crystallite dimensions and orientations at a given porosity. The hydrogen trapping at intercrystallite micro-voids was modeled by assuming that a fraction of the hydrogen atom flux passing through the micro-void was trapped. A parametric study was made of the diffusion and trapping of hydrogen within granules for various trapping fractions at the intercrystallite micro-voids.

Modeling of the Diffusion of Hydrogen in Porous Graphite. M.Warrier, R.Schneider, E.Salonen, K.Nordlund: Physica Scripta T, 2004, T108, 85-9