Two-region model for hydrogen trapping in and release from graphite

A new model has been developed for hydrogen retention and trapping in and release from graphite. Two different regions in the graphite with different hydrogen transport and trapping behaviors are distinguished, the bulk region within, and the surface region on graphite crystallites. The model incorporates new experimental results related to atom diffusion and recombination on inner surfaces. Recombination is explained from a fundamental viewpoint by linking it to diffusion using a classical expression. The model is applied to a number of reemission and thermal desorption experiments, in particular, the reemission of hydrogen atoms during irradiation with energetic hydrogen ions and the formation of HD during irradiation with H+ and D+ or during thermal desorption of graphite that was preimplanted with H+ and D+ ions with different energies.