A model of hydrogen diffusion in spherical particles has been developed. Results from some generic simulations are presented. It is in the model assumed that the processes for hydriding/dehydriding are initiated at the surface and progresses into the bulk of the particle governed by Fick's law of diffusion. The hydrogen flux into or out of the particle is initiated by introducing a phase boundary near the surface. The migrations of several different phase boundaries from the surface and into the centre of the particle have been simulated. Cyclic hydrogen flow into/out of the particle has also been studied. It is shown that the concentration limits at the phase boundary are a determining factor of the phase boundary migration rate. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.