Interplay of diffusion and dissociation mechanisms during hydrogen absorption in metals

Kinetic measurements of gas-solid reactions, in particular hydrogen-sorption kinetics, are usually interpreted according to single rate-limiting step models. However, recent studies gave clear evidence for the interdependence of fundamentally different steps involved in hydrogen sorption. This interdependence is explored in a one-dimensional continuum model in order to estimate the time, temperature, and pressure dependences of the sorption kinetics and the relevance of several materials parameters involved in the process. Quantitative descriptions of the extraction of physical parameters for various scenarios are given. The model is successfully tested for several experimental cases, ranging from model systems (thin films) to practical systems (LaNi5 Hx and MgH2 powder samples). © 2008 The American Physical Society.