Thermodynamics, kinetics and modeling studies of KH- RbH- and CsH-doped 2LiNH2/MgH2 hydrogen storage systems

In this study, the effects of several alkali metal hydride dopants on the thermodynamics and kinetics of the 2LiNH(2)/MgH2 system were determined. The results showed that the stabilities of the doped 2LiNH(2)/MgH2 system are in the order: KH < RbH < CsH. Kinetics measurements showed that the absorption and desorption rates are in the order: RbH > KH > CsH, with absorption rates being about twice as fast as desorption from the corresponding materials. As expected, the activation energies for the reactions were in the order: RbH < KH < CsH with the activation energies for absorption being less than that for the corresponding desorption reaction. Modeling studies revealed that desorption reactions are controlled by diffusion during the entire process. However, for absorption reactions the rate-controlling process changed during the course of the reactions. The rate-controlling process in the first 70% of the absorption reactions was reaction at the phase boundary whereas diffusion controlled the rate in the latter stages. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.