Investigation of surface and near-surface effects on hydrogen desorption kinetics of MgH2

• Published in: International journal of hydrogen energy 2014-01, Vol.39 (2), p.862-867
• Main Authors: Kurko, Sandra, Milanović, Igor, Grbović Novaković, Jasmina, Ivanović, Nenad, Novaković, Nikola
• Format: Article
• Language: English
• Subjects: Ab initio calculations; Alternative fuels. Production and utilization; Applied sciences; Desorption; Diffusion; Energy; Exact sciences and technology; Fuels; Hydrogen; Hydrogen atoms; Hydrogen kinetics; Hydrogen storage; Hydrogen-based energy; Magnesium; MgH2; Preserves; Rutile; Surface effects
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2013.10.107

Desorption of hydrogen atoms from the (110) surface of rutile magnesium hydride (MgH2) was investigated using density functional theory (DFT) and pseudopotential method. System was represented by (110) (2×2) slab MgH2 supercell with 12 atomic layers along the z-axis. The H-desorption was modeled by the successive release of the four two-fold bonded H atoms from the (110) surface of MgH2. Dependence of the H-desorption energy on number and configuration of remaining surface hydrogen atoms has been determined. The features of the H atoms diffusion from the bulk towards the surface have been investigated, too. The results suggest that decrease in number of surface H atoms generally lowers the H-desorption energy in each desorption step and that both the H–H and the Mg–H interatomic interactions strongly influence the H-desorption process. The hydrogen vacancy formation energy in the first three sub-surface layers also exhibits a pronounced dependence on concentration. These findings lead to the conclusion that tendency of the MgH2 (110) surface to preserve a maximum possible surface H concentration in its most stable configuration is the limiting factor for the H-desorption kinetics. In principle, the obtained results allow us to determine preferred paths of surface and sub-surface H-diffusion for a wide range of H concentrations and the principle features of the MgH2 dehydrogenation process, at least for the H-rich region. Being rather comprehensive, the approach is applicable for other metal hydrides, as well. •H-desorption energy dependent on number of surface hydrogen atoms.•Decrease in number of surface H atoms lowers the H-desorption energy.•Maintaining the 50% surface H coverage during desorption improves MgH2 kinetics.