Ab-initio study of hydrogen mobility in the vicinity of MgH2Mg interface: The role of Ti and TiO2

Abstract Doping of MgH 2 with transition metals and their oxides is well-known procedure to improve its hydrogen (de)sorption properties, namely to lower the temperature of desorption and to achieve the kinetics speedup. In order to assess the influence Ti and TiO 2 doping has on H mobility and to characterize structurally and electronically observed differences, MgH 2 Mg interface doped with both Ti and TiO 2 have been studied using ab-initio interface molecular dynamics and bulk calculations. Results suggest different mechanisms of MgH 2 structure destabilization. The presence of dopants significantly stabilize MgH 2 Mg interface, which is confirmed by work of adhesion computation. Calculated formation energies show that interface system with doped TiO 2 is more stable. In terms of H mobility, molecular dynamics simulations confirm that Ti doping is more effective than TiO 2 in lowering the desorption temperature. The mobility of hydrogen atoms close to dopant is much higher in the case of Ti than in the case of TiO 2 . Electronic structure characterization reveals that oxygen atoms with high electron affinity forms more pronounced ionic bonding with Ti and the other neighbor Mg atoms. This in turn cause a shorter Ti H bonds in first coordination than in the case of Ti doping and further reduction of H atoms mobility. This is in accordance with molecular dynamics predictions.