IFISUR   23398
INSTITUTO DE FISICA DEL SUR
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Effects of Nb-doped MgH2 in H desorption energy: A DFT approach
Autor/es:
ESTEFANÍA GERMÁN; ALFREDO JUAN
Lugar:
Barcelona
Reunión:
Conferencia; 31st European Conference on Surface Science (ECOSS-31); 2015
Institución organizadora:
European Conference on Surface Science
Resumen:
Magnesium hydride is one of the most promising candidates as hydrogen storage media in the automotive industry due to its very high capacity (7.6 wt%) and low cost. Nevertheless, a slow hydriding and dehydrogenating kinetics and a high dissociation temperature limit its practical application. The mechanical alloy of MgH2 with transition metal elements has been experimentally proved to be an efficient method. We have studied the preferential site for Nb dopants on MgH2 bulk, MgH2 (001) and (110) surfaces to improve H desorption energy. Calculations have been carried out within the frame of DFT as implemented in the VASP code. The studied bulk structure was simulated using a supercell containing 96 atoms and MgH2 surfaces using a (2 x 2) slab with a 20 Å vacuum in the vertical direction. In order to avoid edge effects, the dopant was located at the center of the supercell, considering substitutional and interstitial configurations. Occupation energy is calculated to recognize the preference site of dopants in the structures and the relative stability of the systems. Positive values were obtained for all systems, this implies that the overall stability of doped bulk and surfaces is reduced comparing to pure systems. The dopant prefers to occupy interstitial sites, in these cases the energy cost to remove one H atom at 0 K is about 36% minor than in pure MgH2 for bulk and (001) surface, but 96% minor for (110) surface. The more appropriate system for H desorption is MgH2 (110) surface containing one interstitial Nb atom. The Mg-H bonds decrease their strength about 27% because of the dopant presence makes easier the dehydrogenation process. Dehydrogenation is improved due to the Nb occupation energy is low as well as the H desorption energy. Nb-H bonds are formed and Mg-H bonds are weakens allowing the process.