Role of vacancies and transition metals on the thermodynamic properties of MgH2: Ab-initio study

Using the Korringa -Kohn -Rostoker method, the effect of doping with transition metals and creating magnesium vacancies into MgH2 is investigated ab to improve its thermo-dynamic properties. The results indicate that the heat of formation increases with increasing the concentration of magnesium vacancies and transition metals and vice versa for the decomposition temperature and stability. In particular, the density of states shows that the decrease in the stability as a function of the concentrations can be explained by the fact that there is a weak hybridization between the doped elements and hydrogen atoms, unlike the pure magnesium hydride, which is mainly composed of a strong hy-bridization between the hydrogen and magnesium atoms. In addition, the decrease in the number of magnesium elements allows the hydrogen atoms to move faster in the struc-ture. This improves the thermodynamic properties of MgH2 by decreasing the temperature of decomposition and increasing the enthalpy of formation. Moreover, the optimal con-centrations (x + y) for practical use are 6.1% for Mg1-x-yMnxH2, 6.4% for Mg1-x-yCrxH2, and 7.1% for Mg1-x-yVxH2.(c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

By using the Korringa-Kohn-Rostoker method, the researchers investigate the effects of doping with transition metals and creating magnesium vacancies on the thermodynamic properties of MgH2. The results show that the heat of formation increases with higher concentrations of magnesium vacancies and transition metals, while the decomposition temperature and stability decrease. The weak hybridization between the doped elements and hydrogen atoms, as well as the faster movement of hydrogen atoms in the structure, contribute to the improvement of the thermodynamic properties. The optimal concentrations for practical use are determined to be 6.1% for Mg1-x-yMnxH2, 6.4% for Mg1-x-yCrxH2, and 7.1% for Mg1-x-yVxH2.