Improving desorption temperature and kinetic properties in MgH2 by vacancy defects: DFT study

Abstract

The aim of this work is the improvement of the desorption temperature and kinetic properties in MgH2 by magnesium vacancy defects VMg. We use the Korringa – Kohn - Rostoker (KKR) calculation combined with the coherent potential approximation (CPA) in this work. In particular, we find that the formation energy increases with the increasing VMg concentration and, vice versa, for the desorption temperature in MgH2. We also find that the magnesium vacancy defects have an effect on the gravimetric hydrogen capacity by making the magnesium hydride more lightweight. Moreover, the densities of states (DOS) indicate that the stability of MgH2 decreases with the increasing VMg concentration by shifting the Mg and H states to the conduction band (CB). In particular, we observe that it is difficult, after ∼4.8%, to storage the hydrogen into the system without cooling, because the desorption temperature becomes less than 0 °C. We also find that the optimal VMg concentration for the hydrogen vehicles is about 3.7% because its desorption temperature is close to the operating temperature of most modern vehicle engines.