The structural, energetic and dehydrogenation properties of pure and Ti-doped Mg(0001)/MgH2(110) interfaces

Abstract

Magnesium hydride has great potential for solid-state hydrogen storage. However, high dehydrogenation temperature and sluggish hydrogen absorption and desorption kinetics restrict its on-board automotive application. Hydrogen desorption from MgH₂ is accompanied by the formation of Mg/MgH₂ interfaces, which may play a key role in the further dehydrogenation process. In this work, first principles methods were used to understand the structural, electronic, energetic and hydrogen diffusion kinetic properties of pure and Ti-doped Mg(0001)/MgH₂(110) interfaces. It is found that Ti interface doping can slightly increase the interfacial stability as revealed by the work of adhesion, interface energy and electronic structure. Additionally, for both the pure and Ti-doped Mg(0001)/MgH₂(110) interfaces, the removal energies for the H atoms in the interface zone are significantly low compared with that of bulk MgH₂. In terms of H mobility, the Ti dopant is beneficial for H atoms migrating from the inner layers to the interface for aggregation. Furthermore, hydrogen desorption from the two interfaces mainly takes place by hydrogen diffusion within the interface rather than across the interface into the Mg matrix, and Ti doping can enhance this process significantly. These theoretical observations for hydrogen diffusion behavior at the interface are further validated by fitting the isothermal dehydrogenation curves of MgH₂–Ti with a series of kinetic models.