Stability, Electronic Structure and Thermodynamic Properties of Nanostructured MgH2 Thin Films

Omar Mounkachi,Amine El Moutaouakil,Marwan Lakhal,Ghassane Tiouitchi,Hamid Ez-Zahraouy,Abdellah El Kenz,Asmae Akrouchi,Abdelkader Kara,Elmehdi Salmani,Abdelilah Benyoussef

doi:10.3390/en14227737

Abstract

Magnesium is an attractive hydrogen storage candidate due to its high gravimetric and volumetric storage capacities (7.6 wt.% and 110 gH2/l, respectively). Unfortunately, its use as a storage material for hydrogen is hampered by the high stability of its hydride, its high dissociation temperature of 573–673 K and its slow reaction kinetics. In order to overcome those drawbacks, an important advancement toward controlling the enthalpy and desorption temperatures of nano-structured MgH2 thin films via stress/strain and size effects is presented in this paper, as the effect of the nano-structuring of the bulk added to a biaxial strain on the hydrogen storage properties has not been previously investigated. Our results show that the formation heat and decomposition temperature correlate with the thin film’s thickness and strain/stress effects. The instability created by decreasing the thickness of MgH2 thin films combined with the stress/strain effects induce a significant enhancement in the hydrogen storage properties of MgH2.

Highlights

The development of power storage methods and technologies is considered one of the most important efforts of this decade, in which hydrogen has become an important element among the clean and renewable sources of energy
Can derived that either after strain. This is a great enhancement of MgH2 storage properties, even though tensile or compressive strain is likely to cause structural deformation of the MgH2 crystal, the strain effect on the thermodynamic properties of the MgH2 thin film has not or its latticebeen distortion becomes studied previously.severe with the increasing magnitude of biaxial strain
The hydrogen storage performances of MgH2 thin films were studied through the investigation of the effect of size and strain on the thermodynamic properties using first principles DFT calculations implemented in the Quantum-espresso package

Summary

Introduction

The development of power storage methods and technologies is considered one of the most important efforts of this decade, in which hydrogen has become an important element among the clean and renewable sources of energy. Its combustion produces around three times more energy compared to fossil fuels and without any greenhouse gas emissions [1]. This has led many researchers and industrialists to consider hydrogen the key to the global energy revolution. There are three technologies available for hydrogen storage, which are storing the gas under high pressure, storing it in liquid form at low temperature or storing it in solid materials. Solid materials have recently been used for hydrogen storage by way of hydrogen atoms being absorbed and stored in metallic matrixes, such as intermetallic materials, organic compounds, metal hydrides, porous materials and complex hydrides [2,3,4,5,6,7,8,9]

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