**1. Introduction**

The history of civilization in terms of energy goes from the use of wood and coal to the use of oil and natural gas. By mid‐twentieth century, oil became the world leader in the energy field. Notwithstanding the great advantages of the hydrocarbon fuel, it is a non‐renewable fossil resource, which is running out and its extraction is becoming more expensive. Besides, their excessive use has led to serious problems of global pollution, which have brought severe climate change on Earth. For this reason, the next step in the energy scale could be the hydrogen (H).

Hydrogen is the most abundant element in nature and can be used as fuel in liquid or gaseous form, but its storage is risky and expensive. However, these drawbacks hydrogen has an alternative solution for storage: metal hydrides (MH), which are chemical compounds formed by a metal (M) and hydrogen (H). One of the main advantages of the use of metal hydrides as energy sources is that unlike the non‐renewable ones, they do not cause pollution when

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

burned, because its by‐product is water. For this reason, hydrogen can be considered as a clean fuel.

Hydrogen can be stored in fuel cells to produce electricity and can be used in applications as diverse as transportation or electronics industry in batteries for laptops and cell phones applications. Undoubtedly, one of the most important challenges that the hydrogen‐based economy has is its storing. In order to use hydrogen as a fuel, it needs to be safely stored in a medium that allows absorption, storage, and desorption, besides an easy transport. There are several ways of storing hydrogen, among them are metal hydrides, hydrides ceramics, carbon‐ based materials, etc.

As a consequence of the so called "Oil Crisis," in the 1970s, metal hydrides started to be considered as good candidates for using in hydrogen energy storage, due to their large capacity to accommodate an extremely high density of hydrogen in their structures. It is possible to pack more hydrogen into a metal hydride than into the same volume of liquid. The reason is that when a metal that forms a hydride is brought in contact with gaseous hydrogen, the hydrogen molecules are adsorbed onto the surface of the material. If enough energy is given to the system, the hydrogen molecules can dissociate into hydrogen atoms, which tend to enter to the crystal lattice of the metal and occupy interstitial sites. As the energy given to the system increases, hydrogen atoms are forced into the crystal until the metal becomes saturated with hydrogen. At this stage, the material goes into a new phase: the metal hydride, which allows the material to absorb hydrogen in larger amounts.
