Hydrogen storage is also divided into two more categories:
- the first category is the atomic hydrogen storage where the material requires the redistribution of the hydrogen molecule in the hydrogen atoms and the binding of the same atoms with the storage mesh of medium;
- second category is the molecular hydrogen storage into the surface of a material with a micro porosity feature. Hydrogen molecular storage is achieved via surface forces. Such materials include nano tubes and nano grid structures that can have different dimensions, shapes, and surface modifications.
Except by pressure, releasing of hydrogen from the storage medium is also achieved by increasing the temperature of the metal hydride. In chemical hydrides hydrogen can be released again only by chemical reaction with another substance, e.g. with water.