Hydrogen can be stored in hydrides, which are materials that can absorb and release hydrogen gas. There are several types of hydrides, including metallic hydrides, covalent hydrides, and ionic hydrides.

Metallic hydrides are formed when hydrogen gas reacts with a metal to form a solid compound. These compounds have a high capacity for hydrogen storage, but they tend to be heavy and bulky, and they require high pressures to release the hydrogen.

Covalent hydrides are formed when hydrogen atoms bond covalently with other atoms to form a compound. These compounds have a moderate capacity for hydrogen storage and can be released at lower pressures than metallic hydrides.

Ionic hydrides are formed when hydrogen ions bond with other ions to form a compound. These compounds have a high capacity for hydrogen storage, but they are generally not as stable as metallic or covalent hydrides and tend to decompose at high temperatures.

There are several challenges to using hydrides for hydrogen storage, including the cost and difficulty of producing and handling the hydrides, as well as the low efficiency of the hydrogen release process. Researchers are working on developing new materials and methods to overcome these challenges and make hydrogen storage in hydrides more practical and cost-effective.

At normal temperature, hydrides are stable, not dissolving and they are relatively safe hydrogen tanks. Their disintegration occurs at high temperatures, in the process hydrogen is released and it is brought to a fuel cell.

The observed parameters with these systems are mainly temperature at which the desorption of hydrogen from a material happens, weight capacity of absorber (in case of the whole system), volume capacity of absorber and last but not the least, the price and the system complexity.  

One of the requirements is to make the decomposition at temperatures slightly higher (150 - 200°C) not to consume excessive energy amount by hydride heating.

There has been designed efficient systems capable of absorption of high amounts of hydrogen. With different types of hydrides, there are different amounts of hydrogen which the materials can absorb. Some hydrides are easily processed liquids at a room temperature and atmospheric pressure, some are firm substances.

These materials have good volumetric energy density, but with respect to their weight their energy density is not ideal. However, for example, for some compounds with light metals, as magnesium, the overall weight of the system results only 30% higher in comparison with the systems for liquefied hydrogen storage. These unfavourable parameters are compensated by a greater need for the thermal desorption high temperature, low pressure of produced hydrogen and last but not the least, a high price of hydrides.

Another important quality is reversibility, or the capability of a material to reabsorb new hydrogen after having used up the stored hydrogen. This is connected with “recharging” of hydrides and their repeated use similarly as with batteries (Krátky, 2012, s. 41).