Ciro Project

how to store hydrogen?

Hydrogen has a very low density. It is very light, but it takes a lot of space to store it. 

There are 3 common ways used to store hydrogen. Tere are three possible ways to store hydrogen:

compressed gas

Hydrogen at atmospheric temperature is a gas. Gases are compressible fluids that can be compressed to occupy less space by forcing molecules to be closer to each other.

Compressed hydrogen gas is stored under very high pressures to increase storage density. It requires strong high-pressure tanks to avoid them from bursting.

This method is often used for many applications, for example in hydrogen cars. Hydrogen cars use highly compressed hydrogen at 700bar, which equals roughly 700 times more pressure than Earth’s atmosphere. High-pressure tanks used in hydrogen cars are usually made of strong lightweight composite materials.

 Compressed hydrogen at 700bar can store 400 times more hydrogen molecules than hydrogen at atmospheric pressure in the same amount of space.  

liquid hydrogen

Another method to store hydrogen is through liquefaction. Storage of hydrogen as a liquid requires cryogenic temperatures. It requires reducing its temperature down to -253°C.

Liquid hydrogen greatly reduces the space hydrogen occupies. However, it requires a lot of energy to bring down the temperature. Usually, this process consumes about 30% of the total energy stored in the hydrogen just to cool it down to cryogenic temperatures. Additionally, extra energy is needed constantly to maintain the temperature inside the liquid hydrogen tank.

Liquid hydrogen is good to make hydrogen denser without requiring high pressures which can be dangerous. However, it is complex and very inefficient energy wise. Liquid hydrogen is used for specific applications, such as rocket fuel.

Liquid hydrogen can store twice as many hydrogen atoms per cubed centimetre than compressed gas hydrogen at 700bar. 

metal hydrides

The third method available to store hydrogen is through metal hydrides. Metal hydrides are specific metallic alloys with special properties that will allow for hydrogen atoms to absorb in between the gaps of the metal atoms in a reversible process. These metallic alloys are usually in the form of a fine powder to increase the exposed surface area. The metal powders are usually enclosed in a sealed tank.

Metal hydrides can store even more hydrogen per volume than compressed or liquid hydrogen can, without the risk of a high pressure or the energy consumption that liquid hydrogen requires. The major disadvantage of metal hydrides is the weight. Metal hydrides tanks are filled to the top with the heavy metallic alloy which makes the tanks very heavy. 

Metal hydrides are mainly used in small portable applications, such as a small bicycle or in stationary applications where the tanks do not need to be moved around, such as a large hydrogen facility.