4.1. Storing Properties

Hydrogen can be physically stored as either a compressed gas, a cryogenic liquid, or with materials-based storage, using metal-hydrides, organic molecules, etc. Storage as a gas (1 atm density of 0.08375 kg/m3 at NTP) typically requires high-pressure tanks (350–700 bar). Storage of hydrogen as a liquid (density of 70.8 kg/m3) requires cryogenic temperatures because the boiling point of hydrogen at one atmosphere pressure (approximately at sea level) is -252.8 ºC. Approximately, 800 liters of gaseous H2 at normal temperature and pressure (20 ºC and 1 atm) can be contained in 1 liter of liquid H2. However, around 10% of the energy content is used to reach a pressure of 200 bar, 15.5% to reach 800 bar, 40% to reach liquid state.

Storage tanks (Air Liquide)

4.2. Storing Forms

Hydrogen can be stored in tanks as compressed gas or cryogenic liquid, but also in materials. There are three ways to store hydrogen in materials: surface adsorption (the hydrogen is attached to the surface of a material as hydrogen molecules); intermetallic hydride (hydrogen molecules dissociate into hydrogen atoms that are incorporated into the solid lattice framework); complex hydride (hydrogen can be strongly bound within molecular structures, as chemical compounds containing hydrogen atoms).

4.3. LOHC

Especially interesting are the Liquid Organic Hydrogen Carriers (LOHCs) that allow storage at normal temperature and pressure. This technology may benefit from existing infrastructure because standard tanks in ports and industrial areas can be used. A process of hydrogenation is needed to transport the hydrogen chemically bonded as an LOHC.

  

4.4. Underground

To achieve large-scale hydrogen energy storage, it is necessary to use underground alternatives. For instance, salt caverns, depleted oil fields, gas fields, or aquifer formations (water containing underground layers) and saline groundwater reservoirs.

   

Gas storage in depleted oil and gas fields (KBB, Underground technologies)

4.5. Interesting facts

The hydrogen tanks of the Mirai, a Toyota fuel cell vehicle (FCV), were shot by a sniper to test their integrity in an accident. The only bullet that was able to pierce a tank was of a high caliber and only pierced the tank after hitting the exact same spot twice.

Toyota Mirai fuel cell stack (left) and hydrogen tank (right) (Mariordo, Wikimedia commons)

previous chapter: how is hydrogen produced? next chapter: how is hydrogen transported?

Deurmat

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