Storage of
Hydrogen
Hydrogen has a high gravimetric energy density of 120 MJ/kg and a significantly low volumetric energy density of 12.75 MJ/Nm³, which poses challenges for storage depending on the application.
In general, hydrogen can be stored by two different methods: physical-based and material-based storage.
In physical storage, hydrogen is stored by increasing the pressure (compressed gaseous hydrogen storage, CGH2) or by lowering the temperature below the vaporization temperature (liquid hydrogen storage, LH2) or both (cryocompressed hydrogen storage, CCH2).
In material-based storage, a ‘carrier’ material is used to store hydrogen. Hydrogen molecules can be physically or chemically bound to the carrier material for safer and higher density storage.
Storage in compressed gas form:
This is the most used and fundamental method for hydrogen storage. It is achieved by storing hydrogen at high pressure in tanks or in the form of compressed gas underground, especially in salt caverns. Today, hydrogen can be stored in tanks that reach pressures of up to 700 bar.
Storage tanks are categorized into five types based on the material they are made from:
Type 1: All Metal Tank
Type 2: Partially Fiber-Reinforced Metal-Lined Tank
Type 3: Composite Tank with Metal Liner
Type 4: Composite Tank with Plastic Liner
Type 5: All Composite Tank
Hydrogen gas can also be stored in pressurized gaseous form in underground reservoirs or salt caverns. Salt caverns are artificial underground cavities created by solution mining by injecting fresh water from the surface into underground salt rocks in a controlled manner. Salt caverns offer a stable environment for hydrogen storage due to their low hydrogen permeability and salinity, which limits microbial hydrogen consumption. Storage capacity increases with depth.
Hydrogen storage in cryogenic liquid form:
Hydrogen can be stored in liquid form by cooling it to -253°C. Double-walled containers are used. Hydrogen liquefaction is a time-consuming and energy-intensive process, and the energy consumed for liquefaction can reach up to 40% of the hydrogen energy content. Liquid hydrogen is often used as rocket fuel in spacecraft.
Cryogenic compressed hydrogen storage: Cryogenically compressed hydrogen is a supercritical gas. At around -233 °C, hydrogen gas can be compressed without liquefaction. A vacuum storage method is used and offers a safe and fast filling.
Material-based Storage:
In this storage method, hydrogen is stored using adsorbents or hydrogen carrier chemical compounds. The most well-known hydrogen storages are magnesium hydride, sodium borohydride and ammonia borane. Magnesium hydride, the most preferred metal hydride, has a high hydrogen storage rate of 7.6% by weight. Sodium borohydride and ammonia borane have a hydrogen carrying capacity of 10.8% and 19.6% by weight, respectively. In the presence of a suitable catalyst, the hydrogen can be released by hydrolysis at room temperature and atmospheric pressure.
Hydrogen storage remains a critical component for energy systems. Each of the different storage methods offer several advantages for increasing the energy density of hydrogen and storing it safely. Storage methods in compressed gas and liquid form provide high energy density and accessibility, while material-based storage alternatives have the potential to improve safety and efficiency. With advancing technologies, the effectiveness of each of these methods is being improved and the discovery of new materials is shaping the future of hydrogen storage. Hence, efficient storage of hydrogen plays an important role in the sustainable energy transition and innovations in this field contribute to the development of the hydrogen economy.
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