Hydrogen, which has the highest energy per mass of any fuel, plays a critical role as an energy carrier in the hydrogen society. In contrast to other energy storage methods such as batteries, hydrogen can be produced from surplus energy and can be stored in large capacity for extended periods of time. However, its lower volumetric energy density requires an innovative storage system. We have been studying hydrogen storage technologies capable of storing and transporting hydrogen safely at a high energy density. We have been focusing on several hydrogen storage technologies: metal hydride, LOHC, and ammonia.

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Metal Hydride

In chemistry, hydrides are compounds and ions where hydrogen is covalently attached to the least electronegative element. In order to store hydrogen, metals such as lanthanum and titanium react with hydrogen to form metal hydrides. This technology allows hydrogen to be stored at several tens of atmospheric pressure, and it has the highest volumetric hydrogen storage density. However, it is limited to specific applications due to its low gravimetric storage density.

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Liquid Organic Hydrogen Carrier

Liquid organic hydrogen carriers (LOHCs) are oil-like liquid compounds that can store hydrogen in the form of compounds by reacting hydrogen and forming a benzene ring. LOHCs are thermally stable at high temperatures. Their hydrogenation and dehydrogenation are easy, and the LOHC technology is more economically competitive than other storage technologies. Furthermore, LOHCs can be handled by the existing oil infrastructure since the materials are liquid hydrocarbons that are widely used in various industries.

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Ammonia(NH3)

Ammonia has received considerable attention due to its high hydrogen storage density. In industry, the Haber-Bosch process has been used for ammonia production. However, its slow reaction rate lowers the efficiency of a small to mid-scale system. Recently, electrochemical synthesis has been studied as a solution for the slow reaction rate. Furthermore, the new technology enables ammonia production at atmospheric pressure, whereas the Haber-Bosch process typically operates at 10 MPa.