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Hydrogen Storage Key Concepts
Hydrogen storage
1. Explanation of key concepts of hydrogen storage
(1) Physical hydrogen storage
Physical hydrogen storage mainly relies on high-pressure compression or low-temperature liquefaction to store hydrogen. High-pressure hydrogen storage is to compress hydrogen to a higher pressure at room temperature, so that hydrogen is stored in a high-pressure container in gaseous form. This method is relatively mature in technology and has a fast filling speed. However, it requires extremely high strength and safety of container materials, and the container has a large weight, resulting in a limited hydrogen storage mass ratio. For example, common high-pressure hydrogen cylinders have a working pressure of 35MPa or even 70MPa. Low-temperature liquefied hydrogen storage is by cooling hydrogen to its boiling point (about -253 ° C) below, so that it can be converted into a liquid state for storage. The energy density of liquid hydrogen is high, which can greatly increase the hydrogen storage capacity per unit volume, but the liquefaction process consumes a lot of energy, and the thermal insulation performance of the storage container is demanding, so as to reduce the evaporation loss of liquid hydrogen.
(2) Chemical hydrogen storage
Chemical hydrogen storage uses chemical reactions to realize the storage and release of hydrogen. Among them, metal hydride hydrogen storage is a more typical way. Some metals or alloys can react reversibly with hydrogen to form metal hydrides, and when necessary, by changing the temperature and pressure conditions, the metal hydride can be decomposed and released to release hydrogen. This type of hydrogen storage material has the advantages of high hydrogen storage capacity and good safety, such as magnesium-based, titanium-iron-based and other metal hydrides. However, there are also problems such as slow absorption and release of hydrogen and the need for higher temperatures. In addition, organic liquid hydrogen storage is the use of unsaturated organic matter and hydrogen to hydrogenate to generate saturated organic matter to store hydrogen. Under appropriate conditions, saturated organic matter can dehydrogenate and release hydrogen. This method has the characteristics of large hydrogen storage and convenient transportation, but the dehydrogenation process often requires high-efficiency catalysts and the reaction conditions are more complicated.
(3) Adsorption hydrogen storage
Adsorption hydrogen storage is the use of materials with high specific surface area, such as activated carbon, metal-organic framework (MOF) materials, etc., to adsorb hydrogen on the surface or pore of the material through physical adsorption or chemical adsorption. Physical adsorption hydrogen storage is based on van der Waals force, the adsorption heat is small, the adsorption and desorption speed is fast, but the adsorption capacity is greatly affected by temperature and pressure, and generally needs to be under low temperature and high pressure conditions to achieve higher hydrogen storage capacity. Chemical adsorption hydrogen storage is through chemical bonding, and the adsorption capacity is large and the stability is good, but the desorption process usually requires a higher temperature, which limits the convenience of its application. MOF materials have received extensive attention in the field of adsorption hydrogen storage due to their strong structural designability and large specific surface area. It is expected to improve their hydrogen storage performance through rational design.
1. Explanation of key concepts of hydrogen storage
(1) Physical hydrogen storage
Physical hydrogen storage mainly relies on high-pressure compression or low-temperature liquefaction to store hydrogen. High-pressure hydrogen storage is to compress hydrogen to a higher pressure at room temperature, so that hydrogen is stored in a high-pressure container in gaseous form. This method is relatively mature in technology and has a fast filling speed. However, it requires extremely high strength and safety of container materials, and the container has a large weight, resulting in a limited hydrogen storage mass ratio. For example, common high-pressure hydrogen cylinders have a working pressure of 35MPa or even 70MPa. Low-temperature liquefied hydrogen storage is by cooling hydrogen to its boiling point (about -253 ° C) below, so that it can be converted into a liquid state for storage. The energy density of liquid hydrogen is high, which can greatly increase the hydrogen storage capacity per unit volume, but the liquefaction process consumes a lot of energy, and the thermal insulation performance of the storage container is demanding, so as to reduce the evaporation loss of liquid hydrogen.
(2) Chemical hydrogen storage
Chemical hydrogen storage uses chemical reactions to realize the storage and release of hydrogen. Among them, metal hydride hydrogen storage is a more typical way. Some metals or alloys can react reversibly with hydrogen to form metal hydrides, and when necessary, by changing the temperature and pressure conditions, the metal hydride can be decomposed and released to release hydrogen. This type of hydrogen storage material has the advantages of high hydrogen storage capacity and good safety, such as magnesium-based, titanium-iron-based and other metal hydrides. However, there are also problems such as slow absorption and release of hydrogen and the need for higher temperatures. In addition, organic liquid hydrogen storage is the use of unsaturated organic matter and hydrogen to hydrogenate to generate saturated organic matter to store hydrogen. Under appropriate conditions, saturated organic matter can dehydrogenate and release hydrogen. This method has the characteristics of large hydrogen storage and convenient transportation, but the dehydrogenation process often requires high-efficiency catalysts and the reaction conditions are more complicated.
(3) Adsorption hydrogen storage
Adsorption hydrogen storage is the use of materials with high specific surface area, such as activated carbon, metal-organic framework (MOF) materials, etc., to adsorb hydrogen on the surface or pore of the material through physical adsorption or chemical adsorption. Physical adsorption hydrogen storage is based on van der Waals force, the adsorption heat is small, the adsorption and desorption speed is fast, but the adsorption capacity is greatly affected by temperature and pressure, and generally needs to be under low temperature and high pressure conditions to achieve higher hydrogen storage capacity. Chemical adsorption hydrogen storage is through chemical bonding, and the adsorption capacity is large and the stability is good, but the desorption process usually requires a higher temperature, which limits the convenience of its application. MOF materials have received extensive attention in the field of adsorption hydrogen storage due to their strong structural designability and large specific surface area. It is expected to improve their hydrogen storage performance through rational design.
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