What Is a Hydrogen Tank?
Hydrogen tanks are tanks that store hydrogen.
Hydrogen tanks are used in fuel cell vehicles powered by fuel cells. In the case of fuel cell stacks, compressed hydrogen is stored in hydrogen tanks installed in the vehicle, and hydrogen can be supplied to the fuel cell stacks.
Hydrogen tanks used in vehicles must withstand higher pressure loads than tanks for natural gas. Hydrogen tanks are made of carbon fiber reinforced plastic or other materials that have been modified to increase their pressure resistance.
Uses of Hydrogen Tanks
Hydrogen tanks are used to store hydrogen. They are installed in fuel cell vehicles and used for hydrogen storage at hydrogen stations.
Hydrogen is very light and requires a large amount of space to store in its original state. Therefore, hydrogen is stored by compressing it at high pressure, liquefying it at low temperatures, adsorbing it onto metals, or converting it into another substance.
The most commonly used storage method is to store hydrogen at high pressure in its gaseous state, which requires high-pressure hydrogen tanks.
Principle of Hydrogen Tanks
Hydrogen tanks used in fuel cell vehicles are a necessary component of a fuel cell vehicle. As a method of storing hydrogen in a fuel cell vehicle, low-pressure hydrogen tanks can easily be used to store hydrogen in gaseous form and supply fuel to Fuel Cell Stacks.
However, the tank volume must be large. The burden of infrastructure development for supplying hydrogen is lighter and is applicable to electric carts and other vehicles that are designed to store small amounts of hydrogen. High-pressure hydrogen tanks are also in practical use in mass-produced fuel cell vehicles,
This is a common method for hydrogen storage. Due to storage space limitations in hydrogen tanks, hydrogen can be compressed and stored to extend the driving range of the vehicle. When hydrogen is cooled to ultra-low temperatures, it can be liquefied and stored in liquefied hydrogen tanks.
Liquefaction greatly reduces the volume of hydrogen compared to gas, which strongly contributes to downsizing. However, temperature control is important because hydrogen vaporizes when the temperature rises.
Structure of Hydrogen Tanks
The structure of hydrogen tanks varies depending on the system.
1. High-Pressure Hydrogen Tanks
Aluminum alloys, special stainless steels, and polymer composite materials are used. Steel cannot be used for high-pressure hydrogen tanks. This is because high-pressure hydrogen enters metals such as steel, causing them to become brittle.
2. Liquefied Hydrogen Tanks
Hydrogen tanks cool hydrogen to -253°C and store it as a liquid in a double-layered container with a vacuum between the tanks. The vacuum prevents heat transfer to the outside and prevents the temperature of the hydrogen from rising.
However, it is not a perfect vacuum, and even vibration produces heat, causing some hydrogen to become a gas. It is important to research technologies to safely remove gaseous hydrogen gas and to reduce the amount of vaporization by approaching a vacuum.
3. Hydrogen Storage Alloys
Hydrogen storage alloys have been put to practical use for storage in nickel-metal hydride batteries. In addition, methods of converting hydrogen to another substance for storage, such as converting toluene to methylcyclohexane by reaction with hydrogen, have been studied in recent years.
Types of Hydrogen Tanks
There are several types of hydrogen tanks.
1. Low-Pressure Hydrogen Tanks
Hydrogen can be stored as a gas, but requires a large tank due to the low pressure. This type of tank is used to store small volumes of hydrogen.
2. High-Pressure Hydrogen Tanks
Since vehicles have limited space for tanks, more hydrogen can be stored in higher pressure tanks with the same tank volume.
3. Liquefied Hydrogen Tanks
Hydrogen tanks store liquefied hydrogen at ultra-low temperatures in insulated tanks. Liquefaction reduces the volume of hydrogen to 1/800th of gas, which is advantageous for installation in vehicles.
4. Hydrogen Storage Alloys
Since the atomic diameter of hydrogen is small, it can be stored when it is absorbed between the molecules of special alloys. When hydrogen is removed from the storage alloy, heat is applied. About 80 kg of storage alloys are needed to store 1 kg of hydrogen, making weight an issue for in-vehicle use.
Hydrogen can also be stored on the surface of carbon nanotubes and molecules with very large surface area.
5. Hybrid Type Hydrogen Tanks
A structure that combines a hydrogen storage alloy and high-pressure hydrogen tanks is used.