Storing Hydrogen

  Hydrogen is usually stored as a liquid, though it can also be stored as a gas or a solid. Because hydrogen is low in density, storing it is a challenge. This is true both for storage at hydrogen production sites as well as on vehicles that might use hydrogen as a fuel. Among the methods for storing hydrogen are the following:

  • Compressing it into cylinders of various sizes. This is one of the most common ways to store hydrogen for industrial use.
  • Using compressed gas tanks for vehicles. Many automotive manufacturers and researchers have been experimenting with these tanks. Instead of cylinders, hydrogen would be pumped into a compressed gas tank on the car and stored there.
  • Storing liquid hydrogen cryogenically (at very low temperatures) . Benefits and drawbacks of storage options

Storage of hydrogen on vehicles is a major concern. Some scientists believe that the storage of hydrogen on cars is the biggest single problem facing the use of hydrogen as a fuel for cars. Vehicles have very limited space for storing hydrogen, and the amount that needs to be stored for hydrogen to be a viable fuel source is rather large.

As mentioned, hydrogen is usually stored as a liquid. However, liquid hydrogen has many drawbacks. For example, liquid hydrogen has to be stored at temperatures at or below 423F (253C). To keep the liquid this cold requires a significant amount of energy. The system also must be insulated. Also, even if liquid hydrogen is stored at the right temperature, about three to four percent is boiled off daily. This situation could be a problem for vehicles that are not being used for a few days at a time.

Because of the low density of hydrogen, the amount of hydrogen that can be compressed into a cylinder is less than more dense substances. This problem means that compression has a significant energy cost and an economic expense. The cylinders also must be transported from the place the hydrogen is manufactured to the market where it is needed.

The same drawback hinders compressed gas tanks on vehicles. As of 2005 most compressed gas tank systems can only carry about 5,000 pounds per square inch (psi) of hydrogen. For the ideal range for a car, researchers hope to develop a tank system that offers 10,000 psi. For now compressed gas tanks are large and hard to fit onto a car. They are also made from materials that are both heavy and expensive. One such material is carbon fiber. There are also safety concerns for hydrogen compressed gas tanks. To be safe, they must be able to withstand a very powerful impact. This is a goal that has not been fully reached in a workable manner.

Storing Hydrogen copyright 2011