Hydrogen Storage

One of the most important factors in introducing hydrogen as future fuel is transportation and on-vehicle storage of hydrogen. Storing hydrogen that flexibly links its production and user are key factor of the hydrogen fuel utilization. The major contribution to the problem is from low gas density of hydrogen. For example, to store energy equivalent to one gasoline tank, an ambient pressure hydrogen gas tank would be more than 3000-fold the volume of the gasoline tank.

Various storage options have been introduced by many researchers and institutions for last two decades. Here is a brief desription for some of them.

• Compressed Hydrogen. Considering both storage and refueling technologies, probably compressed gas storage is the most promising alternative. High strength steel or other metals are an option from a strength perspective, however, diffusivity of hydrogen through the steel and weight of the steel are major issues for vehicular storage.
  

• Liquid Hydrogen. Storing of hydrogen in liquid form at cryogenic condition is attractive in that it offers low weight and volume per unit energy when compared to compressed hydrogen. But, main issues are hydrogen boil-off, the energy required for liquefaction, and tank cost.

• Metal Hydride. Metal hydrides are specific combinations of metallic alloys, which possess the unique ability to absorb hydrogen and release it later. The life of a metal hybride storage tank is directly related to the purity of the hydrogen it is storing. The alloys act as a sponge, which absorbs hydrogen, but it is also absorbs any impurities together with hydrogen. Thus, the hydrogen released from the tank is highly pure, but the tank’s lifetime and ability to store hydrogen is reduces as the impurities are deposited in the metal pores.

• Carbon Nanotubes. Hydrogen can be adsorbed on a carbon surface. Various forms of carbon with high surface area may be utilized for the storage of hydrogen. Research on this technology has focused on the areas of improving manufacturing techniques and reducing costs as carbon nanotubes move toward commercialization.