Hydrogen is probably the purest of all alternative fuels, with virtually non-existent greenhouse gas emissions. After combustion in the engine there is only water vapor and heat as opposed to internal combustion engines that emit harmful gases.

The use of hydrogen (H2) is possible in two ways, as a fuel-powered internal combustion engine or hydrogen-charged cells in electric vehicles.

Compressed hydrogen comes in a liquid or gaseous state and can power internal combustion engines.Compressed hydrogen fuel is efficient but the volumes are large and it is not practical for use and is non-combustable. The most commonly used is liquid form which is very lightweight and also non-flammable.Another negative feature is that it is less efficient than the compressed form. The manner in which it is used in engines is linked to the substances that absorb hydrogen. For this, the most common substance for use is metal hydride or nano porous materials. Metal hydride is very compact but heavy, warm and non-flammable. For nano materials that are very effective the drawback is the long time required for filling the tank (15-30 minutes).

The biggest problem still is the storage of hydrogen. 454 grams of hydrogen gas requires the equivalent of 5500 liters of space (at atmospheric pressure). In liquid form 454 grams of hydrogen requires a volume of 5.5 liters. The vehicles that use this method the most widely is the liquid hydrogen stored in tanks of metal alloys because this requires the minimal amount of space. To remain in liquid form it must be cooled to -252 Fahrenheit, and also needs a high pressure of 1379 bar.