At standard temperature and pressure it is a colorless, odorless, nonmetallic, univalent, tasteless, highly flammable diatomic gas. Having been used as an ingredient in some rocket fuels for several decades, hydrogen, or more specifically H2, is now widely discussed in the context of energy. Hydrogen is not an energy source, since it is not an abundant natural resource and more energy is used to produce it than can be ultimately extracted from it. Hydrogen is obtained by splitting water (H2O) into hydrogen and oxygen. This action requires at least all the energy obtained from burning the hydrogen so that hydrogen is an energy transfer medium rather than a primary source of energy. Therefore, the use of hydrogen as an intermediate is justified only when there is some reason not to use the primary source directly (such as nuclear or solar power plant), while hydrogen can be used as a motor fuel so that the energy is likely to be generated far from where it is used and at a different time. The advantage of using hydrogen in vehicles is that when it is burned the main product is water