The hydrogen is the most common gas in the universe. Each atom of hydrogen contains one proton.
Hydrogen is light, colourless, odourless gas: hydrogen combines with oxygen to form water. Hydrogen composes about 75 percent of the Sun but only a tiny fraction of the Earth.
The use of hydrogen is not practical at present because of the difficulty of storing and carrying hydrogen. Like electricity, hydrogen must be produced from another energy source. It can be converted to electricity in a fuel cell. Hydrogen cars and buses are being trialled in Europe and the USA.
Hydrogen cars are very expensive, and are expected to remain expensive for at least another decade.
A hydrogen vehicle is a vehicle that uses hydrogen as its onboard fuel for motive power. The term may refer to a personal transportation vehicle, such as an automobile, or any other vehicle that uses hydrogen in a similar fashion, such as an aircraft.
Many companies are working to develop technologies that might efficiently exploit the potential of hydrogen energy for mobile uses. The attraction of using hydrogen as an energy currency is that, if hydrogen is prepared without using fossil fuel inputs, vehicle propulsion would not contribute to carbon dioxide emissions. The drawbacks of hydrogen use are low energy content per unit volume, high tankage weights, the storage, transportation and filling of gaseous or liquid hydrogen in vehicles, the large investment in infrastructure that would be required to fuel vehicles, and the inefficiency of production processes.