In a flame of pure hydrogen gas, burning in air, the hydrogen (H) chemically combines with oxygen (O) to form water (H2O) plus a lot of heat is produced. It does not produce other chemical by-products, except for a small amount of nitrogen oxides. Hence a key feature of hydrogen as a fuel is that it is relatively non-polluting (since water is not a pollutant). Pure hydrogen does not occur naturally; it takes energy to manufacture it. Once manufactured it is an energy carrier (i.e. a store for energy first generated by other means). The energy is eventually delivered as heat when the hydrogen is burned. The heat in a hydrogen flame is a radiant emission from the newly formed water molecules. The water molecules are in an excited state on initial formation and then transition to a ground state, and the transition unleashes thermal radiation. When burning in air the temperature is roughly 2000°C. Hydrogen fuel can provide motive power] for cars, boats and airplanes, portable fuel cell applications or stationary fuel cell applications, which can power an electric motor.
The current leading technology for producing hydrogen in large quantities is steam reforming of methane gas (CH4). Primarily because hydrogen fuel is environmentally friendly, there are advocates for its more widespread use. At present, however, there is not a sufficient technical and economic infrastructure to support widespread use. The proposed creation of such an infrastructure is referred to as the hydrogen economy.
At the gas pressure that hydrogen is typically stored at, hydrogen requires four times more storage volume than the volume of gasoline that produces the equivalent energy, but the weight of this hydrogen is nearly three times lighter than the gasoline. With regard to safety from unwanted explosions, hydrogen fuel in automotive vehicles is at least as safe as gasoline.
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