Hydrogen is the most basic and most common element on Earth. Represented by the letter "H" on the periodic table, hydrogen is a gas that combines with oxygen to make water (H2O), and with carbon to form compounds such as methane and coal.
Hydrogen is also a potent source of clean energy. In fact, it has the highest energy content of any fuel we use today [source: U.S. Energy Information Administration]. Hydrogen itself isn't available on Earth, but it can be produced. Using hydrogen energy isn't hard on the environment, because only water and heat are released as byproducts. However, the process needed to produce hydrogen can be less environmentally friendly.
To produce usable hydrogen, it has to be separated from water, biomass (plant and animal waste), coal, or natural gas. About 95 percent of the hydrogen used today is produced by a process called steam reforming -- separating hydrogen atoms from carbon atoms in methane [source: National Renewable Energy Laboratory]. This process releases greenhouse gasses, which contributes to global warming.
The other production method, electrolysis, separates hydrogen from water. Electrolysis can be powered by renewable energy such as wind, hydropower and solar energy, so that it produces no emissions. The downside is that it's expensive. For hydrogen to reach its full potential as an energy source, scientists need to figure out a way to produce it inexpensively from clean, renewable sources.
Currently, the U.S. produces about 9 million metric tons (9 billion kilograms) of hydrogen each year -- enough to power up to 30 million cars [source: EIA]. Most of that hydrogen is used in refining and treating metals, as well as in food processing. NASA also uses hydrogen as a fuel in its space program.
The key to using hydrogen as power is the fuel cell. A hydrogen fuel cell converts the hydrogen energy into electricity. Fuel cells can be used in cars, and to provide electricity to rural areas with no power lines. To power a car, the electricity produced from hydrogen energy flows into the battery, acting much like today's hybrid electric cars.
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