What is hydrogen?
Hydrogen is the third most abundant element on the earth's surface, where it is found primarily in water (H2O) and organic compounds. It is generally produced from hydrocarbons or water; and, when burned as a fuel or converted to electricity, it joins with oxygen to again form water.

Production
There are several technologies with the potential for producing hydrogen to meet future energy demands. These technologies include: thermochemical, electrochemical, photoelectrochemical and photobiological.

Fuel Cells
A fuel cell works like a battery but does not run down or need recharging as long as fuel (hydrogen) is supplied. Fuel cells can be used to power vehicles, provide electricity and heat buildings.

Internal Combustion Engines
Hydrogen can be used in conventional, spark-ignited engines with modifications. Like other gaseous fuels, hydrogen displaces oxygen and compromises engine efficiency unless the engine is modified to take advantage of the fuel's higher-octane rating. Injecting hydrogen is a challenge because of its wide range of flammability in air, which exposes this combustible mixture to pre-ignition by means such as a static charge.

Emissions
Hydrogen has no carbon so the only pollutants related to combustion are oxides of nitrogen.

Additional information
Los Alamos National Laboratory Fuel Cell Project
Alternative Fuels Data Center - Hydrogen