Q: What is hydrogen?

A: Hydrogen (H2) is a naturally occurring, plentiful gas that can be converted into the lightest, simplest energy carrier available. Hydrogen is the simplest known element, but its energy content is the highest per unit of weight of any fuel (52,000 BTUs/pound). While hydrogen always exists in conjunction with other elements, such as in water (H2O), it must be separated from these elements and is therefore considered an energy carrier, as opposed to an energy source (see "Differentiating Energy Sources and Carriers"). The United States government and private sector researchers are giving serious attention to the development of widespread hydrogen use. One problematic issue is the hydrogen transportation infrastructure: because hydrogen is a gas, it cannot be compressed into a liquid form without intensive cost and energy input.

Hydrogen is ideal for secondary energy, i.e., electricity. Hydrogen can be combusted directly, added to natural gas or gasoline to reduce emissions, or stored for use in fuel cells. Hydrogen fuel cells are currently used aboard the U.S. Space Shuttle Program to run all the electrical systems, and crewmembers are able to drink the sterile water that is a byproduct of fuel cell use. At present, NASA is the largest user of hydrogen power in the U.S.; other common venues for hydrogen use at present are chemical production, petroleum refining, metals treating, and electrical applications.

Q: How is hydrogen power produced?

A: 95 percent of the hydrogen currently used is processed by steam reforming natural gas. Although other hydrocarbon (carbon- and hydrogen-based) feedstocks can be used to produce hydrogen, including coal and biomass, the process is currently too expensive for widespread use. A major reason for the high cost is that before producing hydrogen the coal or biomass must be gasified through a cost- and labor-intensive procedure.

Another common method of hydrogen procurement is through electrolysis of water. This method uses electricity derived from any fuel (including renewables) to split water into its component parts of hydrogen (H2) and oxygen (O).

Q: What are the pros and cons of hydrogen?

Pros: Hydrogen is an extremely clean fuel, producing few emissions when combusted directly or in combination with hydrocarbon fuels. When used in a fuel cell, the only byproducts are heat and water.

Cons: Although hydrogen can be procured through electrolysis, it is most commonly separated by a reforming process that uses natural gas and other fossil fuels. Supplies of natural gas are becoming tighter, and coal, one of the most feasible hydrogen feedstocks, is a source of major pollution. The technology to produce, store, and transport hydrogen power at a reasonable cost is not yet in place and likely will not be for some time.