Environmentalists have high hopes for hydrogen as a fuel. Hydrogen burns cleanly, with water its only combustion by-product--a marked contrast to traditional fossil fuels, which produce all manner of pollutants, including carcinogenic toxicants and greenhouse gases.
But there's a catch: virtually all current processes for producing hydrogen themselves release greenhouse gases. Now scientists are working on several promising (although not yet commercially viable) techniques that may someday solve the puzzle of providing inexpensive, mobile, cleaner sources of hydrogen.
Hydrogen: The Fuel of the Future?
Despite the element's promise as a fuel, a dearth of economical and Earth-friendly ways to produce pure hydrogen is slowing adoption of hydrogen-powered technologies. The problem isn't a lack of hydrogen; it's the most abundant element on the Earth's surface. But naturally occurring hydrogen is invariably locked up in molecules, as in water, hydrocarbons, or plants. To use hydrogen for fuel, it must be liberated from other elements.
Most commercially produced hydrogen is used for manufacturing ammonia and methanol and for hydrogenating fats and oils (this makes liquid oils semisolid, makes them less likely to become rancid, and improves the appearance of fats). Small quantities are also used in such applications as welding and the production of rocket fuel and hydrochloric acid. Currently virtually all commercially produced hydrogen is extracted by applying heat and steam to hydrocarbons in fossil fuels, most often natural gas but sometimes gasoline or coal. This process, called "steam reforming," also releases carbon dioxide (C[O.sub.2]), a greenhouse gas.
Proponents of hydrogen as a fuel, however, say that the element's future lies in electricity-generating fuel cells. A fuel cell is much like a battery in that it consists of an anode connected to a cathode by an electrolyte. But unlike a battery's captive chemical source of electrons, which over time becomes depleted, a fuel cell needs an external, ongoing source of electrons, such as hydrogen. Hydrogen fuel cells have already started to appear in industrial settings, where they augment conventional power sources. Fuel cells also provide backup for businesses, such as hospitals and financial operations, where an uninterrupted supply of electricity is critical.
As fuel cell technology advances, the devices are expected to crop up in remarkably diverse settings. They are the critical component of the Department of Energy's (DOE) FreedomCar program, a joint effort between the government and industry to develop fuel cell--powered automobiles and new ways of producing hydrogen. Although FreedomCar is a recent initiative, fuel cells already appear in cars by such companies as Toyota, Mercedes-Benz, and Honda. In November 2002, energy secretary Spencer Abraham announced a "roadmap" for bringing widespread use of fuel cells to the nation's cars and trucks. This, he said, further committed the United States to a hydrogen-based transportation system. The roadmap describes routes to production, delivery, storage, conversion to useful power, and applications for hydrogen fuel.
Public transportation may pave the way for adoption of fuel cell vehicles. In 2003, 10 European cities--Amsterdam, Barcelona, Hamburg, London, Luxembourg, Madrid, Porto, Reykjavik, Stockholm, and Stuttgart--are scheduled to begin using 30 Mercedes-Benz Citaro fuel cell-powered buses. About a year later, the Santa Clara Valley Transportation Authority in San Jose, California, will introduce fuel cell-powered buses as part of a two-year experiment during which such factors as safety, ease of maintenance and operation, and public acceptance will be evaluated.
Fuel cells are also being developed for other applications in which it is not only desirable but necessary to keep combustion by-product emissions to a minimum. For example, a prototypical fuel cell-powered
locomotive for underground mining has been tested in Quebec, Canada, in a joint U. …