Hydrogen is the ultimate clean fuel. Whether it is burned or chemically recombined with oxygen in fuel cells, the reaction produces only water and heat. (See the article by Joan Ogden, Physics Today, April 2002, page 69.) But although it is the most abundant element, convenient sources of pure hydrogen gas are meager.

Water, of course, contains a virtually endless supply of hydrogen, but considerable energy is required to break its chemical bonds through electrolysis or other technologies. Most of the hydrogen produced today is extracted from natural gas, which leaves behind carbon dioxide. Most of the 11 million tons of hydrogen produced in the US every year is used in oil refining, ammonia for fertilizer, and other chemical processes. A small but growing market for the light element is for fuel-cell vehicles.

Today’s commercial fuel cells are so efficient that even with natural gas as the hydrogen...

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