Micro fuel cells are being touted as the hot portable energy source of the future. They pack a lot more punch than batteries and yield only water as a by-product. Yet the revolution in small power sources is not likely to occur until the second half of this decade, when developers expect to unveil miniaturized fuel cells for third-generation cellular phones, laptop computers, personal digital assistants and other portable electronics. "Potential military and consumer users," reports Christopher Dyer, a fuel cell researcher and editor of the International Journal of Power Sources, "say they expect micro fuel cells to make inroads into markets now dominated by batteries within the next five years"--three years if key breakthroughs are made. As it stands today, prototype micro fuel cells still fall short of the mark.

Fuel cells are relatively simple devices that are similar to batteries. Both generate electricity chemically. And both depend on electrodes (an anode and a cathode) connected by an electrolyte. Fuel cells, however, convert hydrogen or hydrocarbon molecules rather than solid electrodes into electricity.

   
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