Hydrogen travels across the membranes, which contain platinum, and reacts with oxygen to create electricity. They are quiet and clean, emitting only heat, water and, with some fuels, carbon dioxide. They have no moving parts. They are fueled by hydrogen, which is difficult to store because it takes high amounts of pressure to contain it conveniently. But hydrogen can be extracted from more common fuels, such as natural gas, propane or gasoline.
Some fuel cells are tiny enough to fit into a cellular phone.
Others are so big they can power a large factory. A fuel cell to power an average home would be about the size of a small refrigerator. Fuel cells are more reliable than the traditional electricity grid, experts say, and are not as susceptible to lightning strikes or fallen trees. But they are still experimental, and experts do not know their maintenance requirements, for example. Less than a dozen companies make fuel cells today, each producing a few hundred a year or more, all by hand.