The FCX, on the other hand, runs on the world's most plentiful element--hydrogen--and doesn't produce any of the pollution that today's gasoline-powered cars do.

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Clean, silent, (well, OK, a high-pitched whistling sound), uses no fuel whatsoever, except hydrogen, the most plentiful element on the planet, and emits only water vapor.

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But hydrogen is difficult to store because it is the lightest element.

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It consists of 1, 000 tonnes of heavy water (the sort that has deuterium, a heavy form of hydrogen, in its molecules, instead of the normal, light form of the element).

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