You could drink the exhaust of the Honda FCX Clarity. The four-door sedan-the first hydrogen fuel-cell car available to the general public-emits only water. Powered by the electricity generated when hydrogen and oxygen combine to form H_2O and with upholstery fabric made of fermented corn, the Clarity sure sounds green. But is it the "zero-emission sedan of the future," as Honda claims? Not yet. Most hydrogen fuel is derived from natural gas in a process that releases plenty of carbon dioxide, so the car and its 134-horsepower electric motor fall short of being footprint-free.
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