8. 燃料电池

    经济实惠的氢动力燃料电池对整整一代研究人员来说就像传说中在远方闪耀的金山（El Dorado）一样，是一个充满诱惑力的目标。氢气之所以这么吸引人，是因为它能在国内生产，而且燃烧清洁，同时燃料电池汽车的能效要比汽油车高两到三倍。妨碍它推广的主要因素是电池生产成本较高，加注氢气的站点也太少。结果，现在汽车厂商正在测试小型燃料电池车车队，但这类车还无法投放普通消费者市场。目前两款有名的车型正在接受极限测试：一个是本田FCX Clarity，另一个是2012款梅赛德斯奔驰F-Cell（见上图），这辆车每公斤氢气（大概相当于一加仑汽油）可行驶52英里。

    8. Fuel cells

    Like a fictional El Dorado glimmering in the distance, affordable hydrogen-powered fuel cells have been an elusive goal for a generation of researchers. Hydrogen is appealing because it can be produced domestically and burns cleanly, and fuel cell vehicles are two or three times more efficient than gasoline-powered ones. What's held them back has been the cost of building the cells themselves and a network of fueling stations to distribute the hydrogen. As a result, small fleets of FCVs are being tested by manufacturers, but no fuel cell vehicles have reached the consumer market. Two notable models in limited tests: the Honda FCX Clarity, and the 2012 Mercedes-Benz F-cell (above), which gets 52 miles per kg of hydrogen (roughly equivalent to a gallon of gasoline).