The Sequel, a G.M. car that runs on a hydrogen fuel cell, will be unveiled today

G.M. has trotted out impressive hydrogen-fueled cars before – most recently the Sequel’s predecessor, the Hy-wire. G.M. says it will theoretically be able to mass-produce fuel cell vehicles affordably by 2010 – even though most competitors, which are also working on the technology, say it will be decades before such vehicles are viable.

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