The prospect of a “hydrogen economy”—in which vehicles powered by fuel cells would travel the nation’s roadways emitting nothing from their tailpipes but wisps of water vapor—was making headlines 12 years ago.

In his 2003 State of the Union address, President George W. Bush issued a challenge to the nation’s scientists and engineers to overcome technical obstacles so that “the first car driven by a child born today could be powered by hydrogen, and pollution free.”

But today that goal remains a long way from realization—still because of numerous technical obstacles. One of the most persistently difficult is the question of how to store hydrogen on board.

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