It's a gas: a hydrogen fuel-cell vehicle at a fueling station in California, June 2014.
Alex Gallardo / Reuters

The appeal of hydrogen fuel cells has long been obvious. Because these devices use electrochemical reactions to generate electricity from hydrogen, emitting only heat and water in the process, they offer a particularly green source of power, especially for vehicles. What has not been so obvious, however, is how to make hydrogen fuel cells practical. In 2009, Steven Chu, then the U.S. secretary of energy, told an interviewer that in order for hydrogen fuel-cell transportation to work, “four miracles” needed to happen. First, scientists had to find an efficient and low-cost way to produce hydrogen. Second, they had to develop a safe, high-density method of storing hydrogen in automobiles. Third, an infrastructure for distributing hydrogen had to be built so that fuel-cell vehicles would have ample refueling options. Fourth, researchers had to improve the capacity of the fuel-cell systems themselves, which were not as durable, powerful, and low cost as

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  • MATTHEW M. MENCH is Robert M. Condra Chair of Excellence Professor and head of the Department of Mechanical, Aerospace, and Biomedical Engineering at the University of Tennessee, Knoxville.
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