On the road to petroleum independence and greenhouse-gas reduction, the old internal combustion engine will someday need to be scrapped. That will only occur when the alternative -- most likely the hydrogen-powered fuel cell -- is as cheap and convenient to use as the conventional automobile is today. It's perhaps the toughest challenge in fuel-cell research: designing a safe, lightweight and compact hydrogen fuel tank. Two recent papers, published in the April 22 and May 6 issues of the journal Physical Review Letters, find the most promising hydrogen storage medium is in something called carbon nanostructures.