There's no doubt that hydrogen holds a lot of promise as the clean energy source of the future (even though it does bring up some potential issues). After all, when it is used as fuel, its only output is water. What remains an outstanding question about its use, though, is how to store it. Hydrogen is highly flammable and finding ways to contain it safely has proven to be quite a challenge for researchers.

We've seen efforts put forth that might lead to the containment of the gas in powders, pastes, cartridges, but at this point, hydrogen-storage solutions are still more in the realm of theory than practice. Adding to the first category is a surprising idea from researchers at Penn State who suggest using coal – yes coal – as a battery of sorts that could contain hydrogen.