I don't think the pressure _can_ be removed. Nothing in the article says this "material" is stable at ordinary pressures. They're just saying that the chemical structure changes as it is squeezed into a smaller and smaller space. If you let go, it presumably expands immediately.

To be clear, I also think the energies they are storing in their experiment are a small fraction of a joule. The "energy density" is high because the sample is very small.

If that's the case then any speculation as to applying this material is completely premature.

It is the case. It's not a ratchet and a spring, it's just a spring which can be compressed further than any spring before. (The phase changes along the way are interesting, but will reverse themselves as you release the pressure).

Now, if you could get a giant diamond anvil cell (with house-sized near-flawless diamonds), you could use it to compress a macroscopic quantity of this down, and then get the energy back. The problem is that while the substance in its compressed form may have more energy per cubic foot than, say, a tank of gasoline, in releasing that energy it would expand to something much larger, so your entire apparatus would be very space-inefficient for energy storage (not to mention the difficulties of obtaining those giant diamonds).

Ok. I got taken in by the 'energy stored in chemical bonds' bit.

"xenon difluoride"

My rough guess is this noble gas + fluorine combination = crazy ultra-reactive material at room temperature and standard pressure.

I'd say this is not something one wants to release into the wild. There might be a clever way to contain it. But it would a bit hard to make laptop batteries of out of it.

Edit: You're right, Alfred only organized other chemical things...

It's a noble gas, not a Nobel gas. Alfred had nothing to do with it... ;-)

Somehow getting noble and Nobel mixed up when talking about stuff that can go boom seems less wrong than in other contexts.