Researchers at the University of Southern Denmark have created crystals based on cobalt (their actual structure is quite complex) that can absorb oxygen in an amazing way. A bucket full of these crystals would be able to remove all oxygen from the air of a normal size room. TO release the oxygen it is sufficient to heat the crystal a bit.
It is not surprising to see cobalt involved. We use iron as the basic molecule to carry oxygen, whilst other animals, like crabs, use copper. Metal molecules have this capability to easily bind with oxygen molecules. Of course just metal is not enough (if you only have iron and oxygen you would see the iron turning into "rust" and the oxygen will be so tightly bound to the iron that you won't be able to release it and use it). The researchers success was to find the right molecule to associate to the cobalt molecule to exploit the metal affinity to oxygen and at the same time stop its strong binding with it.
The crystals act like haemoglobin, the substance in our red blood cell that carries oxygen from the lungs to our cells. It is both an effective means to capture and store oxygen.
One could imagine a new sort of diving support with a small tank containing a few of these crystals that will extract oxygen from the sea water, like gills in a fish. Once full of oxygen the crystals can be heated and the oxygen is ready to be breathed by the diver. The whole system should probably be much more handy to carry since the crystals can store the capacity of a diver tank in a very little volume.
There are quite a few other applications that researchers are targeting, like better support to patients with lungs problem, as a source of energy for cars using fuel cells...