BTW, if you read about the latest version (2016) of the proposal from the Triton, they no longer claim to be 100% filtration based, and instead one of the two branches is a receptacle for small cartridges of liquid oxygen. Breathing that in will also assist you in being able to spend the rest of your life under water.
Triton’s blurb says this: The device uses “artificial gills”, a filter with holes smaller than water molecules but large enough for oxygen to pass through.
I’m wondering on which planet an O[sub]2[/sub] molecule is smaller than an H[sub]2[/sub]O molecule.