Oh, the OP’s linked device is pure BS. Made from pure unobtanium with a magic battery and impossible performance specs. The video sort of implies the existence of a tiny tank and compressor, but the entire thing is just an excuse for a bit of 3D rendering. Maybe you could keep a hamster alive with it, but not a human.
No, it was an excuse for a crowd-funding scam.
Also, Deep Sea News tackles the issue. I’m happy to see that the experts are getting water-volume filtering figures within a power of two of my Google University estimates (that had no relation to debunking the Triton.)
Ugh. I didn’t realise it was that bad. That is go to jail territory IMHO.
[Moderator Note]
The thread title and first paragraph discusses removing dissolved oxygen from water, while the rest of the OP discusses electrolysis. I think that both subjects are therefore fair game for the thread. You don’t need to bicker about who missed what point.
Colibri
General Questions Moderator
One of the news links there has a subtitle “$300 device claims to allow anyone to stay underwater for 45 minutes”
I can undercut that price quite significantly, as well as exceeding the spec. My new concrete wetsuit design allows people to stay underwater for the rest of their lives.
Yeah, I know, but I upped things for a person swimming strenuously, rather than at rest. Kind of a worst-case scenario
That’s gonna be a lot less than 45 minutes.
Not really - I imagine they’ll stay down there a good deal longer.
(But the rest of the person’s life would take up only the first few minutes.) (Same way that chaining yourself down over a bonfire keeps you warm for the rest of your life :))
2110 amps at 1.23 V works out to about 2.6 kW, so say you wanted this to last an hour and the device had 100% efficiency, then you’d need a 2.6kWH battery. A good battery of this size will weigh about 58 lbs.(http://www.amerescosolar.com/sites/default/files/pdf/SimpliPhi%20Spec%20PHI%202.6%20kWh%2060%20Amp.pdf) and that’s just the battery itself.
The heaviest air bottle listed here (Diving cylinder - Wikipedia) is much less half the weight of the battery.
There are two other technologies that are worth mentioning for your quest on tank less or reduced tank
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This question has some similarities to space vehicles and their quest for ever lighter propellant (liquid oxygen in many cases) tanks. So you can use a light composite tank to carry liquid oxygen (or air) similar to here : Game Changing Development - NASA
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The question also has some similarities for the oil and gas industry, where people are always looking for ways to reduce costs (and improve energy efficiency) for natural gas transportation and vehicular tanks. In this area, there is continued research into MOFs - Metal Organic Frameworks (Metal–organic framework - Wikipedia)
Basically, these are like honeycombs that trap the gas molecules, so you do not need to pressurize a vessel to store more of the gas. Think of a sponge for gas. This results in very thin and consequently light tank because the pressure isn’t high.
MOFs are highly specific though and you’ll Need
Specific MOFs that target oxygen.
The only reason you need all the air in a SCUBA tank is because in open-circuit dive gear the excess CO2 is removed by the simple expedient of exhausting the air you exhale to the environment. The real problem is getting rid of the CO2, because the air you exhale still has plenty of oxygen in it.
As others have mentioned, rebreathers are ‘closed circuit’, and recycle the air you breathe. chemical scrubbers absorb the CO2, allowing the oxygen to be reused. Doing this, you can stay down for up to six hours, which is a long time to be submerged at depth.
Rebreathers have not been common in recreational diving until recently, as they require a lot of training and are intolerant of mistakes or neglect. But computers, new sensors and other advancements have made technical gear much more reliable, and modern divers are doing amazing things with it.
As for the Triton device, I blame poor science education for the number of people who fell for the crowdfunding campaign. It should be intuitively obvious that the thing couldn’t work.
I think you’ll find that’s still covered in the small print when you buy your first and only concrete wetsuit.
I can probably manufacture a simple snorkel for a lot less than $300. Stay underwater as long as you want AND survive it.
You do you. My product is guaranteed never to be the subject of customer complaints.
And what about next of kin? 
I think your new device is going to face some competition from the guys who make cement shoes and cement overcoats, and from what I hear, you don’t want to get on their bad side. At some point you may be forced to accept an offer that you can’t refuse.
Can I hire one? I’d like to surprise my mother-in law…
I’ll placate them with a voucher or something.