Can electrolysis provide buoyancy to submerged machines?

Skeezer
I am looking at building a machine that roams underwater, most always completely submerged. I would like at one point for the device to return to the surface and was wondering if it is possible to use electrolysis to turn the water into gas enough to provide buoyancy that would lift the machine out of the water?

I have ran a few buoyancy equations and the machine will weigh in just under 10lbs. I would like to know if this is even possible, and if anyone can tell me the amount of O and H are needed to raise the 10lbs object.

Mentor
This is more of the phys101 combined with chem101 than electrical engineering.

It doesn't matter what is the machine weight, as long as it is balanced at a given depth even a tiny volume of gas will start to pull it up.

What is difficult here is the fact that you are potentially working at high pressures (so the gas produced is compressed) and that producing even small volumes of the gas requires quite large charge (large current or long time). This can be easily calculated from the Faraday's law of electrolysis.

Gold Member
Yes. it is possible to lift the machine using electrolysis of the water. Just put two electrodes in water and supply it with DC. The electrodes will split the water into hydrogen and oxygen gas. However, this mixdure is higly explosive. If you by accident ignite one litre of this gas mixdure, especially if it is salt water sparks can occour, it will probably blow your machine into pieces. So be careful.

Vidar

skeptic2
Electrolysis of salt water introduces another issue. Instead of hydrogen and oxygen, you may get chlorine and sodium hydroxide.

Hello Skeezer - yes it is possible - yes, it is pracitcal seems to be the questions. Mostly due to the energy needed to generate the gas, vs having a small container of compressed gas, that a valve can release?

Skeezer
Thanks for the wealth of information! Windadct, I am open to other ideas, I am actually just currently researching the best way to do this now, and this was one of my thoughts.

sarcasm? I'm ok if so, but not sure.....cheers,

Skeezer
Not at all. The first sentence was to everyone, but yes I really am open to other thoughts.

Mentor
Thanks for the wealth of information! Windadct, I am open to other ideas, I am actually just currently researching the best way to do this now, and this was one of my thoughts.

It would seem that doing it the way regular submarines do it would be the most effective and safest, IMO. Use a small electrical pump to manage moving air back and forth between external bladders and an internal compressed air storage tank... Oh, and include an emergency ballast release system, I would think.

Gold Member
As low-Q said, I see electrolosis as a great way to make a floating (or not floating) bomb. Very very unsafe.

Mentor
That's a non issue. You can separate cells and produce not a mixture, but isolated gases.

But you will still need large amounts of electricity. Assuming you have enough voltage 1 Ah produces below 1 L of gases at STP (and takes a long time, unless you can use high currents). How much do you need to open a valve - 1 mAh? How long does it take, few ms?

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