One day I have opened some major parts of the map, and watched picture of dozens unused geysers, so there must be a solution how do deal with it, and here I'm proposing you one of them, nothing special with simple mechanics, but must works well.
So, system is build near geyser and using it as water source, then via electrolytes it turn H20 into hydrogen and oxygen which are separated. Hydrogen can be used for purposes of power/cooling, and oxygen can be used by dupes.
"<=" means that values must be as much as it can be closer to formula, but not greater. E.g. in my setup W1=2594.7 g/s, H1=290 g/s, H2=79 g/s.
All solid blocks and pipes are made out of Abyssalite, all wire bridges - Wolframite. Other structures can be made of any suitable for you material.
As you see it's using feature with watering electrolyzers, so they are venting gas where it need to be vented. You will need to drop on each electrolyzer 10 kg of polluted and 10 kg of clean water (if you can, you should drop about 1kg of each liquid, it will give you better heat insulation, in my solution there is about 1 kg of each liquid).
How to setup electrolyzers:
Add some oxygen inside.
Build and activate electrolyzers.
Replace left blocks with gas permeable tiles.
How to setup whole system:
Create main box with vacuum inside.
Build all mechanisms, including electrolyzers, tune valves.
Open way to generator and batteries, wait until pressure will be above 1kg then build wall.
Wait until pressure in main area will be about 3-4 kg, activate pump.
Hydrogen is coming out from pipe, at small packets, if you can not deal with all provided hydrogen make sure to create big hydrogen storage for further usage.
And oxygen is using pressure for transportation, so you will need to create gas shaft in order to transport it to your base.
The results. You receive an autonomous setup which in the best case will produce 2.3 kg/s O2 at +30C and 213 g/s H at +30C. What can provide oxygen for 22 dupes or 30 dupes with diver's lungs and give you constant supply of power 1700 W/s using hydrogen, which also can be used for cooling you generators (you should transfer raw hydrogen via pipes, this way you can create lines up to 8000 W/s).
edit: Oh, I see there may be some problem near batteries, as they are heating too much, so It's better to use there polluted water or reduce number of batteries, 1 may be more than enough (or add wire bridges between generator and batteries), I'll need to create little bit another design, will post it when I'll done