I was thinking about how gas vents can be placed in a small amount of water in order to make them operate no matter the gas pressure, and I was wondering if the same thing applied to electrolyzers. I did some experementation and it does, but it takes a bit more effort to get it to work properly. As it turns out, the electrolyzer does not check all the times it is allowed to output to for pressure, but only checks the four tiles it occupies. Filling each of those tiles with a small amount of liquid allows it to operate full time, except that the electrolyzer can displace a liquid to place a gas.
Someone recently posted this about gas pump range. Electrolyzers produce their outputs at range 2 from the upper left tile.
I have observed that elecrtolyzers have the same pattern rotated 90 degrees clockwise, except for producing gas instead of consuming. That means that the tile just above the left column of the electrolyzer and the tile just to the left of the top row of the electrolyzer are valid points to produce gas. To avoid the electrolyzer displacing any liquid, those two tiles should be preloaded with hydrogen and oxygen, and they need to be protected from exposure to other gases.
Once in place, these electrolyzers will happily run forever, producing vast quantities of pressurized hydrogen and oxygen for your experiments.
If building manually, make sure to pump everything but hydrogen out of the top chamber before turning on the electrolyzers (a hard vacuum is fine). Once that is done, pumping hydrogen out is very safe as long as the airflow tile has oxygen in it. (The atmo sensor pictured in the hydrogen chamber is unnecessary).
You could make a few changes to this design. One thing would be to place a liquid airlock to the right of the hydrogen chamber to provide maintenance access, but I would recommend atmo suits first, since even a single breath of CO2 in the hydrogen chamber will probably get stuck in one of the electrolyzer output tiles, when that happens, it could start displacing liquid to create the hydrogen, and then even worse, if the hydrogen trades places with the oxygen in the airflow tile, it has no way out.
If you do end up with a light gas stuck in the top airflow tile, then you can shut off the electrolyzers, remove the full tile above it, rebuild and vacuum the chamber again. If it's a regular occurrence, you can replace those tiles with mechanical airlocks, but I would suggest avoiding the problem anyways as it takes a long time to create the vacuum in the hydrogen chamber.
One gas pump can handle about 4.4 electrolyzers of hydrogen. It can be expanded to any number of electrolyzers,
The liquids you use don't really matter, but my initial thoughts were that oil and petroleum would be less likely to displace than water.
For automation, I have a switch to set the pump to always on, or an atmo sensor to maintain a certian pressure in the hydrogen chamber. On the oxygen side, a switch is set up with an and gate to allow the electrolyzers to be disabled, or enabled when O2 pressure drops below some ammount.
Letting these supply your base with O2 directly is likely to produce popped eardrums anywhere near the oxygen output.
Polluted water produces polluted O2 which may interfere, further experementation needed.
Do not allow gases other than hydrogen into the upper chamber.
Do not allow gases lighter than oxygen to flow up into the airflow tiles.