Guide (Electrolyzer)
From Unofficial Stationeers Wiki
Place the Kit (Atmospherics) and change the variant to Electrolyzer.
There are two pipe connections.
Electrolyzer Input is where you connect the incoming water.
Electrolyzer Output is where the H2 and O2 comes out mixed together.
Before you activate the Electrolyzer, make sure the water input has a low enough temperature to avoid self ignition of the resulting gases (currently 300C).