I am confused, why exactly is a membrane required to keep the hydrogen and oxygen separated? From what I recall in High school science class there was no membrane separating the electrolyte in our electrolysis rig. The fact that both oxygen and hydrogen are lighter than the electrolyte a.k.a. salt water meant that the gas is bubbled up out of the electrolyte above each electrode which were separated distance of about 2 feet which allowed the individual gases to be collected separately.
Something like this : https://a.co/d/3uA06vp