good question. complex answer.  you need to have a good surface area on the electrodes.  the hydrogen ions will bond on the surface to form H2 which will eventually bubble and literally float to the top.  O2 on one electrode and H2 on the other - split the gas collectors and you have pure-ish H2 and O2 seperated.  and the volume of h2 is twice that of o2... ;-)  hydrogen ion migration is a weird one - unlike most things that you think of as migrating through water, H+ ions seem to be about 10x faster.  last i heard (20 year ago memory here) is that the electric field actually messes with the hydrogen bonding in water so instead of migrating the h+ atom from one place to another, you flip the H --- O.....H hydrogen bonds along the line of potential and hey presto a bond where there used to be a hydrogen bond and a hydrogen bond at the other end.  to the casual observer it looks like the H+ atom whipped from end to the other super fast.  the problems associated with using hydrogen as an energy storage medium are still being ignored though.  we don&#x27;t know how to make it, store it, transport it or use it - IMHO it&#x27;s a dead end for the sorts of applications its being sold for, worse it&#x27;s distracting and costly use of time&#x2F;$&#x2F;people when decarbonising the energy system is running out of time.