Once it’s been released how much energy does it take to compress is and where will you get the energy to do it?
L
Electrolysis can be induced by a DC electric current, i.e. battery power. if the hydrogen is used to turn an engine, the alternator can keep the batter charged.
There are a ton of videos (rumble/youtube) and other examples of this out there. The keys are:
what kind of catalysts to be used
how to keep the engine/motor from oxidizing
how to protect fuel in below freezing temps.