What was happening in the video I watched was that the fellow proved that an engine will continue to run for a while, albeit barely, with somewhat watered down gasoline. It died under load. It takes a lot of energy for electrolysis and a lot of energy is lost in the process as heat and so burning the resulting hydrogen will always result in less energy. Its just the law of the conservation of energy. https://en.wikipedia.org/wiki/Conservation_of_energy
I felt sort of bad for the GEET engine guy after I watched the video, if you have a video that seems compelling let me have a look at it and I can probably tell you what is going on there.
RE: Is The Oil Industry Suppressing Alternative Fuels? We can run an engine on tap water!