Quite a confusing collection of websites. The first two seem to be legitimate sites for fuel cell vehicle propulsion, which is still several years away from general use. These cells require you to fill a vehicle tank with hydrogen, which when combined with oxygen generates electricity to drive the vehicle's electric motor.
Again: this requires an electric motor for propulsion. Fuel cell vehicles run off an electric motor.
The third site, however...in short, it's snake oil. They don't offer many details, but from the pictures we can see the terms "Power from H2O" and "electro-mechanical generator". This looks to be a simple hydrogen generator, in which an electric current is passed through water, causing it to separate into hydrogen and oxygen in gaseous form. I would assume this is then sucked into the engine and burned. What they don't tell you is that the amount of gaseous hydrogen/oxygen gained this way is truly microscopic -- far too small to be of any benefit.
Spacecraft use fuel cells to generate electricity and fresh water,but they use liquid oxygen and hydrogen -- neither are easily obtainable. Or cheap.
Their intentions are probably good, but...snake oil.