First of all to run a car on hydrogen each car must have a h2o to h o conversion unit, to start off with the conversion unit works by using DC-current to separate the 2 parts hydrogen from the 1 part oxygen using the excess DC-current provided by the car Alternator which is conventionally used to recharge the car battery only but in this case it is also used for the conversion process. To get the car and the conversion process started the conversion unit draws DC-current from the car battery that has been previously charged-up by the car Alternator when the engine was last running. From there the hydrogen is burnt as fuel in the car engine and by using the engine to burn the gas the car is not only getting energy to propel the car but the car engine is also turning the car Alternator which is producing the excess DC -current energy to power the conversion unit. And so by doing it this way you are converting only the amount of fuel that the car needs when the car needs it(I.e. no pressurized gas tank). And so the amount of DC-current energy that went into the conversion unit and the car battery is only a small percentage of the energy you get when you burn the hydrogen gas in the car engine. So as you can see the energy you use in the conversion process is a different type of energy than the type of energy you get when you burn the hydrogen in the car engine. And by doing all of this the only thing the car emits out of the exhaust pipe is water vapor and all the excess oxygen(just like a tree). When we get a new camera I will upload a video of my dads car that runs on hydrogen by using the conversion unit method. This whole hydrogen conversion unit thing is not a new idea, it has been around for decades and the only reason it has not been used on a large scale is the fact that it is not profitable(I.e. no money in it) unlike fossil fuels! p.s. i hope i did not leave anything out, and if i did i will fill in the gaps at a latter date.