You should look into hydrogen fuel cell technology. The biggest problem is the energy inefficiency in splitting water into hydrogen (energy intensive), and then using it to power a car is essentially using hydrogen as an inefficient battery. The on-board storage of hydrogen is problematic as well. Storing a gas is difficult and requires a lot more material than a tank for liquid patrol.

There are people trying to make it a more practical tech, but also a lot of nay-sayers as well.