Even when you neglect the pollution from the waste caused by creating hydrogen, it is still not a viable fuel for automobiles. There is currently NO commercial method of storing hydrogen in a vehicle other than as a compressed gas. Even when compressed to 10,000 psi, and ignoring the volume of the storage tanks, hydrogen requires 7 times the volume to contain the same energy as in gasoline. Where can you put a 100 gallon fuel tank in a Prius?
Correct. And at 45 megajoules per kilogram, gasoline rules the energy density of any battery or fuel cell.