Steam-reform Natural Gas. 95% of it is produced that way in the US.
http://energy.gov/eere/fuelcells/hydrogen-production-natural-gas-reforming
When you look at all the energy losses to make the hydrogen, along with the required equipment, it is laughable to call it zero emissions and way more expensive than gasoline if not subsidized by Tax Payers.
http://inside.mines.edu/~jjechura/EnergyTech/07_Hydrogen_from_SMR.pdf
Also hydrogen gas leaks rise up and eat the ozone layer. It’s just not going to work as a mass market product.