Hydrogen seems to be presented as an alternative product for the oil companies to evaluate. Who else would have the infrastructure and money to go in this direction?
Yes, hydrogen used in an IC engine will produce NO (unless we get oxygen into the game, and leave the air alone!). However, I never heard that a fuel cell will produce CO2 from hydrogen. Where does this carbon come from?

Compressed hydrogen is not the preferred means of storage. Lithium hydroxide is one of many non-pressurized systems considered, but the advances in graphite storage looks much better. Hydrogen can be safer than gasoline.

Propane is liquid at room temperature? Only if your room is at -42c!

Yes, zinc-air batteries (with solar panels!) would be a fantastic means of propelling our vehicles, but there's that charge-time previously mentioned that's going to be a big problem.

Most likely hydrogen will eventually replace gasoline. However, the price will have us longing for the good-old-days when we were only paying $3 a gallon for fuel.

There are other alternatives. One is hydrazine. It's not too difficult to produce, and combustion produces water and CO (and likely NO as well). Also, it sounds more COOL!