I see, and it has been a long long time since I've had college Physics, but can't seem to shake Newton's laws, and that same motor still has to mobilize the same 2000+ pounds of car that efficently.
If this technoogy if true, and could be managed safely, it would truly be game changing.
Fuel cells have been around for a long time. The way the typical hydrogen fuel cell works is that hydrogen gas is forced through a platinum and ruthenium-laced polymer. The protons pass through while the electrons circle around through a wire. On the other side, oxygen molecules ionize by accepting the electrons through the wire, and then accept the protons passing through the polymer to form water molecules. And the flow of electrons through the wire is what runs the electric motor.
There are other types of fuel cells, but this is the simplest. The cell runs at about 80°C, much cooler than an ICE. These cars already exist and are on the road right now. The problem of course is how to refuel (and store) more hydrogen.
The best way to approach this is to look at hydrogen as a way of storing electricity. In other words, a tank of hydrogen is equivalent to a lead or lithium battery. But storing hydrogen gas is problematic since it leaks through everything. Expect a 1% loss per day. It also has a low energy density at STP (as you have already pointed out) compared to natural gas. So it must undergo extreme pressure to mimic current fuel tank capacities.
Another way to store hydrogen is with sodium borohydride. It is very safe, but would require a minimum concentration to be maintained in a 'fuel tank' in order to generate effective power. Once the sodium borohydride concentration is depleted, the entire tank contents would have to be traded out with fresh stock. So future filling stations would not only provide 'fuel' but they would also be collectors for spend liquid fuel.
And finally, there is the crux of the bisquit - economy. Sure hydrogen fuel cells work. But are people willing to pay a higher cost for fuel than they currently get from gasoline? The answer to that is a resounding 'NO!'. And as long as the price of hydrogen is tied to the price of fossil fuels, it will NEVER be competitive with the ICE. The ONLY way to make hydrogen viable is to bring down the price of electricity to a point where water electrolysis is cheaper than reforming methane.
Fuel Cell Basics (DoE)