Try over a 100 years..... And still they scream it from the rooftops!
The problem with using pure hydrogen for anything is, the molecules are the smallest ones and it's a real bear to make a seal to contain them. Sooner or later you are going to have a build up of pure hydrogen in a fender well and blow your right rear side off.
Back in the old days that was true. Modern technology however, has made that issue a thing of the past.
And yet we don't see it coming out. it's still a problem. If I bounce the system around like it would be in a car leaks will happen. And those leaks are dangerous. There are safer alternatives out there that are coming on line or are already on line.
That's because it is still more expensive in terms of energy usage to separate out the hydrogen. Until they advance the tech to where you get more energy out of the hydrogen than is used to create it you won't see it commercially available. However, if Lockheed can indeed perfect their fusion technology, that too will be a thing of the past. I don't think anyone here has any idea of just how profound a change will come when fusion power is perfected.
That's what pretty well killed off the electric car in 190X. The Gas Car was found to be cheaper when you considered just how crude the electric car was. They did not have the technology to build a battery and electric motor to go much further than 10 miles per charge without one hell a long extension cord. Of course, Trolleys did have one hell of a long extension cord and the Trains ended up doing it 50 years later. But cars didn't have that capability until just recently. Add to the fact, the Military tied up the Rare Earth Motor for about 10 years in the 80s and 90s so they could not be developed for commercial uses. Even so, it hasn't been until recently that the batteries have been capable or cheap enough to complete. It's gotten to the point where it's not real tough to produce a family electric car that has a 250 mile range for just about 5000 more than it's gas counterpart. And most of that difference is the batteries themselves. And that is coming down as better batteries are coming on line.
India, China, California, Oregon and a few other states will not allow gas powered cars by 2030 on their highways. Even in Denver, the push for recharging stations are being pushed. Fedex just placed a large order for a fleet of Electric Trucks with Tesla. Funny how we are going back to the way it was in 1903.
The Fusion has been very elusive for decades now. Even with the best solution just overhead. It's going to happen. Maybe not now, but someday. And it will revolutionize even flight.