While the thought of using hydrogen seems appealing at first glance (some people think it makes only water vapor when it burns) it really isn't a great fuel for engines. There were some hydrogen powered buses running around Vancouver during the 2010 Olympics for clean propaganda reasons. BMW had their 7 series hydrogen powered V12 car 12-13 years ago too. It was a flop. The gasoline version put out 440 hp. while the hydrogen version managed 256 hp. And to get there, it got 4.7 miles per gallon. Hydrogen is prone to detonation, not a great internal combustion fuel. And burning it in air instead of pure oxygen still results in NOx emissions - more than burning natural gas due to the higher flame speed.
However, most hydrogen cars don't burn it in the engine. Instead it is used in a fuel cell that produces electricity. Hyundai, Toyota, Mercedes, Honda are all working on fuel cell cars. Nice. It's still an electric car. And while hydrogen is abundant in the universe, it isn't on Earth. If you have enough electricity available, you can split water to get the hydrogen out. But that isn't the way most hydrogen is made for commercial use; it's extracted from natural gas with the left over CO2 being dumped, because that is the cheaper way of doing it. And even so, the energy it takes for the process is more than you get out of the hydrogen in the end. Perhaps 10 million tons of hydrogen is used in the US each year for industry and commercial purposes - to switch cars to that fuel would increase the demand to ten times that amount.
By the way, German engineers knew of the risks with hydrogen, the Hindenburg was originally designed for Helium. However, the majority of the world supply came from the US and due to the ban on export, (the helium act of 1925
https://en.wikipedia.org/wiki/Helium_Act_of_1925) hydrogen had to be used instead. After only 32-37 seconds of fire, about all that remained of the main ship was the aluminum frame. But even after that it should be remembered that 2/3 of the people on board survived.