>>18891746Hydrogen cars work by using hydrogen gas to fill electric fuel cells, it's just another variant of an electric engine.
Rocket engines work by burning the hydrogen, by using the hydrogen itself as fuel, since hydrogen, above concentrations of 20%, becomes explosive.
Liquid hydrogen is 100% hydrogen which makes it extremely volatile, and the fuel with the highest specific impulse of all we have right now, capable of accelerating rockets like the Saturn V from zero to breaking the sound barrier within 40 seconds.
