I have seen a hydrogen powered car, it didn't get the hydrogen from the air though. Also, releasing water vapor could be just as harmful as releasing CO2, water vapor is actually considered one of the three leading greenhouse gasses, along with CO2 and methane
I'm taking about a plane that gets H from the air and uses it as fuel but you obviously never learned that a cloud is water vapor all it needs to do is merge with a cloud and it will eventually turn in too water and the process keeps going in a circle.