Are hydrogen fuel cells efficient? I dont know anything about them
The primary problem with Hydrogen is storage and transport. Steel tanks look like cheesecloth to Hydrogen.
Think about it, from what do you fabricate a container for the smallest of all elements?
Some light reading on the state of the tech
https://hackaday.com/2019/09/04/are-hydrogen-cars-still-happening/The Hindenburg was able to hold some hydrogen. I am confident the tech has evolved since.