hydrogen engines don't require rare earth minerals. given the current active trajectory to "suppress china" in play right now in the red sea anything involving expensive, china-dominated source materials and the fact that fuel cells have been on the table since 1988 and still have made no progress. the real move is biohydrogen and modified gasoline engines, in my humble opinion. neither are difficult to retool for from this point, it's just a matter of research focus. fusion is still off in the distance. nuclear could go somewhere but it's got the CND psyop around it that despite 3 mile island and chernobyl turning out to be relative nothingburgers relative to the actual toxicity to humans should have changed that trajectory but that doesn't sell tabloids.

The fuel cell is the engine. The problem is the fuel itself. Hydrogen atoms are the smallest atoms therefore they will leak out of any container made of a material made of larger atoms. To really make it safe you'd need to keep it in a box with lead walls 30cm or more thick, which massively increases the weight of the vehicle you're trying to propel. In open air or for a short period of time (like a day) it's not a very serious problem. But in an enclosed space, left for a week, dangerous concentrations of hydrogen are going to build up around the vehicle which can explode. There's also the issue that if you leave your car in a car park for 2 weeks to go on holiday all the hydrogen will leak out while you're away so you can't start it when you get back (as many people used to have problems with dead lead-acid batteries)