[elihu]

Hydrogen fuel cells can't compete with battery EVs on energy efficiency, if the hydrogen is produced from electricity by electrolysis. (Most hydrogen is made from natural gas.)

Hydrogen beats batteries in terms of energy density, so maybe it has a future in aviation. I think ground transport will eventually all transition to battery electric (and hopefully we'll get electrified roads at some point so battery size and range isn't really an issue anymore) unless energy somehow becomes so cheap that we just don't care how inefficiently it's being used. I don't expect that to happen any time soon though.

[WorldMaker]

I've seen some interesting data that suggests hydrogen fuel cells may not even have a future in aviation. Air travel does currently rely on some efficiencies from planes being lighter as they travel due to fuel spend, which is something that hydrogen fuel cells would share. But the theories I've read suggest that torque will be the huge overriding efficiency (and safety) benefit to electric aviation (that electric motors have access to nearly 100% torque at all speeds, if you have the available power draw). In that case, hydrogen fuel cells become a massive power draw bottleneck on torque, dropping motor efficiency, so you want a big parallel battery for moments of large power draw. At that point if you are already building around the weight of a large battery you might as well right size the battery for complete range and drop the inefficient of "dual power sources".

From what I've read that seems to already be playing out in small planes that fully battery electric is winning over hydrogen or hybrid hydrogen/battery. It will probably be another decade or so before we see how it plays out on the larger planes.

The only place I've heard hydrogen might win out is large sea transport (large cargo ships and cruise liners), and even then there are interesting recent developments in wind power for ship's cruising speeds and battery charging that are going to be competing with hydrogen

[elihu]

I agree it makes sense for ships to use hydrogen. You might have a point about power density of fuel cells being too low for aviation. I don't think batteries will work for aviation except for very short flights, unless there's a major technological improvement -- in the near term probably the best low-carbon option is some kind of synthetic liquid fuel.