While not in mass production, there is strong interest from the marine shipping industry. It can be produced near ports, and meets the storage and combustion engine constraints (similar to diesel) of the use case.
A sibling comment mentions scrubbing NOx emissions as a significant issue, and it strikes me that the shipping/cruise industry is already a major polluter in that area. (Unlike cars, which must have catalytic converters because of local landlubber laws.)
I guess my point is that cleaner technology is already being avoided by those companies, because they can save a buck by polluting in international waters.
Generally speaking modern hydrogen pressure vessels are not metal for this reason, they are composite and not affected by embrittlement.
The Toyota Mirai, a production hydrogen car, uses a type IV carbon fiber pressure vessel rated for 70 MPa / 10,000 psi.
Type V are rated for 15,000 psi.
It is not necessary to liquefy hydrogen for adequate range in ground transport applications: The Mirai yields a 402 mile EPA rated range on gaseous hydrogen.
The tanks weigh 93kg filled with 5.65kg hydrogen, yielding an approximately 190 kWh of stored energy.
All without corroding flesh in trace concentrations.
By comparison the Tesla Roadster's 450kg battery pack yields a 200 kWh capacity.
Ammonia is and would likely continue to be stored in metal pressure vessels as an obvious cost optimization and thus would compare unfavorably to hydrogen pressure vessels' effective energy density where that area of the performance versus cost optimization space is not available due to embrittlement.
Direct propane fuel cells have some thermal issues, but recently there was a breakthrough in propane synthesis that would make it efficient to produce. Are ammonia fuelcells efficient?
Not sure if they are today, but Toyota is putting a lot of effort into ammonia turbines. Also ammonia can be fired with coal or natural gas in existing setups. The main issue is neutralization of NOx exhaust.
I think many (most?) combined cycle plants use ammonia to destroy NOx in the exhaust (selective catalytic reduction). Some diesel cars use this technology as well (using urea instead of ammonia).
