There are a lot of papers advocating for a switch away from fossil fuels, and even H2 fuel cells, to ammonia based propulsion in transport. It can be used in combustion engines but there's a risk of NOx production. So the greenest option to me is ammonia to H2 conversion or direct ammonia fuel cells. It's got the same advantages of classic H2 fuel cells but without the constraints of cryogenic or pressurized containment of H2. And ammonia has a better energy density. But it's toxic for humans and, above all, marine life! Especially for fish species. So I'm feeling a bit uneasy about potential mass ammonia spills…
