Ammonia is a liquid at room temperature and pressure, so a simple plastic or metal fuel tank would work - no compression required. It solves the range & recharge problems of battery electric vehicles, in that a larger fuel tank is all that is required to increase range. The larger fuel tank has negligible cost at the system level, whereas the cost of battery electric systems rises proportionally to the range and battery capacity. An ammonia fuel tank can also be refueled in minutes, versus hours or days for battery electric vehicles.
Basically, ammonia is a relatively energy dense way to store and transport hydrogen. In this way, it is not unlike hydrocarbons (fossil fuels), except that carbon capture is not required to make it environmentally friendly. Ammonia can be cracked into nitrogen gas and hydrogen gas using a catalyst at < 1000 deg.C, a relatively low temperature compared to combustion, meaning no nitrogen oxides (smog) will be formed. The Earth's atmosphere is already 78 percent Nitrogen gas, so the Nitrogen produced is not a pollutant, and can simply be emitted out the tailpipe. The Hydrogen gas produced can be burned in an internal combustion engine at 25-40 percent efficiency, or combined with oxygen in a PEM fuel cell to produce water vapor and electricity at 65 percent efficiency, the electricity then driving electric motors.
"One way of making green ammonia is by using hydrogen from water electrolysis and nitrogen separated from the air. These are then fed into the Haber process (also known as Haber-Bosch), all powered by sustainable electricity."
https://royalsociety.org/topics-policy/projects/low-carbon-energy-programme/green-ammonia/
An ammonia fuel infrastructure would represent a variety of hydrogen economy, something that is utterly impractical without an effective means of storing and transporting hydrogen. Since Hydrogen is an extremely light, low-density gas, and tends to leak from tanks, and pipes, simply compressing or liquefying hydrogen requires large, heavy tanks with low energy density, and limited flexibility in shape - they tend to be spherical or cylindrical. This means aircraft have to store hydrogen in the fuselage, where cargo and passengers usually ride, instead of the wings where the fuel usually is stored. Ammonia might resolve these issues, allowing hydrogen to be stored in the wings (as ammonia), and cracked into hydrogen as it is fed into the powerplant. This is more amenable to a traditional aircraft design.
Ammonia can be produced using non-polluting air & water resources, and renewable wind & solar energy. It can also be produced at a central plant for distribution by rail, ship, truck, etc. and doesn't require and enhanced electrical grid at the end-user location. Of course the upstream electrical generating capacity would have to be absolutely ginormous, the same as every other renewable energy scheme out there.
One downside is immediately obvious: Ammonia releases noxious fumes, so people will need to wear appropriate mask, maybe gloves, while refueling their vehicle with ammonia.
I am interested in the NASA study, to find out the cost compared to bio-diesel, or battery electric, solutions.