It is actually cheaper because of existing infrastructure that exists for fertilisers manufacturing.

But the main concern is that ammonia burns slowly. It might work in power plants but not in EVs

Why would you want to burn ammonia in an electric vehicle?

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.

Filter the exhaust through a caustic solution to neutralize NOxs.

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.

https://spectrum.ieee.org/why-the-shipping-industry-is-betti...

https://www.wartsila.com/media/news/30-06-2020-world-s-first...

https://www.lr.org/en/about-us/press-listing/press-release/i...

https://www.ammoniaenergy.org/articles/maritime-fuel-mix-cou...

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.)

High efficiency scrubbing appears to be feasible.

https://pubs.acs.org/doi/10.1021/acs.energyfuels.3c01419

[delayed]

NOxs are practically zero with HCCI at a stoichiometric ratio.

There has been a lot of research in fuel cells that generate electricity from ammonia, with much simpler storage problems than for hydrogen.

Yes, fuel cells need more usage as we move away from oil & unnatural gas.

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?

I'm not sure I'd leap to "much simpler storage problems than for hydrogen" for a highly corrosive gas.

It poses an immediate danger to life and health at concentrations below the lower explosive limit of hydrogen.

Not every hydrogen leak is a concern, but just about every ammonia leak is.

The established OSHA 15 minute exposure limit for ammonia is 35 ppm, 8 hours is 25 ppm.

But hydrogen likes to make invisible fires and leak through solid steel, and it needs to be ludicrously cold to liquify.

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.

By comparison the Tesla Roadster's 450kg battery pack yields a 200 kWh capacity.

All without corroding flesh in trace concentrations.

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.

In Japan they're looking at adding Ammonia co-firing to coal plants:

https://about.bnef.com/blog/japans-ammonia-coal-co-firing-st...

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).