"The raw energy density of liquid ammonia is 11.5 MJ/L,[64] which is about a third that of diesel."

https://en.wikipedia.org/wiki/Ammonia#As_a_fuel

(Note this is energy density by volume, which is the metric most care about. Energy density by weight of H2 gas is great, but the volume is enormous in comparison.)

https://en.wikipedia.org/wiki/Hydrogen_storage

Ammonia has been long recognized as a great medium for energy storage and you can generate at the site of electric generation. But the challenge has been extracting the hydrogen from the ammonia. My understanding is that hydrogen crackers exist, but have only been successful commercially at large scale. A portable cracker that you can put on a car that extracts hydrogen on demand from an ammonia storage tank is the innovation we need to see. Apparently there is work in Denmark that looks promising... (And now there is this new membrane technology from Australia.)

https://www.mvsengg.com/products/hydrogen/ammonia-cracker/

http://www.ammoniaenergy.org/ammonia-cracking-to-high-purity...

Personally, I am cheering for ammonia as a storage means. I am not a fan of batteries found in today's electric vehicles because there are too many conflict minerals in them. Maybe Tesla will succeed mining colbat in Colbat Ontario Canada... But until then, it is probably coming from the Congo or Bolivia.

https://www.washingtonpost.com/graphics/business/batteries/c...

https://www.bloomberg.com/news/features/2017-10-31/the-canad...

> "The raw energy density of liquid ammonia is 11.5 MJ/L, which is about a third that of diesel."

Yes, but that's assuming you'd burn it, I suppose (not a chemist). In this case, you're extracting H atoms using a different process, and I imagine that this wouldn't utilize the full raw energy density of ammonia.

Looking at the process as a whole, it is burning - or at least oxidation. Starts with NH3 and ends up with H2O and N2 (preferably not NO2). The energy liberated from the bonds is the same. The amount of energy available at the wheels depends on a lot of fine details of how it's used.

"what does the chemical reaction look like when harvesting hydrogen from ammonia?"

Reverse Haber process maybe?

2NH3 -> N2 + 3H2

I wonder, does converting ammonia to hydrogen absorb energy or release it? (Ie is it endothermic or exothermic?)

It's highly endothermic. Replacing the hydrogen with oxygen is exothermic.

So one can create some ammonia-air fuel cell. But reducing it first to push the hydrogen into a fuel cell will almost surely net a negative amount of energy because of the losses.

Exothermic as the reverse is endothermic.

How would this work in an ammonia-powered battery?

It doesn't. The membrane "cracks" the ammonia into N2 and H2. The N2 is released to the atmosphere. The H2 is used in a hydrogen fuel cell to power an electrical drivetrain or in an internal combustion engine with a mechanical drivetrain.

how do you regulate the membrane? does it degrade?