The "obvious" answer would be to fuel cars with ammonia directly. It is cheap and safe and energy dense compared to compressed hydrogen. It is still nasty stuff for us water based critters but society has plenty of experience working with it on an industrial scale. Wikipedia has some sections on using
ammonia as fuel and
ammonia as an energy carrier. The article is talking about using it as an energy carrier.
And I agree that it is probably the 2nd most practical way to move hydrogen. Most practical being oil/natgas of course
I've been trying to find a better source for how their membrane works but coming up empty. It probably goes without saying that it is far from perfect. Likely it needs extremely high pressures or temperatures or is extremely slow and needs an unreasonably large facility to produce useful amounts. If it was small and cheap then they would be talking about bolting it into a car and filling up with ammonia directly.
The really big question is how energy intensive is the conversion. Ripping apart molecular bonds takes some energy. If it is based on thermal decomposition then much of the heat could be recovered. Or maybe they have a novel catalyst. But since they are talking about a membrane and not a magic catalyst then it is probably regular thermal decomposition.
Thermal decomposition is where you heat up a gas so hot that the molecules break apart into their elements. For water that happens at 3000C. For ammonia it happens at a slightly lower temperature. 1000C to 2000C depending on the catalyst. Likely the bulk of the system is heat exchangers to extract the heat from the hydrogen/nitrogen outputs and recycle it into the ammonia input.
Compressing gasses also heats them up and normal H2 systems need heat exchangers too. Hopefully that is already a solved problem but H2 has the annoying tendency to leak through metals and embrittle them. Doesn't sound like it was an easy problem.
But one must wonder where they get the ammonia from. Right now it is all
natural gas. So it is a little like running an electric car from coal fired plants. Also interesting is the stat that we globally make 160M tons of ammonia per year. 160M tons of ammonia is only 28M tons of H2.
Given the 50% efficiency of fuel cells 28M tons of compressed H2 (142 MJ/kg) could be turned into 500,000 TWh of electricity. A good electric car might use
200Wh/km. So all the ammonia could move cars 2.5 million million kilometers per year.
The average american drives
21000 km per year. So the
world's entire ammonia production would be used to let
120 million people drive hydrogen powered cars. There are
260 million cars in the US and
1 billion cars in the world. (Ignoring trucks for now.) Ammonia production would need to be ramped up by a factor of 8 which wouldn't be impossible. But that ramp up would be done with conventional ammonia production methods based on natural gas and end up producing lots of CO2.
edit: And the bulk cost of ammonia is
$200 per metric ton wholesale. That works out to only
$300 per year on fuel. I'm surprised it is that economical. The pumping stations and hydrogen gas conversion process will probably 2x or 3x the cost.
It is neat but we need a breakthrough in ammonia production.
