mfb said:
On the positive side: The CO2 is produced in a fixed place, making capturing and sequestration an option. Splitting the CO2 to carbon and oxygen again (using CO2-neutral energy sources) is an option as well. All these things are not possible with internal combustion engines in vehicles.
If the CO2 is split back to O2 and C, then I would agree.
However with sequestering, there is another insidious side effect there not considered, esp if there is large scale global roll out. If sequestering, this process takes oxygen, and carbon out of circulation.
At least with the biological Carbon cycle, its well, a cycle, where CO2 is constantly produced and consumed, ie the oxygen is released as part of the cycle and the same molecules basically just do the rounds repeatedly.
But with sequestering and metal air batteries, you take carbon and bauxite, produce aluminium and CO2, you bury the CO2 (ie its gone now), take the Al and oxidize it with new oxygen. Then you go back, take that oxide with some new carbon to get the Aluminium back and make new CO2, which you bury again.
Which now means every time that 1kg of aluminium does its loop, 10.4kg of CO2 disappears from circulation, ie since by mass CO2 is ~30% carbon and 70% oxygen, ie we're literally loosing 7kg ox oxygen and 3kg of carbon to use 1kg of aluminium to make a meager 29MJ.
Imagine the effect of reducing O2 concentration in the atmosphere, I doubt good things would be the result...
A lot of these things sound good till you zoom out a bit and consider other effects.
Then this really is just an energy storage mechanism, you somehow still have to supply energy to do this from somewhere.
