Moving Artificial Leaves Out of the Lab and Into the Air

I also noticed that about the carbon capture technologies. CO is the common intermediate, while storage/conversion process to another form is the main issue from an energy standpoint as well.

Future fuels do seem to be a commonly discussed endpoint for carbon capture. That could be good or bad. Considering what we have learned about the warming potential of fossil fuels, it would make sense to conserve a reservoir of the same for the (more distant) future, if we really are going to master this issue and become capable of managing earth's climate, including the ability to address a future cooling trend of any cause.

The second issue about stored carbon/fuels is whether we actually control and maintain it in the desired state, or whether it will escape our grasp as global temperature and other conditions change. Buried wood, peat bogs, and other natural carbon sinks lose their stability as temperatures increase...

Making fuel out of the carbon to burn again is just "catch and release". You end up back where you started after expending energy to get nowhere.

Are you objecting to humane trapping of this pesky CO2?

Of course, no one ever thinks about amassing and containing a reserve of live trapped rodents... maybe carbon is not such a difficult creature when you think about it.

It's too bad we already have a surplus of plastics that 'won't break down for 1000 years' or more. But I'm sure we can think of a carbon product we "need" more of. Surely.

Yeah, too bad there isn't some self replicating version of this we could start in various area that would convert the CO2 into products that might be used in longer lasting applications.... maybe even building products. Oh if only there were something like that that would use sunlight and make something other than CO that required very little in the way of maintenance and would spread to available areas easily....

Hmmm.

Yeah, maybe we can't see the forest for the trees...

But you're not back to square one. Sunlight energy is converted to chemical energy, and even if the CO is burned there's no net increase in atmospheric CO2. Though if the CO is used in a heat engine to produce power, the efficiency of the leaf would need to be much better than a PV cell due to the thermal efficiency of the engine. It comes down to cost and efficiency of this thing vs a PV cell.

I agree that it could compete with PV as a solar-powered carbon-neutral energy source, with the handicap of Carnot efficiency and the energy required to concentrate the 0.04% of CO₂ in the atmosphere. I suspect that PV would probably win.

Actually, either removing CO₂ or replacing a process that adds CO₂ with a carbon-neutral process both have the same net effect.

Why would you need to concentrate the CO₂? Leaves (as in plants) use CO₂ straight from the atmosphere. The CO produced by the artificial leaves needn't be diluted with a lot of air, maybe it's produced fairly pure. (It might say something in the link, if so I haven't spotted it.)

You are correct, I shouldn't have put it as "energy required to concentrate CO₂". The reactant concentration (0.04% CO₂) would affect the reaction rate but not the reaction energy.

If the artificial leaf is powered by sunlight of a constant intensity (energy per unit time), the lower the concentration of CO₂, the lower the reaction rate, and the lower the amount of CO produced which can be converted back to energy. So the reaction energy balance itself would not change, but I'm thinking that less of the input energy would be used for the reaction and the efficiency would be lower, which what I was driving at.

So it's not really "energy to concentrate" but an energy penalty to be paid due to the inefficiency of the low concentration of one of the reactants (CO₂).

OK, I wouldn't disagree with that

There has to be some losses in the conversion in both directions or it would be a perpetual motion machine.

If the conversion of CO into fuel is relatively easy,why not convert exhaust from combustion engines into fuel for use by the engines?

I seem to recall such a system being used on city buses to reduce emissions and improve efficiency,but I can't find a link to it.