Seems to me that if you really wanted to sink the carbon, you’d somehow use the ethanol produced as a feedstock for producing some kind of relatively inert plastic or other stable compound.
That way, a ton of carbon you take out of the atmosphere would be well and truly sequestered and lower the atmospheric CO2 load a little bit.
Where I see an application for this is in space. Right now breathing oxygen is a consumable, which becomes a huge burden for long durations (especially for ships, where every kilo of payload means multiple kilos of fuel, engines and dry mass). Being able to convert CO2 back into breathable oxygen using solar or nuclear power would markedly improve the feasibility of manned space missions by making the air supply a closed system.
I don’t know what to think. In the last ten odd years I’ve heard so many stories of some researcher finding some way to pull CO2 out of the atmosphere and convert it to either a usable fuel source or converting it to a solid form that can be buried, and nothing ever comes of it.
Having said that, I could forsee a day far into the future (several decades from now) where this technology has been scaled down enough that a person can put one in the backyard and use it to make everclear. That’d be nice, just making everclear from the air. I’m so useful to these conversations, I really am.
Here’s a chemist’s blog on the topic. http://blogs.sciencemag.org/pipeline/archives/2016/10/19/burning-in-reverse
The comments are definitely worth reading.
If it takes huge amounts of energy to convert the CO2 back into a fuel, then instead of using the nuclear power plant to reclaim the CO2 pumped out by fossil fuels you would be better off just using the nuclear plant to provide energy directly, getting the CO2 out of the energy mix in the first place.
There are already plenty of ways to even out variable power, if we aren’t worried about how much energy it takes. For example, when the sun is shining you can use pumps to pump water into a high reservoir, then when it’s dark you can flow the water back down through turbines. Molten Salt solar thermal plants store heat from solar energy in molten salt which has a very high melting point and therefore can hold a lot of energy. Water is then passed through the molten salt, turned into steam, and the actual electrical power from the plant is generated with steam turbines.
But here’s the problem: Solar and wind power are very diffuse sources of energy. That means lots of raw materials needed to provide the infrastructure, and it means that even tiny efficiency losses can make the whole project non-viable. Store energy in reservoirs, and water that evaporates is a dead loss. The pumps have much less than 100% efficiency, as do the turbines converting the water to electricity on the way back down. Batteries have internal resistance and lose power to heat when charged. Molten salt piles allow some heat to escape through conduction with the storing vessesls, and the steam turbines have conversion losses, as do the power lines from the remote plant to consumers. And so it goes.
The earth is awash in energy. You can reclaim energy from geothermal sources, from wave and tidal power, from river currents… Heck, the potential energy stored in a mountain could be harnessed by taking material from the top and dropping it in buckets attached to a rope attached to a flywheel.
The trick isn’t finding energy sources. The trick is utilizing them in a way that makes them cost-effective and available in quantities that can power an industrial economy.
The point here is that liquid fuels transport more efficiently over long distance than electricity and are more valuable for heavy transportation than electricity. So it’s not just an electrical to electrical storage loop.
But yes, one is generally better off directly decreasing emissions rather than trying to offset them through a scheme like this.
Except your second set of biodevices excrete ethanol and… CO2! :D:smack:
It looks like photosynthesis’ equation is: 6 CO2 + 6 H20 = 1 glucose and 6 O2, while the fermentation of 1 glucose yields 2 ethanol + 2 CO2, for a net loss of 4 atmospheric CO2.
We need to invest in batteries, not this.
<n.m.>
Could someone please translate this for a non-physicist:
Not a physicist (neither is the PI, yay chemistry), but:
A minimum theoretical voltage is needed to make any electrochemical reaction go. The overpotential is how much extra voltage you need in reality above and beyond the theoretical minimum if everything worked perfectly. They’re having to push electrons harder, and thus spending more energy than what is just required by thermodynamics.
An electrochemical cell comprises two electrodes separated by an electrolyte. The electrolyte doesn’t allow electrons through, but is conductive to other charged species. The electrolyte is not perfectly conductive, so they can improve performance by decreasing that resistance. Choice of electrolyte can also affect mobility of reactants and their interaction with the electrode.
I’m not quite sure what they mean about separating hydrogen production to another catalyst. They’re trying to avoid hydrogen production; they see that at high negative overpotential. I’ll try to talk with them about it later this month.
The overall 12-electron reaction is:
2 CO2 + 9 H2O + 12 e- –> C2H5OH + 12 OH-
There are a lot of other product options, especially given that there are multiple steps to form ethanol. They could end up with methane, C1-oxygenates, ethane, ethylene, acetylene, acetaldehyde, acetic acid. The control electrode, without their nanowank, produces CH4 and CO. So it’s surprising that they’re seeing high selectivity to just ethanol.
How’s this?
*The amount of energy required to drive the reaction to completion is too high to be economically viable. However if we can design either a better reaction chain (remove certain product earlier) or better catalysts then it might become easier to do.
Also we think the copper nanostructure we’ve played with is neat and potentially valuable in creating new reactions. *
Much better than my attempt! 
I haven’t had my coffee yet so less typing is always better. 
Thanks to both of you. Although I’ve long been interested in physics (although less so chemistry) and had classes in both at the undergraduate level (30+ years ago), the paper’s language was a little too dense for me to unpack. Both of you made it much more comprehensible.
Thanks again.
I did speak with some of them, and also to a professor I know who is very enthusiastic about direct air capture.
First, my usual complaint about press offices and “science journalists”, who are the guilty parties when it comes to the media hype we saw here. The folks actually working on it are funded out of DOE SC BES SUF (ain’t DC fun?). They geek out making and looking at tiny structures. The team is trying to learn how their carbon spikes work wrt catalysis, and that’s what they want to keep doing. The technology isn’t in a position for actual use, and I’m not sure they would know how to get it to that point.
That said, conversion of CO2 to liquid fuels could have some uses. If we envision some zero(ish)-carbon future, we’ll likely still have liquid fuels. It’s hard to beat their energy density, their transfer rate and efficiency, or the power density of the ICUs they fuel. We can get away with batteries for light-duty vehicles, but I don’t see a realistic path to electric class 8 trucks or passenger planes. Now that liquid fuel could be some hydrogen-containing liquid that doesn’t contain carbon, e.g. ammonia, peroxide, hydrazine. But hydrocarbons still have their advantages.
How to get them if we aren’t digging for them? As others mentioned, plants do it for us, directly capturing CO2 and converting it into carbohydrates or fats, which we can convert into fuels. But plants require arable land and a lot of water. Whereas direct air capture of CO2, water hydrolysis, and reduction could all be done with much less water and without interfering with agricultural pursuits. I’m curious as to how the actual numbers play out, having not run them myself.
No one is attempting a free lunch here. Definitely no first-law violations or even those sneaky second-law violations. Direct air capture and reduction of CO2 takes more energy than you get out when you burn the resulting product. But different forms of energy storage are useful in different times and places. I don’t pour gasoline into my phone. And they don’t plug in the plane I just flew on this morning. Liquid fuels are still useful even if we kick the fossil fuel habit.
Very interesting topic. Their catalyst almost sounds like a designer enzyme.