Is it possible to split $\ce{CO2}$ into C and O? If so, what are some methods and their efficacies?

This question originated because I was wondering if it was possible, and if so, how, to convert ice from the ice caps on Mars (made up of frozen $\ce{H2O}$ and $\ce{CO2}$) into oxygen.

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    $\begingroup$ I would go for water ice, we have found plenty of it on Mars. $\endgroup$ Jun 5 '17 at 1:33
  • $\begingroup$ Of course you can split CO2 up. But it takes energy to do it. So, what is your real question? $\endgroup$
    – Jon Custer
    Jun 5 '17 at 1:38
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    $\begingroup$ What kind of scale are you thinking about? In other words, are you thinking in terms of converting Martian CO2 to O2 and carbon on a global scale, or for supplying a future outpost with oxygen? The former is far beyond our technological capabilities, while the latter could be doable. Also note you don't have to go to the poles, as the atmosphere (what there is of it) is mostly CO2. The biggest problem though, no matter the chemical path for getting there, will be the massive energy requirements. This again underscores that whether this is a reasonable possibility or not depends on the scale. $\endgroup$
    – airhuff
    Jun 5 '17 at 1:46
  • $\begingroup$ The best way on the planet would be to use an electrochemical way, as there will be power (solar/nuclear) but no many other chemicals. Failing that, and probably better, would be to genetically engineer plants here on earth to operate in the cold and at low light levels. $\endgroup$
    – porphyrin
    Jun 5 '17 at 8:23

I assume you meant convert $\ce{CO2}$ into $\ce{O2}$.

Lithium peroxide ($\ce{Li2O2}$) is a substance that does this. It absorbs $\ce{CO2}$ and converts itself into $\ce{Li2CO3}$ and $\ce{O2}$:

$$\ce{2Li2O2 + 2CO2 -> 2Li2CO3 + O2}$$

It was used as an air purifier in the spacecraft to scrub carbon dioxide. It offers it's bonus of releasing oxygen as well as being non-hygroscopic, so it won't remove the moisture content in the air.

But at any day, you would need a lot of lithium peroxide if you want to make Mars habitable.

Edit: The partial pressure of carbon dioxide in the Martian atmosphere is $\pu{575.8Pa}$. Using the ideal gas law, and temperature of Mars is $218K$, we get amount of substance of $\ce{CO2}$ as $\pu{0.32mol/m^3}$.

Such an amount would require $\pu{14.65g}$ of lithium peroxide per cubic meter of martian atmosphere. According to SigmaAldrich, that costs about ₹21.22 (33 US cents) per cubic meter.


Plants do a pretty good job of using solar energy to convert CO2 to O2. But the intensity of sunlight on Mars is weak and you would need a very well-insulated greenhouse to do this sustainably. I would start with Antarctic algae and see where that takes us.

  • $\begingroup$ Nooo! This is very much wrong, and a common misconception. Plants do not convert $\ce{CO2}$ into $\ce{O2}$. In fact the oxygen released comes from water, not carbon dioxide. Plants use the sunlight energy to split water into hydrogen and oxygen. The hydrogen goes into making glucose along with carbon dioxide. There's very little water on Mars anyway. $\endgroup$ Jun 5 '17 at 10:38
  • $\begingroup$ @PrittBalagopal That's true but I don't think it really matters for the question. The OP seems to be interested in how to make oxygen and whether it comes from $\ce{CO2}$ or water doesn't really matter. $\endgroup$
    – bon
    Jun 5 '17 at 10:43
  • $\begingroup$ @iad22agp Exactly, people think that CO2 is broken down in photosynthesis into free oxygen when this is not the case at all. The carbon-oxygen bond in CO2 is very strong and it takes much energy at high temperatures to break the bond no matter what enzymes are used. The free oxygen from photosynthesis actually comes from the break down of water. The hydrogen-oxygen bond is much weaker and the small amount of energy from sun light with the help of some enzymes allows the breakdown of water into free oxygen and the hydrogen is then combined with the CO2 to make sugars, $\endgroup$ Sep 25 '20 at 17:20

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