I think that the new Mars rover in 2020 will make oxygen, from thin Martian atmosphere. I think Mars' atmosphere is 90% $CO_2$. Carbon dioxide is made of $C$ and $O_2$. $O_2$ is oxygen, so can't we separate oxygen from carbon dioxide? We only need to release the carbon, don't we?
The experiment in question, MOXIE, "Mars Oxygen ISRU Experiment" uses a process of solid oxide electrolysis, to produce oxygen from Martian atmospheric $CO_2$.
First, as reversal of the process of burning coal, production of oxygen from carbon dioxide requires significant amount of energy.
Then, due to specifics of the process, and problems of solid residue the produced carbon would create, the actual reaction performs operation of splitting carbon dioxide into oxygen and carbon monoxide, and separating them.
While technologically much simpler than detaching both oxygen atoms from a $CO_2$ particle, this leaves the risk of mixing highly poisonous carbon monoxide with the oxygen produced.
Experiments with utilizing photosynthesis of plants or cyanobacteria were performed; these release oxygen while using carbon as a building material of the organism (and using sunlight energy to do the splitting); this comes with a range of different problems though, and isn't to be tested in the 2020 rover.
I believe your concept is a bit off. I don't think that new Mars rover in 2020 will make oxygen... In order to break apart CO2, into C and O2, energy is required and it isn't as simple as getting a knife and cutting a CO2 molecule in half. Just bring a bunch of plants into Mars where they are in contact with their surroundings but they don't die due to freezing, warm them and give them some light so they will transform CO2 into C and O2. This could work!