4 links have been added on this idea.
  1. NASA has done it! Check out this mini reactor that was used to create oxygen on Mars.
    https://www.smithsonianmag.com/smart-news/an-instrument-aboard-nasas-mars-rover-can-produce-oxygen-at-the-rate-of-a-small-tree-180980699/

  2. Hmm, scientists could use plasma technology to create oxygen in Mars and other space colonies.

  3. A great idea in theory, but it would take so much time and effort to create and sustain a breathable atmosphere on Mars.
    https://www.newscientist.com/article/2175414-terraforming-mars-might-be-impossible-due-to-a-lack-of-carbon-dioxide/