Future Apollo missions mitigated the danger of fires by being really careful about the materials in use, but that's not a good answer for long term missions, particularly if the astronauts are going to conduct industrial activities such as in-situ resource utilization.
If you want to make breathing gas on Mars, O2 covers 20% of it, the rest of it is going to be an inert gas like Nitrogen, Argon, Helium or SF6.
Of course every method of producing O2 in space works by separating O from something else and the "something else" is likely to be useful, such as H2, C, Al, etc.
A major contributing factor to the Apollo 1 fire was they didn't merely have a pure oxygen atmosphere, but a pressurized pure oxygen atmosphere. Pressurized above 1 atmosphere, for testing purposes. In space they would have operated with a substantially lower pressure; I believe about 1/5th of atmospheric pressure. A low pressure pure oxygen environment is still a fire hazard relative to regular air with the same partial pressure of oxygen, but it's not nearly as dangerous as a pressurized oxygen atmosphere.
Sure, the breathing gas for a crewed mission or habitat would need to include an inert gas as well as oxygen. But oxygen is consumed during respiration and the inert gas isn't, so oxygen will be needed in much larger quantities, so in-situ production is a much more pressing problem.
You are probably recycling the CO2 from the astronauts breath which is easier than cracking it from the air. Also many practical breathing systems (especially for spacesuits) leak some of the inert gas for cooling and other purposes.
The real thing you’ll need O2 for is an oxidizer for fuel but of course you need to make fuel too.
If you are interested in making anything interesting such as large plastic sails or small biospheres nitrogen is the big missing piece of the puzzle right now in the moon, mars and asteroids.
CO2 needs to be scrubbed/vented out of the breathable atmosphere. Even if there is abundant of oxygen anyway, too much CO2 will make people feel dizzy and confused, cause splitting headaches, increased heart rated, reduced senses, and eventually death. CO2 can't take the place of inert nitrogen in a breathable atmosphere, that much CO2 in the air just isn't compatible with human life.
being extremely generous, and assuming he meant "martian atmosphere" when he said "air", it _might_ be a bit more challenging (depending on your process and what you've got available) to convert the CO2 at 0.095 PSI into O2, than it would be to pull the CO2 out of ~14.7 PSI human exhalations and convert it to O2.
seems like the kind of thing where there is a bunch of engineering that could be productively done.
Before we sent astronauts to the moon successfully we discovered the hard way that astronauts are likely to die if they breathe pure O2.
https://en.wikipedia.org/wiki/Apollo_1
Future Apollo missions mitigated the danger of fires by being really careful about the materials in use, but that's not a good answer for long term missions, particularly if the astronauts are going to conduct industrial activities such as in-situ resource utilization.
If you want to make breathing gas on Mars, O2 covers 20% of it, the rest of it is going to be an inert gas like Nitrogen, Argon, Helium or SF6.
Of course every method of producing O2 in space works by separating O from something else and the "something else" is likely to be useful, such as H2, C, Al, etc.