The Oxygenator is a large piece of life support equipment that is found on the Hermes, as well on all Ares Missions Habs and allows people to breath.
The Oxygenator uses heat and pressure to loosen the bonds between Oxygen and Carbon in Carbon Dioxide, and then uses electrolysis to break the bonds between Oxygen and the Carbon atoms. The Oxygenator then moves the Oxygen into a chamber, where it is then recombined into O2, or breathable Oxygen. The breathable Oxygen is then directed to the Atmospheric regulator's storage tanks for later use.