Enlarge /. The Pathfinder Rover took this photo. It didn't need oxygen, unlike the weak, fleshy people who want to follow its path.
If humans ever want to visit Mars, they may have to devote some vital resources to survive long enough to explore and replenish the long journey home. Although the days of flowing surface water are long gone, the red planet is not entirely without the raw materials to do this job.
The Mars 2020 mission, launched in July, is conducting an experiment with precisely this aim. MOXIE – Mars' Oxygen In Situ Resource Use Experiment – is a box not much bigger than a toaster that creates oxygen from atmospheric CO2. While a much larger version would be required to make liquid oxygen for a rocket, MOXIE is sized to produce roughly the amount of oxygen an active person needs to breathe.
A new study by Pralay Gayen at Washington University in St. Louis, Missouri, is testing a device that could tap into another resource – perchloratesole, which is believed to be present in some locations on Martian soil. The device can split the water in this brine and produce pure oxygen and hydrogen in the process.
Perchlorate salts (ClO4) are widespread on Mars. These salts have an affinity for water molecules and, over time, can collect water vapor, which turns into a salt solution with a very low freezing temperature. There is evidence of significant amounts of this brine under the surface of the North Pole region of Mars, and smaller amounts have been cited as a possible explanation for the active streaks that sometimes appear on Mars slopes.
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To test whether we could use this resource, the researchers built an electrolysis device that they operated under Mars-like conditions. It uses a standard platinum-carbon cathode and a special lead-ruthenium-oxygen anode that the researchers previously developed. They mixed a plausible concentration of magnesium perchlorate brine and filled the headspace in that container with pure CO2 for a Mars-like atmosphere. The whole was held at -36 ° C (-33 ° F). When switched on, saline solution flowed through the device and split into pure oxygen gas on the anode side and pure hydrogen gas on the cathode side.
The device worked quite well, producing about 25 times as much oxygen as its MOXIE counterpart. MOXIE requires approximately 300 watts of power to operate and this device corresponds to an oxygen output of approximately 12 watts. It also produces hydrogen that could be used in a fuel cell to generate electricity. And it would be smaller and lighter than MOXIE, say the researchers. Ultimately, this just shows that MOXIE is working with a lower quality resource – but more accessible – in atmospheric CO2 instead of water.
Obviously, such a device would have to go through long term stress tests to ensure that performance does not degrade over time and that it is generally robust. The membrane that separates the cathode and anode sides has been carefully operated, for example to prevent the CO2 from contaminating it. If your survival depends on a device you brought to Mars, malfunction is not an option.
PNAS, 2020. DOI: 10.1073 / pnas.2008613117 (About DOIs).
