How can respiratory oxygen and fuel for the return be produced during manned Mars missions? For this purpose, the Mars visitors could use the extremely salty water of the planet, report researchers: They have developed an electrolysis system that can generate oxygen and hydrogen from the Martian water despite its high content of magnesium perchlorate. The scientists say the system could also be used on earth to extract these substances directly from salt water.
Many will probably remember the process from experiments in school lessons: With the so-called electrolysis, certain substances can be broken down into their building blocks with the help of electricity. In this way, water can also be separated into its components hydrogen and oxygen. These gases can then be collected for use. The oxygen can then serve as breathing gas and the H2 as fuel. In theory at least, it is clear that the process cannot only be used on earth – electrolysis could also produce the coveted substances from water on other celestial bodies. This appears particularly interesting in the case of the next big goal of manned space travel: NASA plans to bring the first humans to Mars by 2033.
Various studies have already shown that there are usable water resources in the form of ice on Mars. There could even be reservoirs underground that remain fluid despite the low temperatures on our neighboring planet. The reason for this are very high levels of magnesium perchlorate, which is abundant in the Martian soil. Similar to the road salt on earth’s roads, this salt can greatly lower the freezing point of the brine on Mars. However, this is problematic when it comes to using it as a starting material for electrolysis. Because the conventional processes require pure water.
Martian water is problematic
The Martian water would therefore have to be desalinated first. However, under the difficult and frosty conditions on Mars, this would involve considerable effort. This possibility has not yet been explored. The rover “Perseverance”, which NASA sent on its way to Mars in July 2020, is only equipped with instruments that are supposed to enable the use of atmospheric carbon dioxide by electrolysis. The Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE) can therefore only produce oxygen and not hydrogen. But as it now turns out, there could soon be a practicable way of producing both on Mars.
As the researchers working with Vijay Ramani from Washington University in St. Louis report, they have succeeded in developing an electrolysis system that can also obtain oxygen and hydrogen directly from salt water. The key lies in the materials of the anode connected to the positive pole and the cathode connected to the negative pole. The researchers found a composition that enables it to function even with high salt contents. “Our innovative brine electrolysis system contains a lead ruthenate pyrochlore anode developed by our team in conjunction with a platinum cathode on carbon,” says Ramani. The oxygen development is catalyzed at the anode, and the hydrogen development at the cathode, the scientists explain.
Allows direct salt water electrolysis
The researchers were able to show through experiments that the brine electrolysis system also works under simulated Mars conditions without the water source being treated and without heating. “The perchlorate dissolved in the water is even helpful: It prevents the water from freezing and also improves the performance of the electrolysis system by lowering the electrical resistance,” says co-author Shrihari Sankarasubramanian. It turned out that the concept can produce 25 times more oxygen with the same amount of energy than the MOXIE system of the Perseverance rover, which extracts the gas from carbon dioxide. But above all, brine electrolysis also produces hydrogen at the same time, which can be used as fuel. “Our system could radically change the logistical planning of missions to Mars and beyond,” says Ramani.
The researchers are not only looking at the sky, however: “This technology could also prove useful on earth, where it could open up seawater as a source of oxygen and fuel,” says Ramani. His colleague Pralay Gayen continues: “After we have demonstrated the potential of the concept under Martian conditions, we intend to explore it for terrestrial applications. Brackish or salt water, for example, can be used directly, ”says the researcher. Specifically, the system, for which a patent has now been applied, could supply submarines with oxygen when exploring the deep sea, say the scientists.
Source: Washington University in St. Louis, Article: PNAS, doi: 10.1073 / pnas.2008613117