Adventure novels show that one of the most common ways to die of thirst is to become a castaway and lose yourself in an ocean of … salt water. On Mars, this situation would be no different. Aside from the frigid temperatures or scorching radiation, future explorers will have to deal with the high concentration of salt accumulated in Martian water.
This is essential, when water is not only needed for drinking, but also for get oxygen (O2), with which to breathe, and molecular hydrogen (H2), to be used as rocket fuel. These ambitious goals are made possible by means of electrolysis, which, as its name suggests, applies electricity to break up or lyse water (H2O) molecules. The problem is that normally the salt prevents the electrolyzers from working.
Hence, a team of scientists from the McKelvey School of Engineering, University of Washington, in St. Louis, United States, has taken pains precisely to develop a system to carry out electrolysis with brackish or salty water. As if that weren’t enough, its operation has been tested at typically Martian temperatures of -36ºC. Their advances have been published this week in the scientific journal « Proceedings of the National Academy of Sciences» (PNAS).
“Our Martian brine electrolyzer radically changes the logistics calculations for missions to Mars and beyond,” he explained in a statement. Vijay Ramani, director of the investigation. ‘Furthermore, this technology is equally useful on Earth, where makes the oceans a viable source of oxygen and fuel».
For more than a decade, the presence of underground pools of liquid water has been detected on Mars, despite the low temperatures, thanks to the presence of high concentrations of magnesium perchlorate salts.
The need to produce resources on Mars
Given the enormous average distance that Mars is from Earth (about 600 times more than the average distance between the Moon and Earth), future missions happen because explorers have the ability to obtain at least a part of their own resources in situ.
For this reason, the “Perserverance” rover, which will land on Mars in February, carries instruments to test a way of obtaining oxygen: It is the “Mars Oxygen In-Situ Resource Utilization Experiment” (MOXIE), a system capable of produce oxygen from CO2 in the atmosphere of the red planet.
On this occasion, the system developed by Ramani and company is capable of producing 25 times more oxygen than MOXIE, using the same energy, and on top of producing hydrogen, which can be used as rocket fuel.
The secret: at the anode and at the cathode
The secret of the “recipe” of the new system is in use two novel materials to achieve a cathode and an anode that can work at such low temperatures, without the need to heat the water, and with concentrations as high as those on Mars: these materials are ruthenate pyrochlorine, at the anode, and platinum or carbon, on the cathode.
In fact, their performance allows the salts to be advantageous for this system, because they prevent the water from freezing and because they reduce the electrical resistance.
Having found an electrolyzer that works with cold and impure water, which does not have to be deionized, can also be very advantageous on Earth. «We intend (…) to use salty or brackish water to produce hydrogen and oxygen, through the electrolysis of seawater», Has commented Pralay Gayen, first author of the study. This would be ideal for example for submarines, which could obtain their oxygen from the surrounding sea water.