Oxygen Harvesting System

The active Martian water cycle, i.e., the presence of shallow water and soluble perchlorate salts in the Martian soil, enables the production of hydrogen fuel and life-support oxygen on Mars through electrolysis of perchlorate brines. A team of scientists at Washington University in St. Louis has demonstrated an approach to produce ultrapure hydrogen and oxygen from liquid Martian brines at minus 36 degrees Celsius (minus 32.8 degrees Fahrenheit).

This illustration shows Jezero Crater -- the landing site of NASA’s Mars 2020 Perseverance rover -- as it may have looked billions of years ago on Mars, when it was a lake. Image credit: NASA / JPL-Caltech.

This illustration shows Jezero Crater — the landing site of NASA’s Mars 2020 Perseverance rover — as it may have looked billions of years ago on Mars, when it was a lake. Image credit: NASA / JPL-Caltech.

“Our Martian brine electrolyzer radically changes the logistical calculus of missions to Mars and beyond,” said Professor Vijay Ramani, a researcher in the Center for Solar Energy and Energy Storage at Washington University in St. Louis.

“This technology is equally useful on Earth where it opens up the oceans as a viable oxygen and fuel source.”

NASA’s Perseverance rover is en route to Mars now, carrying instruments that will use high-temperature electrolysis.

However, the Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE) will be producing oxygen only, from the carbon dioxide in the air.

The electrolyzer developed by Professor Ramani and colleagues can produce 25 times more oxygen than MOXIE using the same amount of power. It also produces hydrogen, which could be used to fuel the astronauts’ trip home.

“Our novel brine electrolyzer incorporates a lead ruthenate pyrochlore anode developed by our team in conjunction with platinum on carbon cathode,” Professor Ramani said.

“These carefully designed components coupled with the optimal use of traditional electrochemical engineering principles has yielded this high performance.”

The careful design and unique anode allow the team’s electrolyzer to function without the need for heating or purifying the water source.

“Paradoxically, the dissolved perchlorate in the water, so-called impurities, actually help in an environment like that of Mars,” said Dr. Shrihari Sankarasubramanian, a researcher in the Center for Solar Energy and Energy Storage and the Department of Energy, Environmental and Chemical Engineering at Washington University in St. Louis.

“They prevent the water from freezing and also improve the performance of the electrolyzer system by lowering the electrical resistance.”

Typically, water electrolyzers use highly purified, deionized water, which adds to the cost of the system.

A system that can work with sub-optimal or salty water, such as the technology demonstrated by the team, can significantly enhance the economic value proposition of water electrolyzers everywhere — even right here on Earth.

“Having demonstrated these electrolyzers under demanding Martian conditions, we intend to also deploy them under much milder conditions on Earth to utilize brackish or salt water feeds to produce hydrogen and oxygen, for example, through seawater electrolysis,” said Dr. Pralay Gayen, a postdoctoral researcher in the Department of Energy, Environmental and Chemical Engineering at Washington University in St. Louis.

The team’s work was published in the Proceedings of the National Academy of Sciences.

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Pralay Gayen et al. Fuel and oxygen harvesting from Martian regolithic brine. PNAS, published online November 30, 2020; doi: 10.1073/pnas.2008613117

This article is based on a press-release provided by Washington University in St. Louis.

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