In a discovery that may someday help astronauts on Mars, scientists have found a new way of making oxygen under Martian conditions – one that appears to be 25 times more efficient than that to be tested by NASA’s Perseverance rover, which is due to land on the Red Planet in February.
Not that this means there is anything wrong with the NASA process. “Both will be needed,” says Vijay Ramani, a chemical engineer at Washington University in St. Louis, US.
The NASA process, which will be tested in a shoebox-sized chemical plant called MOXIE (Mars Oxygen ISRU Experiment), uses electrical energy to split carbon dioxide into oxygen and carbon monoxide, both of which are useful: oxygen for life support, and carbon monoxide as a building block for rocket fuel for future astronauts’ return journeys from Mars.
Ramani’s new approach starts with water and uses electricity to break it into oxygen and hydrogen.
At heart, it is simply old-fashioned electrolysis of water: something generations of chemistry students have witnessed in classrooms worldwide. “If you use a cell like a battery, you can pass electricity through water, and split the water into hydrogen and oxygen,” Ramani says.
It hadn’t previously been considered for Mars because Mars is cold. “If you have pure water, it’s going to be frozen.” But Martian water may not be pure, because Martian soils are known to have a lot of perchlorate.
On Earth, perchlorate is an industrial chemical used in explosives, fireworks and road flares: not something you want in your water. On Mars, however, it can act as antifreeze, allowing water to remain liquid even at temperatures of minus 50 degrees Celsius, raising the prospect that Mars may have perchlorate brines close to its surface.
The trick to the new process, Ramani says, was trying to figure out how to do electrolysis of perchlorate-rich water, something that won’t work in conventional electrolysis because chemicals like perchlorate poison the cells and block their operation.
But, his team reports in a paper in the journal PNAS, this isn’t an insurmountable obstacle. By using cells with a mix of exotic compounds, including ruthenium, lead and platinum, they found they could not only cope with the problem, but do so with surprising efficiency.
That said, Ramani thinks his team’s process and the MOXIE process should be viewed as complementary, not competing.
MOXIE has the advantage that it can be used anywhere, since all that it requires is carbon dioxide from the Martian atmosphere – which, although thin, is 95% carbon dioxide. His team’s process needs perchlorate brine, which might not be as ubiquitous.
Also, the two processes produce different products.
Ramini’s produces hydrogen and oxygen. MOXIE’s produces oxygen and carbon, in the form of carbon monoxide. If you are looking for feedstocks for more complex chemical syntheses, you need all three elements.
Most likely, Ramani says, the first manned missions to Mars will draw on multiple technologies for generating oxygen to breathe and fabricating rocket fuel for the return, if for no other reason than that, that far from home, you don’t want to put all of your eggs in one technological basket.
At the same time, efficiency matters. The more breathing air you can get from any given solar panel, the fewer solar panels you have to carry with you, and the easier it is to go to Mars for anything other than a quick touchdown and return.