Making rocket fuel out of Mars' thin air: New breakthrough could make it happen

Astronauts could travel back to Earth from Mars using rocket fuel converted directly from the carbon dioxide in the Red Planet's atmosphere, using a technique known as electrochemical reduction, a recent study reports.

It's an old method involving electrolysis, which is the application of an electrical current to drive a chemical reaction, but the new trick produces methane pure enough to be used as liquid propellant. (A number of rocket engines these days burn liquid oxygen and liquid methane — including the Raptors that power Starship , the rocket SpaceX is developing to help humanity get to Mars.) "The work we're doing is basically taking CO2 and using electricity to convert it into carbon-containing fuels and chemicals," said Carter Racine in a statement .

Racine is a Ph.D. student in mechanical engineering at Texas A&M University and a member of the study team, which was led by University of Mississippi chemical engineer Ahmed Badreldin.

"You can't bring up everything you need [on Mars] from Earth , because every additional kilogram adds enormous cost and complexity to launch and escape Earth's gravity," added Badreldin.

"So the question becomes, How do we make the fuels and chemicals needed for space exploration from the resources already available at the destination ?" One answer is electrochemical reduction, which takes place in an electrolyzer, with electrons flowing from the negatively charged anode to the positively charged cathode.

Water at the anode is oxidized, meaning it loses an electron, which is transferred to the carbon dioxide at the cathode, where one of its atoms gains an electron and becomes what chemists refer to as "reduced" (meaning its oxidation state is lowered).

It can then react with the hydrogen and oxygen atoms that have split from the oxidized water molecules.

The anode contains a catalyst, and the choice of material for the catalyst dictates what carbon-based compounds are produced when the reduced carbon reacts with the hydrogen and oxygen.

For example, a gold catalyst leads to the production of carbon monoxide (CO), while copper produces more complex compounds including alcohols, ethanol and methane (CH4).

What makes the work of Badreldin's team stand apart from previous experiments is that they have developed a nanometer-scale copper catalyst doped in nitrogen that is able to produce nearly pure methane.

Electrochemical reduction of carbon dioxide has been used to produce methane before, in applications on Earth.

The problem is, those methods have produced a lot of byproducts alongside methane.

On Earth we have complex equipment that separates the methane from the other unwanted compounds, but astronauts are not going to be able to take such unwieldy devices to Mars when every kilogram counts.