Can we make enough breathable air in our future MARS colony? - Colonization of MARS Series

This is the start of a scientifically backed series, in which I will combine basic science everyone should learn with data extracted from the main science articles on the matter, trying to assemble a Mars Colonization Handbook that should be easy for everyone to read. And stir your curiosity about the mysteries of science and space.
I know everyone on Steemit loves series for the wrong reasons, but I am a huge space geek and will actually try to gather a massive amount of information into something that would take me a couple of weeks/months to fully document and format.

Source: SpaceX webcast, CC0 license.

The Martian atmosphere is 100 times less dense than Earth's, with 96% of it being Carbon Dioxide (CO₂), 1.93% being Argon (Ar), 1.89% being Nitrogen (N₂) and 0.145 Oxygen (0₂)and less than 0.01% Carbon Monoxide (CO)

Earth - Mars atmospherical composition comparison:

Source: NASA

How much Oxygen does a human consume per hour?

If a person breathes in 12 breathes per minute about 7-8 liters and air on Earth has about 20% oxygen and by the time you exhale, its saturation drops to 15%, it means that the body managed to extract those 5%. This is close to 550 liters per day (140 gallons), 23 liters (6 gallons) per hour, and 0.382 liters or 0.1 gallons per minute.

Keeping in mind that air is light, more specifically 1000 liters ( 264 gallons) would weigh 1.25kg (2.75 pounds), so the weight of the air needed for a person daily is close to 687 grams (1.5 pounds).

Knowing that we can easily realize that it is impossible to bring the air to the colony from Earth and that we should focus on producing it locally. But is it possible?

We have already done it, on the International Space Station

Before 2007, the International Space Station could house a maximum of three crew members at a time due to oxygen limitation and scrubbing capabilities of the orbited modules. But in 2007 a new experimental scrubber, called the Oxygen Generation System (OGS) was introduced in order to double the operational crew and increase the amount of scientific operations performed. The system works by collecting water from waste ( condensation - be it from sweat, humidity in the air exhaled, or from the equipment, wastewater and even urine) and converting it through a process called electrolysis, into hydrogen (H₂). This module is called ECLSS and it was delivered in the Destiny Module,with a similar equipment being located in the Zvezda module, called Elektron.

What is electrolysis?

The process of using a direct electric current (DC) to drive an otherwise unlikely and unspontaneous chemical reaction. It can separate elements and the power input needed for electrolysis is called the decomposition potential.

For the ones interested in bettering themselves let's go deeper:

The process of electrolysis

By using the direct electric current, we can achieve expulsion or attraction of said electrons from the external circuit, basically achieving an interchange of atoms and ions. The products of the said reaction are often found in different physical states from the electrolyte and can be extracted though various processes as output. Two electrodes, named Anode and Cathode are separated by an electrolyte ( in our case a special polymer membrane or PEM).

Source: energy.gov

• A reduction reaction occurs at the cathode, releasing electrons (e^-)
• Electrons combine with the water(H₂O)
• Hydrogen gas (H₂) and hyroxide ions (OH^-): 2H₂O (l) + 2e^- -> H₂ (g) + 2 OH^- (ag).
• Oxidation occurs at the anode, with the electrons moving from the water into the anode.
• Oxiygen gas is released (O₂ and hydrogen ions (H⁺): 2H₂O (l) -> O₂ (g) + 4e^- + 4H⁺

Our fellow Steemian and SteemSTEM poster, @ideas-abstractas has written an in depth article just about electrolysis in general, and @thescienceguy has an article about Faraday's Laws of Electrolysis ( Faraday is the inventor of electrolysis) if you want to learn even more about it and don't want to leave the Steem platform.

The Mars Oxygen ISRU Experiment (MOXIE) aboard the Mars Rover 2020

Mars Rover 2020 is the upcoming NASA's Mars rover mission. Set to launch in 2020 it is focused on finding ancient life on Mars, but the most important is the fact that it will carry a tiny experiment called MOXIE.

This is a small electrolysis equipment, at 1% of the real scale at which could be implemented to sustain a Mars colony.
MOXIE - Mars Oxygen In situ resource utilization Experiment - will produce as estimated of 22 grams of oxygen per hour using a complex electrolysis system. We can already see that this 1% scale model can almost produce enough for a single person, despite its small size (smaller than most computer cases).The full scale will most probably require either an isotopic generator or an extended solar panel field, with a backup isotopic generator due to the fact that sand storms take months to clear because of the thin atmosphere and low gravity.

Source: Wikimedia commons.

MOXIE is a solid oxide electrolysis cell which means that under very high temperatures, ceramic oxides like yttria-stabilized zirconia (YSZ) and doped ceria can undergo a transformation into oxide ion conductors (O^2-).Porous electrodes and a nonporous electrolyte are used to generate oxygen from CO₂ permeating the cathodes and touching the electrode-electrolyte limit.

Source: Moxie Abstract, NASA, aug 2017.

By electrocatalysis and thermal dissociation, an oxygen atom is released from the CO₂ molecule and picks electrons from the cathode to become an oxide ion (O^2-) which is then transported to the anode by the DC applied on the external circuit.
The charge is transferred to the anode and though recombination is merged with another oxygen atom, forming O₂ and diffuses out, thus completing the reaction:

2CO₂ -> 2CO + O₂

Another outstanding benefit of this procedure is that a steady source of oxygen is also needed for various propulsion systems. It is used as an oxidant for the Mars ascent and the subsequent return to Earth. Regardless of the method used, even the revolutionary CH₄/O₂ propulsion system, needs about 78% of its fuel mass to be the oxidizer, or close to 30 metric tons. If we would use the oxygen from Mars it would save the equivalent of 400 metric tons of Earth Launched Oxidizer for each launch, or about 5 heavy lift launches in our current rockets to land a rocket and bring it back home with cargo.

As for energy usage, according to their own documents, MOXIE needs 108W to produce 22g/hr O₂. Another 40W to compesate for heat loss and 20W for preheating. Total energy use is 170W. This means that even the full scale model will be feasible even under the 17 kw for 100 people by using multiple stacked cells for even more efficiency:

The SOXE architecture is a stack of cells, arranged vertically like a multi-story building. The two MOXIE stacks each utilize 11 cells. An assembly of 100 stacks, each containing 20 MOXIE-sized cells, would produce >2 kg/hr of O2 with an energy investment of ~12 kW.

Taking into account the reduced pressure of Mars, another air compressor would be necessary to supply the 0.14 cubic meters per second at 7mbars. They are confident that using a three stage centrifugal compressor and another scrolling compressor could supply the needed volume at only a 38 kg additional mass and under 1.1 kW of power.

But there's more to be discovered in terms of oxygen generation

Another way to create oxygen on Mars is being developed thought the use of plasma. This is a very new study so for now it's theoretical, but its suggestion is that Mars with its high concentration of carbon dioxide is ideal for the experiment. Using a process knows as decomposition, the study, made by the universities of Porto and Lison and with the help of the Polytechnic University in Paris, shows that production of non-thermal plasma could efficiently produce oxygen.

The oxygen is generated by decomposition of CO₂ by direct electron impact, by transferring their energy into vibrational excitation. This splits up the original CO₂ into oxygen and carbon monoxide. This appears to be a very efficient method as the power required to do the split would be equivalent or even lower to the alternatives.

The cold atmosphere (210 degrees Kelvin) is an appropriate environment to induce a stronger vibrational effect than what could be simulated on Earth and the very low temperature also can slow the reaction thus giving more time for the molecule separation. The study author, Dr. Vasco Guerra said:

"The low temperature plasma decomposition method offers a twofold solution for a manned mission to Mars. Not only would it provide a stable, reliable supply of oxygen, but as source of fuel as well, as carbon monoxide has been proposed as to be used as a propellant mixture in rocket vehicles."

In the same article the solid oxide electroliser cells and the plasma dissociation methods are being compared, with the plasma being highlighted as being superior to MOXIE, although the MOXIE numbers being quoted in this comparison are greatly diminished purportedly because of its lower actual Martian efficiency.

Still this could prove a very reliable method of oxygen producing and with further scientific debate it might even be polished sufficiently as to take the lead.

Farming could also help

Either through the use of hydroponics, the growth of plants without soil or by traditional farming in a temperature and pressure controlled environment, plants can supply small quantities of oxygen, although in the beginning of the colony it would be too resource intensive to worth taking into account just for oxygen production, but later, when the main bottleneck will be food production, the thought of using the cultures as a real means for oxygen supply in the colony will be taken into consideration. Perhaps through the use of GMO, plants could be designed to absorb or convert even greater amounts of gasses.

Terraforming in the long run

Some other preliminary studies cover the introduction of certain bacteria and algae, that could survive in the current Martian environment and if spread in a sufficiently big enough area could thrive and contribute to the gradual martian atmospherical composition change. However this is not allowed yet, under the Planetary Protection act. This is in place due to the fact that Mars has a high probability of hosting life which could be endangered by introducing new forms of life.

Further sources or related in depth information: The plasma in situ study, Moxie for Scientists, NASA's Math and Science @ work, Energy.gov fuelcell electrolysis, ISS ECLSS

Conclusion

We already have good technology in development and upcoming technology could improve our chances of producing greater quantities of oxygen in situ (on the surface of Mars). The energy needed to power these systems is reasonable and could be sent from Earth (photo-voltaic cells or ready-made solar panels and an isotope reactor for backup).

I have devoted a lot of time into structuring and documenting my articles so I could guarantee a fun and easy read. Also don't be shy to share the love of science with others, we still have a long way to go and we need future space engineers :)