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ISRU Oxygen Production

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Developing a technique that requires little energy and uses only on site resources is paramount for permanent extraterrestrial colonization. The Martian atmosphere is about 95.72% carbon dioxide, which can be used to create oxygen directly through solid electolysis or by creating water by adding hydrogen and then subjecting the water to electrolysis.

NASA's ISRU O2 production experiments: http://potentiatenebrasrepellendi.blogspot.com/2008/11/nasa-tests-lunar-rovers-and-oxygen.html

Sabatier and RWGS reactions

When hydrogen and carbon dioxide are available, carbon dioxide can be reduced by a number of reactions including the sabatier reaction or the reverse water gas shift(RWGS) reaction:

Sabatier reaction: CO2 + 4H2 ↔ CH4 + 2H20

RWGS reaction: CO2 + H2 ↔ CO + H20

Note that methane mixed with oxygen is a suitable rocket fuel. Once water has been obtained from one of these reactions, or is obtained from another Martian source of water such as melted permafrost or water vapor, oxygen suitable for life support or fuel can be created through the electrolysis of water:

Electrolysis of water: 2H2O ↔ 2H2 + O2

Note that only about half of the original hydrogen is released for being recycled after this stage. One of the major advantages to this approach is that it can be theoretically exothermic overall. Heat from the sabatier reaction can be used for the endothermic RWGS reaction and water electrolysis.

Direct Electrolysis of Carbon Dioxide

Through direct electrolysis of carbon dioxide carbon monoxide and usable oxygen can be obtained without hydrogen:

2CO2 ↔ 2CO + O2

This process generally consists of carbon dioxide accepting electrons from an external source and undergoing a reduction reaction to create carbon monoxide and oxide ions at a cathode. The oxide ions then pass through an electrolyte with a low voltage (usually just ~1V-3V generated from a DC power supply) applied and undergo an oxidation reaction at the anode, forming molecular oxygen and releasing two electrons to be recycled. This process can be very energy consuming, as most electrolytes require about 600-1000 degrees celsius to operate Zirconia is the most tested electrolyte for this process, however ceria and other alternative electrolytes show promise as more efficient and reliable systems. Efficiency and decreased operating temperatures can also be achieved by creating higher ionic conductivity electrolytes with dopants of various polarity and atomic radii.

This process is housed in a ceramic oxygen generator cell, the efficiency of which decreases over time. A plan for building a ceramic oxygen generator cell is not readily available for free, and should be developed for testing purposes. Eventually a permanent colony would need to build on site ceramic oxygen generators to support an increasing population.