Oxygen Track: Electrolysis, Gases and Pressure Systems · Module 1 of 4 · about 15 min
Splitting water and CO2
Electrolysis uses electricity to split water into hydrogen and oxygen: two molecules of water make two of hydrogen and one of oxygen. By mass, making 1 kilogram of hydrogen uses about 9 kilograms of water and gives off about 8 kilograms of oxygen. Most plants today are built to sell the hydrogen, and the oxygen is a byproduct.
DOE describes three main electrolyzer types. Alkaline electrolyzers are the older, proven design using a liquid alkaline electrolyte. Proton exchange membrane (PEM) electrolyzers use a solid polymer membrane, respond quickly to changing power and suit pairing with solar and wind. Solid oxide electrolyzers run hot, around 700 to 800 °C or more, and can use heat to cut the electricity needed.
Solid oxide technology already ran on Mars. NASA's MOXIE instrument on the Perseverance rover pulled oxygen out of the carbon dioxide atmosphere 16 times between 2021 and 2023, making 122 grams in total and up to 12 grams an hour at 98 percent purity or better.
For an operator, the job is mostly watching stacks: voltage, current, temperature, water quality and gas purity. Feed water has to be very pure, because contaminants damage membranes and electrodes.
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Module quiz
5 questions, 4 correct to pass. You'll see what you missed and why, and you can retake it.