Good question! Oxygen is produced and extracted in a wide range of ways depending on whether the goal is **industrial-scale oxygen (tons per day)**, **medical oxygen (high purity, moderate scale)**, or **experimental oxygen (like from water, plants, or even extraterrestrial regolith)**.
Here are the **20 most common methods of extracting oxygen**, grouped by type:
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### **A. Industrial / Large-Scale Production**
1. **Cryogenic Distillation (Fractional Distillation of Air)** – Cooling air until it liquefies, then separating oxygen, nitrogen, and argon by their different boiling points.
2. **Vacuum Swing Adsorption (VSA)** – Uses pressure and vacuum cycles with adsorbents like zeolites to selectively capture nitrogen, leaving concentrated oxygen.
3. **Pressure Swing Adsorption (PSA)** – Similar to VSA, but uses alternating pressure cycles instead of vacuum. Common for hospitals.
4. **Membrane Separation** – Special polymer membranes allow faster diffusion of oxygen compared to nitrogen, enriching oxygen streams.
5. **Chemical Oxygen Generators (Chlorate Candles, Superoxides)** – Heat-triggered compounds (like sodium chlorate or potassium superoxide) release oxygen; used in submarines, planes, and space.
6. **Electrochemical Oxygen Generation (Solid Oxide Electrolysis Cells)** – Splits oxygen ions from air using ceramic electrolytes at high temperatures.
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### **B. From Water (Electrolysis & Beyond)**
7. **Water Electrolysis (Alkaline)** – Passing current through water with an alkaline electrolyte (KOH/NaOH) to release hydrogen and oxygen.
8. **Proton Exchange Membrane (PEM) Electrolysis** – More efficient modern electrolysis using polymer membranes, widely researched for hydrogen fuel + oxygen production.
9. **High-Temperature Steam Electrolysis (SOEC)** – Uses solid-oxide cells and heat to split water more efficiently.
10. **Photocatalytic Water Splitting** – Using sunlight and catalysts (like TiO₂) to generate oxygen from water (research stage, artificial photosynthesis).
11. **Photoelectrochemical Cells (PEC)** – Semiconductor panels split water directly using sunlight.
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### **C. From Solid Materials (Thermochemical / Chemical Methods)**
12. **Metal Oxide Cycle (Thermochemical Splitting)** – Alternating heating and cooling of metal oxides (like cerium oxide) to release oxygen in solar furnaces.
13. **Decomposition of Hydrogen Peroxide (H₂O₂)** – Catalytic breakdown yields oxygen and water; used in rockets, disinfectants, submarines.
14. **Barium Peroxide Thermal Decomposition** – Historical method (19th century) before cryogenics took over.
15. **Magnesium Perchlorate, Lithium Peroxide & Other Peroxides** – Used in rebreathers and spacecraft, they chemically absorb CO₂ and release O₂.
16. **Electrolysis of Molten Salts (e.g., Molten Carbonates)** – Produces oxygen from oxygen-bearing salts.
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### **D. Biological & Novel Methods**
17. **Photosynthesis (Plants, Algae, Cyanobacteria)** – The original and ongoing oxygen generator on Earth.
18. **Algal Bioreactors** – Engineered systems for oxygen + biomass production (space habitats, submarines).
19. **Biosynthetic / Enzyme-Based Oxygen Release** – Enzymes or engineered microbes designed to split water or peroxides.
20. **Extraterrestrial Regolith Electrolysis (e.g., MOXIE on Mars)** – Extracting oxygen from metal oxides in lunar/Martian soil using high-temperature electrolysis.
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✅ **Most common in industry today:** Cryogenic distillation, PSA/VSA, and electrolysis.
✅ **Most common in emergencies/closed systems (submarines, spacecraft):** Chemical oxygen generators and peroxides.
✅ **Most common in nature:** Photosynthesis.
Would you like me to **rank these 20 by how much oxygen they actually supply globally** (from largest industrial contribution down to experimental/niche methods)? That might give you a better sense of scale.
