Oxygen for Mars

Leafy plants are masters of the art of carbon neutrality: during photosynthesis, they convert CO₂ into oxygen and glucose. Hydrogen atoms play an important role as "mediators." However, the process is not particularly efficient. In addition, the oxygen produced does not come from the CO₂ but from the absorbed water. True splitting of CO₂ is not taking place in plants and also could not be achieved at moderate temperatures by technical means so far.

Ping He, Haoshen Zhou, and their team at Nanjing University, in collaboration with researcher from Fudan University (Shanghai) have now achieved their goal to directly split CO₂ into elemental carbon and oxygen. Instead of hydrogen, the "mediator" in their method is lithium. The team developed an electrochemical device consisting of a gas cathode with a nanoscale cocatalyst made of ruthenium and cobalt (RuCo) as well as a metallic lithium anode. CO₂ is fed into the cathode and undergoes a two-step electrochemical reduction with lithium. Initially, lithium carbonate Li₂CO₃ is formed, which reacts further to produce lithium oxide Li₂O and elemental carbon. In an electrocatalytic oxidation process, the Li₂O is then converted to lithium ions and oxygen gas O₂. Use of an optimized RuCo catalyst allows for a very high yield of O₂, over 98.6 %, significantly exceeding the efficiency of natural photosynthesis. As well as pure CO₂, successful tests were also carried out with mixed gases containing varying fractions of CO₂, including simulated flue gas, a CO₂/O₂ mixture, and simulated Mars gas. The atmosphere on Mars consists primarily of CO₂, though the pressure is less than 1 % of the pressure of Earth's atmosphere. The simulated Mars atmosphere thus contained a mixture of argon and 1 % CO₂.

If the required power comes from renewable energy, this method paves the way toward carbon neutrality. At the same time, it is a practical, controllable method for the production of O₂ from CO₂ with broad application potential -- from the exploration of Mars and oxygen supply for spacesuits to underwater life support, breathing masks, indoor air purification, and industrial waste treatment.