Photochemical CO2 hydrogenation to carbon nanotubes and H2O for oxygen recovery in space exploration

The primary source of oxygen in space exploration is derived from water electrolysis. Herein, we discovered a mild photochemical hydrogenation process that can convert CO2 into carbon nanotubes (CNTs) and H2O by using a Co-based catalyst. Hence, astronauts can extract oxygen from CO2 metabolism to close the oxygen recycling loop (overall reaction: CO2- C + O2), allowing for '100% theoretical oxygen recovery. This photochemical technique has enabled a high turnover number (the molar ratio of C to Co) of 240 for CNT formation during a 100 h reaction in a flow reactor. The oxygen recovery efficiency reaches approximately 68% when using flowing CO2 and H2, surpassing the theoretical maximum (50%) for the Sabatier reaction combined with water electrolysis at the International Space Station. The tip-growth mode of CNTs principally allows long-term oxygen recovery from CO2, in addition to space manufacturing of CNTs.