The artificial carbon cycle, inspired by Earth’s natural process, presents a solution to supplying resources for space missions. Artificial photosynthesis through photocatalytic CO2 conversion is a promising approach, but efficiency improvements are needed.
Currently, space missions mainly rely on the transportation of basic needs from the Earth. This is extremely challenging and logistically impossible when we aim to develop stations or habitats on extraterrestrial sites such as the Moon and Mars.
For example, an astronaut needs almost a kilogram of oxygen per day to sustain their life. Therefore, tons of oxygen have to be transported to build a station at extraterrestrial sites every year, raising the cost and risk of the mission.
It is expected such a situation can be changed by building the artificial carbon cycle on the extraterrestrial sites. On Earth, the carbon cycle allows the carbon atoms to move from the atmosphere (presenting in gaseous carbon compounds such as CO2 and CH4) to Earth (presenting in the form of sugar, starch, etc.), and finally back to the atmosphere to close the loop.
The energy input of such a biogeochemical cycle is provided by solar energy, where plants or other organisms absorb the solar energy to convert CO2 and H2O into carbon-based compounds and oxygen via photosynthesis.
Given that the currently targeted extraterrestrial sites (i.e., Moon and Mars) own abundant sunlight irradiation and have shown abundant CO2 and H2O reserves, such a photosynthesis strategy can be adopted to build up artificial carbon cycle system at extraterrestrial sites for providing sufficient propellants and life supports for space missions.
Artificial Photosynthesis: A Sustainable Solution
Given this background, artificial photosynthesis through photocatalytic CO2 conversion holds great promise to achieve a sustainable cycle. Specifically, such a strategy can imitate the role of green plants’ photosynthesis and is expected to reconstruct the carbon cycle in nature on Earth, which is currently interrupted due to excess CO2 emission.
This artificial photosynthesis strategy, if it is successfully implemented at extraterrestrial sites as a part of ISRU, can also allow the artificial carbon cycle to be built at the extraterrestrial sites. Up to today, various products have been successfully produced through photocatalytic CO2 conversions, such as CO, CH4, CH3OH, and HCHO.
Nevertheless, the photocatalytic CO2 conversion efficiency remains dissatisfying to meet the practical applications. Thus, the development of photocatalytic CO2 conversion with excellent photoconversion efficiency and product selectivity is highly sought for its applications not only on the Earth but also on extraterrestrial sites.
Research Perspectives on Extraterrestrial Photocatalysis
Recently, a research team lead by Prof. Yujie Xiong from University of Science and Technology of China write a Comment on extraterrestrial photocatalytic CO2 conversion to provide brief and clear guidelines for the development of photocatalytic CO2 conversion and its application beyond the Earth. They first outline the fundamental and general principles of photocatalytic CO2 conversion.
Then, they summarize the problems that can be encountered by photocatalysis during its implementation at extraterrestrial sites. Finally, perspectives on the development in this field are provided.
The results were published in the Chinese Journal of Catalysis.
Reference: “Photocatalytic CO2 conversion: Beyond the earth” by Jingxiang Low, Chao Zhang, Ferdi Karadas and Yujie Xiong, 10 August 2023, Chinese Journal of Catalysis.