Nitrogen constitutes 78% of the air around us, and is a naturally-abundant raw material that can be used to produce ammonia for fuels and fertilizers. One of the great inventions of 20th century chemistry was the Haber-Bosch process for “nitrogen fixation”, or the conversion of nitrogen to ammonia. The Haber-Bosch process is responsible for about half of the nitrogen found in human bodies today, but because it is performed at very high temperatures and pressures, it consumes as much as 2% of the world's total energy output.
The research group of Ling Xing Yi has developed a novel method for efficiently performing nitrogen fixation without the extreme conditions of the Haber-Bosch process. Their method is to combine a nitrogen-fixing catalyst with a nanostructure known as a Metal-Organic Framework (MOF). By regulating the access of nitrogen and water molecules to the catalyst surface, the MOF allows the nitrogen-to-ammonia conversion to occur with over 18 times the efficiency of conventional electrochemical methods, at room temperature and atmospheric pressure.
Schematic of the nitrogen fixing (reducing) system. Credit: Lee Hiang Kwee, Ling Xing Yi, et al.
In the future, this method may be used to directly harvest chemical fuels, or other ammonia-based commodity chemicals, directly from the atmosphere. If successful, such developments could revolutionize current industrial chemical manufacturing methods, which are often unsustainable and polluting. Professor Ling and her collaborators speculate that the method could even be used to extract greenhouse gases from the atmosphere, in order to mitigate global climate change.
This work was published in the journal Science Advances in March 2018.
H. K. Lee, C. S. L. Koh, Y. H. Lee, C. Liu, I. Y. Phang, X. Han, C.-K. Tsung, and X. Y. Ling, Favoring the unfavored: Selective electrochemical nitrogen fixation using a reticular chemistry approach, Science Advances 4, eaar3208 (2018).