Researchers from the University of Tokyo were among the first to combine atmospheric nitrogen, water, and sunlight. They used two catalysts to create large amounts of ammonia at a low energy cost. Their processes mimic natural mechanisms observed in plants that rely on symbiotic bacteria. The study was published in the journal Nature Communications.
When the reaction takes place in optimal conditions, two nitrogen atoms and three water molecules form two ammonia molecules with only oxygen left over. Image Credit: 2025 Nishibayashi et al.
Ammonia is a chemical necessary for many industrial and agricultural processes, but the energy cost of producing it is extremely high. Numerous efforts are underway to increase the efficiency of ammonia production.
Ammonia is undoubtedly familiar to humans, particularly in agriculture, where it is a crucial part of fertilizers that nourish the crops that support all of existence. However, the following figures illustrate the significance and impact of ammonia: 80% of the annual production of ammonia, which is just under 200 million tons, is used as fertilizer.
Additionally, its production contributes about 2% of global energy consumption and, in turn, 2% of global carbon dioxide emissions. Given these considerations, it makes sense that scientists are working to develop a more effective and cleaner method of producing ammonia.
Professor Yoshiaki Nishibayashi and his colleagues at the University of Tokyo's Department of Applied Chemistry have recently made notable progress in pursuit of this objective. They successfully created a brand-new catalytic system that can produce ammonia from common Earthly molecules like water and atmospheric nitrogen.
The secret is a combination of two types of catalysts. Catalysts are intermediate compounds driven by sunlight that enable or speed up reactions without adding to the final mixture. They are specifically designed for the production of ammonia.
This is the first successful example of photocatalytic ammonia production using atmospheric dinitrogen as a nitrogen source and water as a proton source, that also uses visible light energy and two kinds of molecular catalysts. We used an iridium photocatalyst and another chemical called a tertiary phosphine, which enabled photochemical activation of water molecules. The reaction efficiencies were higher than expected, compared to previous reports of visible light-driven photocatalytic ammonia formation.
Yoshiaki Nishibayashi, Professor, University of Tokyo
The problem with chemical reactions is that they do not always proceed as quickly or in the manner we would like. Humans must include more than just the raw ingredients to control a process's outcome, efficiency, timing, and other aspects.
Nishibayashi and his group used two catalysts for these experiments: one based on the transition metal molybdenum to activate dinitrogen, and another based on the transition metal iridium to photoactivate water and tertiary phosphines. Tertiary phosphines, a third component, are also essential for assisting in removing protons from water molecules.
When the iridium photocatalyst absorbs sunlight, its excited state can oxidize the tertiary phosphines. The oxidized tertiary phosphines then activate water molecules via the formation of a chemical bond between the phosphine’s phosphorus atom and the water, yielding protons. The molybdenum catalyst then enables nitrogen to bond with these protons to become ammonia. The use of water for producing dihydrogen or hydrogen atoms is one of the most important processes for achieving green ammonia production.
Yoshiaki Nishibayashi, Professor, University of Tokyo
Although certain problems remain that could further enhance the safety and efficacy, the team's ability to generate this reaction at a scale ten times larger than that of earlier experiments suggests it is prepared for larger-scale trials.
Specific components, like the tertiary phosphines, could be recycled from phosphine oxides or produced with solar energy. Even though they are stable in and of themselves, they could be poisonous if consumed by humans, so it would be best to recycle or dispose of them responsibly.
In plants, ammonia is formed by biological nitrogen fixation using cyanobacteria and is linked with photosynthesis. Here, the electrons for the reaction are supplied by photosynthesis and protons are derived from water. Therefore, the findings of our recent study can be regarded as a successful example of the artificial photosynthesis of ammonia.
Yoshiaki Nishibayashi, Professor, University of Tokyo
Journal Reference:
Yamazaki, Y., et al. (2025) Catalytic ammonia formation from dinitrogen, water, and visible light energy. Nature Communications. doi.org/10.1038/s41467-025-59727-w.