Japanese scientists showed new method to produce ammonia using sunlight, air and water

Researchers at the University of Tokyo have developed a novel method to produce ammonia using artificial photosynthesis, offering a potential low-energy alternative to the carbon-intensive Haber-Bosch process. The technique mimics natural nitrogen fixation by cyanobacteria and utilizes atmospheric nitrogen, water, and sunlight to synthesize ammonia.

Ammonia is a crucial component in global agriculture, used predominantly in the production of urea-based fertilizers. Current industrial production methods are responsible for about 2% of global carbon dioxide emissions, largely due to their dependence on fossil fuels. The new approach developed by the Japanese research team could significantly reduce the environmental footprint of ammonia production.

The process, led by Professor Yoshiaki Nishibayashi at the University of Tokyo’s Department of Applied Chemistry, relies on a dual-catalyst system to initiate and sustain the conversion reaction. An iridium-based photocatalyst, when exposed to sunlight, activates a compound called tertiary phosphine, enabling the oxidation of water molecules. This step produces protons essential for the subsequent formation of ammonia.

Simultaneously, a molybdenum-based catalyst activates dinitrogen from the air. The reaction between nitrogen and the protons generated from water results in the formation of ammonia molecules. The process yields only oxygen as a byproduct and, under optimal conditions, combines two nitrogen atoms and three water molecules to produce two ammonia molecules.

The researchers report that the new reaction system has achieved higher efficiency than previous artificial nitrogen fixation attempts and can be operated on a scale ten times larger than prior laboratory demonstrations. This progress suggests the method has potential for industrial application, though further work is needed to optimize reaction conditions and improve cost-effectiveness at scale.

Given that over 80% of the 200 million tonnes of ammonia produced annually is used in agriculture, this innovation could play a critical role in promoting more sustainable fertilizer production. If commercialized, the method may help lower energy use and reduce emissions in one of the most resource-intensive sectors of global food production.