A technology has emerged that transforms nitrates in wastewater into ammonia, a high-value energy source. It produces green ammonia without carbon dioxide emissions during the production process and can also purify pollutants in wastewater.
Ulsan National Institute of Science and Technology (UNIST) announced on the 23rd that a team of professors, Seo Kwan-yong and Jang Ji-wook, from the Department of Energy and Chemical Engineering, developed a technology to obtain ammonia from nitrates in wastewater using sunlight.
Ammonia is an essential chemical used in industry and agriculture, with an annual consumption of over 150 million tons, and has garnered attention as a next-generation energy storage and transport medium due to its high hydrogen content. However, over 90% of ammonia is currently produced using the Haber-Bosch process under high-temperature and high-pressure conditions, resulting in massive greenhouse gas emissions.
The research team developed a photoelectrochemical (PEC) system that produces ammonia from nitrates without carbon dioxide emissions. This technology uses nitrates in wastewater as raw materials. High concentrations of nitrates can lead to conditions like cyanosis and gastric cancer; this system selectively reduces nitrates to convert them into ammonia.
The system consists of a silicon photoelectrode and a nickel foil catalyst. When the silicon photoelectrode receives sunlight, it generates electrons, which induce a nitrate reduction reaction through the nickel catalyst.
It has been analyzed that the thin layer of nickel hydroxide that forms on the nickel catalyst surface inhibits competing reactions such as hydrogen generation, enhancing ammonia selectivity. Recently, a professor in the Department of Physics at UNIST conducted a comparative analysis of the nitrate reduction pathways and energy barriers on the surfaces of nickel and nickel hydroxide, confirming that nickel hydroxide provides favorable active sites for ammonia production.
According to the research team, experimental results showed that this system can produce 554 micrograms of ammonia per square centimeter per hour without an external power source, marking the highest performance among PEC-based technologies globally. This figure represents an improvement of over 57% compared to the previous best performance of 353 micrograms. Moreover, the same performance was maintained in a larger device of 25 square centimeters, demonstrating its practical applicability.
Professor Seo Kwan-yong noted, "Transforming the pollutant nitrate into ammonia, the next-generation energy source, allows for simultaneous water purification and carbon neutrality," and added, "We plan to develop a large-scale device using silicon-based photoelectrochemical technology that can produce ammonia outdoors for demonstration research in the future."
The results of this research were published online in the international journal 'Advanced Materials' on June 22.
References
Advanced Materials (2025), DOI: https://doi.org/10.1002/adma.202506567