UNIST Produces Carbon Dioxide-Free 'Green Ammonia' Using Wastewater and Sunlight!

(From left) Researcher Kim Hyo-eun, Professor Lee Jae-sung, and Researcher Na Eun-chul are taking a commemorative photo.

[Asia Economy Yeongnam Reporting Headquarters Reporter Hwang Du-yeol] A technology has been developed to produce ammonia, which is attracting attention as a hydrogen storage medium, without emitting carbon dioxide.

The research team led by Professor Lee Jae-seong of the Department of Energy Chemical Engineering at UNIST developed a photocatalytic technology that obtains ammonia from nitrates in wastewater using sunlight.

The technology is based on the principle that the photocatalyst exposed to sunlight triggers a chemical reaction that converts nitrates into ammonia.

The research was conducted in collaboration with Professor Hemin Zhang of Sichuan University in China and Professor Jang Yoon-jung of Hanyang University.

The research team explained, “This technology can capture carbon dioxide emitted during ammonia production and also treat nitrates in wastewater. If the photocatalyst’s efficiency and stability are improved, it will become an ideal green technology that directly utilizes solar energy, the most abundant renewable energy on Earth.”

The carbon dioxide emitted during ammonia production accounts for about 1.8% of global emissions, which is significant.

As an alternative, technology to produce green ammonia by dissolving nitrogen in water and using electrolysis has been attracting attention, but nitrogen does not dissolve well in water, and there remains the problem that electricity produced from fossil fuels must still be used.

The research team proposed a solution by utilizing the characteristic of nitrates, which dissolve well in water.

Instead of electricity, the team used a self-developed photocatalyst. The photocatalyst directly absorbs sunlight and uses the generated electrons (photoelectrons) to reduce nitrates, synthesizing ammonia.

Experimental results showed that using the photocatalyst, nitrates could be reduced to ammonia with a high selectivity of 95.6% even at very low voltage.

The high reaction selectivity means that the photoelectrons were efficiently used only for the nitrate reduction reaction.

The research team explained that this high efficiency was achieved thanks to the structural characteristics of the photocatalyst, where silicon nanowires were evenly aligned, and trace amounts of gold particles well attached to the nanowire surfaces.

Ammonia, known as a raw material for fertilizers, has recently emerged rapidly as a hydrogen carrier and storage medium.

Converting hydrogen into ammonia allows storing about 1.7 times more hydrogen than simply liquefying hydrogen, and it is more economical because existing ammonia liquefaction facilities and transportation means can be used as they are.

However, the contradiction of large amounts of carbon dioxide being generated during ammonia synthesis remains a challenge to be solved.

The results of this research were published online on the 5th in the Angewandte Chemie International Edition, one of the top chemistry journals published by Wiley in Germany.

The research was supported by the Climate Change Response Project promoted by the Ministry of Science and ICT.

This content was produced with the assistance of AI translation services.