Korean researchers open path to room-temperature ammonia production without chemical additives

The KIST research team behind the study. From left: postdoctoral researcher Lee Ju-won, student researcher Jeon Seong-ju and senior researcher Jeong So-hee. [Provided by KIST]

A new path has opened to producing ammonia — a key fertilizer ingredient and a promising energy carrier for the future hydrogen economy — at room temperature and pressure, without extreme heat or high pressure.

A research team led by Jeong So-hee at the Korea Institute of Science and Technology's Center for Extreme Materials Research announced Thursday that it had jointly developed with a team led by Professor Kim Su-yeon of Myongji University a catalyst that improves ammonia production efficiency at room temperature and atmospheric pressure by slowing hydrogen gas generation during electrochemical ammonia synthesis.

Ammonia has drawn attention not only as a raw material for fertilizer production but also as an energy carrier capable of storing and transporting hydrogen. Conventional ammonia production, however, requires temperatures above 400 degrees Celsius and high pressure. It also relies heavily on fossil fuels, and the carbon dioxide emitted during production accounts for 1 to 2 percent of global energy-sector emissions.

Electrochemical ammonia production — using electricity rather than fossil fuels — has emerged as an alternative, but it comes with a significant drawback: hydrogen gas forms before ammonia can be synthesized, reducing production efficiency.

For ammonia to form, nitrogen (N₂) must combine with hydrogen (H) on the surface of a catalyst. When hydrogen atoms bond with each other first, however, they escape as hydrogen gas (H₂) rather than contributing to ammonia synthesis.

Conventional approaches addressed this by designing catalysts that repel hydrogen, preventing it from adhering to the surface. That left too little hydrogen available for the ammonia synthesis reaction itself.

The research team flipped the approach. Rather than pushing hydrogen away from the catalyst, they engineered it to hold hydrogen tightly, delaying its escape as gas. The trapped hydrogen is then given time to react with nitrogen and form ammonia. The team named this mechanism the "delayed hydrogen evolution reaction."

To achieve this, the catalyst was designed so that tungsten and vanadium on its surface work in tandem to bind both hydrogen and nitrogen simultaneously and effectively.

Performance results were strong. The catalyst produced 381.3 micrograms of ammonia per milligram of catalyst per hour at room temperature and atmospheric pressure. The Faradaic efficiency — the share of input electricity actually used for ammonia production — reached 13.0 percent, the highest recorded domestically among pure catalysts used without additional chemical additives.

A conceptual diagram of the delayed hydrogen evolution (Delayed HER) mechanism of the 2.5-dimensional catalyst. [Provided by KIST]

The team also confirmed the catalyst's durability and potential for scale-up. It maintained stable performance over 30 hours of continuous operation and retained about 80 percent of its performance when the catalyst area was expanded to 30 times its original size.

The research team said combining this technology with renewable energy sources such as solar and wind power could significantly reduce the energy consumption and carbon emissions associated with conventional ammonia production.

Ammonia is particularly well suited for long-distance hydrogen transport and storage because it can hold large amounts of hydrogen per unit volume. If its applications expand to ammonia fuel cells and carbon-free fuels for ships and heavy transport vehicles, the technology could contribute to building a clean hydrogen supply chain and advancing carbon neutrality across the industrial and transportation sectors.

"Instead of simply blocking the hydrogen evolution that was hindering ammonia production, we delayed it — and showed that this delay can be harnessed to produce ammonia at room temperature and atmospheric pressure," said Jeong, a senior researcher at KIST. "We will continue developing large-area catalysts and continuous production technology to bring this closer to commercialization."

The findings were published in the latest issue of the international journal Applied Catalysis B: Environment and Energy.

nbgkoo@heraldcorp.com