A domestic research team has developed an efficient technology to convert liquid ammonia into hydrogen and has also presented a new analysis technology that can find the optimal process environment, drawing attention as a key technology that will bring forward the era of green hydrogen.

Professor Kim Geon-tae's team from the Department of Energy and Chemical Engineering at UNIST (President Yong-Hoon Lee) has succeeded in mass producing green hydrogen (H2) with a purity of nearly 100% by decomposing liquid ammonia (NH₃) using electricity.

Evaluation results using the analytical technology proposed by the research team showed that this method consumed three times less power than producing hydrogen through water electrolysis.

Among the methods of transporting hydrogen, the most efficient method is ammonia synthesis. Synthesizing ammonia with hydrogen allows transport of 1.5 times more hydrogen and has less loss during transport.

Another advantage is that it can utilize the existing liquefied ammonia transportation infrastructure.

On the other hand, although the technology to synthesize hydrogen into ammonia has been commercialized, the technology to extract hydrogen again from ammonia is still in its infancy.

The research team succeeded in extracting hydrogen from liquid ammonia using a porous nickel foam electrode.

The nickel foam electrode surface has high efficiency because the catalyst (platinum) particles are evenly applied using cyclic voltammetry.

If you put liquid ammonia into the electrode synthesized in this way and pass an electric current through it, the liquid ammonia will decompose (electrolyze) and hydrogen can be obtained.

The Faraday efficiency, an indicator of hydrogen purity, was over 90%, and the current density, which indicates the chemical reaction rate, was also high at over 500 mA cm-2.

In addition, a new protocol for quantitatively analyzing the amount of gas generated in real time using gas chromatography (gas analyzer) was proposed, and efficient ammonia electrolysis process conditions (such as acidity of the electrolyte) were also found.

In an optimized driving environment, 569L of hydrogen can be produced with 1kWh of electricity. This is more than three times lower power consumption than water electrolysis. This demonstrates that green hydrogen can be produced using less electricity and cost than water when using ammonia.

“We used a manufacturing method for electrodes that have excellent hydrogen production activity in an ammonia electrolysis environment,” said first author Yang Ye-jin, a researcher in the combined master’s and doctoral program in the Department of Energy Engineering at UNIST. “This electrode is expected to make a great contribution to simplifying the ammonia electrolysis system and reducing the construction cost as it is an electrode that can be used in both oxidation and reduction reactions.”

“This study is significant in that it found the optimal conditions for ammonia electrolysis,” said co-first author Jeongwon Kim, a researcher in the combined master’s and doctoral program in the Department of Energy Engineering at UNIST. “It is also significant as basic research for the future commercialization of ammonia electrolysis.”

Professor Kim Geon-tae said, “If the high-efficiency electrode suggested in this study is applied to the ammonia electrolysis process, the commercialization of ammonia electrolysis hydrogen production technology will be accelerated significantly,” adding, “The possibility of researching the recycling of ammonia, and further waste ammonia, into ‘CO2-free hydrogen’ has been presented in various ways, opening up a new paradigm for renewable energy.”

This study was co-authored by Dr. Lee Min-jae, Dr. Seo Myung-gi, Dr. Min Hyeong-gi, and Dr. Choi Young-heon from Lotte Chemical Basic Materials Research Institute. The results of the study were published in the online version of the Journal of Materials Chemistry A, an international academic journal in the energy and materials field, on March 27, and were selected as the inside front cover paper, awaiting official publication. The research was supported by Lotte Chemical, the Ministry of Science and ICT, and the National Research Foundation of Korea (NRF).