A domestic research team has developed a technology that extracts hydrogen stored in ammonia by adding silicon. During the extraction process, this silicon is transformed into a secondary battery raw material, reducing hydrogen production expense and enabling the recycling of silicon from end-of-life solar panels.
Baek Jong-beom's research team in the Department of Energy and Chemical Engineering at the Ulsan National Institute of Science and Technology (UNIST) said on the 25th that it developed a ball-milling method that separates 100% pure hydrogen from ammonia. The findings were published on Aug. 19 in the international journal the Journal of the American Chemical Society (JACS).
Ammonia is a substance that can store and transport hydrogen, a clean fuel, at low cost. It has a high hydrogen content by weight at 17.6%, and the storage and transport infrastructure for ammonia is already well established. The problem is that to retrieve the hydrogen chemically stored in ammonia for use, high-temperature cracking at 400–600 degrees and additional purification steps are required.
The process developed by the research team operates at a low temperature of around 50 degrees, consuming less energy and yielding hydrogen without additional purification. It involves placing ammonia gas and silicon powder together in a sealed container (a ball mill) containing beads several millimeters in size and shaking it. The impact and friction of the beads activate the silicon, rapidly decomposing the ammonia to release hydrogen. When ammonia decomposes, nitrogen is produced along with hydrogen; the nitrogen is not released as a gas but reacts with silicon to convert into silicon nitride.
In experiments, all the ammonia gas decomposed to generate hydrogen at a rate of 102.5 mmol per hour, and component analysis confirmed 100% pure hydrogen with no gaseous impurities such as nitrogen or unreacted ammonia. The same conversion rate and purity were achieved when silicon recovered from actual end-of-life solar panels was used.
Silicon nitride, a byproduct of the process, is a high value-added material that can be used for secondary battery anodes. A lithium-ion battery made from the produced silicon nitride recorded a capacity of 391.5 mAh/g and maintained 99.9% coulombic efficiency and more than 80% of its initial capacity even after more than 1,000 charge-discharge cycles.
In an economic analysis, taking into account the sales revenue from silicon nitride produced from end-of-life solar panels, the unit hydrogen production cost came to "-$7.14/kg," recording a negative expense and indicating that it could instead generate economic profit.
Professor Baek said, "This is a result that offers a solution to the bottleneck of hydrogen separation and purification that has hampered the ammonia-based hydrogen economy," adding, "When using silicon powder recovered from actual end-of-life solar panels, there was almost no performance difference compared with commercial silicon powder, so it will also have great value as a recycling technology for end-of-life solar panels, which are expected to accumulate more than 80 million tons by 2050."
References
JACS (2025), DOI: https://doi.org/10.1021/jacs.5c10245