Hydrogen and Secondary Battery Materials Produced from Discarded Solar Panels!

A new technology has been developed to extract hydrogen stored in ammonia by using silicon.

During the extraction process, this silicon is transformed into a secondary battery material, attracting attention as a technology that not only reduces hydrogen production costs but also enables the recycling of silicon from discarded solar panels.

The research team led by Professor Paek Jongbeom from the Department of Energy and Chemical Engineering at Ulsan National Institute of Science and Technology (UNIST) has developed a ball milling process that separates 100% pure hydrogen from ammonia.

Research team, (from left) Professor Paek Jongbeom, Professor Lim Hangwon. Provided by Ulsan National Institute of Science and Technology (UNIST)

원본보기 아이콘

Ammonia (NH₃) is a substance that can store and transport hydrogen (H₂), a clean fuel, at low cost. This is because it has a high hydrogen content of 17.6% by weight, and the infrastructure for storing and transporting ammonia is already well established. The challenge, however, is that extracting the chemically stored hydrogen from ammonia requires high-temperature decomposition at 400 to 600 degrees Celsius and additional purification processes.

The process developed by the research team operates at a low temperature of around 50 degrees Celsius, consuming less energy and enabling hydrogen production without any additional purification steps. The method involves placing ammonia gas and silicon powder together in a sealed container (ball mill) containing beads several millimeters in diameter and shaking the mixture.

The impact and friction of the beads activate the silicon, causing the ammonia to decompose rapidly and release hydrogen. When ammonia is decomposed, nitrogen (N₂) is also produced along with hydrogen. However, the nitrogen does not escape as a gas but instead reacts with the silicon to form silicon nitride (Si₃N₄).

In experiments, all the ammonia gas was decomposed, generating 102.5 mmol (millimoles) of hydrogen per hour. Component analysis confirmed that the resulting hydrogen was 100% pure, with no gaseous impurities such as nitrogen or unreacted ammonia. The same conversion rate and purity were achieved even when using silicon recovered from actual discarded solar panels.

Silicon nitride, a byproduct of the process, is a high-value-added material that can be used as an anode material for secondary batteries. Lithium-ion batteries made with the produced silicon nitride recorded a capacity of 391.5 mAh/g, and maintained a coulombic efficiency of 99.9% and more than 80% of their initial capacity after over 1,000 charge-discharge cycles.

Furthermore, an economic analysis showed that when considering the sales revenue from silicon nitride produced from discarded solar panels, the unit cost of hydrogen production could be as low as minus $7.14 per kilogram, meaning that the process can actually generate economic profit.

Professor Paek Jongbeom stated, "This achievement offers a solution to the hydrogen separation and purification challenges that have hindered the ammonia-based hydrogen economy," and added, "There is virtually no performance difference when using silicon powder recovered from actual discarded solar panels compared to commercial silicon powder, so this technology will also have significant value as a recycling solution for the more than 80 million tons of discarded solar panels expected to accumulate by 2050."

Process concept diagram for separating only hydrogen gas from ammonia.

원본보기 아이콘

The research results were published on September 3 in the Journal of the American Chemical Society (JACS), a leading journal in the field of chemistry.

The research was supported by the National Research Foundation of Korea under the Ministry of Science and ICT, and the Korea Institute for Advancement of Technology under the Ministry of Trade, Industry and Energy.

© The Asia Business Daily(www.asiae.co.kr). All rights reserved.