A research team led by Professor Jong-Beom Baek at UNIST has introduced a novel mechanochemical reaction that uses silicon (Si) recovered from retired solar panels and ammonia (NH₃) to produce high-purity hydrogen (H₂) at about 50°C. Traditional ammonia decomposition for hydrogen release typically requires high temperatures (400–600°C) and subsequent purification steps, tells Tech Xplore.
In this ball-milling approach, ammonia and finely powdered silicon are sealed with steel or ceramic beads; mechanical force initiates the reaction, decomposing NH₃ to H₂ and nitrogen (N₂). The nitrogen then reacts with silicon to form silicon nitride (Si₃N₄), which remains in the system rather than exiting as gas. Experiments showed full ammonia conversion, a hydrogen production rate of 102.5 mmol per hour, and confirmed 100% H₂ purity.
Crucially, the process works equally well when using recycled silicon from solar panel waste instead of fresh commercial Si. The Si₃N₄ by-product is itself a high-value material, as evidenced by its performance in lithium-ion batteries, where it delivered a capacity of 391.5 mAh/g and retained over 80% of its initial capacity after 1,000 cycles, with a Coulombic efficiency of 99.9%.
Economic estimates suggest the hydrogen production cost could be negative (about –US$7.14 per kg) when factoring in revenue from selling the silicon nitride derived from waste panels. The team points to the significance of this method, given forecasts that more than 80 million tons of photovoltaic waste could accumulate by 2050.
This process transforms two problems, hydrogen release and solar-panel waste, into a combined solution with strong sustainability credentials.