Summary

Although Earth's abundant silicon (Si) is thermodynamically reactive with water to produce hydrogen (H2) and silicon oxide (SiO2, silica), the Si-water reaction is kinetically self-limited by the silica passivation layer that spontaneously forms on Si surfaces. If this limitation of the Si-water reaction can be overcome, hydrogen (H2) can be directly produced from water. Here, we demonstrate that “dynamic” mechanochemistry can overcome the self-limitation of the Si-water reaction, without using corrosive additives, to reach the theoretical limit. As one real-world application, upcycling end-of-life silicon solar panels was performed, with techno-economic analysis suggesting the strong competitiveness of the proposed method for the Si-water reaction. High-purity hydrogen (∼100%) gas and solid silica as a value-added product were produced under a separation-free process.

In response to the growing accumulation of end-of-life solar panels, researchers at UNIST have unveiled an innovative, environmentally friendly method to convert photovoltaic silicon into high-purity hydrogen and valuable silica. Led by Professor Jong-Beom Baek from the School of Energy and Chemical Engineering at UNIST, this breakthrough promises to revolutionize solar panel recycling and sustainable hydrogen production.

The team led by Professor Jong-Beom Baek developed a mechanochemical process that overcomes the self-limiting silica passivation layer on silicon surfaces. By placing silicon and water with small abrasive beads into a rotating vessel, repeated mechanical collisions strip the silica layer, enabling the reaction to proceed to nearly its theoretical maximum. Experimental results show approximately 1,706 mL of hydrogen per gram of silicon—achieving 99.6% of the maximum yield, significantly surpassing conventional thermochemical methods.  

Moreover, the silica byproduct serves as an effective catalyst support. When used with nickel catalysts, it enhances carbon dioxide conversion and methane selectivity, thanks to its high surface hydroxyl density that improves catalyst dispersion.

“By leveraging waste silicon from decommissioned solar panels, our process produces high-purity hydrogen efficiently while also recovering valuable silica for industrial applications,” says Professor Jong-Beom Baek. “This approach not only advances sustainable energy but also contributes to resource circularity and environmental protection.”  

This technology offers a cost-effective, scalable, and environmentally benign alternative to traditional photovoltaic waste management. Operating continuously, the process boasts higher productivity and energy efficiency, making it suitable for industrial deployment. It paves the way for a circular economy in solar energy, transforming waste into valuable resources and supporting the global shift toward clean hydrogen.