Mechanochemistry in planetary ball mills is a transformative and sustainable chemical process by which mechanical impact is converted into reaction‐driving energy. High‐energy collisions between balls, analogous to meteorite impacts on Earth, generate transient extreme pressures (∼10 GPa) and temperatures (∼1500°C) and supercritical water in microscale “hot spots,” allowing reactions once restricted to high‐temperature or solvent‐intensive laboratory or industrial conditions to proceed. This platform achieves hydrogen evolution efficiencies comparable or superior to electrolysis and even realizes a new phenomenon—room‐temperature thermochemical water‐splitting cycles—without CO 2 emissions, oxygen separation systems, or external heaters. Furthermore, the mechanochemical activation of TiO 2 yields photocatalysts with markedly enhanced absorption from the UV to the near‐infrared through defect and polymorph engineering. Beyond energy applications, the direct halogen‐free, HF‐free synthesis of alkoxysilanes provides a green, scalable route to value‐added chemicals with the coproduction of hydrogen at room temperature. These processes exploit abundant or waste materials, operate in compact setups, and consume very little energy, suggesting their potential for distributed fuel generation and sustainable materials manufacturing. Planetary ball milling can therefore offer a generalizable framework for green chemistry, bridging solid‐state reaction engineering with energy conversion and functional materials synthesis to provide practical routes toward low‐carbon, scalable technologies.
Ken‐ichi Saitow (Mon,) studied this question.