Mechanochemically Tailored Silicon Particles for Efficient H<sub>2</sub> Production: Entropy and Enthalpy Engineering
Tomoya Mizutani, Haruhisa Ohta, Taiki Ueda, Tsutomu Kashiwagi, Takeshi Fukuda, Toshio Shiobara, Ken‐ichi Saitow
Abstract
Silicon–water reactions can generate large amounts of H 2, and hence, discarded solar cells can be upcycled to produce reactants. However, concerns about silicon (Si) particle preparation, hazardous chemicals, and unknown reaction mechanisms must be addressed. Herein, we demonstrate the tailoring of high-enthalpy, high-entropy Si particles for efficient H 2 production using ball milling. Well-defined Si particles, with surface and internal structures characterized by using eight parameters, were reacted with alkaline water at low temperatures (30–70 °C). Two common assumptions, (i) the higher the mechanical energy, the better and (ii) the larger the surface area, the more efficient the reaction, were proved wrong in this case. Indeed, the Si particles exhibiting the best H 2 production capacity were produced by grinding for 3 min without adding any chemicals. In addition, the increases in enthalpy and entropy imparted to the Si particles and the mechanical collision energy and surface and internal structures were determined. Thus, the Gibbs energy of the H 2 production reaction and its activation barrier were well-defined, and the Si–water reaction mechanism was deduced. As scaling-up increased the energy efficiency of mechanochemical H 2 production, which could be comparable to that of electrolysis, sustainable H 2 production in the future is possible.