Mechanochemically Tailored Silicon Particles for Efficient H-2 Production: Entropy and Enthalpy Engineering

Efficient low-temperature H-2 production was demonstratedby mechanochemically treating Si particles, and the Si-waterreaction mechanism was understood. Silicon-water reactions can generate large amountsof H-2, and hence, discarded solar cells can be upcycledto producereactants. 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-entropySi particles for efficient H-2 production using ball milling.Well-defined Si particles, with surface and internal structures characterizedby using eight parameters, were reacted with alkaline water at lowtemperatures (30-70 & DEG;C). Two common assumptions, (i) thehigher the mechanical energy, the better and (ii) the larger the surfacearea, the more efficient the reaction, were proved wrong in this case.Indeed, the Si particles exhibiting the best H-2 productioncapacity were produced by grinding for 3 min without adding any chemicals.In addition, the increases in enthalpy and entropy imparted to theSi particles and the mechanical collision energy and surface and internalstructures 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-upincreased 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.

Automated summary

Efficient low-temperature H-2 production was achieved by mechanochemically treating Si particles, and the Si-water reaction mechanism was understood. The use of discarded solar cells for reactant production is possible, but challenges related to Si particle preparation, hazardous chemicals, and unknown reaction mechanisms must be addressed.