Enhancing Solid-state Hydrogen Storage Properties of Lithium Hydride through Thermodynamic Tuning with Porous Silicon Nanowires

Abstract

Solid-state hydrogen storage technology ensures a safer storage method, eliminating the risks of leaks, boiling losses, and explosions in commercial applications. Based on earlier findings, alloying LiH with silicon (Si) yields substantial storage capacity while lowering the energy needed for absorption and decomposition. Herein, the work explores using the derivative of bulk Si (i.e., porous silicon nanowires (PSiNWs)) mechanical milling with LiH to improve the thermodynamic properties and uptake capacity. The PSiNWs are synthesized by Ag metal-assisted chemical etching to the bulk Si substrate. Nanopores on the nanowires enhance gas physisorption by overlapping attractive fields from opposing pore walls. The large surface area (~ 450 m2 g-1) of PSiNWs provides maximum active sites for hydrogen storage. The hydrogen storage capacity of the LiH-PSiNWs alloy is evaluated through pressure composition isotherms at different temperatures (400 ℃ - 500 ℃ range) and ~ 4 MPa charging pressure. The maximum observed capacity, ~ 3.95 wt.%, occurs at 400 ℃. The thermodynamic analysis signifies the uniform absorption and desorption enthalpy after alloying LiH with PSiNWs. Hydrogen absorption and desorption enthalpies of ~ 118 kJ mol-1 H2 and ~ 115 kJ mol-1 H2 demonstrate a reduced energy requirement than individual LiH. The phase formation and variations before and after hydrogenation are studied by X-ray diffraction. This work investigates using Si nanostructures and light metal hydrides for enhanced hydrogen storage and cyclic functionalities, serving as both storage material and catalyst.