Reactive Precipitation of Anhydrous Alkali Sulfide Nanocrystals with Concomitant Abatement of Hydrogen Sulfide and Cogeneration of Hydrogen

Abstract

Anhydrous alkali sulfide (M₂ S, M=Li or Na) nanocrystals (NCs) are important materials central to the development of next generation cathodes and solid-state electrolytes for advanced batteries, but not commercially available at present. This work reports an innovative method to directly synthesize M₂ S NCs through alcohol-mediated reactions between alkali metals and hydrogen sulfide (H₂ S). In the first step, the alkali metal is complexed with alcohol in solution, forming metal alkoxide (ROM) and releasing hydrogen (H₂ ). Next, H₂ S is bubbled through the ROM solution, where both chemicals are completely consumed to produce phase-pure M₂ S NC precipitates and regenerate alcohol that can be recycled. The M₂ S NCs morphology may be tuned through the choice of the alcohol and solvent. Both synthetic steps are thermodynamically favorable (ΔG_m^o <-100 kJ mol^-1 ), proceeding rapidly to completion at ambient temperature with almost 100 % atom efficiency. The net result, H₂ S+2 m→M₂ S+H₂ , makes good use of a hazardous chemical (H₂ S) and delivers two value-added products that naturally phase separate for easy recovery. This scalable approach provides an energy-efficient and environmentally benign solution to the production of nanostructured materials required in emerging battery technologies.