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

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 (ΔGmo <-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.