High Entropy Sulfide Nanoparticles as Lithium Polysulfide Redox Catalysts.

The polysulfide shuttle contributes to capacity loss in lithium-sulfur batteries, which limits their practical utilization. Materials that catalyze the complex redox reactions responsible for the polysulfide shuttle are emerging, but foundational knowledge that enables catalyst development remains limited with only a small number of catalysts identified. Here, we employ a rigorous electrochemical approach to show quantitatively that the lithium polysulfide redox reaction is catalyzed by nanoparticles of a high entropy sulfide material, Zn0.30Co0.31Cu0.19In0.13Ga0.06S. When 2% by weight of the high entropy sulfide is added to the lithium sulfur cathode composite, the capacity and Coulombic efficiency of the resulting battery are improved at both moderate (0.2 C) and high (1 C) charge/discharge rates. Surface analysis of the high entropy sulfide nanoparticles using X-ray photoelectron spectroscopy provides important insights into how the material evolves during the cycling process. The Zn0.30Co0.31Cu0.19In0.13Ga0.06S nanoparticle catalyst outperformed the constituent metal sulfides, pointing to the role that the high-entropy "cocktail effect" can play in the development of advanced electrocatalytic materials for improved lithium sulfur battery performance.

Electrostatic Screening of Charged Defects in Monolayer MoS2.

Defects in monolayer transition-metal dichalcogenides (TMDCs) may lead to unintentional doping, charge-carrier trapping, and nonradiative recombination. These effects impair electronic and optoelectronic technologies. Here we show that charged defects in MoS2 monolayers can be effectively screened when they are in contact with an ionic liquid (IL), leading to an increase in photoluminescence (PL) yield by up to two orders of magnitude. The extent of this PL enhancement by the IL correlates with the brightness of each pretreated sample. We propose the existence of two classes of nonradiative recombination centers in monolayer MoS2: (i) charged defects that relate to unintentional doping and may be electrostatically screened by ILs and (ii) neutral defects that remain unaffected by the presence of ILs.