Li+-clipping for edge S-vacancy MoS2 quantum dots as an efficient bifunctional electrocatalyst enabling discharge growth of amorphous Li2O2 film

Highlights: • Achieving an atomic level prepare the edge S-vacancy on MoS₂ quantum dots based on Lewis acid-base theory. • Rich-edge S-vacancy MoS₂ QDs facilitate conformal growth of amorphous Li₂O₂ film on the cathode. • Our study for the first time proves that rich-edge S-vacancy MoS₂ QDs is an extraordinary bifunctional catalyst. -- Abstract: Molybdenum disulfide (MoS₂), as an extremely intriguing two-dimensional (2D) material with excellent electrocatalyst, has attracted more and more attentions in recent years. However, the lack of precisely engineered rich-edge S-vacancy MoS₂ constitutes a major obstacle for in-depth studying of structure-activity relationship of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, based on Lewis acid-base theory, we prepared rich-edge S-vacancy MoS₂ quantum dots (MoS₂ QDs) via top-down strategy using lithium bis(trifluoromethylsulphonyl)imide as a stripper and clipper. It is demonstrated for the first time that the rich-edge S-vacancy MoS₂ QDs exhibit an extraordinary ORR/OER catalytic performance in Li-O₂ batteries system by a joint experimental and theoretical study. Importantly, the rich-edge S-vacancy MoS₂ QDs can run more than 230 cycles at high current density, which was almost 9 times longer than the cycle stability of bulk MoS₂. The excellent activity arises primarily due to that the MoS₂ QDs facilitate conformal growth of amorphous Li₂O₂ film on the cathode, originating from the significant differences of adsorption energies between Li⁺ and O₂, which could significantly enhanced Li₂O₂ formation/decomposition kinetics. This work provides a novel way for controllable synthesis of rich-edge S-vacancy MoS₂ QDs, establishes the underlying mechanisms for the high OER/ORR activity, and suggests high translatability to apply other TMDs.