MoS2 nanomaterials have been identified as a cost-effective and earth-abundant alternative to platinum-group metals for electrocatalytic hydrogen evolution. Chemical exfoliation of bulk semiconducting 2H-MoS2 by lithium intercalation is widely employed to synthesize metallic 1T-MoS2 nanosheets with enhanced basal plane activity and improved charge transport. While the catalytic benefits of this phase transition are well established, the mechanisms responsible for stabilizing the metastable 1T phase following exfoliation remain unexplored. Here, detailed compositional analysis by atom probe tomography uncovers the incorporation of lithium as nanoscale clusters within the 2D material, even after acidic treatment. Operando electrochemical measurements reveal the dissolution of weakly adsorbed lithium upon initial contact with the electrolyte, whereas the lithium clusters seem to remain stable under conditions relevant to the hydrogen evolution reaction. These findings establish detailed compositional analysis as essential for understanding lithium incorporation as a potentially overlooked parameter for controlling and modulating the functional properties and the stability of the metallic 1T phase of chemically exfoliated transition metal dichalcogenides.
Krämer et al. (Tue,) studied this question.