Intercalation process as a surface engineering route of two-dimensional molybdenum sulfide (MoS₂): a mini review

Two-dimensional (2D) molybdenum disulfide (MoS₂) has attracted significant attention due to its unique structure and properties, especially following the discovery of graphene. This is mainly attributed due to its flexibility which facilitates the MoS₂ phase and properties exploration. MoS₂ mainly exists in three phases, 2H, 1T and 3R, where the naturally occurring 2H and 3R phase of MoS₂ acts as a semiconductor, with active edge sites and inactive basal planes. Conversely, the metallic 1T phase of MoS₂ features active edge sites and basal planes, making it more favorable for various applications. Numerous efforts have been made to modify bulk MoS₂ which exists as a 2H phase. By utilizing intercalation, which facilitates the conversion from the 2H to the 1T phase, also improves storage capacity and stabilizes metastable 1T phase, etc. To achieve these unique properties, various intercalation methods have been extensively studied and are thoroughly reviewed in this study. The intercalation process involves introducing foreign materials into a host material with adjustable van der Waals gaps. This allows for the insertion of guest material between the layers, making them excellent candidates for intercalation. In this review, we will explore various methods of intercalating MoS₂ material, including the electrochemical, solution-based, wet chemical, and ion-exchange methods.