Rhombohedrally Stacked Layered Transition Metal Dichalcogenides and their Electrocatalytic Applications

Abstract

Layered transition metal dichalcogenides (TMDCs) are extensively investigated as catalyst materials for wide range of electrochemical applications due to their high surface area, versatile electronic and chemical properties. Bulk TMDCs are van der Waals solids which possess strong in-plane bonding and weak inter-layer interactions. In the few-layer 2D TMDCs, several polymorphic structures are reported as each individual layer can either retain octahedral or trigonal prismatic coordination. Among them, 1T (tetragonal), 2H (hexagonal) and 3R (rhombohedral) phases are very common. These polymorphs can display discrepancy in their catalytic activity as their electronic structure diverges due to different d orbital filling. The broken inversion symmetry and large exposed edge sites of some of 3R-phase TMDCS such as MoS2, NbS2 and TaS2 appears to be advantageous for electrocatalytic water reduction and battery applications. We describe recent studies in phase engineering of 2D TMDCs, particularly aiming on 3R polytype and their electrocatalytic properties. Redox ability primarily depends on distinct polymorphic phase in which TMDCs is isolated and hence with rich polymorphic structures are reported, numerous new catalytic applications can be realized. Phase conversion from 2H to 3R phase in some TMDCs enhances structural integrity and establish the robustness under harsh chemical conditions.