Synthesis of a Library of Transition Metal Sulfide@MoS ₂ Core@Shell Nanostructures via Post‐Synthetic Cation Exchange

The rational synthesis of compositionally diverse and structurally well‐defined inorganic heterostructures remains a substantial challenge. Herein, we report a post‐synthetic cation exchange strategy for the programmable construction of a library of transition metal sulfide@MoS 2 core@shell heterostructures. Using Ag 2 S@MoS 2 as a template, we demonstrate a multi‐step transformation pathway via a highly reactive Cu 2‐x S@MoS 2 intermediate. Critically, this approach successfully decouples the formation of the MoS 2 shell from the final core composition, providing a universal route to three distinct classes of architectures—metal sulfide M x S y (M═Cd, Cu, Co, Ni, Mn, Zn), heterostructured (Cu 2‐x S/ZnS), and homogeneous solid‐solution (Ni x Co y S 4 ) cores—while perfectly preserving the integrity of the monolayer MoS 2 shell. The potential of these materials is highlighted by their electrocatalytic performance for the oxygen evolution reaction (OER). The Co 9 S 8 @MoS 2 catalyst exhibits exceptional activity, achieving a low overpotential of 253 mV at 10 mA cm −2 and remarkable long‐term stability. This work establishes cation exchange within a 2D shell as a powerful and general platform for engineering complex hybrid architectures for advanced energy applications.