Synergistically coupling CoS/FeS2 heterojunction nanosheets on a MXene via a dual molten salt etching strategy for efficient oxygen evolution reaction

Abstract

Metal sulfides exhibit good catalytic activity for the oxygen evolution reaction (OER) due to their distinctive electronic and structural properties; however, their inadequate electrical conductivity hinders electron transfer, while easy agglomeration obstructs active sites. Herein, a dual molten salt etching strategy and subsequent sulfidation are employed to anchor CoS/FeS₂ heterojunction nanosheets onto an electrically conductive MXene (MXene@CoS/FeS₂) for efficient OER. The strong electronic interaction between CoS and FeS₂, in conjunction with the conductive MXene, facilitates rapid charge transfer, while the heterostructured nanosheets on the MXene substrate expose abundant catalytic active sites. Dut to its delicate nanostructure, the MXene@CoS/FeS₂ composite demonstrates an exceptionally low overpotential (278 mV achieved at 10 mA cm⁻²) and remarkable stability (over 40 h). Density functional theory (DFT) calculations indicate that the electron transfer at the CoS/FeS₂ interface effectively reduces the energy barrier of the rate-determining step (RDS) for MXene@CoS/FeS₂. Additionally, the simple and straightforward preparation process eliminates the need for HF, enabling efficient and large-scale catalyst production while ensuring safety and environmental friendliness. Overall, the designed MXene@CoS/FeS₂ holds great promise as an OER catalyst.