Intercalation of Cobaltocene into WS2 Nanosheets for Enhanced Catalytic Hydrogen Evolution Reaction

We synthesized cobaltocene (7-20%)-intercalated WS2 nanosheets using a solvothermal process. The intercalation of cobaltocene between the expanded 1T phase WS2 layers was confirmed by scanning transmission electron microscopy and electron energy loss spectroscopy. The intercalated complexes exhibited excellent performance for the catalytic hydrogen evolution reaction, with a Tafel slope of 40 mV dec(-1) and a current density of 10 mA cm(-2) at 0.17 V (vs. RHE). Spin-polarized density functional theory calculations showed that cobaltocene is intercalated with a fivefold symmetry parallel to the WS2 plane, driven by substantial charge transfer. Reaction pathway calculations suggest that the basal S atoms just above the Co atom are the active sites, and the activation barrier of the Heyrovsky reaction determines the catalytic activity.