Two-dimensional metallic CoTe₂ flakes for electrocatalytic hydrogen evolution

Two-dimensional (2D) metallic 1T-CoTe₂ has attracted considerable attention due to its fascinating physical properties and promising applications in electronics and catalysis. However, the production of high-quality 2D 1T-CoTe₂ still remains challenging. Herein, we demonstrate a methodology to realize the facile synthesis of ultrathin, high-quality CoTe₂ flakes with a thickness down to 2.3 nm on mica substrates by an ambient-pressure chemical vapor deposition (CVD) technique. The atomic arrangement is verified by scanning transmission electron microscopy. The theoretical calculations uncover the metallic characteristic of 1T-CoTe₂ in the 2D limit. Remarkably, the CVD-derived 2D metallic CoTe₂ flakes for the hydrogen evolution reaction (HER) catalyst exhibit admirable performance, such as an overpotential of 186 mV at 10 mA·cm⁻², a Tafel slope of 78 mV·dec⁻¹, an exchange current density of 69 μA·cm⁻², and negligible performance degradation after 1000 cycles. These results establish novel approaches for the synthesis and HER application of 2D metallic 1T-CoTe₂.