The quantum anomalous Hall (QAH) effect in two-dimensional (2D) topological materials has attracted widespread attention due to its potential for dissipationless chiral edge transport without an external magnetic field, which is highly promising for low-power electronic applications. However, identifying materials that exhibit these properties remains particularly challenging, as only a limited number of such materials are known, raising the intriguing question of whether it is possible to induce the QAH effect in materials with ordinary properties through structural modifications. In this work, we grow an unreported 2D titanium selenide (Ti3Se4) on a Cu(111) substrate using molecular beam epitaxy. Low-energy electron diffraction and scanning tunneling microscopy characterizations reveal a

Two-dimensional (2D) materials with defects are desired for catalysis after the adsorption of monodispersed noble metal atoms. High-performance catalysts with the absolute value of Gibbs free energy (|ΔGH|) close to zero, is one of the ultimate goals in the catalytic field. Here, we report the formation of monolayer titanium selenide (TiSe2) with line defects. The low-temperature scanning tunneling microscopy/spectroscopy (STM/S) measurements revealed the structure and electronic states of the line defect. Density functional theory (DFT) calculation results confirmed that the line defects were induced by selenium vacancies and the STM simulation was in good agreement with the experimental results. Further, DFT calculations show that monolayer TiSe2 with line defects have good catalytic activity for hydrogen evolution reaction (HER). If the defects are decorated with single Pt atom, the HER catalytic activity will be enhanced dramatically (|ΔGH| = 0.006 eV), which is much better than Pt metal (|ΔGH| = 0.09 eV). Line defects in monolayer TiSe2/Au(111) provide a wonderful platform for the design of high-performance catalysts.