[Display omitted] • The BC-stacking Zr 2 CO 2 / M Se 2 bilayers are energetically favourable. • The twisted Zr 2 CO 2 /WSe 2 -46.8 bilayer has flat–like bands near Fermi level. • The Zr 2 CO 2 –WSe 2 – BC bilayer is a type-II heterojunction. • The Zr 2 CO 2 –WSe 2 – BC bilayer is a promising candidate for photocatalysis. The heterojunctions based on two–dimensional materials have aroused much research interest as they exhibit excellent properties and can be used in various fields such as catalysis, nanoelectronics, and superconductivity. In this study, the typical MXene monolayer, Zr 2 CO 2 , was integrated with the M Se 2 (M = Mo and W) monolayers to build van der Waals Zr 2 CO 2 / M Se 2 bilayers with and without twisted angles. The density functional theory (DFT) calculations were conducted at different levels to study the stability, electronic structure, optical absorption spectra, and carrier mobility of the designed bilayers. The BC –stacking Zr 2 CO 2 / M Se 2 bilayers are energetically favorable and thermodynamically stable. The rotation angle between the Zr 2 CO 2 and M Se 2 layers can effectively modulate the band structures by shifting the band edges. The Zr 2 CO 2 /WSe 2 bilayer with the twisted angle of 46.8° has the flat–like bands in the vicinity of the Fermi level with the bandwidths less than 0.1 eV. The BC –stacking Zr 2 CO 2 /WSe 2 bilayer (Zr 2 CO 2 –WSe 2 – BC) is a type–II heterojunction with an indirect band gap of 1.44 eV. The valence band maximum and conduction band minimum of Zr 2 CO 2 –WSe 2 – BC are dominated by the electronic states of WSe 2 and Zr 2 CO 2 layers, respectively. Zr 2 CO 2 –WSe 2 – BC can be considered a favorable candidate photocatalyst for overall water splitting due to its appropriate band structure, spatial separation of photogenerated carriers, improved response to light, and fast carrier mobility. [ABSTRACT FROM AUTHOR]