Unraveling surface functionalization of Cr2B2T2 (T = OH, O, Cl, H) MBene by first-principles calculations

H 2 O and HCl molecules dissolve on the surface of Cr 2 B 2 MBene in a spontaneous manner, resulting in functionalized MBene and released H 2 gas. • Surface functionalization of Cr 2 B 2 MBene is thermodynamically and kinetically feasible. • H 2 O and HCl molecules spontaneously dissolve on Cr 2 B 2 MBene surface. • Surface structures of Cr 2 B 2 T 2 ( T = OH, O, Cl, and H) were screened. • The functionalized Cr 2 B 2 T 2 ( T = OH, O, Cl, and H) MBenes are metallic. Synthesis of two-dimensional (2D) materials by wet-chemical methods is usually accompanied by surface functionalization, which plays critical roles in stabilizing and functionalizing the targeted materials. These termination reactions can bring thermodynamically stable products and versatile applications, however, leaving experimental characterization of surface structures challenging as well. In this work, newly emerging 2D conductive transition metal borides, Cr 2 B 2 MBene is selected as a prototype to investigate the surface functionalization phenomenon. By first-principles calculation plus efficient structural exploration, we provide an atomistic understanding of the chemical origin and kinetics of surface functionalization occurred in aqueous environment, and screen the surface structure of Cr 2 B 2 T 2 ( T = OH, O, Cl, and H) MBenes. Results clearly unravel the functionalization process of MBenes and the stable surface structures of functionalized MBenes. It is found that both H 2 O and HCl molecules can split on the bare Cr 2 B 2 in a nearly spontaneous manner, enabling functionalization of Cr 2 B 2 T 2 . Binding energy of termination groups on Cr 2 B 2 quantifies the relative stability of functionalized Cr 2 B 2 T 2 in the order: Cr 2 B 2 O 2 > Cr 2 B 2 Cl 2 > Cr 2 B 2 (OH) 2 > Cr 2 B 2 H 2 . Furthermore, we demonstrate that both Cr 2 B 2 and functionalized Cr 2 B 2 T 2 MBenes are electronically conductive 2D materials with zero band gap, which is beneficial for electrochemical applications.