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

Abstract 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, Cr2B2 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 Cr2B2T2 (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 H2O and HCl molecules can split on the bare Cr2B2 in a nearly spontaneous manner, enabling functionalization of Cr2B2T2. Binding energy of termination groups on Cr2B2 quantifies the relative stability of functionalized Cr2B2T2 in the order: Cr2B2O2 > Cr2B2Cl2 > Cr2B2(OH)2 > Cr2B2H2. Furthermore, we demonstrate that both Cr2B2 and functionalized Cr2B2T2 MBenes are electronically conductive 2D materials with zero band gap, which is beneficial for electrochemical applications.