Computational exploration of two-dimensional vacancy-free boridene sheet and its derivatives: high stabilities and the promise for hydrogen evolution reaction

Abstract

The recent synthesis of a two-dimensional (2D) MBene sheet, referred to as the boridene sheet (Mo4B6Tz), has ignited considerable interest in exploring 2D transition metal borides. Boridene has an ordered arrangement of metal vacancies, which are pivotal to its stability. Employing first-principles calculations, we explored the stable phases, electronic properties and catalytic abilities of boridene with different vacancy concentrations (Vm). Our results demonstrate that Vm significantly influences the cohesive energies of boridene sheets. Phonon spectrum and ab initio molecular dynamics simulations reveal the high stability of the vacancy-free boridene Mo6B6T6 (T = O, -OH), underscoring their potential for experimental realization. Substituting Mo atoms with Nb, Ta, or W enhances the structural stability of boridene sheets, leading to the identification of four stable variants: Nb6B6F6, Ta6B6F6, Ta6B6O6, and W6B6O6. These boridene sheets exhibit metallic behavior, with five structures displaying near-zero Gibbs free energy for hydrogen atom adsorption, indicating their potential as catalysts for the hydrogen evolution reaction. The uncovering of vacancy-free boridenes and their 2D derivatives greatly broadens the scope of the MBene family.