Cluster-AssembledB26Monolayer and Its Inverse-SandwichedDerivativeB24P4: Stable 2D Boron-Based Materials with Topological Property, Superconductivity, and Electrocatalytic Activity

Abstract

The rich bonding versatility of boron enables the design of exotic two-dimensional (2D) monolayers with unconventional properties. Previous studies have demonstrated that stable boron sheets can be constructed from combinations of triangles and hexagons, while inverse sandwich nanostructures exhibit remarkable stability and multifunctionality. In this work, we propose a novel B26 monolayer which consists of six B4 rhombuses and two central B atoms connected in a zigzag pattern, forming a planar structure with 28 triangles and 6 hexagons per unit cell. The new B26 monolayer has a cohesive energy very close to that of experimentally prepared β13 and χ3, and it displays nontrivial topological properties, including nontrivial Berry phase of π and the presence of topologically protected edge states. Meanwhile, it exhibits superconductivity with a transition temperature Tc of ~1.46 K. Furthermore, by vertically substituting two central boron atoms located in the fused tri-hexagon units in B26 with P2 dimers, we construct a stable inverse-sandwich B24P4 monolayer. This material not only shows enhanced superconductivity (Tc ~20.10 K), but also acts as a promising metal-free electrocatalyst for the hydrogen evolution reaction (HER), surpassing that of B26, owing to more favourable multi-hydrogen adsorption energetics and closer alignment with ideal thermodynamic conditions for hydrogen evolution. Our findings offer a new strategy for designing boron-based monolayers with exceptional structural stability and multifaceted properties and functionalities.