Two-Dimensional Orthorhombic Molybdenum Boride Enabled by Selective Mo–Al Bond Cleavage in MoAlB

Abstract

Two-dimensional (2D) metal borides (MBenes) exhibit fascinating magnetic, electronic and catalytic properties, originating from the rich chemical bonding schemes of boron. However, the growth or exfoliation of 2D MBene remains extremely challenging due to the close minimal formation energy differences (<0.1 eV) among competing boride phase variations. Herein, we present a liquid-metal-mediated selective bond-breaking strategy that enables orthorhombic 2D MoB nanosheets from non-van der Waals MoAlB precursor. The interplay between gallium, MoAlB and molten salt introduces chemical-potential-driven cleavage of Mo–Al bonds and interlayer steric hindrance, suppressing the undesirable structural evolution to unreactive MoAl0.5B. The subsequent formation of soluble AlF63– species removes aluminum bilayer from MoAlB completely, generating layered MoB that can be readily exfoliated into crystalline 2D sheets with micrometer-scale dimensions and atomic thickness. The abundant exposed Mo–B sites facilitate Lewis acid–base interactions with electrolyte anions, enabling efficient tailoring of electrode–electrolyte interface chemistry. This optimized dense and uniform lithium deposition promotes anode-free Li metal batteries with 200-cycle stability and 2 C rate performance, opening new avenues for interphase-dominated energy storage.