MBenes: emerging 2D materials as efficient electrocatalysts for the nitrogen reduction reaction†
MBenes, an emerging family of two-dimensional (2D) transition metal borides, have recently been synthesized in experiment and hold great promise for 2D ferromagnets and metal ion batteries. With a well-defined layered structure and outstanding electrical conductivity, MBenes provide an ideal platform for exploring the catalytic behavior of boride surfaces at the atomic level. Herein, we exploit ten kinds of MBenes for electrocatalysis of the N2 reduction reaction (NRR). By comprehensive first-principles calculations, we show that MBenes have high stability in aqueous environments and excellent selectivity toward the NRR against the hydrogen evolution reaction (HER). Intriguingly, both the surface boron and metal atoms of MBenes can serve as the active sites owing to the co-existence of occupied and unoccupied p (d) states for the boron (metal) atoms, while the boron reaction centers provide even superior activity compared to the metal atoms. Moreover, the activity of these 2D borides can be tuned by engineering their work function. Our theoretical results shine light on utilizing metal borides as a new category of non-precious catalysts for nitrogen fixation, and illuminate the fundamental principles for controlling their catalytic performance.