Two-dimensional transition metal diborides: promising Dirac electrocatalysts with large reaction regions toward efficient N2 fixation

Abstract

Catalysts with high conductivity, intrinsic activity, and selectivity are essential and highly sought for the nitrogen reduction reaction (NRR). However, combining these advantages into one material is a grand challenge. Herein, we find that two-dimensional (2D) transition metal diborides (TMBs), TiB₂ and NbB₂, could act as high-performance electrocatalysts for the NRR with large reaction regions. TiB₂ and NbB₂ monolayers not only possess unique atomic structures that provide a large number of active catalytic sites for N₂ reduction, but also exhibit rich Dirac states and ultrahigh Fermi velocities, which can accelerate charge transfer between catalysts and reaction intermediates. N₂ can be reduced to NH₃ on the transition atoms of TiB₂ and NbB₂via an enzymatic mechanism with ultralow limiting potentials of −0.58 and −0.64 V, respectively. In particular, NbB₂ monolayers can significantly suppress the hydrogen evolution reaction occurrence, making them a promising NRR electrocatalyst with high efficiency, selectivity, and plentiful active catalytic sites. This work demonstrates the feasibility of 2D Dirac materials for N₂ fixation and could provide a useful guideline for further developing NRR electrocatalysts.