Demagnetization-driven enhancement of electrochemical nitrogen reduction on two-dimensional magnetic transition metal borides

Abstract

The development of efficient electrocatalysts with high activity and selectivity for the electrochemical nitrogen reduction reaction (eNRR) is of great importance for sustainable ammonia production. Ammonia production via electrochemical processes currently faces two critical challenges: (i) intrinsically low catalytic activity due to the strong triple bond of N₂ and (ii) poor selectivity caused by the competitive two-electron hydrogen evolution pathway. In this work, we demonstrate that two-dimensional (2D) hexagonal M₃B₄ (h-M₃B₄, M = Mn, Fe, Cr) magnetic compounds can serve as promising eNRR electrocatalysts through a demagnetization strategy. Specifically, the theoretical limiting potentials of nonmagnetic h-Mn₃B₄ and h-Fe₃B₄ are significantly reduced to −0.29 V and −0.42 V, respectively, compared to their magnetic counterparts (−0.99 V for Mn₃B₄ and −1.62 V for Fe₃B₄). Notably, h-Cr₃B₄ exhibits excellent catalytic activity in both magnetic (−0.24 V) and nonmagnetic (−0.30 V) states, indicating weak dependence on magnetism. All three materials exhibit lower limiting potentials than that of the stepped Ru(0001) surface (−0.43 V), which is widely regarded as one of the most effective noble-metal eNRR catalysts. Kinetic analyses reveal that magnetic moment quenching substantially lifts the energy barrier for the transition from side-on to top-on N₂ adsorption configurations, thereby favoring a consecutive reaction pathway with reduced limiting potential. The spin-mediated effects governing the eNRR activity of h-M₃B₄ compounds are further elucidated using the d-band center model. This study highlights the critical role of spin states in modulating eNRR performance and provides new insights into the design of high-performance 2D catalysts through magnetic-state engineering.