Density Functional Theory Investigation on the Nitrogen Reduction Mechanism in Two-Dimensional Transition-Metal Boride with Ordered Metal Vacancies

Abstract

The creation of ordered collective vacancies in experiment proves challenging within a two-dimensional lattice, resulting in a limited understanding of their impact on catalyst performance. Motivated by the successful experimental synthesis of monolayer molybdenum borides with precisely ordered metal vacancies [Zhou et al. Science 2021, 373, 801-805] through dealloying, the nitrogen reduction reaction (NRR) in monolayer borides was systematically investigated to elucidate the influence of such ordered metal vacancies on catalytic reactions and the underlying mechanisms. The results reveal that the N-containing intermediates tend to dissociate, facilitating the NRR process with reduced U_L. The emergence of ordered metal vacancies modulates the electronic properties of the catalyst and partially facilitates the decomposition of N-containing intermediates. However, the U_L for NRR in Mo_4/3B₂ and W_4/3B₂ exhibits a significant increase. The compromised electrochemical performance is explained through the development of a simple electronic descriptor of the d-p band center (Δd_M-p_B). Among these materials, Mo_4/3Sc_2/3B₂ exhibits the most superior catalytic activity with a U_L of -0.5 V and favorable NRR selectivity over the HER. Our results provide mechanistic insights into the role of ordered metal vacancies in transition-metal boride for the NRR and highlight a novel avenue toward the rational design of superior NRR catalysts.