Elongated heterometal double-sites promote nitrogen reduction on two-dimensional MM′B7 monolayers

Abstract

The efficient activation of the adsorbed N₂ is the initial and crucial step in the electrochemical nitrogen reduction reaction (NRR), but remains a long-standing challenge. Attaching long-distance heterometal M and M′ metals from the two ends of NN (like a curved bonding in Ag₂C₂) is an ingenious strategy to promote the activation and polarization of the intrinsic triple bond during electrocatalysis. Motivated by this strategy and the excellent stability and larger size of the B₇-unit, the global-minimum MM′B₇ monolayers with elongated heterometal double-sites as promising NRR electrocatalysts have been identified from the 10 179 candidates using high-throughput screening. The TiNbB₇ monolayer with a metal distance of 3.56 Å exhibits the optimal NRR catalytic activity with the limiting potential of 0.04 V and the kinetic energy barrier of 0.75 eV through the mixed mechanism, together with a strong capability of suppressing the competitive hydrogen evolution reaction and the surface oxidation. The other eight global-minimum systems (NbMoB₇, ScHfB₇, ScNbB₇, ScTaB₇, ScZrB₇, TiHfB₇, TiNbB₇ and ZrHfB₇) also possess excellent catalytic activity, and the highest limiting potential is only 0.62 V. These data adequately verify that long-distance heterometal double-sites are an excellent strategy to active and polarize the NN triple bond due to the elongated bonding length, asymmetric interaction and favorite orbital matching for the side-on adsorbed N₂ molecule on double-sites. Most importantly, this work opens a new avenue to design and develop efficient NRR electrocatalysts with the long-distance heterometal double-sites.