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

The efficient activation of the adsorbed N-2 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 N equivalent to N (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 B-7-unit, the global-minimum MM ' B-7 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 angstrom 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 N equivalent to N triple bond due to the elongated bonding length, asymmetric interaction and favorite orbital matching for the side-on adsorbed N-2 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.

Automated summary

The efficient activation of adsorbed N-2 in the electrochemical nitrogen reduction reaction has been achieved using B-7 monolayers with elongated heterometal double-sites, with TiNbB7 demonstrating optimal catalytic activity. These catalysts not only exhibit excellent NRR performance, but also effectively suppress competitive reactions and surface oxidation.