Effect of External Electric Field on Nitrogen Activation on a Trimetal Cluster

Abstract

Efficient nitrogen (N₂) fixation and activation under mild conditions are crucial for modern society. External electric fields (F_electric) can significantly affect N₂ activation. In this work, the effect of F_electric on N₂ activation by Nb₃ clusters supported in a sumanene bowl was studied by density functional theory calculations. Four typical systems at different stages of N-N activation were studied, including two intermediates and two transition states. The impact of F_electric on various properties related to N₂ activation was investigated, including the N-N bond length, overlap population density of states (OPDOS), total energy of the system, adsorption energy of N₂, decomposition of energy changes, and electron transfer. The sumanene not only functions as a support and protective substrate, but also serves as a donor or acceptor under different F_electric conditions. Negative F_electric is beneficial to N-N bond activation because it promotes electron transfer to the N-N region and improves the d-π* orbital hybridization between metals and N₂ in the activation process. Positive F_electric improves d-π* orbital hybridization only when the N-N is nearly dissociated. The microscopic mechanism of F_electric's effects provides insight into N₂ activation and theoretical guidance for the design of catalytic reaction conditions for nitrogen reduction reactions (NRR).

Keywords: Density functional theory; External electric field; Nitrogen activation; Nitrogen reduction reactions; Trimetallic cluster.