Unraveling the mechanism of modulating external electric fields for regulating nitrogen fixation and activation on three-atom metal clusters

Abstract

Efficient N2 fixation and activation under mild conditions are critical for green ammonia synthesis. Coupling external electric fields with three-atom transition metal clusters is a promising approach to realizing this vision. Herein, we report an effective strategy by modulating external electric fields to regulate the adsorption and activation of N2 on Sc3. The mechanism is further elucidated through DFT calculations. The most favorable adsorption site for N2 is the hollow site of Sc3. Although external electric fields inhibit the adsorption process of N2 on Sc3, the adsorbing performance of Sc3 is still very superior. Positive fields promote the activation and polarization of the adsorbed dinitrogen on the three-atom cluster, and negative fields have the opposite effect. The synergistic effect of positive/negative electric fields and Sc3 regulates the charge distribution of NN* in different ways. Furthermore, the d-band center (relative to the Fermi level), which determines the adsorption strength of N2, is affected by both positive and negative fields, resulting from the electron donation and back-donation mechanism between the NN* and the Sc3. This work provides guidelines for designing surface-anchored three-atom clusters with superior ammonia synthesis performance under electric fields in the future.