Regulating the charge densities of s-Block calcium single-atom site catalysts for efficient N2 activation and reduction

Abstract

The s-block alkaline earth metal (AM) sites in single atom catalysts (SACs) present promising potential for catalyzing reactions but their application to the N2 electroreduction reaction (eNRR) has so far received little attention. Using first-principles calculations, we propose an effective strategy for regulating the d orbital-related electronic structures of s-block calcium (Ca) in a single-atom-based catalyst for driving the eNRR. In contrast to previous AM SAC studies that involve only s and p valence orbitals, we show that the d orbitals of a Ca atom can be effectively utilized for N2 activation and reduction. The filled Ca d orbital can perform Ca-to-N back-donation by interacting with an antibonding orbital of N2, thus weakening the NN bond. Changes in the local N coordination structure and number regulate the d orbital-related electronic structures of the Ca atom, resulting in moderately positive charge densities on Ca. As a result, the adsorption behavior of key intermediates, especially the *N-*NH, can be optimized, which greatly promotes N2 reduction to NH3. Utilization of a d orbital thus provides a new dimension for designing s-block metal catalysts for efficient catalysis of reactions.