Promoting electrocatalytic nitrogen reduction by introducing low-spin sites in ferromagnetic single-atom alloys†

In ferromagnetic single-atom alloys (FM-SAAs), dopants tend to be induced with local spin moments, providing them with unique electronic structures that can be used as active sites in electrocatalytic nitrogen reduction reactions (e-NRR). Here, we use density functional theory to study the e-NRR activity and selectivity trends of the catalysts doped with 21 different transition metals, namely TM–Fe(110). We reveal the scaling relationships between the d-band centers and the N₂ adsorption free energy, as well as between the N₂ adsorption free energy and the limiting potentials of the catalysts. Due to variations in the magnetic coupling effects between the dopants of different periods and the host metal, the types of the d-band centers in the scaling relationships are divided into the catalyst d-band center (for the fourth-period catalysts) and the dopant d-band center (for the fifth- and sixth-period catalysts). As the valence electrons and spin moments of the dopants vary, we further introduce the average electron spin moment (P) of the dopants, and establish the volcano relationship between P and the activity and selectivity of the catalysts. We find that the catalytic activity and selectivity increase when the P of the dopant is close to zero. N₂ adsorption is a prerequisite and a key process for e-NRR. By introducing dopants with low-spin sites (Zr, Nb and Hf), the N₂ adsorption capacity of the active sites can be improved, which is favorable for promoting e-NRR. Our results reveal the relationships between the spin-dependent electronic structures of FM-SAAs and their N₂ adsorption capacity, e-NRR activity and selectivity, providing theoretical guidance for the preparation of efficient catalysts.