Spin-State Effect of Tetrahedron-Coordinated Single-Atom Catalysts on CO₂ Electroreduction

Spin state of active sites is one of the most influencing factors for the catalytic performance of electrocatalysts. To date, most modulations are conducted on non-tetrahedrally coordinated metal sites, while tetrahedron-coordinated single-atom catalysts (TCSACs) have not been investigated yet. This article presents a correlation between the spin state of TCSACs and their activities toward CO₂ electroreduction. TCSACs are made using ZnO as the substrate. The spin states of metal sites of TCSACs modulate the interactions between the catalyst and adsorbed intermediates. A volcano relationship is found between the transition metal (TM) magnetic moments and the limiting potential (U_L) of the CO₂ reduction reaction. Spin-state analysis indicates that the intermediate spin state of TMs is more favorable for the adsorption and conversion of CO₂. Optimal interaction between the TM-t₂ orbitals of the intermediate spin and the adsorbed molecule-p_z orbitals significantly improves the catalytic activity of the TCSACs. As a result, Fe-TCSAC achieves a high FE_CO of 91.6% at −0.9 V vs RHE. These results provide a theoretical basis and guidelines for the spin-state effects of tetrahedron-coordinated single-atom catalysts.