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 (UL) 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-pz orbitals significantly improves the catalytic activity of the TCSACs. As a result, Fe-TCSAC achieves a high FECO 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.