Itinerant ferromagnetic half metallic Cobalt−Iron couple: promising bifunctional electrocatalysts for ORR and OER
Spin polarization has been recently recognized as a critical factor that affects the catalytic behavior of electrocatalysts. Half metal, with an exotic quantum state of 100% spin-polarized conduction electrons, and the spin associated atomic magnetization could show great potential in catalyst applications, however the corresponding research is insufficient. In this work, a prototype study of (Co and/or Fe)-Nx (x = 1 - 6) embedded configurations (FeCoNx-gra) is conducted within density functional theory (DFT) via spin-polarized calculation. The results indicate that, an itinerant ferromagnetic half metal can be recognized as a promising candidate for bifunctional electrocatalyst for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Specifically, the ferromagnetically coupled spin-polarized electrons in half metal tend to attract oxygen molecular so as to stimulate ORR, while the formation of O-O bond in OER requires spin conservation. The delocalized spin character(metallic spin of half metal) guarantees the moderate binding strength of main reaction intermediates, i.e., *O2, *O, *OH, and *OOH, which can be measured by the atomic spin moment in the reaction center (0.4 - 1.5µB for Fe in this study). This study identifies a new specific link between the electron structure and catalytic activities which has predictive power for catalyst design.