Itinerant ferromagnetic half metallic cobalt-iron couples: 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 metals, 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)-N-x (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 a bifunctional electrocatalyst for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Specifically, the ferromagnetically coupled spin-polarized electrons in a half metal tend to attract oxygen molecules so as to stimulate ORR, while the formation of the O-O bond in OER requires spin conservation. The delocalized spin character (metallic spin of a half metal) guarantees the moderate binding strength of main reaction intermediates, i.e., *O-2, *O, *OH, and *OOH, which can be measured by the atomic spin moment in the reaction center (0.4-1.5 mu(B) 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.