Redox‐Inert Fe3+ Ions in Octahedral Sites of Co‐Fe Spinel Oxides with Enhanced Oxygen Catalytic Activity for Rechargeable Zinc–Air Batteries

Bimetallic cobalt‐based spinel is sparking much interest, most notably for its excellent bifunctional performance. However, the effect of Fe3+ doping in Co3O4 spinel remains poorly understood, mainly because the surface state of a catalyst is difficult to characterize. Herein, a bifunctional oxygen electrode composed of spinel Co2FeO4/(Co0.72Fe0.28)Td(Co1.28Fe0.72)OctO4 nanoparticles grown on N‐doped carbon nanotubes (NCNTs) is designed, which exhibits superior performance to state‐of‐the‐art noble metal catalysts. Theoretical calculations and magnetic measurements reveal that the introduction of Fe3+ ions into the Co3O4 network causes delocalization of the Co 3d electrons and spin‐state transition. Fe3+ ions can effectively activate adjacent Co3+ ions under the action of both spin and charge effect, resulting in the enhanced intrinsic oxygen catalytic activity of the hybrid spinel Co2FeO4. This work provides not only a promising bifunctional electrode for zinc–air batteries, but also offers a new insight to understand the Co‐Fe spinel oxides for oxygen electrocatalysis. A bifunctional oxygen electrode composed of hybrid spinel Co2FeO4 nanoparticles grown on N‐doped carbon nanotubes is a promising candidate for zinc–air batteries. Theoretical calculations and magnetic measurements reveal that the introduction of Fe cations into the Co3O4 network causes Co 3d electron delocalization and spin‐state transition, resulting in enhanced catalytic activity of the as‐prepared spinel Co2FeO4.