Modulation of Phase Transition in Cobalt Selenide with Simultaneous Construction of Heterojunctions for Highly‐Efficient Oxygen Electrocatalysis in Zinc–Air Battery

Abstract Phase transformation of cobalt selenide (CoSe₂) can effectively modulate its intrinsic electrocatalytic activity. However, enhancing electroconductivity and catalytic activity/stability of CoSe₂ still remains challenging. Heterostructure engineering may be feasible to optimize interfacial properties to promote the kinetics of oxygen electrocatalysis on a CoSe₂‐based catalyst. Herein, a heterostructure consisting of CoSe₂ and cobalt nitride (CoN) embedded in a hollow carbon cage is designed via a simultaneous phase/interface engineering strategy. Notably, the phase transition of orthorhombic‐CoSe₂ to cubic‐CoSe₂ (c‐CoSe₂) accompanied by in situ CoN formation is realized to build the c‐CoSe₂/CoN heterointerface, which exhibits excellent/highly stable activities for oxygen reduction/evolution reactions (ORR/OER). Notably, heterostructure can modulate the local coordination environment and increase Co‐Se/N bond lengths. Theoretical calculations show that Co‐site (c‐CoSe₂) with an electronic state near Fermi energy level is the main active site for ORR/OER.Energetical tailoring of the d‐orbital electronic structure of the Co atom of c‐CoSe₂ in heterostructure by in situ CoN incorporation lowers thermodynamic barriers for ORR/OER. Attractively, a zinc‐air battery with a c‐CoSe₂‐CoN cathode displays excellent cycling stability (250 h) and charge/discharge voltage loss (0.953/0.96 V). It highlights that heterointerface engineering provides an option for modulating the bifunctional activity of metal selenides with controlled phase transformation.