Modulation of Phase Transition in Cobalt Selenide with Simultaneous Construction of Heterojunctions for Highly-efficient Oxygen Electrocatalysis in Zinc-Air Battery.

Phase-transformation of cobalt selenide (CoSe 2 ) can effectively modulate its intrinsic electrocatalytic activity. However, enhancing electroconductivity and catalytic activity/stability of CoSe 2 still remains challenging. Heterostructure engineering may be feasible to optimize interfacial property to promote the kinetics of oxygen electrocatalysis on CoSe 2 -based catalyst. Herein, a heterostructure consisting of CoSe 2 and cobalt nitride (CoN) embedded in a hollow carbon-cage is designed via a simultaneous phase/interface engineering strategy. Notably, phase transition of orthorhombic-CoSe 2 to cubic-CoSe 2 accompanied by in-situ CoN formation is realized to build the c-CoSe 2 /CoN heterointerface, which exhibits excellent/highly-stable activities for oxygen reduction/evolution reactions (ORR/OER). Notably, heterostructure can modulate local coordination environment and increase Co-Se/N bond lengths. Theoretical calculations show that Co-site (c-CoSe 2 ) with electronic state near Fermi energy level is main active sites for ORR/OER. Energetical tailoring of d-orbital electronic structure of Co atom of c-CoSe 2 in heterostructure by in-situ CoN incorporation lowers thermodynamic barriers for ORR/OER. Bader charge analyses reveal that the internal electron transfer from c-CoSe 2 to CoN affords high ORR/OER activities. Attractively, a zinc-air battery with c-CoSe 2 -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 bifunctional activity of metal selenides with controlled phase-transformation. This article is protected by copyright. All rights reserved.