Co/Co<sub>9</sub>S<sub>8</sub> Nanofibers Decorated\nwith Carbon Nanotubes as Oxygen Electrocatalysts for Zn–Air\nBatteries

The\nfundamental issues limiting the development of zinc–air\nbatteries (ZABs) are the slow kinetics of the oxygen reduction reaction\n(ORR) and the oxygen evolution reaction (OER) as well as the limited\noperating environment. Herein, a membrane air cathode with a unique\nnanostructure integrating superior bifunctional oxygen electrocatalytic\nactivity was prepared by electrospinning and a simple heat treatment\nstrategy. The membrane is composed of one-dimensional multilevel carbon\nnanofibers covered by the S, N codoped carbon nanotubes encapsulating\nthe nanoscale Co/Co<sub>9</sub>S<sub>8</sub> homogeneous heterostructure\n(Co/Co<sub>9</sub>S<sub>8</sub>@MCF). Because of the tailored built-in\nelectric field facilitating the transport of ions, the ohmic contact\nproperty of the heterostructure, and the intrinsic conductivity of\nthe carbon substrate promoting the electron transport of the overall\nmaterial, cross-linked carbon nanotubes with rich defects form a large\nspecific surface area and porous structure, which provide a pathway\nfor ion transport, and the encapsulation of the heterostructure by\ncarbon nanotubes enhances the stability of the nanostructure; the\nsynthesized Co/Co<sub>9</sub>S<sub>8</sub>@MCF exhibits superior bifunctional\nelectrocatalytic properties. The aqueous ZAB based on the Co/Co<sub>9</sub>S<sub>8</sub>@MCF air cathode demonstrates a peak power density\nof 225.32 mW cm<sup>–2</sup>, a high discharge specific capacity\nof 719.52 mAh g<sup>–1</sup>, and long-term cycling stability\nfor over 200 h at 5 mA cm<sup>–2</sup>. Therefore, designing\nthe internal and external nanostructures of the heterostructure provides\nan opportunity for preparing high-performance ZABs.