Co/Co9S8 Nanofibers Decorated with Carbon Nanotubes as Oxygen Electrocatalysts for Zn-Air Batteries

The fundamental issues limiting the development of zinc-air batteries (ZABs) are the slow kinetics of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) as well as the limited operating environment. Herein, a membrane air cathode with a unique nanostructure integrating superior bifunctional oxygen electrocatalytic activity was prepared by electrospinning and a simple heat treatment strategy. The membrane is composed of one-dimensional multilevel carbon nanofibers covered by the S, N codoped carbon nanotubes encapsulating the nanoscale Co/Co9S8 homogeneous heterostructure (Co/Co9S8@MCF). Because of the tailored built-in electric field facilitating the transport of ions, the ohmic contact property of the heterostructure, and the intrinsic conductivity of the carbon substrate promoting the electron transport of the overall material, cross-linked carbon nanotubes with rich defects form a large specific surface area and porous structure, which provide a pathway for ion transport, and the encapsulation of the heterostructure by carbon nanotubes enhances the stability of the nanostructure; the synthesized Co/Co9S8@MCF exhibits superior bifunctional electrocatalytic properties. The aqueous ZAB based on the Co/Co9S8@MCF air cathode demonstrates a peak power density of 225.32 mW cm-2, a high discharge specific capacity of 719.52 mAh g-1, and long-term cycling stability for over 200 h at 5 mA cm-2. Therefore, designing the internal and external nanostructures of the heterostructure provides an opportunity for preparing high-performance ZABs.