Revealing the effects of conductive carbon materials on the cycling stability of rechargeable Zn-air batteries

Rechargeable zinc-air batteries (RZABs) are considered to be one of the promising electrochemical energy sources, and considerable efforts are devoted to high-performance bifunctional catalysts. Since the conductivity of catalysts is usually unsatisfactory, conductive carbon materials are needed in electrodes to provide the electron pathway. However, the effects of conductive carbon materials on the cycling stability of RZABs are usually overlooked. Herein, this topic is comprehensively investigated combing the electrochemical testes, in-situ oxygen monitor during charging, and characterization of the electrodes and electrolytes. Three kinds of electrodes made of bi-functional catalysts without additional carbon (N/A) and with Vulcan carbon (VC) and carbon nanotubes (CNT) are taken as examples. The results show that the CNT-based electrode releases the most oxygen under the same charging current density, which is 1.43 times that of the VC-based electrode and exhibits high stability in terms of voltage profile, structure morphology, and surface state. In addition, carbon corrosion is a serious issue for RZABs, which not only decreases the oxygen releasing efficiency but also contaminates the electrolyte. This work demonstrates the significant roles of conductive carbon materials in cycling stability and indicates that the in-situ gas analysis is essential to more rigorously evaluate the charging performance of RZABs.