Decorating Co/CoN_x nanoparticles in nitrogen-doped carbon nanoarrays for flexible and rechargeable zinc-air batteries

Efficient and stable air cathodes which catalyze both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are highly desirable but challenging for flexible and rechargeable Zn-air batteries. Here we synthesize unique hybrid cobalt/cobalt nitride (Co/CoN_x) nanoparticles well-integrated with nitrogen-doped carbon (NC) nanoarrays through a facile fabrication using a two-dimensional metal–organic framework (MOF) precursor. Such NC-Co/CoN_x nanoarrays show promising bifunctional catalytic properties toward both ORR and OER, and can be directly used as an active and durable air cathode for flexible sandwich-like layered Zn-air batteries. In addition, a coaxial fiber-shaped solid-state Zn-air battery is assembled using a carbon microfiber covered with the NC-Co/CoN_x nanoarrays as the cathode, a Zn microfiber as the anode and a gel electrolyte. Such fiber-shaped Zn-air battery exhibits much enhanced volumetric power density coupled with good flexibility, showing promising application for flexible energy storage devices.