A 3D hierarchical porous Co3O4 nanotube network as an efficient cathode for rechargeable lithium–oxygen batteries

Herein, a three-dimensional (3D) hierarchical porous Co3O4 nanotube (Co3O4 HPNT) network was prepared using a polypyrrole nanofiber (PPyNF) as a sacrificial template. When employed as a cathode for lithium–oxygen batteries, the 3D Co3O4 HPNT network demonstrated superior bifunctional electrocatalytic activities towards both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), with a relatively low charge overpotential of 99 mV and a high discharge/charge capacity of 4164/4299 mA h g−1. High-resolution scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy measurements on Co3O4 HPNT-based cathode after discharge/recharge showed reversible formation and decomposition of Li2O2. This superior performance is ascribed to the 3D web-like porous tubular structure, which facilitates rapid oxygen flow, provides enough void volume for insoluble Li2O2 deposition, and increases the catalytic utilization of Co3O4. Moreover, the hierarchical porous structure with meso-/nanopores on the walls of the Co3O4 nanotubes facilitates O2 diffusion, electrolyte penetration, and mass transport of all the reactants.