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

Herein, a three-dimensional (3D) hierarchical porous Co 3 O 4 nanotube (Co 3 O 4 HPNT) network was prepared using a polypyrrole nanofiber (PPyNF) as a sacrificial template. When employed as a cathode for lithium-oxygen batteries, the 3D Co 3 O 4 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 Co 3 O 4 HPNT-based cathode after discharge/recharge showed reversible formation and decomposition of Li 2 O 2 . This superior performance is ascribed to the 3D web-like porous tubular structure, which facilitates rapid oxygen flow, provides enough void volume for insoluble Li 2 O 2 deposition, and increases the catalytic utilization of Co 3 O 4 . Moreover, the hierarchical porous structure with meso-/nanopores on the walls of the Co 3 O 4 nanotubes facilitates O 2 diffusion, electrolyte penetration, and mass transport of all the reactants.