Mn/Co oxide on Ni foam as a bifunctional catalyst for Li–air cells

Abstract

Binary Mn/Co oxide sheets with spherical flower-like hierarchical structure are grown directly on the surface of a Ni foam skeleton as a cathode for Li–O2 batteries using a hydrothermal method. This integrated cathode architecture eliminates the negative effects of a conductive carbon additive and binder on the electrochemical performance of Li–O2 batteries and minimizes the processing steps in fabrication of cathodes for Li–O2 batteries. The porous Ni foam acts as a scaffold and current collector, and the highly hierarchical porous flower-like structure of the binary Mn/Co oxide sheet acts as a highly active catalyst. Together, they facilitate effective diffusion of oxygen gas as well as rapid ion and electron conduction during electrochemical reactions. When assembled in Li–O2 cells, the prepared catalyst exhibits excellent catalytic activities, including the oxygen reduction and oxygen evolution reactions. In particular, the Li–O2 cell using the cathode delivers an extremely high specific discharge capacity of 9690 mAh g-1 under a applied specific current of 200 mA g-1 and operate successfully in a long lifespan of 66 cycles even under a high specific current of 600 mA g-1 and a limited discharge-charge capacity mode of 1000 mAh g-1. The simultaneous effect of the fast electron transport kinetics provided by the free-standing structure and the high catalytic activity of the binary Mn/Co oxide show promise for use in air electrodes for Li–O2 batteries.