Electrocatalysts of Mn and Ru oxides loaded on MWCNTS with 3D structure and synergistic effect for rechargeable Li-O2 battery

Abstract

The structure and electrochemical activity of electrocatalysts play a vital role in lithium-oxygen battery. Herein, three-dimensional Mn and Ru oxides loaded on multiwall carbon nanotubes (RuO2-MnO2/MWCNTs) was synthesized via a one-pot hydrothermal approach and served as cathode of rechargeable lithium-oxygen (Li-O2) batteries. SEM and TEM images both illustrated that RuO2 nanoparticles and MnO2 nanoflakes are well dispersed on the surface of MWCNTs and formed a three-dimensional structure, the cyclic voltammetry studies revealed that the RuO2-MnO2/MWCNTs nanocomposite can effectively integrate the oxygen reduction reaction (ORR) activity of MnO2 and oxygen evolution reaction (OER) activity of RuO2. Electrochemical results demonstrated that the RuO2-MnO2/MWCNTs as oxygen cathode of Li–O2 batteries could maintain a reversible capacity of 1000 mAh g−1 within 94 cycles at a rate of 200 mA g−1 and within 120 cycles at a rate as high as 1000 mA g−1. Moreover, the cell with the catalyst RuO2-MnO2/MWCNTs presented much lower voltage polarization (about 0.68 V at a rate of 50 mA g−1) than that measured with MnO2/MWCNTs during charge/discharge processes. Ex-situ SEM were conducted to investigate the morphology and decomposition of Li2O2, which were formed after discharge and decomposed almost after charge process. The excellent electrochemical performance could be contributed to the three-dimensional structure which benefited the diffusion of oxygen and the storage of Li2O2 as well as the synergy effect of MWCNTs as an ideal conductive support for RuO2-MnO2 as co-catalyst in Li-O2 battery.