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

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.