Enhancement of the electrochemical performance of free-standing graphene electrodes with manganese dioxide and ruthenium nanocatalysts for lithium-oxygen batteries

Abstract

Hybrid ternary Graphene/Ruthenium/alpha-MnO2 (rGO/Ru/alpha-MnO2) flexible nanocomposite cathodes were fabricated via controlling both reduction and vacuum filtration processes without using a binder and conductive carbon additives for flexible Li-air battery system. To compare the electrochemical performance of the Graphene/Ruthenium/alpha-MnO2 cathodes, bare rGO and rGO/Ru free-standing cathodes were also manufactured. rGO cathodes with well-dispersed alpha-MnO2 nanowires and ruthenium nanoparticles were successfully synthesized and shown to dramatically increase (decrease) oxygen reduction (evolution) reactions. The enhancement on the electrochemical performance of the synthesized cathodes was attributed not only to catalysis effect of rutheniumand alpha-MnO2 but also well-stacked morphology of the nanocomposite architecture which enables increased oxygen flow between the layers and, hence boosted reaction kinetics. Physical characterization of the cathodes was carried out using FESEM, EDS, TEM, XRD, XPS and Raman spectroscopy. The discharge product of the cathodes was also evaluated using TEM and XPS. Electrochemical performances of the cathodes were evaluated by means of CV, EIS, galvanostatic charge-discharge and electrochemical cycling tests. Thanks to the synergetic effect of Ruthenium and alpha-MnO2 catalysts, our ternary rGO/Ru/alpha-MnO2 cathodes were shown to serve full discharge capacity of 2225 mAh/g while rGO/Ru can deliver only 1670 mAh/g. Besides, the cycling stability of the ternary rGO/Ru/alpha-MnO2 cathodes was shown for 50 cycles at 650 mAh/g capacity limited tests in assembled LieO(2) batteries. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.