Development of rgo/ru/α-mno2 nanocomposite flexible cathodes for li-air batteries

Keywords: Ru, α-MnO2, lithium air cell, free-standing electrode, electrochemical performance. Increasing demand for electronic devices and tools has triggered an interest in high capacity and efficiently operate batteries. Therefore, lithium-air batteries seem as an alternative promising battery technology in terms of their specific energy density when compared to commercial lithium-ion batteries. In this thesis, two different reduction methods, thermal and chemical reduction processes utilized to produce Graphene, Graphene/Ru flexible free-standing cathodes. Because the chemical reduction process supplied a better performance compared to the thermal reduction, Graphene/Ruthenium/α-MnO2 (rGO/Ru/ α-MnO2) flexible hybrid nanocomposite cathodes prepared using this process without an addition of binder and conductive carbon. The electrochemical performances of as-produces rGO, rGO/Ru, and rGO/Ru/ α-MnO2 cathodes performed and the contribution of Ru and α-MnO2 catalyst were determined. Surface morphologies of the rGO, rGO/Ru, and rGO/Ru/α-MnO2 air-breathing cathodes were characterized using FESEM and TEM analysis. The elemental composition of the cathodes and distribution of the α-MnO2 and Ru catalysts were investigated using EDS and EDS-mapping, respectively. Phase structures of the cathodes were determined using Raman spectroscopy and XRD. Electrochemical performances of the cathodes were carried out using CV, EIS, galvanostatic charge-discharge, and electrochemical cycling tests. As a result, well-assembled α-MnO2 nanowire supported and ruthenium nanoparticles loaded graphene hybrid nanocomposite was obtained, and a successful reduction on the OER and dramatic increase on the ORR were observed with the help of ruthenium and α-MnO2 catalysts. It is reported that the rGO/Ru/α-MnO2 cathodes showed 2225 mAh/g while rGO/Ru demonstrated only 1670 mAh/g full discharge capacities. On the other hand, rGO/Ru/α-MnO2 exhibited 650 mAh/g stable discharge capacity up to 50 cycles due to the increment on the reversible Li2O2 formation kinetics with the synergistic effect of Ruthenium and α-MnO2 catalysts.