Synthesis and characterization of CNT/MnO2 nanocomposites for application as active cathode materials in lithium-air batteries

Miscellaneous catalysts have been utilized as air cathodes such as noble metals like Pt, Au [1], and transition metal oxides like MnO2, Fe2O3, Co3O4 and their mixtures [2,3]. Since these catalysts are expensive (like noble metals) or have low electrical conductivity (like metal oxides), the CNT composites with metal oxides are applied to overcome the low conductivity and corrosion drawbacks [4]. A series of CNT–MnO2 nanocomposites containing different values of MnO2 were prepared for application as the cathode materials in the Li-O2 batteries to obtain the optimum rate. The optimum theoretical ratio of MnO2 to the CNT used in synthesis was 60% (w/wcarbon) but the TGA analysis confirmed that the exact MnO2/CNT ratio in the optimum catalyst was 41% (w/wtotal). The CNT–60% MnO2 nanocomposite was characterized by FE-SEM, TEM, XRD, EDS, TGA, FT-IR, and N2 adsorption-desorption analyses. The XRD pattern of CNT–60% MnO2 nanocomposite contained most of the peaks related to both the standard XRD pattern of MnO2 (PDF number 44-0141) and those of the MWCNT structure. The FE-SEM micrograph of the pristine MWCNT indicated that the CNT diameters were almost equal for both CNT and CNT/60%MnO2 composite (~30–40 nm) but in case of composite, the formation of MnO2 particles was evident on the CNT surface. The TEM image of the CNT/60% MnO2 nanocomposite revealed that the CNTs were covered with very fine MnO2 particles forming a layer around the CNT (coreshell system) with the synthesized nanocomposite had a diameter of about 25 nm and the diameter 14th Annual Electrochemistry Seminar of Iran Materials and Energy Research Center (MERC), 12- 13 Dec, 2018 181 of CNT was ranged between 10–15 nm. The N2 physisorption analysis showed a lower surface area for the CNT/60%MnO2 composite (80 m2/g) compared to that of the pristine CNT (103 m2/g) which was attributed to the deposition of the MnO2 nanoparticles over the CNT surface. The average pore volumes for the CNT and CNT-60% MnO2 are 0.2097 and 0.1462 cm3/g, respectively. All of the CNT/MnO2 nanocomposites were intended to be applied as the cathode materials in the Li-O2 batteries in order to achieve the optimum rate.