Investigation of MnO2 and Ordered Mesoporous Carbon Composites as Electrocatalysts for Li-O2 Battery Applications

The electrocatalytic activities of the MnO2/C composites are examined in Li-O2 cells as the cathode catalysts. Hierarchically mesoporous carbon-supported manganese oxide (MnO2/C) composites are prepared using a combination of soft template and hydrothermal methods. The composites are characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, small angle X-ray scattering, The Brunauer–Emmett–Teller (BET) measurements, galvanostatic charge-discharge methods, and rotating ring-disk electrode (RRDE) measurements. The electrochemical tests indicate that the MnO2/C composites have excellent catalytic activity towards oxygen reduction reactions (ORRs) due to the larger surface area of ordered mesoporous carbon and higher catalytic activity of MnO2. The O2 solubility, diffusion rates of O2 and O2‚ ́ coefficients (DO2 and DO ́ 2 ), the rate constant (k f ) for producing O2‚ ́, and the propylene carbonate (PC)-electrolyte decomposition rate constant (k) of the MnO2/C material were measured by RRDE experiments in the 0.1 M TBAPF6/PC electrolyte. The values of k f and k for MnO2/C are 4.29 ˆ 10 ́2 cm ̈ s ́1 and 2.6 s ́1, respectively. The results indicate that the MnO2/C cathode catalyst has higher electrocatalytic activity for the first step of ORR to produce O2‚ ́ and achieves a faster PC-electrolyte decomposition rate.