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 (D and D), the rate constant (k) for producing O 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 and k for MnOC are 4.29 × 10 cm·s and 2.6 s, 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.