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- O-2 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 center dot- coefficients ( DO2 and DO -2), the rate constant ( kf) for producing O2 center dot-, 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 kf and k for MnO2/ C are 4.29 X 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 O-2 center dot - and achieves a faster PC- electrolyte decomposition rate.