Catalytic characteristics of MnO2 nanostructures for the O2 reduction process

Nanorods with an alpha type MnO2 structure and a diameter ranging from 25 to 40 nm, along with tipped needles with a beta MnO2 structure and a diameter of 100 nm were obtained. The 25 nm diameter alpha MnO2 nanorods showed the best catalytic activity for dissociation of HO2- formed during oxygen reduction in a KOH solution. The MnO2 nanostructures preferably followed a two-electron oxygen reduction mechanism in a LiOH solution. The size of the catalyst also affected the specific capacities of the non-aqueous Li/O-2 batteries fabricated using the MnO2 based air electrode. The highest specific capacity of 1917 mA h g(-1) was obtained for an alpha MnO2 nanorod catalyst having a diameter of 25 nm. The cation present in the MnO2 nanostructures appears to determine the catalytic activity of MnO2.