Ternary Spinel MCo2O4 (M = Mn, Fe, Ni, and Zn) Porous Nanorods as Bifunctional Cathode Materials for Lithium-O2 Batteries

The development of Li-O-2 battery electrocatalysts has been extensively explored recently. The Co3O4 oxide has attracted much attention because of its bifunctional activity and high abundance. In the present study, toxic Co2+ has been replaced through the substitution on the tetrahedral spinel A site ions with environmental friendly metals (Mn2+, Fe2+, Ni2+, and Zn2+), and porous nanorod structure are formed. Among these spinel MCo2O4 cathodes, the FeCo2O4 surface has the highest Co3+ ratio. Thus, oxygen can be easily adsorbed onto the active sites. In addition, Fe2+ in the tetrahedral site can easily release electrons to reduce oxygen and oxidize to half electron filled Fe3+. The FeCo2O4 cathode exhibits the highest discharging plateau and lowest charging plateau as shown by the charge-discharge profile. Moreover, the porous FeCo2O4 nanorods can also facilitate achieving high capacity and good cycling performance, which are beneficial for O-2 diffusion channels and Li2O2 formation/decomposition pathways.