Hybrid Spinel Oxides/N-Doped Reduced Graphene Oxide as Highly-Active Bifunctional Electrocatalysts for Oxygen Reduction/Evolution Reactions

A series of Co3O4-MnCo2O4/N-doped reduced graphene oxide (CMO/N-rGO) electrocatalysts with different N-rGO content were developed by using a two-step synthetic method. The electrocatalysts were characterized by X-ray diffraction, scanning electron microscopy/transmission electron microscopy, and X-ray photoelectron spectroscopy. Their catalytic activities toward the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) were evaluated by linear-sweep voltammetry (LSV) in an alkaline electrolyte. It is found that GO is vital for the formation of CMO/N-rGO nanocomposite during the preparation. The CMO hybrid nanoparticles can be obtained through feeding GO during the preparation, but only the single spinel oxide, i.e. MnCo2O4, is formed without adding GO, even if the feeding molar ratio of Co and Mn (Co/Mn) is higher than 2. The CMO/N-rGO nanocomposite electrocatalysts can efficiently take advantages of ORR and OER active sites from the CMO hybrid oxides and N-rGO, as well as the enhanced charge transfer from N-rGO, thus bringing about higher bifunctional activities towards ORR/OER in alkaline electrolyte, as compared with Co3O4, MnCo2O4, and N-rGO. The CMO/N-rGO nanocomposites are considered to be promising bifunctional electrocatalysts for ORR/OER.