Preparation and oxygen reduction performance of GNs-MnO2 composite

Abstract

As a single layer of carbon atoms covalently bonded into a hexagonal lattice, graphene exhibits a wide range of fascinating physical properties, such as remarkable charge-carrier mobility, unique graphitic basal plane structure, excellent conductivity, and a high surface area. These properties lead to very promising applications of graphene in electronic devices, catalysts, and energy-storage devices. In this work, the MnO2 and GNs-MnO2 composites were prepared by an in situ redox reaction of graphene (GNs) with KMnO4. The microstructure and morphology of the as-prepared materials were characterized by using X-ray diffraction (XRD), Raman measurements, thermogravimetric analysis (TGA), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller spectrometry (BET). The results show the obtained MnO2 uniformly anchored on the surface of graphene sheets and increased its specific surface area, which could enhance the electrochemically active surface area and utilization of MnO2. The GNs content of the GNs-MnO2 composites is caculated by according to TG analysis of the product, which reach to 36.2%. The electrocatalytic properties of the GNs-MnO2 and pure MnO2 electrodes are investigated for oxygen reduction reaction by cyclic voltammetry, linear sweep voltammetry (LSV) and rotating disk electrode (RDE) measurements. It is found that the obtained GNs-MnO2 electrocatalyst show superior electrocatalytic activity toward the oxygen reduction reaction (ORR) in alkaline electrolytes via a two-electron pathway. The half-wave potential of GNs-MnO2 for the reduction of O2 shift positively ca. 80 mV and the current density is 1.3 times higher than that of pure MnO2, which may because of the highly porous architectures and high specific surface area of GNs-MnO2. Our work, not only successfully develops a low cost GNs-MnO2 composites with excellent electrocatalytic activity, it also reveals further insight into the ORR mechanism of GNs-MnO2 composites as ORR catalyst. These results could provide useful information to further clarify the ORR mechanism of metal oxide/carbon materials, and further develop other novel low-cost metal oxides/carbon hybrids with high activities for practical fuel cell application. © 2013 Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences.