GNs-MnO2复合催化剂的制备及催化氧还原性能

Preparation and Oxygen Reduction Performance of GNs-MnO_2 composite

石墨烯由单层碳原子组成,具有大的比表面积和超高的导电性,广泛应用于催化与储能领域.本工作结合石墨烯独特的物理化学性质和结构特性,采用原位氧化还原法,以KMnO4和石墨烯(GNs)为原料合成GNs-MnO2氧还原催化剂,通过X射线衍射(XRD)、拉曼光谱(Raman)、透射电镜(TEM)、热重(TG)、BET等分析测试技术研究了纳米GNs-MnO2复合材料的微观结构特征.结果表明,合成的MnO2纳米线直接生长在石墨烯的表面,增加了MnO2的比表面积,提高了催化剂的活性位点.电化学测试表明,合成的GNs-MnO2催化剂在碱性介质中电催化氧还原电位比纯MnO2的氧还原电位正移80 mV,电流提高了1.3倍,在燃料电池氧还原电催化中有一定的应用前景.

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.