Preparation And Oxygen Reduction Reaction Catalytic Activity Of Nitrogen Doped Graphene Base Electrocatalysts

Metal-air batteries,as a new generation of energy devices have attracted wide attention,due to the advantages of high energy density and environment-friendly.However,the slow reaction nature of air cathode(oxygen reduction process)restricts their developments and widespread applications.So,to develop high performance,high stability and low cost of oxygen reduction catalysts becomes the important issue.Nitrogen doped graphene not only can be used as a catalyst support,but itself also shows excellent catalytic activity toward oxygen reduction reaction(ORR).However,more devotions to intensive researches and practical applications on nitrogen doped graphene catalysts should be put.In this paper,we prepared the silver/ nitrogen doped graphene and manganese dioxide nanowire/nitrogen doped graphene composites by the facile hydrothermal reactions.Electrochemical tests exhibit the excellent catalytic activity and long-term stability of the composites toward ORR.Furthermore,we also investigate the active site of manganese dioxide nanowire/nitrogen doped graphene composite for ORR.The details of this dissertation are as follows:1)Graphene oxide(GO)are prepared by a modified Hummer method.In preparation of the 3D Ag/N-RGO composite gel,silver ammonia solution as the sources of nitrogen and silver is used during the hydrothermal reaction process in which the reduction of silver ions and doping of nitrogen atoms are simultaneously occurring.And the existence of silver is beneficial to the generation of pyridine nitrogen.Compared with the Ag/RGO,Ag/C and Ag+N-RGO mixed materials,Ag/N-RGO shows a well outstanding catalytic activity toward ORR.Moreover,its longterm durability is better than the commercial Pt/C catalyst in alkaline solution.2)Manganese dioxide nanowire/nitrogen doped graphene composites are prepared by the hydrothermal reaction method.By controlling temperature and reactant concentration,the structure of manganese dioxide nanowire and nitrogen doped graphene composite can be effectively tailored.The presence of graphene oxide is in favor of the formation of ?-MnO2,and the addition of urea is beneficial to the production of manganese dioxide nanowires with the fine diameter.Electrochemistry catalytic tests show that the composite catalysts exhibit high catalytic activity and long-term stability for ORR in alkaline electrolyte.Mg-air and zinc-air batteries tests also confirm their superior catalytic properties.3)In order to study the relationships between nitrogen configurations and ORR activity,we firstly prepared the nitrogen doped reduced graphene oxides with high nitrogen content by a hydrothermal method,and then obtained the different N configurations through heat treatments at the different temperatures.The study shows that nitrogen content is not a major factor to affect ORR activity of nitrogen doped reduced graphene oxides.The contents of graphitic N and pyridinic N are the key factors that decides the on-set potential and limiting current density of oxygen reduction process,respectively.Furthermore,we further research the catalytic activity of the manganese dioxide toward ORR.And we find the crystal structure,microstructure and specific surface of the manganese dioxide obviously affect their ORR activity which is related to the amounts of the activity sites.In general,? crystal structure and larger specific surface are good for ORR.