Controllable Preparation Of Cobalt/Iron Oxides And Their Application For Electrocatalytic Oxygen Reduction Reaction

With the development of social economy,energy consumption has brought about environmental pollution,air pollution and other issues.It posed serious challenges to human health and social development.As a kind of clean,efficient and sustainable energy devices,Fuel cells have attracted people's attention.Yet,the sluggish kinetics of oxygen reduction reaction is an important factor affecting the performance of the fuel cells.Platinum-based catalysts are the most widely used cathodic catalysts at present,but they are expensive and have limited resources.It is an effective way to develop cathodic oxygen reduction catalyst with low cost,highly efficient catalytic activity for application of commercial fuel cells.Metal organic frameworks?MOFs?are crystalline composites with porous structures,which are formed by orderly coordination of metal ions with organic functional groups.MOFs have the advantages of high chemical stability,thermal stability,large specific surface area,adjustable pore structure.They can be used in oxygen reduction reaction.Unlike precious metals,the reserves of iron,cobalt and nickel are very rich and extensive in the world.In this paper,MOFs materials were prepared based on iron,cobalt and nickel,and their electrocatalytic oxygen reduction properties were discussed.The research content is as follows:Co₃O₄-based metal organic frameworks?MOFs?were prepared by condensation reflux method and annealed in nitrogen.The materials were characterized by XRD,SEM and Raman spectroscopy.The oxygen reduction properties of the materials were tested by three-electrode system.In order to improve the oxygen reduction performance of the material,graphene was doped before preparation and phosphated in nitrogen.The results show that both treatments significantly enhance the electrocatalytic oxygen reduction performance of Co₃O₄,and the limiting current density increased significantly.Finally,the peak current of Co₃O₄-CoP@GO is 18.3%higher than that of the original Co₃O₄.The half-wave potential and limiting current density are better than that of Co₃O₄.The current density increased to 5.618mA/cm².Compared with single metal MOFs catalysts,MOFs based on binary metal oxides can effectively promote the adsorption and reduction of oxygen and greatly enhance the catalytic activity.MOFs materials were prepared by condensation reflux method based on binary compounds of three transition metals:iron,cobalt and nickel.CoFe₂O₄ exhibits uniform nanorod-like structure with a limit current density of 5.099mA/cm².which is 25.3%higher than MOFs based on Co₃O₄.The effects of graphene modification,phosphorus doping and oxygen vacancy concentration on the oxygen reduction performance of CoFe2O4 were studied.It was found that the half-wave potential of argon-hydrogen modified CoFe₂O₄ at 400?was 0.729 V vs RHE,and the limit current density of CoFe₂O₄@GO doped with sodium dihydrogen phosphate was the highest.It was 7.507 mA/cm²,47.2%higher than that of the original CoFe₂O₄.