Manganese Oxides:Synthesis, Characteriazation And Electrochemical Applications

To develop of a high-performance catalyst for air electrode can greatly improve the ability of power output and reduce the cost of Aluminum/air battery, which is of great significance for reaserch. In this paper, in order to improve the catalytic activity of the manganese oxide, the strategies to achieve the superfine nanoparticles with high specific surface area and special morphology nanomaterials with certain crystal face exposure by controllable synthesis. By modified coprecipitation method and hydrothermal process, we prepared a series of manganese oxide catalysts. Meanwhile, to further expand the application of these materials, octahedral LiMn2O4nanomaterials were successfully achieved by the lithiation of the octahedral Mn3O4. Combining the electrochemical test and structure characterizations, we discussed the correlations between material microstructure and electrochemical performance.MnOx/CeO2solid solution was first proposed as a high activity ORR electrocatalyst for air electrode in Aluminum/air battery. A series of MnOx/CeO2solid solutions were fabricated by a modified co-precipitation method. The influence of ratio of Mn/Ce, calcining temperature on electricatalytic activity to MnOx/CeO2solid solutions were investigated in details. Experimental results revealed that the air electrodes with MnOx/CeO2composite oxides exhibited superior power performance than pure MnO2when used as metal/air battery probably due to both effective activation of molecular oxygen and higher surface area. In detail, oxygen transfer from molecular oxygen to Mn4+active sites through CeO2in the solid solution realized the effective activation of molecular oxygen. On the other hand, the higher surface area of solid solution could significantly increase the reaction sites of O2reduction at a three-phase boundary. Therefore, the effective activation of molecular oxygen and high surface area give us the good explanations for the much improved performance under high discharge current density for the air electrode with MnOx/CeO2solid solution.Without using any surfactant or template agent, well-shaped octahedral Mn3O4was easily obtained by the mild hydrothermal reaction of KMnO4in water/N, N-dimethyl formamide (DMF) mixed solution. We studied the influence of different content of DMF and hydrothermal reaction temperature on the morphology of the product. The time evolution of the reaction was recorded in order to trace the growth of the Mn3O4octahedron. This anisotropic crystal growth followed a self-assembly mechanism and then an Ostwald ripening mechanism. Taking electrochemical measurements into consideration, It was believed that the certain exposed facet of the Truncated Mn3O4octahedron was cnsidered to be the main reason for such higher electrochemical performance in comparison with of Mn3O4nanoparticles.As follows, we reported the synthesis of single-crystalline octahedral LiMn2O4particles by a two-step method in which well-shaped octahedral Mn3O4was easily obtained by the hydrothermal reaction of KMnO4in water/N, N-dimethyl formamide(DMF) mixed solution and then transferred to LiMn2O4by the solid-state lithiation process. High crystallinity and phase purity were also observed. When used as cathode for Li-ion battery, the octahedral LiMn2O4particles demonstrated superior electrochemical properties in comparison with the LiMn2O4particles by sol-gel method. A high initial discharge capacity of122.7mAh g-1was exhibited at1C-rate and104mAh g-1was maintained after200cycles for octahedral LiMn2O4. And good rate capability was also achieved. The excellent electrochemical properties should be mainly attributed to the following two factors:(1) the special octahedral morphology, which can restrain the Mn dissolution;(2) single crystalline nature and high crystallinity.