Preparation And Electrochemical Properties Of Manganese-based Electrode Materials

Scientists from various countries have already developed new energy materials and new electrochemical energy storage devices as the research focus to ease the energy crisis,reduce environmental pollution and realize the sustainable development of human society.Supercapacitors,with the advantages of short recharging period,high power density,long cycling life and little environmental pollution,are considered to be a promising energy storage devices.As another new type of portable source,zinc-air batteries possess many advantages,such as high energy density,stable discharge and environmental friendliness.As the core material of the two devices,electrode material has a direct impact on its comprehensive performance and industrialization process.Available and cheap manganese compounds are studied in this paper.The composition and microstructure of the obtained samples was investigated by XRD,TEM,SEM and BET,combined with a series of electrochemical tests(CV,GCD,EIS,etc.).The purpose is to clarify the energy storage mechanism in alkaline and neutral electrolyte as supercapacitors materials and explore the practical performance in zinc-air batteries.Three manganese based compounds of different manganese oxidation states were synthesized using potassium permanganate as the manganese source and sucrose as reducing agent.The electrochemical behaviors in KOH and Na2SO4 solutions were compared and analyzed by fitting the sweep rate and peak current in the cyclic voltammogram.The two processes were both found to be a combination of diffusion control and adsorption control.For KOH electrolyte,the greater influence of adsorption control in redox reaction,the better performance it showed and the reaction was closer to the capacitance process,while in Na2SO4 solution,the tendency to the diffusion control means higher specific capacity,and the reaction was more biased towards the battery process,indicating it was OH-interacts with the electrode material in the KOH solution rather than intercalation/deintercalation of the metal cations like Na2SO4 solution.In addition,the rice-like Mn2O3 exhibited a very high specific capacity,when the current density was 0.5 A g-1,the discharge specific capacity could reach 304 F g-1 in the 2 M KOH electrolyte.In terms of electrocatalysts,a regular dumbbell-like manganese carbonate was synthesized through the hydrothermal method with sodium citrate as structure-directing agent.Dumbbell-like manganese carbonate was creatively used as a bifunction electrocatalyst for air electrode,which not only had better oxygen evolution performance than commercial platinum carbon,but also exhibited good oxygen reduction activity close to platinum carbon.The test results of zinc-air battery showed that the dumbbell-like manganese carbonate possessed lower overpotential,good charge-discharge performance and cycling stability,demonstrating it was a type of non-precious metal catalyst with great research value.Moreover,by comparing with the bulk manganese carbonate prepared in the absence of sodium citrate,it was believed that the good electrochemical performance was due to the loose structure at the edge of dumbbell-like microcrystal,which could provide more active sites and was conducive to charge transfer during the reaction.