Preparation And Electrochemical Properties Of MnO₂/activated Carbon Composites

With the development of science and technology,the increase of population and environmental pollution,China's energy security is facing serious challenges.Therefore,it is urgent to solve the shortage of energy and increasingly serious environmental pollution,the development of high-performance environmental protection of new energy storage device has become the current research hot spot.Supercapacitor is a storage device between the performance of conventional capacitor and battery,because of the low conductivity of metal oxides and low energy density of carbon materials,the preparation of high-performance composite materials as electrode materials for supercapacitors has become an urgent problem to be solved.Due to the poor conductivity of metal oxides and the low energy density of carbon materials,synthesizing composites with excellent properties has become an urgent problem to be used as the electrode materials for supercapacitors.MnO₂ with low cost and low toxicity is considered to be a potential supercapacitor electrode material.What's more,activated carbon as a carrier of metal oxides can not only provide electrical double-layer capacitor,but also improve the electronic migration rate,conductivity,magnification performance and the utilization rate of metal oxides.Therefore,the idea of this paper is to combine activated carbon with MnO₂ to optimize the synthesis conditions of composite while improving the overall specific capacitance of the material.In this paper,the synthesis methods of the composite materials,Mn O₂ loading,the chemical structure of activated carbon surface and the choice of activated carbon on the electrochemical properties of composites were investigated.The structure and electrochemical properties of the composites were characterized through nitrogen adsorption,TEM,XRD,XPS,EDS,cyclic voltammetry and galvanostatic charge/discharge.In order to investigate the effect of the synthesis method of composite materials on the electrochemical properties of MnO₂/activated carbon composites,the activated carbon with K₂S activation?impregnation ratio 1:1?was used as a carrier.The composite materials were prepared by three methods included impregnation mixed heat treatment,ultrasonic method and hydrothermal method.The MnO₂/activated carbon composites were tested for electrochemical properties.It is found that the composites prepared by impregnation mixed heat treatment have relatively good dispersion state and obvious lattice stripes,and possess the most excellent electrochemical properties.The specific capacitance is up to 276 F/g at the scan rate of 5 mV/s increases by 117 F/g compared to the activated carbon.For studying the effect of MnO₂ mass loading on the electrochemical performance of MnO₂/activated carbon composite,the activated carbon with K₂S activation?impregnation ratio2:1?was used as raw material in this paper.The composites of different loading are prepared by impregnation mixed heat treatment,and the electrochemical properties are measured.The results showed that when the loading was 10%,the electrochemical performance of the composites was optimal.The specific capacitance of the 10%Mn O₂/activated carbon at the scan rate of 5 mV/s in the 2 M KOH electrolyte was as high as 294 F/g,after the cycle 5,000 times,the capacitance could still maintain the original 83.6%.What's more,the MnO₂ contributes greatly to the specific capacitance of the composites,although its contribution can still reach 36%of the theoretical value at the current density of the 8 A/g.The XRD pattern of the MnO₂ showed that the crystalline type belonged to?-MnO₂.For discussing the influence of the choice of activated carbon on the electrochemical properties of composite,different composites were produced by selecting activated carbon prepared by different activation methods,and their electrochemical performance test was carried out.The results showed that the specific capacitance of MnO₂/activated carbon composites of K₂S activated carbon was increased from 167 F/g of raw materials to 294 F/g,and the maximum increase was 127 F/g.The physical and chemistry combined activation method was second,and the physical activation method was the smallest.The comparative study showed that the activated carbon prepared by chemical activation method with developed pore structure was more favorable for the loading of MnO₂,and the specific capacitance of the corresponding composites has the most increase.In order to further explore the effect of the chemical structure of activated carbon on the electrochemical properties of composites,commercial coconut shell activated carbon was used as a carrier to load MnO₂.After surface chemical modification,composite materials with different surface chemical structure were prepared by impregnation mixed heat treatment method,and its electrochemical properties were characterized.The results showed that activated carbon had a high specific surface area up to 2000 m²/g and the proportion of mesopores increased to 52%after ammonia activation,and the specific capacitance of the composites prepared by the activated carbon oxidized could reach 243 F/g.Comparing all the composite materials,the more hydrophilic groups contained in the activated carbon,the greater the specific capacitance of the composites increases.In this paper,the cheap,porous and high specific surface area activated carbons were used as a carrier to load MnO₂.MnO₂/activated carbon composites with high performance were prepared by simple synthesis method for supercapacitor electrodes.The effects of the synthesis method of composite materials,MnO₂ loading,surface chemical structure and the selection of activated carbon on the electrochemical properties of composites were explored,which provided significant scientific support for the development of low cost and high-performance supercapacitors,and further promoted the research progress of the commercialization of composites.