Synthesis Of Manganese Dioxide And Carbon Nanotube Composite Materials And Their Electrochemical Performance For Supercapacitors

As a new energy storage device, electrochemical capacitors （also called supercapacitor）have drawn much attention due to their high power density and extremely long cycling life.Owing to its superior capacitive performance, abundance and environmental friendliness,manganese dioxide （MnO₂） has become a spotlight among many potential materials forsupercapacitor application. Combining MnO₂with various carbon materials is an effectiveway to improve its electronic conductivity and electrochemical capacitive performance.In this work, we used carbon nanotube （CNT） both as reducing agent and as support.Potassium permanganate was reduced directly by CNT and the product MnO₂deposited ontothe surface of CNTs to form MnO₂/CNT nanocomposite. This synthetic method, which ismuch simpler than traditional chemical co-deposition method, is also helpful for the uniformdispersion of MnO₂nanosheets. We used FE-SEM and EIS to explore the influence ofmorphology and electronic conductivity on the capacitive performance. On such basis, inorder to maintain the conductivity of CNT to the maxmuim potential, we designed a newsynthetic strategy for capacitance improvement. The strategy presented here is to construct aself-sacrificed reductant layer on the surface of CNT for the subsequent reductive depositionof MnO4-. The conductivity of the resulting MnO₂/CNT composite is enhanced greatly, whichleads to the improved specific capacitance.In addition, we prepared phosphorus-doped carbon nanotube and evaluated the variationof morphology and electronic property brought by Phosphorous-doping. We used P-dopedCNT as substrate for the loading of MnO₂. The characterization results reveal the degradationof capacitive performance brought by P-doping, which provide us a reverse proof on theimportance of the electronic conductivity and porosity to the capacitive behavior of compositematerials. The improvement of electronic conductivity and the optimization of pore structurewas proved to be helpful for the capacitive performance.The research conducted in this work is valuable for optimizing the synthetic method andimproving specific capacitance of materials.