Study On Controllable Fabrication Of MnO₂-Based Nanosheet Arrays For High Performance Supercapacitors

With the over-reliance on fossil fuels and the gradual deterioration of global climate and environment situations,extensive research efforts have currently been dedicated to develop clean and sustainable energy resources such as solar and wind power to combat climate change and to meet the ever-increasing energy demand.However,both wind and solar energy resources inevitably have intermittent and instability characteristics,and thus it is importance to study the matched energy storage technologies.Supercapacitors are a novel type of energy storage devices in between traditional capacitors and batteries,are strongly recommended to be one of the most promising energy storage devices which possess many advantages,such as high power density,long service life,fast charge-discharge and environmentally friendly.The electrode materials are the most important factors for the electrochemical properties of supercapacitors.MnO₂ has been investigated as one of the most attractive electrode materials for supercapacitors due to its natural abundance,low cost,environmentally friendly and high theoretical capacitance.However,the poor conductivity seriously limits its practical application.To directly growing nanosheet arrays structure MnO₂-based materials on conductive substrates has been widely studied,because they can not only preserve the advantages of MnO₂,but improve its electrical conductivity for high electrochemical performance.In this work,three kinds of MnO₂-based materials including ultra-thin NiMn₂O₄,?-MnO₂·1.07H₂O and Ni-doped?-MnO₂ nanosheet arrays on conductive substrates were fabricated.The morphology,composition and structure were studied by SEM,TEM,XRD,XPS,TGA.Electrochemical properties of those materials were characterized by cyclic voltammetry?CV?and galvanostatic charge-discharge?GCD?.The research content and the main conclusion are summarized as below:Ultra-thin NiMn₂O₄ nanosheet arrays on Ni foam were successfully fabricated by a simple hydrothermal method with manganese chloride as only precursor source and subsequent anealling.The thickness and density of nanosheets are controlled through controlling the synthesis temperature and time of hydrothermal reaction.The electrochemical performaces of the corresponding electrodes with different thickness and density of nanosheets are studied in detail.?-MnO₂·1.07H₂O nanosheets arrays on carbon cloth and carbon nanotube film were successfully fabricated by constant current electrodeposition method with Mn?CH₃COO?₂ as only precursor source.Pseudocapacitive performance of different?-MnO₂ film thicknesses was studied,it is found that the material thickness has a great influence on the electrochemical performance of?-MnO₂·1.07H₂O nanosheets when the thickness of active materials are below 0.86?m?1 mg/cm²?.Comparing with samples of carbon nanotube film substrates,the influence of material thickness on the electrochemical performance was verified.Ni-doped?-MnO₂ nanosheets were on carbon cloth were successfully fabricated by cyclic voltammetry electrodeposition method with aqueous solution containing Mn?CH₃COO?₂ and Ni?NO₃?₂ as source of manganese.The Ni-doped?-MnO₂ at a mass loading of 1.01 mg/cm² display excellent mass specific capacitance?601 F/g at a current density of 1 A/g?and good rate performance,because Ni-doped?-MnO₂ materials not only improve the conductivity,but also provide more electrochemical active sites for electrochemical charge storage.In this work,MnO₂-based materials with controllable morphology and structure were fabricated by employing different experimental methods and common chemicals.High specific capacitance and excellent cycling stability can be achieved,and the effect of mass loading's thickness and nickel doping on electrochemical properties was also studied.This study may provide some valuable ideas for optimizing property of supercapacitor electrode material.