Synthesis And Electrochemical Performances Of Manganese Oxide Nanomaterials For Supercapacitor

With the rapid development of the global economy,traditional fossil fuels such as coal and petroleum have been gradually exhausted,more and more waste gas released from incomplete combustion of the fossil fuels and it seriously threatened the global environment and human health.So the improvement and utilization of energy storage devices are attracting more and more attention.Among them,supercapacitor has become an investigation subject for its outstanding merits.As we know,as a representative of noble electrode materials,ruthenium dioxide?RuO₂?has shown excellent electrochemical properties,but high cost and toxicity limit its wide application.Manganese oxides have become one of researching hotspots currently because of its high theoretical pseudocapacitance,abundant,low-cost and environmental compatibility,as well as various valence states.In this thesis,several manganese oxide nanoparticles and relative composites have been prepared through simple chemical methods,their structures and morphologies are characterized by using FT-IR spectra,X-ray powder diffraction?XRD?,scanning electron microscopy?SEM?and so on,electrochemical performances are studied in detail.Part 1:Mechanism for energy storage,composition and classification of supercapacitors were introduced and an advance study of the electrode materials were reviewed.Part 2:Using Mn?NO₃?₂ and KMnO₄ as raw materials,cetyl trimethyl ammonium bromide?CTAB?as structure-directing agent,starch as protective agent,rice flower-like spherical MnO₂ nanoparticles have been prepared at room temperature.They were successfully applied as electrode material of supercapacitor with a good electrochemical performance.At the current density of 0.5 A g^-1 the highest specific capacitance was 235.2 F g^-1 and when the current density was increased to tenfold,the specific capacitance could keep 67%.At a high current density of 10 A g^-1,the specific capacitance only lost 18%after 3000 cycles,showing excellent retention rate and cycling stability.Part 3:In order to improve further the capacitance properties of MnO₂,MnO₂/MWCNTs composite materials were prepared by combining MnO₂ with pre-oxidation MWCNTs using KMnO₄.The composite kept similar rice flower-like spherical morphology to original MnO₂,but the structure was more dispersive and looser with some uniformly distributed MWCNTs.This structural characteristic promised a more excellent electrochemical performance than original manganese oxide.At the current density of 0.5 A g^-1,its specific capacitance was 327.67 F g^-1,39%higher than MnO₂.And at a higher current density of 8 A g^-1,specific capacitance retained 86.36%and Coulombic efficiency maintained 100%after 3000cycles.Part 4:Different morphologies of MnCO₃ microspheres precursors were at first prepared by microemulsion and slow-diffusion methods respectively using Mn?NO₃?₂as raw material,Na₂CO₃ as precipitant and CTAB as surfactant.Then resulted cubic Mn₂O₃ nanoparticles were obtained by calcining the precursors at the same temperature.The structural analysis indicated that Mn₂O₃ particles synthesized by slow-diffusion method possessed more compact structure with higher crystallinity and the product obtained through microemulsion method was more disperse and showed a morphology of hollow and porous sphere composed of many ultrafine particles.Electrochemical investigations showed that Mn₂O₃ obtained by microemulsion method had better capacitance properties.