Preparation And Performance Of Core/sheath Structrured Ultralong MnO_x/PPy With Oxygen Vacancies

Manganese oxide(MnOx)is widely used in catalysis and energy storage due to its special physicochemical properties.However,MnOx has some disadvantages of low utilization and poor conductivity,which can be overcome by adjusting the morphology or compounding with other materials.In this thesis,the catalytic performance of ultralong a-MnO2 nanowires with high ratio of exposed surface lattice and the capacitive performance of core/sheath structured ultralong MnOx/polypyrrole(PPy)nanowires with abundant oxygen vacancies(OVs)are studied.Ultralong MnO2 nanowires with 50-100 nm in diameter and 10?m in length are prepared by hydrothermal method.The ratio of exposed surface lattice is 5.3%.The high ratio of surface lattice exposure can be expected to be very important for rapidly and effectively catalytically degrading methylene blue(MB),a model pollutant.Ultralong MnO2 nanowires can effectively catalyze H2O2 to generate radicals for degrading MB and exhibit good structural and recycling stability at 5.0 ?.The MnO2 nanowires catalytically degrade 98.1%of MB at 5.0 ? within 30 min.The degradation efficiency is up to 93.0%after 5 cycles and the morphology and crystal phase of MnO2 nanowires have no obvious changes.The yield of ·OH radicals in the catalytic degradation system at 5.0 and 25.0 ? is 39.33 and 53.8 mg gMno2-1,respectively.The yield of ·O2-radicals is 1.29 and 1.68 mg 9MnO2-1,respectively.The yield of·OH radicals is 30 times more than that of ·O2-radicals at 5.0 ?,and the probability of collisions between radicals decreases at low temperature,so the high degradation efficiency at 5.0 ? is attributed to high radical content and full utilization ratio of radicals.This work provides a new material that quickly and efficiently degrades organic pollutants in low temperature areas to maintain a better environment.Core/sheath structured ultralong MnOx/PPy nanowires with abundant OVs are assembled by in-situ polymerization of pyrrole on MnO2 nanowires.The MnOx/PPy nanowires possess favorable features.Rich mesopores and large specific area shorten electrolyte ion diffusion path and time.Conductivity PPy sheath consists of characteristic nanoparticles and OVs improve conductivity.In addition,the PPy sheath inhibits the dissolution of MnO.in electrolyte and the structural instability of MnOx due to compositional and volumetric changes during charge/discharge process.The core/sheath structured ultralong MnOx/PPy nanowires shows 1)a larger specific capacitance of 1091.4 F gMnOx/ppy-1 and 1348.4 F gMnOx-1 at 1 A g-1,2)higher rate performance of 81.6%at 20 A g-1 and 3)better cycling stability with capacitance retention of 97.4%after 10000 cycles at 10 A g-1 than so far reported MnOx-based materials.The assembled asymmetrical supercapacitor with the core/sheath structured ultralong MnOx/PPy nanowires as positive electrode and activated carbon(AC)as negative electrode delivers a larger specific capacitance of 214.2 F g-1 and a maximum energy density of 144.0 W h kg-1 at a power density of 1100 W kg-1 than so far reported MnOx-based asymmetrical supercapacitor.This work provides a controllable assembly strategy of high-performance energy storage materials.