Study On Controllable Growth And Electrochemical Performance Of MnO₂ Nanomaterials Assisted By Templates

Due to high specific capacitance,low price and biocompatibility of MnO₂,it is considered to have great application potential in electrochemical energy storage.The electrode material is a decisive factor affecting the property of electrochemical capacitors.MnO₂ is rich in crystalline structure and surface chemical defects,which make MnO₂ exhibit different electrochemical properties.Therefore,the controllable synthesized MnO₂ with different morphologies and the specific structure have been drawn the attention of researches.In this work,MnO₂ nanomaterials with different structures and morphologies are systematically prepared by template methods,then its electrochemical properties are carefully studied,which develops accurate and reliable ideas for the preparation and application of MnO₂ and other nanomaterials.The crucial method and conclusions are as follows:Firstly,?-MnO₂ nanoplates with low crystallinity were patiently fabricated at normal temperature by using Mn(NO₃)₂ as the Mn source,which was used as a sacrifice template to synthesize?-MnO₂ nanofibers.The concentration of Na OH solution,duration and temperature in the hydrothermal solution were all the keys to support the nanosheets transform into nanofibers.In addition,the electrochemical performance after hydrothermal transformation was significantly improved compared to the?-MnO₂nanosheets.The work also provided guidance for later research.Secondly,using KMnO₄ as the Mn source and Cu NWs as the sacrificial templates,the low-crystallinity?-MnO₂ nanotubes were rapidly synthesized through oxidation etching at normal temperature,exhibiting a high specific capacitance of 384.6 F g^-1 at a current density of 0.25 A g^-1.The low-crystalline nanotubes can be further grown or transformed into Mn₃O₄ nanotubes through calcination.Besides,its crystallinity can be improved through hydrothermal treatment to enhance the cycle stability of?-MnO₂nanotubes.The work laid an essential foundation to research the MnO₂parallel sheets.Finally,A three-dimensional networks template was prepared using Mn(NO₃)₂ as a raw material,and the directional connection with the template was constructed to form a MnO₂ parallel sheet array structure.The influences of acid,reaction time and pre-calcination on parallel platelets were cautiously observed,respectively.The acid groups with highest oxidation state cannot interfere with the establishment process of parallel MnO₂,while the acid groups with reducibility can promotes the formation of it.The parallel MnO₂ can be established or changed though the competitive effect between H⁺and K⁺.The parallel MnO₂ grow from a scaly structure,and the long reaction time makes the parallel plates cross or completely collapse.The parallel MnO₂ through direct deposition on the calcined templates exhibited good cycle stability,114%retention of initial specific capacitance after 10 000 cycles.