The Preparation Of MnO₂ And FeO(OH,F)/rGO Submicron Structure And The Study Of Its Capacitance Performance

Supercapacitors have attracted extensive interest due to their high power density and long cycle life.It is widely used in energy storage,electric vehicles and wearable devices.MnO₂ and FeOOH are considered to be promising supercapacitor electrode materials due to high voltage window,low cost,environmental friendliness,non toxicity and high theoretical specific capacitance.But their practical applicationt are limited due to extremely poor conductivity and redox reaction in the surface.In this paper,MnO₂ nanowires and MnO₂ nanoflowers are prepared to increase the specific surface area,which more active sites of MnO₂ is exposed to increases the specific capacitance of MnO₂.FeO?OH,F?@GO was prepared by one-step hydrothermal method.It greatly improved the conductivity of FeOOH,which the capacitance of FeO?OH,F?@GO is obviously improved.In addition,the morphologies,chemical structures and electrochemical properties of MnO₂ nanowires,nanoflowers and FeO?OH,F?@GO materials were characterized by various characterization.?1?The size-controlled MnO₂ nanowires were prepared by simple hydrothermal method.The length and diameter of the nanowires were adjusted by changing the reaction time.When the reaction time was 0.5 h,the diameter and length of MnO₂-NW-1 were the smallest.Electrochemical performance of MnO₂-NW in Na₂SO₄,MgSO₄and Mg?NO₃?₂ electrolytes was tested electrochemically,which found that MnO₂-NW has the best electrochemical performance and cycle stability in Mg?NO₃?₂ electrolyte.?2?Flower-like nanosheet assemblies of MnO₂?MnO₂-NSA?were prepared by PVP as reducing agent and KMnO₄ as precursor.PVP also played a role in surface activity to control sample morphology.The morphology of MnO₂ can be effectively regulated by changing the amount of PVP.The thickness of MnO₂-NSA nanosheets,the size and crystallinity of nanoflowers can be controled by changing hydrothermal reaction time.Electrochemical tests show that the specific capacitance of MnO₂-NSA-0.5 is higher than that of MnO₂-NSA-12 in both Na₂SO₄ and MgSO₄ electrolytes.At the same time,it was found that MnO₂-NSA can achieve higher specific capacitance in MgSO₄electrolyte.The electrochemical data,EDS and XPS data indicate that conversion of Mn²⁺/Mn⁴⁺and battery behavior is introduced during the energy storage process of MnO₂-NSA in MgSO₄ electrolyte.In addition,Mg²⁺insered in tunnels of MnO₂-NSA also plays an important role to improve capacitance.?3?A fluorine-doped FeOOH and graphene composite hydrogel?FeO?OH,F?@rGO?was prepared by one-step hydrothermal method.The amount of NH₄F in hydrothermal process had an important influence on the type,morphology and electrochemical performance of the sample.When the amount of NH₄F is less than 5 mmol,the graphene hydrogel cannot be formed,and the sample produced is powdery?-Fe₂O₃.The sample produce FeO?OH,F?@rGO when the amount of NH₄F used is 5 mmol.FeO?OH,F?@rGO can achieve highest capacitance of 855 F g^-1 at current density of 2A g^-1.In addition,the specific capacitance of FeO?OH,F?r@GO increased after activation due to that the morphology of the sample was changed during CV activation,which exposed more active sites to improve the surface.