| Global warming and the shortage of fossil fuels have made the development and application of energy storage devices more urgent.Among them,supercapacitors have become a hot spot for scholars'research due to their short-time charge/discharge capability and long cycle life.However,the drawback of low energy density of supercapacitor limits its application in daily life,and how to balance the energy density and power density of the device is a difficulty that must be overcome in the process of developing supercapacitor.The energy storage process of Faraday capacitors in superelectricity includes not only the adsorption-desorption process on the material surface,but also the redox reaction inside the active material,thus the pseudocapacitor has a larger specific capacitance value.Transition metals have the advantages of high theoretical specific capacity and low impedance,so they are chosen as the anode material for supercapacitors in this paper,and the main studies are as follows.(1)Nickel foam is used as both substrate and collector,and the hydrothermal in situ growth of Mn Mo O4·H2O nanostructures on top of it is connected with the first and the last flakes,thus avoiding the influence of the binder on the electrochemical performance of the electrode during the traditional sheet-making process by the hydrothermal in situ growth.The connection between the nanosheets and the nickel foam is non-physical contact,which is not only beneficial to the electron transfer between the active material and the collector fluid,but also the active material is more stable and less likely to fall off during the cycling process.The experimental results show that the specific capacitance value of the hydrothermally obtained Mn Mo O4·H2O nanosheets is 1.552 F cm-2 at a current density of 1 m A cm-2,which proves that the bimetallic oxides have a higher conductivity and a wider variety of chemical valence states than the monometallic oxides due to their synergistic effect,and thus have a higher specific capacitance value.(2)Although metal oxides have high theoretical specific capacitance, conductivity is a common problem for them.Transition metal sulfides have higher electrical conductivity,more active chemical reactivity,and better cyclic stability.By introducing sulfides through electrodeposition,Ni3S2is directly deposited on the basis of manganese molybdate generated in the first step to construct a core-shell structure as the anode of supercapacitor.the Mn Mo O4·H2O nanosheets are grown hydrothermally to cover the surface of nickel foam vertically and uniformly,which not only suppresses the stacking of nanosheets,but also facilitates the effective contact between the active material and electrolyte as well as The Mn Mo O4@Ni3S2core-shell structure has a specific capacitance value of 3.77 F cm-2 calculated from the GCD discharge time at a current density of 2 m A cm-2,which has significantly improved the electrochemical performance compared with the single molybdenum-manganese nanosheets.(3)The core-shell structure was constructed to increase the specific capacitance of the cathode material by increasing the active material,but the problem of the conductivity of manganese molybdate itself was not solved.To solve this problem,the hydrothermally generated Mn Mo O4·H2O nanosheets were doped with phosphorus atoms using the gas-solid reaction method.Sodium hypophosphite was heated and decomposed to generate phosphine gas as the phosphorus source,and the phosphorus source content,heating temperature,and heating time were optimized experimentally,respectively.The optimal results PMM-2 reached a specific capacitance value of 2.48F cm-2 at a current density of 1 m A cm-2 and a cycling stability of 88.23%.The negative electrode prepared using dendritic carbide and the positive electrode PMM-2assembled asymmetric capacitors take into account both energy density and power density,which promotes the practical application of manganese molybdate nanomaterials in the field of supercapacitors. |
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