Preparation And Supercapacitor Application Of Nickel Oxide/Polypyrrole Materials

In this thesis,a three-dimensional hierarchical structure of tremella-like?TN4-C1?and pinecone-like?PN4-C2 and PN4-C3?nickel oxide were prepared.We have used urea as a precipitant,temperature as the inducing factor,ethanol and water as the solvent,and nickel nitrate hexahydrate as the nickel source.The regulation of NiO with different morphologies is achieved by regulating the temperature.A possible mechanism was proposed:the preparation of Ni₃?NO₃?₂?OH?₄ precursor at different solvothermal temperatures and the effect of calcination temperature on the composition and structure of NiO microspheres.Nanosheets gradually assemble into the initial microspheres when the solvothermal temperature is lower than 120oC.The initial microspheres gradually dissolve and recrystallize to form the hierarchical nitrate precursors with the solvothermal temperature increase.When the solvothermal temperature reaches 180oC,all of the initial microspheres dissolve and form orbicular spheres?TN4?.In calcination,NiO microspheres were obtained by different high-temperature decomposition of Ni₃?NO₃?₂?OH?₄ precursor.TN4-C1 has more structural water molecules and large cavities,which possibly result from the transformation of amorphous phase to crystalline phase at calcination temperature of350oC.The nanosheets interact with each other,leading to nanosheets necking at 600oC.Calcination temperature inducing the transition from tremella-like morphology to pinecone-like morphology with a decline of structural water molecules.When the calcination temperature reaches 850oC,PN4-C3 is obtained and the structural water molecules disappear.FESEM and TEM measurements prove that TN4-C1 is less aggregated than PN4-C2 and PN4-C3.The results of FT-IR,TG,XPS and XRD showed that TN4-C1 has structural water molecules.N₂ adsorption–desorption results show that TN4-C1 exhibits a higher surface area than PN4-C2 and PN4-C3.Thus,TN4-C1 contains more electro-active sites than PN4-C2 and PN4-C3.The supercapacitor performance was investigated by applying TN4-C1,PN4-C2 and PN4-C3 to the electrode material of the supercapacitor.In a three-electrode supercapacitor,At 3 A g^–1,TN4-C1 exhibits a maximum specific capacitance of 3242F g^–1,which is significantly higher than that of PN4-C2(891 F g^–1)and PN4-C3(486F g^–1)and is close to its theoretical specific capacitance.TN4-C1,PN4-C2,and PN4-C3 were used as positive electrodes,and activated carbon?AC?was used as a negative electrode to assemble a two-electrode asymmetric supercapacitor?ASC?.At a current density of 3 A g^–1,the assembled TN4-C1//AC can achieve a specific capacitance of 656 F g^–1,which is significantly higher than PN4-C2//AC(253 F g^–1)and PN4-C3//AC(150 F g^–1).In addition,TN4-C1//AC exhibits an energy density of233.3 Wh kg^–1at a power density of 2399.8 W kg^–1.This finding is attributable to the abundant structural water molecules of TN4-C1,which ensures rapid ion diffusion.In order to further improve the thermal stability of TN4-C1 and the performance of supercapacitors,Py was supported on the surface of TN4-C1 nanosheets by in-situ polymerization using Py as a raw material.Due to the limitation of the voids of TN4-C1 microsphere nanosheets,polypyrrole polymerization is limited,and the fish scale-like polypyrrole?PPy?with a size of approximates 10 nm is obtained.The fish scale-like PPy provides more active sites for OH^-ion insertion.In the OH^-ion insertion process,OH^-ions are not only inserted into the fish scale-like PPy layer,but also inserted into the TN4-C1 nanosheet,which lays a foundation for the application of the composite material for the electrode material of the supercapacitor.Tremella-like NiO/fish-scale PPy microspheres?diameter of 4?m?composed of homogeneous nanosheets were then used as electrode materials in the supercapacitor.NiO/PPy-6 obtained at a molar ratio of NiO to Py of 6 has a high specific capacitance of 3648.6 F g^-11 at 3 A g^-11 and a good rate capability(1783 F g^-11 at a high current density of 30A g^-1).NiO/PPy-6 was used as a positive electrode,and activated carbon?AC?was used as a negative electrode to assemble an asymmetric supercapacitor.At current densities of 3 A g^–1,the assembled NiO/PPy-6//AC can achieve a specific capacitance of 937.5 F g^–1with a stable voltage window of 1.6 V.In addition,it has a maximum energy density of 333.3 Wh kg^–1,a power density of2399.99 W kg^–1,and excellent cycle stability?88.2%after 10,000 cycles?.The combination of components and unique heterostructures results in superior electrochemical performance.Due to the synergy between NiO and PPy in the NiO/PPy composite,the specific capacitance,rate performance and cycle stability of the material are significantly improved.