Preparation And Electrochemical Properties Of PPy Or MXene Decorated MnCo₂O_4.5/Ni Foam Composite Electrodes

With the rapid development of the age,green sustainable energy has become a hotspot pursued by people in the new era.Ultracapacitors are a new type of electrochemical energy storage device between traditional capacitors and batteries.Supercapacitors have attracted the attention of a large number of scientific and technical enthusiasts due to their high energy density and power density,high charge and discharge efficiency,long cycle life,affordable price,and environmental friendliness.The selection of the suitable electrode materials is the key to optimizing the performance of supercapacitors.Common electrode materials contain carbon materials,various conductive polymers,and metal compounds.Compared with single components,bimetallic oxides own higher electrochemical activity and better electronic conductivity,which have become the focal research of pseudo-capacitive electrode materials.The study found that electrochemical performance of single electrode materials is generally not ideal,and composite electrode materials synthesized from different chemical materials usually possess better performance due to the existing of synergistic effect.By loading the active materials on Ni foam,as-designed materials always display excellent electrochemical properties as binder-and additive free electrodes in supercapactitor.Due to the high theoretical specific capacitance value,high reserves and low price,the main work of this thesis is to design and synthesize new composite materials on Ni foam with unique morphology by combining manganese-based materials(Mn Co₂O_4.5)with conductive polymer polypyrrole?PPy?and two-dimensional metal carbide?MXene?materials,respectively.Then the structure and electrochemical performance was studied.The main works are described as follows:A flower-like Mn Co₂O_4.5@PPy core-shell composite was successfully prepared on Ni foam through simple and environmentally friendly hydrothermal and osmotic polymerization methods.PPy-modified Mn Co₂O_4.5 composites have a large specific surface area and exhibit a high specific capacitance value of 3240 F g^-1 at a current density of 1 A g^-1.Under the same conditions,its capacitance value is much higher than that of Mn Co₂O_4.5(1058 F g^-1).Due to the synergistic effect between PPy and Mn Co₂O_4.5,the composite electrode with excellent charge transport ability has good cycle stability and low system internal resistance.It shows a cycle stability of 80.052%after 1000 cycles.Then the Mn Co₂O_4.5@PPy//r GO asymmetric supercapacitor is fabricated by employing Mn Co₂O_4.5@PPy composite electrode material as the positive electrode and reduced graphene oxide?r GO?as the negative electrode.The device shows a higher specific capacitance value(specific capacitance is 235 F g^-1 at a current density of 1 A g^-1),excellent power density and energy density(up to 97.8 Wh kg^-1at a power density of 320 W kg^-1),and good cycle stability?80.34%of the initial capacity maintained after 3000 cycles?.The Mn Co₂O_4.5@PPy/Ni foam composite material with excellent electrochemical performance can be considered as an ideal electrode material for the new generation of supercapacitors.The sea urchin-shaped Mn Co₂O_4.5/MXene?Ti₃C₂T_x?composite nanomaterial was successfully synthesized on Ni foam through a simple environmentally friendly hydrothermal method and an in-situ electrostatic adsorption process.The composite displays excellent performance directly used as supercapacitor electrode materials.The combination of Ti₃C₂T_x nanosheets and Mn Co₂O_4.5 burr-like can prevent the agglomeration of MXene.Furthermore,the unique urchin-shaped morphology structure provides a larger specific surface area,which greatly promotes the effective transmission of ions during the electrochemical reaction.As-prepared Mn Co₂O_4.5/MXene composite exhibits an excellent specific capacitance value of1563.4 F g^-1 at a current density of 1 A g^-1.The capacitance retention rate of the composite material is 63%when the current density increases to 10 A g^-1,and initial capacitance still maintains 92.4%after 5000 cycles under high current density.Compared with Mn Co₂O_4.5 not combined with MXene,the composite electrode material has significantly improved rate performance and cycle stability.