Preparation,Characterization And Capacitive Performance Of Co-Ni Loaded Porous Carbon Composite Electrode Materials

Supercapacitors,also called electrochemical capacitors,have attracted considerable attention due to their rapid charge-discharge capability,long cycle lifetime,higher power density than lithium-ion batteries and higher energy density than conventional dielectric capacitors.Among the many electrode materials,cobalt nickel bimetal oxides have many advantages,such as high theoretical specific capacitance,abundant reserves and no pollution,but the poor conductivity and electrochemical stability limit their practical application.Porous carbon materials with high surface area as matrix compounded with cobalt nickel bimetal oxides,not only cuold reduce the impedance of cobalt nickel bimetal oxides,leading to the improvement of conductivity and electrochemical stability,but also could greatly improve the capacitive performance.Therefore,it would be the main direction to develop hybrids of cobalt nickel bimetal oxides and porous carbon materials,favourable for the improvement of capacitive performance.In this work,the XCoNi-CoNiO₂-CMK-3-T?X is the molar ratio of Co/C or Ni/C,T is the calcination temperature?composites were synthesized by hard template method using SBA-15 as the template and sucrose as carbon source,and then pyrolytic treatment in an argon atmosphere and using 2 M NaOH solution to remove the template SBA-15.The morphology,pore structure and status of cobalt-nickel element of the composites were characterized by transmission electron microscope?TEM?and scanning electron microscope?SEM?,N₂ adsoprtion/desorption,X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?characterization,respectively.The specific content of cobalt-nickel element and oxide of XCoNi-CoNiO₂-CMK-3-T composites was characterized by hydrogen temperature-programmed reduction?H₂-TPR?and the total reflection X-ray fluorescence?TXRF?characterization.Meanwhile,the supercapacitor performance of composites was measured by electrochemical measurement.It is found that the XCoNi-CoNiO₂-CMK-3-T composite?X=0.008,T=800 ^oC?shows the highest specific capacitance up to 280 F/g at 0.25 A/g?in 6 M KOH?,and keeps a high capacitance retention ratio of 97.7%after 10000 cycles at a current density of 5 A/g.The results demonstrated that composites were ordered mesoporous materials by N₂ adsoprtion/desorption characterization,and specifically,the sample showed the large BET surface areas of 1074 m²/g,the highest volume of 1.03cm³/g and typical mesoporous size of 3.6 nm.In the second part of this thesis,based on the CoNi-CoNiO₂-CMK-3 system,the XCoNi/UMCs?X is the actual mass ratio of Co/C,UMCs are the ultramicroporous carbon microspheres?composites were synthesized by changing the filling method of sucrose,and then pyrolytic treatment in an argon atmosphere and using 2 M NaOH solution to remove the template SBA-15.Meanwhile,the hydrothermal treatment was first applied to impregnate sucrose in the pore and surface of template SBA-15.The morphology,pore structure and actual content of cobalt-nickel element of composites were characterized by TEM and SEM,N₂ adsoprtion/desorption,and TXRF characterization,respectively.It is proved that the cobalt-nickel elements in the composites are in the form of CoNi alloy by XRD,H₂-TPR and TXRF characterization.Meanwhile,the supercapacitor performance of composites was measured by electrochemical measuremen.Though the hydrothermal treatment,the XCoNi/UMCs composites could exhibit the ultramicroporous structure.It is found that the 0.95%CoNI/UMCs sample exhibits the highest specific capacitance up to 268 F/g at a current density of 0.25 A/g?in 6 M KOH?,and keeps a high capacitance retention ratio of 97.8%after 10000 cycles at a current density of 5 A/g.The results demonstrated that composites were ultramicroporous materials by N₂ adsoprtion/desorption characterization,and specifically,the sample showed the largest BET surface areas of800 m²/g,the highest volume of 0.47 cm³/g and typical ultramicroporous size of 3.6 nm.These studies indicate that porous carbon materials with high specific surface area could be synthesized by hard template method.Porous carbon materials as matrix compounded with cobalt nickel bimetal oxides,not only could obtain high specific capacitance,but also exhibit excellent conductivity and electrochemical stability.Compared the two kinds of porous carbon materials?ordered mesoporous carbon CMK-3 and ultramicroporous carbon microspheres UMCs?,we could find that the compsites synthesized by using CMK-3 as matrix exhibit higher capacitance performance using UMCs as matrix when the same loading of cobalt and nickel under the same electrochemical test conditions.