Study On Preparation Of Three-dimensional Hierarchical Porous Nanomaterials And The Performance Of Supercapacitors

The wide application of portable electronic devices has raised a higher requirements for energy storage devices.Among them,supercapacitors(SCs)with high power density and long cycle life have received extensive attention as a new energy storage device.However,low energy density is the core issue restricting the development of SCs.In this dilemma,hybrid supercapacitors(HSCs)combining battery-type electrodes and capacitive electrodes are considered to be an effective way to achieve high energy and power density.Moreover,aqueous zinc ion hybrid supercapacitors(ZHSCs)with a high theoretical capacitance and relatively stable zinc metal as the battery-type negative electrode and carbon material as the capacitive positive electrode is also one of the most promising candidate devices.The performance of HSCs largely depends on the physical and chemical properties,and the structure of active components of the electrode material,including pore size,pore volume,specific surface area,electrochemical activity,etc.In addition,compared with the solid counterparts,porous nanomaterials with higher specific surface area,abundant pores,smaller size,strong structure,etc,show great potential for improving the electrochemical performance of SCs.Based on this,this article will use transition metal compounds,conductive polymers and carbon materials to prepare three-dimensional hierarchical porous nanomaterials as the positive electrodes,and assemble HSCs.It will elaborate from the following three aspects:1.Cu₂S@Ni Co-LDH dual-shell nanotube arrays for high-performance all-solid hybrid supercapacitors.A sequential alkaline corrosion,sulfidation,and electrodeposition method was designed to fabricate hierarchical double-shelled nanotube arrays of hierarchical Cu₂S@nickel-cobalt layered double hydroxide(Cu₂S@Ni Co LDH DSNAs)on a Cu foam(CF)substrate.Benefiting from the unique hierarchical hollow nanostructure and the sophisticated assembly of different active components,the as-prepared Cu₂S@Ni Co-LDH DSNAs as a battery-type electrode exhibit a high specific capacity of 2.8 m A h cm^-2(555.6 m A h g^-1,at the current density of 4 m A cm^-2)even with a high mass loading of 5.0 mg cm^-2,and excellent rate capability with 87%capacity retention when the current density increases tenfold.In addition,a HSC device is assembled with Cu₂S@Ni Co-LDH DSNAs as the positive electrode and metal-organic framework(MOF)-derived nanoporous carbon(NPC)as the negative electrode,exhibiting a high energy density of 1.67 m W h cm^-2at the power density of4.25 m W cm^-2.This prominent electrochemical performance highlights the great potential of Cu₂S@Ni Co-LDH DSNAs for practical energy storage application.2.The N-C@PANI hierarchical porous composite material with high specific capacitance of zinc ion hybrid supercapacitor.The N-C@PANI hierarchical porous composite material were prepared by polymerizing the aniline monomer on the N-doped carbon(N-C)surface derived from the metal-organic framework(MOF).Benefiting from the excellent electrical conductivity and structural stability of N-C,the high theoretical specific capacitance of PANI and the structural advantages of hierarchical porous composite materials,the assembled N-C@PANI//AC ZHSCs have excellent energy storage performance.And the performance of ZHSC was optimized by adjusting the ratio of positive and negative loads,and the specific capacitance and energy density are 159.2 m A h g^-1and 143.3 W h kg^-1,and 80%of the initial capacity is retained after 5000 cycles at 2 A g-1.3.Three-dimensional hierarchical porous carbon materials modified by oxygen functional groups for high performance zinc ion hybrid supercapacitor.The three-dimensional hierarchical porous carbon material(N,O-HPC)modified with oxygen functional groups was obtained by activating the carbonized ficus microcarpa,the pore structure and oxygen functional group content of the material were adjusted by controlling the activation conditions.The electrochemical test of the ZHSC was carried out,which was assembled with N,O-HPC as the positive electrode and zinc foil as the negative electrode.Among them,N,O-HPC-800-1.5,which has a unique three-dimensional hierarchical porous structure and abundant oxygen functional group content,exhibits high specific capacity(220.1 m A h kg^-1),high energy density(181.6 W h kg^-1)and remarkable cycle stability(retaining 100%of the original capacity after 10,000 cycles).In order to further explore the mechanism of oxygen functional group modification on performance improvement,we calculated the adsorption energy of different oxygen functional groups to zinc ions through density functional theory.The results show that carbonyl and carboxyl groups and composite functional groups are easier to adsorb zinc ions,which not only effectively improves the reaction kinetics,but also provides additional pseudocapacitance enhancement performance.