| Supercapacitors(SCs)are new energy storage devices between traditional capacitors and secondary batteries.Due to its high power density,long cycle life,and fast charge-discharge rate,it has been widely used in power transportation,portable electronic devices,and biomedical equipment.The electrode material,as an important component of SCs,plays a decisive role in the performance of the device.At present,different types of electrode materials have been applied to SCs,such as carbon materials,conducting polymers,metal oxides,MOFs,COFs,Mxene,etc.However,no breakthrough has been made in the electrochemical performance of SCs.How to design and synthesize high-performance electrode materials is still one of the key issues in the development of high-performance SCs.MOFs have been widely used in SCs due to their high porosity,large specific surface area,and tunable structure and function.Their large specific surface area and pore size are conducive to charge storage to form electrochemical double layers,and their inherent redox activity site is conducive to the generation of pseudocapacitance.In addition,owing to the precise and adjustable structure of MOFs,it has obvious advantages to study the influence of electrode material structure on their electrochemical performance.In this thesis,with the help of the modifiability of MOFs,by designing their structural frames and functional groups,Eu-MOFs with modified by different functional groups but the same crystal conformation and modified by the same functional group ligands but different framework structures were constructed,then their SCs properties were studied.The electrochemical performance of Eu-MOFs-based electrode materials was tested using a three-electrode system and assembled twoelectrode supercapacitor cell.Through the analysis of test results and theoretical calculations,the charge-discharge mechanism of MOFs-based electrode material SCs was clarified,and the pore structure of electrode material and the effect of the interaction between the electrode material and electrolyte ions on the performance of SCs were revealed.This work not only expands the application of Eu-MOFs,but also provides an ideal material model for the study of the charge-discharge behavior of MOFs-based SCs,as well as experimental and theoretical references for the selection and design of high-performance SCs electrode materials.The specific research of this thesis is as follows.(1)Design and synthesis of Eu-MOFs electrode materials with precisely controllable structures.5-Methylisophthalic acid,5-(hydroxymethyl)-isophthalic acid dimethyl ester and 1,3-benzenedicarboxylic acid-5-(aminomethyl)hydrochloride were used as ligands.The solvothermal method was utilized to synthesized four Eu-MOFs,by regulating the reaction solvent,reaction temperature and reaction time,namely EuCH3,Eu-CH2OH-H,Eu-CH2NH3Cl and Eu-CH2OH-T.Among them,Eu-CH3,EuCH2OH-H and Eu-CH2NH3Cl are formed by the coordination of Eu3+and oxygen of carboxylic acid,which have the same hexagonal pore crystal configuration;EuCH2OH-T is formed by Eu3+ and oxygen from the carboxylic acid and hydroxyl,with a tetragonal pore crystal configuration.The structure,morphology and properties of the materials were characterized using single crystal-X-ray diffractometer,X-ray photoelectron spectroscopy,scanning electron microscopy,etc.It was demonstrated that the materials have a complete structural framework and high phase purity,which lays a foundation for the subsequent study of the relationship between electrode material structure and electrochemical performance.(2)To study the charging and discharging mechanism of MOFs-based SCs.The electrochemical performance of the three-electrode system of four Eu-MOFs-based electrode materials and the assembled two-electrode SCs cell were tested using TEABF4/ACN as the electrolyte.The test results that the capacitive performance regularity was Eu-CH2OH-H>Eu-CH3≈Eu-CH2NH3C1,Eu-CH2OH-H>Eu-CH2OH-T in the TEABF4/ACN electrolyte.Combining the experiment results and theoretical calculations of the electrode materials during the charging and discharging process,the influence of the pore structure of the electrode materials and the interaction between the electrode materials and the electrolyte on the capacitive performance of MOFsbased SCs were revealed.This is demonstrated by the fact that larger pore size facilitates the storage of more charge ions and achieves higher specific capacitance.In addition,the stronger binding energy between electrode materials and electrolyte ions facilitates the adsorption of electrolyte ions on the electrode surface to form a double electric layer.However,an excessively strong binding energy can cause delayed desorption during charging and discharging,resulting in poor capacitance retention. |
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