Preparation,Desalination Properties And Mechanism Of Three Dimensional Sodium Ion Intercalation Electrode

Seawater desalination technology,as one of the important ways to deal with the shortage of freshwater resources in human society,has been paid more and more attention by researchers.At present,the relatively mature seawater desalination technologies include distillation and reverse osmosis,but these technologies suffer from the issues of high energy consumption,environmental pollution and expensive equipment,etc..Capacitive deionization(CDI)emerges as a new desalination technology exhibiting many obvious advantages,such as high energy efficiency and environmental benign.Electrode material is one of the core elements in CDI.In recent years,the sodium-ion intercalation(SII)materials are employed to form ionic bonds through redox reactions instead of the traditional physical adsorption enabled by carbonbased materials.This thesis designs the 3D SII electrodes to improve the desalination performance by template method.The 3D structure enhances the specific surface area of SII materials which is beneficial to strengthen the transport and storage of sodium ions as well as enhance the electrical conductivity and electrochemical activity.The main contents are as follows:1.The multilateral 3D NaCoO₂ and 3D NaO,6CoO2 nanostructures were prepared using metal-organic frameworks as a template.Electrochemical analysis shows that 3D Na_0.6CoO₂ has higher specific capacity than that of 3D NaCoO₂.In a NaCl solution with an initial conductivity of 2000 ?S cm^-1 and an applied voltage of 1.2 V,the salt removal capacity of 3D Na_0.6CoO₂ is 64.48 mg g^-1.The desalination mechanism of 3D Na_0.6CoO₂ electrode was proposed by the X-ray diffraction analysis and electrochemical test results.In addition,benefiting from the 3D structure,the CDI cycle performance of 3D Na_0.6CoO₂ electrode is much better 2D Na_0.71CoO₂ electrode.2.The spinel ZnCo₂O₄(ZCO)was prepared by a simple strategy.The ZCO has a typical spherical structure which provides a 3D diffusion channel for ions.Electrochemical analysis shows that ZCO electrode possesses specific capacitance of 307.9 F g^-1 in 1M NaCl solution at the scan rate of 1 mV s^-1.Conspicuously,the equivalent series resistance and the Warburg impedance of ZCO electrode is only 0.54 and 0.66 ?,respectively.Low resistivity is beneficial to improve the efficiency of charge transfer and the utilization of driven energy.As for desalination,the ZCO electrode illuminates the salt removal capacity of 39.4 mg g^-1 in 2000 ?S cm^-1 NaCl solution at 1.2V.Under the same experimental conditions,the desalination capacity of ZCO electrode is 73.39 mg g"1 while the charge efficiency is 76.8%at a constant current of 10 mA g'1.In addition,the preferential removal of Na⁺,K⁺ and Mg²⁺ by ZCO electrode was investigated,indicating that the hydration ion radius plays an important role.On this basis,the morphology,crystal phase and valence state of ZCO electrode under different desalination/salination states were analyzed,and the possible desalination mechanism was proposed.