The Study On Pseudocapacitive Behavior Based On Two-Dimensional Polyaniline

Electrochemical capacitors have shown great potential in electrochemical energy storage systems because of their fast and significant charge-discharge rate and high power density.In the process of continuous improvement of its electrochemical performance,the in-depth study of electrochemical process and mechanism becomes more and more important.In many advanced supercapacitor systems,the more stored ions and more complex processes result in the inadequate and unclear understanding of ion adsorption and intercalation,interfacial Faradaic reaction,ion transport and diffusion in nano-confined space electrochemistry.Due to the existence of a variety of physical and chemical processes,reaction thermodynamics and electrode process kinetics need to be re-evaluated accurately.Many characteristics of two-dimensional(2D)materials make it easy to construct a model of ionic behavior,and a variety of them have been developed for complete pseudocapacitive model,but few organic materials are involved.However,the 2D conductive polymer with obvious Faradaic reaction and ordered nanochannels is an excellent carrier for the study of complex electrochemical processes.The understanding of the mechanism of its ion interaction is also of great significance to further guide the structural design of electrode materials and achieve the coordinated improvement of electrode performance.In this thesis,the electrode was constructed based on a new 2D conductive polymer(2D PANI).The pseudocapacitive behavior of H~+and Li~+intercalation and the kinetic nature of enhancement of electrode capacitance were revealed by in-situ structure characterization,electrochemical kinetic analysis,theoretical verification and other methods.The main contents and results are as follows:(1)The Faradaic reaction mechanism of PANI in electrochemical cycle was analyzed by using a variety of in-situ characterization methods,the thermodynamic characteristics and differences between acidic and neutral electrolytes were also compared.Hydrogen ions continue to actively participate in the Faradaic reaction at0.2-0.6 V,including oxidation and protonation doping,accompanied by the formation of polaron,bipolaron and quinone ring,which is one of the reasons for the improvement of electrode performance.(2)Different electrochemical kinetic treatment methods were used to find the cause and degree of kinetic acceleration.The electrochemical control and kinetic processes were described according to the results of b-value analysis,capacitance-rate fitting and in-situ EIS kinetic analysis.The kinetic acceleration and fast pseudo-capacitive response caused by H~+appear in 0.4-0.5 V.Faradaic and capacitance behaviors synergistically improve the capacitance of the system.(3)The electrochemical device of ion transport was designed and the ion transport efficiency in the 2D channel was calculated.Combined with the reaction mechanism of material structure evolution and the results of kinetic analysis,the charge storage process was described systematically.The developed multi-dimensional electrochemical method has obvious advantages in analyzing the charge storage mechanism more accurately.