Syntheses And Pseudocapacitive Property Studies Of Micro-nano Structured Transition Mental Hydroxides Based On Conductive Substrates

As one of the most significant new-type energy storage devices,supercapacitors have attached tremendous attention due to their superior power density,fast charge-discharge rate and long cycle life.The electrode materials have played an important role in enhancing the electrochemical performance of supercapacitors.At present,the main study directions of supercapacitors are focused on electrode materials.Transition metal oxides/hydroxides have been developed for supercapacitors extensively,which can provide large number of pseudocapacitive contribution due to the presence of multiple oxidation states.Moreover,they also possess abundant reserve and low fabrication cost.However,most of transition metal electrodes suffer from the inferior conductivity,poor stability and insufficient redox active sites,which limit their further practical applications.In this paper,nickel-based and cobalt-based hydroxides had been taken as the research object,we designed excellent electrodes through fabricating well-ordered nanoarray architecture directly grown on high conductive substrates.The main works in this dissertation are as follow:（1）The Zn-Ni-Co ternary hydroxides（Zn-Ni-Co TOH）nanoarray architecture with different morphology was grown on carbon cloth through controlling hydrothermal parameters.The scanning electron microscope has been employed to reveal their morphology evolution mechanism.Among the different Zn-Ni-Co TOH electrodes,the well-aligned Zn-Ni-Co TOH-130 nanowires architecture is beneficial for the fast transmission of ion and electron.When the mass loading achieve a high value of 7 mg cm^-2,the Zn-Ni-Co TOH-130 electrode still delivered an enhanced areal capacitance of 2.14 F cm^-2 at 3 m A cm^-2 and an excellent rate capability.The asymmetric supercapacitor was fabricated by assembling a Zn-Ni-Co TOH-130cathode and a functionalized partial-exfoliated graphite anode.It exhibited a high energy density of 2.43 m Wh cm^-3 at 6 m W cm^-3,as well as outstanding cycling stability（153%of capacitance retention after 10000 cycles）.This work provides key findings for the growth mechanism and corresponding electrochemical energy storage performances of ternary hydroxides.（2）In order to solve the problems of poor conductivity and underutilization of nickel-based electrodes,high aligned Zn-Ni double hydroxides nanosheets（ZNDH NSAs）were grown on nickel foam.Subsequently,the charge storage capability of ZNDH NSAs was further enhanced by electro-activation process（A-ZNDH NSAs）.We demonstrated that the electro-activation can lead to more defective oxygen,enlarged lattice and reduced Ni valence,which can improve the charge transfer kinetics of ZNDH NSAs synergistically.A-ZNDH NSAs electrode delivered a high areal capacitance of 6834 m F cm^-2 at 3 m A cm^-2,as well as excellent rate capability.The asymmetric supercapacitor was fabricated by employing an A-ZNDH NSAs cathode and functionalized partial-exfoliated graphite anode,this device exhibited outstanding cyclic stability with no capacitive decay over 140000 cycles.Experimental and computational results indicated that the introduction of Zn can not only improve the conductivity of Zn-Ni double hydroxides system,but also suppress the phase transformation during ultralong cyclic test,which played an important role in increasing the stability.This work illustrated the enormous potential of A-ZNDH NSAs as a promising cathode candidate for supercapacitors.