| In the 21st century,due to the shortage of fossil energy and environmental pollution,people pay more attention to the exploration and development of sustainable clean energy.Among all kinds of energy storage and conversion systems,rechargeable lithium-oxygen batteries possess the highest theoretical energy density of 11140 Wh/kg,which is 10 times as much as that of traditional lithium-ion batteries,thus attracting people's interest in the study of lithium-oxygen batteries.However,the widespread use of lithium-oxygen batteries is still limited by many factors,such as a lower-than-expected capacity,high overpotential,low energy conversion efficiency and poor cycle stability.Therefore,developing noble catalysts as LOBs cathode materials is a significant method to improve the electrochemical performance of Li-O2 batteries,which can effectively promote the rate of electrochemical reaction during the discharge and charge process.Among various catalyst materials for Li-O2 batteries,CeO2 is considered to be one of the most promising catalysts for Li-O2 batteries because of its rapid transition between oxidized and reduced states and the efficient adsorption of oxygen and superoxides.In the electrochemical reaction,Ce3+ and Ce4+ can be converted directly and quickly,contributing to the adsorption and release of oxygen.In addition,the crystal structure of CeO2 is very stable,which can guarantee utmost catalytic activity during the discharge and charge process.The cycle life and stability,specific capacity and overpotential are important factors to evaluate the electrochemical performance of lithium-oxygen batteries.The purpose of this study is to explore the effects of different factors on CeO2 catalysts as cathode materials for Li-O2 battery,mainly in the aspects of recombination CeO2 with inverse opal carbon and controlling oxygen vacancy content in CeO2,in order to find out the optimal structure of CeO2 catalyst materials for Li-O2 battery.In this research,the catalytic effect of CeO2 as cathode catalyst for oxygen reduction and oxygen evolution reaction in Li-O2 battery was investigated.The composite and surface engineering methods were used to synthesize Ceo2 catalysts.At the same time,the electrochemical performance and catalytic mechanism of Ceo2 as cathode material for lithium-oxygen battery were further studied.Therefore,the main contents of this research are as follows:(1)using bio-mineralizing method to fabricate the composites of CeO2 nanocubes and inverse opal carbon matrix and study the electrochemical properties of CeO2/IOC composites,including their catalytic effects on Li2O2 adsorption and decomposition,the morphology change of Li2O2 during discharge and charge process,and the changes of morphology and composition of CeO2/IOC;(2)synthesizing CeO2 nanorods by a two-step hydrothermal method,regulating the oxygen vacancy content of CeO2 nanorods by adjusting the reaction temperature of the second step hydrothermal reaction,and further investigating the differences of catalytic activity of CeO2 nanorods caused by different oxygen vacancy content.This work proposed two strategy to improve the catalytic activity of CeO2 as the cathode catalyst in the Li-O2 cell,and achieved satisfying cycle life and capacity,which can provide a new idea to design the catalyst structure for transition metal oxides.The research significance of this paper is as follows:(1)combining CeO2 nanocubes with high catalytic activity with IOC possessing excellent stability and conductivity can provide a theoretical basis for the application of CeO2 cathode catalysts of lithium-oxygen batteries;(2)exploring the electrocatalytic effects of CeO2 nanorods with different oxygen vacancy concentrations on the reaction of oxygen reduction and oxygen evolution can provide an effective and controllable strategy for improving the electrochemical performance of other metal oxide materials as cathode for Li-O2 batteries. |
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