Preparation And Properties Of Electrode Materials For CeO₂-based Surpercapacitors

With the increasing of environmental pollution and the demand for energy consumption,the development of sustainable and environmentally friendly alternative energy and energy storage devices has become the main research direction.Therefore,the development of energy conversion and storage devices with the advantages of light weight,fast energy conversion and low cost has become the main research direction.At present,energy storage devices capable of satisfying the above characteristics include:supercapacitors,secondary batteries,and fuel cells.Compared to batteries and conventional capacitors,supercapacitors are considered to be the most promising energy storage systems because of their fast charging/discharging,excellent power density,long cycle stability,environmental friendliness,low cost and operational safety.The overall performance of supercapacitors largely depends on their performances as well as morphologies of electrode materials.At present,many studies have focused on the design of electrode materials with high capacity,high energy density and long cycle stability.Among them,many efforts have been made to study capacitor metal-based oxide electrode materials because they can produce superior electrochemical properties or Faraday redox reactions than typical carbon-based electric double layer capacitors and electronically conductive polymer capacitors.The CeO₂ that can be cheaply obtained with oxygen vacancies,which is favorable for the Ce³⁺/Ce⁴⁺redox reaction.So it has great potential to be used as supercapacitor electrode material.In this work,a series of CeO₂-transition metal oxide composites were prepared by simple method.The main contents are as follows:（1）The ultra-long MnO₂@CeO₂ nanowire was prepared by a simple method with a length of several micrometers and a diameter range of 30⁸0 nm.Electrochemical studies of MnO₂@CeO₂ active materials were investigated using a three-electrode electrochemical workstation and 2 mol/L potassium hydroxide as the electrolyte solution at a window voltage of 0.18⁰.45 V.MnO₂@CeO₂ has a specific capacitance of 265 F/g at a scan rate of 5 mV/s.The results show that MnO₂@CeO₂ shows good application potential as a supercapacitor electrode material.（2）Using Ce（NO₃）₃?6H₂O and K₄[Fe（CN）₆]·3H₂O as raw materials and deionized water as solvent,the pine cone biconical precursor was successfully prepared by precipitation method,and the air atmosphere was at 500°C.The CeO₂/Fe₂O₃ composites were obtained after calcination for 4 h.The effects of material ratio,reaction temperature and reaction time on the morphology of the products were also investigated.The performance of the CeO₂/Fe₂O₃ composite as a supercapacitor electrode material was investigated.In the 2 mol/L KOH solution,when the potential window is 0.18⁰.45 V（vs.SCE）,CeO₂/Fe₂O₃ exhibits a good specific capacitance as the electrode material.When the sweep speed is 1 mV/s,the specific capacitance can reach 332.9 F/g.（3）The composite CeO₂/Co₃O₄/C hollow polyhedron was successfully obtained by a simple cation exchange route followed by heat treatment.In the synthesis process,a Co-based precursor polyhedral skeleton（ZIF-67）was first prepared,which can be used as a template for exchanging Ce³⁺ions and a composite CeO₂/Co₃O₄/C hollow polyhedron.The electrochemical performance test results show that the CeO₂/Co₃O₄/C polyhedron has a specific capacitance of 131 F/g at 2.5 A/g and has a good stability.This indicates that CeO₂/Co₃O₄/C has far-reaching significance as an electrochemical energy storage material.More importantly,we believe that the route is a simple and versatile strategy for preparing other composite metal oxides having the desired structure,chemical composition and application.