Controllable Preparation Of Niobium Oxide And Its Electrochemical Performance

In recent years,supercapacitors have shown great application potential in large electronic equipment,hybrid electric vehicles,backup power supplies and high-power military equipment due to their high power density,fast charging and discharging speed and high capacitance ratio.However,the low energy density,short service life and low safety factor of supercapacitors,compared with lithium ion batteries which are widely used today,limit their practical application.It is well known that the energy density of supercapacitors mainly depends on the capacitance and working voltage of the electrode material.Therefore,it is of great practical value to study the electrode material of supercapacitors with high efficiency and stability.Niobium oxide has many chemical valence states,it can conduct reversible redox reaction between different valence states in the process of charging and discharging,and its theoretical capacitance value is high.However,the oxide has poor conductivity and is easy to grow into a block-shaped material with a low electrochemical active surface area.Therefore,the actual capacitance of niobium oxide reported so far is relatively low.This paper in order to obtain stable high capacity of niobium oxide micro/nano materials as the goal,through the structure design,form a composite oxide and heterostructure manner niobium oxide preparation of micro/nano materials research,characterization methods,combined with a variety of analysis system to study the electrochemical properties of these materials as well as application in water system of super capacitor electrode.The main research results are as follows:(1)The carbon-supported Nb2O5 thin film was prepared by one-step CVD method.Nb2O5 film was directly coated on the surface of carbon fiber,and the electrical conductivity of Nb2O5 was significantly improved.The larger specific surface area of the films exposes more electrochemical active sites to the composites and promotes the diffusion of ions.As the electrode material of supercapacitor,the prepared material showed good electrochemical energy storage performance:at the current density of 2A g-1,the specific capacity of the material could reach 52.78mAh g-1;The material also has good cycling stability,maintaining an initial capacitance of 97%after 1000 cycles.(2)The netlike FeNb2O6 nanostructure was directly grown on carbon fiber by one-step CVD method.Niobium pentoxide and other transition metal oxides are formed into composite oxides to provide more valence state,which is conducive to the redox reaction in the energy storage process and significantly improves its electrochemical performance.The specific capacity of FeNb2O6/CC composite material prepared can reach 365.9mAh g-1 at the current density of 2.5A g-1.At the current density of 25A g-1,the specific capacity of 75.9mAh g-1 can still be maintained.These composite materials still have high capacitance value at the high current density,indicating their great application prospects.(3)The granular CoNb2O6 nanostructure was successfully grown on carbon fiber by one-step CVD method.At the voltage window of-1.2-0v and the current density of 20A g-1,the specific capacity of the prepared carbon cloth loaded CoNb2O6 nanometer material can reach 587.3mAh g-1,but the stability of the material is poor.CoOOH nanosheets were grown on CoNb2O6 nanoparticles supported by carbon cloth by in situ electrochemical modification,and the CoNb2O6-CoOOH/CC composite structure was obtained.In this composite structure,CoOOH nanoparticles are coated on the surface of CoNb2O6 particles,making CoNb2O6 not in direct contact with the electrolyte,thus significantly improving the stability of the composite material.The initial specific capacity of the composite material can be maintained at an initial capacity of 97%and the coulomb efficiency can be maintained at more than 95%at the current density of 15A g-1 for 40000 cycles.This way of forming heterogeneous structure is beneficial to the improvement of the electrochemical properties of oxide materials and provides a new path for the improvement of the properties of other electrode materials.