Improving Supercapacitor Performance Of Anodic Titanium Oxide Nanotubes Via Low Melting Point Metal Doping Or Alloying

Supercapacitors have attracted extensive attention and research on account of its high power density,fast charging and discharging,long cycle life and so on.Among the super capacitor electrode materials,nanostructured TiO₂ have led to a lot of research as a kind of environmental,economy materials,with unique properties,of which TiO₂ nanotubes have attracted much attention,especially the nanotube arrays（NTAs）prepared by anodization.TiO₂nanotubes have attracted wide interest because of their unique advantages in the application of supercapacitors.However,the low conductivity of TiO₂ material greatly reduces its supercapacitor performance.In this paper,metal doping of low melting point metal or Oxide recombination of alloying were used to conduct metal doping of TiO₂ NTAs to further improve the electrochemical performance of TiO₂ NTAs.The research results are as follows:1.TiO₂ NTAs prepared by the secondary anodization method have regular morphology.TiO₂ NTAs are annealed in metal melt,and Sn-doped TiO₂ NTAs are successfully prepared.Compared with TiO₂ NTAs which is showing n-type semiconductor characteristics,Sn-doped TiO₂ NTAs show p-type semiconductor characteristics.Sn replaces Ti⁴⁺and enters into anatase TiO₂ NTAs with Sn⁴⁺,thus introducing impurity levels,reducing in an increase in carrier concentration of three orders of magnitude,showing excellent electrochemical performance.Compared with undoped TiO₂ NTAs,the area specific capacitance increases by 22.5 times.The retention rate of area ratio capacitance is 92.5%after 5000 cycles.2.The nanotube structures of pure Ti,Ti-5 wt%Mn and Ti-5 wt%Ni were prepared by anodization method.Compared with pure Ti,Ti-5 wt%Mn and Ti-5 wt%Ni,Ti-5 wt%Fe oxide NTAs has higher area ratio capacitance,better carrier concentration and better capacitance characteristics,and has the best electrochemical performance.3.The anodic oxide NTAs of pure Ti,Ti-10 wt%Fe,Ti-15 wt%Fe and Ti-20 wt%Fe were denoted as Ti NTAs,Ti-10 wt%Fe NTAs,Ti-15 wt%Fe NTAs and Ti-20 wt%Fe NTAs,respectively.Ti NTAs,Ti-10 wt%Fe NTAs,Ti-15 wt%Fe NTAs and Ti-20 wt%Fe NTAs after annealing in Ar were tested in neutral test solution.The results show that Ti-15wt%Fe NTAs had the highest area ratio capacitance,higher carrier concentration and lower voltage drop,indicating that Ti-15 wt%Fe NTAs had the best electrochemical performance.Further structural characterization of Ti-15 wt%Fe NTAs shows that Ti-15 wt%Fe NTAs is TiO₂-Fe₂O₃ complex,and there is some iron doping in TiO₂,which generates more oxygen vacancies compared with Ti.After 5000 cycles,the area specific capacitance is 95.63%of the initial value,and the coulomb efficiency is 99.31%.Ti-15 wt%Fe NTAs has good cycling performance and Coulomb efficiency.4.Compared with Ti NTAs,Ti-10 wt%Fe NTAs,and Ti-20 wt%Fe NTAs,Ti-15 wt%Fe NTAs has higher area ratio capacitance and carrier concentration in acid test solution.Besides,Ti-15 wt%Fe NTAs has the highest capacitance retention and coulomb efficiency after 5000cycles.The nanotube structure of the sample was destroyed after cycling,and the slope of Nyquist plots of Ti and Ti-Fe alloys NTAs did not change significantly after cycling,and the internal resistance of electrode materials increases.The samples treated by hydrothermal etching show different morphologic and electrochemical properties.Compared with smooth nanotubes,the surface of samples after hydrothermal etching has some small particles in crystallization.