Study On The Structure Growth Mechanism And Doping Modification Of Anodic Oxide Nanotubes

Supercapacitors have aroused the research enthusiasm of scholars because of their high power density and rapid charge and discharge ability.The anodized nanotube has an ordered array structure that is favorable for electron transport,and the transition metal substrate at the bottom of the nanotube acts as a current collector.Both they can effectively avoid the complex manufacturing steps followed by the traditional process.Therefore,the preparation of electrode materials by anodization shows its advantages that can not be ignored.Anodic TiO₂ nanotubes prepared by anodization have shown excellent application potential in the field of supercapacitors.However,anodic ZrO₂ nanotubes have rarely been reported by researchers.Compared with TiO₂ and other materials,its electrochemical performance still has great room for improvement.This study will be based on mechanism analysis and doping modification to reveal the growth kinetics of oxide nanotubes,so as to realize the controllability of anodization preparation,and create a perfect theoretical reference for application research.Firstly,the total charge transferred during the growth of anodic TiO₂ nanotubes is calculated by integration,so as to quantitatively calculate the Pilling–bedworth ratio（PBR）.It is found that the inner diameter of nanotubes almost remains unchanged with the change of NH₄F concentration in electrolyte,indicating that the formation of nanotubes is based on oxygen bubble model.The pore volume（）,TiO₂ volume（）and total volume（）increase with the increase of NH₄F concentration,indicating that the formation of nanotubes is based on the ionic current and electronic current theories and the incremental output of metal oxide and oxygen bubbles.When the amount of charge transferred by anodization reaction is similar,the total volume is almost unchanged,the k_v value is similar,and the PBR does not decrease with the increase of NH₄F content.And the PBR is about 2.0.In general,the electrochemical performance curves of each sample maintained good charge-discharge symmetry and high Coulomb efficiency.Secondly,the morphology of anodic ZrO₂ nanotube arrays prepared under different conditions and the current-time curves recorded in real time were compared to explore the formation mechanism and growth kinetics.The essential reason for the formation of the large cavity at the bottom of the"bulb"anodic ZrO₂ nanotube is that the large J_e makes a large number of oxygen bubbles accumulate at the bottom of the nanotube.Nano pores are evolved from the splitting of nanotubes,which is due to the excessive pressure inside the nanotubes caused by the violent release of oxygen,resulting in the extrusion of nanotube walls.The double-layer anodic ZrO₂ nanotubes with increased diameter were prepared by one-step anodization.Based on the ionic current and electronic current theorie,oxygen bubble model and viscous flow model,the morphology of the double-layer nanotubes and the six stages of the current-time curve were reasonably explained.Anodic ZrO₂ nanotubes usually have a high aspect ratio,and the nanotube wall is prone to rupture.The reason is that larger J_e promotes more oxygen precipitation,and high-pressure oxygen bubbles lead to nanotube burst.Finally,the doping modification of anodic ZrO₂ nanotubes by metallic aluminum and non-metallic nitrogen elements was realized by steam treatment of low melting point metals and high temperature annealing in ammonia environment.The area specific capacitance of aluminum doped anodic ZrO₂ nanotube array films at a scanning speed of 100 m V s^-1 is 2.261 m F cm^-2,which is 6.6 times that of untreated samples.Compared with the samples annealed in argon,the area specific capacitance of nitrogen doped samples at 100 m V s^-1 is 3.555 m F cm^-2,which is 10.33 times that of argon annealed samples.