Fabrication,Doping And Electrochemical Performances Of Anodic Oxides On Ti And TiN

Anodic films of Ti metal are classified into TiO₂ nanotubes（porous oxide）and compact oxide.TiO₂ nanotubes can be used as electrode materials of supercapacitors because of ordered porous structure and large specific surface area.Although it has been researched for decades,obvious disadvantages of TiO₂ nanotubes,such as easy to split away from the substrates and poor electrochemical performance,limited the applications.As a result,this work firstly compares the differences of morphology and electrochemical performance of TiO₂ nanotubes obtained on Ti foils and Ti wires under various anodizing conditions.Secondly,two methods（one and two-step synthesis processes）to prepare the N-doped TiO₂ nanotubes are studied to improve the areal specific capacitance,compared with that of non-doped TiO₂ nanotubes.Thirdly,this work achieves TiO₂ nanotubes containing N with higher areal specific capacitance on Ti foils coated with TiN（TiN-Ti）to simplify the doping process,contributing to the fabrication of electrode materials of supercapacitors.Lastly,fabrication of TiO₂ compact films on different substrates and under various anodizing conditions are researched with comparisons of leak current,specific capacitance and power loss as few researches focus on fabrication of compact films in spite of the application in dielectric materials.The key points of this work are as follows.Firstly,the morphologies and electrochemical performances of TiO₂ nanotubes obtained on Ti wires under various anodizing conditions are studied,due to its better adhesion to the substrate,compared with that fabricated on Ti foils.Results show that,under larger content of NH₄F in electrolyte and higher temperature,as to TiO₂ nanotubes fabricated on Ti wires,the nanotubes grow longer and areal specific capacitance gets larger.Secondly,the N-doped TiO₂ nanotubes are achieved on Ti foils by one and two-steq synthesis processes.One-step synthesis process is the anodization process of Ti foils in electrolyte containing urea.Two-step synthesis process is divided into two steps.The first step is the anodization process of Ti foils in conventional electrolyte,and the following step is the immersing process of TiO₂ nanotubes in ammonia or urea solutions.The results demonstrate that N-doped TiO₂ nanotubes prepared by above two routes present larger areal specific capacitance,but adhesion of N-doped TiO₂ nanotubes to substrate gets worse after immersing process.Hence,one-step synthesis process has more advantages.Thirdly,TiO₂ nanotubes containing N are prepared on TiN-Ti in conventional electrolyte under different anodizing time and temperatures,TiO₂ nanotubes containing N show shorter length and improved areal specific capacitance of unit length,compared with that obtained on Ti foils under the same anodization time.Also,under higher temperature,TiO₂ nanotubes obtained on TiN-Ti show longer nanotubes and improved areal specific capacitance.Lastly,the influences of electrolyte,applied voltage and temperature on fabrication of TiO₂ compact films based on substrates of TiN and Ti are researched and compared.The results reveal that TiO₂ compact films obtained on TiN-Ti in electrolyte of NH₄B₅O₈ and H₃BO₃ show best properties,compared with that obtained in other three kinds of electrolytes,while there is no significant difference on properties of TiO₂ compact films obtained on Ti foils in four kinds of electrolytes.Also,under the same experimental conditions,compact films fabricated on substrates of TiN-Ti reveal smaller leak current and power loss,compared with that fabricated on Ti foils.Furthermore,with the improvement of applied voltage,compact films fabricated on substrates of TiN-Ti have larger leak current,smaller specific capacitance and power loss,the same as those fabricated on Ti foils.And with the rise of temperature,compact films fabricated on substrates of TiN-Ti and Ti have larger leak current,power loss and smaller specific capacitance.