Structure Control And Photoelectric Conversion Performance Of Nanotubes On The Surface Of Titanium Tube

The rapid development of nanoscience and nanotechnology opens up new opportunities to synthesize various nano-structured materials for diverse functionalities.Nevertheless,scalability of the nanomaterials has been a growing challenge toward practical applications and tangible impacts in the real world.Anodic titania nanotubes have been widely employed in various applications,which are usually demonstrated with limited size and planar geometry.In addition,the nanotubes grown at the outer and/or inner surface of a tubular substrate are promising for solar cell,supercapacitor,self-cleaning,anti-icing,drag reduction,and enhanced heat transfer performances after hydrophobic treatment.Nonetheless,the uniformity control of the nanotubes becomes even more difficult compared with conventional planar ones,especially at the inner surface of the tubular substrates in view of partially opened geometry at only two tube ends.This is not only a technical difficulty,but also a scientific problem.In view of this,this thesis uses titanium tube as the research object,from the controllable growth of nanotubes,the wettability theory on the substrate to the photoelectric conversion performance of nanotubes,conducted a series of systematic studies.The following research results have been obtained:A coaxial electrochemical anodization approach is explored.With this method,uniform titania nanotube arrays are produced at the inner surface of titanium tubular electrodes of 1000 mm in length and 10 mm in diameter,in good contrast to the nonuniform nanotubes attained with conventional anodizing scheme.A tube-in-tube coaxial anodization approach is further developed to generate coatings of nanotube arrays at the outer surface of Ti tubes.The nanotube features was tailored by designing the square wave configuration.The wetting property of the resulting nanotube arrays are further tailored,with a maximum contact angle of 166°for water,exhibiting a superhydrophobic feature.Such a coaxial approach is cost-effective and energy-efficient.It is also capable of processing other valve metals possible for anodization,and even longer tubular substrates.The contact angle,a major parameter to evaluate the wettability,is derived and gradually modified mainly for flat surfaces after Thomas Young?1773-1829?.However,in the case of tubular surfaces,the curvature affects and biases the measurement.In this study,a general equation?₀=f?R,r,??,suitable for tubular surfaces of different wetting states,is hence derived to compute the intrinsic contact angle?₀ in terms of apparent contact angle?,droplet radius r and tube radius R.Intrinsic contact angles calculated using the equation agree well with the values measured directly from the corresponding flat surface,validating its effectiveness.This study provides a theoretical basis to assess the wetting property of tubular or curved surfaces by eliminating the curvature effect.A novel solar tube that combines the photo-electric and photo-thermal conversion is developed.A titanium tube is used as the substrate to collect electrons from the solar cell compartment and convert the unabsorbed photons to thermal energy.The key point is the use of titanium tube,it has a small plasma frequency to enable wide absorption for thermal conversion.It also accommodates TiO₂ nanotube arrays to solve the cracking problem under tensile stress.A sandwiched membrane of high transparency and conductivity is developed for hole transport and collection.It exhibits an FoM of 159,much higher than some recently reported electrodes.Eventually,a total energy efficiency of about 25.2%is obtained.An integrated photo-charging supercapacitor based on nanotubes at the inner and outer surface of the titanium tube is developed.TiO₂ nanotubes were simultaneously prepared on the inner and outer surfaces of the titanium tube by double coaxial anodization.The solar cell on the outer surface of the titanium tube was filled with CsPbBr₃.The supercapacitor on the inner surface of the titanium tube,the TiO₂ nanotube with MnO₂ deposited as a positive electrode,and the carbon fiber with Co₃O₄ deposited as a negative electrode,and is assembled with a coaxial manner.The integrated photo-charging supercapacitor has a higher operating voltage and capacity than conventional dye-sensitized solar cell type devices.This research is expected to provide new insights into the design of new integrated energy devices to facilitate the development of solar energy utilization and portable power technology.In conclusion,the research results of this thesis will provide method support for anodizing on valve metal tubes,and provide theoretical basis for accurate evaluation the contact angle on tube substrate,and provide a new strategic ideas and design concepts for the design and development of new integrated energy devices.