مشخصه يابي خواص الكتروشيميايي و فتوالكتروشيميايي نانو لوله هاي اكسيد تيتانيم آندي

چكيده انگليسي :

Characterization of Electrochemical and Photo electrochemical Properties of Anodic Titanium Oxide Nanotubes Seyed Shahab Miraghaei s miraghaei@ma iut ac ir February 18 2012 Department of Materials Engineering Isfahan University of Technology Isfahan 84156 83111 IranAbstractThe present report describes the main results and achievements regarding the electrochemicaland photoelectrochemical investigation of as formed and annealed TiO2 nanotubes TNTs Titanium oxide nanotubes were prepared by anodic oxidation of titanium within fluoridecontaining ethylene glycol and potassium sulfate solutions Using an electrochemicalapproach it has been shown that as formed nanotubes are not stable on the substrate due tothe dissolution of fluoride rich layer between and beneath them resulting in formation of anew barrier layer between TNTs and metal substrate by re anodization in aqueous solutions This new anodic barrier layer which forms inevitably by any anodic polarization of theunstable interface of titanium nanotubes plays an important role in controlling thephysicochemical behavior of the whole system Weak photoresponse of TNTs beforeannealing which has been considered to be a result of amorphous structure of tube walls nowcan also be related to the lack of electrical and mechanical contact between nanotubes and thesubstrate Annealing nanotubes in air transforms amorphous TiO2 to crystalline polymorphsand forms a new oxide layer on the surface of titanium which noticeably changes theelectrochemical and photo electrochemical behavior of TNTs Sintering of nanotubes bottomto the underlying oxide layer formed during annealing has found to be very important sincea good electrical connection is necessary for charge carriers passage into the metal substrate Crystalline structure of tube walls causes different formation separation and transportation ofcharges in contrast to the as formed nanotubes which is mainly diffusion controlled and isindependent of electrode potential Capacitance behavior of annealed nanotubes wasexplained using a qualitative model showing two kinds of behavior in the anodic and cathodicpotential regions In the anodic region capacitance of TNTs is mainly controlled by thecapacitance of semiconductor space charge layer adjacent to the underlying substrate but inthe cathode region capacitance is controlled by chemical capacitance of double layer alongthe internal surface area of nanotubes In the cathodic region nanotubes behave as a supercapacitor showing several order of magnitude higher values of capacitance Nitrogen wassuccessfully incorporated into the titania barrier layer structure during anodization of titaniumin ammonium containing solutions It has been shown that nitrogen incorporation isresponsible for the increase of the visible light photoresponse of barrier layers due to theformation of electronic localized states within the energy gap of TiO2 above the valence bandedge In spite of some weak visible photoresponse from TNTs formed in ammoniumcontaining electrolytes and after annealing it seems that the mechanism of charge separation transport and collection for photocurrent generation within TNTs and nitrogen incorporatedtitania barrier layers are not coincide According to the electronic band structure of dopedtitanium oxide and the model presented for photocurrent generation in TNTs it has beenexplained that doping if TNTs is not a powerful mean for extending their photoresponse tothe visible region Keywords TiO2 nanotubes Photo electrochemical Annealing Photocurrent Adhesion Re anodization Doping Nitrogen

ميرآقايي، شهاب

مشخصه يابي خواص الكتروشيميايي و فتوالكتروشيميايي نانو لوله هاي اكسيد تيتانيم آندي

بازآندايزينگ، فتوجريان، چسبندگي، تلقيح، نيتروژن.