Study On The Preparation Of Anodic TiO₂ Nanotubes And Their Supercapacitor Properties

The supercapacitor is an energy storage device between a conventional capacitor and a rechargeable battery.Because of its short charge-discharge time?high power density and long cycle life and other advantages,it has a great potential in many applications,such as electric mobile?advancing the development of new energy storage and other portable electronic equipment.Usually,supercapacitor electrode materials have a large surface area,high ionic and electric conductivity,good mechanical and chemical stability and so on.In many nanomaterials,the longitudinal axis of one-dimensional nanostructures can provide efficient transport pathway for both electrons and ions.Compared to solid nanostructures(e.g.nanowires),nanotubular structures can offer higher surface area with less mass,which could lead to more gravimetric specific capacitance.Anodic Ti O2 nanotubes were widely studied due to its simple way to preparation?vertical distribution of nanotubes on Ti substrate?large area preparation can be realized and so on.Ti O2 nanotubes is suitable to be studied as supercapacitor electrode material,due to its large surface area and tubular structure.The main contents are summarized as bellow:Firstly,we did a series of contrast test on parameters in preparation of anodic Ti O2 nanotubes,and we find the relationship between changing the parameters and anodic current – time curve or Ti O2 nanotubes morphology.Concerning the anodic current – time curve: With the increase of electrolyte water content,the increase of NH4 F quantity and the increase of voltage,the anodic oxidation current entering the steady stage is also increasing;with the increase of NH4 F quantity and the reduce of voltage,the peak of anodic current – time curve is reducing,and in the shorter time to form nanotubes.Concerning the Ti O2 nanotubes morphology: The increase in the rotational speed of the stirring rotor,the decrease of spacing between the cathode and anode,the increase of electrolyte water content and the increase of NH4 F quantity and the increase of voltage,they all help to get clean surface with no barrier layer attached to the Ti O2 nanotubes.The well-morphology Ti O2 nanotubes obtained when the water content of the electrolyte is 10vol%,the NH4 F content is 0.5wt%,the stirring rotor speed is 150r/min,the distance between the cathode and the anode is 2.5cm,and the oxidation voltage is 60 V.The diameter of the obtained Ti O2 nanotubes is linearly related to the anodic oxidation voltage,and the diameter of the nanotubes is about four times that of the oxidation voltage.Secondly,we studied the Ti O2 nanotubes at different temperatures and different times of annealing,compared their electrochemical properties: Under the condition of 2h annealing,the capacitance of nanotubes decreased first,then increased and decreased again with the further increase of annealing temperature.At the annealing temperature of 450 ?,the capacitance of the nanotubes decreases with the increase of annealing time.After comparing the charge and discharge characteristics of untreated,annealed and reduced Ti O2 nanotubes,we find: Compared with the untreated nanotubes,the energy storage efficiency of the annealed and reduced Ti O2 nanotubes was improved obviously;The reduced Ti O2 nanotubes have the largest charge and discharge energy and energy storage efficiency.The cycling performance of the untreated,annealed and reduced Ti O2 nanotubes was increased in sequence.The percent retention of capacitors was 2.71%,31.65% and 94.31%,respectively.The three-electrode method for annealed Ti O2 nanotubes showed that it was n-type semiconductors under positive bias,and can attain 1V in a shorter time and with a small current compared to negative bias,which limit to the increasing of capacitance result from electron accumulated in accumulation layer.Finally,we used cathode reduction method to prepare composite electrode material of reduced graphene Ti O2 nanotubes.The capacitance performance of the sample decreases with the increase of voltage at 1V,1.25 V,1.5V,1.75 V and 2V for 30 min,and the cycle performance is improved.The graphene oxide film and the Ti O2 nanotube are composed of asymmetric supercapacitor,after 250 cycles,the capacitor significantly increased,but the complex impedance also increased.