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Esha KHARE

TiO2-Polyaniline Supercapacitor









http://www.dailymail.co.uk/news/article-2327021/Teenager-invents-revolutionary-device-charges-cell-phone-20-seconds.html

19 May 2013

Teenager invents revolutionary device which has the potential to charge a cell phone within just 20 SECONDS.
 


A California teen has attracted the attention of tech giants Google for her potentially revolutionary invention which charges a phone in 20 seconds flat.

The super-fast charging device has been dubbed a supercapacitor by 18-year-old Esha Khare, of Saratoga - as she took home $50,000 from the Intel International Science and Engineering Fair, which took place in Phoenix this week.

The device will make waiting hours for a phone to charge a thing of the past and the gizmo packs more energy into a smaller space than traditional phone batteries and holds the charge for longer.

Eesha Khare, 18, of Saratoga, Calif., received the Intel Foundation Young Scientist Award of $50,000 for the invention of a tiny energy-storage device With great power: The supercapacitor is flexible and tiny, and is able to handle 10,000 recharge cycles, more than normal batteries by a factor of 10

So far, Khare has only used her supercapacitor to power a light-emitting diode or LED - but she sees a bright future that one day will see her invention powering cellphones, cars and any gadget that requires a rechargeable battery.

Heading to Harvard, Khare told CBS San Francisco that this is only the start and that she will 'be setting the world on fire' from here.

'My cellphone battery always dies,' she told NBC News when asked what inspired her to work on the energy-storage technology.

Specializing in nanochemistry allowed Khare to reduce the size of her invention. 'Really working at the nanoscale to make significant advances in many different fields.'

'It is also flexible, so it can be used in rollup displays and clothing and fabric,' Khare added.

'It has a lot of different applications and advantages over batteries in that sense.'

The supercapacitor is flexible and tiny, and is able to handle 10,000 recharge cycles, more than normal batteries by a factor of 10.

How an 18-year-old girl has managed to figure out something that multi-national corporations have not has led to her being flooded with offers for her amazing leap forward.

Google have been in contact with Khare to explore how she plans to change the makeup of cell phone battery life.

The new invention may make waiting hours for a phone to charge a thing of the past.



CALIFORNIA STATE SCIENCE FAIR 2013
PROJECT SUMMARY

Project Title

Design and Synthesis of Hydrogenated TiO2-Polyaniline Nanorods for Flexible High-Performance Supercapacitors

Abstract

Objectives/Goals

With the rapid growth of portable electronics, it has become necessary to develop efficient energy-storage technology to match this development. While batteries are currently used for energy-storage, they suffer from long charging times and short cycle life. Electrochemical supercapacitors have attracted attention as energy-storage devices because they bridge the gap between current alternatives of conventional capacitors and batteries, offering higher energy density than conventional capacitors and higher power density than batteries. Despite these advantages, supercapacitor energy density is much lower than batteries and increasing energy density remains a key challenge in supercapacitor research. The goal of this work was to design and synthesize a supercapacitor with increased energy density while maintaining power density and long cycle life.

Methods/Materials

To improve supercapacitor energy density, I designed, synthesized, and characterized a novel core-shell nanorod electrode with hydrogenated TiO2 (H-TiO2) core and polyaniline shell. H-TiO2 acts as the double layer electrostatic core. Good conductivity of H-TiO2 combined with the high pseudocapacitance of polyaniline results in significantly higher overall capacitance and energy density while retaining good power density and cycle life. This new electrode was fabricated into a flexible solid-state device to light an LED to test it in a practical application.

Results

Structural and electrochemical properties of the new electrode were evaluated. It demonstrated high capacitance of 203.3 mF/cm2 (238.5 F/g) compared to the next best alternative supercapacitor in previous research of 80 F/g, due to the design of the core-shell structure. This resulted in excellent energy density of 20.1 Wh/kg, comparable to batteries, while maintaining a high power density of 20540 W/kg. It also demonstrated a much higher cycle life compared to batteries, with a low 32.5% capacitance loss over 10,000 cycles at a high scan rate of 200 mV/s.

Conclusions/Discussion

This project successfully designed, synthesized and characterized a novel nanorod electrode supercapacitor with increased energy density while retaining power density and long cycle life. This work is an important initial step in introducing this new electrode material in supercapacitors to replace conventional batteries in flexible electronic devices.

Summary Statement

This project designed and synthesized a novel supercapacitor with increased energy density while maintaining power density and long cycle life using a new core-shell structure.

Help Received

Used lab equipment at University of California Santa Cruz under the supervision of Dr. Yat Li



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The invention relates to a method for preparing a titania nano rod array composite electrode by a low-temperature hydrothermal method. The method comprises the following preparation steps: firstly, washing a titanium substrate to be clean, polishing the titanium substrate, using distilled water to wash the titanium substrate, and finally drying the titanium substrate for standby; secondly, placing the dried titanium substrate into a reaction kettle which is filled with an alkaline solution, sealing the reaction kettle, heating the solution, and maintaining at the temperature for reaction for 1 to 120 hours; thirdly, cooling the reaction product to the room temperature after the reaction is over; and fourthly, taking out a prepared composite electrode in the reaction kettle after the cooling is over, using the distilled water to wash the composite electrode, flatly lying the washed electrode on an Al2O3 ceramic chip, heating the electrode in the air, cooling the electrode to the room temperature, taking out the electrode, and obtaining the TiO2 nano rod array composite electrode. The method can realize in-situ generation of crystalline TiO2 nano rod arrays by titanium membranes adhered to different substrates, and can obtain substrate/titanium membrane/TiO2 nano rod arrays or structures of titanium substrate/TiO2 nano rod arrays by a one-step hydrothermal method, wherein the titanium membranes can be taken as excellent conductive layers, so that the application scope of the titanium membranes is greatly widened.

DESCRIPTION

Field of technology

The invention belongs to the field of semiconductor thin film technology, in particular to a low-temperature hydrothermal titanium dioxide nanorods composite electrode method.

Second, Background

Existing technologies: nano-TiO2 is an important inorganic functional materials, with their photoelectric conversion, gas, dielectric effects and excellent photocatalytic properties, etc., so that the solar cells, sensors, dielectric materials, self-cleaning materials and photocatalytic degradation of organic compounds have important applications in areas such prospects, become a hot research.
In recent years, many researchers are committed to synthesize different morphologies of TiO2 nano-, micro objects, such as nanotubes, nanorods, nanowires, nanoparticles, etc. (Wang D, Yu B, Hao J, Liu W.Mater Lett2008 ; 62:2036-2038).

In these TiO2 nanometer, micrometer objects in a uniform orientation nanorod arrays as one-dimensional electron conductivity, large surface area, and good chemical stability and optical properties caused widespread concern.

In general, the titanium alkoxide or titanium halide used in the preparation of TiO2 nanorods precursors, but these two substances are often costly and is easy on the environment pollution.

Meanwhile precursor processing requires multiple steps, time-consuming and laborious.

Therefore, the choice of titanium as a precursor prepared by hydrothermal reaction of TiO2 nanorods composite electrode is a simple and practical approach, but hydrothermal solution type and concentration of TiO2 nanorods is a key factor.

Currently, using a variety of physical, chemical and electrochemical techniques prepared titanium dioxide nanowires, nanotubes, nanorods and other powders.

2001 U.S. scientists Varghese using electrochemical oxidation method, for the first time prepared a TiO2 nanotube arrays (Dawei G, et al, J.Mater. Res., 2001,16:3331), followed by high temperature heat treatment to obtain crystals of the nanotube array and exhibit excellent gas, photocatalytic properties.

Currently on the preparation of TiO2 nanorods thermal oxidation method, template method, hydrothermal method, atomic beam deposition method.

2005 PENG.X method using thermal oxidation temperature oxidation of titanium substrate prepared TiO2 nanorods (PENG.X, Appl.
Phys. A, 2005,80:473), this method requires heating and oxidation step, and the need to carry out in an inert atmosphere under high-temperature oxidation protection, so the process is complicated, the equipment requirements.

Other research group using the AAO template prepared TiO2 nanorods (Jiang Wufeng, etc., Materials Science and Engineering, 2006,104:805), AAO template as a generic template has been applied to the preparation of a variety of substances tube, rod array However, the biggest disadvantage of this method is the use of AAO template can not be repeated, and is not suitable for large-scale preparation.

2006 Nanjing University of Ma Guobin reported using titanium tetrachloride as the precursor, the use of microwave hydrothermal method in silicon and glass coverslips were prepared rutile TiO2 nanorods (Ma Guobin, etc., Chinese Journal of Stereology and Image Analysis , 2006,11 (4): 243), but its preparation process is complicated, the binding force of the film and the substrate is not good, and the titanium tetrachloride may cause pollution to the environment.

2008 Wilson Smith, who used an atomic beam deposition method on silicon or glass slides were prepared composite TiO2 nanorods array and shows excellent photocatalytic properties.

Preparation of this physical equipment requirements, the production cost is higher.

Based on the above advantages and disadvantages of various methods known hydrothermal method is an efficient, low cost, simple and practical step in preparing crystalline TiO2 nanorods array.

Including Zhejiang University, Wu Jinming in 2005, 2006 applications on the surface of the metal titanium, hydrogen peroxide solution in water of TiO2 nanorods patent (Wu Jinming, CN200510060751, CN200610052743.9).

These two patents in a hot solution of water used in the hydrogen peroxide solution are single component.

Thus, the preparation of TiO2 nanorods technical difficulties: (1) titanium dioxide nanorods sexual orientation is difficult to be controlled, or directed to be deposited by means of a template to grow, but this method is cumbersome, and equipment requirements for higher; (2) TiO2 nanorods array and a contact layer for the mechanical properties of nanorod arrays is particularly important.

If TiO2 nanorods grown in situ on titanium surface is made of pure titanium layer as a thin film of TiO2 nanorods contact layer, you can ensure that TiO2 nanorod array film layer has good mechanical properties.

Select other materials as the substrate tends to cause TiO2 nanorods binding properties of the film and the substrate is not good, thus affecting its application performance; (3) hydrothermal method is simple and practical, but the water type and concentration of the hot solution is prepared in a single orientation TiO2 nanorods are two key factors.

Generally, the hydrothermal reaction is a directional dimension of growth characteristics, the product is grown while the three-dimensional space, are often the product particles.

To prepare the product of the growth in a particular dimension, you must use a special solution with directional adsorbed substances can restrict the growth direction of the other dimensions, to ensure the direction of substance in the growth of a particular dimension.
On the other hand, the solution concentration can affect the reaction rate and direction of the reaction.

In the hydrothermal reaction substance is first dissolved in a hot solution of water and high pressure conditions in the nucleation, crystal growth and dissolution reaction is to provide crystal growth material, the crystal growth is the consumption of raw materials.

Therefore, only at the right concentration to make the raw materials under the "output" and "consumption" balance of these two processes carried out in order to ensure a uniform product orientation, or can not control the morphology and orientation.

III SUMMARY OF THE INVENTION

Technical issues: The present invention addresses the above-mentioned technical defects, providing a low-temperature hydrothermal titanium dioxide nanorods composite electrode method, which can be prepared a single orientation, and the substrate with good adhesion of titanium dioxide nanorods composite electrode.

Technical solutions: low-temperature hydrothermal titanium dioxide nanorods composite electrode prepared by the method steps of: titanium substrate processing: first clean the titanium substrate, and then the titanium substrate concentration in HF 1 ~ 38.2wt% of hydrofluoric acid solution, HNO3 concentration of 1 ~ 65wt% of the nitric acid solution and a mixed solution of distilled water polishing 1 ~ 60min, the mixed solution of hydrofluoric acid: nitric acid: distilled water in a volume ratio of 1:1:5 ~ 1:10:100, distilled water, and finally drying stand; titania nanorod array composite electrode preparation: the dried titanium substrate with an alkaline solution into the reaction vessel, the volume of the alkaline solution accounted reactor volume of 1/5 to 4/5; The reactor was sealed and heated, a heating rate of 1 ? / min ~ 20 ? / min, heated to 60 ? ~ 280 ?, maintaining the temperature the reaction 1 ~ 120h; completion of the reaction cooled to room temperature; cool the reactor after completion of the composite electrode was prepared by washing with distilled out, after washing the electrode on the Al2O3 ceramic flat sheet, in air at 5 ? min-1 rate of heating to 300-700 ?, After the temperature control to maintain the desired temperature 2h, then cooled to room temperature, after the removal, to obtain TiO2 nanorods composite electrode.

The alkaline solution is tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, ammonia, sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide, or magnesium hydroxide in combination of one or more alkaline solution, wherein the alkali concentration of the solute 0.001M ~ 10M.

The titanium substrate is titanium body or on the conductive glass, silicon, aluminum or stainless steel carrier by magnetron sputtering or vapor deposition or atomic beam deposition methods such as titanium film was prepared.

The reaction vessel was cooled with liquid nitrogen cooling, air cooling, quenching, water cooling, a cooling ice bath.

The reactor of PTFE lined reaction vessel or a titanium autoclave.

Beneficial effects:

1, attached to the present invention can realize different substrates (such as a conductive glass, stainless steel, silicon) generated in situ crystallization of a titanium film of TiO2 nano-rod array, as long as step hydrothermal method can obtain such a substrate / Ti Film / TiO2 nanorods or titanium substrate / TiO2 nanorods array structure, in which the titanium film can be used as an excellent conductive layer, greatly expand its scope of application.

2, single-component and multi-component alkaline solution can be achieved controlled morphology TiO2 nanorods.

Morphology changes will bring changes in performance, particularly TiO2 specific crystal plane can be regulated in the proportion of the crystals in order to achieve the performance of the controllability, to meet a variety of application requirements.

Fourth, BRIEF DESCRIPTION

Figure 1, the present invention is prepared titanium sheet as the base cone-type TiO2 nanorods array scanning electron micrograph (FESEM)

Figure 2, the present invention is prepared titanium sheet as the base cone-type TiO2 nanorods sectional scanning electron micrograph (FESEM)

Figure 3, the present invention is prepared by conductive glass substrate rectangular columnar TiO2 nanorods array scanning electron micrograph (FESEM)

Figure 4, the present invention is prepared by conductive glass substrate rectangular columnar TiO2 nanorods sectional scanning electron micrograph (FESEM)

Figure 5, the cone-type TiO2 nanorods X-ray diffraction (XRD).

Figure 6, the rectangular columnar TiO2 nanorods X-ray diffraction (XRD).

Figure 7, the present invention is prepared in the basement of the rectangular stainless steel cylindrical TiO2 nanorods array scanning electron micrograph (FESEM)

Fifth, the specific embodiments

Through the implementation of the following specific examples, detailed instructions for preparing TiO2 nanorods.

Example 1

A first step, the first titanium immersed successively put in acetone, alcohol, ultrasonic cleaning in distilled water, respectively, 15min, and titanium was 38.2wt% in the HF concentration of hydrofluoric acid solution, HNO3 concentration of 65wt% nitric acid solution and distilled water The mixed solution (hydrofluoric acid solution: nitric acid solution: distilled water volume ratio: 1:1:5) to polish 1.5min, distilled water 1min, and then dried in an oven at 70 ? stand.

The second step, the configuration of 1M tetramethylammonium hydroxide (TMAOH) solution 70ml, 100ml into a reaction vessel lined with polytetrafluoroethylene in.

The third step will be pre-treated titanium plate placed in an autoclave lined in sealed reactor.

The reaction kettle was heated oven, heating rate 1 ? / min, heated to 200 ? after heat 12h.

The fourth step, the reaction after 12h, close the oven, cooled to room temperature.

Open kettle, remove the titanium plate rinsed with distilled water three times.

After rinsing the electrode flat on Al2O3 ceramic pieces, put in a box furnace in air at 5 ? min-1 speed is raised to 450 ?, insulation 2h, then cooled to room temperature in the furnace samples removed after, you can obtain titanium / TiO2 nanorods composite electrode.
Test Results: Figure 1 shows, titanium surface covered by TiO2 nanorods, TiO2 nanorods have a uniform upward orientation of the nanorods were cone-shaped.

TiO2 nanorods with diameters about 100nm.

Sectional view of Figure 2 can be seen the length of TiO2 nanorods about 600nm, and arranged well, vertical growth substrate.
Figure 5 shows the results of a single nanorod TiO2 anatase crystal.

Example 2

First step, the titanium film is coated with a conductive glass substrate (titanium magnetron sputtering of the conductive film on the glass substrate) were immersed put in acetone, alcohol, distilled water, ultrasonic cleaning, respectively, 15min, and the substrate is HF concentration of 1wt% hydrofluoric acid solution, HNO3 concentration of 30wt% nitric acid solution and distilled water mixed solution (hydrofluoric acid: nitric acid: distilled water volume ratio is: 1:10:100) to polish 60min, distilled water Rinse 1min, and then dried in an oven at 70 ? stand.

The second step, the configuration of 1M solution of tetraethyl ammonium hydroxide (TEAOH) 80ml, 100ml loaded polytetrafluoroethylene lined reactor in.

The third step, the pretreated substrate placed in an autoclave lined in sealed reactor.

The reaction kettle was heated oven, heating rate 10 ? / min, heated to 220 ? after heat 12h.

The fourth step, the reaction after 12h, close the oven, hair cool down to room temperature.

Open kettle, the substrate taken out 3 times with distilled water.

After rinsing the electrode flat on Al2O3 ceramic pieces, put in a box furnace in air at 5 ? min-1 speed is raised to 500 ?, insulation 1h, after the sample was cooled to room temperature in the furnace removed, you can Get conductive glass / titanium film / TiO2 nanorods composite electrode.

Test Results: Figure 3 shows the morphology of four nanorods prism rod, the top of the saddle double cone structure, the rod diameter of about 200nm.

From Figure 4, a uniform nanorods orientation and perpendicular to the growth substrate, length of the rod about 1m.

Figure 6 shows a single nanorod TiO2 anatase crystal.

Example 3

First step, the titanium film is coated with a stainless steel substrate (titanium film is deposited onto the atom beam stainless steel substrate) were immersed put in acetone, alcohol, distilled water, ultrasonic cleaning, respectively, 15min, and the HF concentration in the titanium substrate of 15wt% hydrofluoric acid solution, HNO3 concentration of 1wt% of the nitric acid solution and distilled water mixed solution (hydrofluoric acid: nitric acid: distilled water volume ratio: 1:5:10) to polish 30min, 1min distilled water , and then dried in an oven at 70 ? stand.

The second step, the configuration of 1M tetrabutyl ammonium hydroxide (TBAOH) and 0.01M sodium hydroxide (NaOH) mixed solution of 60ml, 100ml of titanium into the kettle.

The third step, the pretreated substrate placed in an autoclave lined in sealed reactor.

The reaction kettle was heated oven, heating rate 20 ? / min, heated to 230 ?, the heat 24h.

The fourth step, the reaction 24h, close the oven, cooled to room temperature water.

Open kettle, the substrate taken out 3 times with distilled water.

After rinsing the electrode flat on Al2O3 ceramic pieces, put in a box furnace in air at 5 ? min-1 speed is raised to 450 ?, insulation 1h, after the sample was cooled to room temperature in the furnace removed, you can Get stainless steel sheet / titanium film / TiO2 nanorods composite electrode.

Test Results: Figure 7 shows, nanorods quadrangular prism shape is a rod, the top of the saddle biconical structure, the rod diameter of about 200nm.




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