Small-grain-size brookite titanium dioxide nano-powder and preparation method and application thereof

A small particle size brookite titanium dioxide nano powder and its preparation method and applicationTechnical field

[0001] The present invention relates to a small particle size brookite titanium dioxide (Ti02) nano powder and its preparation method and its application in dye-sensitized solar cells, belonging to the technical field of new materials and solar cells.

Background technique

[0002] Since the 20th century, the development and utilization of new energy, especially renewable green energy, has become one of the focus issues that countries around the world pay attention to. Among them, dye-sensitized solar cells (Dye-Sensitized Solar Cells, DSSCs) have received extensive attention because of their high photoelectric conversion efficiency and low cost. Different from traditional silicon-based photovoltaic cells, DSSCs can separate the light absorption and charge transfer processes, and have the advantages of low cost and simple manufacturing process, so they have become a research hotspot in the field of solar cells. Among them, nano-TiO2 has become the most researched photoanode porous film material in the field of DSSCs because of its non-toxic, high thermal and chemical stability, and light corrosion resistance. Generally speaking, adsorption of more dye molecules and fast transport of photogenerated electrons are necessary properties of nano-TiO2 porous film; and the crystal form, band structure, morphology and surface/interface properties of TiO2 can absorb dyes, The transport of photogenerated electrons and the photoelectrochemical process of DSSCs will have obvious effects.

[0003] Among the three TiO2 crystal phases that exist in nature, anatase TiO2 nanomaterials are widely used in the preparation of DSSCs photoanodes, and research on the use of brookite TiO2 as the photoanode porous film material of DSSCs is very rare. Compared with anatase Ti02-based DSSCs, the photoelectric conversion efficiency of brookite Ti02-based DSSCs is much lower. This is mainly limited by the low dye adsorption capacity of brookite Ti02 and poor electron collection efficiency. However, theoretical and experimental results show that brookite TiO2 has a more negative flat band potential and Fermi level than anatase TiO2, and the lower surface activity of brookite TiO2 can reduce charge recombination, which is expected to be more High open circuit voltage of DSSCs. In addition, brookite TiO2 is an orthorhombic crystal structure with low symmetry, which has a very small effect on the formation of charge carriers, and it can exhibit a better-shaped photoelectric conversion behavior spectrum when used in DSSCs cells. The above-mentioned performance advantages have gradually attracted people's attention and provided new ideas for improving the photoelectric conversion performance of DSSCs. However, because brookite TiO2 is a thermodynamic metastable phase, traditional chemical synthesis methods are often difficult to obtain pure brookite TiO2 materials with high crystal phase purity and crystallinity; and there are few literature reports on the synthesis of pure plates. Titanium ore TiO2 are all nano- or sub-micron particles with a larger particle size. The above factors limit the application of brookite Ti02 in DSSCs and its electrical properties. Improved pool efficiency. It can be seen that seeking a new synthesis method to obtain small particle size brookite Ti02 nanopowder can overcome the inherent defects of low dye adsorption and poor electron collection efficiency, thereby improving the photoelectric conversion efficiency of brookite-based DSSCs. Important theoretical value and practical significance.

Summary of the invention

[0004] In order to overcome the inherent defects of low dye adsorption capacity and poor conductivity of brookite TiO2, the present invention provides a brookite TiO2 nanoparticle with a high crystal phase purity and thermal stability with a smaller particle size. Powder and its synthesis method. A simple hydrothermal method is used to prepare a small-diameter brookite TiO2 nanopowder with a particle size of about 10nm, and the product also contains a small amount of brookite TiO2 nanorods with a length of about 100nm. This small particle size brookite Ti02 nano-powder can effectively increase the specific surface area of the brookite Ti02 porous membrane, which is beneficial to increase the dye adsorption capacity of the photoanode porous membrane, thereby making up for the dye-anchored adsorption sites on the brookite Ti02 surface Defects with low point density further improve the photoelectric conversion efficiency of brookite Ti02-based DSSCs.

[0005] The technical solutions adopted by the present invention are specifically as follows:

[0006] A preparation method of small particle size brookite titanium dioxide nano powder includes the following steps:

[0007] 1) Under ice-water bath conditions, titanium tetrachloride was added dropwise to deionized water, and then urea solid, sodium lactate solution and lead nitrate solution were sequentially added, and stirred evenly to obtain a precursor solution;

[0008] 2) Transfer the precursor solution obtained in step 1) to a hydrothermal kettle for a hydrothermal reaction at 200°C for 20 hours;

[0009] 3) The product obtained in step 2) is subjected to centrifugal separation, washing, and drying in sequence, and then the temperature is increased to 500 °C at a rate of 2 °C/min, and then smoked for 3 hours to obtain small particle size brookite TiO2 nano Powder.

[0010] In step 1), the mass ratio of titanium tetrachloride and deionized water is 1:15, the mass ratio of titanium tetrachloride and urea is 1:1.8, and the concentration of sodium lactate in the sodium lactate solution is 60 wt. %, the volume ratio of the deionized water and the sodium lactate solution is 1:8, and the molar ratio of the titanium tetrachloride and lead nitrate is 99:1.

[0011] In step 3), the washing method is: first washing with deionized water, and then washing with ethanol.

[0012] Step 3), the drying method is: 70 ° C air drying.

[0013] A kind of small particle size brookite titanium dioxide nano powder prepared by the above-mentioned preparation method of small particle size brookite titanium dioxide nano powder.

[0014] The application of the above-mentioned small particle size brookite titanium dioxide nano powder in dye-sensitized solar cells.

[0015] A dye-sensitized brookite TiO2 photoanode, prepared by the following method:

[0016] 1) The above-mentioned small particle size brookite TiO2 powder was ball-milled and mixed with ethanol, terpineol, acetic acid and ethyl cellulose for 12 hours to prepare a small particle size brookite TiO2 photoanode slurry;

[0017] 2) Using tape to control the film thickness, use the doctor blade method to scrape the small particle size brookite TiO2 photoanode slurry prepared above on the FT0 conductive glass, dry it and place it in a muffle furnace, and program the temperature Burn at 500°C for 30 minutes to remove organic matter in the membrane to obtain a brookite TiO2 porous membrane photoanode;

[0018] 3) The prepared brookite TiO2 porous film photoanode was immersed in a 0.3mM N719 ethanol solution overnight to obtain a dye-sensitized brookite TiO2 photoanode.

[0019] The application of the above-mentioned dye-sensitized brookite TiO2 photoanode in the field of optoelectronics.

[0020] Use a clamp to clamp the dye-sensitized brookite TiO2 photoanode and the ITO glass counter electrode of the sputtering clamp face-to-face, and inject the liquid electrolyte into the gap between the two to form DSSCs with a sandwich structure.

[0021] The present invention uses a simple hydrothermal synthesis method to prepare small-diameter brookite TiO2 nano-powders. The main body is brookite TiO2 nano-particles with a particle size of about 10nm and a small amount of brookite with a length of about 100nm. Brookite Ti02 nanorods. The product not only has high crystal phase purity and thermal stability, but also has better than commercial TiO2 nanoparticles (P25, the particle size is about 20nm, the specific surface area is about 50m²/g) Smaller particle size (about 10nm) and larger specific surface area (about 122m²/g), which is beneficial to increase the amount of dye adsorption, and can effectively overcome the inherent defects of low dye adsorption and poor electron collection efficiency of brookite TiO2 as a photoanode material, which is the best solution for brookite TiO2-based DSSCs. The improvement of photoelectric conversion performance provides a brand new idea.

[0022] The brookite TiO2 based DSSCs constructed by the traditional method of preparing the slurry effectively overcomes the inherent defects of low dye adsorption and poor electron collection efficiency of the brookite TiO2 as a photoanode material, and significantly Improve the photoelectric conversion efficiency of brookite Ti02-based DSSCs.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0024] 1. The raw materials of the present invention are cheap and easy to obtain, the synthesis process is simple, and the obtained product is brookite TiO2 nanoparticles with a high degree of crystal phase and good thermal stability.

[0025] 2. The main component of the product obtained in the present invention is brookite TiCh nanoparticles with a particle size of ~10nm, and its specific surface area is about 122m²/g, much larger than the specific surface area of commercial TiO2 nanopowder (P25) (about 50m²/g), can effectively increase the dye adsorption capacity of the photoanode porous film, so as to make up for the low density of dye anchors on the surface of brookite TiO2.

[0026] 3. The brookite TiO2 prepared by the present invention has more negative flat band potential and Fermi level, and its lower surface activity can reduce the recombination of electrons, so that its DSSCs have a higher open circuit voltage.

[0027] 4. The present invention constructs the prepared small particle size brookite TiO2 nano powder into brookite-based DSSCs, and its optimal photoelectric conversion efficiency is as high as 6.36%, which is much higher than that of P25-based DSSCs constructed under the same conditions. Photoelectric conversion efficiency (5.22%).

Description of the drawings

[0028] Figure 1 is the XRD spectrum of the synthesized small particle size brookite TiO2 nanopowder.

[0029] FIG. 2 is a TEM image of the small particle size brookite TiO2 nanopowder synthesized in the present invention; FIG. 2(a) is a TEM image enlarged by 100,000 times, and FIG. 2(b) is a TEM image enlarged by 1 million times Figure.

[0030] FIG. 3 is the N2 adsorption-desorption curve of the small particle size brookite TiO2 nano powder and P25 synthesized in the present invention; wherein, curve (a) represents the small particle size brookite TiO2 nano powder synthesized in the present invention Body, curve (b) represents the commercial TiO2 nanoparticles P25_O

[0031] FIG. 4 is the JV curve of the small particle size brookite TiO2-based DSSCs with different film thicknesses and the P25-based DSSC in Example 6.

Detailed ways

[0032] The present invention will be further described below in conjunction with the examples and drawings, but the implementation of the present invention is not limited to this. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

Example 1

[0034] Press TiCl₄: The mass ratio of deionized water is 1:15. TiCh is added dropwise to the deionized water (40mL) whose temperature is 0 °C controlled by an ice water bath, and then urea (5g) and sodium lactate solution (the mass ratio is 60 %, 5mL), and Pb (Νθ3) 2 solution (1mol% Pb(N03) 2 solution), where TiCl₄/Urea mass ratio is 1:1.8, deionized water/sodium lactate solution volume ratio is 1:8, TiCl₄The molar ratio of /Pb(N03)2 is 99:1; after stirring evenly, it is transferred to a hydrothermal kettle (volume 100mL) for hydrothermal reaction at 200 °C for 20 hours, and the product is centrifuged, washed with water and alcohol, and dried in air at 70 °C. Then, the temperature is increased to 500°C at a heating rate of 2°C/min, and then smoked for 3 hours to obtain the small particle size brookite Ti02 nano-powder.

[0035] FIG. 1 is an X-ray diffraction (XRD) spectrum of a small particle size brookite TiO2 nanopowder synthesized by a hydrothermal method. It can be seen from Figure 1 that the characteristic peak of brookite appears at 29 = 30.8°, which corresponds to the (121) crystal plane (JCPDS65-2448) of orthorhombic brookite Ti02, and at 2θ = 25.3°, 20.8 °, 36.2°, 37.3°, 40.1°, 42.4°, 46.0°, 48.0° and 49.1° diffraction peaks correspond to brookite (210), (111), (211), (102), (021) ), (202), (221), (302), (321) and (312) crystal plane diffraction. There is no characteristic diffraction peak belonging to rutile or anatase TiCh in the XRD spectrum of the product smoked at 500 °C, indicating that the small particle size brookite Ti02 nano-powder synthesized in the present invention has high crystallinity and crystallinity. Phase purity and thermal stability.

[0036] It can be clearly observed from Figure 2 (a) that the synthesized small-diameter brookite TiO2 nanopowders are mainly particles with a particle size of about 10 nm, accompanied by a small amount of nanorods with a length of about 100 nm. From the TEM image shown in Figure 2(b), the lattice fringes with a spacing of 0.346 nm can be clearly observed, which corresponds to the interplanar spacing value of the (111) plane of brookite TiCh, which is the same as that observed in the XRD spectrum. The results of the obtained strong characteristic diffraction peaks are consistent, indicating that the small-diameter brookite Ti()2 nanoparticles synthesized in the present invention have higher crystallinity and crystal phase purity.

[0037] FIG. 3 is the N2 adsorption-desorption curve of the small particle size brookite TiCh nano-powder and P25 synthesized in the present invention. It can be seen from the figure that the small particle size brookite Ti02 nanopowder shows a typical type IV N2 adsorption-desorption curve, which is generally considered to be the result of N2 condensation in the pores between the stacked nanoparticles, and its BET specific surface area is about 122m²/g, much larger than the specific surface area of P25 (about 50m7g)_oThe smaller particle size and larger specific surface area of the small particle size brookite Ti02 nano-powder is beneficial to the adsorption of dyes and the improvement of the corresponding DSSCs performance.

[0038] The slurry was prepared using a traditional preparation process. For example, weigh 1g of small particle size brookite Ti02 powder, 5.0 mL ethanol, 3.2 mL terpineol, 0.2 mL acetic acid, and 0.5 g ethyl cellulose, and mix for 12 hours to prepare a TiO2 photoanode slurry. The thickness of the film is controlled by tape, and the small particle size brookite Ti02 porous film photoanode is prepared by the traditional doctor blade method. For example, the small particle size brookite Ti02 slurry prepared above is scraped on the FTO conductive glass, and after drying, the muffle furnace is heated to 500°C and smoked for 30 minutes to remove the organic matter in the film. The prepared small particle size brookite Ti02 porous film photoanode is immersed in a 0.3mMN719 ethanol solution overnight to obtain a dye-sensitized brookite Ti02 photoanode. Use a clamp to clamp the dye-sensitized brookite Ti02 photoanode and the ITO glass counter electrode of the sputtering clamp face-to-face, and inject the liquid electrolyte into the gap between the two to form a sandwich structure of DSSCs ο

[0039] In the same preparation method, small particle size brookite TiO2 nanopowder was replaced with commercial P25 nanopowder to prepare P25 slurry, and P25 photoanode was prepared and P25-based DSSCs were assembled.

Example 2

[0041] With a layer of tape to control the film thickness, the small particle size brookite Ti02 slurry prepared above was scraped on the FTO conductive glass using a doctor blade method, and after drying, the muffle furnace was programmed to heat up to 500 °C, Smoke and burn for 30 minutes to remove organic matter in the film. The prepared brookite Ti02 porous film photoanode was immersed in 0.3mM N719 ethanol solution overnight to obtain the dye-sensitized brookite Ti02 photoanode (BTPl).

Example 3

[0043] The thickness of the film was controlled with two layers of tape, and the small particle size brookite Ti02 slurry prepared above was scraped on the FTO conductive glass using a doctor blade method, and after drying, the muffle furnace was programmed to heat up to 500°C, Calcined for 30 minutes to completely remove the organic matter in the film. The prepared brookite TiO2 porous film photoanode was immersed in a 0.3mM N719 ethanol solution overnight to obtain a dye-sensitized brookite TiO2 photoanode (BTP2).

Example 4

[0045] The thickness of the film was controlled with 3 layers of tape, and the small particle size brookite Ti02 slurry prepared above was scraped on the FTO conductive glass using a doctor blade method. After drying, the muffle furnace was programmed to heat up to 500 °C, Smoke and burn for 30 minutes to remove organic matter in the film. The prepared brookite TiO2 porous film photoanode was immersed in a 0.3mM N719 ethanol solution overnight to obtain a dye-sensitized brookite TiO2 photoanode (BTP3).

Embodiment 5

[0047] The film thickness was controlled with 4 layers of tape, and the small particle size brookite Ti02 slurry prepared above was scraped on the FTO conductive glass using a doctor blade method. After drying, the muffle furnace was programmed to heat up to 500 °C, Smoke and burn for 30 minutes to remove organic matter in the film. The prepared brookite TiO2 porous film photoanode was immersed in a 0.3mM N719 ethanol solution overnight to obtain a dye-sensitized brookite TiO2 photoanode (BTP4).

Example 6

[0049] The thickness of the film was controlled with 2 layers of tape, and the P25 slurry was scraped on the FTO conductive glass using a doctor blade method. After drying, the muffle furnace was heated to 500° C. and burned for 30 minutes to remove the organic matter in the film. The prepared P25 photoanode was immersed in 0.3mMN719 ethanol solution overnight to obtain the dye-sensitized P25 photoanode (P25).

[0050] Battery assembly: Use clamps to clamp the above-mentioned dye-sensitized photoanode (Examples 2-5 and Example 6) and the ITO glass counter electrode of the sputtering clamp face-to-face, and inject liquid electrolyte into the gap between the two , The electrolyte of the sandwich structure DSSCs contains 0.05M 12, 0.5M HI, 0.1M 4-butyl pyrrolidone, and the solvent uses a 1:1 mixed solution of propylene carbonate and ethyl glutamate in a volume ratio. In order to reduce the light scattering phenomenon at the edge of the Ti02 electrode, a self-made light barrier is used to control the light area to 0.25cm² ο

[0051] Performance test:

[0052] The photoelectric performance of the battery was tested under the irradiation of a simulated solar light source (Oriel, USA) of 300W.AM1.5G (light intensity of 100mW/cm²), and use electrochemical workstation (CHI618, Shanghai Chenhua) to record the photocurrent-voltage (JV) curve.

[0053] It can be seen from Figure 4 that the open circuit voltage of the brookite TiO2-based DSSC obtained in Example 2 is 0.72V, and the short-circuit current density is 10.6mA/cm², The fill factor is 0.69, and the corresponding photoelectric conversion efficiency is 5.25%. The open circuit voltage of the brookite Ti02-based DSSC obtained in Example 3 was 0.69V, and the short-circuit current density was 12.8mA/cm², The fill factor is 0.72, and the corresponding photoelectric conversion efficiency is 6.36%. The open circuit voltage of the brookite Ti02-based DSSC obtained in Example 4 was 0.70V, and the short-circuit current density was 12.4mA/cm², The fill factor is 0.72, and the corresponding photoelectric conversion efficiency is 6.17%. The open circuit voltage of the brookite Ti02-based DSSC obtained in Example 5 was 0.67V, and the short-circuit current density was 11.9mA/cm², The fill factor is 0.71, and the corresponding photoelectric conversion efficiency is 5.71%. The open circuit voltage of the P25-based DSSC obtained in Comparative Example 6 was 0.64V, and the short-circuit current density was 11.8mA/cm.², The fill factor is 0.69, and the corresponding photoelectric conversion efficiency is 5.22%.

[0054] Generally speaking, the more dye molecules adsorbed by the photoanode, the more excited electrons will be injected into the conduction band of TiO2, thereby increasing the short-circuit current density of DSSCs. On the other hand, if the transmission path of injected electrons from the TiO2 nanoparticles to the FTO layer is too long, it is not conducive to improving the photoelectric conversion efficiency of DSSCs, because the too long path will increase the probability of electron recombination. In addition, the small particle size brookite TiO2 nano powder provided by the present invention has a very small particle size, and the pores between the particles are very limited. If the film thickness of the photoanode is increased blindly, the photoanode film will become too dense, which is not conducive to the diffusion of the electrolyte in the TiO2 film. This will hinder the transfer of charges in the electrolyte, resulting in a decrease in short-circuit current density. However, the fill factor of DSSCs constructed in Examples 2-5 showed a decreasing trend with the increase of film thickness, which can prove the above conjecture from another aspect. In other words, when the film thickness exceeds the optimal value, continuing to increase the thickness will increase the probability of charge recombination and cause a decrease in the photoelectric conversion efficiency of DSSCs. Among all tested brookite Ti02-based DSSCs, BTP2 has the best battery film thickness, and its battery efficiency is also the best value among the tested batteries (6.36%), which is higher than the reported pure brookite film-based DSSCs. The highest efficiency (5.97%) (ChemPhysChem, 2011, 12, 2461-2467, J.Phys.Chem.C,2014, 118,23459-23467)o

[0055] In the case of the same film thickness, the brookite Ti02-based DSSC (BTP2) obtained in Example 3 can adsorb more dye molecules than the P25 film DSSC (P25). This is because small-particle brookite Ti02 nanoparticles (particle size ~10nm) are smaller than P25 nanoparticles (particle size ~20nm), so brookite TiCh-based DSSC exhibits a greater photocurrent density than P25-based DSSC. Previous literature reports (ChemPhysChem, 2011, 12, 2461-2467, J. Phys. Chem. C, 2014, 118, 23459-23467) pointed out that the density of dye-anchored adsorption sites on the surface of brookite TiCh is lower than that of anatase TiCh, and the poor conductivity of brookite Ti02 will lead to brookite Ti02-based The charge collection efficiency in DSSCs is poor. Because the specific surface area of the small particle size brookite Ti02 nano powder provided by the present invention is 2.4 times more than that of the P25 nano powder, it can absorb more dyes, thereby making up for the dye-anchored adsorption sites on the surface of the brookite Ti02 The insufficiency of lower density promotes the improvement of the photocurrent density value of brookite Ti02-based DSSCs. The optimal photoelectric conversion efficiency of the brookite Ti02-based DSSCs constructed by the porous film photoanode prepared from the small particle size brookite Ti02 powder provided by the present invention can reach 6.36%, which is much higher than that of the P25-based photoanode constructed under the same conditions. The photoelectric conversion efficiency of DSSC (5.22%). It can be seen that the invention provides a large specific surface area and small

The particle size of brookite TiCh powder can effectively overcome the inherent defects of low dye adsorption and poor electron collection efficiency of brookite TiCh as a photoanode material, thereby significantly improving the photoelectricity of brookite Ti02-based DSSCs Conversion performance.