KR100744635B1 - Method for preparing of oxide semiconductive electrode for electrochemical device - Google Patents

Abstract

A method for preparing an oxide semiconductor electrode of an electrochemical device is provided to effectively decompose liquid contaminant or pollutants existing in a water system. A glass substrate coated with an oxide conductor is coated with a mixture of titanium precursor, polymer compound and a solvent through a spin coating method to form a thin film. An annealing process is performed on the formed thin film. The oxide conductor contains a metal selected from the group consisting of indium, tin, zinc, aluminum and fluorine. The titanium precursor is an organic compound comprising Ti of titanium isopropoxide or titanium tetraethoxide.

Description

Method for manufacturing oxide semiconductor electrode for electrochemical device {METHOD FOR PREPARING OF OXIDE SEMICONDUCTIVE ELECTRODE FOR ELECTROCHEMICAL DEVICE}

Figure 1 shows the thermal gravimetric analysis (TGA) thermal analysis results of polyvinyl acetate in accordance with an embodiment of the present invention.

Figure 2 shows the X-ray diffraction of the oxide semiconductor electrode heat-treated according to an embodiment of the present invention.

3a and 3b show the photodegradation rate of the surface TiO ₂ oxide semiconductor according to the spin coating speed when manufacturing the oxide semiconductor electrode in accordance with an embodiment of the present invention.

Figure 4 shows an electron micrograph (SEM) of the surface of the final oxide semiconductor according to the spin coating speed when manufacturing the oxide semiconductor electrode according to an embodiment of the present invention.

5A and 5B show electron microscope (SEM) photographs before and after heat treatment of an oxide semiconductor electrode manufactured according to an embodiment of the present invention.

Figure 6 shows the decomposition characteristics of the BB26 dye according to the applied voltage of the oxide semiconductor electrode prepared according to an embodiment of the present invention.

FIG. 7 illustrates a schematic band-diagram before and after applying a voltage to an oxide semiconductor electrode prepared according to an embodiment of the present invention.

The present invention relates to a method for manufacturing an oxide semiconductor electrode for an electrochemical device, and more particularly, it can efficiently handle household and industrial contaminants, has a strong chemical durability, is very simple to manufacture, and can reduce costs. The present invention relates to a method for producing an oxide semiconductor electrode for an electrochemical device.

Nitrogen, one of the pollutants that exist in the state of nitrate and ammonia / ammonium in water, causes the lack of dissolved oxygen in the water, causing eutrophication, red tide, fish toxin, etc. The government has regulated total nitrogen emissions since 2003. Accordingly, efforts have been made to reduce the nitrogen content in water in order to prevent deterioration and spread of water pollution in accordance with the above regulations.

Recently, as compounds having ion exchange and adsorption performances of ammonia nitrogen and minerals that enhance nitrogen removal efficiency have been found, they are mixed to prepare carriers or filtration membranes, or water treatment devices having various structures can be used to produce biological and / or Attempts have been made to apply chemical treatment methods, but they are not evaluated in terms of cost and time.

While a technique for preventing pollution of water by treating nitrogen in water more efficiently than the existing methods as described above is expected, recently, a water treatment method adopting an electrochemical treatment technology has been studied. The electrochemical treatment method refers to a method of removing contaminants in water or converting them into harmless components by inducing an electrochemical reaction by the oxidation-reduction reaction of the electrode by applying a current by placing the contaminated wastewater between the anode and the cathode. . According to this electrochemical treatment method, solids and freshwater algae contained in the water can be efficiently removed without using a flocculant and can be treated in a short time without requiring a large installation area. In addition to the small amount, only a small amount of the drug used as needed has the advantage that can be reused sludge produced as a fertilizer.

Korean Patent No. 72629 discloses an electric water treatment apparatus for removing contaminants using a metal electrode. In the case of the patent, there is an advantage that the chemical stability of the long-term use is excellent, but different from the oxide semiconductor electrode of the present invention, there is a problem that the chemical durability is lower than the present invention.

Meanwhile, US Patent No. 5,419,824 discloses a method of forming titanium oxide (TiO ₂ ) on the titanium metal electrode by anodizing. In the case of the patent, a method of oxidizing titanium to produce titanium oxide, which is different from the present invention in which a titanium oxide film is formed by a spin coating method, has a problem in that manufacturing cost is higher than that of the present invention.

In addition, the article (Electrochemically assisted photocatalysis.TiO ₂ particulate film electrodes for Photocatalytic degradation of 4-Chlorophenol ", K. Vinodgopal et al, J. Phys. Chem. (1993), prepared oxide semiconductors by slurry coating method, The present invention discloses a method for decomposing harmful substances by applying voltage and ultraviolet light to one electrode simultaneously, but the above paper also forms an oxide electrode by spin coating and does not use the present invention without using ultraviolet light. It is different.

In order to solve the problems of the prior art as described above, the present invention is an oxide semiconductor for an electrochemical device that can efficiently handle household and industrial contaminants, strong chemical durability, very simple manufacturing, and can reduce costs It is an object to provide a method for producing an electrode and an oxide semiconductor electrode thus produced.

In order to achieve the above object, the present invention comprises the steps of coating a mixture of a titanium precursor, a polymer compound, and a solvent by a spin coating method on a substrate coated with an oxide conductor to form a thin film; And it provides a method for producing an oxide semiconductor electrode for an electrochemical device comprising the step of heat-treating the formed thin film.

The present invention also provides a substrate; An oxide conductor layer formed on the substrate; And it provides an oxide semiconductor electrode for an electrochemical device comprising an oxide semiconductor layer formed on the oxide conductor layer.

Hereinafter, the present invention will be described in detail.

The present inventors coated an oxide semiconductor by a spin coating method on a conductive substrate in order to manufacture an electrode for an electrochemical device for decomposing contaminants. As a result, the coating thickness is changed according to the spin coating conditions, and thus the surface morphology is changed. The present invention was completed by confirming the influence on the decomposition rate of the material and finding the optimum spin coating condition.

An oxide semiconductor electrode for an electrochemical device according to the present invention comprises the steps of: coating a mixture of a titanium precursor, a polymer compound, and a solvent on a substrate coated with an oxide conductor by spin coating to form a thin film; And heat treating the formed thin film.

The substrate used in the present invention may use all of the usual transparent or opaque substrates used in the art.

The substrate is coated with an oxide conductor, and the oxide conductor is not limited if the oxide conductor is a conductive oxide conductor, for example, a metal oxide conductor including indium, tin, zinc, aluminum, fluorine, or the like. Indium tin oxide (ITO), indium zinc oxide (IZO), or aluminum doped zinc oxide (Al doped Zinc Oxide) may be used.

Of course, the oxide conductor may be coated on the substrate according to conventional methods used in the art.

A solution in which a titanium precursor, a high molecular compound, and a solvent are mixed is coated on the substrate coated with the oxide conductor as described above. In this case, the mixture is coated on a substrate to form an oxide semiconductor layer, the oxide semiconductor layer formed as a TiO ₂ film, an electrochemical catalytic reaction using TiO ₂ to remove contaminants with an oxide semiconductor electrode prepared according to the present invention. It is possible to oxidize and decompose contaminants in aqueous solution.

The titanium precursor may be an organic compound containing Ti such as titanium isopropoxide (TTIP), titanium tetraethoxide, and the like.

In addition, the mixture of the present invention can further increase the oxidation and decomposition effects of the contaminants caused by TiO ₂ by mixing TiO ₂ with the titanium precursor. In an embodiment of the present invention, Degussa P-25 is used as the TiO ₂ .

In the present invention, in place of the titanium precursor, SiO ₂ , SnO ₂ , WO ₃ , ZnO, ZnS, CdSe, CdS, MoS ₂ , or RuS ₂ may be used alone or in combination of two or more thereof.

The titanium precursor or the mixture of the titanium precursor and TiO ₂ is preferably included in the mixture 10 to 40% by weight, when the content is in the above range is more preferable in forming the TiO ₂ thin film.

The polymer compound acts to impart viscosity to the mixture during spin coating.

The polymer compound is not limited as long as it is a polymer soluble in a solvent, and in one embodiment of the present invention, polyvinylacetate (PVAc) dissolved in a dimethyl formamide solvent was used.

The polymer compound is preferably included in the mixture in 1 to 10% by weight, and if the content is in the above range is better for spin coating.

The solvent is not limited as long as it is a solvent capable of dissolving both the titanium precursor and the polymer compound used in the mixture, for example acetic acid, ethanol, or dimethyl formamide (DMF). ) May be used alone or in combination of two or more thereof.

The solvent is preferably included in the mixture 40 to 70% by weight, when the content is in the above range is better for dissolving the titanium precursor and the polymer compound.

Such a mixture is preferably coated by spin coating on an oxide conductor-coated substrate.

The spin coating speed affects the thickness and surface state of the oxide semiconductor thin film to be formed, the adsorption capacity, and the decomposition efficiency of contaminants. The spin coating speed is preferably 500 to 5,000 rpm, more preferably 2,500 to 4,500, and most preferably 3,000 rpm.

The oxide semiconductor layer formed as described above may have a thickness of 50 nm to 1,000 nm.

After the oxide semiconductor thin film is formed, a step of heat-treating the thin film is performed.

The heat treatment serves to remove the solvent and the polymer compound present in the oxide semiconductor thin film. In addition, the heat treatment step serves to remove the polymer surrounding Ti from the titanium precursor.

Therefore, the heat treatment step is preferably carried out above the temperature at which the polymer is completely decomposed and removed, specifically, the heat treatment at a temperature of 450 to 750 ℃.

In an embodiment of the present invention, polyvinylacetate was used in the mixture for forming the oxide semiconductor thin film. Since the complete decomposition and removal thereof are performed at 550 ° C. or higher, when polyvinylacetate is used as the polymer compound, the polyvinylacetate is used for 10 minutes at 550 ° C. It is good to heat treatment.

After such heat treatment, the titanium precursor is crystallized into an anatase crystal phase which is known to have high contaminant decomposition activity. In general, it is known that TiO ₂ is anatase crystal on the excellent photocatalytic activity compared with the TiO ₂ on the rutile crystal.

Oxide semiconductor electrode for an electrochemical device of the present invention prepared by the above method is a substrate; An oxide conductor layer formed on the substrate; And an oxide semiconductor layer formed on the oxide conductor layer, which can be effectively decomposed by oxidizing contaminants in an aqueous solution or contaminants present in an aqueous environment by being used in an electrochemical device.

Hereinafter, preferred examples are provided to help understanding of the present invention, but the following examples are merely to illustrate the present invention, and the scope of the present invention is not limited to the following examples.

EXAMPLE

Example 1

A conductive substrate was prepared by coating the glass with an indium tin compound at a thickness of 150 nm.

The conductive substrate was coated with a mixture of 10 g of titanium isopropoxide, 1 g of polyvinylacetate, 5 g of acetic acid, 20 mL of dimethyl formamide, and 1 g of TiO ₂ by spin coating to form a thin film having a thickness of 150 to 1,000 nm. Formed. At this time, the spin coating speed was performed by varying the speed at 500 ~ 5,000 rpm.

Then, the formed thin film was heat-treated at 20 to 800 ° C. for 10 minutes to remove the polymer and the solvent present in the thin film, thereby preparing a titanium oxide semiconductor electrode.

Figure 1 shows the results of the thermal gravimetric analysis (TGA) thermal analysis of polyvinyl acetate to obtain the optimum heat treatment temperature, polyvinylacetate was confirmed that completely decomposed and removed at a temperature of 550 ℃ or more. Therefore, when polyvinyl acetate is used as the polymer compound, it was confirmed that the heat treatment was optimally performed at 550 ° C. for 10 minutes.

In addition, FIG. 2 shows X-ray diffraction of the heat-treated oxide semiconductor electrode, and it was confirmed that titanium oxide was crystallized on an anatase known to have high contaminant decomposition activity. In this case, the indium tin compound is already crystallized before the oxide semiconductor coating, it can be seen that there is no change in the crystal structure of the indium tin compound according to the heat treatment temperature.

In order to measure the photoactivity (adsorption and decomposition rate) of the dye according to the spin coating speed in the oxide semiconductor electrode of Example 1, the spin coating speed was varied at 500, 1000, 2000, 3000, 4000, and 5000 rpm, respectively. , Dye was measured using Basic Blue 26 (hereinafter referred to as 'BB26') and the results are shown in Table 1 below.

division Photoactive (Basic blue 26, 1 hr) 500 rpm 37.1% 1,000 rpm 30.3% 2,000 rpm 31.3% 3,000 rpm 44.2% 4,000 rpm 39.5% 5,000 rpm 32.9%

In addition, the photodegradation rate of the surface TiO ₂ oxide semiconductor according to the spin coating speed when the oxide semiconductor electrode of Example 1 was manufactured was measured, and the results are shown in FIGS. 3A and 3B. In this case, the present invention is to decompose contaminants by applying an electric field without using UV, but UV was used in view of the ease of experiment when measuring the photodegradation rate.

As shown in FIG. 3A, the photodegradation rate of the BB26 dye according to UV irradiation time was found to show the largest photodegradation rate at a speed of 3,000 rpm. In addition, as shown in FIG. 3B, the photodegradation rate of the dye according to each spin coating speed under 1 hour UV irradiation condition showed the largest decomposition rate (44.2%) at a speed of 3,000 rpm, from which the optimum speed of spin coating was obtained. Was found to be 3,000 rpm.

Figure 4 shows an electron micrograph (SEM) of the surface of the final oxide semiconductor prepared by varying the spin coating speed in the oxide semiconductor electrode manufacturing of Example 1. The rate of decomposition of contaminants is generally known to be proportional to the increase in the surface area of the oxide semiconductor electrode.

As a result, as the spin coating speed was increased, it was confirmed that the shape, surface area, and thickness of the oxide semiconductor electrode surface were decreased, and that the surface had the most optimized surface at a speed of 3,000 rpm.

5A and 5B show electron microscopy (SEM) images before and after heat treatment using an oxide semiconductor electrode having a structure of TiO ₂ / ITO / glass prepared at a spin coating speed of 3,000 rpm in Example 1.

As a result, as shown in FIG. 5A, most of amorphous TiO ₂ (P-25) having a maximum size of 32 nm was observed before heat treatment, and after heat treatment, as shown in FIG. 5B, a maximum of 17 except TiO ₂ (P-25) Crystallized TiO ₂ of nm size was also observed. It can be seen that due to the heat treatment, the polymer component was removed from the titanium isopropoxide, leaving only Ti, and crystallized TiO ₂ having a maximum size of 17 nm was observed.

In Example 1, the spin coating speed was set at 3,000 rpm, and the applied voltage was changed to (+) 5V and (+) 10V, respectively, using an oxide semiconductor electrode prepared by performing heat treatment at 550 ° C. for 10 minutes to obtain BB26 dye. Decomposition characteristics were measured and the results are shown in FIGS. 6A and 6B. At this time, the voltage was applied to the TiO ₂ / ITO / glass electrode, the experiment was also applied to the ITO / glass electrode as a comparative example. Platinum (Pt) was used as the counter electrode, and the experiment was conducted in a dark room where UV was completely blocked.

Figure 6a shows the decomposition of BB26 dye over time when the applied voltage is (+) 5V. As shown in FIG. 6A, dyes were hardly decomposed regardless of the electrode type under Bias = None under no voltage, and when TiO ₂ / ITO / glass electrode and ITO / were applied when a positive 5V voltage was applied. Decomposition was observed at both glass electrodes. However, the decomposition rate was not large, and it was confirmed that 7.5% of the ITO / glass electrode was used and 3.0% of the TiO ₂ / ITO / glass electrode was decomposed under a 1 hour voltage application condition. As such, the ITO / glass electrode exhibits a higher decomposition rate compared to the TiO ₂ / ITO / glass electrode because a voltage of about 5V is not enough for the electrons to tunnel into the electron conduction band region of TiO ₂ . It was judged to be due to (see Fig. 7b).

In addition, Figure 6b shows the decomposition of BB26 dye with time when the applied voltage is (+) 10V, almost no decomposition of the dye regardless of the type of electrode under the condition Bias = None without voltage applied. However, decomposition was observed at both TiO ₂ / ITO / glass electrodes and ITO / glass electrodes when the voltage was applied at (+) 10V, and 14.1% when ITO / glass electrodes were used at 1 hour voltage application conditions. When TiO ₂ / ITO / glass electrode was used, it was confirmed that the decomposition was 53.3%.

The above results are summarized in Table 2 below.

DC applied voltage ITO / Glass Electrode TiO ₂ / ITO / Glass Electrode None 0 % 0 % 5 V 7.5% 3.0% 10 V 14.1% 53.3%

As shown in Table 2, in the case of the ITO / glass electrode, the decomposition rate was increased to 7.5% at (+) 5V, 14.1% at (+) 10V, which is proportional to the voltage. This is because the dye is decomposed by an electrode of the type). However, for TiO ₂ / ITO / glass electrodes 3.0% at (+) 5V and 53.5% at (+) 10V, the rate of decomposition is exponentially above the voltage sufficient for the electrons to tunnel into the electron conduction band region of TiO ₂ . This increased (see FIG. 7B), which means that when the oxide semiconductor is used, electrons of water molecules (H ₂ O) tunnel and move to the electron conduction band of the oxide semiconductor, and are converted into OH radicals, thereby increasing oxidation efficiency. It was because.

Therefore, when using the oxide semiconductor electrode prepared according to the present invention it can be expected that the contaminant can be efficiently processed without the use of a UV lamp above the threshold voltage.

FIG. 7 shows a schematic band-diagram before / after DC voltage application, in which a Schottky barrier between the solution and the oxide semiconductor electrode is gradually lowered before DC application, and after the threshold voltage. The electrons move through the Schottky barrier, which turns the water molecules into hydroxyl radicals to treat the pollutants.

According to the present invention, it is possible to efficiently treat household and industrial contaminants, has a strong chemical durability, very simple manufacturing, and can reduce costs.

Although only described in detail with respect to the described embodiments of the present invention, it will be apparent to those skilled in the art that various modifications and variations are possible within the technical spirit of the present invention, it is natural that such variations and modifications belong to the appended claims. .

Claims (9)

Coating a mixture of a titanium precursor, a polymer compound, and a solvent on a glass substrate coated with an oxide conductor by spin coating to form a thin film; And heat treating the formed thin film. The method of claim 1, The oxide conductor is a metal oxide conductor comprising at least one metal selected from the group consisting of indium, tin, zinc, aluminum, and fluorine. The method of claim 1, The titanium precursor is an organic compound comprising an organic compound containing Ti of titanium isopropoxide (TTIP) or titanium tetraethoxide (Titanium tetraethoxide). The method of claim 1, Method for producing an oxide semiconductor electrode for an electrochemical device, characterized in that the mixture further comprises TiO ₂ . The method of claim 1, The solvent is a method for producing an oxide semiconductor electrode for an electrochemical device, characterized in that at least one selected from the group consisting of acetic acid, ethanol, and dimethyl formamide (DMF). The method of claim 1, The spin coating is a manufacturing method of the oxide semiconductor electrode for an electrochemical device, characterized in that carried out at a speed of 500 to 5,000 rpm. The method of claim 1, The heat treatment is carried out at a temperature of 450 to 750 ℃ manufacturing method of the oxide semiconductor electrode for an electrochemical device. Glass substrates; An oxide conductor layer formed on the glass substrate; And An oxide semiconductor electrode for an electrochemical device, comprising an oxide semiconductor layer formed on the oxide conductor layer. The method of claim 8, The oxide semiconductor electrode for an electrochemical device, characterized in that the thickness of the oxide semiconductor layer is 50 nm to 1,000 nm.

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