TW201326466A - Method of preparing an electrode material under lower temperature and shorter reaction time - Google Patents

Abstract

A novel method of preparing an electrode material under lower temperature and shorter reaction time is proposed. This method includes providing a carbon substrate to mix with an alcohol solvent, an ionic liquid (IL), water and a precursor of TiO2 to perform a microwave heating process to form TiO2 crystalline nano-particles uniformly dispersed and fixed on the carbon substrate to synthesize an electrode material. The electrode material can be used for a capacitive deionization (CDI) or a supercapacitor.

Description

Method for rapidly synthesizing electrode material at low temperature

The present invention relates to a novel synthesis method of an electrode material, and more particularly to a method for synthesizing titanium dioxide crystal nanoparticle in a rapid low temperature manner and fixing it on a carbon material.

Capacitive deionization (CDI) technology uses a porous electrode material to achieve the desalination effect by using an electric double layer (EDL) to absorb ions in water under normal pressure and low energy consumption conditions, and has a reverse reverse osmosis (reverse). Potential for desalination techniques such as osmosis, RO), electrodialysis (ED) or ion exchange resins. In the electrode material for capacitor desalination, carbon material is the main material. In order to improve the capacitance of the carbon material (such as activated carbon, carbon nanotube or other) electrode, it is often necessary to modify the electrode material. Taking the modification of the activated carbon electrode material as an example, the alkalitity (such as KOH or NaOH) may be used to change the hydrophilicity of the activated carbon, or the addition of the metal oxide may improve the ion electrosorption and desorption properties of the activated carbon, the latter being Think of the most commercial feasibility. The method of adding metal oxide to the activated carbon electrode material includes blending, chemical precipitation or sol-gel, however, mixing and chemical precipitation It is easy to cause metal oxide to aggregate and cannot be uniformly dispersed on the surface of activated carbon. However, the traditional sol-gel method requires high-temperature (200-500 ° C) and high pressure to obtain metal oxide with crystal phase, which not only consumes energy. It is time consuming and complicated in its synthesis steps, which does not meet the environmental protection requirements of energy saving and carbon reduction.

The invention adopts ionic liquid (IL) and microwave heating to perform sol-gel reaction, and the method of the invention can be at normal pressure and 150 ° C compared with the conventional sol-gel method. Under the following low temperature conditions, titanium dioxide crystalline nano-particles are synthesized and dispersed uniformly on the surface of carbon substrates, which can be used as capacitor desalination or supercapacitors. The electrode material effectively enhances the electrode's electrosorption performance (capacitance characteristics) and prolongs the life of the electrode.

Embodiments of the present invention provide a method for synthesizing such an electrode material in a rapid low temperature manner, comprising: subjecting a mixture of a carbon material, a titanium dioxide precursor, an ionic liquid, a water, and an alcohol solvent to a first stage microwave heating; and adding an alcohol The solvent, the ionic liquid and the water are subjected to the second stage microwave heating to synthesize a plurality of titanium dioxide crystal nano particles and are fixed on the carbon material, and the electrode material is a key material for preparing the electrode.

In order to make the above objects, features, and advantages of the present invention more comprehensible, the following embodiments are described in detail below:

The method of the present invention can be divided into two stages: (1) a hydrolysis-condensation reaction stage of titanium dioxide, mixing a carbon material with an alcohol solvent, an ionic liquid, water, and a titanium dioxide precursor to carry out the first stage. Microwave heating, wherein the carbon material: alcohol solvent: titanium dioxide precursor weight ratio ranges from 1-60:60-120:0.2-2, while ionic liquid: water: titanium dioxide precursor molar ratio ( The molar ratio ranges from 1-12:10-60:1-10. (2) In the crystallization stage of titanium dioxide, an alcohol solvent, an ionic liquid and water are further added to the product of the first stage, and the second stage of microwave heating is performed, wherein the carbon material: weight ratio of the alcohol solvent (weight ratio) The range is from 1-10:30-80, while the ionic liquid:water molar ratio ranges from 1-12:10-60.

The microwave power of the first stage microwave heating and the second stage microwave heating is 200-2000 W, the microwave frequency is between 0.3 GHz and 300 GHz, the first stage microwave heating time is about 30 minutes, and the second stage microwave heating The time is about 60 minutes.

A mixture of an alcohol solvent, an ionic liquid, water, and a titanium dioxide precursor used in the first stage is subjected to a sol-gel reaction under microwave heating, wherein the titanium dioxide precursor is directly hydrolyzed to the surface of the carbon material. The functional group such as -COOH or -OH is subjected to a condensation reaction so that the titanium oxide formed by the hydrolysis condensation reaction can be uniformly dispersed and directly fixed on the surface of the carbon material. In one embodiment, the weight ratio of the titanium dioxide precursor to the carbon material is between 1:60 and 1:1. The content of titanium dioxide fixed on the carbon material can be controlled by the weight ratio of the titanium dioxide precursor to the carbon material. The higher the weight ratio of the titanium dioxide precursor, the higher the content of titanium dioxide formed. At the same time, the molar ratio of the titanium dioxide precursor to water can also control the particle size of the titanium dioxide. In addition, the addition of alcohol solvent and ionic liquid and the addition of molar ratio of controlled water can slow down the rate of hydrolytic condensation reaction of TiO ₂ formation, help to increase the content of TiOH in the initial stage of synthesis and increase the hydrophilicity, and avoid the generation of large particles of non-crystal. (amorphous) TiO _2, TiO ₂ and dissolved beneficial recrystallization reaction (dissolution-recrystallization), can be synthesized anatase (anatase) titanium dioxide nanometer particles (nano-particles) is fixed to the surface of carbon material. In one embodiment, the molar ratio of ionic liquid to water used in the microwave heating step of the first and second stages is between 1:60 and 1:10.

In one embodiment, the carbon material may be activated carbon, bamboo carbon, carbon nanotube (CNT), graphene or a mixture thereof, and the specific surface area of the carbon material is preferably greater than 300 m ² / g, and the diameter of the carbon material is preferably between 1 nm and 1000 nm. The alcohol solvent may be ethanol, isopropanol or n-butanol, and the titanium dioxide precursor is titanium tetraisopropoxide (TTIP) or titanium butoxide. .

The ionic liquid used in the second stage absorbs microwave energy and promotes the crystallization reaction of titanium dioxide to form titanium dioxide crystal nanoparticles and is fixed on the carbon material. The content of titanium dioxide is about 30% by weight of the carbon material. the following.

In one embodiment, the ionic liquid consists of a cationic end and an anionic end, wherein the cationic end is, for example, 1-ethyl-3-methylimidazolium ([EMIM] ⁺ ) or 1-butyl 1-Benzyl-3-methylimidazolium ([BMIM] ⁺ ); the anion end is, for example, tetrafluoroborate (BF ₄ ^- ) or triflate (CF ₃ SO ₃ ^- ).

Since the embodiment of the present invention uses the ionic liquid and the microwave heating method to carry out the sol-gel reaction, the temperature is controlled below 150 ° C, and the reaction time is less than 2 hours, the titanium dioxide crystal nano-particles can be formed and fixed on the carbon material. In the conventional sol-gel method, a high-temperature and high-pressure method is required to form titanium dioxide crystal nano-particles, and the method of the embodiment of the invention belongs to a normal pressure, low temperature, time-saving and low-energy production method, and the electrode material is used for preparing an electrode. Key material.

The electrode material synthesized according to the embodiment of the present invention is that the titanium dioxide crystal nano particles are uniformly distributed and fixed on the carbon material, and the titanium dioxide will occupy the polar base position on the surface of the carbon material, thereby contributing to the reduction of the irreversible adsorption phenomenon on the surface of the carbon material. To increase the amount of carbon adsorption, this electrode material can be applied to capacitor desalination or supercapacitor, which helps to increase the electrode's capacitance, desalination efficiency and increase the electrode life.

The following examples illustrate various methods for synthesizing electrode materials in a low-temperature rapid manner and capacitance characteristics:

[Example 1]

The reagents used include deionized water, the titanium dioxide precursor is titanium tetraisopropoxide (TTIP, Merck), the alcohol solvent is isopropanol (IPA, Merck), and the ionic liquid , IL) is 1-butyl-3-methylimidazolium tetrafluoroborate; [Bmim] ⁺ [BF ₄ ] ^- , Merck).

First, 2 g of activated carbon was placed in the reaction flask, and 200 ml (mL) of IPA was used to uniformly disperse the activated carbon. First, a TTIP:IL molar ratio of 1:1 titanium dioxide precursor tetraisopropyl was added. Titanol and ionic liquid [Bmim] ⁺ [BF ₄ ] ^- . Then, different TTIP: water molar ratio deionized water was added, and the molar ratio of TTIP:water used in this example was 1:30, 1:15, and 1:5, respectively. The microwave power used was 800 W, the microwave frequency was 2.45 GHz, and microwave heating was carried out for 30 minutes to obtain a product of the first stage, and the reaction temperature was measured by a thermometer to be about 100 °C.

Then, 80 ml of IPA, ionic liquid and deionized water were added to the product of the first stage. The IL:water used in Example 1 had a molar ratio of 1:18, a microwave power of 800 W, and a microwave frequency of At 2.45 GHz, microwave heating was carried out for 60 minutes to obtain the product of the second stage, and the reaction temperature was measured by a thermometer to be about 100 °C.

The dry powder obtained in the second-stage synthesis product of Example 1 (using TTIP: water molar ratio of 1:30) was detected by a Raman spectrometer, and the results are shown in Fig. 1. It can be seen that the titanium dioxide synthesized on the activated carbon belongs to the anatase crystal phase. The dry powder obtained under the same synthesis conditions (using TTIP: water molar ratio of 1:30) was detected by an Energy Dispersive X-ray Spectrometer (EDS), and the results are shown in Fig. 2. It can be seen that the titanium dioxide is uniformly dispersed and fixed on the activated carbon.

A powder of the synthesized product of Example 1 (using a TTIP: water molar ratio of 1:30) and polyvinylidene fluoride (PVDF, molecular weight 534 k, solid content 5 wt%) and graphite powder ( Mixed with a particle size of 2.7 μm, the product of the synthesis: polydifluoroethylene: graphite powder has a weight ratio of 65:15:25, and a solvent of N-methyl-2-pyrrolidone (NMP) is added as described above. The mixture was uniformly stirred into a paste slurry, and the paste slurry was uniformly coated on a 25 μm-thick aluminum foil using a coater with a 300 μm doctor blade, and dried in an oven at 140 ° C for 2 hours, and then on the opposite side of the same piece of aluminum foil. The paste slurry was applied once and then dried in an oven at 140 ° C for 2 hours to complete the preparation of the electrode.

Capacitance of an electrode prepared by using an electrode material (AC/TiO ₂ ) synthesized using a TTIP:water molar ratio of 1:15 and an activated carbon electrode material (AC) not containing TiO ₂ in Example 1 test. The test method is to use cyclic voltammetry (CV), the electrolyte is 0.5 M Na ₂ SO ₄ , and the scanning range is -0.5 V to 0.5 V. The results are shown in Fig. 3, which shows that it is modified by TiO _{2 .} The active carbon electrode material (AC/TiO ₂ ) can effectively increase the capacitance of the electrode, and the capacitance value can be increased by about 3.5-4 times compared with the activated carbon electrode without the modification of TiO ₂ .

The powder of the product of the synthesis of Example 1 was examined by a thermogravimetric analyzer (TGA), and was heated from 30 ° C to 800 ° C at a temperature increase rate of 20 ° C per minute under air. The results are shown in Fig. 4. From the TGA analysis results in Fig. 4, the content of TiO ₂ immobilized on activated carbon in the powder of the product of Example 1 can be calculated. As a result, as shown in Fig. 5, it can be seen that different molar ratios of TTIP:water are used. : 30, 1:15 and 1:5, the TiO ₂ content (based on the weight of activated carbon) synthesized and fixed on activated carbon was 7.62 wt%, 5.41 wt% and 4.65 wt%, respectively. In addition, Fig. 5 shows the specific capacitance of the electrode, wherein the electrode prepared by the TTIP: water molar ratio of 1:15 has the highest specific capacitance value.

Although the present invention has been disclosed in its preferred embodiments, it is not intended to limit the invention, and the invention may be modified and modified without departing from the spirit and scope of the invention. The scope of protection is subject to the definition of the scope of the patent application attached.

1 is a Raman spectrum of an electrode material powder synthesized in Example 1 (using TTIP: a molar ratio of water of 1:30);

Fig. 2 is a view showing the results of X-ray energy dispersion analysis of the electrode material powder synthesized in Example 1 (using TTIP: water molar ratio of 1:30);

Figure 3 shows the capacitance values of the electrode material (AC/TiO ₂ ) synthesized in Example 1 (using TTIP: water molar ratio of 1:15) and the activated carbon electrode (AC) not containing TiO ₂ . ;

Figure 4 is a graph showing the results of thermogravimetric analysis of the electrode material powder synthesized in Example 1;

Fig. 5 shows the TiO ₂ content of the electrode material synthesized in Example 1 and the specific capacitance value of the electrode prepared therewith.

Claims (15)

A method for rapidly synthesizing an electrode material at a low temperature, comprising: providing a carbon material; adding an alcohol solvent, an ionic liquid, water and a titanium dioxide precursor to perform a first stage microwave heating; and further adding the alcohol solvent, The ionic liquid and water are subjected to a second-stage microwave heating to synthesize a plurality of titanium dioxide crystal nanoparticles and fixed on the carbon material. The method of rapidly synthesizing an electrode material according to claim 1, wherein the carbon material comprises activated carbon, bamboo carbon, carbon nanotubes, graphene or a mixture thereof. The method of rapidly synthesizing an electrode material according to claim 1, wherein the shape of the carbon material comprises powder, granule, fiber, cloth or sphere. The method for rapidly synthesizing an electrode material according to claim 1, wherein the carbon material has a specific surface area of more than 300 m ² /g, and the carbon material has an average pore diameter of between 1 nm and 1000 nm. The method of rapidly synthesizing an electrode material according to claim 1, wherein the ionic liquid comprises a cationic end and an anionic end. The method of rapidly synthesizing an electrode material according to claim 5, wherein the cation end of the ionic liquid comprises 1-ethyl-3-methylimidazole ([EMIM] ⁺ ) or 1-butyl-3 -methylimidazole ([BMIM] ⁺ ). The method of rapidly synthesizing an electrode material according to claim 5, wherein the anion end of the ionic liquid comprises tetrafluoroborate (BF ₄ ^- ) or trifluoromethanesulfonate (CF ₃ SO ₃ ^- ) . The method for rapidly synthesizing an electrode material according to claim 1, wherein the microwave power of the first stage microwave heating and the second stage microwave heating is between 200 and 2000 W, and the microwave frequency is between 0.3 GHz and 300. Between GHz. The method of rapidly synthesizing an electrode material according to claim 1, wherein the alcohol solvent comprises ethanol, isopropanol or n-butanol. The method of rapidly synthesizing an electrode material according to claim 1, wherein the titania precursor comprises titanium tetraisopropoxide or titanium butoxide. The method of rapidly synthesizing an electrode material according to claim 1, wherein the weight ratio of the titanium dioxide precursor to the carbon material is between 1:60 and 1:1. The method of rapidly synthesizing an electrode material according to claim 1, wherein the ionic liquid to water has a molar ratio of between 1:60 and 1:10. A method for rapidly synthesizing an electrode material according to claim 1, wherein the reaction temperature is lower than 150 ° C and the reaction time is less than 2 hours. The method of rapidly synthesizing an electrode material according to claim 1, wherein the content of the titanium dioxide crystal nanoparticles in the electrode material is less than 30% by weight of the carbon material. The method of rapidly synthesizing an electrode material according to claim 1, wherein the electrode material is applied to a capacitor desalination or a supercapacitor.