CN101847729B - Preparation method of high-dispersity organic-inorganic composite electrolyte membrane - Google Patents

Abstract

The invention relates to a method for improving the dispersibility of an organic-inorganic composite membrane of a proton exchange membrane fuel cell. The diffusion process of the macromolecular precursor during the sol-gel hydration reaction is promoted by ultrasonic waves, and the concentration of water is increased to improve the distribution of water in the film, which can significantly improve the dispersion of the generated particles in the composite film. The organic-inorganic composite membrane prepared by the invention has high dispersion and good uniformity of inorganic components in the membrane. The highly dispersed organic-inorganic composite membrane prepared by this method can be applied to traditional and high-temperature (80°C-120°C) proton exchange membrane fuel cells, and exhibits good performance and long-term durability under high temperature and low humidification conditions. There is no significant degradation in time running performance. The organic-inorganic composite membrane prepared by the invention can be used in high-temperature proton exchange membrane fuel cells and direct alcohol fuel cells as a proton conduction medium.

Description

A kind of preparation method of highly dispersed organic-inorganic composite electrolyte membrane

technical field

The invention relates to a proton exchange membrane fuel cell electrolyte composite membrane, in particular to a method for improving the dispersibility of inorganic particles in the proton exchange membrane fuel cell organic-inorganic composite membrane.

Background technique

A proton exchange membrane fuel cell (PEMFC) is a power generation device that can directly convert the chemical energy of fuel and oxidant into electrical energy. The proton exchange membrane is the core material of the entire PEMFC, which plays the role of guiding protons and blocking reaction gases.

Traditional perfluorosulfonic acid membrane (such as DuPont's Nafion membrane series) electrolyte, because the proton conductivity of this type of membrane material has a strong dependence on the water content of the membrane, its normal working temperature is generally maintained at around 60-80°C . The temperature is too low, the electrochemical reaction rate is low, and the battery power is low. If the temperature is too high, such as close to 100°C, the wetness of this type of membrane will drop sharply and the internal resistance will rise sharply. At this time, the performance of the battery will drop sharply, which will reduce the output power and greatly reduce the life of the membrane. It can be seen that the proton conductivity of the traditional proton exchange membrane represented by the perfluorosulfonic acid membrane is strongly related to the water content and temperature, which limits the operating temperature of the battery and makes the work of the traditional proton exchange membrane fuel cell The temperature is limited to a range of about 60-80°C.

However, the working temperature of 60-80°C brings a series of technical problems: First, at 80°C, the water in the battery exists in gas-liquid two-phase, and the instability of the gas-liquid two-phase leads to poor stack performance. The problem of stability and reliability has become a key technical problem. The calculation of gas-liquid two-phase flow itself is quite complicated, and coupled with the electrode process, the difficulty of the problem is further increased. Second, the electrochemical reaction rate at 80°C is not high enough, and the electrochemical polarization of the cathode is relatively serious, which affects the better performance of the battery. Third, the operating temperature of the battery at 60-80°C is not much different from the ambient temperature, which is not conducive to the heat dissipation of the battery, which makes the battery have higher requirements on the cooling system, and the huge cooling system will reduce the volumetric power density of the battery.

The high-temperature proton exchange membrane fuel cell (HT-PEMFC) using a high-temperature proton exchange membrane effectively overcomes the above-mentioned series of problems of the traditional PEMFC, including: 1) the existence of water in the battery in the gas phase simplifies the management of water heat; Humidification requirements are reduced; 3) The electrochemical reaction speed is increased, which effectively reduces the electrochemical polarization overpotential of the cathode; in addition, the high-temperature proton exchange membrane fuel cell simplifies the fuel cell cooling system to a certain extent. Because of this, high-temperature proton exchange membranes have become a hot spot in current research and development. Organic-inorganic composite membranes, as a type of high-temperature proton exchange membranes, have received considerable attention and have been widely reported in literature and patents.

Liu Yonghao, Yi Baolian and Zhang Huamin et al. (Power Technology, 2005, 29(8): 92-94) reported the preparation of Nafion115 by sol-gel method using TEOS (tetraethyl orthosilicate) and commercial Nafion115 membrane as raw materials /SiO2 composite film, and the battery performance test of the composite film was carried out. Experiments show that under the conditions of battery temperature 130°C, operating pressure 0.25MPa, and voltage 0.7V, the current density of the membrane electrode prepared by using Nafion115/SiO2 composite membrane is 1.9 times that of unmodified Nafion115 membrane.

Nafion/ SiO2 composite membrane (preparation conditions are methanol / water = 2: 1, tetraethyl orthosilicate / methanol = 3: 2), and the prepared composite membrane assembled battery was tested. The results show that the current density of the Nafion115/SiO2 composite film is 4 times that of the unmodified Nafion115 film at a battery temperature of 130°C, an operating pressure of 0.3 MPa, and a voltage of 0.4V, indicating that the Nafion/SiO2 composite film significantly improves the high temperature performance of the fuel cell under these conditions.

Mauritz et al. reported the Nafion/SiO ₂ sol-gel preparation method (Macromolecules, 1990, 23(5), 1380-1388). The preparation method is as follows: Nafion membrane is swelled and absorbed in methanol-water solution (volume ratio, methanol: water = 2:1) with a water concentration of 33%, and then transferred to tetraethyl orthosilicate-methanol solution, and then hydrated in In-situ generation of nano-SiO2 particles in Nafion film. There are also certain deficiencies in this method. Due to the large molecular structure of tetraethyl orthosilicate, the influence of diffusion resistance into the film makes the distribution of _SiO2 produced in the film uneven, the dispersion of silicon element is poor, and the silicon content gradually decreases from the surface of the film to the center.

In the patent US Patent 6515190, Harmer et al. adopted the method of recasting, mixed the mixed solution of ethyl orthosilicate, hydrochloric acid and water with 5% Nafion resin solution, cast and recasted to obtain a Nafion/SiO ₂ composite film. The patented film-forming process is complicated and not suitable for large-scale production.

In patent EP0926754, Arico Antonino et al. blended the finished SiO2 particles with Nafion resin solution before casting, and also obtained Nafion/SiO2 organic-inorganic composite film. In the Nafion/SiO2 organic-inorganic composite membrane prepared by this method, the particles in the membrane are easy to aggregate, resulting in poor dispersion of the membrane.

In Chinese Patent No.200510035005.9, the nano-inorganic oxide in solution state or the precursor of the inorganic oxide is blended with the perfluorosulfonic acid resin solution, cast into a film, and an organic-inorganic composite film with water retention capacity is obtained .

In the Chinese patent ZL200310111406.9, the method of swelling order opposite to that of Mauritz et al. was used to improve the dispersion of the composite film. However, due to the large molecule of the oxide precursor, it is difficult to enter the film, and the reaction takes time. The prepared composite film is still not ideal in dispersibility.

When the present invention adopts the sol-gel method to prepare the organic-inorganic composite film, the concentration of water in the mixed solution of co-solvent and water is adjusted, and ultrasonic wave is applied in the reaction process to promote the diffusion of the oxide precursor, thereby improving the raw material content of the film. The uniformity of the distribution of inorganic particles generated by the bit.

Contents of the invention

The purpose of the present invention is to provide a method for preparing a highly dispersed organic-inorganic composite electrolyte membrane, so that it can be applied to a high-temperature proton exchange membrane fuel cell.

To achieve the above object, the technical solution adopted in the present invention is:

1) Soak the proton exchange membrane in a mixed solution of co-solvent and water, and swell for 5-120 minutes. In the mixed solution of co-solvent and water, the volume concentration of water is controlled at 50%-95%; the co-solvent is methanol , ethanol or N-methylpyrrolidone or a mixture of more than one;

2) Take out the above-mentioned swollen membrane, absorb the residual liquid on the surface with filter paper, and place it in air or nitrogen for 10-180 seconds;

3) Transfer the above film into a mixed solution of co-solvent and methyl orthosilicate, ethyl orthosilicate or butyl orthosilicate to react for 1-10 minutes, and the reaction process is accompanied by ultrasonic waves; the volume percentage of the co-solvent in the mixed solution is 20-80%;

4) Take it out after the reaction is over, and use filter paper to absorb the residual liquid on the surface;

5) drying under vacuum conditions at 40-80°C for 6-48 hours to obtain a composite film;

Step 1) The volume concentration of the water is controlled at 60%-90%. In step 3), the ultrasonic wave is applied during the reaction process, the frequency of the ultrasonic wave is 20-600kHz, and the power is 0.3-30W/cm ² . The proton exchange membrane is one of the following membranes, Nafion series membranes of DuPont Company, Dow series membranes of Dow Company, or Aciplex series membranes of Asahi Chemical Company.

Compared with existing materials and technologies, the present invention has the following advantages:

1. The prepared composite membrane can be used in traditional and high temperature proton exchange membrane fuel cells. Because the inorganic water-retaining particles (SiO2, or TiO2) are uniformly distributed in the high-dispersion composite film prepared by the method, the battery can operate stably with excellent performance at high temperature and low humidity.

2. Membrane material has good stability and long service life. Due to the uniformity of the material structure, the membrane has a more uniform water retention capacity during the high-temperature and low-humidity operation of the battery, avoiding local burn-through caused by local water loss, thereby greatly improving the battery operating life.

3. The preparation process is simple and the cost is low. No complex cast film forming equipment is required. The organic-inorganic composite membrane can be prepared by generating inorganic nanoparticles in situ on the basis of the formed membrane, and the equipment requirements are simple and easy to implement.

The highly dispersed organic-inorganic composite membrane prepared by the invention can not only be used in high-temperature proton exchange membrane fuel cells, but also can be used in direct alcohol batteries as a proton conduction medium.

Description of drawings

Fig. 1 is that the Nafion115/ _SiO prepared under the condition of 66% water concentration is the line distribution curve of silicon element in the section of composite film;

Fig. 2 is the Nafion115/ _SiO prepared under the conditions reported by people such as Mauritz (water concentration is 33%) The linear distribution curve of silicon element in the composite film section;

Fig. 3 is a performance curve of the proton exchange membrane prepared in Example 2 applied to a fuel cell.

Detailed ways

Example 1

The Nafion 115 membrane was placed in a mixed solution of methanol and water (volume ratio, methanol:water=1:2) with a water concentration of 66%, and swelled for 60 minutes. The above-mentioned swollen membrane was taken out, and the residual liquid on the surface was absorbed with filter paper, and then left in the air for 3 minutes. Transferred to the mixed solution of methanol and methyl orthosilicate (volume ratio, methanol: ethyl orthosilicate = 3: 2) with a tetraethyl orthosilicate concentration of 40% for diffusion reaction. During the reaction, the reactor was placed in an ultrasonic In the water tank, the ultrasonic frequency is 159kHz, and the ultrasonic power is 3W/cm ² . Take it out after reacting for 3 minutes, and absorb the residual liquid on the surface with filter paper. The composite film was obtained after drying in a vacuum oven at 80° C. for 24 hours. The line distribution of Si element in the cross-section of the composite film is shown in Figure 1. Compared with the line distribution diagram (see accompanying drawing 2) of the Si element of the composite membrane cross section made under the conditions (33% water concentration) reported by people such as Mauritz, under the visible new preparation condition, the content of the Si element of the composite membrane obtained The range of change in the section is small, and the uniformity has been greatly improved, which shows that the distribution uniformity of the generated inorganic particles in the film has been greatly improved.

Example 2

Put the Nafion NRE212 membrane in a mixed solution of methanol and water with a water concentration of 66%, and swell for 30 minutes. Take out the above-mentioned swollen membrane, use filter paper to absorb the residual liquid on the surface, and then transfer it to a mixed solution of methanol and ethyl orthosilicate with a concentration of 40% orthosilicate for hydration reaction. During the reaction, the reactor is placed in an ultrasonic In the water tank, the frequency is 159kHz, and the ultrasonic power is 1W/cm ² . After reacting for 3 minutes, the membrane was taken out, and the residual liquid on the surface was sucked off with filter paper. The composite film was obtained after drying in a vacuum oven at 80° C. for 24 hours.

The composite membrane was washed with hydrogen peroxide at 80° C., acid washed, and deionized water until the pH was greater than 6, and then stored in deionized water for later use. The composite membrane was used as a proton exchange membrane and a membrane-electrode triple-in-one (MEA) was prepared by using Johnson Matthey's 20wt% Pt/C catalyst (the loading was 0.4mg/cm ² ) and Toray carbon paper. The above-mentioned MEA was assembled into a single cell together with the stainless steel pole plate, the sealing gasket, and the flow field of the graphite groove, and the effective area of the electrode was 5 cm ² . The single cell was tested with _H2 as fuel and _O2 as oxidant. The test conditions are: the operating temperature of the battery is 110°C, the humidification temperature of the cathode and anode reaction gases is 95°C, and the operating pressure is 0.2Mpa (gauge pressure). The measured polarization curve of the battery is shown in Figure 3, and the output voltage of the battery can reach 0.7V under the condition of 500mA/cm ² ; the composite membrane membrane electrode has been operated for 20 hours, and no obvious attenuation of membrane electrode performance has been observed.

Under the same conditions, Nafion NRE 212 was used to prepare membrane electrodes, assembled into single cells, and tested. Under the condition of 500mA/cm ² , the output voltage was only 0.2V.

The invention promotes the diffusion process of the macromolecular precursor in the sol-gel method hydration reaction process by ultrasonic waves, and simultaneously increases the water concentration to improve the distribution of water in the film, which can significantly improve the dispersion degree of generated particles in the composite film. The prepared organic-inorganic composite membrane has high dispersion and good uniformity of inorganic components in the membrane. The prepared highly dispersed organic-inorganic composite membrane can be applied to traditional and high-temperature (80°C-120°C) proton exchange membrane fuel cells, and shows good performance and long-term operation performance under high temperature and low humidity conditions No significant attenuation.

Claims (4)

1. the preparation method of a polymolecularity organic and inorganic composite electrolyte membrane, it is characterized in that: process is following,

1) PEM is soaked in the mixed solution of cosolvent and water, swelling 5-120 minute, the volumetric concentration of water was controlled at 50%-95%; Said cosolvent is one or more the mixture in methyl alcohol, ethanol or the N-methyl pyrrolidone;

2) film after the above-mentioned swelling of taking-up removes surperficial residual liquid with the filter paper suction, places air or nitrogen to stop 10-180 second;

3) changed in the miscible fluid of cosolvent and methyl silicate, tetraethoxysilane or positive butyl titanate above-mentioned film over to reaction 1-10 minute, course of reaction is followed ultrasonic wave; The percentage by volume of cosolvent is 20-80% in the miscible fluid;

4) reaction finishes the back taking-up, inhales with filter paper and removes surperficial residual liquid;

5) after under the 40-80 ℃ of vacuum condition dry 6-48 hour, obtain composite membrane.

2. according to claims 1 described preparation method, it is characterized in that: the volumetric concentration of the said water of step 1) is controlled at 60%-90%.

3. according to claims 1 described preparation method, it is characterized in that: the said ultrasonic wave that in course of reaction, applies of step 3), ultrasonic frequency 20-600kHz, power 0.3-30w/cm ²

4. according to claims 1 described preparation method, it is characterized in that: said PEM is a kind of in the following film, the Nafion series membranes of E.I.Du Pont Company, the Dow series membranes of Dow company, perhaps the Aciplex series membranes of Asahi Chemical company.

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