CN111342097A - Preparation method of electrolyte membrane with high conductivity and good mechanical property - Google Patents

Abstract

The invention relates to a preparation method of an electrolyte membrane with high conductivity and good mechanical property, which comprises the following steps: (1) taking phosphoric acid with the mass concentration of 40-85%, reducing the temperature, adding seed crystals, standing for 30-600 h, and filtering to obtain phosphoric acid crystals; heating and melting the crystals to obtain high-concentration phosphoric acid doped liquid; (2) putting the polybenzimidazole electrolyte membrane into the high-concentration phosphoric acid doping solution prepared in the step (1) to be completely immersed below the liquid level; taking out after the temperature is between room temperature and 150 ℃ for 2 to 48 hours. According to the invention, by controlling crystallization conditions and by adopting a solution crystallization method, the purity of the commercial phosphoric acid is improved, and the serial high-concentration electrolyte membrane doping liquid is prepared, so that the preparation of the PBI membrane with controllable acid content and high phosphoric acid doping level is realized.

Description

A kind of preparation method of electrolyte membrane with high electrical conductivity and good mechanical properties

technical field

The invention relates to the preparation of a phosphoric acid-doped polymer electrolyte membrane with high electrical conductivity and good mechanical properties.

Background technique

Compared with the proton exchange membrane fuel cell with a working temperature of 80-90°C, the proton exchange membrane fuel cell with an operating temperature of 120-200°C has technical advantages such as higher CO tolerance and simplified hydrothermal management system. Therefore, the development of high-temperature PEMFC has become one of the most active research fields in recent years. As the core material of high temperature proton exchange membrane fuel cell, proton exchange membrane (PEM) needs to meet the requirements of high proton transfer capacity, good thermal stability and mechanical properties under high temperature and low humidity conditions.

Polybenzimidazole (PBI) is a class of aromatic heterocyclic polymers with outstanding thermal stability and film-forming properties. Affinity allows acid to be doped into the polymer backbone. The proton conductivity of phosphoric acid-doped PBI membranes depends on the phosphoric acid content in the membrane, that is, the higher the phosphoric acid doping level of the membrane, the higher the membrane conductivity. However, the highest concentration of phosphoric acid currently on the market is about 85%, which cannot achieve the preparation of electrolyte membranes with high phosphoric acid doping levels, thus limiting the improvement of the conductivity of phosphoric acid doped membranes.

In view of the above problems, the purpose of the present invention is to utilize the crystallization characteristics of phosphoric acid, in the process of cooling and crystallization of phosphoric acid, by controlling the crystallization conditions of phosphoric acid, a series of high-concentration phosphoric acid can be obtained, thereby preparing a high-concentration electrolyte membrane doping solution, and preparing a controllable acid content , High phosphoric acid doping level electrolyte membrane, improve the conductivity of the electrolyte membrane.

SUMMARY OF THE INVENTION

By controlling the crystallization conditions and improving the purity of commercially available phosphoric acid by solution crystallization, a series of high-concentration electrolyte membrane doping solutions are prepared, thereby realizing the preparation of PBI membranes with controllable acid content and high phosphoric acid doping level.

The preparation of an electrolyte membrane with high electrical conductivity and good mechanical properties comprises the following steps:

(1) Preparation of high concentration phosphoric acid doping solution

Take phosphoric acid with a mass concentration of 40-85%, and let it stand at -20°C to 4°C for 24h to 120h to crystallize part or all of the phosphoric acid. The phosphoric acid was taken out, the supernatant was filtered off, and the solid portion was dissolved by heating to obtain a high-concentration phosphoric acid-doped solution.

(2) Preparation of high phosphoric acid doping level electrolyte membrane

After drying, put the PBI film into the high-concentration phosphoric acid doping solution prepared in step (1), shake it gently to make it all immersed below the liquid level, and continue from room temperature to 150° C. for 2-72 hours.

The phosphoric acid doping content of the PBI electrolyte membrane can be calculated by the change of the membrane quality before and after phosphoric acid doping.

The calculation formula of phosphoric acid doping content is: phosphoric acid doping content%=100*(m _{after dipping-m before dipping} )/m _{before dipping,} where m _{after dipping is the film quality after} phosphoric acid doping, m _{before dipping is before} phosphoric acid doping dry film quality.

The preparation of the electrolyte membrane with high electrical conductivity and good mechanical properties of the present invention has the following advantages:

(1) The process is simple, easy to operate and control;

(2) The prepared electrolyte membrane has high phosphoric acid doping level and low water content;

(3) The prepared phosphoric acid doped electrolyte membrane has high electrical conductivity.

Description of drawings

Fig. 1 is a curve of the electrical conductivity of the prepared electrolyte membrane with high phosphoric acid doping level as a function of temperature.

Figure 2 shows the stress versus strain curve of the prepared electrolyte membrane with high phosphoric acid doping level in the tensile test.

Detailed ways

Example 1

Take 800 g of phosphoric acid with a mass concentration of 85%, heat it in a constant temperature water bath at 60 °C and stir for 40 min; after the temperature drops to room temperature, add 5 g of phosphoric acid crystals, cool down to -8 °C at room temperature, and let stand for 48 h. After the phosphoric acid was taken out, the supernatant was removed by filtration immediately, and the solid part was heated in an oven at 80°C for 12 h. The obtained high-concentration phosphoric acid-doped liquid is stirred.

Cut out 4 PBI films with a size of 10cm*10cm, dry them in an oven at 120°C for 4 hours, and record the weight as m ₀ . The PBI film was placed in the above-mentioned high-concentration phosphoric acid doping solution, and was gently shaken so that it was completely immersed below the liquid surface. Heating in an oven at 80 °C for 10 h yields an electrolyte membrane with a high phosphoric acid doping level. The above-mentioned electrolyte membrane was weighed and recorded as m ₁ after the surface phosphoric acid was wiped off with filter paper.

Table 1 below shows the quality and phosphoric acid doping content of the four films before and after treatment.

It can be seen from Table 1 that such films have higher phosphoric acid doping levels and consistency.

m₀ m₁ Phosphoric acid doping content 483mg 2714mg 462% 480mg 2712mg 465% 475mg 2703mg 469% 482mg 2690mg 458%

FIG. 1 is a curve of the electrical conductivity of the electrolyte membrane with high phosphoric acid doping level prepared in Example 1 as a function of temperature. In Figure 1, the abscissa is the temperature (°C), and the ordinate is the conductivity (mS cm ^-1 ). It can be seen from Figure 1 that the conductivity of this type of membrane at 160°C is >200 mS cm ^-1 , which can meet the requirements of fuel cells. Electrolyte membrane conductivity requirements.

The mechanical strength of the electrolyte membrane with high phosphoric acid doping level was tested by Q800 of TA company. Using stretch mode, the stretch rate is 100%. FIG. 2 is the stress-strain curve of the films prepared above in the tensile test. The ordinate is stress (MPa), and the abscissa is strain (%). The tensile strength of the prepared membrane is greater than 7MPa at room temperature, and its elongation at break is greater than 120%, indicating that this type of membrane has good mechanical properties and can meet the needs of application in fuel cells.

Example 2

Take 800 g of phosphoric acid with a mass concentration of 85%, heat it in a constant temperature water bath at 70 °C and stir for 30 min;

After the temperature dropped to 15°C, 5 g of phosphoric acid crystals were added, and the solution was continued to cool to -18°C and allowed to stand for 30 hours. After the phosphoric acid was taken out, the supernatant was removed by filtration immediately, and the solid part was heated in an oven at 80°C for 12 h. The obtained high-concentration phosphoric acid-doped liquid is stirred.

Cut out 2 PBI films with a size of 10cm*10cm, and dry them in an oven at 150°C for 2h. The PBI film was placed in the above-mentioned high-concentration phosphoric acid doping solution, and was gently shaken so that it was completely immersed below the liquid surface. Heating in an oven at 70°C for 10 h yields an electrolyte membrane with a high phosphoric acid doping level, and the phosphoric acid doping content is 500% and 506%, respectively.

Example 3 (comparative example)

Cut out 2 PBI films with a size of 10cm*10cm, dry them in an oven at 120°C for 4 hours, and record the weight as m ₀ . The PBI membrane was put into phosphoric acid having a mass concentration of 85%, and was gently shaken so that it was completely immersed below the liquid surface. Heating in an oven at 80 °C for 10 h yields a phosphoric acid doped electrolyte membrane. The above-mentioned electrolyte membrane was weighed and recorded as m ₁ after the surface phosphoric acid was wiped off with filter paper.

Table 2 below shows the mass and phosphoric acid doping content of the two films before and after treatment.

m₀ m₁ Phosphoric acid doping content 487mg 2211mg 354% 476mg 2190mg 360%

Claims (4)

1. A preparation method of an electrolyte membrane with high electrical conductivity and good mechanical properties, comprising the following steps: (1) Preparation of high concentration phosphoric acid doping solution Take phosphoric acid with a mass concentration of 40%-85%, in order to obtain a uniformly distributed H ₃ PO ₄ -H ₂ O system, stir the phosphoric acid with a mass concentration of 40%-85% in a constant temperature water bath at 40-70 ° C for 30-60min Carry out pretreatment; lower the temperature of phosphoric acid to room temperature to 10°C, add seed crystals, continue to cool down to 4°C to -20°C, and let stand for 30h to 60h; filter to obtain phosphoric acid crystals; heat and melt the above crystals to obtain high-concentration phosphoric acid mixed with miscellaneous liquid; (2) Preparation of high phosphoric acid doping level electrolyte membrane Put the polybenzimidazole electrolyte membrane into the high-concentration phosphoric acid doping solution prepared in step (1), so that it is completely immersed below the liquid level; it can be taken out after the room temperature reaches 150° C. for 2-48 hours. 2. preparation method according to claim 1 is characterized in that: phosphoric acid mass is concentrated 40%-85%; Pretreatment temperature is 40-70 ℃, stirring duration is 30-60min; ℃～-20℃; the seeds include one or more of phosphoric acid crystals, phosphorus pentoxide, polyphosphoric acid crystals, urea, melamine, etc.; the standing time in the crystallization process is 30h～60h. 3. The preparation method according to claim 1, wherein the heating and dissolving process is 60-100°C. 4. The preparation method according to claim 1, wherein the dipping process is from room temperature to 150°C for 2-48h.

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