CN111342097A

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

Info

Publication number: CN111342097A
Application number: CN201811547775.5A
Authority: CN
Inventors: 王素力; 闫树华; 马文佳; 孙公权
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2018-12-18
Filing date: 2018-12-18
Publication date: 2020-06-26

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

Preparation method of electrolyte membrane with high conductivity and good mechanical property

Technical Field

The invention relates to a preparation method of a phosphoric acid doped polymer electrolyte membrane with high conductivity and good mechanical property.

Background

Compared with the proton exchange membrane fuel cell with the operating temperature of between 120 and 200 ℃, the proton exchange membrane fuel cell with the operating temperature of between 80 and 90 ℃ has the technical advantages of higher CO tolerance capability, simplified hydrothermal management system and the like, so the development of the high-temperature PEMFC is one of the most active research fields in recent years. Proton Exchange Membranes (PEM) as core materials of high temperature PEM fuel cells need 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 kind of aromatic heterocyclic high molecular polymer, has outstanding thermal stability and film-forming property, and excellent mechanical property of film material, and meanwhile, the basic benzimidazole group in the polymer has affinity to acid, so that the acid can be doped in the polymer skeleton. The proton conductivity of phosphoric acid doped PBI membranes depends on the phosphoric acid content in the membrane, i.e. the higher the phosphoric acid doping level of the membrane, the higher the conductivity of the membrane. However, the highest concentration of the phosphoric acid on the market at present is about 85%, and the preparation of the electrolyte membrane with high phosphoric acid doping level cannot be realized, so that the improvement of the conductivity of the phosphoric acid doped membrane is limited.

In view of the above problems, the present invention aims to obtain a series of high-concentration phosphoric acids by controlling the crystallization conditions of phosphoric acid during the cooling crystallization of phosphoric acid by using the crystallization characteristics of phosphoric acid, thereby preparing a high-concentration electrolyte membrane doping solution, preparing an electrolyte membrane with a controllable acid content and a high phosphoric acid doping level, and improving the conductivity of the electrolyte membrane.

Disclosure of Invention

By controlling crystallization conditions and by a solution crystallization method, the purity of the commercial phosphoric acid is improved, and a series of high-concentration electrolyte membrane doping solutions are prepared, so that the preparation of the PBI membrane with controllable acid content and high phosphoric acid doping level is realized.

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

(1) preparation of high-concentration phosphoric acid doping liquid

Taking phosphoric acid with the mass concentration of 40-85%, and standing the phosphoric acid at the temperature of-20-4 ℃ for 24-120 h to crystallize part or all of the phosphoric acid. And taking out the phosphoric acid, filtering the supernatant, and heating to dissolve the solid part to obtain the high-concentration phosphoric acid doped solution.

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

Drying the PBI membrane, then putting the PBI membrane into the high-concentration phosphoric acid doping solution prepared in the step (1), gently shaking the PBI membrane to enable the PBI membrane to be completely immersed below the liquid level, and keeping the PBI membrane at room temperature to 150 ℃ for 2-72 hours.

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

The calculation formula of the phosphoric acid doping content is as follows: phosphoric acid doping content ═ 100 ═ m (m)_{After impregnation}-m_{Before impregnation})/m_{Before impregnation}Wherein m is_{After impregnation}Is the film mass m after phosphoric acid doping_{Before impregnation}The quality of the dry film before phosphoric acid doping.

The preparation of the electrolyte membrane with high conductivity and good mechanical property has the following advantages:

(1) the process is simple, and the operation and the regulation are easy;

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

(3) the prepared phosphoric acid doped electrolyte membrane has higher conductivity.

Drawings

Fig. 1 is a graph of the conductivity versus temperature of the prepared high phosphoric acid doping level electrolyte membrane.

Fig. 2 is a graph showing the stress versus strain of the prepared high phosphoric acid doping level electrolyte membrane in a tensile test.

Detailed Description

Example 1

Taking 800g of phosphoric acid with the mass concentration of 85%, heating and stirring in a constant-temperature water bath at 60 ℃ for 40 min; after the temperature is reduced to the room temperature, 5g of phosphoric acid crystal is added, the temperature is reduced to-8 ℃ at the room temperature, and the mixture is kept stand for 48 hours. After the phosphoric acid was taken out, the supernatant was immediately removed by filtration, and the solid portion was put in an oven at 80 ℃ for 12 hours. Stirring the obtained high-concentration phosphoric acid doped solution.

Cutting 4 pieces of PBI membrane with size of 10cm x 10cm, drying in an oven at 120 deg.C for 4h, weighing and recording m₀. The PBI membrane was placed in the high-concentration phosphoric acid dope solution, and the whole PBI membrane was immersed below the liquid surface by gentle shaking. Heating in an oven at 80 ℃ for 10h to obtain high phosphoric acid doping levelAn electrolyte membrane. The electrolyte membrane was wiped with filter paper to remove phosphoric acid on the surface and weighed as m₁。

The following table 1 shows the mass and the phosphoric acid doping content before and after the treatment of the 4 sheets of films.

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

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

Fig. 1 is a graph of the electrical conductivity versus temperature of the high phosphoric acid doping level electrolyte membrane prepared in example 1. In FIG. 1, the abscissa is temperature (. degree. C.) and the ordinate is conductivity (mS cm)^-1) (ii) a As can be seen from FIG. 1, the conductivity of such a membrane is at 160 ℃>200mS cm^-1And the requirement of the fuel cell on the conductivity of the electrolyte membrane can be met.

The mechanical strength of the high phosphoric acid doping level electrolyte membrane was tested using Q800 of TA corporation. With the stretching mode, the stretching rate was 100%. Fig. 2 is a graph of stress versus strain for the films prepared above under tensile testing. The ordinate is the stress (MPa) and the abscissa is the strain (%). The tensile strength of the prepared membrane is more than 7MPa at room temperature, and the breaking elongation is more than 120%, which indicates that the membrane has good mechanical properties and can meet the application requirements in fuel cells.

Example 2

Taking 800g of phosphoric acid with the mass concentration of 85%, heating and stirring in a constant-temperature water bath at 70 ℃ for 30 min;

after the temperature is reduced to 15 ℃, 5g of phosphoric acid crystal is added, the mixture is continuously cooled to-18 ℃ and kept stand for 30 h. After the phosphoric acid was taken out, the supernatant was immediately removed by filtration, and the solid portion was put in an oven at 80 ℃ for 12 hours. Stirring the obtained high-concentration phosphoric acid doped solution.

2 pieces of PBI membrane with a size of 10cm x 10cm were cut and dried in an oven at 150 ℃ for 2 h. The PBI membrane was placed in the high-concentration phosphoric acid dope solution, and the whole PBI membrane was immersed below the liquid surface by gentle shaking. Heating in a 70 ℃ oven for 10h to obtain the high phosphoric acid doping level electrolyte membrane, wherein the phosphoric acid doping contents are respectively 500% and 506%.

Example 3 (comparative example)

Cutting 2 pieces of PBI membrane with size of 10cm x 10cm, drying in an oven at 120 deg.C for 4h, weighing and recording m₀. The PBI membrane was immersed in phosphoric acid having a mass concentration of 85% under a liquid surface by gently shaking. Heating in an oven at 80 ℃ for 10h to obtain the phosphoric acid doped electrolyte membrane. The electrolyte membrane was wiped with filter paper to remove phosphoric acid on the surface and weighed as m₁。

The following table 2 shows the mass and the phosphoric acid doping content before and after the treatment of the 2 films.

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

Claims

1. A preparation method of an electrolyte membrane with high conductivity and good mechanical property comprises the following steps:

(1) preparation of high-concentration phosphoric acid doping liquid

Taking phosphoric acid with the mass concentration of 40-85% to obtain H with uniform distribution₃PO₄-H₂An O system, wherein phosphoric acid with the mass concentration of 40-85% is stirred in a constant-temperature water bath at 40-70 ℃ for 30-60min for pretreatment; reducing the temperature of the phosphoric acid to room temperature to 10 ℃, adding seed crystals, continuously reducing the temperature to 4 ℃ to-20 ℃, and standing for 30h to 60 h; filtering to obtain phosphoric acid crystal; heating and melting the crystals to obtain high-concentration phosphoric acid doped liquid;

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

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; keeping the temperature between room temperature and 150 ℃ for 2-48h, and taking out.

2. The method of claim 1, wherein: the mass concentration of the phosphoric acid is 40 to 85 percent; the pretreatment temperature is 40-70 ℃, and the stirring time is 30-60 min; the temperature is reduced to room temperature-10 ℃ for the first time, and the termination temperature is 4 ℃ to-20 ℃; the seed crystal comprises one or more than two of phosphoric acid crystal, phosphorus pentoxide, polyphosphoric acid crystal, urea, melamine and the like; standing for 30-60 h in the crystallization process.

3. The method of claim 1, wherein: the heating and dissolving process is 60-100 ℃.

4. The method of claim 1, wherein: the impregnation process is from room temperature to 150 ℃ for 2-48 h.