CN111342098A

CN111342098A - Preparation method of phosphoric acid-doped polybenzimidazole crosslinked membrane

Info

Publication number: CN111342098A
Application number: CN201811547436.7A
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
Anticipated expiration: 2038-12-18
Also published as: CN111342098B

Abstract

The invention relates to a preparation method of a phosphoric acid doped polybenzimidazole crosslinking membrane, which comprises the following steps: (1) preparation of polybenzimidazole solution, 2) preparation of polybenzimidazole crosslinked membrane: adding azacycloolefine and p-chloromethyl styrene into the polybenzimidazole solution in the stirring process to obtain a mixed solution; casting a membrane by using the mixed solution, and drying to obtain a polybenzimidazole crosslinking membrane; (3) preparation of phosphoric acid-doped polybenzimidazole electrolyte membrane: and (3) soaking the polybenzimidazole crosslinked membrane obtained in the step (2) in phosphoric acid with the mass concentration of 85% -90% to obtain the phosphoric acid-doped polybenzimidazole electrolyte membrane. According to the invention, organic micromolecules and PBI are subjected to reaction polymerization and crosslinking film formation after being blended and cast, so that the mechanical property of the phosphoric acid-doped PBI film is improved.

Description

Preparation method of phosphoric acid-doped polybenzimidazole crosslinked membrane

Technical Field

The invention belongs to the field of polymer electrolyte exchange membranes, and particularly relates to a preparation method of a proton exchange electrolyte membrane with high conductivity and good mechanical properties.

Background

The use of acid-doped Polybenzimidazole (PBI) membranes in fuel cells has prompted the development of high temperature Proton Exchange Membrane Fuel Cells (PEMFCs). The proton conductivity of acid doped PBI membranes depends on the 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, higher acid doping levels will significantly reduce the mechanical strength of the membrane, which in turn directly affects fuel cell performance and service life. It is a common and effective way to develop high temperature crosslinked films with both high acid doping levels and good mechanical properties, where high molecular polymers containing halogen functional groups are used as the crosslinking agent with better effect.

However, the halogen functional group has high activity, which often causes the self-crosslinking of the high molecular polymer as a crosslinking agent, so that the preparation of a proton exchange electrolyte membrane with high conductivity and good mechanical properties cannot be realized.

Disclosure of Invention

Aiming at the problems, the invention provides a method for preparing a macromolecular cross-linked membrane, which leads organic micromolecules and PBI to be mixed and cast into a membrane and then to be subjected to reaction polymerization and cross-linking to form the membrane so as to improve the mechanical property of the phosphoric acid doped PBI membrane.

The preparation method of the polybenzimidazole crosslinked membrane with higher conductivity and good mechanical property comprises the following steps:

a preparation method of a phosphoric acid doped polybenzimidazole crosslinking membrane comprises the following steps:

(1) preparing a polybenzimidazole solution;

preparing a polybenzimidazole solution by using an organic solvent A; the organic solvent A is one or more than two of N-methyl pyrrolidone, N-dimethylformamide, N-dimethylacetamide, dimethyl sulfoxide and the like;

(2) preparation of polybenzimidazole crosslinked membrane:

taking a polybenzimidazole solution, and adding azacycloolefine, p-chloromethyl styrene and an initiator in the stirring process to obtain a mixed solution; adopting the mixed solution to cast a membrane and drying to obtain a polybenzimidazole crosslinking membrane;

in the mixed solution, the mass concentration of the polybenzimidazole polymer is 5-20%; the mass concentration of the azacyclo-olefin is 1 to 10 percent; the mass concentration of the p-chloromethyl styrene is 0.1 to 0.5 percent; p-chloromethyl styrene reacts with polybenzimidazole polymer and azacyclo-olefin to form a long-chain network, and the introduction of a heterocyclic group provides a phosphate binding site, so that the phosphate doping content is improved;

(3) preparation of phosphoric acid-doped polybenzimidazole electrolyte membrane:

and (3) soaking the polybenzimidazole crosslinked membrane obtained in the step (2) in phosphoric acid to obtain a phosphoric acid-doped polybenzimidazole electrolyte membrane.

In the step 2), styrene is added into the membrane casting solution, wherein the mass concentration of the styrene is 1-10%.

In the step (2), the nitrogen-containing heterocyclic olefin is one or more than two of vinyl pyrrole, propenyl pyridine and vinyl imidazole.

In the step (2), the initiator is one or more than two of dimethyl azodiisobutyrate, azodiisobutyronitrile, azodiisoheptonitrile and N, N-dimethylaniline; the mass concentration of the initiator in the membrane casting solution is 0.01-0.1%.

And (3) carrying out the following post-treatment process on the polybenzimidazole crosslinked membrane obtained in the step (2), specifically, boiling the prepared polybenzimidazole crosslinked membrane in deionized water for more than 2h, removing the residual solvent, and drying to obtain the treated polybenzimidazole crosslinked membrane.

The preparation method of the polybenzimidazole polymer comprises the following steps: adding biphenyltetramine into polyphosphoric acid, introducing nitrogen for protection, mechanically stirring, and keeping at 160 ℃ for 2-72h at 100-; continuously heating to the temperature of 180 ℃ and 220 ℃, sequentially adding isophthalic acid and phosphorus pentoxide, and reacting for 2-72h to obtain a polymer product; and pouring the product into an aqueous solution of sodium hydroxide, soaking for 10-48h, and filtering to obtain the polybenzimidazole polymer.

The mass ratio of the polyphosphoric acid to the biphenyltetramine is 50:1-5: 1; the mass ratio of the isophthalic acid to the biphenyltetramine is 2:3-1: 1; the mass ratio of the phosphorus pentoxide to the biphenyltetramine is 1:6-1: 3; the mass concentration of the sodium hydroxide aqueous solution is 10-40%.

The preparation of the polybenzimidazole crosslinking membrane has the following advantages:

(1) the film casting process is simple and easy to operate, regulate and control;

(2) the prepared electrolyte membrane has stronger acid binding capacity, so that the electrolyte membrane has higher conductivity;

(3) the prepared electrolyte membrane has excellent mechanical properties;

(4) the prepared electrolyte membrane has uniform and controllable thickness.

Drawings

Fig. 1 is a graph showing the change in conductivity with temperature of the electrolyte membrane in example 3.

Fig. 2 is a graph showing the change of stress with strain of the electrolyte membrane in the tensile test in example 3.

Detailed Description

Example 1

Adding 150g of polyphosphoric acid and 3.25g of biphenyltetramine into a 250ml three-neck flask, introducing nitrogen, mechanically stirring, heating in an oil bath to 140 ℃, and keeping for 3 hours. After further heating to 200 ℃, 2.51g of isophthalic acid and 5.0g of phosphorus pentoxide were added and reacted for 24 hours. The prepared polymer product is slowly poured into a sodium hydroxide aqueous solution to be soaked for 24 hours, filtered, dried and ground into PBI powder.

Example 2 (comparative example)

17g of PBI solution (10 wt%, solvent N-methylpyrrolidone) was weighed out, cast onto a horizontal substrate, and dried to form a film. The prepared polybenzimidazole crosslinking membrane is boiled in deionized water for 12 hours, and residual solvent is removed. Drying at 120 ℃ for 2h, and soaking in phosphoric acid with the mass concentration of 85% at 80 ℃ for 10h to obtain the phosphoric acid doped polybenzimidazole electrolyte membrane.

Example 3

17g of PBI solution (10 wt%, solvent N-methylpyrrolidone) was weighed, 250ul of vinylimidazole, 39ul of p-chloromethylstyrene and 23mg of initiator (azobisisobutyronitrile) were added with stirring, and stirring was continued for 15 min. The prepared solution is cast on a horizontal substrate and dried to form a film. The prepared polybenzimidazole crosslinking membrane is boiled in deionized water for 12 hours, and residual solvent is removed. Drying at 120 ℃ for 2h, and soaking in phosphoric acid with the mass concentration of 85% at 80 ℃ for 10h to obtain the phosphoric acid doped polybenzimidazole crosslinking membrane.

TABLE 1 comparison of electrolyte membranes obtained in example 2 and example 3

Claims

1. A preparation method of a phosphoric acid doped polybenzimidazole crosslinking membrane comprises the following steps:

(1) preparation of polybenzimidazole solution:

dissolving polybenzimidazole polymer powder in an organic solvent A to prepare a polybenzimidazole solution; the organic solvent A is one or more than two of N-methyl pyrrolidone, N-dimethylformamide, N-dimethylacetamide, dimethyl sulfoxide and the like;

(2) preparation of polybenzimidazole crosslinked membrane:

adding azacycloolefine and p-chloromethyl styrene into the polybenzimidazole solution in the stirring process to obtain a mixed solution; casting a membrane by using the mixed solution, and drying to obtain a polybenzimidazole crosslinking membrane;

and (3) soaking the polybenzimidazole crosslinked membrane obtained in the step (2) in phosphoric acid with the mass concentration of 85% -90% to obtain the phosphoric acid-doped polybenzimidazole electrolyte membrane.

2. The method of claim 1, wherein:

in the step 2), styrene can be added into the mixed solution for casting the membrane to adjust the mechanical strength of the obtained cross-linked membrane, and the mass concentration of the styrene in the mixed solution is 1-10%.

3. The method of claim 1, wherein: in the step (2), the nitrogen-containing heterocyclic olefin is one or more than two of vinyl pyrrole, propenyl pyridine and vinyl imidazole.

4. The method of claim 1, wherein:

adding an initiator into the mixed solution for casting the film in the step 2), wherein the initiator in the step 2 is one or more of dimethyl azobisisobutyrate, azobisisobutyronitrile, azobisisoheptonitrile and N, N-dimethylaniline; the mass concentration of the initiator in the membrane casting solution is 0.01-0.1%.

5. The method of claim 1, wherein:

6. The method of claim 1, wherein:

the preparation method of the polybenzimidazole polymer powder comprises the following steps: adding biphenyltetramine into polyphosphoric acid, introducing nitrogen for protection, mechanically stirring, and keeping at 160 ℃ for 2-72h at 100-; continuously heating to the temperature of 180 ℃ and 220 ℃, sequentially adding isophthalic acid and phosphorus pentoxide, and reacting for 2-72h to obtain a polymer product; pouring the product into a sodium hydroxide aqueous solution, soaking for 10-48h, and filtering to obtain a polybenzimidazole polymer; drying and grinding to obtain the required polybenzimidazole polymer powder.

7. The method of claim 6, wherein: