CN115109177B

CN115109177B - MEA durability reinforcing agent and preparation method and application thereof

Info

Publication number: CN115109177B
Application number: CN202210651714.3A
Authority: CN
Inventors: 高佳武; 唐雪君; 赵航; 韩凯凯
Original assignee: Dongfeng Motor Corp
Current assignee: Dongfeng Motor Corp
Priority date: 2022-06-09
Filing date: 2022-06-09
Publication date: 2023-06-20
Anticipated expiration: 2042-06-09
Also published as: CN115109177A

Abstract

The invention particularly relates to an MEA durability enhancer, a preparation method and application thereof, belonging to the technical field of fuel cells, wherein the effective component of the MEA durability enhancer is water-based fluorinated polyacrylate; the realization mechanism is as follows: in the catalyst dispersing process, polyacrylate can be rapidly dissolved with a solvent phase and then coated on the surface of a catalyst carbon carrier, and adjacent polyacrylate can mutually repel due to surface tension so as to uniformly separate carbon particles. Meanwhile, the polyacrylate is partially fluorinated, and electrostatic adsorption force is generated between the polyacrylate and Nafion solution, so that Nafion and carbon particles and Pt particles travel a two-phase reaction interface. As the reaction continues during operation of the membrane electrode, the carbon support will erode, but the fluorinated polyacrylate coated on the surface of the carbon support will retard such erosion, and the Pt particle surface will remain at a lower level due to its presence, the rate of ostwald ripening also decreases greatly, and an increase in MEA lifetime is achieved.

Description

MEA durability reinforcing agent and preparation method and application thereof

Technical Field

The invention belongs to the technical field of fuel cells, and particularly relates to an MEA durability enhancer, a preparation method and application thereof.

Background

The fuel cell is an energy conversion device, can directly convert chemical energy into electric energy, basically does not discharge greenhouse gases in the energy conversion process, can effectively slow down the greenhouse effect, is not limited by the Carlo cycle, has higher conversion efficiency than the traditional internal combustion engine, can reach 90% in theory, can reach 60% in practical application, and has the advantages of high power density, light weight and the like, so the fuel cell becomes a research focus of attention in recent years. The membrane electrode is a key component of the proton exchange membrane fuel cell, and the performance of the membrane electrode determines the performance of the fuel cell to a great extent. The membrane electrode mainly comprises three parts, namely a polymer membrane, a catalytic layer and a gas diffusion layer.

In recent years, proton exchange membrane fuel cells have begun to progress in commercialization, but the cost is too high and the durability is insufficient, which are still the most critical problems restricting the large-scale commercialization thereof. Studies have shown that: the problem of insufficient durability of the fuel cell is mainly caused by the attenuation of the membrane electrode, which is mainly caused by the attenuation of the Pt/C-based catalyst which is widely used at present. Studies have shown that: the main causes of aging of the platinum-based catalyst include: (1) Under the working condition of the fuel cell, platinum nano particle particles on the surface of the catalyst are easy to migrate, fall off, agglomerate, dissolve and the like on the surface of the catalyst carrier, so that the active sites of the catalyst are reduced; (2) Due to the difference in surface energy, the exfoliated and dissolved nanoparticles tend to deposit onto the larger platinum nanoparticles, which can lead to the continued growth of platinum particles, which can reduce the electrochemically active surface area of the catalyst (3) which can lead to high voltages during start-up and shut-down of the fuel cell, which can lead to electrochemical corrosion of the catalyst support, and secondly, chemical corrosion of the support under fuel cell conditions, which can exacerbate the exfoliation and agglomeration of platinum nanoparticles, leading to degradation of fuel cell catalyst and membrane electrode performance. Therefore, the stabilization treatment of the fuel cell catalyst, effective inhibition of agglomeration, migration, dissolution of Pt nanoparticles, and corrosion of the carbon support are important for promoting development and commercialization of fuel cells.

Disclosure of Invention

The invention aims to provide an MEA durability enhancer, a preparation method and application thereof, so as to solve the problem of low durability of the existing catalyst.

The embodiment of the invention provides an MEA durability enhancer, wherein the effective components of the durability enhancer comprise aqueous fluorinated polyacrylate; the polymerization degree of the aqueous fluorinated polyacrylate is preset, and the fluorinated grafting rate of the aqueous fluorinated polyacrylate is preset grafting rate.

Optionally, the aqueous fluorinated polyacrylate has a degree of polymerization of 1 to 4w.

Optionally, the aqueous fluorinated polyacrylate has a degree of polymerization of 2 to 3w.

Optionally, the fluorinated grafting ratio of the aqueous fluorinated polyacrylate is 35-70%.

Optionally, the fluorinated grafting ratio of the aqueous fluorinated polyacrylate is 45% -60%.

Based on the same inventive concept, the embodiment of the invention also provides a preparation method of the MEA durability reinforcing agent, which comprises the following steps:

mixing the raw materials with a fluorinating agent to obtain a raw material mixture;

mixing the raw material mixture with an initiator to perform free radical polymerization to obtain a durability reinforcing agent;

wherein the raw materials comprise acrylic substances and/or acrylic substances.

Optionally, the mass ratio of the fluorinating agent to the raw materials is 1:5-10.

Optionally, the initiator is a dual initiator, the dual initiator comprises BPO and TBPB, and the mass ratio of the BPO to the TBPB to the raw materials is 1:1-3:10-20.

Optionally, the acrylic comprises AA; the acrylic ester substance comprises at least one of BA, MMA and HPA; the fluorinating agent comprises FMA and/or PFOS.

Based on the same inventive concept, embodiments of the present invention also provide an application of the durability enhancing agent for MEA as described above, including use of the durability enhancing agent for preparing a membrane electrode slurry or a membrane electrode.

Based on the same inventive concept, embodiments of the present invention also provide a membrane electrode including a catalyst and an MEA durability enhancing agent as described above.

Optionally, the mass ratio of the durability enhancing agent to the catalyst is 1:5-10.

Based on the same inventive concept, the embodiments of the present invention also provide a fuel cell including the membrane electrode as described above.

One or more technical solutions in the embodiments of the present invention at least have the following technical effects or advantages:

the main component of the MEA durability enhancer provided by the embodiment of the invention is aqueous fluorinated polyacrylate, which is added when the catalyst slurry is prepared, for example, so that the durability of the catalyst can be obviously improved.

The foregoing description is only an overview of the present invention, and is intended to be implemented in accordance with the teachings of the present invention in order that the same may be more clearly understood and to make the same and other objects, features and advantages of the present invention more readily apparent.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a graph showing comparison of initial properties of inventive example 1 and comparative example 1;

FIG. 2 is a graph showing the polarization of the membrane electrode after 500 hours at constant pressure in example 1 and comparative example 1 of the present invention;

fig. 3 is a flow chart of a method provided by an embodiment of the present invention.

Detailed Description

The advantages and various effects of the present invention will be more clearly apparent from the following detailed description and examples. It will be understood by those skilled in the art that these specific embodiments and examples are intended to illustrate the invention, not to limit the invention.

Throughout the specification, unless specifically indicated otherwise, the terms used herein should be understood as meaning as commonly used in the art. Accordingly, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification will control.

Unless otherwise specifically indicated, the various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or may be prepared by existing methods.

Noun interpretation:

MEA: membrane electrode

CCM: catalytic layer

GDL: gas diffusion layer

AA: acrylic acid

BA: butyl acrylate

HPA: hydroxypropyl acrylate

MMA: methyl methacrylate

FMA: tridecafluorooctyl methacrylate

PFOS: perfluorooctane sulfonate

BPO: benzoyl peroxide

TBPB t-butyl peroxybenzoate

The technical scheme of the embodiment of the application aims to solve the technical problems, and the overall thought is as follows:

it is believed that catalyst attenuation is mainly caused by: because the surface energy of Pt particles gradually increases and aggregation occurs during the catalytic process, this reduces the catalytic activity of the catalyst; the carbon carrier of the catalyst can generate corrosion phenomenon in the use process, so that the catalyst on the carbon particles falls off, and the catalytic activity is reduced.

Current methods for improving catalyst durability are: the Chinese patent application CN 110993960A discloses a cathode catalytic layer structure for strengthening catalyst durability and a preparation method thereof, wherein the method improves the durability of a fuel cell by changing the distribution degree of the catalyst, adopts sparse distribution at one side close to a proton membrane and adopts dense distribution at one side close to a GDL. The method is difficult to operate, sparse and dense catalyst distribution is difficult to judge through characterization, and is extremely difficult to prepare, so that the method is not suitable for large-scale application. The Chinese patent application CN 112701308A discloses a preparation method of a fuel cell catalyst with high durability. The method comprises the following steps: firstly, a carbon-supported platinum-based catalyst is coated and modified by a multiple mixture, and the catalyst coated by an oxide with good durability and a carbon material is obtained by roasting in a specific reducing atmosphere. However, this method requires first processing the catalyst purchased on the market, which involves processes such as doping and baking, and during the process, damage may occur to the catalyst structure, and high-temperature baking is required, and the process is complex and consumes energy.

The MEA durability enhancer is designed by the method, the main component of the material is aqueous fluorinated polyacrylate, the aqueous fluorinated polyacrylate is added when catalyst slurry is prepared, the enhancer can be coated on the surface of a carbon carrier, corrosion of the carbon carrier and Pt on the carbon carrier are prevented, the surface energy of Pt particles is effectively reduced, and Ostwald ripening is prevented. The enhancer is hydrophilic, can rapidly separate the carbon carrier and wrap the carbon carrier and Pt particles in the dispersing process, can not precipitate slurry, does not influence the subsequent slurry processing technology, and can remarkably improve the durability of the catalyst.

According to an exemplary embodiment of the present invention, there is provided an MEA durability enhancing agent whose active ingredient comprises an aqueous fluorinated polyacrylate.

The main component of the catalyst is aqueous fluorinated polyacrylate, which can be added when preparing catalyst slurry, for example, so as to remarkably improve the durability of the catalyst.

In some embodiments, the aqueous fluorinated polyacrylate has a degree of polymerization of 2 to 3w; the fluorinated grafting rate of the aqueous fluorinated polyacrylate is 45-60%.

The polymerization degree and the grafting rate can be perfectly matched with the catalyst for the fuel cell so as to improve the durability of the membrane electrode, and the main mechanism is as follows: in the catalyst dispersing process, the polyacrylate can be rapidly dissolved with the solvent and then coated on the surface of the catalyst carbon carrier, and the adjacent polyacrylates can mutually repel due to surface tension, so that the carbon particles are uniformly separated. In addition, polyacrylate generates larger electrostatic adsorption force with Nafion solution according to the similar compatibility principle because of partial fluorination, so that Nafion and carbon particles and Pt particles travel a two-phase reaction interface. As the reaction continues during operation of the membrane electrode, the carbon support will erode, but the fluorinated polyacrylate coated on the surface of the carbon support will retard such erosion, and the Pt particle surface will remain at a lower level due to its presence, and the rate of ostwald ripening will also decrease significantly, thereby extending the life of the MEA.

According to another exemplary embodiment of the present invention, there is provided a method for preparing the MEA durability enhancing agent as described above, the method comprising:

s1, mixing raw materials and a fluorinating agent to obtain a raw material mixture; the raw materials comprise acrylic substances and/or acrylic substances.

Specifically, the raw materials are first added to a beaker, and then the fluorinating agent is added to the beaker. The beaker is placed on a magnetic stirrer to be stirred, so that the raw materials and the fluorinating agent are uniformly mixed.

In some embodiments, the mass ratio of fluorinating agent to the starting material is 1:5-10.

The proportion can lead acrylic acid and acrylic ester substances to reach a better fluorinated state, if the proportion is too large, the fluorination degree is very low, the reinforcing agent is difficult to adhere to the surface of a carbon carrier of the catalyst, the corrosion of carbon is prevented, if the proportion is too small, the hydrophilicity of the polymer is poor, the catalyst is difficult to disperse, and the purpose of uniform coating is achieved.

In some embodiments, the acrylic comprises AA; the acrylic ester substance comprises at least one of BA, MMA and HPA; the fluorinating agent comprises FMA and/or PFOS.

S2, mixing the raw material mixture with an initiator to perform free radical polymerization to obtain a durability reinforcing agent;

specifically, a double initiator is continuously added into the solution for free radical polymerization, the double initiator is BPO and TBPB respectively, the solution is poured into a reaction kettle for reaction for 4 hours in an oven at 120-160 ℃, the reactant is taken out, and the supernatant is filtered out, so that the durability enhancer is obtained.

In some embodiments, the initiator is a dual initiator comprising BPO and TBPB in a mass ratio of 1:1 to 3:10 to 20.

The ratio can initiate free radical polymerization reaction to the greatest extent, so that acrylic acid and acrylic esters are polymerized, and fluoride is grafted on carboxyl of the acrylic acid. If the ratio is too low, the degree of radical polymerization occurs to a low extent, failing to bring the degree of polymerization to the desired level; if the ratio is too high, too much initiator will cause side reactions of the reactants, which is detrimental to the desired material.

According to another exemplary embodiment of the present invention, there is provided a use of the durability enhancing agent for MEA as described above, the use comprising using the durability enhancing agent for preparing a membrane electrode slurry or a membrane electrode.

Specifically, a durability enhancer is added in the preparation process of the membrane electrode slurry, and then a membrane electrode is prepared by adopting a spraying mode. And a 22bb carbon paper and a frame are put into a clamp to test the performance and durability of the membrane electrode.

According to another exemplary embodiment of the present invention, there is provided a membrane electrode characterized in that the membrane electrode includes a catalyst and an MEA durability enhancing agent as described above.

In some embodiments, the mass ratio of the durability enhancing agent to the catalyst is 1:5-10.

The addition amount in the range of the proportion can remarkably enhance the durability of the membrane electrode. If the proportion is too large, the durability enhancer cannot completely coat the carbon support, and the carbon support cannot be well protected from corrosion during the operation of the membrane electrode. If the ratio is too small, the amount of the durability enhancing agent is too large, a thicker layer will be coated on the surface of the carbon carrier, which is unfavorable for oxygen transmission, and the construction of the three-phase reaction interface will reduce the power generation performance of the membrane electrode.

The MEA durability enhancing agent of the present application, and the preparation method and application thereof will be described in detail with reference to examples, comparative examples and experimental data.

Example 1

A method of making an MEA, the method comprising:

firstly, 10g of AA and 5g of BA 5g of MMA are weighed and added into a beaker, then 1g of FMA and 1g of PFOS are added into the beaker, and the solution is placed on a magnetic stirrer for stirring, wherein the temperature is normal temperature, and the stirring speed is 500r/min.

Then 1g of BPO and 1g of TBPB are added into the solution, the solution is poured into a reaction kettle, the reaction kettle is put into an oven, the temperature of the oven is set to 140 ℃, and the temperature is kept for 4 hours. And after the reaction is finished, pouring out the reactant from the reaction kettle, and filtering to obtain supernatant fluid, thus obtaining the MEA durability enhancer.

And then preparing the MEA, firstly weighing 1g of catalyst, adding 5g of deionized water, 5g of Nafion solution, 30g of isopropanol and 0.1g of MEA durability enhancer into the catalyst, carrying out water bath ultrasonic treatment on the mixed solution, wherein the ultrasonic power is 300W, the ultrasonic treatment time is 30min, and spraying the dispersed slurry to obtain the MEA.

Example 2

A method of making an MEA, the method comprising:

firstly, 5g of AA, 5g of BA, 5g of MMA and 5g of HPA are weighed into a beaker, 2g of FMA and 2g of PFOS are added into the beaker, and the solution is placed on a magnetic stirrer for stirring, wherein the temperature is normal temperature, and the stirring speed is 500r/min.

Then 0.3g of BPO and 0.8g of TBPB are added into the solution, the solution is poured into a reaction kettle, the reaction kettle is put into an oven, the temperature of the oven is set to 140 ℃, and the temperature is kept for 4 hours. And after the reaction is finished, pouring out the reactant from the reaction kettle, and filtering to obtain supernatant fluid, thus obtaining the MEA durability enhancer.

And then preparing the MEA, firstly weighing 1g of catalyst, adding 5g of deionized water, 5g of Nafion solution, 30g of isopropanol and 0.15g of MEA durability enhancer into the catalyst, carrying out water bath ultrasonic treatment on the mixed solution, wherein the ultrasonic power is 300W, the ultrasonic treatment time is 30min, and spraying the dispersed slurry to obtain the MEA.

Example 3

A method of making an MEA, the method comprising:

firstly, 10g of AA and 10g of BA are weighed and added into a beaker, then 1.5g of FMA and 1.5g of PFOS are added into the beaker, and the solution is placed on a magnetic stirrer for stirring, wherein the temperature is normal temperature, and the stirring speed is 500r/min.

Then 0.5g of BPO and 1.5g of TBPB are added into the solution, the solution is poured into a reaction kettle, the reaction kettle is put into an oven, the temperature of the oven is set to 160 ℃, and the temperature is kept for 4 hours. And after the reaction is finished, pouring out the reactant from the reaction kettle, and filtering to obtain supernatant fluid, thus obtaining the MEA durability enhancer.

And then preparing the MEA, firstly weighing 1g of catalyst, adding 5g of deionized water, 5g of Nafion solution, 30g of isopropanol and 0.2g of MEA durability enhancer into the catalyst, carrying out water bath ultrasonic treatment on the mixed solution, wherein the ultrasonic power is 300W, the ultrasonic treatment time is 30min, and spraying the dispersed slurry to obtain the MEA.

Example 4

A method of making an MEA, the method comprising:

firstly, 5g of AA and 5g BA 5g MMA 5g HPA are weighed and added into a beaker, then 1.2g of FMA and 1.2g of PFOS are added into the beaker, and the solution is placed on a magnetic stirrer for stirring, wherein the temperature is normal temperature, and the stirring speed is 500r/min.

Then adding 2g of BPO and 2g of TBPB into the solution, pouring the solution into a reaction kettle, putting the reaction kettle into a baking oven, setting the temperature of the baking oven to 160 ℃, and preserving the heat for 4 hours. And after the reaction is finished, pouring out the reactant from the reaction kettle, and filtering to obtain supernatant fluid, thus obtaining the MEA durability enhancer.

Comparative example 1

A method of making an MEA, the method comprising:

firstly, weighing 1g of catalyst, adding 5g of deionized water, 5g of Nafion solution and 30g of isopropanol into the catalyst, carrying out water bath ultrasonic treatment on the mixed solution, wherein the ultrasonic power is 300W, the ultrasonic time is 30min, and spraying the dispersed slurry to obtain the MEA.

Experimental example

The MEAs prepared in example 1 and comparative example 1 were subjected to initial performance and durability performance tests, and the test results are shown in fig. 1 and 2.

As shown in fig. 1, which is a graph comparing initial performances of comparative example 1 and example 1, it can be seen from the graph that the performance of the MEA is substantially unchanged from that of the non-added MEA after the durability enhancing agent is added, which means that the introduction of the material does not cause a decrease in the power generation performance of the MEA.

As shown in fig. 2, in the graph of the polarization of the membrane electrode after the constant voltage of 500h in comparative example 1 and example 1, it can be seen from the graph that the performance of the membrane electrode without the durability enhancing agent is greatly reduced after the constant voltage operation of 500h, the open circuit voltage is attenuated by 40mV, which means that the activity of the catalyst is greatly reduced, but the performance of the membrane electrode with the durability enhancing agent is not greatly changed, and the performance is far better than that of the comparative example after the durability test, which means that the introduction of the durability enhancing agent can greatly improve the durability of the membrane electrode.

(1) The durability reinforcing agent provided by the embodiment of the invention is added in the catalyst dispersing process, and the polyacrylate can be rapidly dissolved with the solvent and then coated on the surface of the catalyst carbon carrier, and the adjacent polyacrylate can mutually repel due to the surface tension, so that the carbon particles are uniformly separated;

(2) The polyacrylate of the durability reinforcing agent provided by the embodiment of the invention generates larger electrostatic adsorption force in Nafion solution according to a similar compatibility principle because of partial fluorination, so that Nafion and carbon particles and Pt particles travel two-phase reaction interfaces. As the reaction continues during operation of the membrane electrode, the carbon support will erode, but the fluorinated polyacrylate coated on the surface of the carbon support will retard such erosion, and the Pt particle surface will remain at a lower level due to its presence, and the rate of ostwald ripening will also decrease significantly, thereby extending the life of the MEA.

Finally, it is also noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. It is therefore intended that the following claims be interpreted as including the preferred embodiments and all such alterations and modifications as fall within the scope of the invention.

It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

1. Use of a durability enhancing agent for an MEA, the use comprising the use of the durability enhancing agent for the preparation of a membrane electrode slurry or membrane electrode, the effective component of the durability enhancing agent comprising an aqueous fluorinated polyacrylate; the polymerization degree of the aqueous fluorinated polyacrylate is 2-3w, the fluorinated grafting rate of the aqueous fluorinated polyacrylate is 45-60%, and the MEA durability enhancer is prepared by mixing raw materials and a fluorinating agent to obtain a raw material mixture; mixing the raw material mixture and an initiator to perform free radical polymerization to obtain the catalyst; the raw materials comprise acrylic substances and/or acrylic substances, and the mass ratio of the fluorinating agent to the raw materials is 1:5-10, the acrylic comprises AA; the acrylic ester substance comprises at least one of BA, MMA and HPA; the fluorinating agent comprises FMA or a mixture of FMA and PFOS.

2. The use according to claim 1, wherein the initiator is a dual initiator comprising BPO and TBPB in a mass ratio of 1:1-3:10-20.

3. A membrane electrode comprising a catalyst and the MEA durability enhancing agent of claim 1.

4. A membrane electrode according to claim 3, wherein the mass ratio of the durability enhancing agent to the catalyst is 1:5-10.