阅读说明：本技术 高耐受性全氟质子膜及其制备方法 (High-tolerance perfluorinated proton membrane and preparation method thereof ) 是由 马晓娟 邹业成 王振华 张永明 张恒 王丽 于 2020-11-30 设计创作，主要内容包括：本发明涉及功能高分子复合材料技术领域,具体涉及一种高耐受性全氟质子膜及其制备方法。所述的高耐受性全氟质子膜,厚度为5-50μm,由全氟磺酸树脂和添加剂组成,添加剂的含量为全氟磺酸树脂质量的0.01-5wt％,其添加剂具有特定结构,对含氧自由基特别是羟基自由基具有较强清除能力,特别适合用到燃料电池环境中清除所产生的羟基自由基,同时对燃料电池性能具有较低影响和低水洗性,从而使膜的耐受性得到几何级数的增加。本发明的高耐受性全氟质子膜,自由基氧化耐受性高,使用寿命长；本发明还提供其制备方法。(The invention relates to the technical field of functional polymer composite materials, in particular to a high-tolerance perfluorinated proton membrane and a preparation method thereof. The high-tolerance perfluorinated proton membrane is 5-50 mu m thick, consists of perfluorinated sulfonic acid resin and an additive, wherein the content of the additive is 0.01-5 wt% of the mass of the perfluorinated sulfonic acid resin, the additive has a specific structure, has strong scavenging capacity on oxygen-containing free radicals, particularly hydroxyl free radicals, is particularly suitable for being used in a fuel cell environment to scavenge the generated hydroxyl free radicals, and has low influence and low water washing performance on the performance of the fuel cell, so that the tolerance of the membrane is increased by geometric progression. The high-tolerance perfluorinated proton membrane has high free radical oxidation tolerance and long service life; the invention also provides a preparation method of the composition.)

1. A high-tolerance perfluorinated proton membrane is characterized in that: the thickness is 5-50 μm, and the resin is composed of perfluorosulfonic acid resin and additive, wherein the content of the additive is 0.01-5 wt% of the mass of the perfluorosulfonic acid resin;

the chemical structure of the additive is selected from one or more of the following structures:

(Ⅰ)(Ⅱ)(Ⅲ)(Ⅳ)(Ⅴ)(Ⅵ)(Ⅶ)(Ⅷ)

wherein R is₁，R₂，R₃，R₄Is H, OH, CH₃(CH₂)_nO、CH₃(CH₂)_n、NH₂、CH₂OH、C₆H₅、CF₃(CF₂)_n、CF₃(CF₂)_nO, COOH, n is an integer from 0 to 10.

2. The highly tolerant perfluorinated proton membrane according to claim 1, wherein: the content of the additive is 0.1-2 wt% of the perfluorosulfonic acid resin.

3. The highly tolerant perfluorinated proton membrane according to claim 1, wherein: the perfluorinated sulfonic acid resin is selected from one or more of long-chain branched perfluorinated sulfonic acid resin or short-chain branched perfluorinated sulfonic acid resin.

4. The highly tolerant perfluorinated proton membrane according to claim 1, wherein: the number average molecular weight of the perfluorinated sulfonic acid resin is 15-70 ten thousand, and the exchange capacity is 0.85-1.6 mmol/g.

5. The highly tolerant perfluorinated proton membrane according to claim 1, wherein: the number average molecular weight of the perfluorinated sulfonic acid resin is 20-60 ten thousand, and the exchange capacity is 0.9-1.4 mmol/g.

6. A method for preparing a high-tolerance perfluorinated proton membrane according to any one of claims 1 to 5, wherein the method comprises the following steps: the method comprises the following steps:

(1) adding perfluorinated sulfonic acid resin and an additive into a solvent to form a dispersion liquid;

(2) and (3) forming a film by using the dispersion liquid obtained in the step (1), and heating to volatilize the solvent to obtain the high-tolerance perfluorinated proton membrane.

7. The method for preparing a perfluorinated proton membrane with high tolerance according to claim 6, wherein the method comprises the following steps: in the step (1), the solvent is one or more of dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, water, methanol, ethanol, N-propanol, isopropanol, N-butanol, isobutanol, ethylene glycol, propylene glycol, glycerol, acetonitrile, acetone, butanone and dimethylacetamide.

8. The method for preparing a perfluorinated proton membrane with high tolerance according to claim 6, wherein the method comprises the following steps: in the step (1), the content of the perfluorosulfonic acid resin in the dispersion liquid is 5-40 wt%.

9. The method for preparing a perfluorinated proton membrane with high tolerance according to claim 6, wherein the method comprises the following steps: in the step (2), the film forming mode is casting, pouring, silk screen printing process, blade coating, spraying or dipping.

Technical Field

The invention relates to the technical field of functional polymer composite materials, in particular to a high-tolerance perfluorinated proton membrane and a preparation method thereof.

Background

Proton Exchange Membrane Fuel Cells (PEMFCs), which convert reactants, i.e., a fuel (e.g., hydrogen) and an oxidant (e.g., oxygen or air), to generate electric energy, are considered to be the first clean and efficient power generation technology in the 21 st century. Proton exchange membranes are a key material of PEMFCs.

The polymer electrolyte membrane serves as a separator to prevent mixing of reactive gases and as an electrolyte to transport protons from the anode to the cathode. During operation of the fuel cell, a small amount of oxygen will always permeate through the membrane from the cathode to the anode and react with the hydrogen attached to the platinum-carbon catalyst to form hydrogen peroxide. The hydrogen peroxide diffuses into the membrane and reacts with trace metal ion impurities in the membrane, such as iron ions, which have a Fenton catalytic effect, and copper ions catalyze the decomposition of the hydrogen peroxide to generate hydroxyl radicals (. OH) or peroxy radicals (. OOH) with strong oxidizing property.

In order to improve the durability of the polymer electrolyte membrane, the membranes currently used are mostly perfluorinated ion exchange membranes. However, since an unstable carboxyl (-COOH) group is inevitably introduced during the synthesis of the perfluorinated ion exchange resin, the generated hydroxyl (-OH) or peroxy (-OOH) groups attack weak groups (such as carboxylic acid groups) on the ionomer molecular chain. Hydroxyl groups attack unstable end groups of the polymer leading to chain scission and/or can also attack SO under dry conditions^3-The groups thus break the polymer chains, both attacks degrading the membrane and eventually leading to membrane rupture, thinning or pinhole formation, the rate of membrane degradation increasing significantly with increasing operating time and decreasing relative humidity of the inlet air (RH).

To improve the performance and/or durability of the film, several approaches have been proposed to address these issues. For example, in a method (US5547551, US 56565041, US5599614) for filling a Nafion ionic conducting solution in Gore-Select series composite membrane solution developed by w.l.gore company, a polytetrafluoroethylene microporous membrane is added as a reinforcing layer of the membrane, so that the membrane has excellent oxidation stability, can locally slow down the degradation of a fuel cell membrane, and cannot fundamentally solve the problem.

Another solution to the long term free radical oxidative stability of the membrane is to add a catalyst to the membrane that can promote free radical degradation, including 1) adding an aqueous material to the membrane for preventing the fuel cell from operating at low humidity (e.g., US 200701564); 2) adding metal element or alloy with free radical trapping effect into the membrane (such as US 2004043283); 3) the free radical scavenger of phenol and hindered amine is added into the film to eliminate hydroxyl free radical.

The above techniques can partially solve the problem of radical tolerance of the membrane, but cannot fundamentally solve the problem. Their major difficulties mainly include: 1) the added water-retaining substances have a limited water content and cannot fundamentally increase the humidity of the reaction environment and solve the dehydration problem of the membrane, and the added substances also reduce the strength and conductivity of the membrane: 2) the added metal or alloy trapping agent requires very precise control of the content and distribution in the membrane, because these metallic species, in addition to having the effect of trapping hydroxyl radicals, also catalyse the degradation of hydrogen peroxide, and if too large an amount will increase the concentration of hydroxyl radicals in the membrane, further promoting the degradation of the membrane. However, because the metal substance has higher density and hydrophilic surface, the metal substance has spontaneous action due to sedimentation and phase separation aggregation with the perfluorinated ion exchange membrane mainly composed of hydrophobic chains in the membrane preparation process. This phenomenon causes unavoidable increases in the local concentration of the metal element leading to accelerated hydrogen peroxide degradation and deterioration of the film. 3) Some added phenol, hindered amine and other substances are used as polymerization inhibitors in free radical polymerization, namely, the added phenol, hindered amine and other substances have very good reactivity to carbon radicals, but the reactivity to oxygen-containing hydroxyl radicals is greatly reduced. Moreover, they are also degraded continuously and disappear finally when scavenging free radicals, are easy to dissolve in water, can be dissolved out of the membrane along with water generated during working, and cannot play a role in protection.

Disclosure of Invention

The invention aims to provide a high-tolerance perfluorinated proton membrane which has high free radical oxidation tolerance and long service life; the invention also provides a preparation method of the composition.

The high-tolerance perfluorinated proton membrane is 5-50 mu m thick, and consists of perfluorinated sulfonic acid resin and an additive, wherein the content of the additive is 0.01-5 wt% of the mass of the perfluorinated sulfonic acid resin;

the chemical structure of the additive is selected from one or more of the following structures:

(Ⅰ)(Ⅱ)(Ⅲ)(Ⅳ)(Ⅴ)(Ⅵ)(Ⅶ)(Ⅷ)

wherein R is₁，R₂，R₃，R₄Is H, OH, CH₃(CH₂)_nO、CH₃(CH₂)_n、NH₂、CH₂OH、C₆H₅、CF₃(CF₂)_n、CF₃(CF₂)_nO, COOH, n is an integer from 0 to 10.

Preferably, the additive is present in an amount of 0.1 to 2 wt% of the perfluorosulfonic acid resin.

The perfluorinated sulfonic acid resin is selected from one or more of long-chain branched perfluorinated sulfonic acid resin or short-chain branched perfluorinated sulfonic acid resin.

The number average molecular weight of the perfluorinated sulfonic acid resin is 15-70 ten thousand, and the exchange capacity is 0.85-1.6 mmol/g.

Preferably, the perfluorinated ion exchange resin has a number average molecular weight of 20 to 60 ten thousand and an exchange capacity of 0.9 to 1.4 mmol/g.

The disclosed additives are selected based on the expected high rate of hydrogen peroxide decomposition reaction, low impact on fuel cell performance, and low water washability. The compound is a good free radical scavenger or hydrogen peroxide decomposer, can capture and scavenge free hydroxyl groups more quickly, and prevents the attack of the free radicals on active sites, thereby improving the tolerance of the membrane. The amount of additive used in the high tolerance proton membrane depends on several factors, and it is preferred to use the minimum amount of additive to achieve these results.

The preparation method of the high-tolerance perfluorinated proton membrane comprises the following steps:

(1) adding perfluorinated sulfonic acid resin and an additive into a solvent to form a dispersion liquid;

(2) and (2) forming the dispersion liquid in the step (1) into a film by adopting a tape casting, pouring, screen printing process, blade coating, spraying or dipping mode, and heating to volatilize the solvent to obtain the high-tolerance perfluorinated proton membrane.

In the step (1), the solvent is one or more of dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, water, methanol, ethanol, N-propanol, isopropanol, N-butanol, isobutanol, ethylene glycol, propylene glycol, glycerol, acetonitrile, acetone, butanone and dimethylacetamide.

The content of the perfluorosulfonic acid resin in the dispersion is 5 to 40 wt%.

Compared with the prior art, the invention has the following beneficial effects:

the additive adopted by the invention has stronger scavenging capability to oxygen-containing free radicals, particularly hydroxyl free radicals, and is particularly suitable for being used in the fuel cell environment to scavenge the generated hydroxyl free radicals; and the voltage attenuation of the fuel cell caused by the pollution related to the dissolution of the catalyst and the degradation of the ionomer electrolyte is reduced; meanwhile, the additive has lower influence on the performance of the fuel cell and low water washability, so that the tolerance of the membrane is increased geometrically.

Detailed Description

The present invention is described in further detail below with reference to the accompanying tables and examples, which are intended to facilitate the understanding of the present invention without limiting it in any way. In the examples, the percentages are by weight unless otherwise specified.

Example 1

Selecting short-chain branch perfluorosulfonic acid resin with exchange capacity of 1.25mmol/g and number average molecular weight of 45 ten thousand and a component accounting for 0.5 wt% of the mass of the perfluorosulfonic acid resin, wherein R in the component₁，R₂Is OCH₃；R₃，R₄Is H.

Dissolving perfluorosulfonic acid resin in DMSO to form 20 wt% resin dispersion, adding the resin dispersion of formula (I), stirring and dispersing uniformly, forming a film by tape casting, and heating to volatilize the solvent to obtain the perfluoroproton membrane with the thickness of 15 μm.

Example 2

Selecting long-chain branched perfluorosulfonic acid resin with exchange capacity of 1.1mmol/g and number average molecular weight of 35 ten thousand and a formula (IV) accounting for 1 wt% of the mass of the perfluorosulfonic acid resin, wherein R in the formula (IV)₁Is H; r₂Is OH.

Dissolving perfluorinated sulfonic acid resin in a propanol-water system to form 22 wt% resin dispersion, adding the resin dispersion of formula (IV), stirring and dispersing uniformly, forming a film by tape casting, and heating to volatilize the solvent to obtain the perfluorinated proton membrane with the thickness of 20 microns.

Example 3

Selecting long-chain branched perfluorosulfonic acid resin with exchange capacity of 1.01mmol/g and number average molecular weight of 30 ten thousand and a component (VII) accounting for 2 wt% of the mass of the perfluorosulfonic acid resin, wherein R in the component (VII)₁Is NH₂；R₂，R₃，R₄Is H.

Dissolving perfluorosulfonic acid resin in DMF to form 27 wt% resin dispersion, adding the resin dispersion of formula (VII), stirring and dispersing uniformly, casting to form a film, and heating to volatilize the solvent to obtain the perfluorinated proton membrane with the thickness of 30 μm.

Example 4

The exchange capacity is selected to be 1.35mmol/g,Short-chain perfluorosulfonic acid resin with number average molecular weight of 40 ten thousand and a compound represented by the formula (III) in which R is 3.5 wt% of the mass of the perfluorosulfonic acid resin₁，R₂Is COOH.

Dissolving perfluorosulfonic acid resin in DMSO to form 27 wt% resin dispersion, adding the resin dispersion of formula (III), stirring and dispersing uniformly, forming a film by tape casting, and heating to volatilize the solvent to obtain the perfluoroproton membrane with the thickness of 35 μm.

Example 5

Selecting long-chain branched perfluorosulfonic acid resin with exchange capacity of 0.9mmol/g and number average molecular weight of 50 ten thousand and a formula (I) accounting for 4.5 wt% of the mass of the perfluorosulfonic acid resin, wherein R in the formula (I)₁，R₂Is C₄H₉；R₃，R₄Is H.

Dissolving perfluorosulfonic acid resin in DMF to form 35 wt% resin dispersion, adding the resin of formula (II), stirring for dispersing uniformly, forming a film by tape casting, and heating to volatilize the solvent to obtain the perfluorinated proton membrane with the thickness of 50 μm.

Example 6

Selecting short-chain branch perfluorosulfonic acid resin with exchange capacity of 1.4mmol/g and number average molecular weight of 55 ten thousand and a formula (II) accounting for 2.5 wt% of the mass of the perfluorosulfonic acid resin, wherein R in the formula (II)₁，R₂Is OH; r₃，R₄Is H.

Dissolving perfluorinated sulfonic acid resin in an ethanol-water system to form 30 wt% resin dispersion, adding the resin dispersion of the formula (II), stirring and dispersing uniformly, forming a film by tape casting, and heating to volatilize the solvent to obtain the perfluorinated proton membrane with the thickness of 40 microns.

Example 7

Selecting short-chain branch perfluorosulfonic acid resin with exchange capacity of 1.3mmol/g and number average molecular weight of 25 ten thousand and a component (I) accounting for 0.1 wt% of the mass of the perfluorosulfonic acid resin, wherein R in the component (I)₁，R₄Is C₆H₅；R₃，R₂Is H.

Dissolving perfluorosulfonic acid resin in DMSO to form 17 wt% resin dispersion, adding the resin dispersion of formula (I), stirring and dispersing uniformly, forming a film by tape casting, and heating to volatilize the solvent to obtain the perfluoroproton membrane with the thickness of 8 μm.

Comparative example 1

Selecting short-chain branch perfluorosulfonic acid resin with exchange capacity of 1.25mmol/g and number average molecular weight of 40 ten thousand, dissolving the resin in DMF to form 22 wt% resin dispersion, adding no additive, stirring and dispersing uniformly, forming a film by tape casting, and heating to volatilize the solvent to obtain the perfluorinated proton membrane with the thickness of 25 mu m.

The perfluor proton membranes prepared in examples 1-7 and comparative example 1 were subjected to performance test as follows.

(1) Accelerated oxidation test.

The experimental test is carried out by a Fenton reagent method, and the method comprises the following specific steps:

80ppm Fe was added to 100mL of 30% hydrogen peroxide solution²⁺Weighing a certain mass (0.06-0.1g) of perfluorinated proton membrane, placing the perfluorinated proton membrane in the perfluorinated proton membrane, keeping the perfluorinated proton membrane at 80 ℃ for 8 hours, taking out a sample from the solution, washing the sample by deionized water, drying the sample at 80 ℃ for 2 hours, weighing, and calculating the weight loss.

(2) And (5) durability test.

The perfluorinated proton membrane sample was bonded between cathode and anode electrodes to prepare an MEA, both cathode and anode having a density of 0.4mg/cm²Pt loading of (a). MEA samples were used to assemble a 41cm thick section²Active area fuel cell, 5 different fuel cells were tested simultaneously using the stack. The durability or chemical stability of the MEA samples was evaluated at 30% Relative Humidity (RH) and 90 c at Open Circuit Voltage (OCV) to provide hydrogen and air gas flow rates of 3.43slpm and 8.37slpm, respectively. OCV of each cell in the stack was monitored over time. OCV of any of 5 cells in the stack reaches 0.8V or H₂Crossover is more than 10mA/cm²And ending the test and stopping the test.

The test results are shown in table 1.

Table 1 results of performance test of the perfluorinated proton membranes of examples 1-7 and comparative example 1

Item	Mass loss (%)	OCV(h)
			Example 1	3.26	235
Example 2	3.89	200
			Example 3	4.02	180
Example 4	3.68	215
			Example 5	2.93	250
Example 6	2.5	270
			Example 7	4.53	170
Comparative example 1	5.43	130

As can be seen from table 1, the perfluorinated proton membranes of examples 1-7, to which the additives were added, reduced the degradation rate of the membranes and effectively improved the durability of the membranes, compared to comparative example 1.