A membrane electrode containing ether-free polybenzimidazole ionomer and based on high-temperature proton exchange membrane and its preparation method

Abstract

The present invention discloses a membrane electrode comprising a polybenzimidazole ionomer containing no ether bonds and based on a high-temperature proton exchange membrane, and a method for preparing the same. The membrane electrode based on a high-temperature proton exchange membrane comprises a proton exchange membrane, a catalyst layer and a gas diffusion layer located on either side of the proton exchange membrane. The catalyst layer comprises a catalyst and an ionomer, wherein the ionomer is the polybenzimidazole ionomer containing no ether bonds. The membrane electrode prepared by the present invention exhibits higher fuel cell performance than membrane electrodes using commercial PTFE emulsions.

Description

Technical Field

[0001] The present invention belongs to the technical field of fuel cells, and in particular relates to a method for preparing a membrane electrode containing an ether-free polybenzimidazole ionomer and a polybenzimidazole-based high-temperature proton exchange membrane. background

[0002] Fuel cells are a clean and efficient energy technology that can directly convert the chemical energy of fuels into electrical energy and are widely considered a promising clean technology. In recent years, high-temperature proton exchange membrane fuel cells (HT-PEMFCs) have garnered increasing attention due to their multiple advantages over low-temperature proton exchange membrane fuel cells (LT-PEMFCs). HT-PEMFCs simplify water and heat management, improve catalyst efficiency, and enhance the fuel cell's CO tolerance. These advantages, benefiting from the fuel cell's high operating temperature and dry operation, may offer the potential for using catalysts with low or even no Pt metal loading, enabling the development of low-cost and highly efficient fuel cell systems. Conventional membranes, such as Nafion and sulfonated membranes, are unstable at higher temperatures and cannot be used as high-temperature PEMs. However, by using phosphoric acid as a proton carrier, phosphoric acid-doped polybenzimidazole membranes have been developed as high-temperature PEMs, achieving relatively high proton conductivity at high temperatures.

[0003] The membrane electrode assembly (MEA) primarily consists of a proton exchange membrane, a gas diffusion layer, and a catalyst layer. Electrochemical reactions involving three distinct "phases" (gas, protons, and electrons) occur within the catalyst layer, making its composition crucial for optimal fuel cell performance. The catalyst layer primarily consists of a catalyst, an ionomer, and a void region, which form the three-phase boundary region for the electrochemical reaction.

[0004] In membrane electrode preparation, the power density provided by MEA using commercial PTFE ionomer in traditional catalyst slurry is low, and PTFE ionomer can only play a bonding and hydrophobic role in binding Pt / C catalyst. Summary of the Invention

[0005] The object of the present invention is to provide a membrane electrode containing a polybenzimidazole ionomer without an ether bond and based on a high-temperature proton exchange membrane and a preparation method thereof.

[0006] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a polybenzimidazole ionomer containing no ether bonds, which is prepared by the following steps: nitrogen is introduced into a reaction kettle to evacuate the reactor; then phosphorus pentoxide and polyphosphoric acid are added, the temperature is raised to 100-140°C, 3,3'-diaminobenzidine monomer is added after mechanical stirring, and the mixture is stirred until dissolved. Then, a pyridine dicarboxylic acid monomer is added, and the mixture is stirred for 1-2 hours under an N2 atmosphere. The temperature is raised to 180-220°C and prepolymerized for 2-10 hours. The system is then cooled to 80-100°C, and a dibasic fatty acid monomer is added. The mixture is stirred until dissolved, and the temperature is raised to 140-180°C. The reaction is terminated until the viscosity of the reaction system increases significantly and the color deepens. The polymer solution is poured into a saturated NaHCO3 aqueous solution to produce a filamentous solid. After sufficient soaking, the solid is filtered, washed, and dried to obtain a polybenzimidazole ionomer containing no ether bonds.

[0008] Preferably, the pyridine dicarboxylic acid-containing monomer is one or more of 2,3-pyridinedicarboxylic acid, 2,4-pyridinedicarboxylic acid, 2,5-pyridinedicarboxylic acid, 2,6-pyridinedicarboxylic acid, 3,5-pyridinedicarboxylic acid, and 2,2'-bipyridine-4,4'-dicarboxylic acid.

[0009] Preferably, the dibasic fatty acid monomer is one or more of pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, tetradecanedioic acid and hexadecanedioic acid.

[0010] Preferably, the mass fraction of phosphorus pentoxide in polyphosphoric acid is 1-10 wt %, more preferably 3-6 wt %.

[0011] Preferably, after all monomers of the 3,3'-diaminobenzidine monomer, the pyridine dicarboxylic acid monomer and the dibasic fatty acid monomer are stirred and mixed in polyphosphoric acid, the total monomer concentration is 1 to 20 wt%; the ratio of the total molar number of the pyridine dicarboxylic acid monomer and the dibasic fatty acid monomer to the molar number of the 3,3'-diaminobenzidine monomer is 1:1; and the molar ratio of the pyridine dicarboxylic acid monomer to the dibasic fatty acid monomer is 1:3-3:1.

[0012] In a second aspect, the present invention provides a membrane electrode based on a high-temperature proton exchange membrane, comprising a proton exchange membrane and a catalytic layer and a gas diffusion layer located on both sides of the proton exchange membrane, wherein the catalytic layer comprises a catalyst and an ionomer, and the ionomer is a polybenzimidazole ionomer containing no ether bonds.

[0013] Preferably, the proton exchange membrane is a phosphoric acid-doped polybenzimidazole proton exchange membrane.

[0014] Preferably, the catalyst is a platinum-carbon catalyst. Further preferably, the platinum content in the platinum-carbon catalyst is 40-60 wt%.

[0015] Preferably, the gas diffusion layer is a carbon paper gas diffusion layer or a carbon cloth gas diffusion layer.

[0016] In a third aspect, the present invention provides a method for preparing a membrane electrode based on a high-temperature proton exchange membrane, comprising the following steps:

[0017] (1) Preparation of phosphoric acid-doped polybenzimidazole proton exchange membrane: soak the polybenzimidazole membrane in a phosphoric acid solution (preferably 85 wt % phosphoric acid) at 80-100° C. for 24-48 hours, remove the membrane and wipe off excess phosphoric acid on the surface, and dry the membrane at 100-120° C. to remove excess water;

[0018] (2) dissolving a polybenzimidazole ionomer containing no ether bonds in a solvent to obtain a 2.5-5 wt% ionomer solution;

[0019] (3) preparing a catalyst slurry containing a proton conductor: taking an appropriate amount of platinum carbon catalyst, adding it to a container, adding a small amount of water to wet the catalyst surface, then adding the ionomer solution obtained in step (2), phosphoric acid, alcohol A and methanol, wherein the alcohol A is ethylene glycol or isopropanol, and ultrasonically treating to obtain a uniform catalyst slurry;

[0020] (4) Membrane electrode preparation: The catalyst slurry prepared in step (3) is evenly sprayed on both sides of the proton exchange membrane prepared in step (1), pre-dried under hot air conditions at 60-80°C, and then a carbon paper gas diffusion layer is placed on the outside of the catalyst layer. The membrane electrode is formed by hot pressing at 100-150°C and a pressure of 2-5 MPa for 3-10 minutes.

[0021] Preferably, in step (2), the solvent is one or a mixture of two or more of dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, phosphoric acid and ethylene glycol.

[0022] Preferably, in step (3), the platinum content in the platinum-carbon catalyst is 40-60wt%, and the mass ratio of the platinum-carbon catalyst, ionomer solution, phosphoric acid, alcohol A and methanol is 1-3:1-10:1-10:15-25:45-85. More preferably, when the total mass of the platinum-carbon catalyst, ionomer solution, phosphoric acid, alcohol A and methanol is 100%, the mass ratio of the platinum-carbon catalyst, ionomer solution, phosphoric acid, alcohol A and methanol is 1-3%:1-10%:1-10%:15-25%:45-85%.

[0023] Preferably, in step (4), the platinum loading on the surface of the membrane electrode catalyst layer is 0.1-1 mg / cm 2 , more preferably 0.2-1 mg / cm 2 .

[0024] The membrane electrode prepared by the present invention can be applied to the field of fuel cells.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The present invention introduces a proton conductor into the catalyst slurry so that the proton conductor is evenly distributed in the catalyst layer, forming a continuous proton transport channel and constructing an efficient electrochemical reaction boundary in the entire catalyst layer. Compared with the traditional PTFE emulsion, the MEA of the ether-bond-free PyPBI ionomer containing a proton conductor prepared by the present invention shows higher fuel cell performance than the MEA using commercial PTFE emulsion. The ionomer can effectively eliminate the gap between the catalyst layer and the proton exchange membrane and enhance the interfacial compatibility. Its ether-bond-free design makes the membrane have good chemical stability at high temperatures, the block structure has a nanophase separation morphology, and the nitrogen atoms of the pyridine group can stabilize the free proton conductor phosphoric acid molecules through Coulomb interaction, reduce the loss of phosphoric acid, form a continuous proton transport channel, and construct an efficient electrochemical reaction boundary in the entire catalyst layer. It has a good application prospect in high-temperature proton exchange membrane fuel cells.

[0027] The membrane electrode prepared by the present invention is used in the field of fuel cells. Its resistance is greatly reduced during charge transfer, and it shows excellent phosphoric acid retention, which can achieve long-term stable operation in high-temperature fuel cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a physical picture of the membrane electrode prepared by the present invention.

[0029] Figure 2 This is a schematic diagram of the membrane electrode prepared in Example 1 of the present invention.

[0030] Figure 3 This is a graph showing the oxidation stability of the ether-free PyPBI polymer prepared in the present invention.

[0031] Figure 4 It is a polarization curve diagram of the membrane electrode test prepared in the embodiment of the present invention and the comparative example. DETAILED DESCRIPTION

[0032] To make the objects, technical solutions, and advantages of the present invention more apparent, the technical solutions will be further described clearly and completely below through the examples. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer were followed. Reagents or instruments used, where the manufacturer is not specified, are all commercially available conventional products.

[0033] Platinum-carbon catalyst and carbon paper gas diffusion layer were purchased from Shanghai Hesen Electric Co., Ltd.; PTFE emulsion was purchased from Shengernuo Energy Mall.

[0034] Example 1:

[0035] The polybenzimidazole membrane was immersed in 85 wt % phosphoric acid and placed at 80° C. for 48 h. The excess phosphoric acid on the surface was wiped off and the excess water was dried at 100° C. to obtain a phosphoric acid-doped polybenzimidazole membrane for standby use.

[0036] The reactor was purged with nitrogen and evacuated. 2g of phosphorus pentoxide and 45g of polyphosphoric acid were added, heated to 120°C, and mechanically stirred for 0.5h. 4.28g of 3,3'-diaminobenzidine was then added and stirred until completely dissolved. 1.67g (10 mmol) of 2,6-pyridinedicarboxylic acid was then added and stirred under a nitrogen atmosphere for 2h. The temperature was then raised to 220°C and prepolymerized for 3h. The system was cooled to 100°C, and 1.6g of pimelic acid was added and stirred until dissolved. The temperature was then raised to 160°C. The reaction was complete when the viscosity of the solution increased significantly. The polymer solution was poured into a large amount of deionized water saturated with NaHCO₃, resulting in a filamentous solid. After soaking for 24h, the solution was filtered, washed with water and ethanol, dried at 80°C to constant weight, and ground into a powder to obtain ionomer powder. The ionomer powder was dissolved in N-methylpyrrolidone to obtain a 5wt% ionomer solution.

[0037] A catalyst slurry was prepared containing a small amount of water-wetted 1.5 wt% platinum carbon catalyst (40% platinum content), 5 wt% ionomer solution, 5 wt% phosphoric acid, 20 wt% ethylene glycol, and 68.5 wt% methanol. The slurry was ultrasonically treated for 1 hour. The catalyst slurry was evenly sprayed on both sides of the phosphoric acid-doped polybenzimidazole membrane. The platinum loading was 0.6 mg / cm 2 , pre-dried under 80℃ hot air conditions, then placed the carbon paper gas diffusion layer on the outside of the catalyst layer, and hot pressed at 120℃ with a pressure of 2MPa for 3 minutes to prepare a membrane electrode.

[0038] Example 2:

[0039] The polybenzimidazole membrane was immersed in 85 wt % phosphoric acid and placed at 80° C. for 48 h. The excess phosphoric acid on the surface was wiped off and the excess water was dried at 100° C. to obtain a phosphoric acid-doped polybenzimidazole membrane for standby use.

[0040] The reactor was purged with nitrogen and evacuated. 2g of phosphorus pentoxide and 45g of polyphosphoric acid were added, heated to 120°C, and mechanically stirred for 0.5h. 4.28g of 3,3'-diaminobenzidine was then added and stirred until completely dissolved. 1.67g (10 mmol) of 2,2'-bipyridine-4,4'-dicarboxylic acid was then added and stirred under a nitrogen atmosphere for 2h. The temperature was then raised to 220°C and prepolymerized for 5h. The system was cooled to 100°C, and 1.9g of azelaic acid was added and stirred until dissolved. The temperature was then raised to 160°C. The reaction was complete when the viscosity of the solution increased significantly. The polymer solution was poured into a large amount of deionized water saturated with NaHCO₃, resulting in a filamentous solid. After soaking for 24h, the solution was filtered, washed with water and ethanol, and dried at 80°C to constant weight. The polymer was then ground into a powder to obtain an ionomer powder. The ionomer powder was dissolved in N-methylpyrrolidone to obtain a 5wt% ionomer solution.

[0041] A catalyst slurry was prepared containing a small amount of water-wetted 1.5 wt% platinum carbon catalyst (40% platinum content), 5 wt% ionomer solution, 5 wt% phosphoric acid, 20 wt% ethylene glycol, and 68.5 wt% methanol. The slurry was ultrasonically treated for 1 hour. The catalyst slurry was evenly sprayed on both sides of the phosphoric acid-doped polybenzimidazole membrane. The platinum loading was 0.6 mg / cm 2 , pre-dried under 80℃ hot air conditions, then placed the carbon paper gas diffusion layer on the outside of the catalyst layer, and hot pressed at 120℃ with a pressure of 2MPa for 3 minutes to prepare a membrane electrode.

[0042] Example 3:

[0043] The proton exchange membrane and ionomer were prepared in the same manner as in Example 1.

[0044] A catalyst slurry was prepared containing a small amount of water-moistened 1.5 wt% platinum carbon catalyst (40% platinum content), 10 wt% ionomer solution, 5 wt% phosphoric acid, 15 wt% ethylene glycol, and 68.5 wt% methanol. The slurry was ultrasonically treated for 1 hour. The catalyst slurry was evenly sprayed on both sides of the phosphoric acid-doped polybenzimidazole membrane. The platinum loading was 0.6 mg / cm 2 , pre-dried under 80℃ hot air conditions, then placed the carbon paper gas diffusion layer on the outside of the catalyst layer, and hot pressed at 120℃ with a pressure of 2MPa for 3 minutes to prepare a membrane electrode.

[0045] Example 4:

[0046] The preparation of the proton exchange membrane and ionomer was consistent with that in Example 2.

[0047] A catalyst slurry was prepared containing a small amount of water-moistened 1.5 wt% platinum carbon catalyst (40% platinum content), 10 wt% ionomer solution, 5 wt% phosphoric acid, 15 wt% ethylene glycol, and 68.5 wt% methanol. The slurry was ultrasonically treated for 1 hour. The catalyst slurry was evenly sprayed on both sides of the phosphoric acid-doped polybenzimidazole membrane. The platinum loading was 0.6 mg / cm 2 , pre-dried under 80℃ hot air conditions, then placed a carbon paper gas diffusion layer on the outside of the catalyst layer, and hot pressed at 120℃ with a pressure of 2MPa for 3 minutes to prepare a membrane electrode. Comparative Example 1:

[0048] The proton exchange membrane is the same as that in Example 1.

[0049] A catalyst slurry was prepared containing a small amount of water-moistened 1.5 wt% platinum-on-carbon catalyst (40% platinum content), 5 wt% PTFE (60 wt% solid content) emulsion, 5 wt% phosphoric acid, 20 wt% ethylene glycol, and 68.5 wt% methanol. The slurry was ultrasonically treated for 1 hour. The catalyst slurry was evenly sprayed on both sides of the phosphoric acid-doped polybenzimidazole membrane. The platinum loading was 0.6 mg / cm 2 , pre-dried under 80℃ hot air conditions, then placed the carbon paper gas diffusion layer on the outside of the catalyst layer, and hot pressed at 120℃ with a pressure of 2MPa for 3 minutes to prepare a membrane electrode.

[0050] Test method:

[0051] 1. Oxidation stability test: Weigh the mass of a piece of ionomer and then soak it in 50mL Fenton reagent (3wt% H2O2, 4ppm Fe 2+ ) at 80°C for 24 hours. Then, remove the sample, rinse repeatedly with deionized water, and dry completely in a vacuum oven at 120°C. The sample was weighed. The Fenton reagent was replaced every 24 hours.

[0052] 2. Fuel cell test: The anode H2 gas flow rate was set to 200 sccm, and the cathode O2 gas flow rate was set to 200 sccm. Recorded using a Xinwei high-performance battery test system.

[0053] The results are as follows Figure 3 As shown in the data, the ether-free structural design can effectively prevent the free radical degradation of the catalytic layer ionomer. After 144 hours of testing, the remaining weight of all ether-free polymers (88 wt%) is higher than the 73 wt% of the original OPBI polymer. The improvement of oxidation stability is more conducive to the long-term durability of the corresponding fuel cell.

[0054] The results are as follows Figure 4 As shown, the introduction of the ether-free polybenzimidazole ionomer improves the interface contact between the catalyst layer and the proton exchange membrane. Both Example 1 and Example 2 show a value of 680 mW "cm -2The peak power of the comparative example 1 containing commercial PTFE ionomer is only 364mWcm -2 However, the introduction of excessive ionomers will hinder electron transfer and cover the catalytic active sites of the catalyst, thereby increasing impedance and reducing fuel cell performance. It can be seen that the use of the ionomer provided by the present invention has more excellent electrochemical performance.

Claims

1. A membrane electrode based on a high-temperature proton exchange membrane, characterized in that: The membrane electrode based on the high-temperature proton exchange membrane includes a proton exchange membrane and a catalyst layer and a gas diffusion layer located on both sides of the proton exchange membrane. The catalyst layer includes a catalyst, an ionomer and a proton conductor phosphoric acid. The ionomer is a polybenzimidazole ionomer containing no ether bonds. The polybenzimidazole ionomer containing no ether bonds is prepared by the following steps: nitrogen is introduced into the reactor to evacuate; then phosphorus pentoxide and polyphosphoric acid are added, the temperature is raised to 100-140°C, mechanically stirred evenly, and then 3,3'-diaminobenzidine monomer is added and stirred until dissolved. , then add the pyridine dicarboxylic acid monomer, stir for 1-2 hours under N2 atmosphere, heat to 180-220℃, carry out prepolymerization for 2-10 hours, then cool the system to 80-100℃, then add the dibasic fatty acid monomer, stir until dissolved, heat to 140-180℃, react until the viscosity of the reaction system increases significantly and the color deepens, then the reaction is completed, pour the polymer solution into a saturated NaHCO3 aqueous solution, and a filamentous solid appears. After sufficient soaking, filter, wash, and dry to obtain a polybenzimidazole ionomer containing no ether bonds; The catalyst is a platinum-carbon catalyst, the platinum content in the platinum-carbon catalyst is 40-60wt%, and the mass ratio of the platinum-carbon catalyst, the ionomer solution, and the phosphoric acid is 1-3:1-10:1-10, wherein the ionomer solution refers to a 2.5-5 wt% ionomer solution obtained by dissolving a polybenzimidazole ionomer containing no ether bonds in a solvent.

2. The membrane electrode based on a high temperature proton exchange membrane according to claim 1, characterized in that: The pyridine dicarboxylic acid-containing monomer is one or more of 2,3-pyridinedicarboxylic acid, 2,4-pyridinedicarboxylic acid, 2,5-pyridinedicarboxylic acid, 2,6-pyridinedicarboxylic acid, 3,5-pyridinedicarboxylic acid, and 2,2'-bipyridine-4,4'-dicarboxylic acid; The dibasic fatty acid monomer is one or more of pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, tetradecanedioic acid and hexadecanedioic acid.

3. The membrane electrode based on a high temperature proton exchange membrane according to claim 1, characterized in that: The mass fraction of phosphorus pentoxide in polyphosphoric acid is 1-10wt%; after all monomers of the 3,3'-diaminobenzidine monomer, the pyridine dicarboxylic acid monomer and the dibasic fatty acid monomer are stirred and mixed in the polyphosphoric acid, the total monomer concentration is 1-20wt%; the ratio of the total molar number of the pyridine dicarboxylic acid monomer and the dibasic fatty acid monomer to the molar number of the 3,3'-diaminobenzidine monomer is 1:1; and the molar ratio of the pyridine dicarboxylic acid monomer to the dibasic fatty acid monomer is 1:3-3:

1.

4. The membrane electrode based on a high temperature proton exchange membrane according to claim 1, characterized in that: The proton exchange membrane is a phosphoric acid-doped polybenzimidazole proton exchange membrane.

5. The membrane electrode based on a high temperature proton exchange membrane according to claim 1, characterized in that: The gas diffusion layer is a carbon paper gas diffusion layer or a carbon cloth gas diffusion layer.

6. A method for preparing a membrane electrode based on a high-temperature proton exchange membrane according to claim 1, characterized in that: The preparation method comprises the following steps: (1) Preparation of phosphoric acid-doped polybenzimidazole proton exchange membrane: soak the polybenzimidazole membrane in phosphoric acid solution at 80-100°C for 24-48 hours, remove the excess phosphoric acid from the surface, and dry the excess water at 100-120°C; (2) dissolving the polybenzimidazole ionomer containing no ether bond in a solvent to obtain a 2.5-5 wt% ionomer solution; (3) Preparing a catalyst slurry containing a proton conductor: taking an appropriate amount of platinum carbon catalyst, adding it to a container, adding a small amount of water to wet the catalyst surface, then adding the ionomer solution obtained in step (2), phosphoric acid, alcohol A and methanol, wherein the alcohol A is ethylene glycol or isopropanol, and ultrasonically treating to obtain a uniform catalyst slurry; (4) Membrane electrode preparation: The catalyst slurry prepared in step (3) is evenly sprayed on both sides of the proton exchange membrane prepared in step (1), pre-dried under hot air conditions at 60-80°C, and then a carbon paper gas diffusion layer is placed on the outside of the catalyst layer. The membrane electrode is formed by hot pressing at 100-150°C with a pressure of 2-5 MPa for 3-10 minutes.

7. The preparation method according to claim 6, wherein: In step (3), the mass ratio of the platinum-carbon catalyst, the ionomer solution, the phosphoric acid, the alcohol A and the methanol is 1-3:1-10:1-10:15-25:45-85.

8. The preparation method according to claim 7, wherein: In step (3), taking the total mass of the platinum-carbon catalyst, ionomer solution, phosphoric acid, alcohol A and methanol as 100%, the mass ratio of the platinum-carbon catalyst, ionomer solution, phosphoric acid, alcohol A and methanol is 1-3%: 1-10%: 1-10%: 15-25%: 45-85%.

9. The preparation method according to claim 6, wherein: In step (4), the platinum loading on the surface of the membrane electrode catalyst layer is 0.1-1 mg / cm 2 .

10. The preparation method according to claim 9, wherein: In step (4), the platinum loading on the surface of the membrane electrode catalyst layer is 0.2-1 mg / cm 2 .

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