A direct methanol fuel cell membrane electrode assembly and its preparation method

Abstract

The present invention relates to the technical field of fuel cells and specifically discloses a direct methanol fuel cell membrane electrode complex and a preparation method thereof. The preparation method comprises dissolving 4,4'-(9-fluorenylene)diphenylamine, terephthalic acid, 2,5-diaminobenzenesulfonic acid and anhydrous LiCl in N-methylpyrrolidone, pyridine and triphenyl phosphite, heating and stirring under an argon atmosphere, precipitating, washing and drying to obtain polyamide, preparing a proton exchange membrane, and coating an anode catalyst and a cathode catalyst on both sides of the proton exchange membrane to obtain a catalyst-loaded proton exchange membrane; hot-pressing the anode diffusion layer, the catalyst-loaded proton exchange membrane and the cathode diffusion layer to obtain a membrane electrode complex, and stacking the anode diffusion layer and the cathode diffusion layer to obtain a battery membrane electrode complex. The membrane electrode complex of the direct methanol fuel cell prepared by the method has low methanol permeability and can adapt to higher concentrations of methanol. At the same time, the preparation process is simple, and the time cost of testing is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of fuel cells, and in particular relates to a direct methanol fuel cell membrane electrode complex and a preparation method thereof. Background Art

[0002] A fuel cell is an electrochemical power generation device that converts the chemical energy of fuel and oxidant directly into electrical energy through an electrochemical reaction without going through a thermal engine process. It is not restricted by the Carnot cycle and therefore has a very high energy conversion efficiency. Secondly, the product is usually water, which has little pollution to the environment. This makes direct methanol fuel cells likely to become the mainstream application of future portable electronic products. At the same time, they have broad application prospects in transportation, military, aerospace and other fields.

[0003] Proton exchange membrane fuel cells are the most promising fuel cells. They mainly use clean energy such as hydrogen, methanol, and ethanol. However, due to the huge investment in the construction of hydrogen supply facilities and the relatively backward hydrogen transportation, storage, and on-site hydrogen production technologies, it is easier to handle liquid fuels such as methanol than hydrogen. It is a commonly used energy source for fuel cells. The proton exchange membrane is the core component of the fuel cell. It not only conducts protons, but also plays the role of separating fuels and determines the power output of the fuel cell.

[0004] Existing direct methanol fuel cells (DMFCs) consist of a fuel tank, a membrane electrode assembly (MEA), a current collector, and electrode plates. The MEA comprises, in sequence, an anode diffusion layer, an anode catalyst layer, a proton exchange membrane, a cathode catalyst layer, and a cathode diffusion layer. Its fabrication method involves coating the anode catalyst layer and cathode catalyst layer on the anode diffusion layer and cathode diffusion layer, respectively, placing the proton exchange membrane between the two layers, and hot-pressing the two layers together to form the MEA. The operating process of existing DMFCs is as follows: Fuel diffuses through the anode current collector and the anode diffusion layer, ultimately reaching the anode catalyst layer. In the anode catalyst layer, the fuel methanol is oxidized to produce protons, electrons, carbon dioxide, and heat. This reaction is known as the methanol oxidation reaction (MOR). The electrons and protons generated in the methanol oxidation reaction travel through an external circuit and the proton exchange membrane, respectively, to reach the cathode catalyst layer. Oxygen flows through the cathode current collector and the cathode diffusion layer to the cathode catalyst layer, where it combines with the protons and electrons to form water and release heat.

[0005] Although direct methanol fuel cells have many advantages, they also have certain defects, the main one being severe methanol permeation. Methanol permeation mainly produces a mixed potential, leading to battery voltage loss, poisoning the cathode catalyst, and aggravating cathode water injection, resulting in decreased battery performance, decreased fuel efficiency, and damage to the proton exchange membrane.

[0006] In order to solve the serious methanol permeation problem of direct methanol fuel cells, the existing technology also provides a variety of methods, mainly designing a new proton exchange membrane to replace the perfluorosulfonic acid proton exchange membrane. For example, Chinese patent application number CN116666712A discloses a method for preparing an organic proton exchange membrane for a direct methanol fuel cell, which can effectively solve the problem caused by methanol permeation.

[0007] For example, Chinese patent application number CN111477922A discloses a method for preparing a proton exchange membrane and its membrane electrode, in which graphene oxide is sprayed on the surface of a Nafion 117 proton exchange membrane. The graphene oxide coating can effectively block methanol, but it also causes the proton conductivity of the proton exchange membrane to decrease.

[0008] Based on the above analysis, this patent proposes a direct methanol fuel cell membrane electrode assembly and its preparation method to solve the current problems of poor proton conductivity and high methanol permeability of proton exchange membranes. Summary of the Invention

[0009] The object of the present invention is to provide a direct methanol fuel cell membrane electrode assembly and a preparation method thereof, so as to solve the problems raised in the above background technology.

[0010] To achieve the above object, the present invention provides the following technical solutions:

[0011] A method for preparing a direct methanol fuel cell membrane electrode assembly comprises the following steps:

[0012] (1) 4,4'-(9-fluorenylidene)diphenylamine, terephthalic acid, 2,5-diaminobenzenesulfonic acid and anhydrous LiCl were dissolved in N-methylpyrrolidone, pyridine and triphenyl phosphite, and heated and stirred under an argon atmosphere for reaction. After the reaction, the mixture was precipitated in ice methanol, washed several times with methanol and deionized water, and then dried in a forced air drying oven and then dried in a vacuum drying oven to obtain polyamide;

[0013] (2) A proton exchange membrane was prepared by a solution casting method. A certain amount of the above-synthesized polyamide was weighed and dissolved in DMSO. The solution was heated and stirred until completely dissolved to obtain a transparent solution. The solution was then filtered into a culture dish using an organic filter tip and placed in an oven to remove the solvent. The solution was then placed in a vacuum drying oven to dry and remove the remaining residual solvent. The membrane was peeled off from the culture dish and then activated with an HCl solution at room temperature. The activated membrane was then washed with deionized water until it was neutral to obtain a proton exchange membrane.

[0014] (3) Coating an anode catalyst and a cathode catalyst on both sides of the proton exchange membrane to obtain a catalyst-loaded proton exchange membrane;

[0015] (4) The anode diffusion layer, the catalyst-loaded proton exchange membrane, and the cathode diffusion layer are hot-pressed to form a membrane electrode assembly.

[0016] Preferably, in step (1), the molar ratio of the 4,4'-(9-fluorenyl)diphenylamine, terephthalic acid, and 2,5-diaminobenzenesulfonic acid is 1:3:2, the volume ratio of the N-methylpyrrolidone, pyridine, and triphenyl phosphite is 3:1:1, the heating temperature is 100 ° C, the reaction time is 24 h, the drying temperature is 80 ° C, and the drying time is 12 h and 24 h.

[0017] Preferably, in step (2), the polyamide is 0.4 g, the DMSO is 20 mL, the drying temperature is 80 ° C, and the HCl solution is 1 mol / L.

[0018] Preferably, in step (3), the anode catalyst layer is a PtRu / C electrocatalyst.

[0019] Preferably, the cathode catalyst layer is a Pt / C electrocatalyst.

[0020] Preferably, the coating comprises spraying or brushing.

[0021] Preferably, the anode catalyst layer and the cathode catalyst layer are carbon paper and carbon cloth.

[0022] A direct methanol fuel cell membrane electrode assembly (MEA) comprises an anode diffusion layer, a catalyst-loaded proton exchange membrane, and a cathode diffusion layer. The catalyst-loaded proton exchange membrane comprises a proton exchange membrane, an anode catalyst, and a cathode catalyst. The proton exchange membrane is stacked at the bottom end of the anode diffusion layer, and the cathode diffusion layer is stacked at the bottom end of the catalyst-loaded proton exchange membrane. The anode catalyst and the cathode catalyst are coated on both sides of the proton exchange membrane, respectively.

[0023] A direct methanol fuel cell membrane electrode assembly (MEA) includes an anode support plate, an anode current collector, an anode plate, an anode sealing sheet, an anode diffusion layer, a proton exchange membrane carrying a catalyst, a cathode diffusion layer, a cathode sealing sheet, a cathode plate, a cathode current collector, and a cathode support plate, which are sequentially bonded together.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention prepares a proton exchange membrane, coats an anode catalyst and a cathode catalyst on both sides of the proton exchange membrane, respectively, to obtain a catalyst-loaded proton exchange membrane, and then stacks an anode diffusion layer and a cathode diffusion layer to obtain a battery membrane electrode complex. The membrane electrode complex of the direct methanol fuel cell prepared by this method has low methanol permeability, can adapt to higher concentrations of methanol, and thus exhibits high energy density in fuel cell tests. At the same time, the production process is simple, reducing the time cost of testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic structural diagram of a membrane electrode assembly of a direct methanol fuel cell according to the present invention;

[0027] Figure 2 This is a schematic diagram of the exploded structure of a direct methanol fuel cell of the present invention;

[0028] Figure 3 This is a schematic diagram of the assembly structure of a direct methanol fuel cell of the present invention;

[0029] Figure 4 This is a schematic diagram of a polarization curve of a direct methanol fuel cell according to the present invention.

[0030] In the figure: 1. Anode diffusion layer; 2. Proton exchange membrane loaded with catalyst; 3. Cathode diffusion layer; 21. Proton exchange membrane; 22. Anode catalyst; 23. Cathode catalyst; 4. Cathode sealing sheet; 5. Cathode plate; 6. Cathode current collector; 7. Cathode support plate; 8. Anode support plate; 9. Anode current collector; 10. Anode plate. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention. Embodiment one:

[0032] See also Figures 1 to 4 As shown, a direct methanol fuel cell and its membrane electrode assembly and preparation method include the following steps:

[0033] 4,4'-(9-fluorenylidene)diphenylamine, terephthalic acid, 2,5-diaminobenzenesulfonic acid and anhydrous LiCl are dissolved in N-methylpyrrolidone, pyridine and triphenyl phosphite, and heated and stirred under an argon atmosphere for reaction. After the reaction is completed, the mixture is precipitated in ice methanol, washed several times with methanol and deionized water, and then dried in a forced air drying oven and then in a vacuum drying oven to obtain polyamide;

[0034] The proton exchange membrane was prepared by a solution casting method. A certain mass of the synthesized polyamide was weighed and dissolved in DMSO. The solution was heated and stirred until completely dissolved to obtain a transparent solution. The solution was then filtered into a culture dish using an organic filter head and placed in an oven to remove the solvent. The solution was then placed in a vacuum drying oven to dry and remove the remaining residual solvent. The membrane was peeled off from the culture dish and then activated with an HCl solution at room temperature. The activated membrane was then washed with deionized water until it was neutral to obtain a proton exchange membrane.

[0035] An anode catalyst and a cathode catalyst are coated on both sides of the proton exchange membrane to obtain a catalyst-loaded proton exchange membrane;

[0036] The anode diffusion layer, the proton exchange membrane loaded with the catalyst and the cathode diffusion layer are composited by hot pressing to obtain a membrane electrode composite.

[0037] The molar ratio of 4,4'-(9-fluorenylene)diphenylamine, terephthalic acid, and 2,5-diaminobenzenesulfonic acid is 1:3:2, the volume ratio of N-methylpyrrolidone, pyridine, and triphenyl phosphite is 3:1:1, the heating temperature is 100°C, the reaction time is 24 h, the drying temperature is 80°C, and the drying time is 12 h and 24 h.

[0038] The amount of polyamide is 0.4 g, the amount of DMSO is 20 mL, the drying temperature is 80° C., and the amount of HCl solution is 1 mol / L.

[0039] The proton exchange membrane used in this embodiment is a proton exchange membrane prepared by dissolving a polyamide synthesized from 4,4'-(9-fluorenylene)diphenylamine, terephthalic acid, and 2,5-diaminobenzenesulfonic acid in a molar ratio of 1:3:2 in a solvent, and has a thickness of 0.102 mm.

[0040] The anode diffusion layer and the cathode diffusion layer are both carbon papers provided by Shengernuo Technology Co., Ltd., with a thickness of 0.23 mm.

[0041] The anode catalyst and cathode catalyst are both electrocatalysts provided by MacLean, with PtRu / C on the anode side and Pt / C on the cathode side, and the loading of each is 2 mg / cm 2 .

[0042] The specific operations are as follows:

[0043] 1. The anode catalyst and cathode catalyst were uniformly sprayed on the anode diffusion layer and the cathode diffusion layer respectively. The thickness of the anode catalyst layer and the cathode catalyst layer were both , to obtain an anode and a cathode with a size of 2 cm×2 cm.

[0044] 2. The anode diffusion layer and the cathode diffusion layer were sandwiched between the two sides of the catalyst-loaded proton exchange membrane and hot-pressed to obtain a membrane electrode assembly. The hot-pressing process was set at a temperature of 120°C, a pressure of 8 MPa, and a hot-pressing time of 1.5 min.

[0045] 3. Attach the corresponding positions on both sides of the membrane electrode assembly prepared in step 2 to the anode plate and cathode plate respectively. The outermost layer is the support plate. Fix the anode current collector, anode plate anode seal, membrane electrode assembly, cathode seal, cathode plate, and cathode current collector on the fuel tank in sequence and fix them with insulating bolts to make a self-breathing passive direct methanol fuel cell.

[0046] The performance of the membrane electrode of the above embodiment was tested. The performance of the proton exchange membrane is shown in Table 1, and the performance of the electrode is shown in Table 1. Figure 4 shown.

[0047] Membrane performance test conditions are as follows:

[0048] 1. Tensile strength: The proton exchange membrane was cut into rectangular strips of 1×7 cm and tested on an electronic tensile testing machine at a tensile speed of 50 mm / min.

[0049] 2. Methanol permeability:

[0050] The methanol permeability of the proton exchange membrane was tested using an "H"-type membrane diffusion test apparatus. The apparatus consists of two compartments: one containing 20 mL of a 1 M methanol solution and the other containing the same volume of deionized water. The membrane was sandwiched between the two compartments. A gas chromatograph was used to measure changes in methanol concentration at room temperature. The methanol permeability was calculated using the following formula:

[0051] ;

[0052] 3. Proton Conductivity: The membrane's proton conductivity was measured using an electrochemical workstation (CHI, 604e) from Shanghai Chenhua Instrument Co., Ltd. using the AC impedance spectroscopy method. The prepared membrane was cut into 1 cm × 3 cm rectangles and activated by immersion in a 1M HCl solution for 12 hours. The membrane's proton conductivity was then measured at 20 to 80°C under 100% relative humidity. The calculation formula is as follows:

[0053] ;

[0054] 4. Selectivity: Selectivity is used to evaluate the comprehensive performance of proton exchange membranes and is defined as the ratio of proton conductivity to methanol permeability. The calculation formula is as follows:

[0055] ;

[0056] Table 1 Performance of proton exchange membrane

[0057]

[0058] It will be appreciated that in the development of any actual embodiment, as in any engineering or design project, numerous implementation-specific decisions may be made. Such a development effort may be complex and time-consuming, but will, for those of ordinary skill having the benefit of this disclosure, be a routine undertaking of design, fabrication, and production without undue experimentation.

[0059] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a direct methanol fuel cell membrane electrode assembly, characterized in that: The following steps are involved: (1. Dissolve 4,4'-(9-fluorenylidene)diphenylamine, terephthalic acid, 2,5-diaminobenzenesulfonic acid, and anhydrous LiCl in N-methylpyrrolidone, pyridine, and triphenyl phosphite, and heat and stir to react under an argon atmosphere. After the reaction, precipitate the mixture in ice methanol, wash it several times with methanol and deionized water, and then dry it in a blast drying oven and then in a vacuum drying oven to obtain a polyamide, wherein the molar ratio of 4,4'-(9-fluorenylidene)diphenylamine, terephthalic acid, and 2,5-diaminobenzenesulfonic acid is 1:3:2; (2) A proton exchange membrane was prepared by a solution casting method. 0.4 g of the synthesized polyamide was weighed and dissolved in DMSO. The solution was heated and stirred until completely dissolved to obtain a transparent solution. The solution was then filtered into a culture dish using an organic filter tip and placed in an oven to remove the solvent. The solution was then dried in a vacuum drying oven to remove the remaining residual solvent. The membrane was peeled off from the culture dish and activated with an HCl solution at room temperature. The activated membrane was then washed with deionized water until neutral to obtain a proton exchange membrane. (3. Coating an anode catalyst layer and a cathode catalyst layer on both sides of the proton exchange membrane to obtain a catalyst-loaded proton exchange membrane; (4. Hot-pressing the anode diffusion layer, the catalyst-loaded proton exchange membrane, and the cathode diffusion layer to obtain a membrane electrode assembly.

2. The method for preparing a direct methanol fuel cell membrane electrode assembly according to claim 1, characterized in that: The volume ratio of N-methylpyrrolidone, pyridine and triphenyl phosphite used in step (1) is 3:1:1, the heating temperature is 100 ° C, the reaction time is 24 h, the drying temperature is 80 ° C, and the drying time is 12 h and 24 h.

3. The method for preparing a direct methanol fuel cell membrane electrode assembly according to claim 1, characterized in that: In step (2), the polyamide is 0.4 g, the DMSO is 20 mL, the oven temperature is 80 ° C, and the HCl solution is 1 mol / L.

4. The method for preparing a direct methanol fuel cell membrane electrode assembly according to claim 1, characterized in that: In step (3), the anode catalyst layer is a PtRu / C electrocatalyst.

5. The method for preparing a direct methanol fuel cell membrane electrode assembly according to claim 1, characterized in that: The cathode catalyst layer is a Pt / C electrocatalyst.

6. The method for preparing a direct methanol fuel cell membrane electrode assembly according to claim 1, characterized in that: The coating includes spraying or brushing.

7. The method for preparing a direct methanol fuel cell membrane electrode assembly according to claim 1, characterized in that: The anode catalyst layer and the cathode catalyst layer are carbon paper and carbon cloth.

8. A composite prepared by the method for preparing a direct methanol fuel cell membrane electrode assembly according to any one of 1 to 7, characterized in that: The membrane electrode complex comprises an anode diffusion layer (1), a catalyst-loaded proton exchange membrane (2), and a cathode diffusion layer (3); the catalyst-loaded proton exchange membrane (2) comprises a proton exchange membrane (21), an anode catalyst (22), and a cathode catalyst (23); the proton exchange membrane (2) is stacked at the bottom end of the anode diffusion layer (1); the cathode diffusion layer (3) is stacked at the bottom end of the catalyst-loaded proton exchange membrane (2); and the anode catalyst (22) and the cathode catalyst (23) are coated on both sides of the proton exchange membrane (21), respectively.

9. The composite prepared by the method for preparing a direct methanol fuel cell membrane electrode assembly according to claim 8, characterized in that: The fuel cell comprises an anode support plate (8), an anode current collector (9), an anode plate (10), an anode sealing sheet (11), an anode diffusion layer (1), a catalyst-carrying proton exchange membrane (2), a cathode diffusion layer (3), a cathode sealing sheet (4), a cathode plate (5), a cathode current collector (6), and a cathode support plate (7) that are sequentially bonded together.

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