Cathode catalyst layer slurry of fuel cell membrane electrode and preparation method thereof

Abstract

The present invention provides a fuel cell membrane electrode cathode catalyst layer slurry, which comprises a platinum-based catalyst, an alcohol organic solvent, a long side chain perfluorosulfonic acid ionomer solution, water and an oxalic acid organic compound, a long-side-chain perfluorosulfonic acid ionomer with a high EW value has a longer hydrophobic skeleton and fewer hydrophilic sulfonate groups, the rejection ability of a catalyst layer and water can be enhanced, and meanwhile, the transmission efficiency of reaction gas and the discharge ability of water are affected by the pore structure of a cathode catalyst layer. Under the condition that other hydrophobic substances are not introduced, the perfluorosulfonic acid ionomer with the long side chain structure can enhance the repulsive capacity of the cathode catalyst layer and water, the hydrophobic effect of the cathode catalyst layer under high current density is improved, and the cathode catalyst layer has a good water-gas transmission channel.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and particularly to a cathode catalyst layer slurry for a fuel cell membrane electrode and a preparation method thereof. Background Art

[0002] Proton exchange membrane fuel cells (PEMFCs) have the advantages of simple structure, stable operation, high energy conversion efficiency, and no pollutant emissions, and are considered to be one of the most promising power sources. As the key core component of a fuel cell, the membrane electrode is composed of a proton exchange membrane, cathode and anode catalyst layers, and cathode and anode gas diffusion layers. The cathode and anode catalyst layers are the main sites of electrochemical reactions. Since the kinetic process of ORR is slower than that of HOR, the cathode catalyst layer directly affects the speed of the electrochemical reaction. Therefore, it is necessary to ensure the continuous supply of reaction gases to maintain the normal progress of the reaction. However, it should be noted that during the electrochemical reaction process, protons, electrons, and oxygen react to form water in the cathode catalyst layer. And at high current densities, if a large amount of liquid water generated inside the catalyst layer cannot be discharged in time, it will affect the mass transfer efficiency and reduce the performance of the fuel cell. Therefore, it is necessary to reasonably design the structure of the cathode catalyst layer to improve the water drainage ability and gas mass transfer ability of the cathode catalyst layer, thereby improving the output performance of the battery.

[0003] The patent with the publication number CN115207375B discloses a cathode catalyst layer and a preparation method thereof. In this method, ammonium carbonate, ammonium oxalate, and ammonium nitrate are used as pore-forming agents and added to the catalyst layer slurry, successfully forming a mesoporous structure in the cathode catalyst layer, improving the mass transfer inside the electrode, and enhancing the proton transport ability. It is also concluded that using ammonium carbonate as the pore-forming agent can make the battery have the best output performance. However, there are the following problems: the method used in this patent is relatively complex and requires steps such as calcination and freeze-drying, which reduces the production efficiency of the membrane electrode. More seriously, when the calcination temperature exceeds the critical glass transition temperature of the perfluorosulfonic acid ionomer, the side chain structure of the perfluorosulfonic acid ionomer will be damaged, making the resin unable to fully adsorb on the surface of the platinum-based catalyst and unable to play the role of transporting protons, reducing the utilization rate of platinum and seriously affecting the progress of the reaction; and this patent uses ammonium carbonate as the preferred pore-forming agent. Although it improves the pore structure in the catalyst layer, the decomposition temperature of ammonium carbonate is relatively low, and a certain amount of heat will be generated during the high-speed ball milling of the cathode catalyst layer slurry. This heat can cause ammonium carbonate to decompose, resulting in ammonium carbonate being unable to play the role of pore formation and optimizing the pore size.

[0004] The patent with the publication number CN109904469A mixes PS microspheres into the cathode catalyst layer slurry, optimizing the pore size and porosity inside the cathode catalyst layer, improving the concentration polarization at high current densities, and enhancing the performance of the membrane electrode. However, the method in this patent requires soaking in organic solvents to remove the PS microspheres, which makes the process relatively complex. Moreover, long-term soaking of the cathode catalyst layer in organic solvents will damage the surface morphological structure of the catalyst layer. At the same time, the PS microspheres used in this patent have a particle size of 50 - 800 nm. If the PS microspheres are not completely removed, the residues will block the pore channels in the catalyst layer, affecting the transmission of reactive gases and being unfavorable for the catalytic reaction.

[0005] Currently, when a fuel cell operates at high current densities, more liquid water is generated by the electrochemical reaction, increasing the mass transfer resistance of the reactive gases, intensifying the concentration polarization of the cell, and thus affecting the cell performance. To improve the water drainage ability of proton exchange membrane fuel cells, hydrophobic substances are usually introduced into the cathode catalyst layer. However, the introduction of hydrophobic substances will affect the binding state between the platinum-based catalyst and the resin, and hydrophobic substances generally do not have the property of electrical conductivity, increasing the resistance of the catalyst layer and being unfavorable for the conduction of electrons in the catalyst layer. At the same time, the pore structure within the catalyst layer affects the diffusion resistance of the reactant gases. Therefore, it is necessary to design a cathode catalyst layer slurry to improve the hydrophobic ability of the cathode catalyst layer, optimize the pore size distribution of the cathode catalyst layer, enable the cathode catalyst layer to have excellent gas mass transfer ability, and enhance the cell performance. Summary of the Invention

[0006] Embodiments of this application are proposed to make up for the deficiencies of the prior art and provide a cathode catalyst layer slurry for a fuel cell membrane electrode and its preparation method to solve the problems existing in the prior art.

[0007] To solve the above technical problems, the present invention provides the following technical solutions:

[0008] A cathode catalyst layer slurry for a fuel cell membrane electrode includes: a platinum-based catalyst, an alcohol organic solvent, a long-chain perfluorosulfonic acid ionomer solution, water, and an oxalic acid organic compound. Among them, the perfluorosulfonic acid ionomer solution acts as a proton conductor and a binder. The long-chain perfluorosulfonic acid ionomer with a high EW value has a longer hydrophobic backbone and fewer hydrophilic sulfonic acid groups, which can enhance the repulsive ability of the catalyst layer to water. At the same time, the pore structure of the cathode catalyst layer affects the transmission efficiency of reactive gases and the water discharge ability. In view of this, embodiments of the present invention propose the preparation and application of a cathode catalyst layer slurry, a cathode catalyst layer, a membrane electrode, and a fuel cell.

[0009] An embodiment of the present invention provides a cathode catalyst layer slurry, which includes a platinum-based catalyst, an alcohol organic solvent, a long-side-chain perfluorosulfonic acid solution, water, and an oxalic acid organic compound, wherein the mass ratio of the oxalic acid organic compound to the platinum-based catalyst is not less than 1:5.

[0010] The advantages and technical effects brought by the cathode catalyst layer slurry of the embodiment of the present invention are as follows:

[0011] 1. In the cathode catalyst layer slurry of the embodiment of the present invention, without introducing other hydrophobic substances, the perfluorosulfonic acid ionomer with a long-side-chain structure can enhance the repulsive ability between the cathode catalyst layer and water, improve the hydrophobic effect of the cathode catalyst layer at high current density, and enable the cathode catalyst layer to have a good water-vapor transmission channel.

[0012] 2. In the cathode catalyst layer slurry of the embodiment of the present invention, the oxalic acid organic compound will not adsorb on the surface of the platinum-based catalyst. At the same time, the oxalic acid organic compound is easily decomposed by heat and can be removed by using temperature during the preparation of the cathode catalyst layer and the membrane electrode, so that the cathode catalyst layer forms an effective pore structure and improves the mass transfer efficiency in the catalyst layer.

[0013] 3. The cathode catalyst layer slurry of the embodiment of the present invention is easy to prepare, increases the three-phase reaction interface in the catalyst layer, and is suitable for the design and research and development of the cathode catalyst layer of a fuel cell operating at low relative humidity.

[0014] In some embodiments, the mass ratio of the oxalic acid organic compound to the platinum-based catalyst is 1:(2.5 - 3.5).

[0015] In some embodiments, the mass ratio of the oxalic acid organic compound to the platinum-based catalyst is 1:(3.5 - 4.5).

[0016] In some embodiments, the mass ratio of the oxalic acid organic compound to the platinum-based catalyst is 1:(4.5 - 5.5).

[0017] In some embodiments, the EW value of the long-side-chain perfluorosulfonic acid ionomer is 700 - 1000 g / cm 2 .

[0018] In some embodiments, the carbon carrier of the platinum-based catalyst can be one of a carbon nanotube carrier, a mesoporous carbon carrier, a noble metal carrier, a gel carrier, a conductive ceramic carrier, graphene, etc.

[0019] In some embodiments, the alcohol organic solvent includes at least one of methanol, ethanol, n-propanol, isopropanol, and tert-butanol.

[0020] In some embodiments, the oxalic acid organic compound includes at least one or more of oxalic acid dihydrate, magnesium oxalate dihydrate, zinc oxalate dihydrate, and ammonium oxalate monohydrate, and the boiling point of the oxalic acid organic compound is lower than 180°C.

[0021] In some embodiments, the mass ratio of the perfluorosulfonic acid ionomer to the catalyst carbon support is (0.6-1):1.

[0022] An embodiment of the present invention provides a method for preparing a cathode catalyst layer slurry, comprising the following steps:

[0023] (1) Dispersing the perfluorosulfonic acid ionomer solution in an alcohol organic solvent for 1-5 hours to obtain an ionomer dispersion.

[0024] (2) Evenly mix the platinum-based catalyst and water to obtain a catalyst aqueous solution.

[0025] (3) The ionomer dispersion and the catalyst aqueous solution are mixed uniformly and stirred sufficiently to obtain a cathode catalyst layer solution.

[0026] (4) Mixing the pore-forming agent with the cathode catalyst layer solution, grinding and dispersing the mixture, and preparing a cathode catalyst layer slurry.

[0027] The advantages and technical effects of the cathode catalyst layer slurry preparation method of the embodiment of the present invention are as follows: the platinum-based catalyst is first fully moistened with water, thereby avoiding the risk of flammability during the subsequent mixing process of the catalyst aqueous solution and the ionomer dispersion due to the excessive activity of the platinum-based catalyst, and at the same time, the ionomer can be fully wrapped on the surface of the platinum-based catalyst; by changing the order of adding oxalic acid organic compounds, the problem that oxalic acid organic compounds will first be adsorbed on the surface of the platinum-based catalyst is solved; the preparation method is simple and suitable for laboratory operation.

[0028] An embodiment of the present invention provides a cathode catalyst layer, which is prepared by coating and drying the cathode catalyst layer slurry described in the embodiment of the present invention.

[0029] One or more technical solutions provided in the embodiments of the present application have at least the following technical effects or advantages:

[0030] (1) The cathode catalyst layer slurry contains long side chain perfluorosulfonic acid ionomers, which enhance the hydrophobic effect of the cathode catalyst layer, improve the drainage capacity of the cathode catalyst layer at high current density, and reduce the mass transfer resistance of the reaction gas at high current density.

[0031] (2) The oxalic acid organic compound in the cathode catalyst layer is easily decomposed by heat and can be removed by the vacuum drying temperature and the transfer hot pressing temperature, which can generate rich pore channels in the cathode catalyst layer, facilitating the transport efficiency of reaction gases and the water discharge capacity, and improving the mass transfer efficiency in the catalyst layer.

[0032] (3) The combined use of the long-chain perfluorosulfonic acid ionomer and the oxalic acid organic compound enables the fuel cell to have excellent output performance when operating at low relative humidity.

[0033] An embodiment of the present invention provides a membrane electrode, including a proton exchange membrane, an anode catalyst layer, a cathode catalyst layer, and a gas diffusion layer covering the anode and cathode catalyst layers, wherein the cathode catalyst layer is the cathode catalyst layer of the embodiment of the present invention.

[0034] The membrane electrode of the embodiment of the present invention has all the advantages brought by the cathode catalyst layer of the embodiment of the present invention, which will not be elaborated here.

[0035] An embodiment of the present invention provides a fuel cell, including the membrane electrode described in the embodiment of the present invention, having all the advantages of the membrane electrode, which will not be elaborated here. Description of the Drawings

[0036] Figure 1 It is the I-V polarization curve graph of the membrane electrodes prepared in the examples and comparative examples. Detailed Embodiments

[0037] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0038] An embodiment of the present invention provides a cathode catalyst layer slurry, including a platinum-based catalyst, an alcohol organic solvent, a long-chain perfluorosulfonic acid solution, water, and an oxalic acid organic compound, wherein the mass ratio of the oxalic acid organic compound to the platinum-based catalyst is not less than 1:5.

[0039] The long-chain perfluorosulfonic acid ionomer of the cathode catalyst layer slurry in the embodiment of the present invention has fewer hydrophilic sulfonic acid groups and a longer hydrophobic backbone. Without introducing other hydrophobic substances, the cathode catalyst layer has excellent hydrophobic properties. When the fuel cell operates at a low relative humidity, in the high current density region, due to the strong repulsive ability of the long-chain perfluorosulfonic acid ionomer with water, water is difficult to converge in the catalyst layer and can be better discharged through the gas diffusion layer, thereby improving the gas transmission rate in the catalyst layer. At the same time, by introducing an oxalic acid organic compound into the cathode catalyst layer slurry in the embodiment of the present invention, the introduction of the oxalic acid organic compound does not poison the platinum-based catalyst and cause the inactivation of the platinum-based catalyst. At the same time, the oxalic acid organic compound is easily soluble in water and alcohol organic solvents and is easily decomposed by heat, which can optimize the pore structure in the cathode catalyst layer, effectively increase the pore size of the catalyst layer, reduce the diffusion resistance of the reaction gas in the catalyst layer, and provide more effective water-vapor transmission channels for the catalyst layer. The mutual cooperation of the long-chain perfluorosulfonic acid ionomer and the oxalic acid organic compound improves the mass transfer efficiency in the catalyst layer, reduces the adverse impact of concentration polarization on the battery performance, and further improves the battery performance.

[0040] In the cathode catalyst layer slurry of the embodiment of the present invention, the EW value of the long-chain perfluorosulfonic acid ionomer should not be lower than 750 g / mol. The EW value represents the grams of dry polymer per ionic group, that is, g / mol·SO3. - , specifically, for example,

[0041] 750 g / mol, 800 g / mol, 850 g / mol, 900 g / mol, 950 g / mol, 1000 g / mol. The long-chain perfluorosulfonic acid ionomer (EW > 750 g / mol) has a strong repulsive ability with water, endowing the cathode catalyst layer with good drainage ability.

[0042] In the cathode catalyst layer slurry of the embodiment of the present invention, the mass ratio of the oxalic acid organic compound to the platinum-based catalyst is not lower than 1:5. Introducing an appropriate amount of the oxalic acid organic compound can enable the cathode catalyst layer to form an excellent pore structure and provide more mass transfer channels for the catalyst layer. If the content of the introduced oxalic acid organic compound is too low, the pore-forming effect cannot be achieved and the pore structure of the catalyst layer cannot be optimized; if the content of the introduced oxalic acid organic compound is too high, some of the oxalic acid organic compounds will be unevenly dispersed in the cathode catalyst layer slurry, resulting in the formation of a macroporous structure with a larger pore size in the catalyst layer. The macroporous structure is beneficial to gas transmission, but at the same time it will reduce the conductivity of the catalyst layer, increase the ohmic polarization of the battery, and lead to a decline in battery performance.

[0043] In some embodiments, the carbon carrier of the platinum-based catalyst can be one of a carbon nanotube carrier, a mesoporous carbon carrier, a noble metal carrier, a gel carrier, a conductive ceramic carrier, graphene, etc.

[0044] In some embodiments, the EW value of the long side chain perfluorosulfonic acid ionomer should not be lower than 750 g / mol. Specifically, for example,

[0045] 750 g / mol, 800 g / mol, 850 g / mol, 900 g / mol, 950 g / mol, 1000 g / mol. By optimizing the EW value of the ionomer, the performance of the fuel cell at low relative humidity and high current density can be improved.

[0046] In some embodiments, the oxalic acid-based organic compound includes at least one or more of oxalic acid dihydrate, magnesium oxalate dihydrate, zinc oxalate dihydrate, ammonium oxalate monohydrate, etc. The boiling point of the oxalic acid-based organic compound is higher than 40 °C and lower than 180 °C. If the boiling point of the oxalic acid-based organic compound is lower than 40 °C, the oxalic acid-based organic compound will volatilize during the ball milling process of the cathode catalyst layer slurry and cannot play a role in pore formation. If the boiling point of the oxalic acid-based organic compound is higher than 180 °C, during the process of removing the oxalic acid compound by heat treatment, part of the oxalic acid cannot be completely removed and remains in the cathode catalyst layer, increasing the resistance of the catalyst layer and blocking some pores in the catalyst layer, affecting the transmission of reaction gases. Preferably, the boiling point of the oxalic acid-based organic compound is 40-180 °C, such as 90 °C, 100 °C, 110 °C, 120 °C, 130 °C, 140 °C.

[0047] In some embodiments, the mass ratio of the perfluorosulfonic acid ionomer to the platinum-based catalyst carbon support is (0.6-1):1. If the mass ratio of the perfluorosulfonic acid ionomer to the platinum-based catalyst carbon support is too high, the proton transport ability is improved, but the porosity of the catalyst layer decreases, affecting the transport of reaction gases. If the mass ratio of the perfluorosulfonic acid ionomer to the platinum-based catalyst carbon support is too low, the porosity of the catalyst layer increases, which is beneficial to the transport of reaction gases, but the proton transport ability weakens.

[0048] In some embodiments, the alcohol-based organic solvent includes at least one of methanol, ethanol, n-propanol, isopropanol, tert-butanol, ethylene glycol, etc.

[0049] In some embodiments, the mass ratio of water to the alcohol-based organic solvent is 1:(3-5). Under rich alcohol conditions, flammable phenomena are likely to occur during the mixing process of the catalyst aqueous solution and the ionomer dispersion. Under rich water conditions, there is a strong interaction between the ionomer and the carbon support of the platinum-based catalyst, which can make the ionomer better wrap around the surface of the carbon support.

[0050] In some embodiments, the solid content in the cathode catalyst layer slurry is 7%-10%, specifically, for example, 7%, 8%, 9%, 10%.

[0051] The embodiment of the present invention provides a method for preparing a cathode catalyst layer slurry, which specifically comprises the following steps:

[0052] (1) Dispersing the long side chain perfluorosulfonic acid ionomer solution in the alcohol organic solvent at a stirring speed of 200-300 rpm for a stirring time of 1-5 h to obtain an ionomer dispersion.

[0053] (2) dripping water into the platinum-based catalyst to completely wet the platinum-based catalyst with water and stirring the mixture sufficiently at a stirring speed of 50-150 rpm for 3-6 min to obtain a catalyst aqueous solution.

[0054] (3) The catalyst aqueous solution and the ionomer dispersion are uniformly mixed and fully stirred at a stirring speed of 350-550 rpm and a stirring time of 30-60 min to obtain a catalyst mixed solution.

[0055] (4) adding the oxalic acid organic compound into the catalyst mixture and stirring the mixture sufficiently at a stirring speed of 350-550 rpm for 30-60 min to obtain a cathode catalyst layer aqueous solution.

[0056] (5) Grinding and dispersing the cathode catalyst layer aqueous solution to improve the dispersion state of various substances in the cathode catalyst layer to obtain a cathode catalyst layer slurry.

[0057] The cathode catalyst layer slurry prepared in the embodiment of the present invention can make the platinum-based catalyst evenly dispersed in the organic solvent, which is beneficial for the ionomer to be fully wrapped on the catalyst surface, while avoiding the adverse effects of oxalic acid organic compounds on the ionomer-wrapped catalyst state. The cathode catalyst layer slurry preparation method is simple and suitable for laboratory operation and production.

[0058] The present invention also provides a method for preparing a cathode catalyst layer, which specifically comprises the following steps:

[0059] (1) A clean Teflon release film is spread flat on the surface of a scraper, and the surface of the Teflon release film is scrubbed with 95 wt % ethanol to remove impurities on the surface of the Teflon release film, thereby avoiding the adverse effects of impurities on the cathode catalyst layer.

[0060] (2) Select a coating rod of suitable thickness and control the coating speed of the coating machine to coat the cathode catalyst layer slurry on the surface of the PTFE substrate membrane. At this time, the cathode catalyst layer slurry is in liquid state.

[0061] (3) The coated PTFE substrate membrane is placed in a vacuum drying oven for drying to obtain the cathode catalyst layer.

[0062] In some embodiments, the platinum loading in the cathode catalyst layer is 0.35-0.55 mg / cm2 , specifically, for example, the platinum loading can be 0.35 mg / cm 2 、0.4 mg / cm 2 、0.45 mg / cm 2 。

[0063] In some embodiments, the temperature of the vacuum drying oven is 100 - 140 °C. At this temperature, the oxalic acid organic compound can be decomposed by heat, so as to achieve the purpose of optimizing the pores of the cathode catalyst layer. It should be noted that the side chain structure of the long-chain perfluorosulfonic acid ionomer will not be damaged at this temperature. Preferably, the drying temperature can be 110 °C, 120 °C, 130 °C, 140 °C.

[0064] The embodiment of the present invention provides a membrane electrode, including an anode catalyst layer, a cathode catalyst layer, a proton exchange membrane, and a gas diffusion layer covering the surfaces of the anode and cathode catalyst layers, wherein the cathode catalyst layer is the cathode catalyst layer of the present invention.

[0065] In some embodiments, the preparation method and process flow of the anode catalyst layer slurry and the anode catalyst layer are consistent with those of the cathode catalyst layer slurry and the cathode catalyst layer in the embodiment of the present invention, which will not be elaborated here. The difference is that no oxalic acid organic compound is introduced into the anode catalyst layer slurry.

[0066] In some embodiments, the carbon support of the anode platinum-based catalyst can be one of a carbon nanotube support, a mesoporous carbon support, a noble metal support, a gel support, a conductive ceramic support, graphene, etc.

[0067] In some embodiments, the platinum loading in the anode catalyst layer is 0.03 - 0.2 mg / cm 2 。

[0068] In some embodiments, the proton exchange membrane is a perfluorosulfonic acid resin membrane.

[0069] The embodiment of the present invention also provides a preparation method of a membrane electrode, specifically including the following steps:

[0070] (1) Place the anode catalyst layer and the cathode catalyst layer in the embodiment of the present invention on both sides of the proton exchange membrane respectively.

[0071] (2) Through a hot pressing process, at a certain hot pressing temperature, apply a certain hot pressing pressure to the anode catalyst layer, the proton exchange membrane, and the cathode catalyst layer in the embodiment of the present invention, and the anode catalyst layer and the cathode catalyst layer can be transferred to both sides of the proton exchange membrane, that is, a three-in-one CCM is prepared.

[0072] (3) Cover the cathode gas diffusion layer and the anode gas diffusion layer on the cathode catalyst layer and the anode catalyst layer respectively, that is, a membrane electrode is prepared.

[0073] In some embodiments, the hot pressing temperature can be 135 - 190 °C. By using the hot pressing temperature and pressure during the transfer process, the oxalic acid organic compound remaining in the embodiments of the present invention can be removed, thereby achieving the purpose of pore formation. Preferably, the hot pressing temperature can be 140 °C - 1800 °C.

[0074] The embodiments of the present invention also provide a fuel cell, including the membrane electrode of the embodiments of the present invention.

[0075] The present invention will be further explained below in conjunction with specific embodiments and the accompanying drawings.

[0076] It should be noted that the preparation methods of the cathode catalyst layer slurry, cathode catalyst layer, anode catalyst layer slurry, anode catalyst layer, and membrane electrode in the following examples and comparative examples are all prepared by the preparation methods of the said embodiments.

[0077] Example 1:

[0078] Preparation of the cathode catalyst layer slurry: First, 2.56 g of a long-chain perfluorosulfonic acid ionomer solution (D520, Nafion, solid content 20 wt%) was dispersed in 20.5198 g of isopropanol by magnetic stirring at a stirring speed of 300 rpm for 1 h to obtain an ionomer dispersion. After 1 h, 4.7606 g of ultrapure water was weighed and added to the ball mill jar. Then, 2 g of a self-made 60 wt% platinum-carbon catalyst (brand: SPIC-BCM60) was weighed and added to the ball mill jar containing ultrapure water, and the catalyst was completely wetted by magnetic stirring to avoid the phenomenon of open flame when the catalyst aqueous solution and the ionomer dispersion were mixed. The magnetic stirring speed was 130 rpm, and the magnetic stirring time was 2 min. Then, the ionomer dispersion was dropped into the catalyst aqueous solution to obtain a catalyst mixture. The magnetic stirring speed was adjusted to 350 rpm, and magnetic stirring was continued for 30 min to enable the catalyst to be fully dispersed in the ionomer dispersion. After 30 min, 0.559 g of oxalic acid dihydrate was added to the catalyst mixture, and high-speed stirring was continued at the current magnetic stirring speed for 30 min. Finally, 136.35 g of zirconia balls were added to the catalyst mixture, the ball mill jar was sealed and placed in a ball mill for high-speed ball milling for 3 h to obtain the cathode catalyst layer slurry. In this catalyst layer slurry, I / C is 0.8, the mass ratio of ultrapure water to n-propanol is 1:3, and the total solid content in the cathode catalyst layer slurry is 10%.

[0079] Preparation of cathode catalyst layer: Place a Teflon release film flat on the automatic coating instrument, and turn on the vacuum pump to make the Teflon release film completely adsorbed on the automatic coating instrument, select a suitable coating rod thickness, add a certain amount of cathode catalyst layer slurry on the left side of the coating rod, control the coating speed to 27m / min, start the coating machine, and make the cathode catalyst layer slurry completely coated on the Teflon release film, then transfer the wet cathode catalyst layer after coating to an 80°C blast drying oven for drying for 5 minutes to obtain a dry cathode catalyst layer, and finally transfer the dry cathode catalyst layer to a 120°C vacuum drying oven for drying for 5 hours to completely volatilize the n-propanol and ultrapure water and remove the oxalic acid dihydrate. At this point, the cathode catalyst layer is prepared, and the platinum loading of the cathode catalyst layer is 0.4mg / cm 2 .

[0080] Preparation of membrane electrode: Cut the above-mentioned anode catalyst layer and cathode catalyst layer into coatings of 5cm*5cm size, and place them on both sides of the proton exchange membrane respectively. The proton exchange membrane is 10cm*10cm in size, and Teflon release film, cardboard, and silicone pad are placed on both sides respectively. Place it on a transfer machine for transfer. The hot pressing temperature is 165°C, the hot pressing time is 200s, and the hot pressing pressure is 1000N. After the transfer is completed, a three-in-one CCM is obtained. Then cut the anode gas diffusion layer and cathode gas diffusion layer of 6cm*6cm in size, and paste them on the anode catalyst layer and the cathode catalyst layer respectively to obtain a membrane electrode.

[0081] Preparation of proton exchange membrane fuel cell: The above membrane electrode is assembled into a single cell, and the cell assembly compression rate is 20%.

[0082] Embodiment 2:

[0083] Preparation of cathode catalyst layer slurry: The preparation method is the same as that in Example 1, except that the mass of ultrapure water added is 4.9456 g, the mass of n-propanol is 21.1948 g, the mass of oxalic acid dihydrate is 0.699 g, and the I / C, mass of ultrapure water, mass of n-propanol and total solid content in the cathode catalyst layer slurry are the same as those in Example 1.

[0084] Preparation of cathode catalyst layer: the same as the preparation method in Example 1.

[0085] Preparation of membrane electrode: the preparation method is the same as that in Example 1.

[0086] Preparation of proton exchange membrane fuel cell: the preparation method is the same as that in Example 1.

[0087] Embodiment 3:

[0088] Preparation of cathode catalyst layer slurry: The preparation method is the same as that in Example 1, except that the mass of ultrapure water added is 5.241 g, the mass of n-propanol is 22.2743 g, and the mass of oxalic acid dihydrate is 0.9237 g. The I / C, the mass ratio of ultrapure water to n-propanol, and the total solid content in the cathode catalyst layer slurry are the same as those in the cathode catalyst layer slurry of Example 1.

[0089] Preparation of cathode catalyst layer: The preparation method is the same as that in Example 1.

[0090] Preparation of membrane electrode: The preparation method is the same as that in Example 1.

[0091] Preparation of proton exchange membrane fuel cell: The preparation method is the same as that in Example 1.

[0092] Comparative Example 1:

[0093] Preparation of cathode catalyst layer slurry: The preparation method is the same as that in Example 1, except that oxalic acid dihydrate is not added to the cathode catalyst layer slurry. The mass of ultrapure water added is 4.02 g, the mass of n-propanol is 17.82 g. The I / C, the mass ratio of ultrapure water to n-propanol, and the total solid content in the cathode catalyst layer slurry are the same as those in the cathode catalyst layer slurry of Example 1.

[0094] Preparation of cathode catalyst layer: The preparation method is the same as that in Example 1.

[0095] Preparation of membrane electrode: The preparation method is the same as that in Example 1.

[0096] Preparation of proton exchange membrane fuel cell: The preparation method is the same as that in Example 1.

[0097] Test conditions: Anode H2 / Cathode Air, the battery temperature is 80 °C, the anode / cathode humidity is 40% RH, the anode / cathode stoichiometric ratio is 1.5 / 2.0, the anode / cathode back pressure at the outlet is 100 kPa / 90 kPa, and the I-V performance is tested. The battery performance results of the above examples and comparative examples are shown in Figure 1 .

[0098] Figure 1 are the polarization curves of the comparative example and the examples. From Figure 1 it can be seen that in the low current density region (electrochemical polarization region), the performance of the comparative example and the examples is basically the same, and no significant difference is observed, indicating that adding an appropriate amount of oxalic acid dihydrate to the cathode catalyst layer will not significantly increase the internal resistance of the membrane electrode, and at the same time will not affect the proton transport in the catalyst layer. Analyzing the performance of Examples 1-3 and Comparative Example 1 at 0.65 V, the current density of Comparative Example 1 is 2000 mA / cm 2 @0.65 V, and the current density of Example 1 is 2167 mA / cm 2@ 0.65V, an increase of 8.35% compared with Comparative Example 1. The current density of Example 2 is 2243 mA / cm 2 @ 0.65V, an increase of 12.15% compared with Comparative Example 1. The current density of Example 3 is 2328 mA / cm 2 @ 0.65V, an increase of 16.4% compared with Comparative Example 1. In the medium and high current density region, the performance improvement is more obvious. The membrane electrode output performance of Examples 1 - 3 is still higher than that of the membrane electrode of Comparative Example 1. The reason is that in this electro - chemical reaction stage, the performance of the fuel cell mainly depends on the transport of reaction gases. The reaction gases need to be replenished to the catalytic layer in time to maintain the normal reaction. The mutual cooperation of the long - chain perfluorosulfonic acid ionomer and oxalic acid dihydrate can generate more effective gas - liquid transport channels in the catalytic layer, reduce the transport resistance of the reaction gases, facilitate the oxygen to reach the three - phase reaction interface to participate in the reaction, and improve the mass transfer effect in the catalytic layer.

[0099] Through Figure 1 It can be analyzed from the polarization curve shown that the order of battery performance from good to bad is: Example 3 > Example 2 > Example 1 > Comparative Example 1. Therefore, it is preferred that the mass ratio of oxalic acid dihydrate to platinum - based catalyst is 1:3. In the embodiments of the present invention, the combination of the long - chain perfluorosulfonic acid ionomer solution and oxalic acid dihydrate can make the fuel cell have the best performance.

[0100] In the present invention, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0101] Although the above - mentioned embodiments have been shown and described, it can be understood that the above - mentioned embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions, and variations made by those of ordinary skill in the art to the above - mentioned embodiments are within the protection scope of the present invention.

[0102] It is obvious to those skilled in the art that the present invention is not limited to the details of the above-described exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, in any regard, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the present invention.

[0103] In addition, it should be understood that although this specification is described in terms of embodiments, not every embodiment only contains an independent technical solution. This narrative style of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment have been appropriately combined to form other embodiments that are easily understood by those skilled in the art.

Claims

1. A cathode catalyst layer slurry for a fuel cell membrane electrode, characterized in that: Comprising: A platinum-based catalyst, an alcohol organic solvent, a long-side-chain perfluorosulfonic acid ionomer solution, water, and an oxalic acid organic compound.

2. The cathode catalyst layer slurry of a fuel cell membrane electrode according to claim 1, characterized in that The carbon support of the platinum-based catalyst is one of a carbon nanotube support, a mesoporous carbon support, a noble metal support, a gel support, a conductive ceramic support, and graphene. The mass ratio of the platinum-based catalyst to the pore-forming agent is (1 - 6):

1.

3. The cathode catalyst layer slurry of a fuel cell membrane electrode according to claim 1, wherein The alcohol organic solvent is one or a mixture of methanol, ethanol, n-propanol, isopropanol, tert-butanol, and ethylene glycol.

4. The cathode catalyst layer slurry of a fuel cell membrane electrode according to claim 1, characterized in that The EW value of the long-side-chain perfluorosulfonic acid ionomer solution is 700 - 1000 g / mol, and the mass ratio of the perfluorosulfonic acid ionomer to the catalyst carbon support is (0.6 - 1):

1.

5. The cathode catalyst layer slurry of a fuel cell membrane electrode according to claim 1, wherein The oxalic acid organic compound is one or a mixture of oxalic acid dihydrate, magnesium oxalate dihydrate, zinc oxalate dihydrate, and ammonium oxalate monohydrate, and the boiling point of the oxalic acid organic compound is lower than 180°C.

6. The cathode catalyst layer slurry of a fuel cell membrane electrode according to claim 1, characterized in that, The solid content in the cathode catalyst layer slurry is 7% - 10%.

7. A method for preparing a cathode catalyst layer slurry of a fuel cell membrane electrode, characterized in that, Including the following steps: Step 1: Disperse the long-side-chain perfluorosulfonic acid solution in the alcohol organic solvent for 1 - 5 h to obtain an ionomer dispersion. Step 2: Mix the platinum-based catalyst and water evenly to obtain a catalyst aqueous solution. Step 3: Mix the ionomer dispersion and the catalyst aqueous solution evenly and stir well to prepare a cathode catalyst layer solution. Step 4: Mix the pore-forming agent and the cathode catalyst layer solution, and perform grinding and dispersion to prepare a cathode catalyst layer slurry.

8. A cathode catalyst layer, characterized in that, The cathode catalyst layer is prepared by doctor blading and drying according to the cathode catalyst layer slurry as described in any one of claims 1 - 7.

9. A membrane electrode, comprising a proton exchange membrane, a cathode catalyst layer and an anode catalyst layer on both sides of the proton exchange membrane, and a gas diffusion layer covering the cathode catalyst layer and the anode catalyst layer, characterized in that, Comprising the cathode catalyst layer as described in claim 8.

10. A fuel cell, characterized in that, Comprising the membrane electrode as described in claim 9.

Images