A kind of catalytic layer slurry and its preparation method and application

Abstract

The application discloses a kind of catalytic layer slurry and its preparation method and application, it is related to fuel cell technical field.The catalytic layer slurry includes platinum-based catalyst, perfluorosulfonic acid type ionomer, solvent and hydroxy acid;Wherein, the hydroxy acid is the organic compound of formula simultaneously containing at least one hydroxyl and at least one carboxyl group.This application utilizes carboxyl in hydroxy acid molecule and Pt forms coordination structure and directly anchors Pt active site, prevents Pt particle migration, ripening and agglomeration;Through carboxyl and hydroxyl in hydroxy acid molecule and the hydrogen bond network formed by sulfonic acid group in ionomer, the distribution of ionomer on Pt surface is regulated, and the sulfonic acid group poisoning is reduced;And with the dissociation equilibrium of hydroxy acid in acidic environment, the dynamic exposure and stability of Pt active site are realized.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, specifically to a catalyst layer slurry, its preparation method, and its application. Background Technology

[0002] The industrialization of proton exchange membrane fuel cells (PEMFCs) is primarily constrained by the performance of the membrane electrode assembly (MEA) in terms of activity and stability. The catalyst layer, as a core component of the MEA, is directly responsible for catalyzing the oxygen reduction reaction (ORR) and the hydrogen oxidation reaction (HOR). The uniformity of the platinum-based catalyst's dispersion determines its electrochemical active surface area (ECSA), which in turn affects the fuel cell's output power and lifespan.

[0003] In existing technologies, the catalyst slurry typically uses isopropanol (IPA) or an IPA / water mixture to disperse the Pt-based catalyst and ionomer. However, this method faces technical bottlenecks in suppressing platinum particle agglomeration. Under the acidic environment and potential cycling conditions of actual fuel cell operation, platinum particles are prone to dissolution, and the dissolved Pt... 2+ Migration occurs under the influence of a concentration gradient or electric field. This migration process is prone to the following problems: First, Pt... 2+ Ostwald ripening occurs, depositing on the surface of other Pt particles, leading to particle coarsening; secondly, Pt... 2+ The particles migrate with the water to the proton exchange membrane and deposit to form Pt bands. In addition, Pt particles may also merge through microcrystal migration mechanisms, further leading to an increase in particle size.

[0004] The aforementioned degradation mechanism leads to a sharp reduction in available Pt active sites and an irreversible decrease in the electrochemical active surface area (ECSA), resulting in a significant slowdown in oxygen reduction reaction kinetics and a sharp increase in activation polarization voltage loss. Simultaneously, Pt particle agglomerates may clog the catalyst layer pores, leading to a decrease in oxygen transport capacity, all contributing to the degradation of fuel cell membrane electrode performance and reduced durability. Therefore, improving the catalyst layer slurry formulation to enhance the stability of Pt-based catalysts is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] This invention provides a catalyst layer slurry, its preparation method, and its application, aiming to solve the problem that existing catalyst layer slurries cannot effectively inhibit the migration, agglomeration, and aging of Pt-based catalysts, leading to a reduction in the electrochemical active area of ​​the fuel cell membrane electrode and a decline in performance and durability.

[0006] In a first aspect, the present invention provides a catalyst layer slurry comprising a platinum-based catalyst, a perfluorosulfonic acid ionomer, a solvent, and a hydroxy acid; wherein the hydroxy acid is an organic compound containing at least one hydroxyl group and at least one carboxyl group in its molecular formula.

[0007] In some embodiments, the mass of the hydroxy acid is 0.1-5% of the mass of the perfluorosulfonic acid ionomer.

[0008] In some embodiments, the hydroxy acid has 2-6 carbon atoms.

[0009] In some embodiments, the hydroxy acid includes at least one of glycolic acid, lactic acid, citric acid, and gluconic acid.

[0010] In some embodiments, the solvent includes at least one of isopropanol and water.

[0011] In some embodiments, the platinum-based catalyst includes at least one of Pt / C, PtCo / C, PtNi / C, and PtCoMn / C.

[0012] Secondly, the present invention provides a method for preparing the catalyst layer slurry, comprising the following steps: mixing the platinum-based catalyst, the perfluorosulfonic acid ionomer, the solvent and the hydroxy acid, and dispersing them to obtain the catalyst layer slurry.

[0013] In some embodiments, the method for preparing the catalyst layer slurry includes: The platinum-based catalyst was mixed with a solvent to obtain a mixture. The mixture, hydroxy acid, and perfluorosulfonic acid ionomer are mixed and stirred in an ice-water bath to obtain the catalyst layer slurry.

[0014] Thirdly, the present invention provides a membrane electrode comprising a proton exchange membrane and a catalyst layer coated on at least one side surface of the proton exchange membrane, the catalyst layer being formed by curing the catalyst layer slurry.

[0015] Fourthly, the present invention provides a fuel cell, the fuel cell including the membrane electrode assembly described above.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The carboxyl group in the hydroxy acid molecule can act as a ligand to form a relatively stable coordination structure with Pt, directly anchoring the active site of Pt and preventing Pt particles from migrating, ripening and agglomerating.

[0017] 2. Both the carboxyl and hydroxyl groups in the hydroxy acid molecule can form a hydrogen bond network with the sulfonic acid groups in the ionomer. This network can regulate the distribution of the ionomer on the Pt surface through the steric exclusion effect, reduce the toxicity of the sulfonic acid groups to the active sites of Pt, and further limit the migration, ripening and aggregation of Pt particles.

[0018] 3. Hydroxy acid molecules containing multiple hydroxyl groups can form a denser and more stable hydrogen bond network, promoting proton conduction. Furthermore, hydroxy acids have a lower acid dissociation constant pKa, allowing for the formation of a carboxyl / carboxylate dynamic equilibrium (R-COOH) in the acidic reaction environment of a fuel cell. R-COO - +H + R-COO achieves dynamic exposure and stabilization of Pt active sites under locally strongly acidic conditions. - Protonation to R-COOH weakens the coordination of Pt, which helps expose more Pt active sites to promote the oxygen reduction reaction; in a locally weakly acidic environment, R-COOH deprotonates to form R-COO. - This helps stabilize Pt active sites, while also providing protons and enhancing local proton conduction, synergistically improving the reaction kinetics of Pt anchoring with the hydrogen bonding network. Hydroxy acid molecules containing multiple carboxyl groups can further enhance the buffering and regulating capabilities of this dynamic equilibrium.

[0019] 4. By adding hydroxy acids to anchor Pt, a mechanism for dynamic exposure and stabilization of Pt can be achieved, which can effectively alleviate the degradation of Pt particles and improve the performance and durability of membrane electrodes. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0021] Against the backdrop of global clean energy transition and sustainable development strategies, the industrialization of hydrogen fuel cells still faces the dual challenges of membrane electrode assembly (MEA) activity and stability. The catalyst layer, as a core component of the MEA in proton exchange membrane fuel cells (PEMFCs), is directly responsible for catalyzing the oxygen reduction reaction (ORR) and the hydrogen oxidation reaction (HOR). The uniformity of Pt-based catalyst dispersion determines its electrochemical active surface area (ECSA), which in turn affects the fuel cell's output power and lifespan.

[0022] Current catalyst slurries commonly use isopropanol (IPA) or IPA / water mixed solvents to disperse Pt-based catalysts and ionomers. However, this method faces technical bottlenecks in suppressing Pt particle agglomeration. Under the acidic environment and potential cycling conditions of actual fuel cell operation, Pt particles are prone to dissolution, and the dissolved Pt... 2+ Migration occurs under the influence of a concentration gradient or electric field. The migration process may lead to the following problems: 1. Pt 2+Ostwald ripening occurs, depositing on the surface of other Pt particles, leading to particle coarsening; II. Pt 2+ The particles migrate with the water to the proton exchange membrane and deposit to form Pt bands. In addition, Pt particles may also merge through microcrystal migration mechanisms, further leading to an increase in particle size.

[0023] The direct consequences of the aforementioned Pt degradation process are: a sharp reduction in available Pt active sites and an irreversible decrease in the electrochemical active surface area (ECSA), leading to a significant slowdown in oxygen reduction reaction kinetics and a sharp increase in activation polarization voltage loss; at the same time, Pt particle agglomerates may clog the pores of the catalyst layer, resulting in a decrease in oxygen transport capacity, all of which contribute to the degradation of fuel cell membrane electrode performance and a decrease in durability.

[0024] In view of this, the present invention provides a catalyst layer slurry, its preparation method and application, aiming to solve the problem that existing catalyst layer slurries cannot effectively inhibit the migration, agglomeration and aging of Pt-based catalysts, resulting in a decrease in the electrochemical active area of ​​the fuel cell membrane electrode and a decline in performance and durability.

[0025] In a first aspect, the present invention provides a catalyst layer slurry. According to an embodiment of the present invention, the catalyst layer slurry comprises a platinum-based catalyst, a perfluorosulfonic acid ionomer, a solvent, and a hydroxy acid; wherein the hydroxy acid is an organic compound containing at least one hydroxyl group and at least one carboxyl group in its molecular formula.

[0026] The catalyst slurry provided by this invention introduces hydroxy acids containing both hydroxy and carboxyl groups. The carboxyl groups in the hydroxy acid molecules can act as ligands to form stable coordination structures with the surface of platinum-based catalysts. This chemical anchoring effect restricts the migration, Ostwald ripening, and aggregation behavior of Pt particles during electrochemical cycling, thereby effectively maintaining the electrochemical active area. Furthermore, both the hydroxyl and carboxyl groups in the hydroxy acid can form hydrogen bond networks with the sulfonic acid groups of perfluorosulfonic acid ionomers. This utilizes steric hindrance to optimize the coverage morphology of the ionomers on the catalyst surface, reducing the poisoning of Pt active sites by sulfonic acid groups and further enhancing the physical confinement effect on Pt particles.

[0027] Furthermore, the selected hydroxy acid possesses a suitable acid dissociation constant, enabling the establishment of a dynamic equilibrium between carboxyl and carboxylate groups under acidic operating conditions in fuel cells. Under locally strongly acidic conditions, coordination weakens to expose more active sites and promote oxygen reduction reactions, while under locally weakly acidic conditions, deprotonation enhances the anchoring of Pt and provides a proton conduction pathway. This dynamic regulation mechanism, in conjunction with the hydrogen bonding network, achieves a balance between high activity exposure and high stability anchoring of Pt active sites, thereby delaying catalyst degradation and improving the output performance and durability of the membrane electrode assembly.

[0028] In some embodiments of the present invention, the mass of the hydroxy acid is 0.1-5% of the mass of the perfluorosulfonic acid ionomer. By limiting the mass of the hydroxy acid within the above range, it can be ensured that the hydroxy acid plays a regulatory role in the slurry. If the addition amount is too low (<0.1%), the coordination anchoring effect between the carboxyl group and Pt is insufficient, making it difficult to effectively inhibit the migration and aggregation of Pt particles. At the same time, the hydrogen bond network is incomplete, and the regulatory effect on the distribution of ionomers is limited. If the addition amount is too high (>5%), the hydroxy acid may excessively compete for Pt surface active sites, leading to a decrease in the initial ECSA. At the same time, the residual hydroxy acid may form an insulating barrier in the catalyst layer, increasing the ohmic resistance. Within the range of 0.1-5%, the hydroxy acid can achieve a balance between stable anchoring and dynamic exposure of Pt active sites, synergistically optimizing the distribution of ionomers, thereby taking into account both the initial performance and long-term durability of the membrane electrode.

[0029] In some embodiments of the present invention, the hydroxy acid has 2-6 carbon atoms. Hydroxy acids with 2-6 carbon atoms have suitable pKa values ​​and can establish a dynamic equilibrium of carboxyl / carboxylate groups (R-COOH) under the acidic operating environment of a fuel cell. R-COO- + H + When the catalyst layer is locally in a strongly acidic environment, the equilibrium shifts towards the formation of R-COOH, and the coordination effect of hydroxy acids on Pt weakens accordingly, thereby exposing more Pt active sites and promoting the oxygen reduction reaction; when the catalyst layer is locally in a weakly acidic environment, the equilibrium shifts towards the formation of R-COO - The directional shift of the deprotonated carboxylate group enhances the anchoring stability of the Pt active site and provides a proton conduction pathway. This dynamic regulatory mechanism, in conjunction with the hydrogen bonding network, achieves a balance between high activity exposure and high stability anchoring of the Pt active site.

[0030] In some embodiments of the present invention, the hydroxy acid includes at least one of glycolic acid, lactic acid, citric acid, and gluconic acid. These hydroxy acids have low acid dissociation constants and readily form a carboxyl / carboxylate dynamic equilibrium in the acidic environment of a fuel cell. This equilibrium mechanism weakens coordination in locally strongly acidic environments to expose Pt active sites and promote oxygen reduction reactions; in locally weakly acidic environments, the deprotonated form helps stabilize Pt sites and enhance proton conduction. Simultaneously, these hydroxy acid molecules, through carboxyl group coordination anchoring with Pt and the formation of hydrogen bond networks with ionomer sulfonic acid groups, effectively limit the migration and aggregation of Pt particles and reduce the toxicity of sulfonic acid groups. This specific selection achieves dynamic exposure and stabilization of Pt active sites, synergistically improving reaction kinetics, thereby significantly improving the performance and durability of the membrane electrode assembly.

[0031] This application does not impose any particular restrictions on the specific types of platinum-based catalysts, perfluorosulfonic acid ionomers, and solvents in the catalyst layer slurry. Those skilled in the art can make reasonable selections based on actual performance requirements and process conditions.

[0032] Exemplarily, the Pt-based catalyst may be selected from platinum metal or platinum alloy catalysts supported on a carbon support, including at least one of Pt / C, PtCo / C, PtNi / C, and PtCoMn / C; the perfluorosulfonic acid ionomer may be selected from commercially available perfluorosulfonic acid resin solutions; the solvent may be selected from at least one of methanol, ethanol, n-propanol, isopropanol, and water, and this solvent system not only has good dispersibility. The specific selection of the above components should not be construed as limiting the scope of protection of this application.

[0033] Secondly, the present invention provides a method for preparing the catalyst layer slurry. According to an embodiment of this application, the preparation method includes the following steps: mixing the platinum-based catalyst, the perfluorosulfonic acid ionomer, the solvent and the hydroxy acid, and dispersing them to obtain the catalyst layer slurry.

[0034] This preparation method involves co-dispersing hydroxy acids with a platinum-based catalyst, a perfluorosulfonic acid ionomer, and a solvent. This ensures the hydroxy acids are uniformly distributed in the slurry system, allowing them to fully contact the sulfonic acid groups and solvent molecules in the ionomer and establish a hydrogen bond network before coating and drying. This guarantees the hydroxy acids' effective regulatory role in the subsequent film formation process. The carboxyl groups form a stable coordination structure with Pt, directly anchoring the active sites and inhibiting the migration, ripening, and aggregation of Pt particles. Simultaneously, the dynamic equilibrium of carboxyl / carboxylic acid groups based on the low pKa value of the hydroxy acids can regulate the exposure and stability of Pt sites under different local acidic environments, synergistically mitigating the poisoning of sulfonic acid groups and enhancing local proton conduction through the hydrogen bond network. As a result, the prepared catalyst slurry film exhibits a uniformly interconnected pore structure, and the obtained membrane electrode displays low ohmic resistance, high electrochemical active area, and excellent durability.

[0035] In a preferred embodiment of the present invention, the method for preparing the cathode catalyst slurry includes the following steps: S100: Mix the platinum-based catalyst with a solvent to obtain a mixture; S200: The mixture, hydroxy acid and perfluorosulfonic acid ionomer are mixed and stirred in an ice-water bath to obtain the catalyst layer slurry.

[0036] In this step, the platinum-based catalyst is first pre-dispersed in a solvent to avoid agglomeration caused by direct contact between the catalyst and the ionomer. Subsequently, hydroxy acids and perfluorosulfonic acid ionomers are introduced under ice-water bath conditions. The low-temperature environment suppresses the temperature rise during stirring, preventing heat from interfering with the coordination stability of the carboxyl groups of the hydroxy acid and the active sites of Pt, as well as the formation of the hydrogen bond network between the hydroxy acid and the sulfonic acid groups of the ionomer. The resulting slurry exhibits good dispersibility and high stability. After film formation, it can fully utilize the hydroxy acids to anchor Pt and mitigate the poisoning of sulfonic acid groups, thereby improving the uniformity of the catalyst layer and the durability of the membrane electrode.

[0037] Thirdly, the present invention provides a membrane electrode. According to an embodiment of this application, the membrane electrode includes a proton exchange membrane and a catalyst layer coated on at least one side surface of the proton exchange membrane, wherein the catalyst layer is formed by curing the catalyst layer slurry.

[0038] This membrane electrode is formed by curing the aforementioned catalyst layer slurry. The catalyst layer retains the interaction network between the hydroxy acid, the platinum-based catalyst, and the ionomer. The hydroxy acid forms stable coordination with the Pt active sites through its carboxyl groups, directly anchoring the Pt particles and inhibiting their migration, ripening, and aggregation. Simultaneously, the hydrogen bond network constructed by the carboxyl, hydroxyl, and sulfonic acid groups of the ionomer regulates the distribution of the ionomer, reduces the poisoning of the sulfonic acid groups, and enhances local proton conduction. Furthermore, the hydroxy acid has a low pKa value, allowing the catalyst layer to maintain a dynamic balance between carboxyl and carboxylate groups during operation, dynamically adjusting the exposure and stability of Pt sites according to the local acidic environment. Therefore, the catalyst layer slurry provided in this application enables the membrane electrode to possess both high electrochemical active area and excellent long-term durability.

[0039] Fourthly, the present invention provides a fuel cell, wherein, according to an embodiment of the present application, the fuel cell includes the membrane electrode assembly described above.

[0040] This fuel cell employs the aforementioned membrane electrode assembly (MEA). Under normal operating conditions, the hydroxy acid is anchored to Pt via carboxyl groups, effectively suppressing catalyst migration and aggregation, thus ensuring long-term stable output voltage. Simultaneously, the hydrogen bond network formed by the hydroxy acid and ionomer optimizes the proton conduction pathway, reduces sulfonic acid group poisoning, and lowers ohmic losses to improve power density. Furthermore, a dynamic equilibrium mechanism based on a low pKa value allows the cell to adjust the Pt site exposure state under different acid and alkaline environments, maintaining high reaction kinetics. Therefore, this fuel cell combines high electrochemical performance with excellent cycle durability, contributing to extended service life.

[0041] The technical solution provided by the present invention will be described in detail below with reference to the embodiments.

[0042] Unless otherwise specified, the raw materials used in the examples and comparative examples are commercially available analytical grade materials.

[0043] Example 1 This embodiment provides a catalyst layer slurry, a membrane electrode assembly, and a fuel cell, and the preparation method is as follows: (1) Preparation of catalyst layer slurry: Weigh platinum carbon catalyst and add it to a mixed solvent of isopropanol and water. The mass ratio of isopropanol to water is 1:2, and the mixture is dispersed evenly. Add perfluorosulfonic acid resin solution and glycolic acid to the above mixture. Control the mass ratio of perfluorosulfonic acid resin to carbon support in the catalyst to be 1.0. The amount of glycolic acid added is 0.5% of the solid mass of perfluorosulfonic acid resin. The pKa of glycolic acid is 3.83. Place the mixed system in an ice-water bath and mechanically stir for 30 minutes to obtain cathode catalyst layer slurry.

[0044] (2) Preparation of membrane electrode: The obtained cathode catalyst slurry is added to the spray gun, the gun is turned on and the stirring power is set to 10% of the maximum stirring power; a proton exchange membrane with a size of 100×100mm is taken and fixed on a heating stage at 90℃. The cathode catalyst slurry in the gun is uniformly sprayed onto the surface of the proton exchange membrane by spraying. The spraying amount is controlled so that the platinum loading is 0.3mg / cm² to obtain the cathode catalyst layer. The cathode catalyst layer is hot-pressed onto the surface of the proton exchange membrane to obtain the membrane electrode.

[0045] (3) The assembly of fuel cell single cells shall be carried out in accordance with the relevant provisions of Section 7.3 of the national standard GB / T 20042.5-2024 "Proton Exchange Membrane Fuel Cells Part 5: Membrane Electrode Test Methods" regarding "Single Cell Assembly". Specifically, the membrane electrode prepared above shall be placed between the bipolar plates and assembled in accordance with the order and tightening torque required by the standard to complete the preparation of the single cell.

[0046] Example 2 The difference between this embodiment and Example 1 is that in the preparation of the catalyst layer slurry, citric acid (a hydroxy acid containing multiple carboxyl groups, with a pKa1 of 3.13) of equal mass is used to replace glycolic acid, while other preparation conditions are the same as in Example 1.

[0047] Example 3 The difference between this embodiment and Example 1 is that in the preparation of the catalyst layer slurry, gluconic acid (a hydroxy acid containing multiple hydroxyl groups, with a pKa of 3.86) of equal mass is used to replace glycolic acid, while other preparation conditions are the same as in Example 1.

[0048] Example 4 The difference between this embodiment and Example 1 is that in the preparation of the catalyst layer slurry, the amount of glycolic acid added is 0.1% of the mass of the perfluorosulfonic acid resin solid, and the other preparation conditions are the same as in Example 1.

[0049] Example 5 The difference between this embodiment and Example 1 is that the amount of glycolic acid added is 5% of the mass of the perfluorosulfonic acid resin solid, while the other preparation conditions are the same as in Example 1.

[0050] Comparative Example 1 This comparative example provides a conventional catalyst layer, which differs from Example 1 in that no hydroxy acid is added during the preparation of the catalyst layer slurry, while the other preparation conditions are the same as in Example 1.

[0051] Comparative Example 2 The difference between this comparative example and Example 1 is that an equal mass of acetic acid (containing carboxyl groups but not hydroxyl groups) was added instead of hydroxy acids.

[0052] Comparative Example 3 The difference between this comparative example and Example 1 is that an equal mass of ethanol (containing hydroxyl groups but not carboxyl groups) was added to replace the hydroxy acid.

[0053] Performance testing The electrochemical performance of the membrane electrodes of Examples 1-5 and Comparative Examples 1-3 was tested. The testing process included: 1. Catalyst durability test method: First, the test conditions were set as follows: the battery reaction temperature was 80 °C, the relative humidity (RH) of the reaction gas was 100%, the stoichiometric ratio of hydrogen at the anode to air at the cathode was 1.5 and 2.5, respectively, the purity of the gases was 99.999%, and the system back pressure was 150 kPa.

[0054] Next, battery activation and pretreatment are performed: under the aforementioned conditions, the battery voltage is maintained at approximately 0.6 V for at least 4 hours; subsequently, the battery is purged with high-purity nitrogen for at least 4 hours until the battery voltage drops below 0.1 V.

[0055] Finally, accelerated stress testing was performed: nitrogen gas was introduced into the anode at a flow rate of 100 cc / min, and hydrogen gas was introduced into the cathode at a flow rate of 100 cc / min. A square wave potential signal was applied, with the potential maintained at 0.6 V for 3 s and at 0.95 V for 3 s, and the test was repeated 20,000 times.

[0056] 2. Electrochemical Active Area (ECSA) Degradation Rate: Before and after the catalyst durability test, the electrochemical active area of ​​the membrane electrode was measured using cyclic voltammetry. The ECSA value was obtained from the hydrogen adsorption / desorption peak charge in the integrated cyclic voltammetry curve. Based on the measured initial ECSA value and the ECSA value after the test, the ECSA degradation rate of each sample was calculated to evaluate the durability of the catalyst layer.

[0057] 3. Performance degradation of a single cell: During the catalyst durability test, the rated voltage was recorded at the initial stage (cycle 0) and the final stage (cycle 20,000). The rated voltage degradation value was defined as the difference between the rated voltage at the initial stage and the rated voltage at the final stage.

[0058] The test results are shown in Table 1: Table 1 Performance Test Results

[0059] As shown in Table 1, comparing Examples 1-5 with Comparative Example 1, the ECSA degradation rate of all examples was lower than that of Comparative Example 1 (30%), and the performance degradation value was also significantly lower than that of Comparative Example 1 (45 mV). Among them, Example 2 (citric acid) performed best, with an ECSA degradation rate of only 19% and a performance degradation of 20 mV; Examples 1 (glycolic acid) and 3 (gluconic acid) were next; Examples 4 (0.1% addition) and 5 (5% addition) were slightly higher than Example 1, but still significantly better than Comparative Example 1. This indicates that the addition of hydroxy acids can effectively inhibit the migration, ripening, and aggregation of Pt particles through carboxyl anchoring of Pt, regulation of ionomer distribution through hydrogen bond network, and dynamic equilibrium mechanism, thereby significantly reducing the decay of electrochemical active area and delaying fuel cell performance degradation.

[0060] Comparing Examples 1-5 with Comparative Example 2, it can be seen that the ECSA degradation rate of Comparative Example 2 is 28%, with a performance degradation of 42 mV, both higher than all examples. Although acetic acid contains a carboxyl group, which can coordinate with Pt, it lacks a hydroxyl group and cannot form an effective hydrogen bond network with the ionomer sulfonic acid group, nor can it enhance steric hindrance and proton conduction through the synergistic effect of multiple functional groups. The hydroxy acids (glycolic acid, citric acid, gluconic acid) in the examples, which contain both hydroxyl and carboxyl groups, showed a lower degradation rate, demonstrating that the introduction of hydroxyl groups plays an indispensable role in optimizing ionomer distribution, mitigating the toxicity of sulfonic acid groups, and enhancing the anchoring effect.

[0061] Comparing Examples 1-5 with Comparative Example 3, it can be seen that the ECSA degradation rate of Comparative Example 3 was 29%, with a performance degradation of 44 mV, only slightly better than Comparative Example 1, but significantly worse than all examples. Ethanol contains only hydroxyl groups and no carboxyl groups, and therefore cannot form a stable coordination anchor with Pt. Thus, its inhibitory effect on Pt particle migration and aggregation is extremely weak, and it also lacks the dynamic balance regulation ability of carboxyl groups. This comparison fully demonstrates that the carboxyl group in hydroxy acids is the core functional group for achieving Pt active site anchoring and dynamic exposure, while the hydroxyl group plays a synergistic role; both are indispensable.

[0062] The above results demonstrate that the catalyst slurry provided in this application, by introducing hydroxy acids containing both hydroxy and carboxyl groups in its molecular formula, achieves two main effects: firstly, by utilizing the stable coordination structure formed between the carboxyl group and Pt, it directly anchors the active sites of Pt, inhibiting the migration, Ostwald ripening, and aggregation of Pt particles; secondly, by utilizing the carboxyl and hydroxyl groups to construct a hydrogen bond network with the ionomer sulfonic acid groups, it regulates the distribution of the ionomer through the space exclusion effect, reducing the poisoning of Pt by the sulfonic acid groups and further limiting the migration of Pt particles. Furthermore, hydroxy acids with 2-6 carbon atoms have suitable pKa values, enabling the establishment of a dynamic equilibrium of carboxyl / carboxylate groups under the acidic operating environment of fuel cells: under locally strong acid conditions, the equilibrium shifts towards R-COOH, weakening coordination to expose more active sites and promote the reaction; under locally weak acid conditions, the equilibrium shifts towards R-COO. - The movement enhances anchoring and provides proton conduction. This dynamic regulation mechanism, in conjunction with the hydrogen bond network, achieves a balance between high activity exposure and high stability anchoring of Pt active sites. Table 1 data shows that the ECSA degradation rate of the examples using hydroxy acids (especially citric acid, Example 2) is as low as 19%, with a performance degradation of only 20 mV, far superior to the comparative examples without added hydroxy acids or containing only a single functional group. Therefore, the catalyst slurry of this invention can effectively improve the durability and output performance of the membrane electrode assembly, providing a reliable technical solution for long-life applications of fuel cells.

[0063] In the description of this specification, the references to terms such as "one embodiment / mode," "some embodiments / modes," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment / mode or example is included in at least one embodiment / mode or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment / mode or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments / modes or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments / modes or examples described in this specification, as well as the features of different embodiments / modes or examples.

[0064] It should be noted that in this invention, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, technology, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, technology, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, technology, article, or apparatus that includes said element. In this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise expressly specified.

[0065] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features of the invention herein.

Claims

1. A catalyst layer slurry, characterized in that, It includes a platinum-based catalyst, a perfluorosulfonic acid ionomer, a solvent, and a hydroxy acid; wherein the hydroxy acid is an organic compound containing at least one hydroxyl group and at least one carboxyl group in its molecular formula.

2. The catalyst layer slurry as described in claim 1, characterized in that, The mass of the hydroxy acid is 0.1-5% of the mass of the perfluorosulfonic acid ionomer.

3. The catalyst layer slurry as described in claim 1, characterized in that, The hydroxy acid has 2-6 carbon atoms.

4. The catalyst layer slurry as described in claim 1, characterized in that, The hydroxy acid includes at least one of glycolic acid, lactic acid, citric acid, and gluconic acid.

5. The catalyst layer slurry as described in claim 1, characterized in that, The solvent includes at least one of isopropanol and water.

6. The catalyst layer slurry as described in claim 1, characterized in that, The platinum-based catalyst includes at least one of Pt / C, PtCo / C, PtNi / C, and PtCoMn / C.

7. A method for preparing a catalyst layer slurry as described in any one of claims 1-6, characterized in that, Includes the following steps: The platinum-based catalyst, the perfluorosulfonic acid ionomer, the solvent, and the hydroxy acid are mixed and dispersed to obtain the catalyst layer slurry.

8. The preparation method according to claim 7, characterized in that, The method for preparing the catalyst layer slurry includes: The platinum-based catalyst was mixed with a solvent to obtain a mixture. The mixture, hydroxy acid, and perfluorosulfonic acid ionomer are mixed and stirred in an ice-water bath to obtain the catalyst layer slurry.

9. A membrane electrode, characterized in that, It includes a proton exchange membrane and a catalyst layer coated on at least one side of the proton exchange membrane, the catalyst layer being formed by curing a catalyst layer slurry as described in any one of claims 1-6.

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

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