Sulfonated carbon material additive for fuel cells and method for preparing the same, catalyst slurry and membrane electrode

Abstract

This invention discloses a sulfonated carbon material additive for fuel cells, its preparation method, catalyst slurry, and membrane electrode assembly (MEA). The additive comprises a carbon-based support and perfluorosulfonic acid ionomer segments. In preparation, the carbon-based support is first mixed with a hydrogen peroxide solution and subjected to a hydrothermal reaction in a sealed reaction vessel to obtain a hydroxylated carbon material with oxygen-containing functional groups introduced onto its surface. Then, the hydroxylated carbon material is mixed with a perfluorosulfonic acid ionomer solution and subjected to a hydrothermal reaction. The oxygen-containing functional groups on the surface of the hydroxylated carbon material undergo a dehydration condensation reaction with the sulfonic acid groups at the ends of the perfluorosulfonic acid ionomer segments to generate the sulfonated carbon material additive. Through this method, this invention, by using hydroxylation pretreatment and hydrothermal homologous grafting with Nafion, constructs sulfonic acid groups on the surface of the carbon material with a chemical structure consistent with the MEA host ionomer, solving the performance degradation problem caused by material heterogeneity and interfacial incompatibility in traditional additives. This improves low-humidity performance without affecting high-humidity performance.

Description

Technical Field

[0001] This invention relates to the field of proton exchange membrane fuel cell technology, and particularly to a carbon-based additive for improving the performance of fuel cells under low humidity conditions, as well as a method for preparing the additive and a catalyst slurry and membrane electrode containing the additive. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) are considered highly promising clean energy conversion devices due to their high energy conversion efficiency, zero emissions, and rapid start-up at low temperatures. The membrane electrode assembly (MEA) is the core component of a PEMFC, serving as the site of electrochemical reactions.

[0003] In the field of PEMFCs, to improve the operational stability and durability of the membrane electrode, especially the cathode side, under low or variable humidity conditions, researchers commonly introduce additives with water-retaining or proton-conducting functions into the catalyst layer. Currently, the mainstream technical solutions mainly fall into the following two categories:

[0004] Category 1: Inorganic oxide additives:

[0005] Nanoparticles such as silicon dioxide (SiO2), titanium dioxide (TiO2), and aluminum oxide (Al2O3) have strong hydrophilicity and can retain moisture through physical adsorption, maintaining the wet state of the film and ionomer under low humidity conditions. Their preparation methods usually involve directly purchasing commercial nanoparticles or preparing them through wet chemical methods such as sol-gel method, and then blending them with catalyst slurry.

[0006] The second category is sulfonated carbon material additives:

[0007] To obtain better proton conduction assist capabilities, sulfonation treatment of carbon materials (such as carbon black, carbon nanotubes, and graphene) is a common method to introduce sulfonic acid groups (-SO3H) on their surface. Among them, the closest existing scheme is to use strong sulfonating agents such as concentrated sulfuric acid, fuming sulfuric acid, or chlorosulfonic acid to directly sulfonate carbon materials under high temperature conditions (such as 150-200℃).

[0008] However, the aforementioned existing technical solutions have significant defects and shortcomings in practical applications:

[0009] For the first type of inorganic additives: their drawbacks lie in the fact that the material is not from the same source as carbon-based catalysts and perfluorosulfonic acid (such as Nafion) ionomers, resulting in poor interfacial compatibility. This makes it easy to form discontinuous "islands" in the electrode, which not only makes dispersion difficult but also physically blocks the electron conduction path and gas diffusion pores. In addition, their hydrophilicity is physical adsorption, which may cause local over-wetting, which is not conducive to the timely discharge of liquid water in the gas diffusion layer and deteriorates mass transfer. More importantly, these inorganic materials are essentially proton insulators. Their introduction will block the continuous proton conduction network formed by the ionomer and increase the proton transport impedance.

[0010] For the second type of strong acid sulfonation method:

[0011] Its drawbacks are that the preparation method is too harsh, not gentle, and highly dangerous, requiring high standards for equipment (which must be resistant to strong acid corrosion) and operators; the harsh sulfonation conditions destroy the excellent conductive framework of the carbon material itself, resulting in a significant decrease in its conductivity; more importantly, although this method can graft a high content of sulfonic acid groups, its surface chemical properties are not the same as those of the Nafion ionomers used as proton conductors and binders in MEA slurries, and the interfacial bonding between the carbon support and the ionomer molecular chains still needs to be improved, failing to achieve optimal interfacial compatibility.

[0012] In summary, existing technical solutions generally suffer from the following common problems:

[0013] Poor material compatibility: The additives are not from the core materials of MEA (Pt / C catalyst, Nafion ionomer) in terms of chemical properties and surface characteristics, resulting in uneven dispersion in the slurry and weak interfacial bonding with the ionomer and catalyst. During battery operation, the additives are prone to agglomeration, migration or detachment, which damages the three-phase interface structure of the electrode.

[0014] While improving a single property such as water retention, many additives often impair other properties of the electrode, such as: hindering gas transport: additives clog electrode pores, hindering the diffusion of reactive gases (H2, O2) to the active site; affecting water management: additives change the hydrophilic / hydrophobic balance of the electrode, leading to poor drainage or localized dryness; hindering proton conduction: non-proton conductors or insulating additives can block or prolong the proton conduction path, increasing proton transport impedance.

[0015] The preparation process is complex: the existing synthesis methods for high-performance additives are complex, often involving strong acid and strong base treatment, high temperature and high pressure or multi-step reaction, which are highly dangerous and difficult to scale up.

[0016] Poor adaptability to operating conditions: Many additives may show certain gains under standard test conditions, but under actual dynamic operating conditions, the gains are unstable or even fail, especially in maintaining low interfacial impedance, which affects the dynamic response and long-term efficiency of the battery.

[0017] Therefore, there is an urgent need to provide a novel carbon-based additive that is highly compatible with the MEA system, has a mild and simple preparation process, and can improve low-humidity performance without compromising high-humidity performance and other key functions. Summary of the Invention

[0018] The main technical problem solved by this invention is to provide a sulfonated carbon material additive for fuel cells, its preparation method, catalyst slurry, and membrane electrode assembly. Through a two-step method of hydroxylation pretreatment and Nafion hydrothermal homologous grafting, sulfonic acid groups with the same chemical structure as the MEA host ionomer and connected by covalent bonds are constructed on the surface of the carbon material. This solves the problem of performance degradation caused by material heterogeneity and interfacial incompatibility of traditional additives in principle, while ensuring that low-humidity performance is improved without affecting high-humidity performance.

[0019] To solve the above-mentioned technical problems, one technical solution adopted by the present invention is: to provide a sulfonated carbon material additive for fuel cells, comprising: a carbon-based support; perfluorosulfonic acid ionomer segments, which are covalently grafted onto the surface of the carbon-based support; wherein the perfluorosulfonic acid ionomer segments are perfluorosulfonic acid ionomers that serve as proton conductors and / or binders in the catalyst layer of a proton exchange membrane fuel cell, so as to make them homologous with the catalyst layer material.

[0020] In a preferred embodiment of the present invention, the carbon-based support includes one or more of conductive carbon powder, carbon nanotubes, and mesoporous carbon.

[0021] In a preferred embodiment of the present invention, the covalent bond is formed by the dehydration condensation reaction between the oxygen-containing functional groups on the surface of the carbon-based support and the sulfonic acid groups at the end of the perfluorosulfonic acid ionomer chain segment.

[0022] In a preferred embodiment of the present invention, the covalent bond is an ester bond or an ether bond, and the perfluorosulfonic acid ionomer segment is a perfluorosulfonic acid ionomer side chain grafted onto the surface of a carbon-based support.

[0023] To solve the above-mentioned technical problems, another technical solution adopted by the present invention is: to provide a method for preparing sulfonated carbon material additives, comprising the following steps:

[0024] S1, Hydroxylation of carbon materials:

[0025] A carbon-based support was mixed with a hydrogen peroxide solution, and a first hydrothermal reaction was carried out in a sealed reaction vessel to obtain a hydroxylated carbon material with oxygen-containing functional groups introduced on its surface.

[0026] S2, homologous grafting:

[0027] The hydroxylated carbon material obtained in step S1 is mixed with a perfluorosulfonic acid ionomer solution and subjected to a second hydrothermal reaction in a sealed reaction vessel. The oxygen-containing functional groups on the surface of the hydroxylated carbon material undergo a dehydration condensation reaction with the sulfonic acid groups at the ends of the perfluorosulfonic acid ionomer chain segments to generate the sulfonated carbon material additive.

[0028] In a preferred embodiment of the present invention, the reaction temperature of the first hydrothermal reaction is 120-160°C, the reaction time is 2-12 h, and the mass fraction of the hydrogen peroxide solution is 10-30 wt%; the reaction temperature of the second hydrothermal reaction is 120-160°C, and the reaction time is 4-24 h.

[0029] In a preferred embodiment of the present invention, the perfluorosulfonic acid ionomer solution is an alcoholic solution or a water-alcoholic solution of the perfluorosulfonic acid ionomer, and the perfluorosulfonic acid ionomer is a Nafion-type ionomer.

[0030] In a preferred embodiment of the present invention, after step S2, a separation and filtration step is further included: the reaction product is washed until the conductivity is less than 5µS / cm, and then dehydrated and dried to obtain sulfonated carbon material additive.

[0031] To solve the above-mentioned technical problems, another technical solution adopted by the present invention is to provide a catalyst slurry for fuel cells, wherein the catalyst slurry includes the sulfonated carbon material additives mentioned above.

[0032] To solve the above-mentioned technical problems, another technical solution adopted by the present invention is: to provide a membrane electrode assembly (MEA) for a fuel cell, wherein the cathode catalyst layer and / or anode catalyst layer of the MEA comprises the catalyst slurry.

[0033] The beneficial effects of this invention are:

[0034] A two-step method, consisting of hydroxylation pretreatment and Nafion hydrothermal homologous grafting, was used to construct sulfonic acid groups on the surface of carbon materials with a chemical structure consistent with the ionomer of the membrane electrode substrate. This method offers the following advantages:

[0035] The reaction process is mild and environmentally friendly: both hydrothermal reactions are carried out at 120-160℃, which is far lower than the high temperature and severe conditions of the traditional strong acid sulfonation method, effectively protecting the conductive framework of carbon materials; hydrogen peroxide is used as the oxidant, and the by-products are only water and oxygen, eliminating nitrogen / sulfur waste gas, making the whole process environmentally friendly.

[0036] Achieving molecular-level homology: Nafion ionomers in the catalyst layer are directly used as sulfonation sources, and Nafion segments are grafted onto the carbon surface through covalent bonds, making the additives and ionomers completely identical in chemical nature. This fundamentally solves the problems of dispersion difficulties and interface defects caused by heterogeneous materials in traditional additives.

[0037] Improved performance in low humidity without affecting performance in high humidity: The grafted Nafion segments have both hydrophilicity and proton conductivity, effectively maintaining electrode humidity under low humidity conditions, while not causing water flooding or mass transfer obstruction under high humidity conditions. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein:

[0039] Figure 1 Polarization curves of four parallel comparison groups of membrane electrodes under condition a;

[0040] Figure 2 Electrochemical impedance spectroscopy for four parallel control groups under condition a;

[0041] Figure 3 Polarization curves of four parallel comparison groups of membrane electrodes under condition b;

[0042] Figure 4 Electrochemical impedance spectroscopy for four parallel control groups under condition b;

[0043] Figure 5 Polarization curves of four parallel comparison groups of membrane electrodes under condition c;

[0044] Figure 6 Electrochemical impedance spectroscopy for four parallel control groups under condition c;

[0045] Figure 7 This is a flowchart of the method for preparing sulfonated carbon material additives for fuel cells according to the present invention. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0047] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0048] The embodiments of the present invention include: Example 1:

[0049] A sulfonated carbon material additive for fuel cells includes: a carbon-based support and perfluorosulfonic acid ionomer segments, wherein the perfluorosulfonic acid ionomer segments are perfluorosulfonic acid ionomers that serve as proton conductors and / or binders in the catalyst layer of a proton exchange membrane fuel cell, and the perfluorosulfonic acid ionomer segments are covalently grafted onto the surface of the carbon-based support.

[0050] The carbon-based support is selected from one or more of conductive carbon powder, carbon nanotubes, and mesoporous carbon.

[0051] Furthermore, the covalent bond is formed by a dehydration condensation reaction between the oxygen-containing functional groups on the surface of the carbon-based support and the sulfonic acid groups at the ends of the perfluorosulfonic acid ionomer segments, specifically an ester bond or an ether bond.

[0052] Furthermore, the perfluorosulfonic acid ionomer segments are preferably perfluorosulfonic acid ionomer side chains grafted onto the surface of a carbon-based support to ensure that the sulfonic acid groups are connected to the carbon skeleton through flexible side chains, thus preserving its proton conduction function to the greatest extent.

[0053] The core of the above-mentioned method for preparing sulfonated carbon material additives lies in achieving chemical bonding with perfluorosulfonic acid ionomers on the surface of a carbon-based carrier through a two-step hydrothermal reaction, thereby preparing homologous sulfonated carbon material additives. The specific steps are as follows.

[0054] Step S1, hydroxylation (pre-activation) of carbon materials: This aims to introduce oxygen-containing active functional groups into the carbon-based support, providing reaction sites for subsequent grafting. The specific operation is as follows:

[0055] A carbon-based support is mixed with a hydrogen peroxide solution, and a first hydrothermal reaction is carried out in a sealed reaction vessel to achieve a mild and controllable oxidation process, resulting in a hydroxylated carbon material with oxygen-containing functional groups introduced on its surface.

[0056] In the first hydrothermal reaction, hydrogen peroxide decomposes under heating conditions to generate hydroxyl radicals (•OH). These radicals have strong oxidizing properties and attack the inert sp244 atoms on the surface of the carbon-based support. 2The carbon skeleton or defect sites are used to gradually introduce oxygen-containing functional groups such as hydroxyl (-OH), carbonyl (C=O), and even carboxyl (-COOH) groups onto the carbon surface, thereby achieving hydroxylation activation of the carbon-based support. The main chemical reaction formulas include:

[0057] Initial oxidation: C (carbon-based support) + H₂O₂ → C-OH + •OH;

[0058] Deep oxidation (carboxyl group formation pathway 1): C-OH + 2H₂O₂ → C-COOH + 2H₂O + O₂↑, or

[0059] Deep oxidation (carboxyl group formation pathway 2): C=O + H2O2 → C-COOH.

[0060] The key process parameters for this step are: the mass fraction of hydrogen peroxide solution is 10-30 wt%, the reaction time of the first hydrothermal reaction is 2-12 h, and the reaction temperature is 120-160 ℃.

[0061] Compared with traditional strong acid oxidation methods, the advantages of this step are:

[0062] The reaction conditions are mild: the reaction temperature (120-160℃) is much lower than that of concentrated nitric acid or concentrated sulfuric acid oxidation methods (usually >200℃ or even higher), which effectively protects the conductive framework of the carbon-based support and avoids structural damage caused by excessive oxidation.

[0063] The products are pure and environmentally friendly: the main reaction byproducts are water and oxygen, which avoids the large amount of nitrogen / sulfur oxide waste gas and acidic wastewater generated by strong acid oxidation, and the post-treatment is simple and environmentally friendly.

[0064] Controllable active sites: The generated surface hydroxyl and carboxyl groups are ideal active sites for subsequent condensation reactions, providing a good basis for homologous grafting in step S2.

[0065] Step S2, Homologous Grafting: This step is the core of the invention. The hydroxylated carbon material generated in the first step is directly reacted with a perfluorosulfonic acid ionomer solution under hydrothermal conditions. Through esterification and etherification reactions, perfluorosulfonic acid ionomer segments are covalently grafted onto the surface of the carbon material, thereby obtaining a sulfonated carbon material additive that is completely homologous to the catalyst layer. The perfluorosulfonic acid ionomer is preferably a Nafion-type ionomer. The specific operation is as follows:

[0066] The hydroxylated carbon material obtained in step S1 is mixed with a perfluorosulfonic acid ionomer solution, and a second hydrothermal reaction is carried out in a sealed reaction vessel. During the reaction, the oxygen-containing functional groups on the surface of the hydroxylated carbon material undergo a dehydration condensation reaction with the sulfonic acid groups at the ends of the perfluorosulfonic acid ionomer chain segments to form stable covalent bonds, generating the target product—sulfonated carbon material additive.

[0067] In the second hydrothermal reaction, the hydroxyl (-OH) or carboxyl (-COOH) groups on the surface of the carbon material undergo a dehydration condensation reaction with the sulfonic acid groups (-SO3H) at the end of the side chains of the perfluorosulfonic acid ionomer solution, forming covalent bonds. The main chemical reaction formulas include:

[0068] Esterification reaction (main pathway): C-COOH+HO-S(O)2-O-(Nafion side chain)→CC(O)OS(O)2-O-(Nafion)+H2O;

[0069] Etherification reaction: C-OH+HO-S(O)2-O-(Nafion side chain)→COS(O)2-O-(Nafion)+H2O.

[0070] This step utilizes homologous grafting: directly using Nafion ionomer, a key component of the MEA slurry, as the sulfonation source and linker molecule. After the reaction, the sulfonic acid groups form covalent bonds with the carbon skeleton through the flexible side chains of Nafion itself. Chemically, this is completely homologous to the Nafion binder used as a proton conductor and binder in the catalyst layer. This homologous structure achieves molecular-level interfacial compatibility between the additive and other components of the catalyst layer, fundamentally solving the problem of poor interfacial compatibility of traditional additives.

[0071] The key process parameters for this step are: the reaction temperature of the second hydrothermal reaction is 120-160℃, and the reaction time is 4-24h.

[0072] The advantage of this step is that:

[0073] The reaction is specific with few side reactions: the hydrothermal conditions (preferably 150℃) are much lower than the decomposition temperature of the Nafion backbone (>280℃), effectively inhibiting the excessive degradation of Nafion. The main side reactions involve only trace amounts of water molecules, resulting in a clean reaction pathway and high product purity.

[0074] The reaction conditions are extremely mild: it eliminates the use of highly toxic and corrosive reagents such as chlorosulfonic acid and fuming sulfuric acid used in the traditional sulfonation of carbon materials. The reaction is carried out in a single water-alcohol solvent system, which is safe, environmentally friendly and requires minimal equipment.

[0075] Excellent interface compatibility: Since the grafted Nafion segments are chemically identical to the Nafion ionomers in the catalyst slurry, the two can form a continuous and interconnected proton conduction network in the electrode, while avoiding the interface defects and compatibility problems caused by different sources of traditional additives.

[0076] Explanation of side reaction suppression: The potential side reactions mentioned above are mainly trace hydrolysis of Nafion side chains and possible excessive oxidation of carbon surfaces. However, this invention has suppressed these side reactions to a minimum by precisely controlling the reaction temperature, time and material ratio. Even if trace byproducts are generated, they can be completely removed by subsequent strict separation and filtration steps (washing with conductivity <5μS / cm as the standard), ensuring the high purity and high performance of the final product.

[0077] To further improve production purity, a separation and filtration process is performed after step S2. The specific operation is as follows:

[0078] The reaction product obtained in step S2 is separated by centrifugation or filtration, and repeatedly washed with an appropriate washing medium until the conductivity of the washing liquid is lower than 5 μS / cm, so as to completely remove unreacted perfluorosulfonic acid ionomers, possible by-products and other impurities. Finally, the separated and filtered product is dehydrated and dried to obtain high-purity sulfonated carbon material additives. Example 2:

[0079] A sulfonated carbon material additive based on solid carbon powder, the preparation steps of which are as follows:

[0080] S1, Hydroxylation (pre-activation) of carbon materials:

[0081] S11, Dispersion preparation:

[0082] Accurately weigh 0.4g of high specific surface area conductive solid carbon powder, place it in a clean container, and add 45g of high-purity deionized water and 5g of anhydrous ethanol in sequence.

[0083] The resistivity of high-purity deionized water is ≥18.2 MΩ·cm. The addition of ethanol is intended to improve the wettability of carbon black, prevent it from floating, and promote its uniform dispersion in the subsequent process. Furthermore, a water-ethanol mixed solvent system is constructed, and the hydroxylation effect is significantly improved by regulating solvent polarity, proton transfer efficiency, and free radical reaction.

[0084] S12, pre-dispersion:

[0085] The mixture was placed in an ice-water bath and pre-dispersed for 30 minutes at 5000 rpm using a high-speed shear disperser to form a uniform and stable preliminary dispersion slurry.

[0086] S13, initiated by oxidation reaction:

[0087] Under continuous stirring, 4.0 g of 30 wt% hydrogen peroxide solution was slowly added dropwise to the slurry, with the mass ratio of conductive solid carbon powder to hydrogen peroxide being 1:10 to ensure sufficient oxidation. The dropping speed was strictly controlled during the dropping process to avoid local over-concentration leading to uneven dispersion. After the dropping was completed, stirring was continued for 5 minutes to ensure that the reactants were fully mixed.

[0088] S14, hydrothermal hydroxylation reaction:

[0089] Transfer the above mixture into a 100mL polytetrafluoroethylene liner, and control the filling degree to be less than 70%, because the decomposition of hydrogen peroxide will produce a large amount of gas, and sufficient space needs to be reserved.

[0090] The liner is sealed in a stainless steel reactor (maximum pressure resistance ≤6MPa, equipped with a pressure relief hole), placed in a programmable temperature controlled oven, heated to 150℃ at a heating rate of 5℃ / min, preferably 140-160℃, and reacted at a constant temperature for 10h, preferably 9-11h.

[0091] S15, Product separation and primary filtration:

[0092] S15a. Selection of separation method: Since solid carbon powder usually forms micron-sized agglomerates that are easy to settle after hydrothermal reaction, it is preferred to use a sand core funnel (G5 or G6 specification) for suction filtration to achieve rapid and efficient solid-liquid separation.

[0093] S15b Washing procedure: Wash the filter cake thoroughly with warm deionized water at about 50°C to remove residual hydrogen peroxide, small molecule organic acids (such as formic acid and acetic acid) generated in the reaction, and soluble ions; then wash twice with anhydrous ethanol to replace water and remove some organic residues; the above washing process can be repeated 1-2 times until the filtrate is clear, transparent and close to neutral.

[0094] S16, intermediate acquisition: After washing, wet hydroxylated carbon powder is obtained, which can be directly used in the next reaction to maintain the reactivity of the surface active groups.

[0095] S2, homologous grafting, i.e., the sulfonation treatment of hydroxylated toner:

[0096] S21, Preparation of reaction solution:

[0097] The above wet hydroxylated carbon powder was transferred to a reaction vessel, and 40.0g of Nafion aqueous alcohol solution with a solid content of 5% (containing about 2g of solid Nafion) was added. To ensure sufficient sulfonation, the mass ratio of carbon powder to dry Nafion was controlled to be 1:5-1:10 (considering material loss during the experiment, this embodiment uses a ratio of no less than 1:5). The mixture was initially mixed by magnetic stirring (about 500 rpm).

[0098] S22, homogenization treatment:

[0099] The mixture was placed in an ultrasonic cell disruptor and ultrasonically treated for 30 minutes in an ice-water bath with a pulse mode of 500W, working for 2 seconds and then intermittent for 2 seconds, to form a highly uniform and stable black suspension.

[0100] S23, hydrothermal sulfonation reaction:

[0101] The homogenized suspension was transferred to a clean 100 mL polytetrafluoroethylene liner, with the filling degree controlled to be ≤80%. After sealing the reactor, it was placed in an oven and the sulfonation grafting reaction was carried out using the same heating program as the hydroxylation step (heating to 150 °C at 5 °C / min and holding for 10 h).

[0102] S24, Deep filtration of the product:

[0103] S24a, Solid-liquid separation: After sulfonation, the product system becomes more stable due to the dispersing effect of Nafion, making it difficult to separate by ordinary filtration.

[0104] This embodiment uses membrane filtration for efficient separation. A filter device is assembled using aqueous or organic microporous membranes (pore size 0.22µm or 0.45µm) for suction filtration. This method can effectively trap nanoscale particles, but care must be taken to prevent membrane clogging.

[0105] Alternatively, high-speed centrifugation can be used as an alternative: transfer the reaction mixture to a centrifuge tube and centrifuge at 12,000 rpm for 15 minutes.

[0106] S24b, Washing and Filtration: Add a large amount of deionized water to the solid obtained in the previous step, redisperse it by vortexing or brief sonication, and then centrifuge or filter it again. Repeat the above washing process at least 10 times until the last washing solution is neutral and the conductivity is less than 5 μS / cm. Finally, wash twice with anhydrous ethanol to remove water.

[0107] S25, Drying and Post-treatment:

[0108] The pure wet filter cake was placed in a freeze dryer and freeze-dried for 8 hours at -50℃ to 50℃ and a vacuum degree of less than 100kPa to obtain a fluffy black solid. After being gently ground in an agate mortar, it was passed through a 100-mesh (150μm) sieve to obtain the final sulfonated carbon powder additive, which was then sealed and stored in a desiccator. Example 3:

[0109] A sulfonated carbon material additive based on a carbon powder and carbon nanotube composite carrier is described in this embodiment. The specific preparation steps are the same as those in Example 2, except that the composition of the starting materials and the corresponding separation and filtration are different.

[0110] First, raw material preparation: accurately weigh 0.32g of high specific surface area conductive solid carbon powder and 0.08g of multi-walled carbon nanotubes (outer diameter <15nm, length <30μm), and mix them evenly by mechanical dry mixing. The mass ratio of carbon powder to carbon nanotubes is 8:2.

[0111] Then, hydroxylation treatment: The above mixed carbon material is subjected to hydroxylation reaction according to steps S11 to S14 of Example 2, with the reaction conditions and parameters being exactly the same.

[0112] Secondly, separation optimization: Due to the presence of carbon nanotubes, the mixture after the reaction does not easily settle naturally. Therefore, it is no longer suitable to use a sand core funnel during the separation process, as it is easy for carbon nanotubes to penetrate the filter or clog the filter plate. At this time, the membrane filtration method or high-speed centrifugation method recommended in step S24a of Example 2 is used for separation and washing to ensure product collection rate and separation efficiency.

[0113] Finally, the subsequent steps, such as sulfonation reaction, deep separation filtration (using centrifugation or membrane filtration) to freeze drying, grinding and sieving, are all completely consistent with step S2 of Example 1, thereby obtaining a sulfonated carbon material additive composed of carbon powder and carbon nanotubes. Example 4:

[0114] A sulfonated carbon material additive based on commercially available hydroxylated carbon nanotubes, the preparation steps of which are as follows:

[0115] First, raw material preparation:

[0116] Accurately weigh 0.4g of commercially available hydroxylated multi-walled carbon nanotubes (hydroxyl content ≥2.0wt%, outer diameter <15nm, length <30μm);

[0117] Secondly, sulfonation reaction and separation filtration:

[0118] The hydroxylated carbon nanotubes were directly mixed with 40.0 g of Nafion aqueous alcohol solution with a solid content of 5%. From mixing, ultrasonic homogenization, hydrothermal reaction to subsequent deep separation filtration (using high-speed centrifugation or membrane filtration), freeze drying, grinding and sieving, all operating conditions and process parameters were exactly the same as in step S2 of Example 1.

[0119] Because commercially available hydroxylated multi-walled carbon nanotubes exhibit excellent dispersibility in water-alcohol systems and readily form stable colloidal systems, high-speed centrifugation or membrane filtration must be employed in the separation and filtration steps to ensure product collection rate and purity.

[0120] Further verification of the effectiveness of hydrothermal hydroxylation treatment:

[0121] It should be noted that the grafting in this invention is not solely based on the absolute number of carboxyl groups produced in the first hydrothermal reaction. The key is that the generation of sufficient oxygen-containing functional groups (especially hydroxyl groups generated in the initial oxidation) on the surface of the carbon material through the first hydrothermal oxidation reaction does not depend on the absolute number of carboxyl groups formed by deep oxidation.

[0122] Subsequently, in the second hydrothermal reaction, these active sites undergo complex interfacial interactions with the Nafion solution under a closed heating environment, providing sufficient landing sites for the anchoring of Nafion segments, and ultimately firmly grafting the sulfonic acid groups in Nafion onto the carbon skeleton surface.

[0123] To more intuitively understand the actual treatment effect of hydrothermal carboxylation, supplementary verification tests were conducted on the wettability (contact angle) of the carbon materials prepared by hydroxylation treatment in Examples 1-2, the commercial hydroxylated carbon nanotubes used in Example 3, and the carbon materials obtained from an untreated comparative example. The test method is as follows: The untreated carbon materials of each example and comparative example were coated onto a carbon paper substrate, and the static contact angle of deionized water on its surface was measured by an optical contact angle meter. The test results are shown in Table 1 below.

[0124] Table 1, Contact Angle Data:

[0125]

[0126] Analysis of the data in the table above shows that:

[0127] The contact angle of Comparative Example 1 (untreated carbon material) is as high as 144.73°, which is greater than 140°, and belongs to a typical superhydrophobic surface;

[0128] The contact angles of the carbon materials prepared after the hydrothermal hydroxylation process decreased sharply, dropping to 121.55°, 118.76° and 105.49°, respectively.

[0129] The significant reduction in contact angle demonstrates that the addition of hydrophilic groups such as hydroxyl groups makes the overall surface of the carbon material hydrophilic, directly confirming the successful introduction of surface functional groups.

[0130] Further, regarding the effectiveness verification of homologous grafting:

[0131] In a hydrothermal environment, the etherification reaction of this invention is a sulfonic acid group grafting process driven by multiple factors, including acidic autocatalysis, esterification dominance, and physical entanglement, rather than a simple intermolecular dehydration etherification. Specifically:

[0132] Catalytic effect under acidic environment: The raw material used in this invention is Nafion (perfluorosulfonic acid resin solution). Perfluorosulfonic acid resin is the strongest known solid superacid material. Its sulfonic acid groups provide an acidic environment. Under hydrothermal reaction (120-160℃), the acidic environment catalyzes the hydroxyl groups on the surface of the carbon material to undergo ring-opening or nucleophilic substitution reactions with the ether bonds (-O-CF2-) in the side chain of Nafion perfluoroalkyl ether, thereby achieving grafting.

[0133] Esterification with carboxyl groups: Carboxyl groups can undergo dehydration esterification with Nafion's sulfonic acid groups to form a mixed anhydride bond of the -COO-SO2- type, which can also stably connect the sulfonic acid groups.

[0134] Synergy of physical entanglement and chemical bonding: Under hydrothermal conditions, the mobility of Nafion chain segments is enhanced, allowing them to penetrate deeper into the pores of carbon materials. While the aforementioned chemical bonding occurs, physical entanglement and adsorption may also take place, forming a stable composite structure.

[0135] To more intuitively understand the actual effect of homologous grafting and the changes in the chemical bonding state of carbon material surface, sulfonated carbon material additives obtained according to the preparation methods described in Examples 1-3, and an untreated comparative example 1 (original carbon material) were subjected to supplementary verification tests by infrared spectroscopy (FTIR).

[0136] Test method: The carbon material samples obtained in each example and comparative example were washed until the conductivity of the filtrate was below 5 µS / cm and thoroughly dried. Then, the samples were scanned in transmission mode on a Fourier transform infrared spectrometer using the potassium bromide pellet method, with a scanning range of 4000-400 cm⁻¹. -1 The test results are shown in Table 2-4 below.

[0137] Table 2, Infrared Spectral Data (Carbonyl):

[0138]

[0139] Table 3, Infrared Spectral Data (Ether Bonds):

[0140]

[0141] Table 4, Infrared Spectral Data (Hydroxyl):

[0142]

[0143] Analysis of the data in Table 2-4 above shows that:

[0144] Based on the characteristic absorption peaks of the infrared spectrum, no significant polar functional group characteristic absorption peaks were observed in the infrared spectrum of Comparative Example 1 (original untreated carbon material) in either the functional group region or the fingerprint region.

[0145] Examples 1-3 at wavelengths of 3630-3200cm -1 This proves that the presence of a -OH absorption peak indicates that the carbon material has increased -OH content after treatment.

[0146] At wavelengths of 1710-1680 cm -1 A stretching vibration peak of the carbonyl group was observed at a wavelength of 1000-1100 cm⁻¹. -1 The presence of ether bonds indicates that the carbon material, after treatment, gained ester functional groups (-COO-), ether bonds (-O-), and hydroxyl functional groups. This demonstrates that esterification and etherification reactions occurred on the surface of the carbon material under the catalysis of perfluorosulfonic acid. Example 5:

[0147] Membrane electrode fabrication and performance comparison testing:

[0148] Based on the preparation of the above-mentioned sulfonated carbon material additive, in order to verify the actual effect of the sulfonated carbon material additive of the present invention in proton exchange membrane fuel cells, a membrane electrode (MEA) with a reaction area of ​​25 cm² was prepared according to the following standardized process, and a systematic performance comparison test was conducted.

[0149] (I) Experimental Materials and Grouping:

[0150] To eliminate the impact of batch variations in raw materials on test results, all comparative experiments used standardized membrane electrode materials of the same brand and batch, specifically including:

[0151] Catalyst: 60% Pt / C catalyst (commercial source, 60wt% platinum loading);

[0152] Ionomer: 5wt% Nafion solution;

[0153] Proton exchange membrane: perfluorosulfonic acid proton exchange membrane (12 μm thick);

[0154] Solvents: Isopropanol, deionized water (resistivity ≥ 18.2 MΩ·cm);

[0155] Gas diffusion layer: carbon paper-based gas diffusion layer (GDL).

[0156] Experimental Groups: Four parallel control groups were set up, with the three sulfonated carbon materials prepared in Examples 2, 3, and 4 used as additives in the experimental groups.

[0157] Control group A consisted of ordinary catalyst slurry without any additives;

[0158] Experimental group B consisted of sulfonated carbon material prepared based on solid carbon powder, as described in Example 2.

[0159] Experimental group C consists of sulfonated carbon material prepared based on a carbon powder and carbon nanotube composite carrier as described in Example 3.

[0160] Experimental group D consists of sulfonated carbon materials prepared by direct sulfonation of commercially available hydroxylated carbon nanotubes, as described in Example 4.

[0161] When the additive is added, the mass of the sulfonated carbon material is included in the calculation of the "IC ratio" in the slurry formulation to ensure that each slurry has the exact same ratio of ionomer to total carbon carrier (total carbon carrier = carbon in Pt / C + additive carbon).

[0162] (II) Catalyst slurry preparation and CCM spraying:

[0163] 1. Slurry preparation and dispersion:

[0164] Based on the above grouping, four catalyst slurries were prepared using the exact same I / C ratio (e.g., I / C = 0.75), solid content (e.g., 1.0 wt%), and solvent ratio (e.g., deionized water: isopropanol = 1:1).

[0165] The preparation process is as follows: Take the calculated amount of Pt / C catalyst, and add the calculated amount of additive (control group A does not add additive), deionized water, Nafion solution, and isopropanol in sequence;

[0166] Each group of slurries was subjected to the same high-speed mechanical stirring for 30 minutes, ultrasonic cell disruption for 30 minutes, and low-speed stirring and maturation for 2-12 hours to ensure uniform dispersion and consistent rheological properties.

[0167] 2. Catalyst spraying:

[0168] Using an ultrasonic spraying device, the above slurry was sprayed onto both sides of the proton exchange membrane. The spraying parameters were: 0.1 mg / cm² for the anode platinum loading and 0.3 mg / cm² for the cathode platinum loading. Four CCMs with the same specifications were obtained.

[0169] (III) Membrane electrode assembly and activation:

[0170] Hot-press encapsulation: The above four CCMs and the matching gas diffusion layer are subjected to limiting hot-pressing under the same working conditions. The hot-pressing temperature is 120℃, the limiting hot-pressing height is (according to the compression ratio guided by GDL manufacturer), and the hot-pressing pressure is 1T, to encapsulate four complete membrane electrodes.

[0171] Single cell assembly: These four MEAs are respectively installed into four identical single cell test fixtures to ensure that the gas diffusion layer compression is consistent. They are numbered sequentially as single cells A, B, C, and D, corresponding to the four groups of slurries mentioned above.

[0172] Standardized activation: Four single cells were synchronously activated on the same test platform under the same activation conditions. The activation conditions were as follows:

[0173] Battery temperature 80℃, anode and cathode humidification 100% RH, anode and cathode flow rates in metering ratio mode (1.5 / 2.5), back pressure 2000KPa;

[0174] Activation procedure: Scan voltage mode, starting from the initial voltage and gradually scanning down to 0.5V, 0.02V per step, with each potential held for 1 minute, for 10 cycles. Synchronous activation ensures that the initial state of the four batteries is consistent.

[0175] (iv) Performance comparison test:

[0176] After activation, the four single cells were subjected to the following standardized performance comparison test to quantify the technical effects of the present invention:

[0177] 1. Polarization curve test: The current density curves of four single cells were measured under three different humidity conditions (a, b, c).

[0178] a. 100% humidification: Battery temperature 75℃, anode / cathode dew point temperature 75℃, anode / cathode back pressure 200Kpa;

[0179] b. 40% humidification: Battery temperature 80℃, anode / cathode dew point temperature 58.91℃, anode / cathode back pressure 150Kpa;

[0180] c. 30% humidification: Battery temperature 80℃, anode / cathode dew point temperature 52.86℃, anode / cathode back pressure 150Kpa;

[0181] High-frequency impedance testing: Under the above three different test conditions and at rated current, the electrochemical impedance spectra of each MEA were measured.

[0182] a. 100% humidification: Rated current 30A, amplitude 5% of DC current percentage;

[0183] b. 40% humidification: Rated current 15A, amplitude 5% of DC current percentage;

[0184] c. 30% humidification: Rated current 15A, amplitude 5% of DC current percentage.

[0185] Test data presentation and analysis:

[0186] To systematically verify the effect of the sulfonated carbon material additive of the present invention on the performance of the membrane electrode, polarization curves and electrochemical impedance spectroscopy were performed on control group A (without additive) and experimental groups B, C, and D (with the sulfonated carbon material prepared in Examples 2-4 added, respectively) under three conditions: 100% humidification (high humidity), 40% humidification (medium-low humidity), and 30% humidification (low humidity). The test data are presented in comparative graphs ( Figures 1 to 6 Presented in the form of ), the specific analysis is as follows.

[0187] Condition a, 100% humidification (high humidity condition):

[0188] Figure 1 The graph shows the polarization curves of four parallel comparison groups of membrane electrodes under condition a. From the graph, we can see that:

[0189] In the activation polarization and ohmic polarization regions (low to medium current density regions), the performance of experimental groups B, C, and D was lower than that of control group A;

[0190] In the mass transfer polarization region (high current density region), the performance of experimental groups B, C, and D is higher than that of control group A;

[0191] Overall performance variation ranges from -10% to 2.4%. Excluding differences at the engineering scale, performance variation under high conditions is relatively small.

[0192] Figure 2 The figures show the electrochemical impedance spectroscopy of four parallel control groups under condition a, with a rated current of 30 A (current density of 1200 mA / cm²). At this point, the potential drops to the ohmic polarization region, as can be seen from the figure:

[0193] Charge transfer impedance R of experimental groups B, C, and D ct Slightly higher than control group A, but the total impedance of the four groups was relatively similar.

[0194] Therefore, under high humidity conditions, the addition of additives thickens the catalyst layer, alters the electrode's microstructure, and leads to an increase in charge transfer impedance R. ct The overall impedance difference was small, but the macroscopic battery performance was not significantly affected. This indicates that the additive of the present invention has good compatibility under high humidity conditions and will not damage the battery performance.

[0195] Condition b, 40% humidification (medium to low humidity conditions):

[0196] Figure 3 The graph shows the polarization curves of four parallel comparison groups of membrane electrodes under condition b. From the graph, we can see that:

[0197] In the high-potential region, the performance of experimental groups B, C, and D was approximately 90% higher than that of control group A.

[0198] In the low potential region, the performance of experimental groups B, C, and D was improved by approximately 40% compared to the control group A;

[0199] All three experimental groups significantly outperformed the control group across the entire current density range.

[0200] Figure 4 The figures show the electrochemical impedance spectroscopy of four parallel control groups under condition b, with a rated current of 15 A (current density of 600 mA / cm²). At this point, the potential drops to the ohmic polarization region, as can be seen from the graph:

[0201] The high-frequency impedance of control group A was significantly greater than that of experimental groups B, C, and D;

[0202] High-frequency charge transfer impedance R of control group A ct The semicircle diameter from high frequency to mid frequency is larger than that of experimental groups B, C, and D;

[0203] The impedance spectrum morphology of experimental groups B, C, and D is similar, all showing low impedance values.

[0204] Therefore, under 40% low-humidity conditions, control group A, lacking effective water retention assistance, experienced insufficient moisture inside the membrane electrode, leading to a decrease in the proton conductivity of the ionomer and a significant performance degradation. In contrast, experimental groups B, C, and D, which incorporated the sulfonated carbon material of this invention, exhibited excellent hydrophilicity and proton conductivity due to the Nafion segments grafted onto their surfaces. This effectively maintained the internal humidity level of the electrode, significantly reducing charge transfer impedance and ohmic impedance, thereby substantially improving the battery performance under low-humidity conditions. The impedance spectroscopy results directly revealed the mechanism of action of the additive: by maintaining electrode humidity, reducing R... ct Improve performance.

[0205] Condition c, 30% humidification (low humidity condition):

[0206] Figure 5 The graph shows the polarization curves of four parallel comparison groups of membrane electrodes under condition c. The graph shows that:

[0207] In the high-potential region, the performance of experimental groups B, C, and D was approximately 10% higher than that of control group A;

[0208] In the low potential region, the performance of experimental groups B, C, and D was approximately 20% higher than that of control group A.

[0209] All three experimental groups outperformed the control group across the entire current density range.

[0210] Figure 6 The figures show the electrochemical impedance spectroscopy of four parallel control groups under condition c, with a rated current of 15 A (current density of 600 mA / cm²). At this point, the potential drops to the ohmic polarization region, as can be seen from the figure:

[0211] The high-frequency impedance and the semi-circular diameter from high to mid frequency of control group A are greater than those of groups B, C, and D.

[0212] The impedance spectrum morphology of experimental groups B, C, and D was similar, and their impedance values ​​were significantly lower than those of the control group.

[0213] Therefore, it can be seen that when the relative humidity is further reduced to the extreme low humidity condition of 30%, the performance of control group A has been severely degraded. Although experimental groups B, C, and D can still maintain a certain advantage, due to the extreme lack of environmental moisture, the water retention capacity of the additives is also close to its limit. Therefore, the performance improvement is narrower than that under the 40% humidification condition. Even so, under the extreme low humidity condition of 30%, the additive of this invention can still effectively maintain the internal humidity of the electrode and reduce R. ct This improved performance and proved its applicability over a wide humidity range.

[0214] In summary, under 100% humidification conditions, the overall performance is not significantly affected (-10% to 2.4%), and the difference in total impedance is small; under 40% humidification conditions, the overall performance is significantly improved (40% to 90%), and the charge transfer impedance R0 is significantly increased. ct The ohmic impedance is reduced; under 30% humidification conditions, the overall performance is significantly improved (10%–20%), and the charge transfer impedance R0 is reduced. ct The ohmic impedance is still lower than that of the control group.

[0215] Therefore, the sulfonated carbon material additive prepared by this invention possesses the following characteristics:

[0216] Wide humidity range adaptability: It does not damage battery performance under high humidity conditions, and significantly improves performance under medium and low humidity conditions, demonstrating excellent adaptability to wide humidity conditions.

[0217] The mechanism of action is clear: through electrochemical impedance spectroscopy verification, the efficacy of the additive comes from its ability to reduce charge transfer impedance and ohmic impedance, which is highly consistent with the water retention and proton conduction assist function provided by the Nafion segments grafted on the surface of the additive.

[0218] Good process versatility: The additives prepared in the three examples showed similar trends in performance improvement, proving that the preparation method of the present invention has good versatility and scalability.

[0219] The beneficial effects of the sulfonated carbon material additive for fuel cells, its preparation method, and membrane electrode of this invention are:

[0220] A two-step reaction method, consisting of hydroxylation pretreatment and Nafion hydrothermal homologous grafting, was used to construct covalently linked sulfonic acid groups on the surface of carbon materials, exhibiting a chemical structure identical to that of the membrane electrode host ionomer. This reaction has the following significant advantages:

[0221] Mild reaction conditions: Both hydrothermal reactions are carried out under mild conditions of 120-160℃, which is much lower than the high temperature (usually >200℃) and violent reaction conditions required by the traditional strong acid sulfonation method. This effectively protects the conductive framework of carbon materials, avoids structural damage caused by excessive oxidation, and greatly reduces equipment requirements and energy consumption.

[0222] The reaction process is environmentally friendly: the first step of hydroxylation uses hydrogen peroxide as an oxidant, and the main byproducts are only water and oxygen, which completely eliminates the large amount of nitrogen / sulfur oxide waste gas and acidic wastewater generated by the traditional strong acid sulfonation method. The second step of homologous grafting is carried out in a single water-alcohol solvent system. The reaction path is clean, with very few side reactions, and the whole process is environmentally friendly.

[0223] The reaction mechanism is clear: the first step introduces oxygen-containing functional groups by attacking the carbon surface with hydroxyl radicals, and the second step covalently grafts Nafion segments onto the carbon surface through esterification / etherification reaction. The chemical mechanism of the two-step reaction is clear and highly controllable.

[0224] Homogenization of additives and catalyst layer substrate materials was achieved:

[0225] Chemically homologous: Nafion ionomer, a key component in the membrane electrode catalyst slurry, is directly used as the sulfonation source and linking molecule. Nafion segments are grafted onto the surface of carbon materials through covalent bonds. After the reaction, the sulfonic acid groups are connected to the carbon skeleton through the flexible side chains of Nafion itself. In chemical essence, it is completely consistent with the Nafion ionomer used as a proton conductor and binder in the catalyst layer.

[0226] Excellent interface compatibility: This homology enables molecular-level interface compatibility between the additive and the Nafion ionomer in the catalyst layer, fundamentally solving the problems of dispersion difficulties, agglomeration and detachment, and interface defects caused by the heterogeneity of materials and interface incompatibility of traditional additives (such as inorganic oxides, strong acid sulfonated carbon, etc.).

[0227] Synergistic enhancement of function: The grafted Nafion segments retain the proton conduction ability of the sulfonic acid groups and can form a continuous proton transport channel with the ionomer network in the catalyst layer through their flexible side chains, thus realizing the enhancement effect of additives and host materials.

[0228] It can improve low-humidity performance without affecting high-humidity performance:

[0229] The Nafion segments grafted onto the surface of the additive have good hydrophilicity and proton conductivity, effectively maintaining the humidity level inside the electrode and the proton conduction function of the ionomer under low humidity conditions. The additive will not cause problems such as water flooding or mass transfer obstruction under high humidity conditions, thus improving low humidity performance without affecting high humidity performance.

[0230] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A sulfonated carbon material additive for a fuel cell, characterized by, include: Carbon-based carrier; Perfluorosulfonic acid ionomer segments are covalently grafted onto the surface of the carbon-based support; The perfluorosulfonic acid ionomer segment is a perfluorosulfonic acid ionomer that serves as a proton conductor and / or binder in the catalyst layer of a proton exchange membrane fuel cell, so that it is homologous to the catalyst layer material. The covalent bond is formed by the dehydration condensation reaction between the oxygen-containing functional groups on the surface of the carbon-based support and the sulfonic acid groups at the end of the perfluorosulfonic acid ionomer chain segment, wherein the perfluorosulfonic acid ionomer chain segment is a perfluorosulfonic acid ionomer side chain grafted onto the surface of the carbon-based support.

2. The sulfonated carbon material additive for a fuel cell according to claim 1, characterized by, The carbon-based carrier includes one or more of conductive carbon powder, carbon nanotubes, and mesoporous carbon.

3. The sulfonated carbon material additive for a fuel cell according to claim 1, characterized by, The covalent bond is an ester bond or an ether bond.

4. A method for producing a sulfonated carbon material additive as claimed in any one of claims 1 to 3, characterized by, Includes the following steps: S1, Hydroxylation of carbon materials: A carbon-based support was mixed with a hydrogen peroxide solution, and a first hydrothermal reaction was carried out in a sealed reaction vessel to obtain a hydroxylated carbon material with oxygen-containing functional groups introduced on its surface. S2, homologous grafting: The hydroxylated carbon material obtained in step S1 is mixed with a perfluorosulfonic acid ionomer solution and subjected to a second hydrothermal reaction in a sealed reaction vessel. The oxygen-containing functional groups on the surface of the hydroxylated carbon material undergo a dehydration condensation reaction with the sulfonic acid groups at the ends of the perfluorosulfonic acid ionomer chain segments to generate the sulfonated carbon material additive.

5. The method for preparing the sulfonated carbon material additive according to claim 4, characterized in that, The first hydrothermal reaction has a reaction temperature of 120-160℃ and a reaction time of 2-12h, and the hydrogen peroxide solution has a mass fraction of 10-30wt%; the second hydrothermal reaction has a reaction temperature of 120-160℃ and a reaction time of 4-24h.

6. The method for preparing sulfonated carbon material additive according to claim 4, characterized in that, The perfluorosulfonic acid ionomer solution is an alcoholic or aqueous alcoholic solution of the perfluorosulfonic acid ionomer, and the perfluorosulfonic acid ionomer is a Nafion-type ionomer.

7. The method for preparing sulfonated carbon material additive according to claim 4, characterized in that, Step S2 is followed by a separation and filtration step: the reaction product is washed until the conductivity is below 5 µS / cm, and then dehydrated and dried to obtain sulfonated carbon material additive.

8. A catalyst slurry for a fuel cell, characterized by, The catalyst slurry includes the sulfonated carbon material additive as described in any one of claims 1-3.

9. A membrane electrode for a fuel cell, characterized by, The cathode catalyst layer and / or anode catalyst layer of the membrane electrode comprise the catalyst slurry as described in claim 8.

Images