Platinum catalyst for fuel cell as well as preparation method and application of platinum catalyst

Abstract

The invention relates to a platinum catalyst for a fuel cell as well as a preparation method and application of the platinum catalyst. The platinum catalyst comprises a nitrogen-phosphorus co-doped porous carbon carrier and sub-nano platinum particles loaded on the surface and in pores of the nitrogen-phosphorus co-doped porous carbon carrier. The preparation method comprises the following steps: mixing a nitrogen-containing organic matter, a phosphorus-containing compound and a pore-forming agent, drying, and carrying out pyrolysis carbonization treatment in an oxygen-free environment to generate the nitrogen-phosphorus co-doped porous carbon carrier; in the presence of organic alkali, platinum salt and a thiol compound are subjected to a coordination reaction, and the platinum organic complex is prepared; the preparation method comprises the following steps: dissolving a platinum organic complex in a solvent containing a thiol compound to form platinum precursor sol; enabling the nitrogen-phosphorus co-doped porous carbon carrier to adsorb the platinum precursor sol, and collecting a composite material through centrifugal filtration; and carrying out reduction treatment on the composite material to obtain the platinum catalyst. The mass activity of the platinum catalyst prepared by the invention can reach 246-272 A / g; and when the platinum load is 0.2 mg / cm < 2 >, the performance of the membrane electrode under high current density is remarkably improved, namely, the performance is improved by 37mV under 2A / cm < 2 >.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fuel cells, in particular to a platinum catalyst for fuel cells and a preparation method and application thereof. BACKGROUND

[0002] Proton exchange membrane fuel cell (PEMFC) is a kind of high-efficiency clean energy device taking hydrogen as fuel and oxygen as oxidant, and its core structure is composed of proton exchange membrane, anode catalyst layer, cathode catalyst layer and bipolar plate. The catalyst layer supports active substances through porous structure and plays a key role in electrochemical reaction: the anode catalyst promotes hydrogen oxidation reaction (HOR), and the cathode catalyst accelerates oxygen reduction reaction (ORR). Among them, platinum group metal (PGM) catalyst is widely used due to its high activity and stability, but its high cost and resource scarcity significantly restrict the commercialization process of PEMFC.

[0003] Currently, reducing the catalyst load in the cell without sacrificing overall performance is the current research focus. According to the oxygen reduction reaction rule, if the platinum dosage is reduced by half under the condition that the catalyst particle size and platinum atom utilization rate remain unchanged, the cell voltage will only decrease by about 21 millivolts. But the actual research found that when the cathode platinum load is less than 0.2 mg / cm 2 , the hydrogen-oxygen fuel cell will have additional performance loss. Especially in the high current area (>1.5 A·cm -2 ) of hydrogen-air fuel cell, this performance decline is more obvious, the main reason is that the local oxygen transmission resistance increases significantly, which has been confirmed by the expansion of the low-frequency impedance arc in the electrical test. Specifically, when the catalyst dosage is reduced, the amount of oxygen that a single platinum particle needs to handle increases, leading to the problem of insufficient oxygen supply appearing in advance. Studies have shown that the local mass transfer resistance is inversely proportional to the platinum load: when the platinum load is reduced to 0.12 mg / cm 2 , the local mass transfer resistance accounts for more than 50% of the total resistance at high current density, becoming a key bottleneck for further reducing platinum load.

[0004] To solve the problem of local mass transfer, the ideal solution is to improve the platinum atom utilization rate - by reducing the size of platinum particles to sub-nanometer level, increasing the number of particles in the catalyst layer, thereby reducing the oxygen transmission pressure of a single platinum particle. At the same time, higher platinum atom utilization rate can also speed up the oxygen reduction reaction efficiency and improve the catalytic activity.

[0005] However, the preparation of these sub-nanometer platinum particles faces two major challenges: the synthesis process is complex, and the sub-nanometer platinum particles are prone to agglomeration. Although some studies have reduced the particle size by adsorbing platinum atoms through defects on the surface of carbon materials or by wrapping platinum particles with carbon layers, achieving both uniform distribution and high stability while meeting the requirements of actual proton exchange membrane fuel cells remains a technical challenge that has not yet been overcome. Summary of the Invention

[0006] To address the above technical problems, this invention provides a platinum catalyst for fuel cells, its preparation method, and its application. The platinum catalyst prepared by this invention has a support with abundant microporous / mesoporous structures, and sub-nanometer platinum particles are uniformly loaded on the surface and within the pores, achieving a mass activity of 246~272 A / g; at a platinum loading of 0.2 mg / cm³... 2 This significantly improved the performance of the membrane electrode at high current densities, i.e., 2A / cm. 2 Performance improved by 37mV.

[0007] The technical solution provided by this invention is as follows: In a first aspect, the present invention provides a method for preparing a platinum catalyst for fuel cells, comprising the following steps: Nitrogen-containing organic matter, phosphorus-containing compound and pore-forming agent are mixed and dried, and then subjected to pyrolysis carbonization treatment in an oxygen-free environment to generate nitrogen-phosphorus co-doped porous carbon support. Platinum organic complexes are prepared by coordinating platinum salts with thiols in the presence of organic bases. Platinum organic complexes are dissolved in a solvent containing thiol compounds to form platinum precursor sols; The platinum precursor sol is adsorbed onto the nitrogen-phosphorus co-doped porous carbon support, and the composite material is collected by centrifugation and filtration. The composite material was subjected to reduction treatment to obtain a platinum catalyst.

[0008] In conjunction with the first aspect of the invention, some embodiments include: The nitrogen-containing organic compound has no more than 10 carbon atoms; and / or, The phosphorus-containing compound does not contain any metal elements; and / or, The pore-forming agent is an inorganic pore-forming agent; and / or, The platinum salt is a platinum ion salt; and / or... The organic base has no more than 10 carbon atoms; and / or, The thiol compound has no more than 10 carbon atoms.

[0009] In conjunction with the first aspect of the invention, some embodiments include: The nitrogen-containing organic compound is an amine organic compound, a nitrile organic compound, or an isocyanate organic compound; and / or, The phosphorus-containing compound is phosphoric acid or an organophosphorus compound; and / or, The pore-forming agent is a chemical activator; and / or, The platinum ion salt is a tetravalent platinum salt; and / or... The organic base is an organic tertiary amine compound; and / or, The thiol compound has at least two functional groups, at least one of which is a thiol group.

[0010] In conjunction with the first aspect of the invention, some embodiments include: The nitrogen-containing organic compound is one or more of melamine, aniline, o-phenylenediamine, and urea; and / or, The phosphorus-containing compound is one or more of diphenylphosphonic acid and phytic acid; and / or, The pore-forming agent is one or more selected from ZnCl2, KCl, and CaCl2; and / or, The platinum salt is PtCl4; and / or The organic base is one or more selected from N,N-diisopropylethylamine, triethylamine, and N-methylmorpholine; and / or The thiol compound is one or more of 1-octylthiol, 1,2-benzenedithiol, 4-mercaptobenzoic acid, and 4-aminobenzenethiol.

[0011] In conjunction with the first aspect of the invention, some embodiments include: The molar ratio of nitrogen-containing organic matter to nitrogen-containing compound is 1:0.8~1.2.

[0012] In conjunction with the first aspect of the invention, some embodiments include: In coordination reactions, the molar ratio of thiol groups to Pt atoms in thiols and platinum salts is greater than 4.

[0013] In conjunction with the first aspect of the invention, some embodiments include: The mass ratio of Pt atoms in the platinum precursor sol to the nitrogen-phosphorus co-doped porous carbon support is 1:(10~50).

[0014] In conjunction with the first aspect of the invention, some embodiments include: The pyrolysis temperature is 700~1200 ℃; and / or, In conjunction with the first aspect of the invention, some embodiments include: The temperature for the coordination reaction is 90~100 ℃.

[0015] The solvent temperature for thiol compounds is 170~190 ℃.

[0016] In conjunction with the first aspect of the present invention, some embodiments include: reducing the composite material by means of reducing the composite material at 200-300°C using a reducing gas.

[0017] Secondly, the present invention provides a platinum catalyst for fuel cells, the platinum catalyst comprising a nitrogen-phosphorus co-doped porous carbon support and platinum particles loaded on the surface and within the pores of the nitrogen-phosphorus co-doped porous carbon support, wherein the particle size of the platinum particles is sub-nanometer.

[0018] In conjunction with the second aspect of the invention, in some embodiments: the particle size of the platinum particles is <1 nm.

[0019] In conjunction with the second aspect of the present invention, in some embodiments: the proportion of platinum particles in the platinum catalyst is 1wt% to 10wt%.

[0020] In conjunction with the second aspect of the invention, in some embodiments: the platinum particle loading in the platinum catalyst is ≤0.2 mg / cm³. 2 .

[0021] Thirdly, the present invention provides a membrane electrode assembly (MEA) comprising a catalyst layer, the catalyst layer comprising a resin and an encapsulated catalyst, wherein the catalyst is the aforementioned platinum catalyst for fuel cells.

[0022] In conjunction with a third aspect of the invention, in some embodiments: the membrane electrode assembly includes a proton exchange membrane (PEM), a catalyst layer, and a gas diffusion layer (GDL).

[0023] Fourthly, the present invention provides a proton exchange membrane fuel cell, the proton exchange membrane fuel cell including the above-mentioned membrane electrode assembly.

[0024] The technical solution provided by this invention has at least the following beneficial effects: 1. The preparation method of the present invention involves high-temperature treatment of a mixture of nitrogen-containing organic matter, phosphorus-containing compound and pore-forming agent, which causes the nitrogen-containing organic matter to pyrolyze and carbonize and the pore-forming agent to volatilize, forming a porous carbon support with pores of different size levels. At the same time, nitrogen and phosphorus atoms remain in the porous carbon support, forming an electron-rich nitrogen-phosphorus co-doped porous carbon support.

[0025] 2. The preparation method of the present invention involves the coordination reaction of platinum salt and thiol compound to form a platinum organic complex with restricted Pt ion movement; the insoluble matter is removed by redissolution, and the complex is prepared into a platinum precursor sol with uniformly dispersed platinum element, which is conducive to the uniform loading of platinum element on nitrogen and phosphorus co-doped porous carbon support.

[0026] 3. The preparation method of the present invention involves adsorbing platinum precursor sol onto a nitrogen-phosphorus co-doped porous carbon support, thereby uniformly loading platinum precursor onto the surface and pores of the nitrogen-phosphorus co-doped porous carbon support.

[0027] 4. The preparation method of the present invention reduces the platinum ions in the platinum organic complex to form zero-valent platinum atoms by performing a reduction treatment on the composite material.

[0028] 5. The platinum catalyst prepared by this invention has a mass activity of 246~272 A / g; at a platinum loading of 0.2 mg / cm³, the catalyst can achieve this activity. 2 This significantly improved the performance of the membrane electrode at high current densities, i.e., 2A / cm. 2 Performance improved by 37mV. Attached Figure Description

[0029] 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 accompanying 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.

[0030] Figure 1 XPS spectrum of the platinum catalyst prepared in Example 1.

[0031] Figure 2 Transmission electron microscopy image of the platinum catalyst prepared in Example 1.

[0032] Figure 3 Transmission electron microscopy image of the platinum catalyst prepared in Comparative Example 1.

[0033] Figure 4 Linear sweep voltammetry (LSV) curves of the platinum catalysts prepared in Example 1 and Comparative Example 2.

[0034] Figure 5 Polarization test curves of membrane electrode samples prepared using the platinum catalyst prepared in Example 1 and the commercially available platinum catalyst (TKK-Pt / C catalyst) from Tanaka Precious Metals Industries (TKK). Detailed Implementation

[0035] 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.

[0036] For simplicity, this paper only discloses some explicitly defined numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range. Similarly, any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit, combined with any other point or individual value, or combined with other lower or upper limits to form an undefined range.

[0037] It should be noted that, in the description herein, unless otherwise stated, "above" and "below" include the number itself, and "multiple" in "one or more" means two or more. 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. Moreover, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, 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, method, 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, method, article, or apparatus that includes said element.

[0038] In the description of this specification, the references to terms such as "any embodiment / mode," "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.

[0039] The above description of the invention is not intended to describe every disclosed embodiment or implementation. Instead, exemplary embodiments are described in more detail below. These embodiments can be used in various combinations. The examples listed are representative only and should not be construed as exhaustive.

[0040] In this invention, the term "nitrogen-containing organic matter" refers to organic compounds containing nitrogen, including amines, nitriles, amides, or nitrogen-containing heterocyclic compounds. Its function is to provide nitrogen and a carbon framework through high-temperature pyrolysis, thus providing a structural basis for the formation of nitrogen-phosphorus co-doped porous carbon supports.

[0041] In this invention, the term "phosphorus-containing compound" refers to an organic or inorganic compound containing phosphorus. Its function is to provide phosphorus through pyrolysis, which, in conjunction with nitrogen, regulates the electronic structure of the carbon support.

[0042] In this invention, the term "pore-forming agent" refers to a substance capable of volatilizing in anaerobic calcination and forming micropores in situ, including inorganic salts or organic pore-forming agents. Its function is to form a hierarchical pore structure through volatilization.

[0043] In this invention, the term "organic base" refers to an organic compound that enables the solvent to maintain an alkaline environment, including short-chain amines or nitrogen-containing heterocyclic compounds. Its function is to promote the alkalinity of Pt. 4+ It coordinates with thiols and simultaneously assists in the reduction of platinum ions through an electron-donating effect.

[0044] In this invention, the term "thiol compound" refers to an organic compound containing a mercapto group (-SH), such as 1-octylthiol, 4-aminophenylthiol, or 1,2-phenylenediol. Its function is as a Pt... 4+ The ligands stabilize platinum species through a multidentate coordination network.

[0045] In this invention, the term "nitrogen-phosphorus co-doped porous carbon support" refers to a porous carbon material formed by high-temperature pyrolysis of nitrogen-containing organic matter and phosphorus-containing compounds, which has a high specific surface area and strong anchoring points.

[0046] In this invention, the term "platinum organic complex" refers to Pt 4+ Centered on a thiol compound as a ligand, the complex functions by restricting the free movement of Pt ions through steric hindrance and electron density regulation, thus forming a stable platinum precursor.

[0047] In this invention, the term "platinum precursor" refers to a sol formed by dissolving a platinum organic complex in a solvent containing a thiol compound. Its function is to act as a precursor to platinum clusters, which, after adsorption on a support, undergo reduction treatment to generate sub-nanometer-sized platinum particles.

[0048] In this invention, the term "organic amine" refers to an organic compound having an amine group, such as N,N-diisopropylethylamine or triethylamine, which acts as a coordination promoter.

[0049] In this invention, the term "organophosphorus compound" refers to an organic compound with a phosphine group, which releases phosphorus through thermal decomposition and synergistically enhances the mechanical strength of the carrier with nitrogen.

[0050] In this invention, the term "platinum particle" refers to a platinum atomic group, which has a disordered structure.

[0051] In this invention, the term "sub-nanometer" refers to a size less than 1 nm.

[0052] In this invention, the term "membrane electrode assembly" refers to an electrochemical assembly consisting of a proton exchange membrane, a catalyst layer, and a gas diffusion layer, which serves as the core reaction interface of a fuel cell.

[0053] In this invention, the term "fuel cell" refers to an electrochemical device consisting of a membrane electrode assembly, a proton exchange membrane, and bipolar plates. Its function is to achieve efficient hydrogen oxidation and oxygen reduction reactions through the high activity of a platinum catalyst.

[0054] The present invention provides a method for preparing a platinum catalyst for fuel cells, comprising the following steps: mixing a nitrogen-containing organic compound, a phosphorus-containing compound, and a pore-forming agent, drying the mixture, and then subjecting it to pyrolysis and carbonization in an oxygen-free environment to generate a nitrogen-phosphorus co-doped porous carbon support; in the presence of an organic base, causing a coordination reaction between a platinum salt and a thiol compound to obtain a platinum organic complex; dissolving the platinum organic complex in a solvent containing a thiol compound to form a platinum precursor sol; adsorbing the platinum precursor sol onto the nitrogen-phosphorus co-doped porous carbon support, collecting the composite material by centrifugation and filtration; and reducing the composite material to obtain a platinum catalyst.

[0055] The principle of this invention for preparing platinum catalysts is as follows: A mixture of nitrogen-containing organic matter, phosphorus-containing compounds, and a pore-forming agent undergoes pyrolysis and carbonization at high temperature. Simultaneously, nitrogen and phosphorus atoms are doped into the carbon framework, forming an asymmetric coordination environment. This induces a redistribution of surface charge on the carbon, generating strong anchoring sites. The pore-forming agent volatilizes, leaving behind a rich microporous / mesoporous structure, increasing the specific surface area of ​​the carbon support. Platinum salts undergo coordination reactions with thiol compounds, forming platinum organic complexes with restricted Pt ion movement. The solvent containing the thiol compounds provides a continuous ligand environment for the platinum organic complexes, ensuring their stable existence in sol form and preventing Pt agglomeration before loading. The high specific surface area and surface functional groups (such as CN and CP bonds) of the nitrogen-phosphorus co-doped porous carbon support uniformly fix the platinum precursor on the support surface and within the pores through electrostatic adsorption and chemical anchoring. Subsequently, platinum ions are reduced to zero-valent Pt, forming platinum particles. The uniform distribution of the platinum precursor on the support surface and within the pores, along with the low loading, makes the platinum particles formed during the reduction process less prone to agglomeration and have a small particle size.

[0056] The platinum catalyst prepared by the method of this invention has a nitrogen-phosphorus co-doped porous carbon support with abundant microporous / mesoporous structures, and sub-nanometer-sized platinum particles are uniformly loaded on the surface and within the pores. Furthermore, the platinum loading is 0.2 mg / cm³. 2 Under certain conditions, the mass activity can reach 246~272 A / g.

[0057] In some embodiments of the present invention, the nitrogen-containing organic compounds have no more than 10 carbon atoms; these nitrogen-containing organic compounds can be efficiently decomposed at high temperature (700~1300℃), leaving a porous carbon support, and ensuring that nitrogen element remains uniformly in the porous carbon support, thereby providing a uniform anchor point for the platinum precursor. Further, the nitrogen-containing organic compounds are amine organic compounds, nitrile organic compounds, or isocyanate organic compounds.

[0058] In some preferred embodiments of the present invention, the nitrogen-containing organic compound is one or more of melamine, aniline, o-phenylenediamine, and urea. These small-molecule organic amines have high nitrogen content, ensuring sufficient nitrogen remains in the porous carbon support even if some nitrogen is lost through volatilization during pyrolysis. Melamine and o-phenylenediamine decompose completely at high temperatures, providing a stable nitrogen source, while urea is low in cost but requires controlled pyrolysis temperature to avoid excessive decomposition and structural collapse. The cyanamide groups produced by melamine decomposition bind tightly to the carbon skeleton, forming uniform nitrogen doping; the aromatic structure of aniline enhances the conductivity of the carbon support; and the low cost of urea makes it suitable for large-scale production.

[0059] In some embodiments of the present invention, the phosphorus-containing compound does not contain any metal elements, and therefore can stably release phosphorus during high-temperature pyrolysis without introducing other inorganic impurities. Further, the phosphorus-containing compound is preferably phosphoric acid or an organophosphorus compound.

[0060] In some preferred embodiments of the present invention, the organophosphorus compound is diphenylphosphonic acid (decomposition temperature about 280°C, phosphorus content 13.7 wt%) and / or phytic acid (decomposition temperature about 300°C, phosphorus content 39.0 wt%). These two compounds have compatible pyrolysis kinetics, enabling them to stably release phosphorus during carbonization. Although there is a small amount of volatility loss at high temperatures, their high phosphorus content ensures sufficient phosphorus participation in the carbon framework doping, avoiding insufficient phosphorus doping due to loss. Simultaneously, the decomposition temperature is lower than the carbonization temperature (e.g., 700~1200°C), allowing phosphorus to be preferentially released before the carbon structure forms. This achieves a synergistic effect of nitrogen-phosphorus co-doping through local coordination environment regulation, ultimately obtaining a composite carrier with high electronic conductivity and a porous structure.

[0061] In some embodiments of the present invention, the pore-forming agent is preferably an inorganic pore-forming agent, which works synergistically with nitrogen-containing organic matter: the nitrogen-containing organic matter carbonizes at high temperature to form a macroporous structure, while the inorganic pore-forming agent forms a uniform microporous structure through complete volatilization, thereby constructing a micropore-macropore hierarchical pore system. Preferably, the pore-forming agent is a chemical activator, which melts and penetrates the carbon layer, leaving micropores after subsequent water washing. Compared with organic pore-forming agents, the pores formed after the inorganic pore-forming agent volatilizes are smaller and have less impact on the structural stability of the nitrogen-phosphorus co-doped porous carbon support. Therefore, it is possible to further increase the specific surface area of ​​the porous carbon support while ensuring its structural stability, thereby providing more anchoring points for the platinum precursor.

[0062] In some preferred embodiments of the present invention, the pore-forming agent is one or more of ZnCl2, KCl, and CaCl2. These compounds exhibit moderate pyrolysis kinetics at pyrolysis temperatures of 700–1200 °C, enabling them to form microporous structures through high-temperature volatilization and provide physical support within the carbon framework through residues (such as ZnO and CaO), thus stabilizing the expansion of macroporous structures during pyrolysis. In contrast, while traditional inorganic salts (such as NH4Cl and MgCl2) are volatilizable at low temperatures, their decomposition products are NH3 and MgO, and the residues easily melt at high temperatures, failing to effectively support macroporous structures and leading to pore collapse or a decrease in specific surface area. Therefore, the present invention achieves synergistic regulation of micropores and macropores by selecting inorganic pore-forming agents with matching pyrolysis temperatures and stable residues, ensuring the hierarchical porous structure and high specific surface area of ​​the nitrogen-phosphorus co-doped carbon support.

[0063] In some embodiments of the present invention, the platinum salt is a platinum ion salt, which can form a platinum ion-centered complex with organic ligands; the platinum salt is preferably a tetravalent platinum salt (such as PtCl4), whose high oxidation state endows platinum ions with stronger coordination ability (usually a six-coordinate structure), and can form a multidentate coordination network with ligands. This network significantly restricts the free diffusion of platinum ions in solution through steric hindrance effect and electron density regulation, avoiding their aggregation in the platinum precursor sol, thereby enabling the platinum precursor sol to be more uniformly adsorbed on the nitrogen-phosphorus co-doped porous carbon support.

[0064] In some embodiments of the present invention, the number of carbon atoms in the organic base is limited to no more than 10 to reduce steric hindrance and achieve a triple synergistic effect: a. pH regulation: by providing an alkaline environment (e.g., pKa≈10.2 for N,N-diisopropylethylamine), the oxidative decomposition of thiols is inhibited, ensuring ligand activity; b. Coordination promotion: the amino groups of short-chain organic bases (e.g., triethylamine, N-methylmorpholine) can react with Pt 4+A highly efficient coordination network is formed, while the coordination efficiency of long-chain organic bases decreases due to steric hindrance; c. Reduction-assisted: Some organic bases (such as N,N-diisopropylethylamine) assist Pt in carbonization through electron donor effects (such as the release of free electrons from their quaternary ammonium salt structure). 4+ Reduction promotes the formation of sub-nanometer clusters.

[0065] In a preferred embodiment, the organic base is an organic tertiary amine compound to provide a highly alkaline environment; preferably, the organic base is one or more of N,N-diisopropylethylamine, triethylamine, and N-methylmorpholine. These short-chain organic bases have synergistic effects of coordination, dispersion, and reduction, ultimately achieving high dispersibility and structural stability of the platinum particles.

[0066] In some embodiments of the present invention, the number of carbon atoms in the thiol compound is limited to 10 or less, and its mechanism of action is based on the positive correlation between chain length and steric hindrance: thiol compounds with ≤10 carbon atoms can react with Pt due to their lower steric hindrance. 4+ A multidentate coordination network is formed to stabilize platinum species; however, thiols with more than 10 carbon atoms may cause excessive steric hindrance, leading to Pt... 4+ The coordination efficiency with thiols decreases, and the long carbon chains remaining after reduction treatment of long-chain thiols may block the pores and reduce the specific surface area of ​​the support.

[0067] In some embodiments of the present invention, the thiol compound has at least two functional groups, at least one of which is a thiol group for coordination with platinum, and the remaining functional groups (such as amino, carboxyl, or thiol groups) are used to bind to the nitrogen / phosphorus active sites on the nitrogen-phosphorus co-doped carbon support. In the coordination reaction, the thiol group reacts with Pt. 4+ Strong coordination bonds (such as Pt-S bonds) are formed, thereby forming platinum organic complexes. During the adsorption of platinum precursor sols on nitrogen-phosphorus co-doped porous carbon supports, the functional groups at the free ends of the platinum organic complexes bind to the nitrogen / phosphorus active sites on the nitrogen-phosphorus co-doped carbon supports through hydrogen bonds, π-π interactions, or coordination bonds, thereby achieving the directional adsorption of platinum organic complexes and improving the dispersibility of platinum organic complexes on nitrogen-phosphorus co-doped porous carbon supports.

[0068] In some embodiments of the present invention, the thiol compound is one or more of 1-octylthiol, 1,2-benzenedithiol, 4-mercaptobenzoic acid, and 4-aminobenzenethiol.

[0069] In some preferred embodiments of the present invention, the molar ratio of nitrogen and phosphorus in the nitrogen-containing organic compound and the phosphorus-containing compound is precisely controlled at 1:0.8 to 1.2. The reason for nitrogen-phosphorus co-doping in the carbon support is that nitrogen acts as an electron donor, filling vacancies in the carbon framework with lone pairs of electrons, increasing the density of states (DOS) near the Fermi level, and enhancing the electron transfer efficiency of platinum particles; phosphorus acts as an electron acceptor, attracting electrons to form electron-deficient sites, optimizing the d-band center position of platinum particles. When the N / P ratio is 1:1, the electronic effects of nitrogen and phosphorus are optimally matched, avoiding heterocyclic structural defects caused by excessive nitrogen or support embrittlement caused by excessive phosphorus. Nitrogen doping can suppress excessive graphitization of the carbon framework, preserving the mesoporous / macroporous structure; phosphorus doping enhances the mechanical strength of the carbon framework by forming PC bonds, avoiding pore collapse caused by high-temperature carbonization.

[0070] In some preferred embodiments of the present invention, the molar ratio of thiol compounds to Pt atoms in the platinum salt is greater than 4 during the coordination reaction. A molar ratio >4 ensures that each Pt atom is surrounded by at least four thiol ligands, forming a dynamic coordination network through multi-point coordination, effectively suppressing the Brownian motion of Pt ions in the sol, and enabling Pt ions to be uniformly and stably dispersed in the platinum precursor sol.

[0071] In some preferred embodiments of the present invention, the mass ratio of Pt atoms in the platinum precursor sol to the nitrogen-phosphorus co-doped porous carbon support is 1:(10~50). Controlling the mass ratio ≥10 ensures that the Pt species can adequately cover the nitrogen / phosphorus active sites on the surface of the nitrogen-phosphorus co-doped porous carbon support, avoiding underutilization of active sites due to insufficient platinum loading. Controlling the mass ratio ≤50 ensures that the concentration of Pt species is sufficiently low to suppress aggregation, while avoiding pore blockage caused by excessive platinum.

[0072] In some preferred embodiments of the present invention, the pyrolysis temperature is 700~1200 °C. Controlling the pyrolysis temperature at or below 1200 °C can suppress excessive graphitization of the nitrogen-phosphorus co-doped porous carbon support because excessive graphitization leads to densification of the carbon support structure, significantly reducing the specific surface area and thus reducing the exposed active sites of platinum clusters. Furthermore, excessive graphitization weakens the electronic control capability of nitrogen-phosphorus co-doping. The pyrolysis temperature can be selected from any two points among 700 °C, 800 °C, 900 °C, 1000 °C, 1100 °C, and 1200 °C as endpoints.

[0073] In some preferred embodiments of the present invention, the coordination reaction temperature is set to 90-100 °C, while the solvent temperature for the thiol-containing compound is set to 170-190 °C. During the low-temperature coordination reaction (90-100 °C) stage, Pt... 4+The platinum species react fully with thiols to form a multidentate coordination network (such as Pt-SC bonds), ensuring uniform dispersion. High-temperature solvent treatment (170~190℃): This temperature range promotes the selective precipitation of uncoordinated platinum salts (such as unreacted PtCl4) and thiols, improving system purity. Simultaneously, the high temperature induces the formation of micellar stable structures by the thiols ligands, enhancing sol stability through hydrophobic and charge-shielding effects.

[0074] The platinum catalyst for fuel cells provided by the present invention comprises a nitrogen-phosphorus co-doped porous carbon support and platinum particles loaded on the surface and pores of the nitrogen-phosphorus co-doped porous carbon support, wherein the particle size of the platinum particles is sub-nanometer.

[0075] In some embodiments of the invention, the particle size of the platinum particles is limited to <1 nm. Sub-nanometer-sized platinum particles of this size have a high proportion of exposed Pt atoms, low surface energy of platinum atoms, and a low tendency to aggregate.

[0076] In some embodiments of the present invention, the proportion of platinum particles in the platinum catalyst is 1 wt% to 10 wt%. This range balances catalytic activity and cost, avoids pore blockage caused by excessive platinum loading, and ensures sufficient platinum particles cover the support surface, exposing sufficient platinum active sites. The proportion of platinum particles in the platinum catalyst can be taken from any two points of 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, and 10 wt%.

[0077] In some embodiments of the present invention, the platinum particle loading in the platinum catalyst is ≤0.2 mg / cm². This loading can reduce the local resistance of the catalyst layer, and compared with existing catalysts, the present invention can reduce the amount of platinum used while maintaining the same performance.

[0078] The membrane electrode assembly provided by this invention includes a proton exchange membrane, a catalyst layer, and a gas diffusion layer. The catalyst layer comprises resin and an encapsulated catalyst, which is the aforementioned platinum catalyst used in fuel cells. By employing this platinum catalyst, the membrane electrode assembly can be coated with less platinum catalyst while achieving catalytic performance similar to existing platinum catalysts, thereby reducing production costs.

[0079] The proton exchange membrane fuel cell provided by this invention includes the aforementioned membrane electrode assembly. Since the catalyst coated on the catalyst layer of the membrane electrode assembly is the aforementioned platinum catalyst used in fuel cells, the proton exchange membrane fuel cell can achieve high catalytic activity with less platinum catalyst, thereby reducing production costs.

[0080] The following are embodiments of the present invention. These embodiments are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0081] Example 1: The method for preparing a platinum catalyst for fuel cells provided in this embodiment specifically includes the following steps: 1) Weigh 2.52 g of melamine and 100 mL of ultrapure water, heat and stir at 100 °C. After the solution becomes clear, add 1.09 g of diphenylphosphonic acid and react at 100 °C for 3 hours. Then evaporate the water to obtain the nitrogen-phosphorus composite precursor. Mix 2.0 g of the nitrogen-phosphorus composite precursor with 500 mg of ZnCl2, place in a quartz boat, and calcine at 1100 °C for 1 hour under N2 atmosphere (heating rate 2 °C / min) to obtain a nitrogen-phosphorus co-doped porous carbon support.

[0082] 2) Dissolve 0.90 mmol PtCl4 in a mixed solvent (monochlorobenzene / acetonitrile = 1 mL / 1300 mL), and heat the solution at 90 °C for 60 minutes in the presence of 69 mmol N,N-diisopropylethylamine and 3.6 mmol 1-octylthiol. Then evaporate the solution to dryness to obtain crude platinum organic complex.

[0083] The crude platinum organic complex was redissolved in monochlorobenzene containing 9.0 mmol of 1-octylthiol, and reacted at 180 °C for 60 min. After the reaction was completed, the reaction solution was allowed to stand for a certain period of time, and the insoluble matter was filtered off as a precipitate. The remaining part was an orange-yellow platinum precursor sol.

[0084] 3) 30 mg of nitrogen-phosphorus co-doped porous carbon support was dispersed in 200 mL of hexane by ultrasonic dispersion to obtain a nitrogen-phosphorus co-doped porous carbon support suspension. While stirring at 500 rpm, 1 mL of platinum precursor sol was added dropwise to the nitrogen-phosphorus co-doped porous carbon support suspension. After stirring for 15 minutes, the suspension was filtered through a 0.2 μm filter. The collected fine powder was heated to 250 °C at a rate of 2 °C / min in a 3% H₂ / N₂ atmosphere and held at this temperature for 18 h to obtain the platinum catalyst.

[0085] Example 2: The method for preparing a platinum catalyst for fuel cells provided in this embodiment specifically includes the following steps: 1) Weigh 2.52 g of melamine and 100 mL of ultrapure water, heat and stir at 100 °C. After the solution becomes clear, add 1.09 g of diphenylphosphonic acid and react at 100 °C for 3 hours. Then evaporate the water to obtain the nitrogen-phosphorus composite precursor. Mix 2.0 g of the nitrogen-phosphorus composite precursor with 500 mg of ZnCl2, place in a quartz boat, and calcine at 1100 °C for 1 hour under N2 atmosphere (heating rate 2 °C / min) to obtain a nitrogen-phosphorus co-doped porous carbon support.

[0086] 2) Dissolve 0.90 mmol PtCl4 in a mixed solvent (monochlorobenzene / acetonitrile = 1 / 1300 mL), and heat the solution at 90 °C for 60 minutes in the presence of 69 mmol N,N-diisopropylethylamine and 3.6 mmol 4-aminobenzenethiol. Then evaporate the solution to dryness to obtain crude platinum organic complex.

[0087] The crude platinum organic complex was redissolved in monochlorobenzene containing 9.0 mmol of 4-aminobenzenethiol, and the reaction was carried out at 180 °C for 60 min. After the reaction was completed, the solution was allowed to stand for a certain period of time, and the insoluble matter was filtered off. The remaining part was an orange-yellow platinum precursor sol.

[0088] 3) 30 mg of nitrogen-phosphorus co-doped porous carbon support was dispersed in 200 mL of hexane by ultrasonic dispersion to obtain a nitrogen-phosphorus co-doped porous carbon support suspension. While stirring at 500 rpm, 1 mL of platinum precursor sol was added dropwise to the nitrogen-phosphorus co-doped porous carbon support suspension. After stirring for 15 minutes, the suspension was filtered through a 0.2 μm filter. The collected fine powder was heated to 250 °C at a rate of 2 °C / min in a 3% H₂ / N₂ atmosphere and held at this temperature for 18 h to obtain the platinum catalyst.

[0089] Example 3: The method for preparing a platinum catalyst for fuel cells provided in this embodiment specifically includes the following steps: 1) Weigh 2.52 g of melamine and 100 mL of ultrapure water, heat and stir at 100 °C. After the solution becomes clear, add 1.09 g of diphenylphosphonic acid and react at 100 °C for 3 hours. Then evaporate the water to obtain the nitrogen-phosphorus composite precursor. Mix 2.0 g of the nitrogen-phosphorus composite precursor with 500 mg of ZnCl2, place in a quartz boat, and calcine at 1100 °C for 1 hour under N2 atmosphere (heating rate 2 °C / min) to obtain a nitrogen-phosphorus co-doped porous carbon support.

[0090] 2) Dissolve 0.90 mmol PtCl4 in a mixed solvent (monochlorobenzene / acetonitrile = 1 mL / 1300 mL), and heat the solution at 90 °C for 60 minutes in the presence of 69 mmol N,N-diisopropylethylamine and 3.6 mmol 1-octylthiol. Then evaporate the solution to dryness to obtain crude platinum organic complex.

[0091] The crude platinum organic complex was redissolved in monochlorobenzene containing 9.0 mmol of 1-octylthiol, and reacted at 180 °C for 60 min. After the reaction was completed, the solution was allowed to stand for a certain period of time, and the insoluble matter was filtered off as a precipitate. The remaining part was an orange-yellow platinum precursor sol.

[0092] 3) 30 mg of nitrogen-phosphorus co-doped porous carbon support was dispersed in 200 mL of hexane by ultrasonic dispersion to obtain a nitrogen-phosphorus co-doped porous carbon support suspension. While stirring at 500 rpm, 1.5 mL of platinum precursor sol was added dropwise to the nitrogen-phosphorus co-doped porous carbon support suspension. After stirring for 15 minutes, the suspension was filtered through a 0.2 μm filter. The collected fine powder was heated to 250 °C at a rate of 2 °C / min in a 3% H₂ / N₂ atmosphere and held at this temperature for 18 h to obtain the platinum catalyst.

[0093] Example 4: The method for preparing a platinum catalyst for fuel cells provided in this embodiment specifically includes the following steps: 1) Weigh 2.52 g of melamine and 100 mL of ultrapure water, heat and stir at 100 °C. After the solution becomes clear, add 1.09 g of diphenylphosphonic acid and react at 100 °C for 3 hours. Then evaporate the water to obtain the nitrogen-phosphorus composite precursor. Mix 2.0 g of the nitrogen-phosphorus composite precursor with 500 mg of ZnCl2, place in a quartz boat, and calcine at 900 °C for 1 hour under N2 atmosphere (heating rate 2 °C / min) to obtain a nitrogen-phosphorus co-doped porous carbon support.

[0094] 2) Dissolve 0.90 mmol PtCl4 in a mixed solvent (monochlorobenzene / acetonitrile = 1 mL / 1300 mL), and heat the solution at 90 °C for 60 minutes in the presence of 69 mmol N,N-diisopropylethylamine and 3.6 mmol 1-octylthiol. Then evaporate the solution to dryness to obtain crude platinum organic complex.

[0095] The crude platinum organic complex was redissolved in monochlorobenzene containing 9.0 mmol of 1-octylthiol, and reacted at 180 °C for 60 min. After the reaction was completed, the solution was allowed to stand for a certain period of time, and the insoluble matter was filtered off as a precipitate. The remaining part was an orange-yellow platinum precursor sol.

[0096] 3) 30 mg of nitrogen-phosphorus co-doped porous carbon support was dispersed in 200 mL of hexane by ultrasonic dispersion to obtain a nitrogen-phosphorus co-doped porous carbon support suspension. While stirring at 500 rpm, 1.5 mL of platinum precursor sol was added dropwise to the nitrogen-phosphorus co-doped porous carbon support suspension. After stirring for 15 minutes, the suspension was filtered through a 0.2 μm filter. The collected fine powder was heated to 250 °C at a rate of 2 °C / min in a 3% H₂ / N₂ atmosphere and held at this temperature for 18 h to obtain the platinum catalyst.

[0097] (Note: The only difference between Example 4 and Example 3 is that the roasting temperature in step 1 is adjusted from 1100℃ to 900℃, while the other steps and parameters remain the same.) Example 5: The method for preparing a platinum catalyst for fuel cells provided in this embodiment specifically includes the following steps: 1) Weigh 2.52 g of melamine and 100 mL of ultrapure water, heat and stir at 100 °C. After the solution becomes clear, add 1.09 g of diphenylphosphonic acid and react at 100 °C for 3 hours. Then evaporate the water to obtain the nitrogen-phosphorus composite precursor. Mix 2.0 g of the nitrogen-phosphorus composite precursor with 500 mg of ZnCl2, place in a quartz boat, and calcine at 1100 °C for 1 hour under N2 atmosphere (heating rate 2 °C / min) to obtain a nitrogen-phosphorus co-doped porous carbon support.

[0098] 2) Dissolve 0.90 mmol PtCl4 in a mixed solvent (monochlorobenzene / acetonitrile = 1 mL / 1300 mL), and heat the solution at 100 °C for 60 minutes in the presence of 69 mmol N,N-diisopropylethylamine and 3.6 mmol 1-octylthiol. Then evaporate the solution to dryness to obtain crude platinum organic complex.

[0099] The crude platinum organic complex was redissolved in monochlorobenzene containing 9.0 mmol of 1-octylthiol, and reacted at 180 °C for 60 min. After the reaction was completed, the solution was allowed to stand for a certain period of time, and the insoluble matter was filtered off as a precipitate. The remaining part was an orange-yellow platinum precursor sol.

[0100] 3) 30 mg of nitrogen-phosphorus co-doped porous carbon support was dispersed in 200 mL of hexane by ultrasonic dispersion to obtain a nitrogen-phosphorus co-doped porous carbon support suspension. While stirring at 500 rpm, 1.5 mL of platinum precursor sol was added dropwise to the nitrogen-phosphorus co-doped porous carbon support suspension. After stirring for 15 minutes, the suspension was filtered through a 0.2 μm filter. The collected fine powder was heated to 250 °C at a rate of 2 °C / min in a 3% H₂ / N₂ atmosphere and held at this temperature for 18 h to obtain the platinum catalyst.

[0101] (Note: The only difference between Example 5 and Example 3 is that the solution heating temperature in step 2 is adjusted from 90°C to 100°C; all other steps and parameters remain the same.) Example 6: The method for preparing a platinum catalyst for fuel cells provided in this embodiment specifically includes the following steps: 1) Weigh 2.52 g of melamine and 100 mL of ultrapure water, heat and stir at 100 °C. After the solution becomes clear, add 1.09 g of diphenylphosphonic acid and react at 100 °C for 3 hours. Then evaporate the water to obtain the nitrogen-phosphorus composite precursor. Mix 2.0 g of the nitrogen-phosphorus composite precursor with 500 mg of ZnCl2, place in a quartz boat, and calcine at 1100 °C for 1 hour under N2 atmosphere (heating rate 2 °C / min) to obtain a nitrogen-phosphorus co-doped porous carbon support.

[0102] 2) Dissolve 0.90 mmol PtCl4 in a mixed solvent (monochlorobenzene / acetonitrile = 1 mL / 1300 mL), and heat the solution at 90 °C for 60 minutes in the presence of 69 mmol N,N-diisopropylethylamine and 3.6 mmol 1-octylthiol. Then evaporate the solution to dryness to obtain crude platinum organic complex.

[0103] The crude platinum organic complex was redissolved in monochlorobenzene containing 9.0 mmol of 1-octylthiol, and reacted at 180 °C for 60 min. After the reaction was completed, the solution was allowed to stand for a certain period of time, and the insoluble matter was filtered off as a precipitate. The remaining part was an orange-yellow platinum precursor sol.

[0104] 3) 30 mg of nitrogen-phosphorus co-doped porous carbon support was dispersed in 200 mL of hexane by ultrasonic dispersion to obtain a nitrogen-phosphorus co-doped porous carbon support suspension. While stirring at 500 rpm, 1.5 mL of platinum precursor sol was added dropwise to the nitrogen-phosphorus co-doped porous carbon support suspension. After stirring for 15 minutes, the suspension was filtered through a 0.2 μm filter. The collected fine powder was heated to 200 °C at a rate of 2 °C / min in a 3% H₂ / N₂ atmosphere and held at this temperature for 18 h to obtain the platinum catalyst.

[0105] (Note: The only difference between Example 6 and Example 3 is that the fine powder treatment temperature in step 3 is adjusted from 250℃ to 200℃, while the other steps and parameters remain the same.) Example 7: The method for preparing a platinum catalyst for fuel cells provided in this embodiment specifically includes the following steps: 1) Weigh 2.52 g of melamine and 100 mL of ultrapure water, heat and stir at 100 °C. After the solution becomes clear, add 1.09 g of diphenylphosphonic acid and react at 100 °C for 3 hours. Then evaporate the water to obtain the nitrogen-phosphorus composite precursor. Mix 2.0 g of the nitrogen-phosphorus composite precursor with 500 mg of ZnCl2, place in a quartz boat, and calcine at 1100 °C for 1 hour under N2 atmosphere (heating rate 2 °C / min) to obtain a nitrogen-phosphorus co-doped porous carbon support.

[0106] 2) Dissolve 0.90 mmol PtCl4 in a mixed solvent (monochlorobenzene / acetonitrile = 1 mL / 1300 mL), and heat the solution at 90 °C for 60 minutes in the presence of 69 mmol N,N-diisopropylethylamine and 3.6 mmol 1-octylthiol. Then evaporate the solution to dryness to obtain crude platinum organic complex.

[0107] The crude platinum organic complex was redissolved in monochlorobenzene containing 9.0 mmol of 1-octylthiol, and reacted at 180 °C for 60 min. After the reaction was completed, the solution was allowed to stand for a certain period of time, and the insoluble matter was filtered off as a precipitate. The remaining part was an orange-yellow platinum precursor sol.

[0108] 3) 30 mg of nitrogen-phosphorus co-doped porous carbon support was dispersed in 200 mL of hexane by ultrasonic dispersion to obtain a nitrogen-phosphorus co-doped porous carbon support suspension. While stirring at 500 rpm, 1.5 mL of platinum precursor sol was added dropwise to the nitrogen-phosphorus co-doped porous carbon support suspension. After stirring for 15 minutes, the suspension was filtered through a 0.2 μm filter. The collected fine powder was heated to 300 °C at a rate of 2 °C / min in a 3% H₂ / N₂ atmosphere and held at this temperature for 18 h to obtain the platinum catalyst.

[0109] (Note: The only difference between Example 7 and Example 3 is that the fine powder treatment temperature in step 3 is adjusted from 250℃ to 300℃, while the other steps and parameters remain the same.) Comparative Example 1: This comparative example only omits diphenylphosphonic acid in step 1), while the remaining steps are the same as in Example 1, resulting in a nitrogen-doped porous carbon support-supported Pt cluster catalyst.

[0110] 1) Weigh 2.52 g of melamine and 100 mL of ultrapure water, heat and stir at 100 °C for 3 hours, then evaporate the water to obtain a nitrogen-phosphorus composite precursor. Mix 2.0 g of the nitrogen-phosphorus composite precursor with 500 mg of ZnCl2, place in a quartz boat, and calcine at 1100 °C for 1 hour under N2 atmosphere (heating rate 2 °C / min) to obtain a nitrogen-phosphorus co-doped porous carbon support.

[0111] 2) Dissolve 0.90 mmol PtCl4 in a mixed solvent (monochlorobenzene / acetonitrile = 1 mL / 1300 mL), and heat the solution at 90 °C for 60 minutes in the presence of 69 mmol N,N-diisopropylethylamine and 3.6 mmol 1-octylthiol. Then evaporate the solution to dryness to obtain crude platinum organic complex.

[0112] The crude platinum organic complex was redissolved in monochlorobenzene containing 9.0 mmol of 1-octylthiol, and reacted at 180 °C for 60 min. After the reaction was completed, the reaction solution was allowed to stand for a certain period of time, and the insoluble matter was filtered off as a precipitate. The remaining part was an orange-yellow platinum precursor sol.

[0113] 3) 30 mg of nitrogen-phosphorus co-doped porous carbon support was dispersed in 200 mL of hexane by ultrasonic dispersion to obtain a nitrogen-phosphorus co-doped porous carbon support suspension. While stirring at 500 rpm, 1 mL of platinum precursor sol was added dropwise to the nitrogen-phosphorus co-doped porous carbon support suspension. After stirring for 15 minutes, the suspension was filtered through a 0.2 μm filter. The collected fine powder was heated to 250 °C at a rate of 2 °C / min in a 3% H₂ / N₂ atmosphere and held at this temperature for 18 h to obtain the platinum catalyst.

[0114] Comparative Example 2: The difference between Comparative Example 2 and Example 1 lies in the different methods of preparing the platinum precursor: 1) Weigh 2.52 g of melamine and 100 mL of ultrapure water, heat and stir at 100 °C. After the solution becomes clear, add 1.09 g of diphenylphosphonic acid and react at 100 °C for 3 hours. Then evaporate the water to obtain the nitrogen-phosphorus composite precursor. Mix 2.0 g of the nitrogen-phosphorus composite precursor with 500 mg of ZnCl2, place in a quartz boat, and calcine at 1100 °C for 1 hour under N2 atmosphere (heating rate 2 °C / min) to obtain a nitrogen-phosphorus co-doped porous carbon support.

[0115] 2) Dissolve 0.90 mmol PtCl4 in a mixed solvent (monochlorobenzene / acetonitrile = 1 mL / 1300 mL), and heat the solution at 90 °C for 60 minutes in the presence of 69 mmol N,N-diisopropylethylamine and 3.6 mmol 1-octylthiol. Evaporate the resulting solution to dryness to obtain crude platinum organic complex.

[0116] The crude platinum organic complex was redissolved in monochlorobenzene containing 9.0 mmol of 1-octylthiol, and reacted at 200 °C for 120 min. After the reaction was completed, the solution was allowed to stand for a certain period of time, and the insoluble matter was filtered off as a precipitate. The remaining part was an orange-yellow platinum precursor sol.

[0117] 3) 30 mg of nitrogen-phosphorus co-doped porous carbon support was dispersed in 200 mL of hexane by ultrasonic dispersion to obtain a nitrogen-phosphorus co-doped porous carbon support suspension. While stirring at 500 rpm, 1 mL of platinum precursor sol was added dropwise to the nitrogen-phosphorus co-doped porous carbon support suspension. After stirring for 15 minutes, the suspension was filtered through a 0.2 μm filter. The collected fine powder was heated to 250 °C at a rate of 2 °C / min in a 3% H₂ / N₂ atmosphere and held at this temperature for 18 h to obtain the platinum catalyst.

[0118] Comparative Example 3: The method for preparing the platinum catalyst for fuel cells provided in this comparative example specifically includes the following steps: 1) Weigh 2.52 g of melamine and 100 mL of ultrapure water, heat and stir at 100 °C. After the solution becomes clear, add 1.09 g of diphenylphosphonic acid and react at 100 °C for 3 hours. Then evaporate the water to obtain the nitrogen-phosphorus composite precursor. Mix 2.0 g of the nitrogen-phosphorus composite precursor with 500 mg of ZnCl2, place in a quartz boat, and calcine at 1300 °C for 1 hour under N2 atmosphere (heating rate 2 °C / min) to obtain a nitrogen-phosphorus co-doped porous carbon support.

[0119] 2) Dissolve 0.90 mmol PtCl4 in a mixed solvent (monochlorobenzene / acetonitrile = 1 mL / 1300 mL), and heat the solution at 90 °C for 60 minutes in the presence of 69 mmol N,N-diisopropylethylamine and 3.6 mmol 1-octylthiol. Then evaporate the solution to dryness to obtain crude platinum organic complex.

[0120] The crude platinum organic complex was redissolved in monochlorobenzene containing 9.0 mmol of 1-octylthiol, and reacted at 180 °C for 60 min. After the reaction was completed, the reaction solution was allowed to stand for a certain period of time, and the insoluble matter was filtered off as a precipitate. The remaining part was an orange-yellow platinum precursor sol.

[0121] 3) 30 mg of nitrogen-phosphorus co-doped porous carbon support was dispersed in 200 mL of hexane by ultrasonic dispersion to obtain a nitrogen-phosphorus co-doped porous carbon support suspension. While stirring at 500 rpm, 1 mL of platinum precursor sol was added dropwise to the nitrogen-phosphorus co-doped porous carbon support suspension. After stirring for 15 minutes, the suspension was filtered through a 0.2 μm filter. The collected fine powder was heated to 250 °C at a rate of 2 °C / min in a 3% H₂ / N₂ atmosphere and held at this temperature for 18 h to obtain the platinum catalyst.

[0122] (Note: The only difference between Comparative Example 3 and Example 1 is that the calcination temperature in step 1 was adjusted from 1100 ℃ to 1300 ℃. Due to the excessively high temperature, the nitrogen content of the support was too low, resulting in poor performance of the prepared catalyst.) Performance testing: 1. XPS Detection: X-ray photoelectron spectroscopy analysis was performed on the carbon support prepared in Example 1, such as... Figure 1 As shown, the XPS spectrum of the nitrogen-phosphorus co-doped porous carbon support obtained in Example 1 shows characteristic peaks of nitrogen and phosphorus functional groups, indicating that nitrogen-phosphorus co-doping was successful.

[0123] 2. TEM detection: The platinum catalysts prepared in Example 1 and Comparative Example 1 were characterized and analyzed by electron microscopy. The results are as follows: Figure 2 , Figure 3 As shown, compared with Comparative Example 1, the platinum particles on the surface of the platinum catalyst prepared in Example 1 are more uniform and better dispersed, indicating that nitrogen and phosphorus co-doping in porous carbon support can make platinum particles more dispersed and more stable than nitrogen doping alone.

[0124] 3. Electrochemical performance testing: Electrochemical performance was determined using the standard three-electrode method. The platinum catalysts prepared in Example 1 and Comparative Example 2 were used as working electrodes, respectively. a) Weigh an appropriate amount of platinum catalyst into a centrifuge tube; b) Add deionized water, Nafion solution and isopropanol to the weighed platinum catalyst in sequence, mix well to form a slurry; c) The above slurry is ultrasonically dispersed, and the temperature of the slurry during the ultrasonic process is not higher than 25°C; d) According to a certain catalyst loading on the electrode surface, take an appropriate amount of well-dispersed slurry and evenly drop it onto the smooth and clean surface of the platinum-carbon electrode. Let it air dry naturally to obtain the working electrode.

[0125] The test conditions were as follows: The working electrode was subjected to potential scanning tests at 0.1 mol / L HClO4 aqueous solution saturated with oxygen at 25 ℃, and the polarization curves in the redox process are shown in [Figure number missing]. Figure 4 .Depend on Figure 4 It can be seen that the platinum catalyst obtained in Example 1 has a higher half-wave potential and a higher mass-to-volume activity at 0.9 V than the platinum catalyst obtained in Comparative Example 2, indicating that the platinum catalyst obtained in Example 1 performs better than the platinum catalyst obtained in Comparative Example 2. The platinum particles are highly dispersed on the nitrogen-phosphorus co-doped porous carbon support and exhibit strong electronic interactions, achieving higher electrochemical active area and mass activity.

[0126] Table 1 shows the mass activity of the platinum catalysts prepared in each example and comparative example.

[0127] 4. Single-cell performance testing: The platinum catalyst prepared in Example 1 and the commercially available TKK-Pt / C catalyst were respectively used to prepare cathode catalyst layers, and then the cathode catalyst layers were used to prepare membrane electrodes. The specific steps are as follows: (a) Prepare a catalyst slurry by mixing and dispersing appropriate amounts of platinum catalyst, water, resin, and alcohol; (b) Apply the slurry to the PTFE membrane and let it dry; (c) The dried cathode catalyst layer and proton exchange membrane are hot-pressed to form a proton exchange membrane-catalyst layer composite membrane (CCM). (d) Fix the CCM and gas diffusion layer in a single cell test fixture to form a membrane electrode.

[0128] The membrane electrode assembly (MEA) was tested in a single-cell test bench. Throughout the MEA testing process, the temperature of both the cell and the gas humidifier was maintained at 80 °C. The back pressure of both H2 and air was maintained at 150 kPa, and the effective area was approximately 25 cm². 2 The cathode loading is 0.2 mg / cm³. 2 .like Figure 4 As shown, the membrane electrode performance using the platinum catalyst obtained in Example 1 is superior to that prepared with the TKK-Pt / C catalyst, especially with a significant improvement in membrane electrode performance at high current densities, i.e., 2 A / cm 2 Performance improved by 37 mV.

[0129] 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 claimed herein.

Claims

1. A method for the preparation of a platinum catalyst for fuel cells, characterized in that The method comprises the following steps: mixing nitrogen-containing organic matter, phosphorus-containing compounds and pore-forming agents, drying, pyrolysis and carbonization in an oxygen-free environment to obtain a nitrogen-phosphorus co-doped porous carbon carrier; under the presence of an organic base, a coordination reaction occurs between a platinum salt and a mercaptan compound to obtain a platinum organic complex; the platinum organic complex is dissolved in a solvent containing the mercaptan compound to form a platinum precursor sol; the nitrogen-phosphorus co-doped porous carbon carrier is used to adsorb the platinum precursor sol, and a composite material is collected by centrifugal filtration; the composite material is subjected to reduction treatment to obtain a platinum catalyst.

2. The method according to claim 1, wherein: the nitrogen-containing organic matter has no more than 10 carbon atoms; and / or, the phosphorus-containing compound contains no metal element; and / or, the pore-forming agent is an inorganic pore-forming agent; and / or, the platinum salt is a platinum ion salt; and / or, the organic base has no more than 10 carbon atoms; and / or, the mercaptan compound has no more than 10 carbon atoms.

3. The method according to claim 1, wherein: the nitrogen-containing organic matter is an amine organic matter, a nitrile organic matter or an isocyanic acid organic matter; and / or, the phosphorus-containing compound is phosphoric acid or an organic phosphine compound; and / or, the pore-forming agent is a chemical activator; and / or, the platinum ion salt is a tetravalent platinum salt; and / or, the organic base is an organic tertiary amine compound; and / or, the mercaptan compound has at least two functional groups, at least one of which is a mercapto group.

4. The method according to claim 1, wherein: the nitrogen-containing organic matter is one or more of melamine, aniline, o-phenylenediamine and urea; and / or, the phosphorus-containing compound is one or more of diphenylphosphinic acid and phytic acid; and / or, the pore-forming agent is one or more of ZnCl2, KCl and CaCl2; and / or, the platinum salt is PtCl4; and / or, the organic base is one or more of N,N-diisopropylethylamine, triethylamine and N-methylmorpholine; and / or, the mercaptan compound is one or more of 1-octanethiol, 1,2-benzenedithiol, 4-mercaptobenzoic acid and 4-aminobenzenethiol.

5. The method according to claim 1, wherein: the molar ratio of N elements and P elements in the nitrogen-containing organic matter and the phosphorus-containing compound is 1:0.8-1.

2.

6. The method according to claim 1, wherein: in the coordination reaction, the molar ratio of mercapto groups in the mercaptan compound and Pt atoms in the platinum salt is greater than 4.

7. The method according to claim 1, wherein: the mass ratio of Pt atoms in the platinum precursor sol to the nitrogen-phosphorus co-doped porous carbon carrier is 1: (10-50).

8. The method according to claim 1, wherein: the pyrolysis temperature is 700-1200 ℃.

9. The method according to claim 1, wherein: the coordination reaction temperature is 90-100 ℃; and / or, the temperature of the solvent containing the mercaptan compound is 170-190 ℃.

10. The method of claim 1, wherein: the reduction treatment of the composite material comprises: The composite material is reduced by a reducing gas at 200-300 DEG C.

11. A platinum catalyst for use in a fuel cell, characterized by: The platinum catalyst comprises a nitrogen-phosphorus co-doped porous carbon carrier and platinum particles supported on the surface and in the pores of the nitrogen-phosphorus co-doped porous carbon carrier, the platinum particles having a sub-nanometer size.

12. The platinum catalyst for a fuel cell according to claim 11, characterized by: The platinum particles have a size of less than 1 nm.

13. The platinum catalyst for a fuel cell according to claim 11, characterized by: The platinum particles account for 1-10 wt% of the platinum catalyst.

14. The platinum catalyst for a fuel cell according to claim 11, characterized by: The platinum catalyst has a platinum particle loading of < 0.2 mg / cm 2 .

15. A membrane electrode assembly, characterized by: The membrane electrode assembly comprises a catalyst layer, and the catalyst layer comprises a resin and a wrapped catalyst, the catalyst being the platinum catalyst for fuel cells according to any one of claims 11-14.

16. The membrane electrode assembly of claim 15, wherein: The membrane electrode assembly comprises a proton exchange membrane, a catalyst layer and a gas diffusion layer.

17. A proton exchange membrane fuel cell characterized by: The proton exchange membrane fuel cell comprises the membrane electrode assembly according to claim 15 or 16.

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