Carbon-coated platinum-based catalyst for fuel cell and preparation method of carbon-coated platinum-based catalyst

Abstract

The invention discloses a carbon-coated platinum-based catalyst for a fuel cell and a preparation method thereof, and the preparation method comprises the following steps: dispersing a carbon carrier and a surfactant in a water-alcohol solution to obtain a carbon carrier solution; preparing a platinum-containing precursor solution; the mass of platinum in the platinum-containing precursor is 30-70% of the mass of the carbon carrier; mixing the carbon carrier solution and the platinum-containing precursor solution, and removing the solvent to obtain platinum-loaded carbon carrier particles; immersing the platinum-loaded carbon carrier particles into a weakly alkaline buffer solution, and adding dopamine hydrochloride to form polydopamine to coat the surfaces of the platinum-loaded carbon carrier particles; the reaction product is placed in reducing gas for carbonization treatment, and the carbon-coated platinum-based catalyst is obtained. According to the prepared catalyst, the poisoning effect of sulfonic acid groups of ionomers on Pt is avoided, the problem of large oxygen mass transfer resistance is solved, and stable electric energy output provided by a fuel cell is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular to a carbon-coated platinum-based catalyst for fuel cells and a preparation method thereof. Background Art

[0002] Hydrogen fuel cells, as a highly efficient and clean energy conversion technology, have garnered widespread attention in recent years. The performance of the catalyst layer within the membrane electrode assembly (MEA), its core component, directly determines the cell's energy conversion efficiency. However, current problems with the ionomer distribution within the catalyst layer severely restrict fuel cell performance.

[0003] The ionomer is a type of functional polymer containing ionic groups (such as sulfonic acid groups -SO3H), and its functions in proton exchange membrane fuel cells include: 1. Proton conduction: the sulfonic acid groups in the ionomer dissociate into protons (H + ) to form a continuous proton conduction channel, ensuring efficient proton transfer between the catalyst layer and the proton exchange membrane; 2. Three-phase interface construction: The ionomer wraps the platinum catalyst particles, forming a three-phase reaction interface of "catalyst-proton conductor-oxygen", which promotes the oxygen reduction reaction (Oxygen Reduction Reaction, ORR). Studies have found that the uneven distribution of ionomers may lead to the following limitations:

[0004] (1) Sulfonic acid group poisoning effect: The uneven distribution of ionomers causes part of the Pt surface to be covered by excessive ionomers, and the sulfonic acid groups (-SO3 - ) are adsorbed on the Pt surface, occupying active sites, hindering the ORR reaction, and reducing the utilization rate of the Pt catalyst.

[0005] (2) Increase oxygen mass transfer resistance: During oxygen transfer, oxygen needs to be transferred through the interface between the ionomer and Pt. Uneven distribution of ionomers will cause the ionomer on some Pt ​​surfaces to be too thick or insufficiently covered. If the ionomer on the Pt surface is too thick, it will greatly increase the length and tortuosity of the oxygen transfer path, significantly increasing the oxygen mass transfer resistance. At the same time, it will affect proton conduction, causing protons to be unable to smoothly reach the Pt active sites, thereby reducing the electrochemical reaction rate. If the ionomer coverage on the Pt surface is insufficient, it will cause the protons to be unable to form good contact with the Pt catalyst, resulting in a decrease in local reaction activity.

[0006] These issues lead to varying reaction activity and mass transfer at different locations within the fuel cell. This results in significant fluctuations in battery performance at varying current densities, making it difficult to provide stable power output. Performance degradation is even more pronounced at high current densities, limiting the application of fuel cells in high-power scenarios.

[0007] Existing technologies attempt to improve these issues by coating the surface of Pt catalysts with a shell material. For example, CN109675583B discloses a method for producing a core-shell electrocatalyst for fuel cells. However, this method uses a precious metal shell (Co, Ni) to protect the platinum core, resulting in a complex and costly preparation process. CN105406087B discloses a method for producing a core-shell electrocatalyst for low-temperature fuel cells. However, this method also uses a precious metal shell (Pt, Pd) to protect the platinum core and relies on atomic layer deposition technology, resulting in a complex and costly synthesis process.

[0008] The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art. Summary of the Invention

[0009] The present invention is directed to a carbon-coated platinum-based catalyst and a preparation method thereof, aiming to solve the problems of Pt poisoning by the sulfonic acid groups of the ionomers in the catalyst layer of existing fuel cells and the high oxygen mass transfer resistance.

[0010] In order to achieve the above objectives, a method for preparing a carbon-coated platinum-based catalyst for a fuel cell comprises:

[0011] Step 1, dispersing a carbon support and a surfactant in a water-alcohol solution to obtain a carbon support solution;

[0012] Step 2, preparing a platinum-containing precursor solution; the mass of platinum in the platinum-containing precursor is 30% to 70% of the mass of the carbon support;

[0013] Step 3, mixing the carbon support solution and the platinum-containing precursor solution, and removing the solvent to obtain platinum-loaded carbon support particles;

[0014] Step 4, immersing the platinum-loaded carbon support particles in a weakly alkaline buffer solution, and adding dopamine hydrochloride to form polydopamine coating on the surface of the platinum-loaded carbon support particles;

[0015] Step 5: placing the product of step 4 in a reducing gas for carbonization treatment to obtain a carbon-coated platinum-based catalyst.

[0016] Optionally, the platinum-containing precursor solution contains any one or more of H2PtCl6, K2PtCl4, ammonium chloroplatinate, and platinum acetylacetonate.

[0017] Optionally, the carbon support comprises any one or more of carbon black, acetylene black, graphene, and carbon nanotubes.

[0018] Optionally, the surfactant comprises any one or more of Triton X-114, Triton X-100, Triton X-45, sodium lauryl sulfate, and Tween-20.

[0019] Optionally, before step 1, the method further comprises: treating the surface of the carbon support by chemical etching.

[0020] Optionally, in step 4, the mass ratio of the dopamine hydrochloride to the carbon carrier is 1:4 to 1:2.

[0021] Optionally, in step 4, the reaction temperature is 0-4° C., and the reaction time is 1 h-3 h.

[0022] Optionally, in step 5, the temperature of the carbonization treatment is 600° C. to 1000° C., and the time is 0.5 h to 2 h.

[0023] Optionally, in step 5, the reducing gas includes any one of a nitrogen-hydrogen mixed gas and an argon-hydrogen mixed gas.

[0024] The present invention also provides a carbon-coated platinum-based catalyst for a fuel cell, which is prepared using the above-mentioned method for preparing the carbon-coated platinum-based catalyst for a fuel cell. The mass percentage of platinum in the carbon-coated platinum-based catalyst is 30% to 70%.

[0025] Compared with the prior art, the beneficial effects of the technical solution of the present invention include at least:

[0026] The present invention utilizes the adhesiveness of dopamine molecules and their self-polymerization characteristics to cause dopamine to self-polymerize on the surface of platinum-loaded carbon carrier particles to form a layer of polydopamine structure. Then, through high-temperature carbonization treatment, a carbon coating layer is formed on the surface of the platinum-loaded carbon carrier particles to obtain a carbon-coated platinum-based catalyst. On the one hand, the carbon coating layer can effectively block the direct adsorption of sulfonic acid groups in the ionomer and the Pt active sites, reduce the aggregation of sulfonic acid groups at the Pt active sites, avoid the poisoning effect of sulfonic acid groups on Pt, release more Pt surface for oxygen reduction reaction, and thus improve the utilization rate of Pt active sites; on the other hand, the carbon coating layer can form a hydrophobic microenvironment between the ionomer and the ionomer, reducing the enrichment of water molecules at the interface, avoiding water blockage, and facilitating the transmission of oxygen, thereby helping to inhibit the oxidation reaction of platinum and delay the deactivation of Pt active sites. On the other hand, during the carbonization treatment of polydopamine, some oxygen-containing functional groups (such as hydroxyl and carboxyl groups) are retained on the surface of the carbon coating layer in the form of chemical bonds. These oxygen-containing functional groups form weak interactions with the sulfonic acid groups of the ionomer through hydrogen bonds and electrostatic interactions, which is conducive to the adsorption of the ionomer and can also limit its excessive aggregation, guiding the uniform distribution of the ionomer on the surface of the carbon-coated platinum-based catalyst, further reducing the oxygen mass transfer resistance, and thus helping the fuel cell to provide stable power output. In addition, the present invention does not require the use of precious metal shell materials, and the preparation process is simple, which greatly reduces the production cost of the catalyst layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The present invention is a process flow chart of a method for preparing a carbon-coated platinum-based catalyst for a fuel cell.

[0028] Figure 2 This is a high-angle annular dark-field scanning transmission electron microscope image of the Pt / C@C catalyst obtained in Example 1.

[0029] Figure 3 This is a transmission electron microscope image of the Pt / C@C catalyst obtained in Example 1.

[0030] Figure 4 This is the EDS energy spectrum linear scan diagram of the Pt / C@C catalyst obtained in Example 1.

[0031] Figure 5 This is a comparison diagram of the CV curves of the Pt / C@C catalysts with different Nafion contents obtained in Example 1.

[0032] Figure 6 This is a comparison chart of CV curves of Pt / C catalysts with different Nafion contents obtained in the comparative example.

[0033] Figure 7 This is a comparison chart of the three-electrode ORR performance of the Pt / C@C catalyst with different Nafion contents obtained in Example 1 of the present invention.

[0034] Figure 8 This is a comparison chart of the three-electrode ORR performance of the Pt / C catalyst with different Nafion contents obtained in the comparative example.

[0035] Figure 9 This is a comparison chart of the three-electrode ORR performance of the Pt / C@C catalysts obtained in Example 2 and Example 3.

[0036] Figure 10 4fX-ray photoelectron spectra of the Pt / C catalyst and Pt / C@C catalyst obtained in the comparative example and Example 1. DETAILED DESCRIPTION

[0037] The following is a further detailed description of a carbon-coated platinum-based catalyst for a fuel cell and a preparation method thereof proposed by the present invention, in conjunction with the accompanying drawings and specific embodiments. According to the following description, the advantages and features of the present invention will be clearer. It should be noted that the drawings are in a very simplified form and use non-precise proportions, which are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention. In order to make the purposes, features and advantages of the present invention more obvious and easy to understand, please refer to the accompanying drawings. It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the conditions for the implementation of the present invention, so they have no technical significance. Any structural modification, change in proportional relationship or adjustment of size should still fall within the scope of the technical content disclosed by the present invention without affecting the efficacy and purpose that can be achieved by the present invention.

[0038] As described in the background technology, the existing catalyst layer has problems such as the Pt catalyst being poisoned by sulfonic acid groups and losing its activity, and large oxygen mass transfer resistance. This leads to uneven reaction activity and mass transfer conditions inside the battery, and significant performance degradation at high current density, making it difficult to meet the needs of high-power applications.

[0039] To address the above-mentioned issues, the present invention provides a method for preparing a carbon-coated platinum-based catalyst for fuel cells. This method covers the surface of the platinum-based catalyst with a carbon coating. This carbon coating prevents direct contact between the ionomer and the Pt, thereby preventing Pt from being poisoned by sulfonic acid groups. The carbon coating also utilizes the hydrophobic microenvironment formed between the carbon coating and the ionomer to provide a smooth oxygen transmission path, thereby enhancing oxygen mass transfer. Furthermore, the oxygen-containing functional groups retained on the surface of the carbon coating form weak interactions with the sulfonic acid-containing ionomer through hydrogen bonding and electrostatic interactions, facilitating the adsorption of the ionomer while limiting its excessive aggregation, thereby achieving uniform distribution of the ionomer.

[0040] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] like Figure 1 As shown, the present invention provides a method for preparing a carbon-coated platinum-based catalyst for a fuel cell, comprising:

[0042] Step 1: Dispersing a carbon carrier and a surfactant in a water-alcohol solution to obtain a carbon carrier solution.

[0043] The mass ratio of the carbon carrier to the hydroalcoholic solution is 2:3 to 1:1, and the volume ratio of water to anhydrous ethanol in the hydroalcoholic solution is 2:3 to 1:1. The carbon carrier comprises any one or more of carbon black, acetylene black, graphene, and carbon nanotubes; and the surfactant comprises any one or more of Triton X-114, Triton X-100, Triton X-45, sodium lauryl sulfate, and Tween-20. Due to the strong interaction between carbon carrier particles, they tend to agglomerate, affecting dispersibility. The addition of a surfactant can reduce the interaction between carbon carrier particles, weakening their tendency to agglomerate and achieving uniform dispersion of the carbon carrier.

[0044] In some embodiments, the carbon carrier is ultrasonically dispersed in a water-alcohol solution for 60 min to 180 min. After the ultrasonication is completed, the surfactant is added thereto and stirred for 10 h to 15 h. After the stirring is completed, the obtained carbon carrier solution is stirred at a constant temperature of 25 ° C for standby use.

[0045] In some embodiments, before step 1, the step further includes: treating the surface of the carbon carrier by chemical etching. The etching solution used in the chemical etching contains at least one of sulfuric acid, hydrochloric acid, phosphoric acid, and nitric acid. The carbon carrier is ultrasonically dispersed in the etching solution and placed in a 60°C oven for etching, and the etching time is 12h to 14h. After etching, it is centrifuged and washed, and placed in a vacuum drying oven for drying. The purpose of the chemical etching is to remove other organic impurities and metal ions in the carbon carrier and improve the purity of the carbon carrier. As an example, the etching solution is sulfuric acid, and the mass ratio of the carbon carrier to the sulfuric acid is 1: (1.5 to 2). Since sulfuric acid has strong oxidizing properties, after etching with sulfuric acid, oxygen-containing functional groups (-COOH, -OH) will be introduced onto the surface of the carbon carrier, enhancing the surface hydrophilicity and chemical activity, and providing anchoring sites for the subsequent adsorption of dopamine molecules.

[0046] Step 2: preparing a platinum-containing precursor solution; the mass of platinum in the platinum-containing precursor is 30% to 70% of the mass of the carbon support.

[0047] In some embodiments, the platinum-containing precursor solution comprises any one or more of H2PtCl6, K2PtCl4, ammonium chloroplatinate, and platinum acetylacetonate. Platinum-containing precursor solutions of different concentrations can be prepared as needed.

[0048] Step 3: Mix the carbon support solution and the platinum-containing precursor solution, and remove the solvent to obtain platinum-loaded carbon support particles.

[0049] After mixing the carbon support solution and the platinum-containing precursor solution, stirring is started for 10 to 15 hours. The purpose of stirring is to make the platinum-containing precursor solution and the carbon support solution mix more completely, which is more conducive to the loading of the platinum-containing precursor on the carbon support.

[0050] In some embodiments, the method for removing the solvent is any one of freeze drying, natural air drying, oven drying, water bath evaporation, rotary evaporation or oil bath evaporation.

[0051] Step 4: immersing the platinum-loaded carbon support particles in a weakly alkaline buffer solution, and adding dopamine hydrochloride to form polydopamine coating on the surface of the platinum-loaded carbon support particles.

[0052] Wherein, the reaction temperature of step 4 is 0-4°C, and the reaction time is 1h-3h. The mass ratio of the dopamine hydrochloride to the carbon carrier is 1:4-1:2. The weak alkaline buffer solution comprises any one of tris(hydroxymethylaminomethane) hydrochloride solution (Tris solution), phosphate buffer, borate buffer, carbonate buffer, and 4-hydroxyethylpiperazineethanesulfonic acid buffer. As an example, the weak alkaline buffer solution is tris(hydroxymethylaminomethane) hydrochloride solution with a concentration of 0.01mol / L-0.1mol / L. The tris(hydroxymethylaminomethane) hydrochloride solution is used to provide a stable weakly alkaline environment (pH=8.0-8.5) to ensure that the oxidative self-polymerization reaction of dopamine is efficient and controllable.

[0053] In step 4, dopamine hydrochloride is in a weakly alkaline buffer solution, H + is neutralized, releasing free dopamine molecules (C8H 11NO2), dopamine molecules are reactive because they contain catechol groups (-C6H3(OH)2) and amino groups (-NH2). Dissolved oxygen (O2) in the solution or trace oxidizing substances in the solution (such as oxygen in the air) act as oxidants to oxidize the catechol groups of dopamine into o-quinone structures (-C6H3(O)2), releasing electrons and generating active intermediates. The quinone structures polymerize through free radical chain reactions to form polydopamine chains. Because the surface of the carbon support has been chemically etched in advance (for example, using sulfuric acid to etch the carbon support), a large number of oxygen-containing functional groups are introduced to its surface. In the early stages of the reaction, the dopamine molecules form hydrogen bonds with the oxygen-containing functional groups on the surface of the carbon support through the catechol groups and amino groups, and at the same time, the amino groups form coordination with the platinum metal surface, thereby stably adsorbing on the surface of the platinum-loaded carbon support particles. Furthermore, the reaction rate is reduced by low-temperature reaction conditions (0-4°C), ensuring that the dopamine molecules have sufficient time to adsorb on the surface of the platinum-loaded carbon support particles. The adsorbed dopamine molecules undergo oxidative self-polymerization on the surface of the platinum-loaded carbon support particles, forming polydopamine chains. Because the resulting polydopamine is rich in polar groups such as hydroxyl, amino, and quinone groups, these polar groups have strong adhesion, prompting the polydopamine to grow layer by layer along the surface of the platinum-loaded carbon support particles, gradually forming a uniformly coated polydopamine layer.

[0054] After the polymerization reaction, the solvent is removed to obtain a polymerization product. In some embodiments, the method for removing the solvent is any one of freeze drying, natural air drying, oven drying, water bath evaporation, rotary evaporation, or oil bath evaporation.

[0055] Step 5: placing the product of step 4 in a reducing gas for carbonization treatment to obtain a carbon-coated platinum-based catalyst.

[0056] The carbonization treatment temperature is 600° C. to 1000° C., and the time is 0.5 h to 2 h. The carbonization gas includes any one of nitrogen-hydrogen mixed gas and argon-hydrogen mixed gas.

[0057] After carbonization, a carbon coating is formed on the surface of the platinum-based catalyst. The present invention has found that the functions of the carbon coating include at least:

[0058] (1) The physical barrier effect of the carbon coating weakens the adsorption between the sulfonic acid groups and Pt, thereby preventing the sulfonic acid groups from poisoning Pt and releasing more Pt surface for oxygen reduction reaction, which is beneficial to improving the utilization rate of Pt active sites. In addition, this physical barrier effect also effectively reduces the aggregation of sulfonic acid groups at Pt active sites, which is beneficial to the uniform distribution of ionomers.

[0059] (2) A hydrophobic microenvironment is formed between the carbon coating and the ionomer, which reduces the accumulation of water molecules at the interface, avoids water blockage, and provides a smooth path for oxygen transport, which is beneficial to oxygen transport, thereby inhibiting the oxidation reaction of Pt and delaying the deactivation of Pt active sites. The oxidation reaction of Pt will cause Pt to oxidize to form Pt-O, Pt-OH, etc., resulting in a decrease in catalytic activity.

[0060] (3) During the carbonization process (carbonization treatment process) of polydopamine, some oxygen-containing functional groups (such as hydroxyl and carboxyl groups) are not completely decomposed due to their high thermal stability and remain on the surface of the carbon coating layer in the form of chemical bonds. These oxygen-containing functional groups can form weak interactions with the sulfonic acid groups of the ionomer through hydrogen bonds or electrostatic interactions, which is beneficial to the adsorption of the ionomer and limits its excessive aggregation, thereby making the ionomer uniformly distributed on the surface of the carbon-coated platinum-based catalyst, further reducing the oxygen mass transfer resistance, and helping the fuel cell provide stable power output.

[0061] Unless otherwise specified, the chemicals used in the present invention are all conventional commercially available chemical reagents. These chemicals can be purchased from a number of chemical reagent suppliers and do not require special preparation or synthesis.

[0062] The sulfuric acid and chloroplatinic acid hexahydrate in the following comparative examples and Examples 1-3 were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. A 20 mg / mL chloroplatinic acid hexahydrate solution was prepared as follows: 2.72 mL of sulfuric acid (18.4 mol / L) was dissolved in 1 L of water to obtain 0.05 mol / L sulfuric acid, and 20 mg of chloroplatinic acid hexahydrate was dissolved in 1 mL of water to obtain a 20 mg / mL chloroplatinic acid hexahydrate solution.

[0063] Comparative Example

[0064] 30 mg of carbon black was placed in 30 mL of sulfuric acid (0.05 mol / L) and sonicated for 60 minutes. The mixture was then etched in a 60°C oven for 12 hours, washed by centrifugation, and dried in a vacuum oven. 20 mg of the dried carbon black was placed in 20 mL of a hydroalcoholic solution and sonicated for 60 minutes. 5 mg of Triton X-114 was then added and magnetically stirred for 10 hours to obtain a carbon black solution. 0.734 mL of 20 mg / mL chloroplatinic acid hexahydrate solution was then added to the carbon black solution. After magnetic stirring for 12 hours, the solvent was removed by rotary evaporation. Finally, the solution was carbonized at 900°C in a tube furnace under an argon-hydrogen mixture for 2 hours. After cooling, the Pt / C catalyst was obtained.

[0065] Example 1

[0066] 30 mg of carbon black was ultrasonically placed in 30 mL of sulfuric acid (0.05 mol / L) for 60 minutes, etched in a 60°C oven for 12 hours, washed by centrifugation, and dried in a vacuum oven. 20 mg of the dried carbon black was ultrasonically placed in 20 mL of a hydroalcoholic solution for 60 minutes, followed by the addition of 5 mg of Triton X-114 and magnetic stirring for 10 hours to obtain a carbon black solution. 0.734 mL of 20 mg / mL chloroplatinic acid hexahydrate solution was then added to the carbon black solution. After magnetic stirring for 12 hours, the solvent was removed by rotary evaporation. The resulting particles were added to 10 mL of Tris solution and stirred for 5 minutes. 5 mg of dopamine hydrochloride particles were added and stirred at 0-4°C for 1.5 hours. The solvent was removed and the mixture was carbonized at 900°C in a tube furnace under an argon-hydrogen mixture for 2 hours. After cooling, the carbon-coated platinum-based catalyst, designated Pt / C@C, was obtained.

[0067] Example 2

[0068] The difference between this embodiment and embodiment 1 is that the added amount of dopamine hydrochloride is 8 mg.

[0069] Example 3

[0070] The difference between this embodiment and embodiment 1 is that the high-temperature carbonization temperature is 600°C.

[0071] Figures 2 to 4 These are the morphology pictures and line scans of the carbon-coated platinum-based catalyst obtained in Example 1. Figure 1 This is a high-angle annular dark field scanning transmission electron microscope image of the obtained Pt / C@C catalyst. Figure 2 It can be seen that the obtained Pt / C@C catalyst has a core-shell structure, and the surface of the Pt nanoparticles is covered with a thin carbon layer with a thickness of about 0.8 nm. Figure 2 The microstructure of a carbon-coated platinum nanoparticle catalyst is shown. The black area in the figure (labeled as Pt NPs) represents platinum nanoparticles. It can be seen that the platinum nanoparticles are uniformly coated with a carbon coating layer, which fully demonstrates that the method of the present invention can be successfully used to prepare a Pt / C@C catalyst with a core-shell structure. Figure 3 This is a transmission electron microscope image of the Pt / C@C catalyst prepared in Example 1. The arrows in the figure indicate the line scan path. The Pt / C@C catalyst was linearly scanned. Figure 4 As shown, CK edge represents the K-edge absorption of carbon element, which corresponds to the absorption characteristics of the electrons in the K layer (1s orbit) outside the carbon nucleus transitioning to higher energy levels. Figure 4 The fluctuation of CK edge indicates that there are multiple bonding states or structures of carbon elements in Pt / C@C catalysts; Pt-M edge represents the M-edge absorption of platinum elements, and the M-edge corresponds to the transition of high energy levels (for example, 3s, 3p electrons). Figure 4The Pt-M edge indicates that Pt in the Pt / C@C catalyst coexists in multiple states, including metallic and oxidized states, indicating that there is electron transfer or interaction between carbon and platinum elements, thereby proving that the method of the present invention achieves the formation of a carbon coating layer outside the platinum-based catalyst.

[0072] The catalyst particles prepared in the comparative example and Examples 1 to 3 were treated by adding an appropriate amount of Nafion. The Nafion is a perfluorosulfonic acid (PFSA) resin, which is an ionomer widely used in fuel cells.

[0073] The catalyst particles prepared in the comparative example and Examples 1 to 3 were treated with an appropriate amount of Nafion (denoted as Nafion 1): 2 mg of the catalyst particle sample was dispersed in a mixed solution of 500 μL of deionized water and 1500 μL of isopropanol, 2 μL of 5 wt.% Nafion solution was added and ultrasonically mixed for 30 minutes to obtain a uniform slurry, and then 10 μL of the slurry was drop-coated on the surface of a glassy carbon electrode with a diameter of 5 mm as a working electrode. After the slurry was completely dried, the electrocatalytic oxygen reduction test could be carried out.

[0074] The catalyst particles prepared in the comparative example and Example 1 were treated with excess Nafion (denoted as Nafion 10): 2 mg of the catalyst particle sample was dispersed in a mixed solution of 500 uL deionized water and 1500 uL isopropanol, 20 uL of 5 wt% Nafion solution was added and ultrasonically mixed for 30 minutes to obtain a uniform slurry, and then 10 uL of the slurry was drop-coated on the surface of a glassy carbon electrode with a diameter of 5 mm as the working electrode. After the slurry was completely dry, the electrocatalytic oxygen reduction test could be performed.

[0075] The above-mentioned Nafion 1 represents that the mass ratio of Nafion to the carbon support is 1:1, and Nafion 10 represents that the mass ratio of Nafion to the carbon support is 10:1.

[0076] An electrochemical workstation with a three-electrode system was used to characterize the oxygen reduction activity of the carbon-coated platinum-based catalyst. In the three-electrode system used, a CHI-760 electrochemical analyzer was used to evaluate the electrochemical performance of the catalyst. A platinum sheet was used as the counter electrode, a standard hydrogen electrode (Reversible Hydrogen Electrode, RHE) was used as the reference electrode, and a glassy carbon electrode loaded with the catalyst was used as the working electrode. A 0.1MHClO4 solution saturated with Ar gas was used as the acidic electrolyte. Cyclic voltammetry (CV) tests were performed in the range of 0.05V to 1.2V to obtain the CV curve of the material for comparison of its electrochemical active surface area (ECSA); then, a 0.1MHClO4 solution saturated with O2 gas was used as the acidic electrolyte, and the rotating disk electrode speed was set to 1600rpm to obtain the ORR performance curve of the material. The test results are as follows: Figures 5-10 shown.

[0077] Figure 5 CV curve comparison diagram of Pt / C@C catalyst with different Nafion contents prepared in Example 1; Figure 6 The CV curve comparison diagram of the Pt / C catalyst with different Nafion contents obtained in the comparative example. The electrochemical performance of the catalyst introduced with the carbon coating layer was studied using CV technology. In the voltage range of 0.05V to 0.40V, the curve shows the characteristic signal of hydrogen adsorption / desorption of Pt, reflecting the adsorption and desorption process of hydrogen atoms on the Pt surface and the situation of the Pt active site. When the voltage exceeds 0.6V, the curve shows the oxidation signal of oxygen-containing species formed on the Pt surface. The corresponding ECSA value was obtained by calculating the hydrogen desorption charge value. The ECSA value of Example 1-Nafion 1 is the largest, which is 57m 2 / g Pt , indicating that under this condition, the exposure of active sites on the catalyst surface is high, which is conducive to the electrochemical reaction.

[0078] contrast Figure 5 、 6, it can be seen that the hydrogen adsorption / desorption charge of the Pt / C@C catalyst of Example 1 and the ionomer (Nafion) is slightly reduced after the action. This may be due to the adsorption of components or impurities in the carbon coating on the Pt surface, which affects the hydrogen adsorption / desorption behavior. In the potential range of the CV curve greater than 0.6V, the Pt oxidation peak of the Pt / C@C catalyst (Example 1) is significantly weakened compared with the Pt oxidation peak of the Pt / C catalyst (Comparative Example), and the onset potential of Pt oxidation is significantly positively shifted, which shows that the presence of the carbon coating can inhibit the formation of oxygen-containing species on the Pt surface. It should be noted that the oxygen-containing species on the Pt surface are considered to be inactive and will lead to blockage of the Pt active sites, while the carbon coating can create a hydrophobic microenvironment at the interface between the catalyst and the ionomer electrolyte, which helps to prevent the active sites of Pt from being partially oxidized, thereby retaining more effective active sites, which is beneficial to maintaining catalyst performance.

[0079] Figure 7 This is a comparison chart of the three-electrode ORR performance of the Pt / C@C catalyst with different Nafion contents obtained in Example 1; Figure 8 The figure is a comparison chart of the ORR performance of three electrodes with different Nafion contents of the Pt / C catalyst obtained in the comparative example. Figure 7 、 8 The ORR polarization curve of Pt / C@C catalyst shows that when the mass ratio of Nafion to carbon support is 1, the half-wave potentials of the ORR polarization curves of Pt / C@C catalyst and Pt / C catalyst are 0.87V (vs.RHE) and 0.86V (vs.RHE), respectively. The half-wave potential of Pt / C@C catalyst is 10mV higher than that of Pt / C catalyst. When the mass ratio of Nafion to carbon support increases to 10, the half-wave potentials of the ORR polarization curves of Pt / C@C catalyst and Pt / C catalyst are 0.85V (vs.RHE), respectively. ) and 0.78V (vs.RHE), the half-wave potential of the Pt / C@C catalyst is 70mV higher than that of the Pt / C catalyst. The comparison results of different Nafion contents show that the half-wave potential of the Pt / C@C catalyst is higher, indicating that compared with the Pt / C catalyst, the Pt / C@C catalyst has the fastest kinetics in the ORR reaction and has higher ORR activity, thereby proving that the Pt / C@C catalyst can improve the poisoning effect of Nafion on Pt, indicating that the Pt / C@C catalyst prepared by the present invention has excellent resistance to Nafion poisoning.

[0080] Figure 9 The figure is a comparison of the ORR performance of the three electrodes of the Pt / C@C catalyst (treated with Nafion 1) obtained in Example 2 and Example 3. Figure 7 、 9The ORR polarization curve of the Pt / C@C catalyst shows that when the mass ratio of Nafion to the carbon support is 1, the half-wave potential of the ORR polarization curve of the Pt / C@C catalyst prepared in Example 1 is 0.87 V (vs. RHE), the half-wave potential of the ORR polarization curve of the Pt / C@C catalyst prepared in Example 2 is 0.85 V (vs. RHE), and the half-wave potential of the ORR polarization curve of the Pt / C@C catalyst prepared in Example 3 is 0.79 V (vs. RHE). It can be seen that the half-wave potential of the Pt / C@C catalyst in Example 1 is the highest, indicating that the Pt / C@C catalyst obtained by the preparation method of Example 1 exhibits the best ORR activity.

[0081] Figure 10 The figure shows a comparison of the Pt 4f X-ray photoelectron spectra (XPS) of the Pt / C catalyst and the Pt / C@C catalyst (treated with Nafion 1) obtained in the comparative example and Example 1. Compared with the Pt / C catalyst (71.61 eV) after Nafion treatment, the Pt 4f7 / 2 peak of the Pt / C@C catalyst (71.51 eV) shifts slightly toward lower binding energy. Moreover, comparing the two curves, the peak intensity of the Pt / C@C catalyst is significantly higher than that of the Pt / C catalyst, indicating that the Pt content on the surface of the Pt / C@C catalyst is increased compared with the Pt / C catalyst. This proves that the formation of the carbon coating layer on the surface of the Pt / C@C catalyst can effectively avoid the strong adsorption of sulfonic acid groups on Pt, which is conducive to exposing more Pt atoms on the surface, which is beneficial to improving the electrocatalytic performance of the Pt / C@C catalyst.

[0082] In summary, the present invention coats a polydopamine structure on the surface of platinum-loaded carbon support particles through dopamine self-polymerization, and forms a carbon coating layer after reduction treatment. This carbon coating layer can block the direct adsorption of the ionomer sulfonic acid groups and the Pt active sites to avoid poisoning, release more Pt surface for oxygen reduction reaction, and form a hydrophobic microenvironment with the ionomer, reducing the enrichment of water molecules to facilitate oxygen transmission and inhibit Pt oxidation. At the same time, the oxygen-containing functional groups retained on the surface of the carbon coating layer weakly interact with the ionomer sulfonic acid groups through hydrogen bonds and electrostatic effects, guiding the uniform distribution of the ionomer, reducing the oxygen mass transfer resistance, and ensuring the stable output of electrical energy by the fuel cell. In addition, this method does not require precious metal shell materials, the preparation process is simple, and the production cost of the catalytic layer can be greatly reduced.

[0083] It should be noted that, in this document, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or apparatus comprising the element.

[0084] Although the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description is not intended to limit the present invention. After reading the above description, various modifications and substitutions of the present invention will become apparent to those skilled in the art. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for preparing a carbon-coated platinum-based catalyst for a fuel cell, characterized in that: include: Step 1, dispersing a carbon support and a surfactant in a water-alcohol solution to obtain a carbon support solution; Step 2, preparing a platinum-containing precursor solution; The mass of platinum in the platinum-containing precursor is 30% to 70% of the mass of the carbon support; Step 3, mixing the carbon support solution and the platinum-containing precursor solution, and removing the solvent to obtain platinum-loaded carbon support particles; Step 4, immersing the platinum-loaded carbon support particles in a weakly alkaline buffer solution, and adding dopamine hydrochloride to form polydopamine coating on the surface of the platinum-loaded carbon support particles; Step 5: placing the product of step 4 in a reducing gas for carbonization treatment to obtain a carbon-coated platinum-based catalyst.

2. The method for preparing a carbon-coated platinum-based catalyst for a fuel cell according to claim 1, wherein: The platinum-containing precursor solution contains any one or more of H2PtCl6, K2PtCl4, ammonium chloroplatinate, and platinum acetylacetonate.

3. The method for preparing a carbon-coated platinum-based catalyst for a fuel cell according to claim 1, wherein: The carbon support comprises any one or more of carbon black, acetylene black, graphene, and carbon nanotubes.

4. The method for preparing a carbon-coated platinum-based catalyst for a fuel cell according to claim 1, wherein: The surfactant comprises any one or more of Triton X-114, Triton X-100, Triton X-45, sodium lauryl sulfate, and Tween-20.

5. The method for preparing a carbon-coated platinum-based catalyst for a fuel cell according to claim 1, wherein: Before step 1, the method further comprises: treating the surface of the carbon support by chemical etching.

6. The method for preparing a carbon-coated platinum-based catalyst for a fuel cell according to claim 1, wherein: In the step 4, the mass ratio of the dopamine hydrochloride to the carbon carrier is 1:4 to 1:

2.

7. The method for preparing a carbon-coated platinum-based catalyst for a fuel cell according to claim 1, wherein: In the step 4, the reaction temperature is 0-4° C. and the reaction time is 1 h-3 h.

8. The method for preparing a carbon-coated platinum-based catalyst for a fuel cell according to claim 1, wherein: In step 5, the temperature of the carbonization treatment is 600° C. to 1000° C., and the time is 0.5 h to 2 h.

9. The method for preparing a carbon-coated platinum-based catalyst for a fuel cell according to claim 1, wherein: In step 5, the reducing gas includes any one of a nitrogen-hydrogen mixed gas and an argon-hydrogen mixed gas.

10. A carbon-coated platinum-based catalyst for a fuel cell, characterized in that: The carbon-coated platinum-based catalyst is prepared by the method for preparing a fuel cell carbon-coated platinum-based catalyst according to any one of claims 1 to 9, wherein the mass percentage of platinum in the carbon-coated platinum-based catalyst is 30% to 70%.

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