Carbon supported catalyst with through-hole multi-stage pore structure and preparation method thereof

Abstract

The application discloses a carbon-supported catalyst with a through multi-stage pore structure and a preparation method thereof. The catalyst comprises a carbon carrier, a plurality of mesopores are distributed on the carbon carrier, the plurality of mesopores are randomly connected to each other, pore walls of the mesopores and an outer surface of the carbon carrier are both distributed with micropores, the micropores are all loaded with nanoparticles, and the nanoparticles are Pt or an alloy formed by Pt and a transition metal element. A carbon precursor material is impregnated with an activation solution and subjected to two-step acid etching treatment to obtain a primary carbon carrier; the primary carbon carrier is subjected to heat treatment by controlling temperature and time to obtain a partially graphitized carbon carrier; nanoparticles are loaded on inner pore walls and an outer surface of the carbon carrier by using a microwave combined with a liquid phase reduction method; and finally, the product is treated to obtain the catalyst. The catalyst is used as a fuel cell oxygen reduction catalyst and exhibits more excellent active area, catalytic activity and stability.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell catalyst technology, specifically relating to a carbon-supported catalyst with a through-hole multi-level pore structure and its preparation method. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) utilize renewable hydrogen as fuel, which undergoes an electrochemical reaction with oxidants such as oxygen to convert chemical energy into electrical energy. They are considered a promising alternative for improving energy efficiency and reducing carbon emissions. Fuel cells offer advantages such as high energy conversion efficiency, environmental friendliness, and fast start-up speed, making them a clean and efficient power generation technology with broad application prospects in distributed power stations, transportation, aerospace, and other fields. During operation, highly active catalysts are required to efficiently complete the electrochemical reaction, especially the oxygen reduction reaction at the cathode. Fuel cells also experience start-up, shutdown, idling, low-temperature environments, and short-term overload operation. Furthermore, the catalyst is exposed to an acidic environment, inevitably leading to catalyst performance degradation and reduced catalytic activity, which in turn affects the fuel cell's power generation performance. Therefore, catalysts also need to possess good stability and lifespan.

[0003] Currently, widely used commercial fuel cell catalysts are mainly Pt nanoparticle catalysts supported on activated carbon particles. Platinum-based catalysts exhibit high activity in various energy conversion processes; however, their cost and scarcity have hindered their development and application to some extent. Currently, alloying with non-precious metal elements is often employed to reduce Pt usage and enhance catalytic activity by utilizing electronic effects between Pt and transition metal atoms. However, under harsh conditions such as strong acidity and high potential during fuel cell operation, Pt nanoparticle catalysts supported on carbon particles are prone to Ostwald ripening, dissolution, migration, and aggregation of Pt nanoparticles on the support surface. This leads to a significant decrease in catalyst active area and catalytic activity, and the catalyst's stability fails to meet the requirements for fuel cell use.

[0004] To improve the activity and stability of carbon-supported Pt catalysts, researchers have invented various novel catalysts and preparation methods. For example, surface-modified carbon supports or graphene composites can effectively support Pt-based nanoparticles, but they cannot prevent the migration and aggregation of metal nanoparticles on the support surface during fuel cell use. Furthermore, surface-supported catalysts cannot avoid contact with proton-conducting resin ionomers during fuel cell electrode use, leading to some poisoning of the catalyst by the ionomer molecules and preventing the full realization of catalytic activity. In addition, there are catalysts based on hollow carbon spheres, carbon nanotubes, ordered mesoporous carbon, or modified support materials that support Pt-based nanoparticles. These catalysts have improved stability. However, for hollow carbon spheres, carbon nanotubes, and ordered mesoporous carbon (which constructs ordered mesoporous structures, and the materials are generally large, with a size of several micrometers, and the mesopores are slender and non-connected), the reaction precursors are not easy to enter the interior of the pores and tend to accumulate near the ends of the pores. Therefore, on the one hand, it is not conducive to the effective loading of active metal nanoparticles in the pores or tubes. On the other hand, during the catalytic electrode reaction, it is not conducive to the reaction gas entering the interior of the pores to participate in the reaction. The utilization rate of the active components inside the catalyst is low, and the mass transport resistance is also high, which is not conducive to improving the efficiency of the electrode reaction.

[0005] The carbon supports of currently used or invented carbon-supported catalysts have relatively simple structures and insufficient functionality, which indirectly prevents the fundamental achievement of significant improvements in both catalytic activity and stability of fuel cell catalyst materials. Summary of the Invention

[0006] The purpose of this invention is to provide a carbon-supported catalyst with a through-hole multi-level porous structure and its preparation method; when applied to the catalytic electrode reaction of a fuel cell, it has a high specific surface area and electrochemical active area, as well as high catalytic activity and good stability.

[0007] The present invention provides a carbon-supported catalyst, comprising a carbon support, wherein a plurality of mesopores are distributed on the carbon support, and the plurality of mesopores are interconnected in a random number, wherein the pore walls of the mesopores and the outer surface of the carbon support are distributed with micropores, and each micropore supports nanoparticles, wherein the nanoparticles are Pt or an alloy formed by Pt and transition metal elements.

[0008] In the above technical solution, the carbon support has a size of 100nm-1μm;

[0009] The size of the mesopores is 5-15 nm;

[0010] The micropore size is 0.5-1.5 nm;

[0011] The nanoparticles have a size of 2-3 nm;

[0012] The mass fraction of Pt or Pt alloys formed with transition metal elements in the nanoparticles is 30%-70% in the catalyst.

[0013] In the above technical solution, the mass ratio of Pt or the alloy formed by Pt and transition metal elements to the carbon support is 0.5-2.5:1.

[0014] Another aspect of the present invention provides a method for preparing the above-mentioned carbon-supported catalyst, the method comprising the following steps:

[0015] S1. The carbon precursor material is immersed in a concentrated nitric acid activation solution and then subjected to the first step of activation and acid etching under an inert atmosphere. After that, it is placed in a dilute nitric acid activation solution and subjected to the second step of activation and acid etching under an inert atmosphere. Finally, it is washed and dried to obtain the primary carbon support.

[0016] The concentration of the concentrated nitric acid activation solution is 5-8 mol / L, and the concentration of the dilute nitric acid activation solution is 0.5-1 mol / L.

[0017] S2. The primary carbon support obtained in step S1 is graphitized. After the graphitization process is completed, the product is ground to obtain carbon support powder.

[0018] S3. The carbon support powder obtained in step S2 is dispersed in an ethylene glycol solution and ultrasonically treated. Then, an ethylene glycol solution of sodium borohydride is added to the solution. Under vigorous stirring at 5000-10000 rpm, an aqueous solution of platinum precursor, or an aqueous solution of platinum precursor and a chloride ethylene glycol solution of a transition metal element, is added to obtain a mixed solution. The solution is then placed in a microwave reactor for reaction and then transferred to an oil bath for stirring reaction. The platinum precursor in the aqueous solution of platinum precursor is chloroplatinic acid or potassium chloroplatinate.

[0019] S4. After the above reaction is completed, cool to room temperature, centrifuge, wash and vacuum dry the reaction product, and finally grind the obtained product to obtain the carbon-supported catalyst.

[0020] In the above technical solution, further, in step S1, the carbon precursor material is activated carbon or carbon material supporting non-precious metal particles, wherein the mass fraction of non-precious metal particles is 50%-70%.

[0021] The inert gas one and inert gas two are independently nitrogen or argon;

[0022] The reaction temperature for the first step of activation and acid etching is 60-120℃, and the reaction time is 1-5h.

[0023] The reaction temperature for the second step of activation and acid etching is 120-150℃, and the reaction time is 10-24h.

[0024] The drying temperature is 60-80℃, and the drying time is 12-24h.

[0025] In the above technical solution, further, in step S2, the graphitization process is carried out in a vacuum graphitization furnace, the heating rate of the vacuum graphitization furnace is 5-10℃ / minute, the temperature is set at 800-1500℃, and the temperature is maintained for 0.5-4h.

[0026] In the above technical solution, further, in step S3, the concentration of the carbon support dispersed in the ethylene glycol solution is 5 mg / mL;

[0027] The concentration of the sodium borohydride in ethylene glycol solution is 0.5-3 mg / mL;

[0028] The concentration of the platinum precursor aqueous solution is 30-60 mmol / L;

[0029] The concentration of the ethylene glycol chloride solution of the transition metal element is 0.05-0.2 mol / L.

[0030] In the above technical solution, further, in step S3, the set temperature inside the microwave reactor is 80-110℃, and the microwave time is 5-20min;

[0031] The stirring temperature in the oil bath is 100-120℃, and the reaction time is 1-4h.

[0032] In the above technical solution, further, in step S4, the vacuum drying temperature is 60-80℃ and the time is 12-24h.

[0033] In summary, the functional carbon-supported catalyst with a through-hole multi-level porous structure provided by this invention has the following advantages compared with other types of carbon-supported fuel cell catalysts currently in widespread commercial use and invented:

[0034] 1) Porous carbon supports have a larger specific surface area, and the micropores on the mesoporous walls and the support surface provide effective loading sites for active metal nanoparticles, enabling the preparation of catalysts with high metal loading and providing more active sites in the catalytic electrochemical reaction process.

[0035] 2) The carbon support surface is covered with mesopores, which are randomly distributed and interconnected. On the one hand, during the loading of active components, this can effectively ensure that metal ions and reducing agents can enter the interior of the carbon support, realizing the reduction and deposition of metal active components on the surface of the internal pores. On the other hand, during the catalytic electrode reaction, the appropriate mesopore size allows the reaction gas (oxygen) to enter the internal pores of the support, and the metal active components on the surface of the internal pores can also participate in the reaction, effectively improving the utilization rate of Pt noble metal, while also reducing the resistance to the transport of gaseous substances inside the catalyst and improving the catalytic reaction efficiency.

[0036] 3) When catalysts are used in fuel cell electrodes, they must be used together with polymer ionomer resins that have proton (H+) conduction function. Studies have shown that polymer resins in fuel cell electrodes are usually coated on the surface of carbon support and coexist with active nanoparticles. O in the side chain functional groups of polymer ionomer resins will interact with Pt, affecting the electronic structure of Pt and thus affecting its catalytic performance.

[0037] Since the carbon support of the present invention has a connected mesoporous structure, it is easy for the precursor solution to fully enter its interior. Therefore, most of the reduction reaction can naturally nucleate and grow inside the pores. Secondly, multiple micropores are distributed on the surface of the mesoporous structure. Micropores and other defects are advantageous nucleation sites. Therefore, most of the active metal nanoparticles in the catalyst provided by the present invention are located on the surface of the internal pore walls. This can avoid direct contact with the polymer resin coating on the outer surface of the carbon support, effectively alleviate the poisoning effect of the side chain functional groups of the ionomer resin on Pt, and improve the catalytic activity of the catalyst.

[0038] 4) The carbon support is graphitized during the catalyst preparation process, which can effectively improve the corrosion resistance of the carbon support and the stability of the catalyst. Partial graphitization can also ensure that the already formed interconnected hierarchical pore structure is not destroyed. The high-temperature heat treatment of the carbon support also avoids the phenomenon of metal nanoparticle agglomeration and reduced active area caused by the heat treatment of the final catalyst product.

[0039] 5) Fuel cells operate under complex conditions, and the strong acid environment can easily accelerate the decay of catalyst active area and activity, leading to poor stability. The catalyst provided by this invention has most of its active metal nanoparticles dispersed in the micropores on the surface of the internal pore walls. The micropore defects play a certain anchoring role for the metal nanoparticles. Therefore, under fuel cell operating conditions, it can effectively avoid and alleviate the migration of metal nanoparticles on the carbon support surface and the occurrence of nanoparticle agglomeration, thus significantly improving the stability of the catalyst. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the structure of catalyst I prepared using the method of the present invention;

[0041] Figure 2 The CV curve of catalyst I prepared in Example 1;

[0042] Figure 3 The ORR diagram is for catalyst I prepared in Example 1;

[0043] Figure 4 The CV curve for the stability test of catalyst I prepared in Example 1;

[0044] Figure 5 ORR graph for the stability test of catalyst I prepared in Example 1;

[0045] Figure 6 CV curves for stability testing of commercial carbon-supported Pt catalysts;

[0046] Figure 7 ORR plot for stability testing of commercial carbon-supported Pt catalysts;

[0047] Figure 8 Microscopic morphology of the commercial carbon-supported Pt catalyst before stability testing;

[0048] Figure 9 Microscopic morphology of the commercial carbon-supported Pt catalyst after stability testing;

[0049] Figure 10 The image shows the microstructure of catalyst I prepared in Example 1 after stability testing.

[0050] Figure 11 The active area decay ratio of catalyst I prepared in Example 1, catalyst II prepared in Example 2, and commercial carbon-supported Pt catalyst after high-potential accelerated decay test. Detailed Implementation

[0051] The present invention will be further described in detail below with reference to the accompanying drawings.

[0052] Example 1

[0053] The method of this invention is used to prepare carbon-supported Pt catalysts with a through-hole multi-level porous structure.

[0054] First, 500 mg of carbon material supported on Fe particles (60 wt%) was immersed in an activation solution for activation and acid etching. The first step of acid etching used 6 mol / L concentrated nitric acid under an argon atmosphere at 90°C for 2 hours. The second step used 0.5 mol / L dilute nitric acid at 140°C for 15 hours. After washing and drying at 80°C for 24 hours, a primary carbon support was obtained. This primary carbon support was then placed in a vacuum graphitization furnace at 1200°C with a heating rate of 10°C / min for 1 hour. After the reaction, the material was cooled to room temperature, and the product was then subjected to further processing. The carbon support was obtained by grinding. 30 mg of carbon support was dispersed in 6 mL of ethylene glycol solution and sonicated until homogeneous. Then, a sodium borohydride ethylene glycol solution with a concentration of 2 mg / mL was added. Under vigorous stirring, 3 mL of potassium chloride platinum aqueous solution with a concentration of 50 mmol / L was added. The mixture was placed in a microwave reactor, the temperature was set to 90 °C, and the microwave time was 8 min. Then, it was transferred to an oil bath and reacted at 110 °C for 2 h under stirring. After the reaction was completed, the mixture was cooled to room temperature, and the reaction product was centrifuged, washed, and dried under vacuum overnight at 60 °C. The resulting product was then ground into fine powder to obtain the final carbon-supported Pt nanoparticle catalyst with a hierarchical porous structure, denoted as catalyst I.

[0055] A schematic diagram of the microstructure of catalyst I prepared in Example 1 is shown below. Figure 1 As shown: The carbon support of catalyst I has interconnected mesoporous structures, and microporous structures are distributed on the inner walls of the mesopores and the outer surface of the carbon support.

[0056] The oxygen reduction catalytic performance of this catalyst and a commercially available carbon-supported Pt catalyst were tested. Figure 2 The figure shows the CV curves of catalyst I and a commercial carbon-supported Pt catalyst (carbon spheres with Pt nanoparticles supported on their surface). Under the same electrode loading and test conditions, catalyst I exhibits a larger current density in the desorption peak region at low potential H, indicating that it has a larger electrochemical active area. The calculated electrochemical active area of ​​catalyst I is 10¹ m². 2 / g, while the active surface area of ​​commercially available carbon-supported Pt is 82m². 2 / g, the presence of hierarchical porous structure in the support provides more sites for the active components, and catalyst I has a larger electrochemical active area. Figure 3The ORR polarization curves of catalyst I and a commercial carbon-supported Pt catalyst are shown. Catalyst I exhibits a higher oxygen reduction onset potential and half-wave potential, indicating stronger activity. Calculations show that the specific activity of the commercial carbon-supported Pt catalyst is 0.23 A / mg@0.9V, while that of catalyst I is 0.29 A / mg@0.9V, representing a 26% increase. The utilization rate of Pt in catalyst I is improved, and a higher proportion of Pt nanoparticles dispersed on the inner pore surface reduces the poisoning effect of the resin on the catalyst, thus exhibiting superior catalytic activity. To investigate the stability of the carbon-supported catalyst with a through-hole hierarchical porous structure prepared in this invention, accelerated degradation tests were conducted on catalyst I and the commercial carbon-supported Pt catalyst. Figure 4 These are the CV curves before (solid line) and after (dashed line) the accelerated cycling test of catalyst I. Figure 6 The CV curves are before (solid line) and after (dashed line) accelerated cycling tests of commercial carbon-supported Pt catalysts under the same conditions. According to the change of the desorption peak region curve at low potential H, the decline in the active area of ​​commercial carbon-supported Pt catalyst is much greater than that of catalyst I. After calculation, the active area of ​​commercial carbon-supported Pt catalyst declined by 47% after accelerated testing, while that of catalyst I declined by only 16%. Figure 5 These are the ORR curves before (solid line) and after (dashed line) the accelerated cycling test of catalyst I. Figure 7 These are the ORR curves of a commercially available carbon-supported Pt catalyst before (solid line) and after (dashed line) accelerated cycling tests under the same conditions. Figure 5 In the process, the polarization curve of catalyst I did not show a significant activity decay, while Figure 7 Significant activity degradation was observed on the polarization curves. The microstructure and morphology of the two different catalysts were characterized after accelerated degradation testing. Figure 9 This is the microstructure of a commercial carbon-supported Pt catalyst after accelerated degradation testing. The image shows that the Pt nanoparticles on the support surface have undergone very severe aggregation. Figure 8 This is a commercially available carbon-supported Pt catalyst that has not undergone accelerated degradation testing (the nanoparticles are uniformly distributed on the surface of the carbon support), which is also the main reason for the degradation of its active area and mass activity. Figure 10 The image shows the microstructure of the catalyst I after accelerated decay test. It can be seen from the image that the Pt nanoparticles on the outer surface of the support also exhibited a certain degree of aggregation. However, a higher proportion of the Pt nanoparticles dispersed inside the pores did not exhibit obvious aggregation or detachment from the support, and remained highly uniformly dispersed on the surface of the inner pore wall.

[0057] Example 2

[0058] The method of this invention is used to prepare carbon-supported PtCo catalysts with a through-hole multi-level porous structure.

[0059] The carbon support preparation steps were the same as in Example 1, and the carbon support was obtained for later use. 30 mg of carbon support was dispersed in 6 mL of ethylene glycol solution and sonicated until homogeneous. Then, a sodium borohydride ethylene glycol solution with a concentration of 3 mg / mL was added. Under vigorous stirring, 2.3 mL of potassium chloroplatinate aqueous solution with a concentration of 50 mmol / L and 1.2 mL of cobalt chloride ethylene glycol solution with a concentration of 0.1 mol / L were added. The above mixture was placed in a microwave reactor, the temperature was set to 90 °C, and the microwave time was 15 min. Then, it was transferred to an oil bath and reacted at 110 °C for 3 h under stirring. After the reaction was completed, it was cooled to room temperature, and the reaction product was centrifuged, washed, and dried under vacuum overnight at 60 °C. The obtained product was ground into fine powder to obtain the final carbon-supported PtCo alloy nanoparticle catalyst with a hierarchical porous structure, denoted as Catalyst II.

[0060] The oxygen reduction catalytic performance of the catalyst was tested. The calculated electrochemical active area of ​​catalyst II was 122.6 m². 2 The active area of ​​catalyst II is significantly improved compared to commercial carbon-supported Pt catalysts and catalyst I. This is due to two factors: firstly, the hierarchical porous structure of the support provides more loading sites for active components; secondly, the catalytic activity is enhanced by the electronic effects of Pt after alloying. Through ORR polarization testing and calculation, the specific activity of catalyst II reached 0.67 A / mg@0.9V, which is 191% and 131% higher than that of commercial carbon-supported Pt catalysts and catalyst I, respectively. To focus on investigating the stability and durability of the support for catalyst II prepared in this invention, accelerated decay tests were conducted on catalyst II under high-potential cycling, and the results were compared with those of catalyst I and commercial carbon-supported Pt catalysts. Figure 11 As shown, after accelerated degradation testing, the active area of ​​the commercial carbon-supported Pt catalyst decreased by 80.7%, while catalysts I and II decreased by 30.5% and 41.2%, respectively. The decrease in the active area of ​​the commercial carbon-supported Pt catalyst was twice or more than that of the catalyst prepared by this invention, indicating that the catalyst prepared by the method of this invention has significantly improved stability and durability. However, it can be noted that the active area degradation of catalyst II was greater than that of catalyst I, possibly due to the dissolution of transition metal elements in the active component of catalyst II at a higher potential.

[0061] Comparative Example 1

[0062] The difference from Example 1 is that the carbon support only undergoes one step of acid etching.

[0063] 500 mg of carbon material supported on Fe particles (60 wt%) was immersed in an activation solution for activation and acid etching. The acid etching was performed using 6 mol / L concentrated nitric acid under an argon atmosphere at 110 °C for 3 h. After washing and drying at 80 °C for 24 h, a primary carbon support was obtained. This primary carbon support was then placed in a vacuum graphitization furnace at 1200 °C with a heating rate of 10 °C / min for 1 h. After the reaction, the material was cooled to room temperature and then ground to obtain a new carbon support. 30 mg of this carbon support was then... The mixture was dispersed in 6 mL of ethylene glycol solution and sonicated until homogeneous. Then, a 2 mg / mL sodium borohydride ethylene glycol solution was added, followed by 3 mL of a 50 mmol / L potassium chloroplatinate aqueous solution under vigorous stirring. The mixture was placed in a microwave reactor, set to 90 °C for 8 min, and then transferred to an oil bath. The mixture was reacted at 110 °C for 2 h under stirring. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed, and dried under vacuum overnight at 60 °C. The resulting product was then ground into fine powder to obtain the final carbon-supported Pt nanoparticle catalyst, designated as Catalyst III.

[0064] Based on testing and calculations, the active surface area of ​​catalyst III is 95m². 2 The specific activity of catalyst III is higher than that of commercial carbon-supported Pt catalysts, but lower than that of catalyst I. This is because the support treatment only involves a single acid etching step, resulting in the absence of micropores on the inner pore walls or outer surface of the carbon support, or a limited number of micropore active sites, leading to a lower effective loading of the active component. Performance tests and calculations show that catalyst III has a specific activity of 0.27 A / mg@0.9V, similar to catalyst I. Accelerated degradation tests were conducted under the same conditions as catalyst I. Catalyst III showed slightly worse cycle durability than catalyst I, with a decrease in active area and mass activity of 25% and 19%, respectively. This is presumably because the carbon support of catalyst III only underwent a single acid etching step, resulting in a lack of effective micropore anchor catalyst active components on the pore walls and support surface, leading to poorer stability compared to catalyst I.

[0065] Comparative Example 2

[0066] The difference from Example 1 is that the carbon support was not graphitized.

[0067] 500 mg of carbon material supported on Fe particles (60 wt%) was impregnated in an activation solution for activation and acid etching. The first step of acid etching used 6 mol / L concentrated nitric acid under an argon atmosphere at 90 °C for 2 h. The second step used 0.5 mol / L dilute nitric acid at 140 °C for 15 h. After washing and drying at 80 °C for 24 h, a primary carbon support was obtained. 30 mg of the primary carbon support was dispersed in 6 mL of ethylene glycol solution and subjected to ultrafiltration... The mixture was homogenized, and then a 2 mg / mL sodium borohydride ethylene glycol solution was added. Under vigorous stirring, 3 mL of a 50 mmol / L potassium chloroplatinate aqueous solution was added. The mixture was placed in a microwave reactor, the temperature was set to 90 °C, and the microwave time was 8 min. Then it was transferred to an oil bath and reacted at 110 °C for 2 h under stirring. After the reaction was completed, the mixture was cooled to room temperature, and the reaction product was centrifuged, washed, and dried under vacuum overnight at 60 °C. The resulting product was then ground into fine powder to obtain a hierarchical porous carbon-supported Pt catalyst, denoted as catalyst IV.

[0068] The ORR catalytic activity and cycle stability of catalysts IV and I were mainly tested. Catalyst IV had an active area and mass activity of 99 m². 2 / g and 0.28A / mg@0.9V. The weight loss of the carbon support was measured by electro-corrosion of catalysts I and IV to compare the corrosion resistance of the supports. Cells were assembled using catalysts I and IV for testing at 1000 mA / cm². 2 Long-term transverse current discharge at a given current density was conducted, and the corrosion resistance of the carbon support was determined by detecting and calculating the weight loss. Under the same conditions, the carbon support loss rate for catalyst I was 3%, while that for catalyst IV was 11%. The graphitized support of catalyst I exhibited a significantly lower corrosion rate and superior corrosion resistance. Cyclic durability testing was also performed on catalyst IV. Under accelerated durability testing under the same conditions as catalyst I, the active area decay was 21%, slightly higher than that of catalyst I (16%), but its stability was still superior to commercially available carbon-supported Pt catalysts. This is mainly because the structure of the carbon support provides excellent protection for the catalyst's stability.

[0069] Comparative Example 3

[0070] The difference from Example 1 is that porous carbon without a through-structure and without graphitization treatment is used as the carrier.

[0071] 30 mg of porous carbon powder was dispersed in 6 mL of ethylene glycol solution and sonicated until homogeneous. Then, a sodium borohydride ethylene glycol solution with a concentration of 2 mg / mL was added. Under vigorous stirring, 3 mL of a potassium chloride platinum aqueous solution with a concentration of 50 mmol / L was added. The mixture was placed in a microwave reactor, the temperature was set to 90 °C, and the microwave time was 8 min. Then, it was transferred to an oil bath and reacted at 110 °C for 2 h under stirring. After the reaction was completed, the mixture was cooled to room temperature, and the reaction product was centrifuged, washed, and dried under vacuum overnight at 60 °C. The resulting product was then ground into fine powder to obtain the porous carbon-supported Pt catalyst, denoted as catalyst V.

[0072] The prepared catalyst V was subjected to ORR catalytic activity and cycle stability tests. The test results showed that the active area and mass activity of catalyst V were 89 m² and 89 m², respectively. 2 The performance of catalyst V (0.24 A / mg @ 0.9 V) is slightly higher than that of commercial Pt / C catalysts, indicating that the porous structure does indeed help improve the active area and catalytic activity of the catalyst. However, both the active area and mass activity of catalyst V are lower than those of catalysts I and IV. This is mainly because although the porous carbon structure increases the active area, the improvement effect of the Pt catalyst supported by the interconnected hierarchical porous support provided in this invention is more significant. The transport of substances during the electrocatalytic reaction also has an important impact. The interconnected structure of the support described in this invention not only increases the active area and the number of catalytic active sites, but also facilitates the transport of substances during the electrode reaction, thus having a more significant enhancing effect on catalytic activity.

[0073] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A method for preparing a carbon-supported catalyst, characterized in that: The method includes the following steps: S1. The carbon precursor material is immersed in a concentrated nitric acid activation solution and then subjected to the first step of activation and acid etching under an inert atmosphere. After that, it is placed in a dilute nitric acid activation solution and subjected to the second step of activation and acid etching under an inert atmosphere. Finally, it is washed and dried to obtain the primary carbon support. The concentration of the concentrated nitric acid activation solution is 5-8 mol / L, and the concentration of the dilute nitric acid activation solution is 0.5-1 mol / L. S2. The primary carbon support obtained in step S1 is graphitized. After the graphitization process is completed, the product is ground to obtain carbon support powder. S3. The carbon support powder obtained in step S2 is dispersed in an ethylene glycol solution and ultrasonically treated. Then, an ethylene glycol solution of sodium borohydride is added to the solution. Under vigorous stirring at 5000-10000 rpm, an aqueous solution of platinum precursor, or an aqueous solution of platinum precursor and a chloride ethylene glycol solution of a transition metal element, is added to obtain a mixed solution. The solution is then placed in a microwave reactor for reaction and then transferred to an oil bath for stirring reaction. The platinum precursor in the aqueous solution of platinum precursor is chloroplatinic acid or potassium chloroplatinate. S4. After the above reaction is completed, cool to room temperature, centrifuge, wash and vacuum dry the reaction product, and finally grind the obtained product to obtain the carbon-supported catalyst.

2. The preparation method according to claim 1, characterized in that: In step S1, the carbon precursor material is activated carbon or carbon material supported on non-precious metal particles, wherein the mass fraction of the non-precious metal particles is 50%-70%. The inert atmosphere one and inert atmosphere two are independently nitrogen or argon; The reaction temperature for the first step of activation and acid etching is 60-120℃, and the reaction time is 1-5h. The reaction temperature for the second step of activation and acid etching is 120-150℃, and the reaction time is 10-24h. The drying temperature is 60-80℃, and the drying time is 12-24h.

3. The preparation method according to claim 1, characterized in that: In step S2, the graphitization process is carried out in a vacuum graphitization furnace. The heating rate of the vacuum graphitization furnace is 5-10℃ / minute, the temperature is set at 800-1500℃, and the temperature is maintained for 0.5-4 hours.

4. The preparation method according to claim 1, characterized in that: In step S3, the concentration of the carbon support dispersed in the ethylene glycol solution is 5 mg / mL; The concentration of the sodium borohydride in ethylene glycol solution is 0.5-3 mg / mL; The concentration of the platinum precursor aqueous solution is 30-60 mmol / L; The concentration of the ethylene glycol chloride solution of the transition metal element is 0.05-0.2 mol / L.

5. The preparation method according to claim 1, characterized in that: In step S3, the set temperature inside the microwave reactor is 80-110℃, and the microwave time is 5-20min; The stirring temperature in the oil bath is 100-120℃, and the reaction time is 1-4h.

6. The preparation method according to claim 1, characterized in that: In step S4, the vacuum drying temperature is 60-80℃ and the time is 12-24h.

7. A carbon-supported catalyst prepared by the method according to any one of claims 1-6, characterized in that: The catalyst includes a carbon support with multiple mesopores distributed on it. The multiple mesopores are interconnected in a random number. The walls of the mesopores and the outer surface of the carbon support are both covered with micropores. The micropores support nanoparticles, which are Pt or an alloy of Pt and transition metal elements.

8. The carbon-supported catalyst according to claim 7, characterized in that: The carbon support has a size of 100 nm-1 μm; The size of the mesopores is 5-15 nm; The micropore size is 0.5-1.5 nm; The size of the nanoparticles is 2-3 nm; The mass fraction of Pt or Pt alloys formed with transition metal elements in the nanoparticles is 30%-70% in the catalyst.

9. The carbon-supported catalyst according to claim 7, characterized in that: The mass ratio of Pt or the alloy formed by Pt and transition metal elements to the carbon support is 0.5-2.5:1.

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