Microporous carbon-coated platinum nanoparticle electrocatalyst and method of making same

Abstract

The present application relates to a kind of microporous carbon-coated platinum nanoparticles electrocatalyst and its preparation method.The method includes the following steps: adding noble metal ion solution and volatile metal ion solution to carbon substrate solution, and uniformly dispersed;Again, soluble carbon-nitrogen compound solution is added, and after mixing uniformly, freeze-drying;The product is carbonized under inert atmosphere, and microporous carbon-coated nanoparticles are obtained;After the product is pickled again, carbonization is carried out, and microporous carbon-coated platinum nanoparticles electrocatalyst is obtained.Compared with prior art, the present application can be in situ loaded with porous carbon-coated noble metal Pt catalyst on carbon substrate, can inhibit the fusion of adjacent platinum particles in long cycle process without sacrificing the stability of catalyst, overcome the difficult problem that the activity and stability of existing Pt / C catalyst are difficult to obtain. In addition, the method also provides a reference for preparing other high-activity, high-stability porous carbon-coated noble metal catalyst.

Description

Technical Field

[0001] This invention relates to the field of electrocatalysts, specifically to a microporous carbon-coated platinum nanoparticle electrocatalyst and its preparation method. Background Technology

[0002] The oxygen reduction reaction (ORR) at the cathode of a hydrogen fuel cell involves multiple electron transfer steps, resulting in a slow kinetic process that heavily relies on the scarce and expensive precious metal platinum (Pt) catalyst. This has become a major factor limiting the large-scale industrialization of hydrogen fuel cell power technology. Therefore, reducing the Pt loading in the ORR catalyst while maintaining catalytic performance is a pressing issue that needs to be addressed to reduce fuel cell costs and promote the commercialization of fuel cell power technology.

[0003] Currently, the main technical approach to reducing Pt loading is to decrease catalyst size, i.e., to prepare ultrafine Pt nanoparticles (≤5 nm), which allows for more active sites per unit mass of Pt, thereby increasing the electrochemically effective active area (ECSA) of the catalyst. However, ultrafine Pt nanoparticles have poor thermodynamic stability and are prone to agglomeration into large particles during start-up and cyclic loading through physical aggregation and / or Ostwald ripening, leading to a gradual decrease in ECSA and durability. On the other hand, maintaining the same power density or current density under low Pt loading conditions also leads to an increase in O2 and H2O transport rates, thereby accelerating Pt atom dissolution and Ostwald ripening, further exacerbating catalyst degradation during PEMFC operation.

[0004] Chinese invention patents CN 114225935 A (Preparation and Application of Onion-Shaped Supported Carbon-Coated Platinum Catalyst) and CN114142044 A (A Method for Carbon Coating Platinum-Carbon Catalyst) both start with Pt / C catalysts, blending them with carbon source compounds or organic molecules and then carbonizing them to obtain carbon-coated Pt / C catalysts, effectively improving the stability of Pt / C catalysts. However, most of the reported carbon-coated Pt / C catalysts currently reported have a closed carbon layer on their surface, and their activities are lower than those of uncoated Pt / C. The reason for this is that the surface carbon layer hinders the direct contact between Pt particles and reactants. The outer d orbitals of Pt atoms must hybridize with the p orbitals of the outermost carbon atoms to enhance the electron cloud density and Fermi level of the carbon layer electrons in order to accelerate the reaction process. However, this interaction weakens with the increase of carbon layer thickness, resulting in a decrease in the activity of Pt / C catalysts. Summary of the Invention

[0005] The purpose of this invention is to overcome at least one of the defects of the prior art and provide a microporous carbon-coated platinum nanoparticle electrocatalyst with a porous carbon coating that can protect Pt particles while allowing reactants to pass through, and a method for preparing the same.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] The inventors understand that, in existing technologies, due to the lack of high-temperature pore-forming agents, the carbon-coated Pt / C catalysts obtained by these methods are mostly covered with a thick, closed carbon layer, resulting in lower activity than uncoated Pt / C. This invention starts with Pt / C catalysts, coating their surface with a carbon layer to form a closed structure, restricting the migration and aggregation of Pt nanoparticles. The specific solution is as follows:

[0008] A method for preparing a microporous carbon-coated platinum nanoparticle electrocatalyst, the method comprising the following steps:

[0009] Add noble metal ion solution and volatile metal ion solution to carbon-based solution and disperse evenly;

[0010] Add a soluble carbon and nitrogen compound solution, mix well, and then freeze-dry.

[0011] The product was carbonized in an inert atmosphere to obtain microporous carbon-coated nanoparticles.

[0012] The product was acid-washed and then carbonized again to obtain a platinum nanoparticle electrocatalyst coated with microporous carbon.

[0013] During carbonization, Zn and Pt ions are reduced to metals or alloys. Carbonitrides are carbonized to form a carbon layer that coats the metal surface. Some Zn volatilizes onto the carbon layer, creating micropores. After acid washing, the Zn in the alloy is corroded, leaving only metallic Pt. After re-carbonization, a microporous carbon-coated platinum nanoparticle electrocatalyst can be obtained.

[0014] This invention ingeniously introduces a pore-forming agent, zinc, into Pt nanoparticles before carbon coating, followed by high-temperature carbonization. Utilizing the high volatility of metallic Zn at high temperatures, micropores are introduced into the carbon layer coating the metal surface. Residual metallic Zn and unstable Pt atoms are then washed away using hot nitric acid, and a second carbonization process yields microporous carbon-coated Pt nanoparticles.

[0015] After acid washing, Zn is removed from the Pt-Zn particles, leaving a large number of unsaturated coordinated Pt atoms on the surface of the Pt particles, such as atoms at the edges and corners of irregular Pt particles and Pt-O bonds. Simultaneously, the carbon substrate is partially oxidized, forming CO and NO bonds on the surface. Recarbonization provides sufficient energy to cause the irregular Pt particles to rearrange and remove oxide species from the carbon substrate, thereby improving the catalyst's activity and stability. Without recarbonization, the catalyst's activity and stability will decrease to some extent.

[0016] Furthermore, the volatile metal is a metal that is volatile at 700-900℃, including zinc. The pore-forming agent metal is volatile after the carbon coating layer is formed at 700-900℃, and the residual pore-forming agent is easily removed by acid washing; zinc is a preferred pore-forming agent.

[0017] Furthermore, the pore-forming agent precursor is a zinc salt solution, including aqueous solutions of zinc chloride, zinc sulfate, zinc nitrate, or zinc acetate.

[0018] Furthermore, the carbon substrate includes carbon aerogel or Ketjen black; the noble metal ion solution includes an aqueous solution of platinum tetrachloride, chloroplatinic acid, or potassium chloroplatinate; and the soluble carbon-nitrogen compound solution is an aqueous solution of dicyandiamide or melamine.

[0019] Furthermore, the catalyst contains 20-50 wt% noble metals; the mass ratio of volatile metals to noble metals is 1:(0.5-1); and the mass ratio of soluble carbon and nitrogen compounds to noble metals is 1:(1-10).

[0020] Furthermore, the carbonization temperature is 700-900℃, and the time is 1-3 hours.

[0021] Furthermore, during pickling, nitric acid with a concentration range of 0.1-5M is used, and the pickling temperature range is 50-90℃.

[0022] Furthermore, the re-carbonization temperature is 50-100°C lower than the carbonization temperature, and the time is 20-40 minutes.

[0023] Furthermore, the carbonization conditions are as follows: under a nitrogen atmosphere, first hold at 180-300℃ for 1-3 hours, then hold at 700-900℃ for 1-3 hours.

[0024] A microporous carbon-coated platinum nanoparticle electrocatalyst prepared by the method described above.

[0025] Compared with existing technologies, this invention can support noble metal Pt catalysts with porous carbon coating in situ on a carbon substrate, such as... Figure 1 This method can suppress the fusion of adjacent platinum particles during long-cycle processes without sacrificing catalyst stability, overcoming the challenge of achieving both activity and stability in existing Pt / C catalysts. Furthermore, this method also provides a reference for the preparation of other highly active and stable porous carbon-coated noble metal catalysts. Attached Figure Description

[0026] Figure 1 This invention provides a comparison between the concepts of carbon coating and microporous carbon coating.

[0027] Figure 2 This is a BET comparison chart of the materials in Example 1 and Comparative Example 1;

[0028] Figure 3 This is a comparison chart of the LSV values ​​of the materials in Example 1 and Comparative Example 1;

[0029] Figure 4 This is a comparison of LSV before and after CV10000 cycles in Example 1. Detailed Implementation

[0030] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0031] A microporous carbon-coated platinum nanoparticle electrocatalyst and its preparation method, comprising the following steps:

[0032] (1) Add Pt and Zn ion solutions to the carbon-based solution and sonicate to disperse them evenly; the noble metal ion solution is an aqueous solution of platinum tetrachloride, chloroplatinic acid or potassium chloroplatinate, and the volatile metal ion solution is an aqueous solution of zinc chloride, zinc sulfate, zinc nitrate or zinc acetate; add platinum precursor according to the theoretical platinum content of 20-50 wt%. The mass ratio of Zn to Pt is in the range of 1:(0.5-1).

[0033] (2) Add a soluble carbon-nitrogen compound solution to the solution obtained in step (1), mix well and freeze dry; the soluble carbon-nitrogen compound solution is a dicyandiamide or melamine aqueous solution; the mass ratio of soluble carbon-nitrogen compound to Pt is 1:(1-10).

[0034] (3) The product obtained in step (2) is carbonized in an inert atmosphere to obtain microporous carbon-coated platinum-zinc nanoparticles; the carbonization conditions are: in a nitrogen atmosphere, heat at 180-300℃ for 1-3 hours and then heat at 700-900℃ for 1-3 hours.

[0035] (4) The product obtained in step (3) is acid-washed and then carbonized again to obtain a microporous carbon-coated platinum nanoparticle electrocatalyst, namely microporous carbon-coated Pt / C. The acid is nitric acid, the concentration of which is 0.1-5M, and the acid washing temperature is 50-90℃.

[0036] Example 1

[0037] A microporous carbon-coated platinum nanoparticle electrocatalyst and its preparation method, comprising the following steps:

[0038] (1) Disperse 30 mg of carbon aerogel in 20 ml of deionized water and sonicate for 30 minutes to make it uniformly dispersed to obtain a carbon-based solution.

[0039] (2) Slowly add 1.5 ml of 1 mol / L chloroplatinic acid aqueous solution and 1.5 ml of 2 mol / L zinc chloride aqueous solution to the solution obtained in step (1), and sonicate for 30 minutes to disperse it evenly.

[0040] (3) Slowly add 3 ml of 1 mol / L dicyandiamide aqueous solution to the solution obtained in step (2), stir for 4 hours and freeze dry.

[0041] (4) The precursor obtained in step (3) is placed in a tube furnace for pyrolysis to obtain microporous carbon-coated Pt-Zn nanoparticles. The pyrolysis conditions are 180℃ for 3 hours and 750℃ for 2 hours under an argon atmosphere. At this time, Pt and Zn ions are reduced to metals or alloys, and carbonitrides are carbonized to form a carbon layer that coats the metal surface. Some Zn volatilizes on the coated carbon layer to create micropores.

[0042] (5) Place the microporous carbon-coated Pt-Zn nanoparticles obtained in step (4) at 85°C and stir with 0.5M dilute nitric acid for 2 hours, then filter and rinse with deionized water 3 times.

[0043] (6) After drying the solid obtained in step (5), carbonize it again to obtain microporous carbon-coated Pt nanoparticle electrocatalyst.

[0044] Comparative Example 1

[0045] The difference from Example 1 is that, except for the absence of adding metallic Zn and acid washing, the other steps are the same as the preparation method of microporous carbon-coated Pt / C catalyst, resulting in carbon-coated platinum nanoparticle electrocatalyst, i.e. carbon-coated Pt / C.

[0046] Test conditions:

[0047] Preparation of catalyst slurry: 6 mg catalyst and 40 μL Nafion membrane solution were dispersed in 960 μL water-isopropanol mixed solution (volume ratio 3:1), and ultrasonicated for 1 h to obtain a homogeneous slurry.

[0048] LSV Testing: A traditional three-electrode system was used to evaluate the electrochemical performance of the synthesized catalyst on a Shanghai Chenhua CHI 760E electrochemical workstation. The electrolyte was 0.1M HClO4, the working electrode was a platinum-carbon electrode, and the reference and counter electrodes were SCE and graphite rods, respectively. 10 μL of catalyst slurry was pipetted onto the surface of the platinum-carbon electrode and allowed to air dry at room temperature, forming a thin electrode film. Before ORR testing, high-purity O2 was passed through the electrolytic cell for at least 0.5 h until the electrolyte was O2 saturated. Linear sweep voltammetry (LSV) was performed within a specific voltage range to obtain the catalyst's ORR performance. The LSV scan rate was set to 5 mV / s. Automatic solution compensation was performed by the electrochemical workstation during the test.

[0049] Stability test: The LSV-tested samples were cycled 10,000 times in the potential range of 0.6-1.0V vs RHE at a scan rate of 20mV / s.

[0050] Figure 2 The image shows a BET comparison of microporous carbon-coated Pt / C and carbon-coated Pt / C. Figure 2 As can be seen, the micropore content of the Pt / C catalyst coated with microporous carbon is much greater than that of the carbon-coated Pt / C catalyst, indicating that the introduction of zinc effectively introduces micropores on the surface of microporous carbon.

[0051] Figure 3 Comparison of LSV (Laser Vibration Value) between microporous carbon-coated Pt / C and carbon-coated Pt / C. From Figure 3 As can be seen, the half-wave potential of the microporous carbon-coated Pt / C catalyst is higher than that of the carbon-coated Pt / C catalyst, indicating that the activity of the microporous carbon-coated Pt / C catalyst is superior to that of the carbon-coated Pt / C catalyst.

[0052] Figure 4 Comparison of LSV (Liquid Vapor Spectroscopy) before and after CV 10,000 cycles for a microporous carbon-coated Pt / C catalyst. Figure 4 As can be seen, the half-wave potential of the microporous carbon-coated Pt / C catalyst did not change significantly after 10,000 cycles, indicating that the microporous carbon-coated Pt / C catalyst has excellent stability.

[0053] Example 2

[0054] A microporous carbon-coated platinum nanoparticle electrocatalyst and its preparation method, comprising the following steps:

[0055] (1) Disperse 40 mg of Ketjen black in 20 ml of deionized water and sonicate for 30 minutes to make it uniformly dispersed to obtain a carbon-based solution.

[0056] (2) Slowly add 1.5 ml of 1 mol / L chloroplatinic acid aqueous solution and 1.5 ml of 2 mol / L zinc chloride aqueous solution to the solution obtained in step (1), and sonicate for 30 minutes to disperse it evenly.

[0057] (3) Slowly add 3 ml of 1 mol / L dicyandiamide aqueous solution to the solution obtained in step (2), stir for 4 hours and freeze dry.

[0058] (4) The precursor obtained in step (3) is placed in a tube furnace for pyrolysis to obtain microporous carbon-coated Pt-Zn nanoparticles. The pyrolysis conditions are 180℃ for 3 hours and 750℃ for 2 hours under an argon atmosphere. At this time, Pt and Zn ions are reduced to metals or alloys, and carbonitrides are carbonized to form a carbon layer that coats the metal surface. Some Zn volatilizes on the coated carbon layer to create micropores.

[0059] (5) Place the microporous carbon-coated PtZn nanoparticles obtained in step (4) at 85°C and stir with 0.5M dilute nitric acid for 2 hours, then filter and rinse with deionized water 3 times.

[0060] (6) After drying the solid obtained in step (5), carbonize it again to obtain Pt nanoparticles coated with microporous carbon.

[0061] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a microporous carbon-coated platinum nanoparticle electrocatalyst, characterized in that, The method includes the following steps: Add noble metal ion solution and volatile metal ion solution to carbon-based solution and disperse evenly; Add a soluble carbon and nitrogen compound solution, mix well, and then freeze-dry. The product was carbonized in an inert atmosphere to obtain microporous carbon-coated nanoparticles. The product was acid-washed and then carbonized again to obtain a microporous carbon-coated platinum nanoparticle electrocatalyst. The volatile metals mentioned are metals that are volatile at 700-900℃, and the volatile metals include zinc; The carbonization temperature is 700-900℃, and the time is 1-3 h; The carbonization is used to reduce Zn and Pt ions into metals or alloys. Carbon nitrides are carbonized to form a carbon layer that coats the metal surface. Some noble metals volatilize on the coated carbon layer, creating micropores. During pickling, nitric acid with a concentration ranging from 0.1 to 5 M is used, and the pickling temperature range is 50 to 90°C; the pickling is used to remove volatile metals. The re-carbonization temperature is 50-100°C lower than the carbonization temperature, and the time is 20-40 min; the re-carbonization is used to provide energy to cause irregular Pt particles to rearrange and remove oxide species on the carbon substrate.

2. The method for preparing a microporous carbon-coated platinum nanoparticle electrocatalyst according to claim 1, characterized in that, The carbon substrate includes carbon aerogel or Ketjen black; the noble metal ion solution includes an aqueous solution of platinum tetrachloride, chloroplatinic acid, or potassium chloroplatinate; and the soluble carbon nitrogen compound solution is an aqueous solution of dicyandiamide or melamine.

3. The method for preparing a microporous carbon-coated platinum nanoparticle electrocatalyst according to claim 1, characterized in that, The catalyst contains 20-50 wt% noble metals; the mass ratio of volatile metals to noble metals is 1:(0.5-1); and the mass ratio of soluble carbon and nitrogen compounds to noble metals is 1:(1-10).

4. The method for preparing a microporous carbon-coated platinum nanoparticle electrocatalyst according to claim 1, characterized in that, The carbonization conditions are as follows: under a nitrogen atmosphere, first keep at 180-300℃ for 1-3 hours, then keep at 700-900℃ for 1-3 hours.

5. A microporous carbon-coated platinum nanoparticle electrocatalyst prepared by the method according to any one of claims 1-4.

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