A method for regenerating a deactivated Pt / C catalyst

Abstract

This invention relates to a method for regenerating deactivated Pt / C catalysts. The deactivated Pt / C catalyst is Pt nanoparticles supported on conductive carbon black. The method involves uniformly mixing a Zn-based zeolite imidazolium ester framework material and the deactivated Pt / C catalyst at a mass ratio of 5:1 to 20:1, adding an etchant at a mass ratio of 1 to 5 times the mixture, and calcining at 900°C to 1200°C. The Zn-based zeolite imidazolium ester framework material is composed of Zn-containing... 2+ The material is synthesized by reacting with 2-methylimidazole; the etching agent is a substance that can generate etching gas under high temperature conditions. The regeneration method of the deactivated Pt / C catalyst designed in this invention is simple to operate, has mild reaction conditions, and is green and safe. Existing industrial equipment can meet the requirements for all operation steps. The regenerated Pt / C catalyst obtained has good oxygen reduction activity, stability and resistance to poisoning.

Description

Technical Field

[0001] This invention relates to a method for regenerating a deactivated Pt / C catalyst; this invention also relates to the application of the regenerated Pt / C catalyst. Background Technology

[0002] Technologies for storing renewable electrical energy as chemical energy, such as hydrogen fuel cells, methanol fuel cells, and rechargeable metal-air batteries, have developed rapidly. The oxygen reduction reaction (ORR) is the cathode reaction in such technologies. However, this process involves four electron transfers, and the slow reaction kinetics result in high overpotentials, requiring catalysts to reduce the overpotential and accelerate the reaction.

[0003] Currently, platinum-supported carbon (Pt / C) is the most widely used oxygen reduction catalyst. However, Pt resources are scarce and expensive, and commercially available Pt / C catalysts have low stability. Therefore, efficient recovery and regeneration of deactivated Pt / C catalysts can significantly reduce the production and operating costs of fuel cells and promote their large-scale application. Currently, hydrometallurgy is the main method for the industrial recovery of deactivated Pt / C catalysts. Through processes such as incineration, acid leaching, reduction, and filtration, the Pt element in the deactivated Pt / C catalyst is first converted into Pt ions, which are then reduced and deposited onto a porous carbon support to regenerate the Pt / C catalyst. Hydrometallurgical processes are lengthy, requiring high-temperature calcination and aqua regia dissolution, and suffer from drawbacks such as high energy consumption, severe pollution, and low recovery efficiency. Summary of the Invention

[0004] The purpose of this invention is to design and develop a method for regenerating deactivated Pt / C catalysts and the application of the regenerated Pt / C catalysts obtained based on this method.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for regenerating deactivated Pt / C catalysts, wherein the deactivated Pt / C catalyst is Pt nanoparticles supported on conductive carbon black, wherein Zn-based zeolite imidazole ester framework material and deactivated Pt / C catalyst are uniformly mixed at a mass ratio of 5:1 to 20:1, and then an etching agent of 1 to 5 times the mass of the mixture is added, and the mixture is heated at 900 °C. o C~1200 o The Zn-based zeolite imidazole ester framework material is prepared by calcination at C; it is composed of Zn-containing... 2+ The material is synthesized by reacting it with 2-methylimidazole; the etching agent is a substance that can generate an etching gas under high temperature conditions.

[0007] The technical principle of the deactivated Pt / C catalyst regeneration method described in this invention is as follows: Under high temperature, the etchant decomposes and releases corrosive gas, which etches the aggregated Pt particles in the deactivated Pt / C catalyst, causing the Pt-Pt bonds to break and generating free Pt atoms. At the same time, the Zn-based zeolite imidazole ester framework material is carbonized to generate a defect-rich heteroatom-doped carbon conductive framework, which captures free Pt atoms at its defects, generating highly dispersed Pt single atom or Pt nanocluster sites.

[0008] The aforementioned deactivated Pt / C catalyst refers to a Pt / C catalyst whose electrochemical performance has degraded due to the agglomeration and growth of 3nm to 5nm Pt particles supported on a conductive carbon substrate after a long period of electrochemical reaction. The regenerated Pt / C catalyst obtained is a black powdery Pt / C catalyst supported on a nitrogen-doped carbon conductive substrate, wherein the catalytic active sites are Pt single atoms or Pt nanoclusters with a diameter of less than 2 nm.

[0009] The specific steps of the above-mentioned regeneration method for deactivated Pt / C catalyst are as follows:

[0010] 1) Weigh zinc nitrate hexahydrate and dissolve it in methanol to prepare a solution with a concentration of 0.2 mol / L-0.5 mol / L. Then, uniformly disperse the deactivated Pt / C catalyst in the solution at an addition rate of 0.25 mg / L-0.5 mg / L, and record this as dispersion 1.

[0011] 2) Weigh out 2-methylimidazole and dissolve it in methanol to prepare a solution with a concentration of 0.8 mol / L-1.6 mol / L, which is denoted as solution 2;

[0012] 3) Mix dispersion 1 and solution 2 at a volume ratio of 1:1, sonicate for 5 to 20 minutes, and let stand at room temperature for 12 to 36 hours to obtain a mixed powder of Zn-based zeolite imidazole ester framework and deactivated Pt / C catalyst. Wash several times with ethanol and deionized water, and dry for later use.

[0013] 4) After mixing the mixed powder obtained in step (3) with the etchant, grind it evenly, and then grind it at 2-5 g / L under a nitrogen or argon inert gas atmosphere. o Heat to 900 °C / min o C~1200 o After calcining in C for 1–5 h, the catalyst is naturally cooled to room temperature and then ground into powder to obtain a regenerated nitrogen-doped carbon conductive substrate supported Pt / C catalyst.

[0014] The deactivated Pt / C catalyst in step (1) is a Pt / C catalyst with degraded electrochemical performance, with a Pt loading of 20wt%-60wt%, preferably 50wt%; the amount of the deactivated Pt / C catalyst is preferably 0.25 mg / L; the volume of the zinc nitrate hexahydrate solution is 20 mL-40 mL, and the concentration is 0.2 mol / L-0.5 mol / L, preferably 0.2 mol / L;

[0015] Preferably, the concentration of the 2-methylimidazole solution in step (2) is 0.8 mol / L.

[0016] The etching agent added in step (4) is preferably ammonium chloride or ammonium fluoride, and the mass of the etching agent is 1 to 5 times the mass of the mixed powder obtained in step (3).

[0017] Regenerated Pt / C catalysts can be applied to new energy systems where Pt catalysts are suitable for catalysis, such as hydrogen fuel cells, methanol fuel cells, and water electrolysis; especially when using alkaline electrolytes at temperatures of 10~95°C. o C.

[0018] Beneficial effects: This invention directly regenerates the Pt / C catalyst by separating it from the end-of-life fuel cell through direct high-temperature heat treatment. Compared with existing hydrometallurgical technologies, this invention has the following advantages:

[0019] 1) The regeneration method for the deactivated Pt / C catalyst designed in this invention is simple to operate, has mild reaction conditions, and is green and safe. Existing industrial equipment can meet the requirements for all operation steps.

[0020] 2) The regeneration method for deactivated Pt / C catalyst designed in this invention reduces the process flow, and the utilization rate of Pt in the regenerated Pt catalyst exceeds 95%, reducing Pt loss during the recovery process;

[0021] 3) The regeneration method of the deactivated Pt / C catalyst designed in this invention transforms agglomerated Pt particles into Pt single atoms or Pt nanoclusters, which are highly dispersed on the surface of heteroatom-doped carbon conductive framework. The Pt loading is reduced from the original 20 wt% - 60 wt% to about 10 wt%, but the original oxygen reduction activity is still maintained, and the stability and resistance to poisoning are improved. Attached Figure Description

[0022] Figure 1 X-ray powder diffraction (XRD) patterns of the 50 wt% Pt / C catalyst and the regenerated Pt / C catalyst prepared in Example 1.

[0023] Figure 2The image shows a scanning electron microscope (SEM) image of the regenerated Pt / C catalyst prepared in Example 1.

[0024] Figure 3 Transmission electron microscopy (TEM) images of the 50 wt% Pt / C catalyst and the regenerated Pt / C catalyst prepared in Example 1.

[0025] Figure 4 The image shows a scanning tunneling microscope (STEM) image of the prepared regenerated Pt / C catalyst.

[0026] Figure 5 A comparison of linear voltammetry (LSV) curves of the 50 wt% Pt / C catalyst and the regenerated Pt / C catalyst prepared in Example 1.

[0027] Figure 6 The graph shows the stability test results of the regenerated Pt / C catalyst prepared in Example 1.

[0028] Figure 7 Comparison of the poisoning resistance test results of the 50wt% Pt / C catalyst and the regenerated Pt / C catalyst prepared in Example 1.

[0029] Figure 8 This is a SEM image of the regenerated Pt / C catalyst prepared in Example 2.

[0030] Figure 9 This is a comparison chart of LSV test results for the deactivated Pt / C catalyst at the fuel cell anode described in Example 2 and the regenerated Pt / C catalyst prepared in Example 2.

[0031] Figure 10 The graph shows the stability test results of the regenerated Pt / C catalyst prepared in Example 2.

[0032] Figure 11 This is a SEM image of the regenerated Pt / C catalyst prepared in Example 3.

[0033] Figure 12 This is a comparison chart of LSV test results for the deactivated Pt / C catalyst at the fuel cell cathode described in Example 3 and the regenerated Pt / C catalyst prepared in Example 3.

[0034] Figure 13 The graph shows the stability test results of the regenerated Pt / C catalyst prepared in Example 3. Implementation

[0035] The technical solutions in the embodiments of the present invention will be described in further detail below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0036] The electrocatalytic oxygen reduction activity testing conditions used in this invention are as follows: a three-electrode system is used, with 0.1 mol / L KOH as the electrolyte, a platinum sheet as the counter electrode with a purity higher than 99.99%, and a saturated calomel electrode as the reference electrode. The testing instrument is a Shanghai Chenhua CHI660e electrochemical workstation. All test voltage values ​​are converted to the voltage values ​​relative to the standard hydrogen electrode. Example

[0037] 1) Weigh 1069 mg of zinc nitrate hexahydrate and dissolve it in 15 mL of methanol. Then, uniformly disperse 1 mg of 50 wt% Pt / C catalyst in the methanol solution and record it as dispersion 1.

[0038] 2) Weigh 1161 mg of 2-methylimidazole and dissolve it in 15 mL of methanol, which is recorded as solution 2;

[0039] 3) After mixing dispersion 1 and solution 2, ultrasonic treatment was performed for 20 min, and the mixture was allowed to stand at room temperature for 12 h to obtain a mixed powder of Zn-based zeolite imidazole ester framework and Pt / C catalyst.

[0040] 4) Grind the mixed powder obtained in step 3) with 0.2 g of ammonium chloride until uniform, then calcine it at 950 °C for 3 h under N2 atmosphere at a rate of 5 °C / min. After naturally cooling to room temperature, grind it to obtain the regenerated Pt / C catalyst.

[0041] See Figure 1 Based on the XRD patterns of the 50 wt% Pt / C catalyst and the regenerated Pt / C catalyst prepared in Example 1, it can be seen that the regenerated Pt / C catalyst does not contain crystalline Pt, and Pt mainly exists in the form of single atoms or nanoclusters.

[0042] See Figure 2 , Figure 2 The image shows an SEM image of the regenerated Pt / C catalyst prepared in Example 1. It can be seen that the size of the heteroatom-doped carbon conductive framework particles is about 200 nm.

[0043] See Figure 3 , Figure 3 TEM images of a 50 wt% Pt / C catalyst and the regenerated Pt / C catalyst prepared in Example 1. Before regeneration, the Pt particle size was about 2 nm, and after regeneration, Pt clusters were distributed on the surface of the heteroatom-doped carbon conductive framework.

[0044] See Figure 4 , Figure 4 The image shows a STEM image of the regenerated Pt / C catalyst prepared in Example 1. It can be seen that the active sites on the material surface are Pt single atoms or nanoclusters smaller than 2 nm.

[0045] See Figure 5 , Figure 5 Comparison of LSV test results for the 50 wt% Pt / C catalyst and the regenerated Pt / C catalyst prepared in Example 1.

[0046] The electrode preparation method is as follows: a catalyst dispersion was prepared using 5 mg of catalyst and a mixed solvent, comprising 50 μL of 5 wt% Nafion solution and 950 μL of ethanol. 6 μL of the catalyst dispersion was dropwise added to a glassy carbon surface to form the working electrode. The electrolyte was 0.1 mol / L KOH saturated with O2. The LSV scan rate was 10 mV / s, and the rotation speed was 1600 r / min. The Pt / C used was 50 wt% of a commercial Pt / C catalyst (manufactured by Tanaka Precious Metals, Japan, product model TEC10EA50E). The figure shows that the half-wave potential of the Pt / C catalyst prepared using conventional commercial carbon black was 0.84 V (vs. RHE, where RHE is the reversible hydrogen electrode), while the half-wave potential of the regenerated Pt / C catalyst reached 0.91 V (vs. RHE). This indicates that the regenerated Pt / C catalyst prepared in this invention has sufficient oxygen reduction catalytic activity.

[0047] See Figure 6 , Figure 6 The stability test diagram of the regenerated Pt / C catalyst prepared in Example 1 shows the excellent stability of the regenerated Pt / C catalyst.

[0048] See Figure 7 , Figure 7 Comparison of the poisoning resistance test results of the 50 wt% Pt / C catalyst and the regenerated Pt / C catalyst prepared in Example 1.

[0049] It can be seen that the oxygen reduction current of commercial Pt / C catalysts decreases significantly after the addition of ethanol or carbon monoxide. However, the oxygen reduction current of regenerated Pt / C catalysts does not decrease significantly, proving that regenerated catalysts have significant resistance to certain liquid or gaseous poisoning substances. Example

[0050] 1) Weigh 1603 mg of zinc nitrate hexahydrate and dissolve it in 20 mL of methanol. Then, uniformly disperse 3 mg of Pt / C catalyst for fuel cell anode deactivation in the methanol solution. This is called dispersion 1.

[0051] 2) Weigh 1741 mg of 2-methylimidazole and dissolve it in 20 mL of methanol, which is recorded as solution 2;

[0052] 3) After mixing dispersion 1 and solution 2, ultrasonic treatment was performed for 20 min, and the mixture was allowed to stand at room temperature for 12 h to obtain a mixed powder of Zn-based zeolite imidazole ester framework and deactivated Pt / C catalyst.

[0053] 4) Grind the mixed powder obtained in step 3) with 0.3 g of ammonium fluoride until uniform, then calcine it at 1100 °C for 2 h under N2 atmosphere at a temperature of 2 °C / min. After naturally cooling to room temperature, grind it to obtain the regenerated Pt / C catalyst.

[0054] See Figure 8 , Figure 8 The image shows a SEM image of the regenerated Pt / C catalyst prepared in Example 2. Figure 8 It can be concluded that... Figure 2 The regenerated Pt / C catalyst prepared in Example 1 shows similar conclusions.

[0055] See Figure 9 , Figure 9 This is a comparison graph showing the LSV test results of the deactivated Pt / C catalyst at the fuel cell anode described in Example 2 and the regenerated Pt / C catalyst prepared in Example 2. (The last sentence appears to be incomplete and possibly refers to a different topic.) Figure 4 Under the same electrode preparation method, it can be concluded that... Figure 4 The conclusions are similar to those drawn from the regenerated Pt / C catalyst prepared in Example 1.

[0056] See Figure 10 , Figure 10 The stability test graph of the regenerated Pt / C catalyst prepared in Example 2 is shown below. Figure 5 The regenerated Pt / C catalyst prepared in Example 1 shows a similar conclusion. Example

[0057] 1) Weigh 2672 mg of zinc nitrate hexahydrate and dissolve it in 40 mL of methanol. Then, uniformly disperse 10 mg of Pt / C catalyst deactivated at the fuel cell cathode in the methanol solution. This is called dispersion 1.

[0058] 2) Weigh 2902 mg of 2-methylimidazole and dissolve it in 40 mL of methanol, which is recorded as solution 2;

[0059] 3) After mixing dispersion 1 and solution 2, ultrasonic treatment was performed for 20 min, and the mixture was allowed to stand at room temperature for 12 h to obtain a mixed powder of Zn-based zeolite imidazole ester framework and deactivated Pt / C catalyst.

[0060] 4) Grind the mixed powder obtained in step 3) with 0.5g of ammonium chloride until uniform, then calcine it at 1000℃ for 4h under N2 atmosphere at a rate of 3℃ / min. After naturally cooling to room temperature, grind it to obtain the regenerated Pt / C catalyst.

[0061] The electrocatalytic electrodes prepared by the electrocatalysts in the above embodiments can all be applied to new energy systems that require oxygen reduction reactions, such as water electrolysis for hydrogen production, hydrogen fuel cells, and methanol fuel cell systems.

[0062] See Figure 11 , Figure 11 The image shows a SEM image of the regenerated Pt / C catalyst prepared in Example 3, compared with... Figure 2 The regenerated Pt / C catalyst prepared in Example 1 shows a similar conclusion.

[0063] See Figure 12 , Figure 12 This is a comparison chart of LSV test results for the deactivated Pt / C catalyst at the fuel cell cathode described in Example 3 and the regenerated Pt / C catalyst prepared in Example 3. (The chart is used in conjunction with...) Figure 4 Under the same electrode preparation method, it can be concluded that... Figure 4 The conclusions are similar to those drawn from the regenerated Pt / C catalyst prepared in Example 1.

[0064] See Figure 13 , Figure 13 The stability test graph of the regenerated Pt / C catalyst prepared in Example 3 is shown below. Figure 5 The regenerated Pt / C catalyst prepared in Example 1 shows a similar conclusion.

[0065] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for regenerating a deactivated Pt / C catalyst, wherein the deactivated Pt / C catalyst is Pt nanoparticles supported on conductive carbon black, characterized in that... Zn-based zeolite imidazolium ester framework material and deactivated Pt / C catalyst were uniformly mixed at a mass ratio of 5:1 to 20:1, and then 1 to 5 times the mass of the mixture of etching agent was added. The mixture was then calcined at 900 °C to 1200 °C. The Zn-based zeolite imidazolium ester framework material was prepared from Zn-containing... 2+ The material is synthesized by reacting it with 2-methylimidazole; the regeneration method includes the following steps: 1) Weigh zinc nitrate hexahydrate and dissolve it in methanol to prepare a solution with a concentration of 0.2 mol / L-0.5 mol / L. Then, uniformly disperse the deactivated Pt / C catalyst in the solution at an addition rate of 0.25 mg / L-0.5 mg / L, and record this as dispersion 1. 2) Weigh out 2-methylimidazole and dissolve it in methanol to prepare a solution with a concentration of 0.8 mol / L-1.6 mol / L, which is denoted as solution 2; 3) Mix dispersion 1 and solution 2 at a volume ratio of 1:1, sonicate for 5 to 20 minutes, and let stand at room temperature for 12 to 36 hours to obtain a mixed powder of Zn-based zeolite imidazole ester framework and deactivated Pt / C catalyst. Wash several times with ethanol and deionized water, and dry for later use. 4) The mixed powder obtained in step (3) is mixed with the etchant and ground evenly. Then, under a nitrogen or argon inert gas atmosphere, it is heated to 900 ℃ to 1200 ℃ at a rate of 2 to 5 ℃ / min and calcined for 1 to 5 hours. After cooling naturally to room temperature, it is ground into powder to obtain the regenerated nitrogen-doped carbon conductive substrate supported Pt / C catalyst. The etching agent added in step (4) is ammonium chloride or ammonium fluoride.

2. The regeneration method for the deactivated Pt / C catalyst as described in claim 1, characterized in that... The regenerated Pt / C catalyst obtained is a Pt / C catalyst supported on a nitrogen-doped carbon conductive substrate, wherein the catalytic active sites are Pt single atoms or Pt nanoclusters with a diameter of less than 2 nm.

3. The regeneration method for the deactivated Pt / C catalyst as described in claim 1, characterized in that: The deactivated Pt / C catalyst in step (1) is the Pt / C catalyst after its electrochemical performance has degraded; the zinc nitrate hexahydrate solution has a volume of 20 mL-40 mL and a concentration of 0.2 mol / L-0.5 mol / L.

4. The application of the nitrogen-doped carbon conductive substrate-supported Pt / C catalyst prepared by the regeneration method according to any one of claims 1-3, characterized in that: The regenerated nitrogen-doped carbon conductive substrate-supported Pt / C catalyst is applied to new energy systems using suitable Pt catalysts for hydrogen fuel cells, methanol fuel cells, and water electrolysis; an alkaline electrolyte is used, and the electrolyte temperature is 10~95℃. o C.

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