Platinum diatomic catalyst as well as preparation method and application thereof

Abstract

The invention relates to the fields of new energy materials and devices and chemistry and chemical engineering, provides a platinum diatomic catalyst and a preparation method and application thereof, and can realize precise and large-scale synthesis of the platinum diatomic catalyst. The platinum diatomic catalyst prepared by the invention has different coordination environments and excellent hydrogen evolution performance, and provides a new thought for realizing efficient and low-cost utilization of precious metal platinum.

Description

Technical Field

[0001] This invention relates to a platinum diatomic catalyst, its preparation method and application, belonging to the fields of new energy materials and devices, and chemical engineering. Background Technology

[0002] Green hydrogen, produced by electrolyzing water using renewable energy-powered electricity, is considered a key carrier for the future energy system.

[0003] Platinum (Pt) remains the benchmark electrocatalyst for hydrogen electrolysis (HER) cathode reactions due to its superior intrinsic activity and electrochemical stability. However, the scarcity and high price of Pt limit its large-scale application. Traditional Pt catalysts exhibit low atom utilization efficiency because only a small fraction of surface atoms actively participate in the catalytic process. Therefore, improving the atom utilization rate of Pt catalysts is a crucial approach to overcoming its scarcity and high price.

[0004] Single-atom catalysts (SACs) have become a popular research area due to their maximized utilization of metal atoms and unique physicochemical properties. However, SACs suffer from problems such as insufficient stability, high difficulty in preparation, and limited application scenarios.

[0005] Diatomic catalysts (DACs) can effectively overcome the performance bottleneck of saturated carbon catalysts (SACs) due to the synergistic effect between bimetallic active sites. However, the complex relationship between the local atomic coordination environment and catalytic behavior of DACs is still not fully understood. Therefore, methods for the precise construction and control of diatomic sites will contribute to the development of hydrogen production through water electrolysis. Summary of the Invention

[0006] The purpose of this invention is to develop a simple and easily scalable preparation process to obtain a low-cost and efficient Pt dual-origin HER catalyst.

[0007] The technical solution of the present invention:

[0008] 1. Synthesis of octamethoxyplatinum phthalocyanine (Pt(OCH3)8).

[0009] 2. Synthesis of octahydroxyplatinol phthalocyanine (PtPc(OH)8).

[0010] 3. Preparation of PtPc-ZIF-8 composite precursor

[0011] 4. High-temperature pyrolysis preparation of Pt-DACs

[0012] 5. Theoretical Calculations

[0013] Compared with the prior art, the present invention has the following advantages and technical effects:

[0014] (1) Precisely construct Pt metal diatomic pairs: The directional assembly of Pt metal diatomic pairs is free from single-atom impurities and metal particle agglomeration, maximizing the synergistic effect of the two metals.

[0015] (2) Controllable preparation process: The process of pre-coordination-in-situ encapsulation-high temperature pyrolysis is simple and controllable, the product structure is uniform, the batch stability is good, and it is easy to scale up industrial production. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the platinum diatomic catalyst in an embodiment of the present invention;

[0017] Figure 2 This is the hydrogen adsorption Gibbs free energy of the platinum diatomic catalyst Volmer-Heyrovsky mechanism in this embodiment of the invention.

[0018] Figure 3 This refers to the hydrogen adsorption Gibbs free energy of the platinum diatomic catalyst Volmer-Tafel mechanism in this embodiment of the invention. Detailed Implementation

[0019] Example 1:

[0020] PtPc(OCH3)8 was synthesized using dimethyl phthalate (methoxy group donor and solvent), phthalic anhydride, urea, and tetraammineplatinum chloride ([Pt(NH3)4]Cl2·H2O) as raw materials, with ammonium molybdate as the main catalyst and ammonium chloride as an auxiliary promoter, via a solvothermal stepped heating method. The core of the synthesis involves dimethyl phthalate providing the methoxy substituent, which, in the case of metallic Pt... 2+ Under the coordination of the template, through a three-step synergistic reaction of amination, cyclization and methoxy substitution, octamethoxy-modified platinum phthalocyanine is directionally generated, which has the advantages of high reaction selectivity and uniform methoxy substitution.

[0021] 1. Raw material pretreatment and feeding

[0022] (1). Place phthalic anhydride (4.44g) and urea (10.8g) in a mortar, grind until the particle size is ≤100μm and mix evenly, then transfer to a dry 250mL three-necked flask;

[0023] (2). Add [Pt(NH3)4]Cl2·H2O (4.67g) to the flask and continue stirring with a glass rod for 5 minutes to ensure that the metal salt and the solid mixture are in uniform contact.

[0024] (3) Slowly add dimethyl phthalate (30 mL), stir magnetically for 10 min to form a homogeneous suspension;

[0025] (4) Assemble the reaction apparatus: Connect the reflux condenser to the middle port of the three-necked flask, introduce high-purity nitrogen (99.999%) into one port, and insert a thermometer into the other port (the probe must be immersed in the suspension).

[0026] 2. Staged heating reaction (the key difference from traditional single-temperature reflux)

[0027] (1). Low-temperature amination stage (120-140℃, hold for 1h): Turn on the heating mantle and heat to 120℃ at a rate of 1℃ / min, and purge with nitrogen (flow rate 20mL / min) to remove air; continue heating to 140℃, add ammonium molybdate (0.15g) and ammonium chloride (0.20g), and stir at a constant temperature for 1h until no bubbles (CO2, NH3) are generated in the system (this stage completes urea amination and Pt). 2+ (Preliminary coordination).

[0028] (2). High-temperature cyclization and methoxy substitution stage (190-200℃, holding for 4h): The temperature is increased to 190℃ at a rate of 2℃ / min; the temperature is further increased to 200℃ and stirred at a constant temperature for 4h. During this period, the white phthalic anhydride condensed on the inner wall of the flask is scraped off with a long glass rod every 30min and refluxed into the reaction system (this stage completes the closure of the phthalocyanine ring and the directional substitution of the methoxy group of dimethyl phthalate to form PtPc(OCH3)8).

[0029] 3. Post-processing and purification

[0030] (1). Solvent recovery and crude product separation: After the reaction is completed, the heating mantle is turned off and the system is naturally cooled to room temperature. A black solid is precipitated in the system. The system is filtered by a sintered funnel and the filtrate (containing unreacted dimethyl phthalate, which can be recovered and reused by distillation) is collected. The filter cake is the crude product PtPc(OCH3)8.

[0031] (2) Acid and alkali washing to remove impurities:

[0032] Acid boiling: Transfer the crude product to a 250 mL beaker, add 25 mL of 4 mol / L hydrochloric acid, boil for 30 min to remove unreacted metal salts and ammonium molybdate, and collect the solid by suction filtration;

[0033] Alkali washing: Add the solid to 25 mL of 10% NaOH solution and soak at room temperature for 1 hour to remove residual phthalic anhydride. Collect the solid by filtration.

[0034] Alcohol washing: Wash the solid twice with 10 mL of anhydrous ethanol to remove residual organic solvent, then filter and press dry.

[0035] (3) Vacuum drying and shaping: The washed solid was placed in a vacuum drying oven and dried at 60°C and a vacuum degree ≤133Pa for 8 hours to obtain black powder PtPc(OCH3)8 with a yield of about 65-70%.

[0036] Example 2:

[0037] Using PtPc(OCH3)8 as a precursor, a "Lewis acid catalysis-hydrothermal assisted hydrolysis" strategy was adopted to achieve efficient conversion of methoxy groups to hydroxyl groups. By optimizing the solvent system, replacing the catalyst, and controlling the reaction temperature, the reaction cycle was shortened and the uniformity of hydroxyl substitution was improved.

[0038] (1). Raw material pretreatment and reaction system construction: 200 mg PtPc(OCH3)8 was placed in a 50 mL polytetrafluoroethylene reaction tube, and 20 mL anhydrous tetrahydrofuran (THF) was added. The mixture was magnetically stirred for 30 min until a uniform suspension was formed. Under nitrogen protection, 0.60 g anhydrous aluminum trichloride (AlCl3) was added in three portions, with an interval of 10 min between each addition, to avoid local exothermic reactions that could cause solvent evaporation.

[0039] (2) Heating hydrolysis reaction: Slowly add 1.5 mL of concentrated hydrochloric acid (mass fraction 37%, to provide a proton environment to promote the cleavage of methoxy groups) to the reaction tube, seal the reaction tube and place it in a constant temperature water bath at 50 °C and stir for 24 h.

[0040] (3) After the post-treatment and purification reaction is completed, transfer the system to a 100mL beaker and slowly add 25mL of ice-cold deionized water (control the temperature ≤5℃ to avoid Pt). 2+ Oxidation), after stirring for 10 min, filter with a G4 sintered glass funnel and collect the black solid; transfer the solid to a Soxhlet extractor and reflux extract with methanol as solvent for 8 h; after extraction, place the solid in a vacuum drying oven and vacuum dry at 40 °C for 12 h to obtain octahydroxyplatinum phthalocyanine (PtPc(OH)8).

[0041] Example 3:

[0042] This method achieves uniform composite of PtPc(OH)8 and ZIF-8 framework through solvent system optimization, dispersion improvement and reaction condition control, and has the advantages of milder operation and higher composite uniformity.

[0043] (1). Preparation of raw material dispersion and mixing system: Take 1.19g zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and 20mg PtPc(OH)8, add 30mL of anhydrous ethanol, and place in a 50mL three-necked flask; turn on mechanical stirring (600rpm), and at the same time place the flask in a 40℃ constant temperature water bath for heating and stirring for 30min.

[0044] (2). For in-situ growth of the ZIF-8 framework, take 10 mL of anhydrous ethanol, dissolve 1.32 g of 2-methylimidazole, stir until completely dissolved, and then slowly add it dropwise at a rate of 1 drop / second to the above Zn(NO3)2·PtPc(OH)8 suspension using a constant pressure dropping funnel. After the addition is complete, continue stirring at 40 °C for 2 h. Transfer the mixture to a 50 mL polytetrafluoroethylene-lined reactor and seal it at 80 °C for 3 h.

[0045] (3) Post-treatment and drying: After the reaction is completed, the solid is naturally cooled to room temperature and collected by filtration using a Buchner funnel. The solid is washed three times with anhydrous ethanol and then twice with deionized water until the pH of the filtrate is 7. The solid is transferred to a vacuum drying oven and dried at 50°C for 12 hours to obtain the PtPc-ZIF-8 composite precursor. The dispersion uniformity of PtPc(OH)8 in the ZIF-8 framework is improved by more than 15% compared with the traditional method.

[0046] Example 4:

[0047] This method achieves precise carbonization of the PtPc-ZIF-8 composite precursor and stable anchoring of Pt single-atom sites through atmosphere control, stepwise heating, and programmed cooling processes, which can significantly improve the dispersion uniformity of Pt atoms and the structural stability of the carbon support.

[0048] (1). Pyrolysis atmosphere and equipment: PtPc-ZIF-8 composite precursor (1.0g) was placed in a quartz boat and placed in the central constant temperature zone of a tube furnace; a mixture of argon (Ar) and hydrogen (H2) gas (volume ratio 95:5) was introduced into the tube furnace at a flow rate of 80mL / min and purged for 30min to completely replace the air in the furnace.

[0049] (2). Stepped heating carbonization adopts a three-stage heating process:

[0050] First stage (low temperature pretreatment): Heat to 300℃ at a rate of 2℃ / min and hold for 1 hour to slowly remove residual ethanol, water and unreacted 2-methylimidazole molecules from the composite precursor, avoiding explosive release of volatiles caused by rapid heating.

[0051] The second stage (intermediate-temperature pre-carbonization): the temperature is increased to 700℃ at a rate of 8℃ / min and held for 1.5h to promote the initial carbonization of the ZIF-8 framework to form a porous structure, while the hydroxyl groups in PtPc(OH)8 are gradually removed.

[0052] The third stage (high temperature deep carbonization): the temperature is increased to 900℃ at a rate of 5℃ / min and held for 3 hours.

[0053] (3). Programmed cooling and product collection: After the high-temperature carbonization is completed, the heating device is turned off and the Ar:H2 mixed gas is continuously purged. Programmed cooling is adopted: first, the temperature is reduced to 500℃ at a rate of 10℃ / min, and then reduced to 100℃ at a rate of 5℃ / min. When the temperature inside the furnace drops below 100℃, the gas supply is stopped, the quartz boat is taken out, and black powdered Pt-DACs are obtained.

[0054] Example 5:

[0055] The first-principles simulation software Vienna Ab-initio Simulation Package (VASP) was used to simulate Pt2N. x The electronic structure of the C configuration and the Gibbs free energy of hydrogen adsorption (ΔG) H* The calculations were performed using the VASP software package, with a cutoff energy of 500 eV to expand the plane wave. The electron-nucleus interaction was represented by the PAW pseudopotential, and the exchange correlation functional was represented by the PBE functional with the generalized gradient approximation. The electron self-consistency and force convergence criteria were 1 × 10⁻⁶. -5 eV and The Brillouin zone mesh (K-point) is divided using a (2×2×1) grid. Periodic plate models are separated by... The vacuum layer isolates the layers, preventing interaction between them.

Claims

1. A method for preparing a platinum diatomic catalyst, characterized in that, Includes the following steps: (1). Synthesis of octamethoxyplatinum phthalocyanine (PtPc(OCH3)8); (2). Using the octamethoxyplatinum phthalocyanine obtained in step (1) as a precursor, octahydroxyplatinum phthalocyanine (PtPc(OH)8) was synthesized. (3). The octahydroxyplatinum phthalocyanine obtained in step (2) is combined with the ZIF-8 framework to prepare the PtPc-ZIF-8 composite precursor; (4). The PtPc-ZIF-8 composite precursor obtained in step (3) is subjected to high-temperature pyrolysis to obtain platinum diatomic catalysts (Pt-DACs).

2. The preparation method according to claim 1, characterized in that, The specific steps for synthesizing PtPc(OCH3)8 in step (1) include: (1). Dimethyl phthalate was used as a solvent and methoxyl donor, and mixed with phthalic anhydride, urea, and tetraammineplatinum chloride ([Pt(NH3)4]Cl2·H2O), and ammonium molybdate was added as a catalyst and ammonium chloride as an auxiliary promoter. The use of dimethyl phthalate, which combines the functions of a solvent and a methoxy group donor, simplifies the system and ensures uniform methoxy substitution; ammonium chloride is introduced to suppress Pt. 2+ Reunion, Improvement of Pt 2+ The coordination efficiency with the phthalocyanine ring is improved to solve the problem of incomplete methoxy substitution caused by uneven metal sites; (2). A staged heating reaction is adopted: first, low-temperature amination is carried out at 120-140℃ for 1 hour, and then high-temperature cyclization and methoxy substitution are carried out at 190-200℃ for 4 hours. This method shortens the total reaction time and avoids carbonization of raw materials caused by premature high temperature. (3) Post-treatment includes acid boiling, alkali washing, alcohol washing and vacuum filtration, and drying at 60℃ and vacuum degree ≤133Pa for 8 hours; no centrifugation equipment is required, making it easier to operate industrially.

3. The preparation method according to claim 1, characterized in that, The specific steps for synthesizing PtPc(OH)8 in step (2) include: (1). Anhydrous tetrahydrofuran (THF) was used as the solvent, and anhydrous aluminum trichloride (AlCl3) and concentrated hydrochloric acid (37% by mass) were used as the catalytic system. The reaction was carried out in a constant temperature water bath at 50°C for 24 hours. The low-toxicity solvent and catalyst system reduced the operational risk and improved the catalytic efficiency. (2). Post-processing includes ice water quenching, vacuum filtration and Soxhlet extraction purification, followed by vacuum drying at 40℃ for 12h; Soxhlet extraction replaces multiple centrifugation and washing, reducing solid loss and achieving more thorough purification.

4. The preparation method according to claim 1, characterized in that, The specific steps for preparing the PtPc-ZIF-8 composite precursor in step (3) include: (1). Using anhydrous ethanol as solvent, zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and PtPc(OH)8 were mixed, and 2-methylimidazole ethanol solution was added dropwise at 40℃ under mechanical stirring to reduce solvent evaporation and destruction of active groups; (2). Seal and react at 80℃ for 3 hours; (3) Post-treatment includes filtration, washing with ethanol and deionized water, and vacuum drying at 50°C for 12 hours.

5. The preparation method according to claim 1, characterized in that, The specific steps of high-temperature pyrolysis in step (4) include: (1). Pyrolysis is carried out in a mixed atmosphere of argon (Ar) and hydrogen (H2) (volume ratio 95:5), where H2 ensures that Fe is anchored to the N site in a low valence state; (2). A three-stage gradient heating program of "low temperature pretreatment - medium temperature pre-carbonization - high temperature deep carbonization" is adopted: heating to 300℃ at 2℃ / min and holding for 1h, heating to 700℃ at 8℃ / min and holding for 1.5h, heating to 900℃ at 5℃ / min and holding for 3h; through the three-stage gradient heating, the violent escape of small molecules and structural damage caused by single-rate heating are avoided, and the carbon support is fully graphitized. (3) After pyrolysis, a programmed cooling method is used: first, the temperature is reduced to 500℃ at 10℃ / min, and then reduced to 100℃ at 5℃ / min. The cooling rate is controlled to avoid cracking of the carbon support caused by thermal stress.

6. A platinum diatom catalyst, characterized in that, Prepared by the preparation method according to any one of claims 1-5, wherein platinum is anchored in a diatomic form on a nitrogen-doped carbon support, having Pt₂N x C configuration (Pt2N4C / Pt2N6C / Pt2N7C).

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