Bi2Pd electrocatalyst as well as preparation method and application thereof

Abstract

The invention discloses a Bi2Pd electrocatalyst as well as a preparation method and application thereof, relates to the field of electrocatalysis, and solves the problems that the preparation of a traditional intermetallic compound catalyst depends on high-temperature and high-pressure conditions, the energy consumption is high, the reaction rate is slow and the crystal phase is difficult to control in a catalytic nitrogen reduction synthesis ammonia technology. The preparation method comprises the following steps: preparing a metal precursor solution by using a bismuth source and a palladium source, and sequentially adding a surfactant and a crystal phase regulator into the metal precursor solution to form a reaction precursor solution; placing the reaction precursor solution in an oil bath pan for heating reaction; after the reaction is finished, a product is cooled, centrifuged, washed and subjected to vacuum drying, and the Bi2Pd intermetallic compound electrocatalyst with the controllable crystal phase is prepared. By using different crystal phase regulators NH4Br and NH4Cl, accurate synthesis of tetragonal-phase and monoclinic-phase Bi2Pd intermetallic compound catalysts is realized, the catalyst can be applied to electrocatalytic nitrogen reduction synthesis ammonia reaction, and the ammonia production rate is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the field of electrocatalysis, and particularly relates to a Bi2Pd electrocatalyst, a preparation method thereof, and an application thereof. Background Art<>

[0002] Electrochemical technologies exhibit great application potential in the fields of efficient resource utilization and clean energy. Among them, the electrochemical nitrogen reduction reaction for ammonia synthesis technology has attracted much attention as a green and sustainable emerging process. The electrochemical nitrogen reduction reaction for ammonia synthesis technology can convert nitrogen into ammonia by using renewable electric energy at normal temperature and pressure, and is expected to solve the problems of the traditional ammonia synthesis process that relies on high temperature and high pressure conditions, consumes a large amount of energy, and is environmentally unfriendly. However, at present, the electrochemical nitrogen reduction reaction for ammonia synthesis technology has the defect of slow reaction rate, which is mainly because the ammonia production rate of the currently developed electrocatalysts for ammonia synthesis does not exceed 30 μg h -1 mg -1 , and the Faraday efficiency does not exceed 10%, which limits the application of the nitrogen reduction reaction for ammonia synthesis technology in industrial production. Therefore, the development of efficient electrocatalysts helps to promote the large-scale application and popularization of the nitrogen reduction reaction for ammonia synthesis technology in industrial production.

[0003] Intermetallic compounds are formed by the diffusion of one metal atom into the lattice of another metal to form metal-metal bonds, with a highly ordered atomic arrangement, a definite stoichiometric ratio, and a lattice structure. This structure not only endows intermetallic compounds with unique physical and chemical properties but also solves problems such as poor stability and poor repeatability caused by the disordered distribution of atoms in traditional alloys. Therefore, intermetallic compounds are commonly used in the preparation of electrocatalysts. Chinese invention patent CN103551147A discloses a method for synthesizing a fast and controllable PtBi intermetallic compound electrocatalyst, achieving one-step phase control and size control synthesis of the PtBi intermetallic electrocatalyst. However, its synthesis system requires a temperature above 200 °C and a pressure of 2 MPa, which not only increases energy consumption and risks but also poses high requirements for the high-temperature and high-pressure resistance of the reaction system. The selection of noble metals (such as platinum and palladium) is also crucial for developing intermetallic compounds with high catalytic performance. For example, a method for preparing and applying a PtBi2 intermetallic compound electrocatalyst with controllable crystal phases disclosed in Chinese invention patent CN118835264A precisely synthesizes bismuth-platinum intermetallic compound electrocatalysts with different crystal phases in the same system, demonstrating that the platinum (Pt) element exhibits good activity in the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER), and can be applied to the electrocatalytic oxidation of methanol. However, this invention requires precise pH regulators to control the crystal phase, and it is difficult to achieve precise control of the crystal phase by manual operation. Minor errors may lead to impure crystal phases or unstable performance. At the same time, the Pt element does not have nitrogen reduction (NRR) activity because its electronic structure and surface properties are not conducive to the adsorption and activation of nitrogen molecules. During the NRR process, excessive hydrogen atom adsorption will promote the HER process, occupying the active sites for nitrogen activation and greatly inhibiting the NRR process. This invention is not applicable to the electrochemical nitrogen reduction synthesis of ammonia technology.

[0004] To solve the defects existing in the preparation process of the above intermetallic compounds, to improve the conversion efficiency of the nitrogen reduction synthesis of ammonia technology, and to develop a simple and controllable preparation method to achieve the precise synthesis of intermetallic compounds with different crystal phases is of great significance for promoting the development of the electrochemical synthesis of ammonia technology. Summary of the Invention

[0005] To solve the problems that the preparation of traditional intermetallic compound catalysts relies on high-temperature and high-pressure conditions, high energy consumption, slow reaction rate, and difficulty in controlling crystal phases in the catalytic nitrogen reduction synthesis of ammonia technology, the present invention proposes a Bi2Pd electrocatalyst and its preparation method and application. The technical solution of the present invention is as follows:

[0006] A method for preparing a Bi2Pd electrocatalyst, comprising the following preparation steps:

[0007] Dissolve the bismuth source and palladium source in a solvent to obtain a metal precursor solution. Sequentially add a surfactant and a crystal phase regulator to the metal precursor solution, and stir to form a reaction precursor solution; transfer the reaction precursor solution to a round-bottom flask and place it in an oil bath for heating reaction; after the reaction is completed, cool the product to room temperature, perform centrifugation and washing, and vacuum dry the washed product to prepare a Bi2Pd intermetallic compound electrocatalyst with controllable crystal phase;

[0008] Further, the bismuth source is selected from any one of bismuth nitrate pentahydrate, bismuth chloride, or bismuth acetate; the palladium source is selected from any one of palladium acetylacetonate, palladium chloride, or palladium nitrate;

[0009] Further, the molar ratio of the bismuth source to the palladium source is 2:1; the solvent is ethylene glycol;

[0010] Further, the surfactant is polyvinylpyrrolidone (PVP), and the mass ratio of the surfactant to the solvent is 1:158.57 - 222;

[0011] Further, the crystal phase regulator is one or a combination of two of NH4Br or NH4Cl, and the mass ratio of the crystal phase regulator to the solvent is 1:185 - 555;

[0012] Further, the stirring time is 0.5 - 1 h;

[0013] Further, the temperature of the heating reaction is 120 - 180 °C, and the reaction time is 12 - 20 h;

[0014] Further, the rotation speed of the centrifugation is 9000 r / min, and the number of washing times is 5 - 7 times;

[0015] Further, the temperature of the vacuum drying is 40 - 60 °C; the time of the vacuum drying is 6 - 12 h.

[0016] A Bi2Pd electrocatalyst is prepared by the above preparation method.

[0017] An application of the Bi2Pd electrocatalyst is applied to the electrocatalytic nitrogen reduction reaction for ammonia synthesis.

[0018] Compared with the prior art, the present invention solves the problems of the preparation of traditional intermetallic compound catalysts relying on high-temperature and high-pressure conditions, high energy consumption, slow reaction rate in the catalytic nitrogen reduction reaction for ammonia synthesis, and difficulty in controlling the crystal phase. The specific beneficial effects are as follows:

[0019] 1. Achieving the crystal phase regulation of electrocatalysts: In the present invention, by using different crystal phase regulators NH4Br and NH4Cl, the precise synthesis of Bi2Pd intermetallic compounds with different crystal phases is realized in the same reaction system. The bromide ions (Br - ) and chloride ions (Cl - ) ionized by NH4Br and NH4Cl in the reaction system can coordinate with bismuth ions (Bi 3+ ) and palladium ions (Pd 2+ ), changing the reaction activity and spatial electron cloud distribution of metal ions, which is beneficial to the aggregation of Bi 3+ and Pd 2+ to form crystal nuclei. When adding NH4Cl, NH4 + and Cl - can change the ionic strength and pH value of the solution, promoting the formation of monoclinic crystal nucleus precursors of bismuth and palladium ions. Cl - selectively adsorbs on specific crystal planes of monoclinic Bi2Pd crystals, thereby regulating the growth of the monoclinic phase and finally forming the structure of monoclinic Bi2Pd intermetallic compounds. When adding NH4Br, Br - , due to its large radius, forms a complex with metal ions with a unique spatial structure, guiding the formation of tetragonal crystal nuclei of Bi 3+ and Pd 2+ , promoting the growth of tetragonal Bi2Pd crystals in this direction and finally forming the structure of tetragonal Bi2Pd intermetallic compounds. This regulation method realizes the self-assembly process of intermetallic compounds with different crystal phases, which is simple and efficient, providing a new idea for the crystal phase design of intermetallic compounds.

[0020] 2. Effectively improving the catalytic performance: The pure crystal phase intermetallic compounds prepared in the present invention can be applied to the electrocatalytic nitrogen reduction to ammonia technology, having excellent electrocatalytic performance and stability. Among them, due to the unique electron cloud distribution of the surface atoms of the tetragonal Bi2Pd intermetallic compound, nitrogen molecules can be efficiently adsorbed and activated, and the ammonia production rate can reach 82.78 μg h -1 mg -1 , and the Faraday efficiency can reach 22.5%; the crystal structure symmetry of the monoclinic Bi2Pd intermetallic compound is low, having multiple active sites for nitrogen adsorption, thereby increasing the nitrogen adsorption rate. The ammonia production rate of the monoclinic Bi2Pd catalyst is 70.69 μg h -1 mg -1 , and the Faraday efficiency is 19.2%, effectively solving the defect of slow ammonia production rate of electrocatalysts in the existing technology.

[0021] 3. Mild reaction: The intermetallic compound catalyst is prepared by a one-step oil bath method in the present invention. The reaction temperature is only 120 - 180 °C, with low energy consumption. The preparation method is simple, without the need for expensive experimental reagents and complex experimental equipment, and has high economic efficiency and practicability, being suitable for large-scale industrial applications. Description of the Drawings

[0022] Figure 1 It is the X-ray diffraction pattern of the tetragonal Bi2Pd intermetallic compound;

[0023] Figure 2 It is the transmission electron microscope image of the tetragonal Bi2Pd intermetallic compound;

[0024] Figure 3 It is the particle size distribution diagram of the tetragonal Bi2Pd intermetallic compound;

[0025] Figure 4 It is the X-ray diffraction pattern of the monoclinic Bi2Pd intermetallic compound;

[0026] Figure 5 It is the transmission electron microscope image of the monoclinic Bi2Pd intermetallic compound;

[0027] Figure 6 It is the particle size distribution diagram of the monoclinic Bi2Pd intermetallic compound;

[0028] Figure 7 It is the X-ray diffraction pattern of the mixed-phase Bi2Pd intermetallic compound;

[0029] Figure 8 It is the transmission electron microscope image of the mixed-phase Bi2Pd intermetallic compound;

[0030] Figure 9 It is the particle size distribution diagram of the mixed-phase Bi2Pd intermetallic compound;

[0031] Figure 10 It is the chronoamperometry curve of the Bi2Pd intermetallic compound;

[0032] Figure 11 It is the ultraviolet spectrum diagram of the Bi2Pd intermetallic compound;

[0033] Figure 12 It is the ammonia production rate and Faraday efficiency diagram of the Bi2Pd intermetallic compound. Detailed Embodiments

[0034] To make the technical solutions of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the specification drawings of the present invention. It should be noted that the following embodiments are only used to better understand the technical solutions of the present invention and should not be construed as a limitation of the present invention.

[0035] Example 1.

[0036] Dissolve 72.8 mg of bismuth nitrate pentahydrate and 22.8 mg of palladium acetylacetonate in 10 mL of ethylene glycol solvent, and stir to obtain a metal precursor solution; successively add 60 mg of PVP (molecular weight 1000) and 50 mg of NH4Br, and stir for 1 h to obtain a reaction precursor solution; transfer the reaction precursor solution to a round-bottom flask and place it in an oil bath, and react at 150 °C for 15 h; after the reaction is completed, centrifuge and wash the sample with ethanol, the number of centrifugation and washing is 5 times, and the centrifugation speed is 9000 r / min; the washed sample is vacuum dried at 40 °C for 12 h to prepare a tetragonal Bi2Pd intermetallic compound.

[0037] As Figure 1 is the X-ray diffraction pattern of the tetragonal Bi2Pd intermetallic compound. The diffraction peaks shown in the figure are completely corresponding to the standard card of tetragonal Bi2Pd, and no impurity peaks are observed, indicating that the tetragonal Bi2Pd intermetallic compound has high purity and good crystallinity. As Figure 2 is the transmission electron microscopy image of the tetragonal Bi2Pd intermetallic compound. It can be seen from the figure that the tetragonal Bi2Pd intermetallic compound is in the shape of nanospheres, the boundaries between the particles are distinct, no agglomeration phenomenon appears, and the size distribution of each nanosphere is uniform, showing good dispersibility and homogeneity. As Figure 3 is the particle size distribution diagram of the tetragonal Bi2Pd intermetallic compound. It can be seen from the figure that the particle size of the tetragonal Bi2Pd intermetallic compound is concentrated in the range of 6 - 10 nm, and the average particle size is 8.1 nm, showing good size uniformity.

[0038] Example 2.

[0039] Dissolve 72.8 mg of bismuth nitrate pentahydrate and 22.8 mg of palladium acetylacetonate in 10 mL of ethylene glycol solvent, and stir to obtain a metal precursor solution; successively add 60 mg of PVP (molecular weight 1000) and 30 mg of NH4Cl, and stir for 1 h to obtain a reaction precursor solution; transfer the reaction precursor solution to a round-bottom flask and place it in an oil bath, and react at 150 °C for 15 h; after the reaction is completed, centrifuge and wash the sample with ethanol, the number of centrifugation and washing is 5 times, and the centrifugation speed is 9000 r / min; the washed sample is vacuum dried at 40 °C for 12 h to prepare a monoclinic Bi2Pd intermetallic compound.

[0040] As Figure 4is the X-ray diffraction pattern of the monoclinic Bi2Pd intermetallic compound. The diffraction peaks in the figure match perfectly with the standard card of monoclinic Bi2Pd, and no impurity peaks are observed, indicating that the monoclinic Bi2Pd intermetallic compound has high purity and good crystallinity. As Figure 5 is the transmission electron microscopy image of the monoclinic Bi2Pd intermetallic compound. It can be seen from the figure that the monoclinic Bi2Pd intermetallic compound is in the shape of nanospheres, with no obvious agglomeration phenomenon and uniform size distribution. As Figure 6 is the particle size distribution diagram of the monoclinic Bi2Pd intermetallic compound. It can be seen from the figure that the particle size of the monoclinic Bi2Pd intermetallic compound is concentrated in the range of 7 - 9 nm, and the average particle size is 8.2 nm, proving that the monoclinic Bi2Pd intermetallic compound has good size uniformity.

[0041] Example 3.

[0042] Dissolve 72.8 mg of bismuth nitrate pentahydrate and 22.8 mg of palladium acetylacetonate in 10 mL of ethylene glycol solvent, and stir to obtain a metal precursor solution; sequentially add 60 mg of PVP (molecular weight 1000), 30 mg of NH4Br, and 20 mg of NH4Cl, and stir for 1 h to obtain a reaction precursor solution; transfer the reaction precursor solution to a round-bottom flask and place it in an oil bath, and react at 150 °C for 15 h; after the reaction is completed, centrifuge and wash the sample with ethanol, the number of centrifugation and washing is 5 times, and the centrifugation speed is 9000 r / min; the washed sample is vacuum dried at 40 °C for 12 h to prepare a mixed-phase Bi2Pd intermetallic compound.

[0043] As Figure 7 is the X-ray diffraction pattern of the mixed-phase Bi2Pd intermetallic compound. The characteristic diffraction peaks corresponding to both monoclinic and tetragonal Bi2Pd appear in the pattern, proving the coexistence of monoclinic and tetragonal crystal phases in the mixed-phase Bi2Pd intermetallic compound. Figure 8 is the transmission electron microscopy image of the mixed-phase Bi2Pd intermetallic compound. It can be seen from the figure that the mixed-phase Bi2Pd intermetallic compound presents a nanospherical shape, with no obvious agglomeration phenomenon and uniform size distribution. Figure 9 is the particle size distribution diagram of the mixed-phase Bi2Pd intermetallic compound. The figure shows that the particle size is concentrated in the range of 7 - 9 nm, and the average particle size is 8.2 nm, proving that the mixed-phase Bi2Pd intermetallic compound has good size uniformity.

[0044] Catalyst stability test:

[0045] Weigh 3 mg of the Bi2Pd intermetallic compounds prepared in Examples 1-3 respectively, disperse them in 0.8 mL of absolute ethanol, then add 0.2 mL of 5 wt% perfluorosulfonic acid-based ion exchange resin (Nafion) solution, and ultrasonically form a uniform suspension. Take 20 μL of the suspension and drop-coat it onto a glassy carbon electrode with a diameter of 5 mm, and then dry it at room temperature to form a working electrode. The working electrode is combined with a three-electrode system consisting of a graphite rod anode and an Ag / AgCl reference electrode for electrochemical testing. As Figure 10 Shown in Figure 10 are the chronoamperometric curves of the Bi2Pd intermetallic compounds prepared in Examples 1-3. It can be seen from the figure that the current densities of the Bi2Pd intermetallic compounds with different crystal phases fluctuate relatively little during the electrocatalytic nitrogen reduction process for a relatively long time (7200 s), indicating that during the electrocatalytic nitrogen reduction process, both the pure crystal phase Bi2Pd intermetallic compound and the mixed crystal phase intermetallic compound can maintain a relatively stable current output, showing good current response and stability.

[0046] Catalytic nitrogen reduction performance test:

[0047] Place the Bi2Pd intermetallic compounds prepared in Examples 1-3 in an electrolytic cell, use a reversible hydrogen electrode (RHE) as the reference electrode, and perform electrolysis at a potential of -0.3 V for 2 h. As Figure 11 Shown in Figure 11 is the ultraviolet spectrum of the Bi2Pd intermetallic compound. It can be seen from the figure that the Bi2Pd intermetallic compounds with different crystal phases all show obvious absorption peaks for ultraviolet light at a specific wavelength (655 nm), indicating that the reaction of nitrogen reduction to ammonia has been successfully carried out.

[0048] As Figure 12 Shown in Figure 12 are the ammonia production rate and Faraday efficiency diagrams of the Bi2Pd intermetallic compound. It can be seen from the figure that the tetragonal Bi2Pd intermetallic compound prepared in Example 1 significantly accelerates the ammonia production rate, and the ammonia production rate can reach 82.78 μg h -1 mg -1 , and the Faraday efficiency can reach 22.5%. This is because the atoms on the surface of the tetragonal Bi2Pd can form a strong interaction with nitrogen molecules by virtue of their special electron cloud distribution, causing the π electron cloud of nitrogen molecules to shift, effectively weakening N≡N, reducing the initial energy barrier of the nitrogen reduction reaction, and making the reaction easier to occur, thereby increasing the ammonia production rate; the ammonia production rate of the monoclinic Bi2Pd catalyst prepared in Example 2 is 70.69 μg h -1 mg -1, the Faraday efficiency is 19.2%. The high catalytic efficiency is mainly due to the fact that the crystal structure of monoclinic Bi2Pd has a relatively low symmetry, resulting in more atoms with different coordination environments on its crystal surface, thereby providing multiple active sites to interact with nitrogen molecules, increasing the probability of effective activation of nitrogen molecules, promoting the subsequent hydrogenation reaction, and thus increasing the ammonia production rate. The ammonia production rate of the mixed-phase intermetallic compound catalyst prepared in Example 3 is 73.56 μg h -1 mg -1 , the Faraday efficiency is 19.8%, realizing the efficient conversion of nitrogen molecules, solving the defect of slow ammonia production rate of existing electrocatalysts, and laying a solid foundation for promoting the green development of electrochemical ammonia synthesis technology.

[0049] In the present invention, by using different crystal phase regulators NH4Br and NH4Cl, the precise synthesis of Bi2Pd intermetallic compound catalysts with different crystal phases is achieved in the same reaction system, significantly increasing the ammonia production rate, and having excellent catalytic performance and stability. At the same time, the present invention adopts a one-step oil bath method to prepare the intermetallic compound catalyst, with mild reaction conditions, high economy and practicability, and is suitable for large-scale industrial applications.

[0050] The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0051] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A preparation method of a Bi2Pd electrocatalyst, characterized in that, It includes the following preparation steps: Dissolve a bismuth source and a palladium source in a solvent to obtain a metal precursor solution, and sequentially add a surfactant and a crystal phase regulator to the metal precursor solution, and stir to form a reaction precursor solution; Transfer the reaction precursor solution to a round-bottom flask and place it in an oil bath for heating reaction; after the reaction is completed, cool the product to room temperature, and perform centrifugation, washing, and vacuum drying to prepare a Bi2Pd intermetallic compound electrocatalyst with controllable crystal phase.

2. The preparation method of the Bi2Pd electrocatalyst according to claim 1, characterized in that, The bismuth source is selected from any one of bismuth nitrate pentahydrate, bismuth chloride, or bismuth acetate; the palladium source is selected from any one of palladium acetylacetonate, palladium chloride, or palladium nitrate.

3. The preparation method of the Bi2Pd electrocatalyst according to claim 1, characterized in that, The molar ratio of the bismuth source to the palladium source is 2:1; the solvent is ethylene glycol.

4. The preparation method of the Bi2Pd electrocatalyst according to claim 1, wherein The surfactant is polyvinylpyrrolidone, and the mass ratio of the surfactant to the solvent is 1:158.57 - 222; the crystal phase regulator is one or a combination of two of NH4Br or NH4Cl, and the mass ratio of the crystal phase regulator to ethylene glycol is 1:185 - 555.

5. The preparation method of the Bi2Pd electrocatalyst according to claim 1, wherein The stirring time is 0.5 - 1 h.

6. The preparation method of the Bi2Pd electrocatalyst according to claim 1, wherein, The temperature of the heating reaction is 120 - 180 °C, and the reaction time is 12 - 20 h.

7. The preparation method of the Bi2Pd electrocatalyst according to claim 1, characterized in that, The rotation speed of the centrifugation is 9000 r / min, and the number of repetitions of centrifugation and washing is 5 - 7 times.

8. The preparation method of the Bi2Pd electrocatalyst according to claim 1, characterized in that The temperature of the vacuum drying is 40 - 60 °C; the time of the vacuum drying is 6 - 12 h.

9. A Bi2Pd electrocatalyst, characterized in that, Prepared by the preparation method described in any one of claims 1 - 8.

10. Use of the Bi2Pd electrocatalyst according to claim 9, characterized in that, Applied to the electrocatalytic nitrogen reduction reaction for ammonia synthesis.

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