A palladium / tin dioxide composite catalyst for electro-oxidation of formic acid and a preparation method thereof

Abstract

The application belongs to the field of chemistry and particularly relates to a palladium / stannic oxide composite catalyst for electro-oxidation of formic acid and a preparation method thereof. The method comprises the following steps: generating stannic oxide nanospheres by hydrolysis of stannate; taking the stannic oxide as a seed, reducing a palladium precursor to synthesize a palladium / stannic oxide catalyst with low palladium loading; and taking the palladium / stannic oxide catalyst with low palladium loading as a seed, reducing the palladium precursor again to prepare a palladium / stannic oxide catalyst with high palladium loading.

Description

[0001] This application claims priority to Chinese invention patent application [CN2022116501813], filed on December 21, 2022, entitled "A palladium-tin dioxide composite catalyst for electro-oxidation of formic acid and its preparation method", which is incorporated herein by reference in its entirety. Technical Field

[0002] This invention belongs to the field of chemistry, specifically relating to a palladium / tin dioxide composite catalyst for the electro-oxidation reaction of formic acid and its preparation method. Background Technology

[0003] Direct formic acid fuel cells (DFAFCs) are currently a hot topic in fuel cell research due to their advantages such as being non-toxic, non-flammable, easy to store and transport, having a high theoretical potential, and low permeability to proton exchange membranes.

[0004] The anode catalysts for formic acid fuel cells are mainly platinum-based (Pt) and palladium-based (Pd) catalysts. Platinum-based materials exhibit excellent electrocatalytic activity for various small fuel molecules, but the low reserves of platinum (only 37 ppb in the Earth's crust), its high price (accounting for more than 55% of the total equipment cost), and its susceptibility to carbon monoxide poisoning limit its further widespread use. Palladium has a similar electronic structure to platinum, its reserves are higher, and it has high electro-oxidation activity for formic acid. Therefore, recent strategies for designing palladium-based catalysts for formic acid oxidation have mainly focused on improving catalytic activity, reducing Pd metal content, and improving stability.

[0005] Modulating catalyst structure is a crucial approach to enhancing catalyst activity. Current mainstream methods include adjusting the shape, size, and crystal structure of palladium-based catalysts, or introducing a second or third component (such as metals, non-metals, or metal oxides) into palladium catalysts to prepare composite catalysts, thereby regulating the electronic structure. Commonly added metals include Au, Pt, Ir, Pb, Sn, Co, Ni, and Cu, while non-metals include B and P. However, the catalytic activity and stability of these composite catalysts still do not meet the requirements for the commercialization of DFAFCs. Furthermore, although palladium-based catalysts have achieved some success in formic acid oxidation, their performance (mass-specific activity) generally does not currently exceed 10 A·mg⁻¹. Pd –1 .

[0006] In conclusion, designing a highly active palladium-based nanocatalyst remains a significant challenge. Summary of the Invention

[0007] In view of this, the purpose of the present invention is to provide a method for preparing a catalyst for the electro-oxidation of formic acid, the specific technical solution of which is as follows.

[0008] A method for preparing palladium / tin dioxide composite nanoparticles includes the following steps:

[0009] 1) Hydrolyze stannate to generate spherical tin dioxide particles. Prepare a dispersion of the spherical tin dioxide particles and use it as a seed in the seed growth system to reduce the palladium precursor into cubic palladium particles while allowing the palladium particles to grow along the surface of the spherical tin dioxide particles, thereby obtaining low palladium loading intermediate l-PdNCs@SnO2 particles.

[0010] 2) The l-PdNCs@SnO2 particles were made into a dispersion and used as seeds in the seed growth system to reduce the palladium precursor into cubic palladium particles while growing the palladium particles along the surface of the spherical tin dioxide particles to obtain palladium / tin dioxide composite nanoparticles h-PdNCs@SnO2 with high palladium loading.

[0011] The seed growth system includes a ligand, a directing agent, and a reducing agent, with the reaction temperature maintained at 120-150℃; the directing agent is a morphology directing agent, mainly used to control the formation of palladium cubes.

[0012] Preferably, the reaction temperature is 120℃.

[0013] Furthermore, in step 1), the mass ratio of Pd to SnO2 in the l-PdNCs@SnO2 particles obtained is 4:5 to 3:5.

[0014] Preferably, the mass ratio of Pd to SnO2 in l-PdNCs@SnO2 particles is 4:5.

[0015] Furthermore, the palladium precursor is palladium acetylacetonate.

[0016] Furthermore, the palladium particles in the cube have a particle size of 9-11 nm.

[0017] Furthermore, the particle size of the spherical tin dioxide particles is 40-50 nm.

[0018] Furthermore, the ligand in the seed growth system is polyvinylpyrrolidone, the directing agent is sodium iodide, and the reducing agent is N,N-dimethylformamide.

[0019] Furthermore, the stannate is sodium stannate trihydrate.

[0020] The palladium / tin dioxide composite nanoparticles h-PdNCs@SnO2 were synthesized according to the above method.

[0021] Furthermore, the mass ratio of Pd to SnO2 in the h-PdNCs@SnO2 is 3:2 to 2:1.

[0022] Preferably, the mass ratio of Pd to SnO2 in h-PdNCs@SnO2 is 2:1.

[0023] The above-mentioned palladium / tin dioxide composite nanoparticles are used in the preparation of formic acid electrooxidation catalysts.

[0024] Beneficial technical effects

[0025] First, this invention provides a simple and easy-to-operate preparation method that yields high palladium-loaded h-PdNCs@SnO2 composite nanoparticles through two consecutive rounds of seed growth. In this method, uniform cubic palladium particles are prepared simultaneously with the growth of these particles along the surface of tin dioxide particles in a seed growth system. Two consecutive rounds of growth aim to increase the number of Pd NCs (palladium nanocubes) on each tin dioxide particle. The resulting high palladium-loaded h-PdNCs@SnO2 composite nanoparticles, expressed as the ratio of the total contact area of ​​PdNCs to the total surface area of ​​the tin dioxide nanospheres, exhibit a surface coverage rate as high as 83%. The interfacial effect caused by the contact between the high-loaded palladium and tin dioxide significantly enhances the catalytic activity of the material. The high palladium-loaded h-PdNCs@SnO2 composite nanoparticles prepared by this method exhibit excellent formic acid electrooxidation catalytic activity, with a specific activity as high as 14.55 A·mg. Pd –1 .

[0026] Furthermore, the method of the present invention has a certain degree of universality; by replacing tin dioxide with oxides such as indium trioxide, cerium dioxide, titanium dioxide, and copper oxide, samples with high palladium loading can also be obtained. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 The image shows the TEM morphology of tin dioxide obtained in an embodiment of the present invention.

[0029] Figure 2 The image shows the TEM morphology of the high palladium-loaded palladium / tin dioxide composite catalyst prepared in the embodiments of the present invention.

[0030] Figure 3The image shows the TEM morphology of the high palladium loading palladium / indium trioxide composite nanoparticles prepared in the comparative example of this invention.

[0031] Figure 4 This is a comparison chart of the electro-oxidation performance of formic acid catalyzed by composite nanoparticles prepared in the embodiments of the present invention;

[0032] Figure 5 The image shows the TEM morphology of the palladium / tin dioxide composite material obtained at a reaction temperature of 90℃ in the seed growth system of this invention.

[0033] Figure 6 The image shows the TEM morphology of the palladium / tin dioxide composite material prepared at a reaction temperature of 150℃ in the seed growth system of this invention.

[0034] Figure 7 TEM images of composite nanoparticles prepared using CTAB as a ligand.

[0035] Figure 8 TEM morphology image of composite nanoparticles prepared without the addition of morphology guiding agents. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0037] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0038] As used in this specification, the term "about" typically means + / - 5% of the value, more typically + / - 4%, more typically + / - 3%, more typically + / - 2%, even more typically + / - 1%, even more typically + / - 0.5% of the value.

[0039] In this specification, certain embodiments may be disclosed in a range-bound format. It should be understood that this "range-bound" description is merely for convenience and brevity and should not be construed as a rigid limitation on the disclosed range. Therefore, the description of the range should be considered as having specifically disclosed all possible subranges and independent numerical values ​​within those ranges. For example, range The description should be considered as having specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as individual numbers within this range, such as 1, 2, 3, 4, 5, and 6. The above rules apply regardless of the breadth of the range.

[0040] Example 1

[0041] Example of preparation of spherical tin dioxide (SnO2)

[0042] This preliminary example provides tin dioxide and a method for its preparation, the preparation method comprising the following steps:

[0043] Weigh 0.0200g sodium stannate trihydrate and 0.3377g glucose, dissolve them in 6mL of water to form a homogeneous solution, heat and stir in a 60℃ water bath, wash three times by centrifugation with water, collect the precipitate, and disperse it in 1mL of water.

[0044] The morphology of the tin dioxide obtained in this preliminary example was characterized, and its TEM image is shown below. Figure 1 As shown, by Figure 1 As can be seen, the tin dioxide obtained in this embodiment is spherical and uniform in size, with a particle size between 40-50 nm.

[0045] Example 2

[0046] Example of preparation of composite nanoparticles

[0047] 1) Weigh 0.0200g sodium stannate trihydrate and 0.3377g glucose, dissolve them in 6mL of water to form a homogeneous solution, heat and stir in a 60℃ water bath, wash three times by centrifugation with water, collect the precipitate and disperse it in 1mL of water.

[0048] 2) Weigh 0.0115g palladium acetylacetonate and 0.0177g polyvinylpyrrolidone, dissolve them in 10mL of N,N-dimethylformamide, and then add 1mL of 0.15g·mL⁻¹ –1NaI solution and 0.5 mL of the tin dioxide dispersion obtained in Example 1 were sonicated for 1 minute to obtain a homogeneous solution. After heating and stirring in an oil bath at 120°C for 2 hours, the solution was cooled to room temperature and washed sequentially by centrifugation with acetone (20 mL), ethanol / acetone (20 mL, 1:1 v / v), ethanol (20 mL), and ethanol / water (20 mL, 1:1 v / v). The precipitate was collected and dispersed in 1 mL of water to obtain the intermediate product, the composite nanoparticles l-PdNCs@SnO2.

[0049] 3) Weigh 0.0115g palladium acetylacetonate and 0.0177g polyvinylpyrrolidone, dissolve them in 10mL of N,N-dimethylformamide, and then add 1mL of 0.15g·mL⁻¹ –1 NaI solution and 0.5 mL of the low-load palladium / tin dioxide aqueous solution (l-SnO2@Pd) obtained in step 1) were sonicated for 1 minute to obtain a homogeneous solution. After heating and stirring in an oil bath at 120°C for 2 hours, the solution was cooled to room temperature and washed sequentially with acetone (20 mL), ethanol / acetone (20 mL, 1:1 v / v), ethanol (20 mL), and ethanol / water (20 mL, 1:1 v / v). The high-load palladium-tin dioxide was collected and dispersed in 1 mL of water to obtain the final product, composite nanoparticles h-PdNCs@SnO2.

[0050] The seed growth system and reaction conditions provided in this embodiment are optimal, but not limited to them. This invention also verified different seed growth systems and reaction conditions. Results showed that lower temperatures (90°C) were acceptable. Figure 5 It is impossible to completely reduce the Pd precursor, and increasing the temperature (150℃) is necessary. Figure 6 This induced rapid nucleation, resulting in discrete PdNCs. Replacing PVP with CTAB... Figure 7 Alternatively, using a stronger reducing agent (such as ascorbic acid) will result in free Pd nanoparticles that tend to aggregate rather than grow on SnO2. Finally, iodide ions play a crucial role, acting as a morphology-directing agent to successfully obtain cubic target particles; without iodide ions, irregular and larger palladium nanoparticles are obtained. Figure 8 ).

[0051] Morphology diagram of h-PdNCs@SnO2 as follows Figure 2 As shown in the figure, a uniform raspberry-like nanostructure is displayed, with a large number of PdNCs uniformly distributed on each tin dioxide nanosphere.

[0052] Example 3

[0053] Electrocatalytic performance testing

[0054] Measure 10 μL of l-PdNCs@SnO2 or h-PdNCs@SnO2 containing 2 mg palladium, and disperse it in 1 mL of carbon black / isopropanol (2 mg / mL). –1 The catalyst sample ink was ultrasonicated in the solution for 40 minutes to obtain a uniform ink. 40 μL of the catalyst sample ink was dropped onto a glassy carbon electrode and dried for later use.

[0055] The reaction employed a three-electrode system, using a glassy carbon electrode with the palladium catalyst supported on its surface as the working electrode, KCl-saturated Ag / AgCl as the reference electrode, and a gold wire as the counter electrode. 30 mL of a solution of 0.5 M formic acid and 1 M perchloric acid was used as the electrolyte. Cyclic voltammetry was used to determine the electrocatalytic activity of l-PdNCs@SnO2 and h-PdNCs@SnO2, with a scan voltage ranging from -0.05 to 1 V and a scan rate of 50 mV·s. –1 .

[0056] Experimental results: such as Figure 4 The specific activity of l-PdNCs@SnO2 is 4.72 A·mg. Pd –1 The specific activity of h-PdNCs@SnO2 is 14.55 A·mg. Pd –1 The difference in palladium coverage between l-PdNCs@SnO2 and h-PdNCs@SnO2 particles leads to different interfacial effects, which in turn significantly affect the catalytic activity.

[0057] Current palladium-based catalysts generally fail to achieve a performance (mass-to-specific activity) exceeding 10 A·mg. Pd –1 The inventors have listed and compared the performance of some existing palladium-based catalysts in the table below.

[0058] Table 1

[0059]

[0060]

[0061] Here, Mass activity represents the mass-to-activity ratio; Specific activity represents the surface area activity; and ECSA represents the electrochemically active area.

[0062] Example 4

[0063] It is understood that the method of the present invention has a certain degree of universality and can also be used to prepare composite nanomaterials with other oxides as supports.

[0064] Weigh 0.0115 g palladium acetylacetonate and 0.0177 g polyvinylpyrrolidone, dissolve them in 10 mL of N,N-dimethylformamide, and then add 1 mL of 0.15 g / mL solution. –1 NaI solution, 0.5 mL indium trioxide aqueous solution (0.02 g·mL) –1 The solution was sonicated for 1 minute to obtain a homogeneous solution. After heating and stirring in an oil bath at 120°C for 2 hours, the solution was cooled to room temperature and washed successively with acetone (20 mL), ethanol / acetone (20 mL, 1:1 v / v), ethanol (20 mL), and ethanol / water (20 mL, 1:1 v / v). The precipitate was collected and dispersed in 1 mL of water. The resulting catalyst was named l-PdNCs@In2O3.

[0065] Weigh 0.0115 g palladium acetylacetonate and 0.0177 g polyvinylpyrrolidone, dissolve them in 10 mL of N,N-dimethylformamide, and then add 1 mL of 0.15 g / mL solution. –1 NaI solution and 0.5 mL of the l-In₂O₃@Pd dispersion obtained in step 1) were sonicated for 1 minute to obtain a homogeneous solution. After heating and stirring in an oil bath at 120°C for 2 hours, the solution was cooled to room temperature and washed sequentially with acetone (20 mL), ethanol / acetone (20 mL, v / v ratio 1:1), ethanol (20 mL), and ethanol / water (20 mL, v / v ratio 1:1). The palladium / indium trioxide with high palladium loading was collected and dispersed in 1 mL of water. The resulting catalyst was named h-PdNCs@In₂O₃.

[0066] TEM images of h-PdNCs@In2O3 (palladium / indium trioxide) are shown below. Figure 3 As shown, this invention has a certain degree of universality; even if tin dioxide is replaced with indium trioxide, samples with high palladium loading can still be prepared.

[0067] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A method for preparing palladium / tin dioxide composite nanoparticles, characterized in that, Includes the following steps: 1) Hydrolyzing stannate to generate spherical tin dioxide particles, preparing a dispersion of the spherical tin dioxide particles, and using it as a seed in a seed growth system to simultaneously reduce the palladium precursor into cubic palladium particles while allowing the palladium particles to grow along the surface of the spherical tin dioxide particles, thus obtaining an intermediate with low palladium loading. l -PdNCs@SnO2 particles; The ligand in the seed growth system is polyvinylpyrrolidone, the directing agent is sodium iodide, and the reducing agent is N,N-dimethylformamide; 2) The above l - A dispersion of PdNCs@SnO2 particles was prepared and used as a seed in a seed growth system. Simultaneously, the palladium precursor was reduced to cubic palladium particles, and these palladium particles were grown along the surface of the spherical tin dioxide particles to obtain palladium / tin dioxide composite nanoparticles with high palladium loading. h -PdNCs@SnO2; The seed growth system includes ligands, directing agents, and reducing agents, with the reaction temperature maintained at 120-150℃.

2. The preparation method according to claim 1, characterized in that, The result obtained in step 1) l The mass ratio of Pd to SnO2 in PdNCs@SnO2 particles is 4:5 to 3:

5.

3. The preparation method according to claim 1, characterized in that, The palladium precursor is palladium acetylacetonate.

4. The preparation method according to claim 1, characterized in that, The palladium particles in the cube have a particle size of 9-11 nm.

5. The preparation method according to claim 1, wherein the particle size of the spherical tin dioxide particles is 40-50 nm.

6. The preparation method according to claim 1, characterized in that, The stannate is sodium stannate trihydrate.

7. Palladium / tin dioxide composite nanoparticles obtained by the preparation method according to any one of claims 1-6 h -PdNCs@SnO2.

8. The palladium / tin dioxide composite nanoparticles as described in claim 7 h -PdNCs@SnO2, characterized in that, The h In -PdNCs@SnO2, the mass ratio of Pd to SnO2 is 3:2 to 2:

1.

9. The palladium / tin dioxide composite nanoparticles according to claim 7 h Application of PdNCs@SnO2 in the preparation of formic acid electrooxidation catalysts.

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