A graphene-supported platinum praseodymium / praseodymium oxide nanoparticle composite catalyst and its preparation method

Abstract

A graphene-supported platinum praseodymium / praseodymium oxide nanoparticle composite catalyst and its preparation method, which relates to the technical field of energy materials. It includes using polyol as a solvent and reducing agent, mixing the carrier graphene and the platinum praseodymium metal precursor salt, and under the condition of heating, realizing the co-reduction of the metal alloy and precipitating it on the graphene carrier to obtain a graphene-supported platinum praseodymium alloy nanoparticle composite catalyst precursor powder. The precursor powder is heat-treated in an air atmosphere to obtain a graphene-supported platinum praseodymium / praseodymium oxide nanoparticle catalyst powder. The prepared alloy catalyst is a solid powder, and the nano-alloy particles are uniformly dispersed on the graphene, with a particle size of 2-10 nm. This catalyst has high electrocatalytic activity and stability for the oxygen reduction reaction in acidic media, and its performance is superior to that of commercial Pt / C catalysts.

Description

Technical Field

[0001] The present invention relates to the technical field of energy materials, and in particular to a graphene-supported platinum praseodymium / praseodymium oxide nanoparticle composite catalyst and a preparation method thereof. Background Art

[0002] The slow kinetics of the oxygen reduction reaction (ORR) requires scarce and expensive platinum to accelerate its reaction rate, which seriously hinders the widespread application of low-temperature polymer electrolyte membrane fuel cells (PEMFCs) in automobiles. In recent years, researchers have conducted in-depth studies on Pt-based binary alloys. The combination of Pt and late transition metals such as Co and Ni catalysts can achieve a catalytic activity that is 2-4 times that of pure Pt catalysts. In recent years, due to the unique physical and chemical properties of lanthanide metal elements, Pt-lanthanide element catalysts have been studied. The research results show that the activities of Pt-lanthanide element alloy catalysts have all been improved. The paper Science 2016, 352(6281), 73-76 provides the research on Pt-lanthanide element binary alloy catalysts. The Pt-lanthanide element alloys in the paper include Pt-La, Pt-Ce, Pt-Tm, Pt-Dy, Pt-Sm, Pt-Gd, Pt-Tb. The oxygen reduction activities of these binary alloy catalysts are 3.5-5.5 times that of commercial platinum carbon; the atomic ratio of Pt to lanthanide metal is 5:1, and for the most active Pt5Tb, after 10,000 cycles of durability testing, the activity decreases by 33%. The paper ACS Applied Materials & Interfaces 2019, 11(5), 5129-5135 provides the research on Pt-Pr binary alloy catalysts. The oxygen reduction activity of the Pt-Pr binary alloy catalyst in the paper is 3.2 times that of commercial platinum carbon.

[0003] The above literature reports that although the redox activities of Pt-lanthanide element binary alloy catalysts are several times higher than that of commercial platinum carbon, their activity durability is poor, and the activity decreases by 21% before and after 1000 cycles of durability testing. The comparison of the oxygen reduction activities and durabilities of different Pt-lanthanide elements is shown in Table 1. The activities and durabilities of Pt-lanthanide element catalysts need to be improved. Summary of the Invention

[0004] In order to solve the technical problems existing in the prior art, the present invention aims to find a redox catalyst with good activity and durability.

[0005] Praseodymium (Pr), as the third element of lanthanide metals, has strong oxygen affinity, and praseodymium oxide (Pr6O 11) has variable valence states, and these properties have a positive regulatory effect on the ORR activity of the Pt catalyst. Herein, the present invention combines a simple and easy-to-operate one-step method and an annealing treatment method. Using polyol as a solvent and a reducing agent, the carrier graphene and two metal precursor salts are mixed. Under heating conditions, the co-reduction of the two metals is achieved and precipitated on the graphene carrier. Then, heat treatment is carried out in an air or oxygen-containing gas atmosphere to obtain a graphene-supported platinum praseodymium / praseodymium oxide nanoparticle catalyst powder. After testing, it is unexpectedly found that this method effectively improves the activity of the catalyst. The obtained catalyst has higher activity for the oxygen reduction reaction in acidic media than the Pt-Pr alloy and is 5.9 times that of the state-of-the-art Pt / C, and at the same time, it also has excellent stability.

[0006] On the one hand, a graphene-supported platinum praseodymium / praseodymium oxide nanoparticle composite catalyst is provided, wherein the particle size of the platinum praseodymium / praseodymium oxide nanoparticles is about 2 nm to about 10 nm, and they are uniformly dispersed on the surface of the graphene carrier. The mass ratio of the platinum praseodymium / praseodymium oxide nanoparticles to graphene is about 1:10 to about 1:1, and the atomic ratio of the platinum praseodymium is about 1:1 to about 4:1.

[0007] In some embodiments, the particle size of the platinum praseodymium / praseodymium oxide nanoparticles is about 3 nm, or about 4 nm, or about 5 nm, or about 6 nm, or about 7 nm, or about 8 nm, or about 9 nm; in some embodiments, the mass ratio of the platinum praseodymium / praseodymium oxide nanoparticles to graphene is about 1:10, about 1:9, about 1:8, about 1:7, about 1:6, about 1:5, about 1:4, about 1:3, about 1:2, etc.; in some embodiments, the atomic ratio of the platinum praseodymium is about 1.5:1, about 2.0:1, about 2.5:1, about 3.0:1, about 3.5:1.

[0008] In some embodiments, the X-ray diffraction pattern of the graphene-supported platinum praseodymium / praseodymium oxide nanoparticle composite catalyst is substantially as Figure 1 shown in A.

[0009] On the other hand, a method for preparing a graphene-supported platinum praseodymium / praseodymium oxide nanoparticle composite catalyst is provided, which includes using polyol as a solvent and a reducing agent, mixing the carrier graphene and the platinum praseodymium metal precursor salt, and under heating conditions, achieving the co-reduction of the metal alloy and precipitating it on the graphene carrier to obtain a graphene-supported platinum praseodymium alloy nanoparticle composite catalyst precursor powder. The precursor powder is heat-treated in an air or oxygen-containing gas atmosphere to obtain a graphene-supported platinum praseodymium / praseodymium oxide nanoparticle catalyst powder.

[0010] In some embodiments, the method for preparing a graphene-supported platinum praseodymium / praseodymium oxide nanoparticle composite catalyst includes the following steps:

[0011] Step 1: Preparation of platinum praseodymium / praseodymium oxide catalyst: Take polyol in a container, add reduced graphene powder, then add a certain concentration of chloroplatinic acid polyol solution and praseodymium nitrate polyol solution for mixing, ultrasonic for about 30 min to about 60 min, and adjust the pH value of the solution to 6 - 12 with an alkali solution to obtain a suspension;

[0012] Step 2: Heat at about 100 - about 150 °C and react with stirring. After the reaction is completed, obtain a black slurry, wash, filter by suction, and dry to obtain a precursor powder of graphene-supported platinum praseodymium alloy nanoparticles composite catalyst;

[0013] Step 3: Heat-treat in a muffle furnace under an air atmosphere to obtain a graphene-supported platinum praseodymium / praseodymium oxide nanoparticles catalyst powder.

[0014] In some embodiments, the polyol is selected from one or more of ethylene glycol, 1,2 - propylene glycol, 1,4 - butanediol, glycerol, and diethylene glycol.

[0015] In some embodiments, it further includes a grinding treatment step. Place the catalyst powder obtained in step (3) in a mortar and grind for 1 - 2 h to obtain the final graphene-supported platinum praseodymium / praseodymium oxide nanocomposite catalyst.

[0016] In some embodiments, the platinum praseodymium metal precursor salts are hexahydrate chloroplatinic acid and hexahydrate praseodymium nitrate.

[0017] In some embodiments, the heating temperature in step 2 is about 130 °C, and the rotation speed of the magnetic stirrer with stirring is controlled at 200 - 400 rpm.

[0018] In some embodiments, the heat treatment temperature in step 3 is about 400 - about 600 °C, and the heat treatment time is 1 - 3 hours.

[0019] In some embodiments, the heat treatment gas atmosphere is air.

[0020] Provided in one aspect is the application of the described graphene-supported platinum praseodymium / praseodymium oxide nanoparticles composite catalyst as a catalyst in the oxygen reduction reaction in an acidic medium.

[0021] The present invention provides a simple and rapid preparation method for a graphene-supported platinum praseodymium / praseodymium oxide nanoparticle composite catalyst with an activity 4 times higher than that of commercial platinum carbon in an acidic medium and metal oxide nanoparticles attached around alloy particles. The graphene-supported platinum praseodymium alloy nanoparticle composite catalyst prepared by this method has a higher activity for the oxygen reduction reaction in an acidic medium than Pt-Pr alloy and is 5.9 times that of the state-of-the-art Pt / C, and at the same time has excellent stability. The present invention relates to a preparation method for a graphene-supported platinum praseodymium / praseodymium oxide nanoparticle composite catalyst. The catalyst is a solid powder, and the particle size of the platinum praseodymium / praseodymium oxide nanoparticles is 2-10 nm and is uniformly dispersed on the surface of the graphene support. The mass ratio of the alloy nanoparticles to graphene is between 1:10 and 1:1. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A is the XRD pattern of the catalysts obtained in Examples 1-4. It can be seen that the diffraction peaks of the obtained catalysts correspond to the characteristic peaks of Pt and Pr6O 11 respectively. Among them, Figure 1 The Pt(111) characteristic peak in B is shifted to the left relative to pure Pt, indicating that Pr dissolves in the lattice of Pt to form a platinum praseodymium solid solution alloy. The above two phenomena illustrate the formation of Pt-Pr alloy and Pr6O 11 ; Figure 1 C is the SEM image of the catalysts obtained in Examples 1-4. It can be seen that the morphologies of the catalysts with different ratios are not much different, the particles are very small, and they are uniformly loaded on the carrier graphene; Figure 1 D is the oxygen reduction activity of the catalysts obtained in Examples 1-4. Taking commercial platinum carbon as a reference for comparison, it can be seen that when the ratio of PtPr is 3:1, the oxygen reduction activity is the best, and the oxygen reduction activities of the other several PtPr ratios are not much different from that of commercial platinum carbon.

[0023] Figure 2 is the TEM image of the catalyst obtained in Example 3. It can be seen that the alloy particles are uniformly dispersed on the surface of the support, and the particle size is 2-10 nm;

[0024] Figure 3 Figure A of is the comparison diagram of the rotating disk curves of the catalyst obtained in Example 3 and the commercial Pt / C (the state-of-the-art Pt / C) catalyst in an acidic medium (electrolyte solution: 0.1 M HClO4; scanning rate: 10 mV / s; scanning voltage range: -0.3 to 0.9 V; rotation speed: rpm = 1600). Figure 3 B is the calculated specific activity of each catalyst. From Figure 3 B, it can be seen that the specific activity of platinum praseodymium / praseodymium oxide is 2.01 mAcm-2 , which is 1.6 times that of the platinum-praseodymium alloy (1.23 mA cm -2 ), and 5.9 times that of commercial Pt / C (0.34 mA cm -2 ). It has a higher improvement factor in activity than the best Pt-lanthanide binary alloy catalyst in the literature (Science 2016, 352(6281), 73 - 76, where the specific activity of the best sample Pt5Tb is 5.5 times that of commercial Pt / C), and in Example 3, the ratio of Pt to Pr is 3:1, and the usage amount of Pt further decreases.

[0025] Figure 4 Figures A and C are the polarization curve comparison diagrams of the catalyst of Example 3 and the commercial Pt / C catalyst in the durability test (10,000 cycles); Figures B and D are the comparison diagrams of the changes in specific activity and specific mass activity before and after the calculated durability test. It can be seen that before and after 10,000 cycles in Example 3, the specific activity decreased by 10.4%, which is much lower than the specific activity decrease rate of commercial Pt / C (35%), and is also smaller than the specific activity decrease rate of Pt5Tb in the literature; it is much more durable than the Pt-Pr binary alloy catalyst in the paper (ACS Applied Materials & Interfaces 2019, 11(5), 5129 - 5135, where the specific activity decreased by 21% after 1,000 cycles). Detailed implementation mode

[0026] The XRD of the present invention is tested by a method well-known in the art, and the raw materials used in the present invention are all purchased from the market. "Substantially as shown" mentioned in the claims and the specification means that at least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95%, or at least 99% of the peaks in the X-ray powder diffraction pattern (XRD) appear in the figure.

[0027] In the context description, all numerical values disclosed in the present invention are approximate values, whether or not the words "about / approximately" or "approximate" are used in connection with them. They may differ by 1%, 2%, 5%, or sometimes even by 10% to 20%. Whenever a numerical range with a lower limit RL and an upper limit RU is disclosed, any numerical value falling within the range is considered specifically disclosed. Specifically, the following numerical values within the range are specifically disclosed: R = RL + k*(RU - RL), where k is a variable with a range from 1% to 100% and an increment of 1%, that is, k is 1%, 2%, 3%, 4%, 5%,..., 50%, 51%, 52%, …, 95%, 96%, 97%, 98%, 99%, or 100%. In addition, any numerical range defined by two R numbers defined as above is also specifically disclosed.

[0028] The "reduced graphene powder" mentioned in the context of the present invention was purchased from Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, and is high-conductive graphene TNERGO-10.

[0029] Example 1

[0030] Prepare a reduced graphene supported platinum praseodymium / praseodymium oxide nanoparticle composite catalyst with a platinum praseodymium alloy ratio of 1:1

[0031] (1) Take 50 ml of ethylene glycol, and add 9.3 ml of 0.01 M chloroplatinic acid ethylene glycol solution and 2.7 ml of 0.023 M praseodymium nitrate ethylene glycol solution respectively. Then add the reduced graphene powder (purchased from Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, high-conductive graphene TNERGO-10) to the above mixed solution, ultrasonicate for 60 min, and adjust the pH of the solution to 10 with NaOH solution to obtain a suspension;

[0032] (2) Put the suspension obtained in step (1) into a round-bottom flask, place it in an oil bath at 130 °C and stir at a speed of 300 rpm for a reduction reaction, and react at this temperature for 3 h. After the reaction, a black slurry is obtained;

[0033] (3) Filter the black slurry obtained in step (2) by suction and wash it with deionized water, and perform a drying treatment to obtain a graphene supported platinum praseodymium alloy nanoparticle composite catalyst precursor powder.

[0034] (4) Heat-treat in a muffle furnace under an air atmosphere at 500 °C for 1 - 3 hours to obtain a graphene supported platinum praseodymium / praseodymium oxide nanoparticle catalyst powder;

[0035] (5) Place the powder obtained in (4) in a mortar and grind it carefully for 1 - 2 h to finally obtain a graphene supported platinum praseodymium / praseodymium oxide nanoparticle composite catalyst powder.

[0036] Example 2

[0037] Prepare a reduced graphene supported platinum praseodymium / praseodymium oxide nanoparticle composite catalyst with a platinum praseodymium alloy ratio of 2:1

[0038] (1) Take 50 ml of ethylene glycol, and add 9.3 ml of 0.01 M chloroplatinic acid ethylene glycol solution and 1.67 ml of 0.023 M praseodymium nitrate ethylene glycol solution respectively. Then add the reduced graphene powder to the above mixed solution, ultrasonicate for 60 min, and adjust the pH of the solution to 6 - 12 with NaOH solution to obtain a suspension;

[0039] (2) Put the suspension obtained in step (1) into a round-bottom flask, place it in an oil bath at 130 °C and stir for a reduction reaction, and react at this temperature for 3 h. After the reaction, a black slurry is obtained;

[0040] (3) Filter the black slurry obtained in step (2) by suction filtration, wash it with deionized water, and perform freeze-drying to obtain the precursor powder of the graphene-supported platinum-praseodymium alloy nanoparticle composite catalyst.

[0041] (4) Heat-treat in a muffle furnace under an air atmosphere for 1 to 3 hours to obtain the graphene-supported platinum-praseodymium / praseodymium oxide nanoparticle catalyst powder.

[0042] (5) Place the powder obtained in (4) in a mortar and carefully grind it for 1 to 2 h to finally obtain the graphene-supported platinum-praseodymium / praseodymium oxide nanoparticle composite catalyst powder.

[0043] Example 3

[0044] Prepare a reduced graphene-supported platinum-praseodymium / praseodymium oxide nanoparticle composite catalyst with a platinum-praseodymium alloy ratio of 3:1

[0045] (1) Take 50 ml of ethylene glycol, add 9.3 ml of 0.01 M chloroplatinic acid ethylene glycol solution and 1.35 ml of 0.023 M praseodymium nitrate ethylene glycol solution respectively. Then add the reduced graphene powder to the above mixed solution, ultrasonicate for 60 min, and adjust the pH of the solution to 6 - 12 with NaOH solution to obtain a suspension.

[0046] (2) Put the suspension obtained in step (1) into a round-bottom flask, place it in an oil bath at 130 °C and stir to carry out the reduction reaction, and react at this temperature for 3 h. After the reaction is completed, a black slurry is obtained.

[0047] (3) Filter the black slurry obtained in step (2) by suction filtration, wash it with deionized water, and perform drying to obtain the precursor powder of the graphene-supported platinum-praseodymium alloy nanoparticle composite catalyst.

[0048] (4) Heat-treat in a muffle furnace under an air atmosphere for 1 to 3 hours to obtain the graphene-supported platinum-praseodymium / praseodymium oxide nanoparticle catalyst powder.

[0049] (5) Place the powder obtained in (4) in a mortar and carefully grind it for 1 to 2 h to finally obtain the graphene-supported platinum-praseodymium / praseodymium oxide nanoparticle composite catalyst powder.

[0050] Example 4

[0051] Prepare a reduced graphene-supported platinum-praseodymium / praseodymium oxide nanoparticle composite catalyst with a platinum-praseodymium alloy ratio of 4:1

[0052] (1) Take 50 ml of ethylene glycol, and add 9.3 ml of 0.01 M ethylene glycol solution of chloroplatinic acid and 1 ml of 0.023 M ethylene glycol solution of praseodymium nitrate respectively. Then add the reduced graphene powder into the above mixed solution, ultrasonicate for 60 min, and adjust the pH of the solution to 6 - 12 with NaOH solution to obtain a suspension;

[0053] (2) Put the suspension obtained in step (1) into a round-bottom flask, place it in an oil bath at 130 °C and stir to carry out a reduction reaction, and react at this temperature for 3 h. After the reaction is completed, a black slurry is obtained;

[0054] (3) Filter the black slurry obtained in step (2) by suction filtration and wash it with deionized water, and then carry out a drying treatment to obtain a precursor powder of a composite catalyst of graphene-supported platinum-praseodymium alloy nanoparticles.

[0055] (4) Heat-treat in a muffle furnace under an air atmosphere for 1 - 3 hours to obtain a graphene-supported platinum-praseodymium / praseodymium oxide nanoparticle catalyst powder;

[0056] (5) Place the powder obtained in (4) in a mortar and grind it carefully for 1 - 2 h, and finally obtain a graphene-supported platinum-praseodymium / praseodymium oxide nanoparticle composite catalyst powder.

[0057] Table 1 Comparison of oxygen reduction activities of different Pt-lanthanide element catalysts

[0058]

[0059] (1) Fichtner, J.; Garlyyev, B.; Watzele, S.; E1-Sayed, H.A.; J.N.; Li, W.-J.; Maillard, F.M.; Dubau, L.; J.; Macak, J.M.; Holleitner, A.; Bandarenka, A.S., Top-Down Synthesis of Nanostructured Platinum-LanthanideAlloy Oxygen Reduction Reaction Catalysts: Ptxpr / C as an Example.ACS AppliedMaterials&Interfaces 2019, 11(5), 5129 - 5135.

[0060] (2) Escudero-Escribano, M.; Malacrida, P.; Hansen, MH; Vej-Hansen, UG; Velazquez-Palenzuela, A.; Tripkovic, V.; Schiotz, J.; Rossmeisl, J.; Stephens, IEL; Chorkendofff, I., Tuning the Activity of Pt Alloy Electrocatalysts by Means of the Lanthanide Contraction.Science 2016, 352(6281), 73-76.

[0061] The above specific embodiments describe the basic principles and main features of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and any changes or modifications that are not thought of through creative work should be included in the protection scope of the present invention. Without departing from the scope of the present invention, the present invention will also have various changes and improvements, and these changes and improvements will fall within the scope of the protection required.

Claims

1. A graphene-supported platinum praseodymium / praseodymium oxide nanoparticle composite catalyst, characterized in that, In the composite catalyst, the particle size of the platinum praseodymium / praseodymium oxide nanoparticles is 2-10 nm, and they are uniformly dispersed on the surface of the graphene support; among them, the mass ratio of the platinum praseodymium / praseodymium oxide nanoparticles to graphene is between 1:10 and 1:1, and the atomic ratio of platinum to praseodymium is between 1:1 and 4:1; The preparation process is as follows: Using polyol as a solvent and reducing agent, the support graphene and the platinum praseodymium metal precursor salt are mixed. Under heating conditions, metal alloy co-reduction is achieved and precipitated on the graphene support to obtain a graphene-supported platinum praseodymium alloy nanoparticle composite catalyst precursor powder; the precursor powder is heat-treated in an air or oxygen-containing gas atmosphere to obtain a graphene-supported platinum praseodymium / praseodymium oxide nanoparticle catalyst powder.

2. The graphene-supported platinum praseodymium / praseodymium oxide nanoparticle composite catalyst according to claim 1, wherein The X-ray diffraction pattern of the composite catalyst is shown in Figure 1A.

3. The graphene-supported platinum praseodymium / praseodymium oxide nanoparticle composite catalyst according to claim 1, wherein, The preparation process includes the following steps: (1) Take polyol in a container, add reduced graphene powder, then add a chloroplatinic acid polyol solution and a praseodymium nitrate polyol solution for mixing, ultrasonic for 30 min - 60 min, and adjust the pH value of the solution to 6 - 12 with an alkali solution to obtain a suspension; (2) Heat at 100 - 150 °C and react with stirring. After the reaction, a black slurry is obtained, washed, filtered by suction, and dried to obtain a graphene-supported platinum praseodymium alloy nanoparticle composite catalyst precursor powder; (3) Heat-treat in an air atmosphere to obtain a graphene-supported platinum praseodymium / praseodymium oxide nanoparticle catalyst powder.

4. The graphene-supported platinum praseodymium / praseodymium oxide nanoparticle composite catalyst according to claim 1, wherein The polyol is selected from one or more of ethylene glycol, 1,2-propanediol, 1,4-butanediol, glycerol, and diethylene glycol.

5. The graphene-supported platinum praseodymium / praseodymium oxide nanoparticle composite catalyst according to claim 3, wherein It also includes a grinding treatment step. The catalyst powder obtained in step (3) is placed in a mortar and ground for 1 - 2 h to obtain the final graphene-supported platinum praseodymium / praseodymium oxide nanocomposite catalyst.

6. The graphene-supported platinum praseodymium / praseodymium oxide nanoparticle composite catalyst according to claim 1, wherein The platinum praseodymium metal precursor salt is chloroplatinic acid hexahydrate and praseodymium nitrate hexahydrate.

7. The graphene-supported platinum praseodymium / praseodymium oxide nanoparticle composite catalyst according to claim 3, wherein The heating temperature in step (2) is 130 °C, and the rotation speed of the magnetic stirrer with stirring is controlled at 200 - 400 rpm.

8. The graphene-supported platinum praseodymium / praseodymium oxide nanoparticle composite catalyst according to claim 3, wherein, The temperature of the heat treatment in step (3) is 400 - 600 °C, and the heat treatment time is 1 - 3 hours.

9. Use of the graphene-supported platinum praseodymium / praseodymium oxide nanoparticle composite catalyst according to any one of claims 1 - 8 as a catalyst in the oxygen reduction reaction in an acidic medium.

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