Preparation method and application of Pd / O-OMS-2 direct methanol fuel cell bifunctional catalyst

Abstract

The invention discloses a preparation method of a Pd / O-OMS-2 direct methanol fuel cell bifunctional catalyst with a Pd-O-Mn interface chemical bond and high Mn < 3 + > content. The Pd / O-OMS-2 bifunctional catalyst with high Mn < 3 + > content is prepared by constructing a Pd-O-Mn interface chemical bond on a Pd and OMS-2 oxygen-enriched oxide interface through a wet chemical reduction method on the basis of strong interaction of metal and a carrier. Due to introduction of a Pd-O-Mn interface chemical bond, redistribution of charges is effectively promoted, the electronic state of a noble metal Pd active site is adjusted, and the catalytic ability of the catalyst is improved. The prepared Pd / O-OMS-2 catalyst shows excellent catalytic performance, long-term stability and efficient four-electron path selectivity in oxygen reduction reaction and methanol oxidation reaction, and is suitable for direct methanol fuel cells. The catalyst is simple in preparation process and low in cost, and has a wide commercial prospect.

Description

Technical Field

[0001] The present invention relates to the preparation and application of a bifunctional catalyst for the oxygen reduction reaction at the cathode and the methanol oxidation reaction at the anode in a direct methanol fuel cell, and particularly to the preparation and application of a Pd / O-OMS-2 bifunctional catalyst having a Pd-O-Mn interfacial chemical bond and a high Mn 3+ content. Background Art

[0002] With the continuous consumption of global fossil fuels and the increasingly severe environmental pollution problems, the demand for clean and renewable energy technologies is becoming more urgent. As an efficient energy conversion system, direct methanol fuel cells (DMFCs) efficiently convert the chemical energy of small organic molecules into electrical energy through electrochemical reactions, showing great application potential. In DMFCs, the methanol oxidation reaction (MOR) occurs at the anode, while the oxygen reduction reaction (ORR) occurs at the cathode. However, the sluggish kinetic processes and high overpotentials of these reactions limit the overall energy conversion efficiency. Therefore, the development of efficient, low-cost, and stable catalysts is crucial for the widespread application of DMFCs. Currently, platinum-based catalysts have received extensive attention due to their excellent activity and selectivity in ORR and MOR. However, the scarcity and high cost of platinum remain the main obstacles to their large-scale application. Palladium (Pd), as a noble metal with similar chemical and electronic properties to platinum, has become a potential substitute for platinum. By adjusting the local structure of palladium atoms, its electronic configuration and intermediate adsorption energy can be optimized, thereby enhancing its intrinsic activity to reach or exceed the level of platinum.

[0003] Adjusting the electronic structure of palladium is the key to improving its catalytic efficiency. Constructing strong metal-support interactions (SMSI) is an effective strategy for optimizing the electronic structure of palladium. Through the electron transfer between the metal and the support, the electronic configuration and adsorption energy of the metal active sites are adjusted, thereby enhancing the activity, selectivity, and stability of the catalyst. Currently, transition metal oxides have been widely favored as catalyst supports in fuel cells. When these oxides are used as supports, the oxygen atoms on their surfaces form Pd-O bonds with palladium, thereby changing the electronic structure of palladium. In recent years, researchers have combined SMSI with interfacial chemical bonds to construct noble metal-O-metal oxide connected interfacial chemical bonds at the metal-oxide heterointerface, promoting the redistribution of charges, adjusting the electronic states of noble metal active sites, and improving the catalytic ability of catalyst active sites. Among many metal oxides, those with Manganese octahedral molecular sieve (OMS-2) with a microporous tunnel structure is often used as a good support for noble metal catalysts due to its unique pore structure and variable valence states, and the electronic structure of metal active sites is adjusted through SMSI at the interface. In addition, the one-dimensional OMS-2 nanorod morphology enhances the high exposure of active sites and the charge transfer rate. Therefore, the present invention proposes a preparation method of a Pd / O-OMS-2 bifunctional catalyst with Pd-O-Mn chemical bonds and high Mn 3+ content, providing a new idea for the research and development of direct methanol fuel cell catalysts. Summary of the Invention

[0004] In view of this, the first object of the present invention is to provide a preparation method of a Pd / O-OMS-2 bifunctional catalyst with Pd-O-Mn chemical bonds and high Mn 3+ content. Secondly, the prepared Pd / O-OMS-2 catalyst has excellent ORR and MOR catalytic performances in the application of direct methanol fuel cells and has broad prospects in the application of direct methanol fuel cells.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] (1) O-OMS-2 nanorods are prepared by using the reflux method and high-temperature annealing in an oxygen-rich environment.

[0007] (2) Using the O-OMS-2 obtained in step (1) as a support, a Pd / O-OMS-2 bifunctional catalyst with Pd-O-Mn interface chemical bonds and high Mn 3+ content is prepared by a wet chemical reduction method.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] Further, in step (1), first, a certain amount of MnSO4·H2O is dissolved in a certain amount of deionized water, and a certain amount of HNO3 is added to form solution A. Secondly, a certain amount of KMnO4 is dissolved in a certain amount of deionized water to form solution B. Solution B is added dropwise to solution A, and the reaction is refluxed at a certain temperature. After the reaction is completed, the sample is washed and dried, and finally, OMS-2 nanorods are prepared. Finally, the OMS-2 nanorods are placed in a muffle furnace and subjected to high-temperature annealing at a certain heating rate and in an oxygen-rich environment to prepare O-OMS-2.

[0010] Further, in step (2), first, a certain amount of Pd metal precursor is dissolved in a mixed solution of a certain amount of deionized water and ethanol. Secondly, the O-OMS-2 support obtained in step (1) is uniformly dispersed in this solution, a certain amount of reducing agent and surfactant are added, and after stirring evenly, filtering, washing, and drying, the Pd / O-OMS-2 catalyst is prepared.

[0011] Further, in step (1), first, a certain amount of MnSO4·H2O is dissolved in a certain amount of deionized water, and a certain amount of HNO3 is added to form solution A.

[0012] Further, in step (1), a certain amount of KMnO4 is dissolved in a certain amount of deionized water to form solution B, and solution B is slowly added dropwise to solution A.

[0013] Further, in step (1), the mass ratio of MnSO4·H2O to deionized water is 0.1 - 0.6.

[0014] Further, in step (1), the mass ratio of KMnO4 to deionized water is 0.02 - 0.10.

[0015] Further, in step (1), the mass of MnSO4·H2O is 1.0 - 2.0 times that of KMnO4.

[0016] Further, in step (1), the obtained mixed solution is transferred to a 250 mL three-necked flask, placed in an oil bath, and refluxed at 70°C - 120°C for 16 - 30 hours. After the reaction is completed, it is filtered, washed, and dried at 70 - 90°C for 5 - 10 hours to obtain OMS-2 nanorods.

[0017] Further, in step (1), the obtained OMS-2 nanorods are placed in a muffle furnace for high-temperature annealing, the annealing temperature is 200°C - 500°C, the annealing time is 1 - 5 hours, and the heating rate is 2 - 5°C / minute.

[0018] Further, in step (2), the Pd metal precursor used is Na2PdCl4, the reducing agent is sodium borohydride, and the surfactant is polyvinylpyrrolidone.

[0019] Further, in step (2), first, a certain amount of Na2PdCl4 is added to a mixed solution of a certain amount of deionized water and ethanol.

[0020] Further, in step (2), a certain amount of sodium borohydride, polyvinylpyrrolidone, and O-OMS-2 nanorods are added to the solution containing Na2PdCl4, and stirred for 11 - 13 h.

[0021] Further, in the step 2), the mass-to-volume ratio of Na2PdCl4 to the mixed solution is 0.0002 - 0.0006, and the volume ratio of deionized water to ethanol is 0.7 - 1.2.

[0022] Further, in the step 2), the mass ratio of Na2PdCl4 to sodium borohydride is 0.5 - 1.0, and the mass ratio of Na2PdCl4 to polyvinylpyrrolidone is 4 - 6.

[0023] Further, the catalytic performance of the Pd / O-OMS-2 catalyst with Pd-O-Mn interfacial chemical bonds in the oxygen reduction reaction and methanol oxidation reaction is tested.

[0024] The beneficial effects of the present invention are as follows: The present invention uses the reflux method to prepare the OMS-2 support, performs annealing treatment in an oxygen-rich environment, and synthesizes the oxygen-rich surface Pd / O-OMS-2 catalyst by the sodium borohydride reduction method. This catalyst exhibits excellent catalytic activity and long-term stability in the oxygen reduction reaction and methanol oxidation reaction, and the preparation process is simple and the conditions are mild, having good potential for commercial application. Description of the Drawings

[0025] In order to make the objectives, technical solutions, and beneficial effects of the present invention clearer, taking the O-OMS-2 support annealed in an oxygen-rich environment as an example in the present invention, a Pd / O-OMS-2 bifunctional catalyst for direct methanol fuel cells with Pd-O-Mn interfacial chemical bonds and high Mn 3+ content is prepared, and the following drawings are provided for illustration:

[0026] Figure 1 XRD pattern of the Pd / O-OMS-2 bifunctional catalyst for direct methanol fuel cells obtained in Example 1;

[0027] Figure 2 SEM image of the Pd / O-OMS-2 bifunctional catalyst for direct methanol fuel cells obtained in Example 1;

[0028] Figure 3 TEM image of the Pd / O-OMS-2 bifunctional catalyst for direct methanol fuel cells obtained in Example 1;

[0029] Figure 4 XPS spectrum of the Pd / O-OMS-2 bifunctional catalyst for direct methanol fuel cells obtained in Example 1;

[0030] Figure 5 CV curve of the Pd / O-OMS-2 bifunctional catalyst for direct methanol fuel cells obtained in Example 1 in 1.0 mol / L KOH;

[0031] Figure 6CV diagram of the Pd / O-OMS-2 bifunctional catalyst obtained in Example 1 under O2 conditions for a direct methanol fuel cell;

[0032] Figure 7 Comparison diagram of LSV and ORR performance of the Pd / O-OMS-2 bifunctional catalyst obtained in Example 1 for a direct methanol fuel cell;

[0033] Figure 8 Multiple repeated LSV diagrams of the Pd / O-OMS-2 bifunctional catalyst obtained in Example 1 for a direct methanol fuel cell;

[0034] Figure 9 Diagram of the number of electron transfers and hydrogen peroxide yield of the Pd / O-OMS-2 bifunctional catalyst obtained in Example 1 for a direct methanol fuel cell at a potential of 0.2 - 0.8 V;

[0035] Figure 10 Diagram of methanol crossover resistance of the Pd / O-OMS-2 bifunctional catalyst obtained in Example 1 for a direct methanol fuel cell;

[0036] Figure 11 LSV diagrams of the Pd / O-OMS-2 bifunctional catalyst obtained in Example 1 for a direct methanol fuel cell before and after 10,000 times of accelerated durability testing;

[0037] Figure 12 MOR performance diagram of the Pd / O-OMS-2 bifunctional catalyst obtained in Example 1 for a direct methanol fuel cell;

[0038] Figure 13 I-t diagram of the Pd / O-OMS-2 bifunctional catalyst obtained in Example 1 for a direct methanol fuel cell. Detailed implementation mode

[0039] The preferred embodiments of the present invention will be described in detail below. For experimental methods where specific conditions are not indicated in the examples, they are generally in accordance with conventional conditions or the conditions recommended by the manufacturer.

[0040] Example 1

[0041] Taking the O-OMS-2 support annealed in an oxygen-rich environment as an example, the preparation of a Pd / O-OMS-2 bifunctional catalyst for a direct methanol fuel cell with Pd-O-Mn interfacial chemical bonds and a high Mn 3+ content.

[0042] (1) Dissolve 52 mmol of MnSO4·H2O in 30 mL of deionized water, and add 3 mL of HNO3 to form solution A; then dissolve 37 mmol of KMnO4 in 100 mL of deionized water to form solution B. Add solution B to solution A, and the mixture is refluxed at 100 °C for 24 h. After the reaction, filter and collect the product, wash it with deionized water, and then dry it at 80 °C for 8 h to obtain OMS-2 nanorods. Place the OMS-2 nanorods in a porcelain boat and perform heat treatment at 300 °C for 3 h in an oxygen atmosphere to form the O-OMS-2 oxygen-rich material.

[0043] (2) Weigh 10.58 mg of Na2PdCl4 and dissolve it in a mixed solution of 15 mL of deionized water and 15 mL of ethanol. Subsequently, add 15 mg of NaBH4, 2 mg of polyvinylpyrrolidone, and 15 mg of O-OMS-2 nanorods, and stir for 12 h. Filter the resulting solution, wash it with deionized water, and dry it overnight at 60 °C to obtain the Pd / O-OMS-2 bifunctional catalyst.

[0044] Example 2

[0045] Based on the Pd / O-OMS-2 bifunctional catalyst prepared in Example 1, electrodes for the oxygen reduction reaction at the cathode and the methanol oxidation reaction at the anode of a direct methanol fuel cell are prepared, and the oxygen reduction reaction and methanol oxidation performance are tested.

[0046] Take 2 mg of the Pd / O-OMS-2 catalyst prepared in Example 1, add 0.5 mg of carbon powder, and disperse it in 816 μL of a mixed solution of ultrapure water, ethanol, and Nafion (5 wt%) solution (the volume ratio of ethanol to ultrapure water is 1:1, and the volume of Nafion is 16 μL). Subsequently, drop 12.5 μL of the ink on the rotating disk electrode head and let it dry naturally. For the oxygen reduction reaction, use a glassy carbon electrode with a diameter of 5 mm as the working electrode, a platinum sheet as the counter electrode, and a saturated Ag / AgCl as the reference electrode. In a 0.1 mol / L KOH solution, perform cyclic voltammetry (CV), linear sweep voltammetry (LSV), methanol crossover test, and accelerated durability test (ADT) in the potential range of 0.05 - 1.2 V (vs. RHE). Use a rotating ring-disk electrode to measure the number of electrons transferred (n) and the hydrogen peroxide yield (H2O2%). For the methanol oxidation reaction, use a glassy carbon electrode with a diameter of 4 mm as the working electrode, a platinum sheet as the counter electrode, and a saturated Hg / HgO as the reference electrode. In a mixed solution of 1.0 mol / L KOH and 1.0 mol / L CH3OH, perform CV and I-t tests in the potential range of 0.05 - 1.2 V.

[0047] Figure 1XRD pattern of the Pd / O-OMS-2 bifunctional catalyst for direct methanol fuel cells obtained in Example 1. It can be seen that the Pd / O-OMS-2 catalyst was successfully prepared.

[0048] Figure 2 SEM image of the Pd / O-OMS-2 bifunctional catalyst for direct methanol fuel cells obtained in Example 1. SEM shows that O-OMS-2 exhibits a nanoflower-like structure and confirms that it is composed of nanorods with a diameter of approximately 42.5 nm.

[0049] Figure 3 TEM image of the Pd / O-OMS-2 bifunctional catalyst for direct methanol fuel cells obtained in Example 1. TEM and HRTEM reveal that the interplanar spacing of O-OMS-2 is consistent with the lattice spacing in the XRD pattern. The average length of the nanorods is approximately 650 nm, the diameter is approximately 42.5 nm, and the aspect ratio is approximately 15. After depositing Pd nanoparticles, the nanorod morphology of the catalyst does not change. The EDS mapping shows that Pd is uniformly distributed on the surface of O-OMS-2 nanorods.

[0050] Figure 4 XPS spectrum of the Pd / O-OMS-2 bifunctional catalyst for direct methanol fuel cells obtained in Example 1. Elements Pd, Mn, O, and C are present in the Pd / O-OMS-2 catalyst, where Pd mainly exists in the form of Pd 2+ , Mn mainly exists in the form of Mn 3+ , the average oxidation state of Mn is 3.5, and O mainly exists as O latt .

[0051] Figure 5 CV curve of the Pd / O-OMS-2 bifunctional catalyst for direct methanol fuel cells obtained in Example 1 in 1.0 mol / L KOH. The curve shows two distinct oxidation peaks, corresponding to the oxidation of Mn 2+ to Mn 3+ (Mn a peak) and the oxidation of Mn 3+ to Mn 4+ (Mn b peak), further confirming the high concentration of Mn 3+ in O-OMS-2.

[0052] Figure 6 CV curve of the Pd / O-OMS-2 bifunctional catalyst for direct methanol fuel cells obtained in Example 1 under O2 conditions. The CV curve has a strong oxygen reduction peak, indicating that the catalyst has strong ORR potential.

[0053] Figure 7Comparison diagram of LSV and ORR performance of the Pd / O-OMS-2 bifunctional catalyst for direct methanol fuel cells obtained in Example 1. It can be seen that the Pd / O-OMS-2 calcined in an oxygen atmosphere has the best half-wave potential (0.901 V) and the optimal ORR performance.

[0054] Figure 8 Multiple repeated LSV diagram of the Pd / O-OMS-2 bifunctional catalyst for direct methanol fuel cells obtained in Example 1. It can be seen that the Pd / O-OMS-2 catalyst has stable ORR activity.

[0055] Figure 9 Diagram of the number of electron transfers and hydrogen peroxide yield of the Pd / O-OMS-2 bifunctional catalyst for direct methanol fuel cells obtained in Example 1 at a potential of 0.2 - 0.8 V. In the potential range of 0.2 - 0.8 V (vs. RHE), the number of electron transfers is 3.94 - 3.99, and the hydrogen peroxide yield is less than 3%, showing a typical "four-electron" transfer process.

[0056] Figure 10 Diagram of methanol crossover resistance of the Pd / O-OMS-2 bifunctional catalyst for direct methanol fuel cells obtained in Example 1. After adding methanol, the current density of the Pd / O-OMS-2 catalyst remains almost unchanged, showing excellent methanol crossover resistance performance.

[0057] Figure 11 LSV diagram of the Pd / O-OMS-2 bifunctional catalyst for direct methanol fuel cells obtained in Example 1 before and after 10,000 accelerated durability tests. After 10,000 accelerated aging experiments, the half-wave potential of the Pd / O-OMS-2 catalyst hardly decays, showing excellent stability.

[0058] Figure 12 MOR performance diagram of the Pd / O-OMS-2 bifunctional catalyst for direct methanol fuel cells obtained in Example 1. It can be seen that the Pd / O-OMS-2 catalyst shows the best mass activity and a more negative onset potential for the methanol oxidation reaction.

[0059] Figure 13 I-t diagram of the Pd / O-OMS-2 bifunctional catalyst for direct methanol fuel cells obtained in Example 1. The Pd / O-OMS-2 maintained a higher steady-state current within 7200 s, showing excellent stability.

[0060] It should be noted that in the present invention, parameters such as the Pd metal precursor, solvent, reaction temperature, and reaction time can be adjusted accordingly according to common knowledge.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail through preferred embodiments, those skilled in the art should understand that various adjustments can be made to its form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A preparation method and application of a Pd / O-OMS-2 direct methanol fuel cell bifunctional catalyst, characterized in that: (1) O-OMS-2 one-dimensional nanorods were prepared by reflux method and high temperature annealing in an oxygen-rich environment; (2) Using the O-OMS-2 obtained in step (1) as a carrier, a Pd-O-Mn interface chemical bond and a high Mn 3+ Pd / O-OMS-2 direct methanol fuel cell bifunctional catalyst with high content.

2. The preparation method as claimed in claim 1, taking the O-OMS-2 carrier annealed in an oxygen-rich environment as an example, has a Pd-O-Mn interface chemical bond and a high Mn 3+ A method for preparing a Pd / O-OMS-2 direct methanol fuel cell bifunctional catalyst with a high content of Pd, characterized in that: (1) preparing OMS-2 nanorods by a reflux method and annealing them in a muffle furnace to prepare an O-OMS-2 carrier; (2) placing the O-OMS-2 nanorods obtained in step (1) into a reaction vessel, using sodium borohydride as a reducing agent, to prepare a nanorod having a Pd-O-Mn interface chemical bond and a high Mn 3+ content of Pd / O-OMS-2 bifunctional catalyst.

3. The method of claim 2 having a Pd-O-Mn chemical bond and a high Mn 3+ A method for preparing a Pd / O-OMS-2 direct methanol fuel cell bifunctional catalyst with a high content of Pd, characterized in that: In step (1), firstly, a certain amount of MnSO4·H2O is dissolved in a certain amount of deionized water, and a certain amount of HNO3 is added to form solution A. Secondly, a certain amount of KMnO4 is dissolved in a certain amount of deionized water to form solution B. Solution B is added dropwise to solution A, and refluxed at a certain temperature for reaction. After the reaction is completed, the sample is washed and dried to finally obtain OMS-2 nanorods. Finally, the OMS-2 nanorods are placed in a muffle furnace and subjected to high temperature annealing at a certain heating rate and in an oxygen-rich environment to prepare O-OMS-2.

4. The method of claim 2 having a Pd-O-Mn chemical bond and a high Mn 3+ A method for preparing a Pd / O-OMS-2 direct methanol fuel cell bifunctional catalyst with a high content of Pd, characterized in that: In step (2), a certain amount of Pd metal precursor is first dissolved in a mixed solution of a certain amount of deionized water and ethanol. Next, the O-OMS-2 carrier obtained in step (1) is uniformly dispersed in the solution, a certain amount of reducing agent and surfactant are added, stirred evenly, filtered, washed, and dried to prepare a Pd / O-OMS-2 catalyst.

5. The method according to claim 2 having a Pd-O-Mn chemical bond and a high Mn 3+ A method for preparing a Pd / O-OMS-2 direct methanol fuel cell bifunctional catalyst with a high content of Pd, characterized in that: In step (1), the mass ratio of MnSO4·H2O to deionized water is 0.1-0.6; the mass ratio of KMnO4 to deionized water is 0.02-0.10; and the mass of MnSO4·H2O is 1.0-2.0 times that of KMnO4.

6. The method according to claim 2 having a Pd-O-Mn chemical bond and a high Mn 3+ A method for preparing a Pd / O-OMS-2 direct methanol fuel cell bifunctional catalyst with a high content of Pd, characterized in that: In step (1), the obtained mixed solution is transferred to a 250 mL three-necked flask, placed in an oil bath, and refluxed at 70° C. to 120° C. for 16 to 30 hours. After the reaction is completed, the mixture is filtered, washed, and dried at 70 to 90° C. for 5 to 10 hours.

7. The method according to claim 2 having a Pd-O-Mn chemical bond and a high Mn 3+ A method for preparing a Pd / O-OMS-2 direct methanol fuel cell bifunctional catalyst with a high content of Pd, characterized in that: In step (1), the OMS-2 nanorods are placed in a muffle furnace for high-temperature annealing, the annealing temperature is 200° C. to 500° C., the annealing time is 1 to 5 hours, and the heating rate is 2 to 5° C. / minute.

8. The method according to claim 2 having a Pd-O-Mn chemical bond and a high Mn 3+ A method for preparing a Pd / O-OMS-2 direct methanol fuel cell bifunctional catalyst with a high content of Pd, characterized in that: In step (2), the Pd metal precursor used is Na2PdCl4, the reducing agent is sodium borohydride, and the surfactant is polyvinyl pyrrolidone. Na2PdCl4 is added to a mixed solution of deionized water and ethanol, wherein the mass ratio of Na2PdCl4 to the mixed solution is 0.0002-0.0006, and the volume ratio of deionized water to ethanol is 0.7-1.

2. Subsequently, sodium borohydride and polyvinyl pyrrolidone are added, the mass ratio of Na2PdCl4 to sodium borohydride is 0.5-1.0, and the mass ratio of Na2PdCl4 to polyvinyl pyrrolidone is 4-6. Stirring is continued for 8-16 hours, the solution is filtered and the sample is washed with deionized water, and finally dried at 60°C-80°C for 5-10 hours.

9. The method according to claim 4 to 8 having a Pd-O-Mn chemical bond and a high Mn 3+ The Pd / O-OMS-2 bifunctional catalyst with high content is used in the cathode oxygen reduction reaction and the anode methanol oxidation reaction of direct methanol fuel cells.

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