Preparation method of PdIr alloy electrocatalyst for fuel cell

Abstract

The present invention provides a method for preparing a PdIr alloy electrocatalyst for a fuel cell. Potassium chloropalladate and iridium trichloride are dissolved in water to obtain solution A; P123 is dissolved in ethanol to obtain solution B; KI is dissolved in water to obtain solution C. Solutions A, B and C are mixed evenly and transferred to a hydrothermal reactor, reacted at a certain temperature, and centrifuged and washed to obtain a PdIr-KI catalyst. The test results show that since Ir is inert to methanol oxidation, the PdIr catalyst has almost no activity to methanol oxidation. After adding KI, I ‑ Ion part and PdCl6 2‑ Cl ‑ Exchange to obtain a more stable PdI x Cl 6‑x 2‑ , thereby slowing down the PdCl6 2‑ The reduction rate of PdIr-KI was uniform. The PdIr-KI catalyst showed significantly enhanced catalytic activity for methanol oxidation. The addition of an appropriate amount of KI can adjust the structure and surface composition of the PdIr system catalyst, turning the originally inert Ir into a PdIr alloy catalytic system that can promote the methanol oxidation activity of Pd.

Description

Technical Field

[0001] The invention belongs to the technical field of fuel cells and relates to a preparation method of an anode catalyst material, and in particular to a synthesis method and application of a PdIr catalyst structure and surface composition for a fuel cell using KI. Background Art

[0002] Up to now, the precious metal Pt is still an irreplaceable catalyst for direct methanol fuel cells (DMFC), especially under low temperature conditions. How to reduce the amount of precious metal Pt while improving its electrocatalytic performance is one of the difficulties in DMFC research. At the same time, the activity of the catalyst is closely related to its structure and surface composition, so the regulation of the catalyst structure and surface composition is particularly important. Pd and Ir are also precious metals, but their prices are lower than Pt, especially Pd, which has good catalytic activity itself; although Ir itself has almost no catalytic activity for methanol oxidation, Ir can not only remain stable at high anode potentials, but more importantly, Ir is more likely to break the HO bond of H2O in the electrolyte to generate OH species intermediates with adsorption. However, Ir precursors usually need to be reduced and prepared using strong reducing agents or higher temperatures, and it is often difficult to control the morphology and composition of their alloy catalysts. Summary of the invention

[0003] In the present invention, a solvent thermal reduction method is adopted, P123 is used as a reducing agent and a protective agent, and ethanol is used as a solvent to prepare an alloy PdIr catalyst; potassium iodide (KI) is added to regulate the catalyst structure and surface composition to prepare a PdIr-KI catalyst.

[0004] The technical solution adopted by the present invention to achieve the above-mentioned purpose is as follows:

[0005] (1) Solution A: A certain amount of potassium chloropalladate (K2PdCl6) and iridium trichloride (IrCl3) are dissolved in a small amount of deionized water (H2O) and ultrasonicated until completely dissolved to obtain a reddish brown solution A. The mass concentration of potassium chloropalladate solution in solution A is 0.001-0.01 g / ml, and the mass concentration of iridium trichloride solution is 0.001-0.005 g / ml.

[0006] Solution B: A certain amount of triblock copolymer P123 was dissolved in ethanol, and the concentration of P123 was controlled at 0.1 mol·L -1 -1.0mol·L -1 The mixture was ultrasonically dissolved to obtain a colorless transparent solution B. The concentration of the ethanol solution of the triblock copolymer P123 in solution B was 0.1 mol·L -1 -1.0mol·L -1 .

[0007] Solution C: A certain amount of potassium iodide (KI) is dissolved in water and ultrasonicated until completely dissolved to obtain a colorless transparent solution C. The mass concentration of the potassium iodide solution in solution C is 0.01-0.1 g / mL.

[0008] (2) After mixing solutions A and B evenly, transfer them to a hydrothermal reactor and react them at 100-250°C for 4-24 hours. The obtained product is centrifuged and washed and recorded as PdIr. In the mixture of solutions A and B, the amount of P123 is controlled to be 2-10 times the total amount of the precursors Pd and Ir.

[0009] (3) After mixing solutions A, B and C evenly, transfer them to a hydrothermal reactor and react them at 100-250°C for 4-24 hours. The obtained product is centrifuged and washed and recorded as PdIr-KI. In the mixture of solutions A, B and C, the amount of P123 is controlled to be 2-10 times the total amount of precursors Pd and Ir; the amount of KI is controlled to be 0.1-0.8 times the total amount of Pd and Ir.

[0010] The technical solution of the present invention is to dissolve a certain proportion of potassium chloropalladate and iridium trichloride in water to obtain solution A, and dissolve a certain amount of P123 in ethanol to obtain solution B. A certain amount of KI is dissolved in water to obtain solution C. After mixing solutions A, B and C evenly, they are transferred to a hydrothermal reactor, reacted at a certain temperature, and centrifuged and washed to obtain a PdIr-KI catalyst. Under the same conditions, the catalyst obtained by mixing solutions A and B and reacting is recorded as PdIr. Test results show that without adding KI, due to Ir 3+ It is difficult to reduce and the reduction rate is slow. The PdIr obtained is a core-shell structure of PdIr@Ir with Ir-rich surface, rather than a uniform PdIr alloy structure. Since Ir is inert to methanol oxidation, the PdIr catalyst has almost no activity for methanol oxidation. After adding KI, I - Ion part and PdCl6 2- Cl - Exchange to obtain a more stable PdI x Cl 6-x 2- , thereby slowing down the PdCl6 2- The reduction rate of PdIr-KI is a uniform alloy structure. The PdIr-KI catalyst exhibits significantly enhanced catalytic activity for methanol oxidation. In the present invention, the addition of an appropriate amount of KI can adjust the structure and surface composition of the PdIr system catalyst, so that the originally inert Ir becomes a PdIr alloy catalyst system that can promote the methanol oxidation activity of Pd. Ir and Pd form an alloy to exert the catalytic effect of Ir in the alloy.

[0011] The PdIr-KI catalyst prepared by adding an appropriate amount of KI has excellent electrocatalytic methanol oxidation performance. This synthesis method has great application and development prospects in fuel cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 : (a) TEM and (bd) energy spectra of the fuel cell PdIr electrocatalyst prepared in Example 1.

[0013] Figure 2 : XRD patterns of the fuel cell PdIr, PdIr-KI-1 and PdIr-KI-2 electrocatalysts prepared in Examples 1 and 2

[0014] Figure 3 : CV curve of the PdIr electrocatalyst prepared in Example 1 in 1.0 M NaOH + 1.0 M CH3OH.

[0015] Figure 4 : (a) TEM and (bd) energy spectra of the fuel cell PdIr-KI electrocatalyst prepared in Example 2.

[0016] Figure 5 : CV curve of the PdIr-KI electrocatalyst prepared in Example 2 in 1.0 M NaOH + 1.0 M CH3OH.

[0017] Figure 6 : Comparison of methanol oxidation CV curves of the two electrocatalysts prepared in Examples 1 and 2.

[0018] Figure 7 : Comparison of methanol oxidation CV curves of the three electrocatalysts prepared in Examples 2 and 4. DETAILED DESCRIPTION

[0019] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation cases. It should be stated here that these implementation cases are only used to illustrate the present invention rather than to limit the scope of the present invention. After reading the present invention, modifications to various equivalent forms by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0020] Example 1

[0021] (1) 0.0135 g K2PdCl6 and 0.0091 g IrCl3 were dissolved in 5 mL H2O and stirred by ultrasonic to obtain solution A.

[0022] (2) Add 1.0043 g of P123 into 20 mL of CH3CH2OH and stir under ultrasonication to dissolve it completely to obtain solution B.

[0023] (3) 0.04 g KI was dissolved in 1 mL H2O and dissolved by ultrasonic stirring to obtain solution C.

[0024] (4) After mixing solutions A and B evenly, transfer them to a hydrothermal reactor and react at 180°C for 12 h. The obtained product is centrifuged and washed and recorded as PdIr.

[0025] Figure 1 TEM image of the fuel cell PdIr electrocatalyst prepared in Example 1. Figure 1 It can be seen from a that there are some small particles on the large agglomerates, and there is an obvious interface between the large and small particles, indicating that the obtained product is a mixture of Pd and Ir, rather than an alloy structure. Figure 1 It can be seen from the superimposed energy spectrum in d that the Ir element mainly exists on the surface.

[0026] Figure 2 The XRD results show that Pd and Ir form a face-centered cubic (fcc) structure alloy. Due to the rich Ir on the surface, the XRD diffraction angle shifts significantly to a lower angle compared to the standard PdIr alloy. This further confirms that the surface of the PdIr catalyst is rich in inert Ir elements.

[0027] Example 2

[0028] (1) 0.0135 g K2PdCl6 and 0.0091 g IrCl3 were dissolved in 5 mL H2O and stirred by ultrasonic to obtain solution A.

[0029] (2) Add 1.0043 g of P123 into 20 mL of CH3CH2OH and stir under ultrasonication to dissolve it completely to obtain solution B.

[0030] (3) 0.04 g KI was dissolved in 1 mL H2O and dissolved by ultrasonic stirring to obtain solution C.

[0031] (4) Solutions A, B, and C were mixed evenly and transferred to a hydrothermal reactor for reaction at 180°C for 12 h. The obtained product was centrifuged and washed and recorded as PdIr-KI.

[0032] Figure 4 TEM image of the PdIr-KI catalyst prepared in Example 2. Figure 4 It can be seen from a that the prepared PdIr-KI catalyst is a three-dimensional nanostructure formed by small particles of uniform size agglomerated together, with a uniform surface and no Figure 1 Small particles in the Figure 4From the superimposed energy spectrum in d, it can be seen that the distribution of Pd and Ir elements in the prepared catalyst is very uniform, indicating that a uniform PdIr alloy catalyst is prepared.

[0033] Figure 2 This is the XRD pattern of the PdIr-KI-1 catalyst prepared in Example 2. It can be seen from the figure that the XRD diffraction peak corresponding to the PdIr-KI-1 alloy catalyst is between the diffraction peaks of pure Pd and pure Ir, which means that the product is a PdIr alloy catalyst. The comparative XRD patterns of PdIr and PdIr-KI further demonstrate the different structures and surface compositions of the two.

[0034] Example 3

[0035] 0.034 mg of the PdIr obtained in Example 1 and the PdIr-KI catalyst obtained in Example 2 were taken and modified on the glassy carbon electrode respectively, and 10 μL of Nafion was added to fix the catalyst to prepare the working electrode, and its methanol oxidation performance was tested. Test conditions: the solution was a nitrogen-saturated 1.0 mol / L NaOH+1.0 mol / L CH3OH solution, and the scanning range was -0.8~0.4V ( vs. SCE) with a scan rate of 50 mV / s.

[0036] Figure 3 From the CV curve, it can be seen that the PdIr catalyst has almost no activity for methanol oxidation due to the inert Ir element covering its surface, and the maximum current density in the forward scan is only 23.4 mA mg Pd -1 .

[0037] Figure 5 The CV curve shows that the PdIr-KI alloy catalyst exhibits very good electrocatalytic activity for methanol oxidation due to the bifunctional mechanism between Pd and Ir, the electronic effect and the co-catalytic function of Ir. The peak current density corresponding to the forward scan is 974.4 mA mg Pd -1 , which is about 41.6 times that of PdIr catalyst.

[0038] from Figure 6 The CV comparison diagram fully demonstrates that the addition of KI can regulate the structure and surface composition of the PdIr catalyst, thereby improving its catalytic activity for methanol oxidation.

[0039] Example 4

[0040] The method and steps are the same as in Example 2, except that the mass of KI added is changed to 0.02 g to obtain the product PdIr-KI-2;

[0041] The method and steps are the same as in Example 2, except that the mass of KI added is changed to 0.06 g to obtain the product PdIr-KI-3;

[0042] The method and steps are the same as those in Example 2, except that the added mass of K2PdCl6 is 0.0135 g and the added mass of IrCl3 is 0.0273 g IrCl3, to obtain the product PdIr-KI-4;

[0043] The method and steps are the same as those in Example 2, except that the added mass of K2PdCl6 is 0.0405 g and the added mass of IrCl3 is 0.0091 g IrCl3, to obtain the product PdIr-KI-5;

[0044] The methanol oxidation performance of the PdIr-KI, PdIr-KI-2 and PdIr-KI-3 prepared above was tested by the method of Example 3. The results are as follows: Figure 7 The maximum oxidation current of PdIr-KI-2 and PdIr-KI-3 in the MOR forward scan was 434.0 mA mg Pd -1 , 690.6mA mg Pd -1 The above results show that too little or too much KI will lead to reduced catalyst activity. When a small amount of KI is added, due to the small amount, the structure of the obtained catalyst (PdIr-KI-2) is in the transition stage from the core-shell structure of Pd and Ir mixture to the PdIr alloy. The inert Ir element on the catalyst surface gradually decreases, exposing a small amount of PdIr alloy surface, making the PdIr-KI-2 catalyst show a certain methanol oxidation catalytic activity (434.0mAmg Pd -1 When KI is moderate, the uniform PdIr alloy catalyst exhibits the highest catalytic activity (974.4 mA mg Pd -1 When the amount of KI added is too much (PdIr-KI-3), the catalyst will be over-agglomerated, and iodides of PdI2 and IrI3 may appear, which will lead to a decrease in the active sites on the catalyst surface and a decrease in the catalytic oxidation performance of methanol.

[0045] While keeping the optimal KI dosage consistent (0.004 g), the PdIr-KI (PdIr = 1:1), PdIr-KI-4 (PdIr = 1:3) and PdIr-KI-5 (PdIr = 3:1) catalysts were obtained by changing the ratio of Pd to Ir. When Pd:Ir = 1:1, the bifunctional mechanism between Pd and Ir is more in-depth, and the amount of OH adsorbed by Ir also matches the same amount of Pd, showing the highest electrocatalytic oxidation activity (974.4 mA mg Pd -1 Due to the inertness of Ir, the highest MOR oxidation current density of PdIr-KI-4 catalyst decreased to 355.6 mA mg with the increase of Ir content. Pd -1 When the Pd content increases to 3 times that of Ir, the highest MOR oxidation current density of the PdIr-KI-5 catalyst is 670.5 mA mg Pd -1 This is mainly due to the weakening of the promoting effect of Ir on the bifunctional mechanism of Pd.

Claims

1. A method for preparing a PdIr alloy electrocatalyst for a fuel cell, characterized in that: The steps include: (1) 0.0135 g K2PdCl6 and 0.0091 g IrCl3 were dissolved in 5 mL H2O and dissolved by ultrasonic stirring to obtain solution A; (2) 1.0043 g P123 was added to 20 mL CH3CH2OH and stirred ultrasonically to completely dissolve it to obtain solution B; (3) 0.04 g KI was dissolved in 1 mL H2O and dissolved by ultrasonic stirring to obtain solution C; (4) Solutions A, B, and C were mixed evenly and transferred to a hydrothermal reactor for reaction at 180 °C for 12 h. The obtained product was centrifuged and washed and recorded as PdIr-KI.

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