Iridium-loaded molybdenum carbide nanoflower spheres, their preparation and application in the hydrogen oxidation reaction

Abstract

The present invention discloses an iridium-loaded molybdenum carbide nanoflower sphere and its preparation and application in the hydrogen oxidation reaction, relating to the field of electrocatalytic technology. Compared with the prior art, the present invention provides an iridium-loaded molybdenum carbide with a specific nanoflower sphere structure and its preparation method. Its controllable nanospherical morphology gives it a relatively broad application prospect, showing high catalytic activity, stability and conductivity in the hydrogen oxidation reaction, especially suitable for the hydrogen oxidation reaction in alkaline media, and can provide practical guidance for the development of efficient molybdenum-based electrocatalytic catalysts.

Description

Technical Field:

[0001] The present invention relates to the field of electrocatalytic technology, and specifically relates to an iridium-loaded molybdenum carbide nanoflower sphere, its preparation and application in the hydrogen oxidation reaction. Background Art:

[0002] As a green and efficient secondary energy source, hydrogen energy has the characteristics of rich reserves, diverse sources, low-carbon environmental protection, etc., and is the most promising sustainable energy source in the 21st century. With the intensification of energy shortage and environmental pollution, developing clean and sustainable energy paths is of great significance. Proton Exchange Membrane Fuel Cell (PEMFC), as a hydrogen energy efficient utilization technology, has the advantages of rapid startup, low operating temperature, high energy density, high energy conversion efficiency, wide application, etc. However, due to the need for a high loading amount of Pt or Pt-based alloys to drive the slow cathode oxygen reduction reaction (ORR), the cost competitiveness of PEMFCS is low.

[0003] Alkaline anion exchange membrane fuel cells (AEMFCs) have a battery structure similar to that of PEMFCs. However, compared with PEMFCs, AEMFCs have more obvious advantages. Nevertheless, the activity of the anodic hydrogen oxidation reaction (HOR) in AEMFCs in alkaline media is still limited by the slow reaction kinetics, and its performance is far inferior to the current most advanced PGM-based materials. To accelerate the reaction kinetics and reduce the reaction energy consumption, platinum group noble metal catalysts such as Ir, Ru, Pt, and Pd still have good catalytic performance at present.

[0004] It is worth noting that a large number of PGM-free electrocatalysts, such as transition metal carbides and their heterostructures, all show high HER (hydrogen evolution reaction) activity during the catalytic reaction process, and also have good performance in HOR activity. Transition metal carbides (TMCs) are intermetallic compounds composed of carbon atoms. The interaction between TMCs and surface metal substances is very strong, so they are good carriers for synthesizing catalysts. The role of the carrier may have a significant impact on the catalytic properties, similar to the ligand molecules in homogeneous catalysts. Therefore, designing nanostructured transition metal carbides with customized morphologies has been proven to be an effective strategy to solve these problems.

[0005] Patent CN114713253A discloses a preparation method of a molybdenum carbide catalyst for the water gas shift reaction, but it requires the induction of precious metal rhodium. Patent CN109999840A discloses a preparation method of a molybdenum carbide catalyst for the selective oxidation desulfurization of hydrogen sulfide. First, molybdenum carbide (Mo 2 C) is prepared by a primary heat treatment, and then Mo 2C is mixed with graphitic carbon nitride and then subjected to secondary heat treatment to obtain a catalyst of MoC supported on nitrogen-doped carbon. Patent CN101656314A discloses the application of molybdenum carbide as an anode catalyst for microbial fuel cells. The present invention aims to provide a molybdenum carbide with a special structure and use it in the electrocatalytic reaction of alkaline HOR to exhibit good catalytic performance. Summary of the Invention:

[0006] The technical problem to be solved by the present invention is to provide an iridium-supported molybdenum carbide nanosphere and its preparation and application in the hydrogen oxidation reaction. The molybdenum carbide nanosphere shows relatively excellent catalytic activity, stability, and conductivity.

[0007] The technical problem to be solved by the present invention is achieved by adopting the following technical solutions:

[0008] One of the purposes of the present invention is to provide a preparation method of an iridium-supported molybdenum carbide nanosphere, including the following steps:

[0009] (1) Dissolve molybdate in a solvent, add ammonia water to adjust the pH value, then add hydrochloric acid dopamine, stir and react, centrifuge, separate, wash, and dry to obtain a precursor.

[0010] (2) Perform Joule heat shock on the precursor prepared above in an inert gas atmosphere to obtain a molybdenum carbide nanosphere.

[0011] (3) Use an iridium source to load metallic iridium on the molybdenum carbide nanosphere prepared above and calcine it in an argon-hydrogen atmosphere to obtain an iridium-supported molybdenum carbide nanosphere.

[0012] Another purpose of the present invention is to provide an iridium-supported molybdenum carbide nanosphere prepared according to the foregoing preparation method.

[0013] Another purpose of the present invention is to provide the application of the foregoing iridium-supported molybdenum carbide nanosphere in the electrocatalytic hydrogen oxidation reaction.

[0014] The beneficial effects of the present invention are as follows: Compared with the prior art, the present invention provides an iridium-supported molybdenum carbide with a specific nanosphere structure and its preparation method. Its controllable nanosphere morphology makes it have a relatively broad application prospect, and it shows high catalytic activity, stability, and conductivity in the hydrogen oxidation reaction, especially suitable for the hydrogen oxidation reaction in alkaline media, and can provide practical guidance for the development of efficient molybdenum-based electrochemical catalysts. Description of the Drawings:

[0015] Figure 1 The structural characterization results of the Ir / MoC sample prepared in Example 1 of the present invention: (a) X-ray diffraction pattern; (b) Scanning electron microscope image; (c) Elemental analysis diagram;

[0016] Figure 2 Performance test results of the Ir / MoC sample prepared in Example 1 of the present invention and commercial Pt / C in the electrocatalytic hydrogen oxidation reaction: (a) HOR polarization curves at different rotation speeds in a H 2 saturated 0.1 M KOH electrolyte; (b) Koutecky-Levich plot obtained at a 50 mV overpotential; (c) HOR Tafel plot; (d) H 2 OR polarization curve at a rotation speed of 1600 rpm in a saturated 0.1 M KOH electrolyte; (e) Comparison diagram of HOR catalytic activity before and after 2000 cycles of CV at a 50 mV overpotential and a rotation speed of 1600 rpm; (f) Current-time plot at a 50 mV overpotential. Detailed implementation manners:

[0017] In order to make the technical means, creative features, achieved purposes and effects of the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments and illustrations.

[0018] The present invention provides a method for preparing iridium-loaded molybdenum carbide nanoflower spheres, including the following steps:

[0019] (1) Dissolve molybdate in a solvent, add ammonia water to adjust the pH value, then add hydrochloric acid dopamine, stir and react, centrifuge, separate, wash, and dry to obtain a precursor;

[0020] (4) Perform Joule heat shock on the above-prepared precursor in an inert gas atmosphere to obtain molybdenum carbide nanoflower spheres;

[0021] (5) Use an iridium source to load metallic iridium on the above-prepared molybdenum carbide nanoflower spheres and calcine in an argon-hydrogen atmosphere to obtain iridium-loaded molybdenum carbide nanoflower spheres.

[0022] Preferably, the molybdate is ammonium molybdate or its hydrate.

[0023] Preferably, the solvent is deionized water and ethanol with a volume ratio of (3-4):1.

[0024] Preferably, the pH value is 8.5-9.0.

[0025] Preferably, the mass ratio of the molybdate to the hydrochloric acid dopamine is (1-3):1.

[0026] Preferably, the voltage of the Joule heat shock is 28-30 V, the shock time is 5-6 s, and the second shock is performed after an interval of 4-5 s.

[0027] Preferably, the iridium source is iridium trichloride. Other iridium sources can also be used as the precursor of metallic iridium.

[0028] Preferably, the iridium metal is loaded by an impregnation method.

[0029] Preferably, the loading amount of iridium is 2-3%.

[0030] Preferably, the hydrogen content in the argon-hydrogen atmosphere is 5%.

[0031] Preferably, the calcination temperature is 300 °C and the calcination time is 2-2.5 h.

[0032] In step (1), molybdate anions (MoO 4 2- ) rapidly chelate with dopamine to form a Mo-polydopamine (Mo-PDA) precursor; in step (2), a joule thermal shock is performed in a nitrogen atmosphere based on the precursor morphology to obtain molybdenum carbide with a nano-flower ball structure; in step (3), a metal iridium-loaded molybdenum carbide nano-flower ball is synthesized.

[0033] The present invention also provides an iridium-loaded molybdenum carbide nano-flower ball prepared by the foregoing preparation method.

[0034] The present invention further provides an application of the foregoing iridium-loaded molybdenum carbide nano-flower ball in an electrocatalytic hydrogen oxidation reaction.

[0035] Preferably, the electrocatalytic hydrogen oxidation reaction is a hydrogen oxidation reaction in an alkaline medium with 0.1 M KOH as the electrolyte.

[0036] Example 1

[0037] Preparation of iridium-loaded molybdenum carbide nano-flower ball:

[0038] (1) Dissolve 650 mg of ammonium molybdate tetrahydrate in 40 mL of a mixed solvent (30 mL of deionized water + 10 mL of ethanol), slowly add 0.4 mL of ammonia water, adjust the pH value to 8.5-9 and continuously stir for 1 h, then add 300 mg of hydrochloric acid dopamine, stir and react for 12 h, centrifuge with water and ethanol, separate, wash, and freeze-dry to obtain the precursor Mo-PDA.

[0039] (2) Place 50 mg of the Mo-PDA prepared above in carbon cloth and under a nitrogen atmosphere, impact at 29 V for 5 s, and perform a second impact after an interval of 4 s to obtain a molybdenum carbide nano-flower ball, denoted as MoC.

[0040] (3) Take MoC, add water and ultrasonically homogenize it, then add iridium trichloride, heat and evaporate it on a heating plate, and then calcine it at 300 °C for 2 h in an argon-hydrogen atmosphere (hydrogen content is 5%) to obtain an iridium-loaded molybdenum carbide nano-flower ball, denoted as Ir / MoC. Among them, the loading amount of iridium is 3%.

[0041] The structural characterization of the Ir / MoC sample prepared in Example 1 was carried out, and the results are shown in Figure 1 .

[0042] Figure 1 All the diffraction peaks appearing in (a) correspond one by one to the diffraction peaks of pure MoC. After loading Ir, the diffraction peaks of MoC do not shift compared with the pure phase, and no peaks related to Ir clusters appear. It can be seen that the loading amount of Ir is low; Figure 1 (b) shows that the Ir / MoC sample has a nano-flower ball structure morphology; Figure 1 (c) indicates that Mo element, Ir element and C element are uniformly distributed in the Ir / MoC sample.

[0043] Example 2

[0044] Application research of the Ir / MoC sample prepared in Example 1 as a catalyst in electrocatalytic methanol conversion:

[0045] Using a standard three-electrode system, the HOR electrocatalytic test was carried out on an electrochemical workstation. A 1M KOH solution filled with hydrogen was used as the electrolyte, and a rotating disk electrode (RDE) modified with Ir / MoC was used as the working electrode (4 mg of the Ir / MoC sample prepared in Example 1 was dispersed in 1000 μL of ethanol containing 40 μL of 5 wt% Nafion and sonicated for 1 h to prepare the ink; then 7.5 μL of the ink was dropped onto the polished rotating disk electrode to obtain the working electrode), a platinum wire was used as the counter electrode, and a Hg / HgO electrode was used as the reference electrode.

[0046] At the same time, a control example was set in which commercial Pt / C was used instead of Ir / MoC as the catalyst to prepare the working electrode. The Pt content in Pt / C was 20%, and the other conditions were the same as above.

[0047] As Figure 2 (b) shows, there is a linear relationship between the kinetic current density j of the RDE and ω 1 / 2 at a 50 mV overpotential, and the fitted straight line is represented by the Koutecky-Levich equation, with a slope of 4.51 cm 2 ·mA -1 ·s -1 / 2 , close to the theoretical value (4.87 cm 2 ·mA -1 ·s -1 / 2 ) for the two-electron HOR.

[0048] From Figure 2 (c) and Figure 2 (d), it can be seen that the HOR catalytic activity of Ir / MoC in alkaline medium is significantly better than that of Pt / C.

[0049] From Figure 2(e) It can be seen that Ir / MoC has extremely high stability in alkaline media.

[0050] From Figure 2 (f) It can be seen that the HOR catalytic activity of Ir / MoC in alkaline media can remain stable within 24 h.

[0051] In summary, the Ir / MoC prepared by the present invention has better HOR catalytic activity than commercial Pt / C catalysts and good stability in alkaline media.

[0052] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and what is described in the above embodiments and the specification is only to illustrate the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. Application of iridium-loaded molybdenum carbide nanoflower spheres in electrocatalytic hydrogen oxidation reaction, and preparation method of the iridium-loaded molybdenum carbide nanoflower spheres The method comprises the following steps: (1) Dissolve molybdate in a solvent, add ammonia water dropwise to adjust the pH value, then add hydrochloric acid dopamine, stir and react, centrifuge, separate, wash, and dry to obtain a precursor; Perform Joule heat shock on the precursor prepared above in an inert gas atmosphere to obtain molybdenum carbide nanoflower spheres; Use an iridium source to load metallic iridium on the molybdenum carbide nanoflower spheres prepared above, and calcine in an argon-hydrogen atmosphere to obtain iridium-loaded molybdenum carbide nanoflower spheres.

2. The application according to claim 1, wherein: The molybdate is ammonium molybdate or its hydrate.

3. The application according to claim 1, wherein: The solvent is deionized water and ethanol with a volume ratio of (3 - 4) :

1.

4. The application according to claim 1, wherein: The pH value is 8.5 - 9.

0.

5. The application according to claim 1, wherein: The mass ratio of the molybdate to hydrochloric acid dopamine is (1 - 3) :

1.

6. The application according to claim 1, wherein: The voltage of the Joule heat shock is 28 - 30V, the shock time is 5 - 6s, and the second shock is carried out after an interval of 4 - 5s.

7. The application according to claim 1, wherein: The iridium source is iridium trichloride.

8. The application according to claim 1, wherein: The metallic iridium loading adopts the impregnation method.

9. The application according to claim 1, wherein: The loading amount of iridium is 2 - 3%.

10. The application according to claim 1, wherein: The content of hydrogen in the argon-hydrogen atmosphere is 5%.

11. The application according to claim 1, wherein: The calcination temperature is 300°C, and the calcination time is 2 - 2.5h.

12. The application according to claim 1, wherein: The electrocatalytic hydrogen oxidation reaction is a hydrogen oxidation reaction in an alkaline medium with 0.1M KOH as the electrolyte.

13. Iridium-loaded molybdenum carbide nanoflower spheres prepared by the preparation method of the iridium-loaded molybdenum carbide nanoflower spheres in the application according to any one of claims 1 - 12.

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