P-CoNiMoO-coated Co2P-Ni2P core-shell structure catalyst as well as preparation method and application thereof

Abstract

The invention discloses a catalyst with a P-CoNiMoO-coated Co2P-Ni2P core-shell structure as well as a preparation method and application of the catalyst. The preparation method of the catalyst comprises the following steps: step 1, treating a nickel substrate to remove an oxide layer and oil stains on the surface; 2, synthesizing a cobalt-nickel molybdate precursor on the nickel substrate through a hydrothermal reaction; and step 3, carrying out phosphating treatment on the precursor in an argon / hydrogen mixed atmosphere, so as to obtain the P-CoNiMoO-coated Co2P-Ni2P core-shell structure catalyst. The preparation method is simple, required raw materials are low in price and easy to obtain, and the preparation method is suitable for large-scale production. The prepared catalyst grows on a nickel substrate in a rodlike structure array, the electrocatalytic performance of the catalyst is remarkably improved through the synergistic effect of different components of a core shell, and the catalyst shows excellent activity and high stability in the hydrogen evolution reaction of electrolyzed water.

Description

Technical Field

[0001] The present invention belongs to the field of electrocatalysts, and specifically relates to a P-CoNiMoO@Co 2 P-Ni 2 P core-shell structure catalyst and its preparation method and application. Background Art

[0002] Electrocatalytic water splitting technology is an important way to obtain clean hydrogen energy. However, the performance of existing electrocatalysts in the hydrogen evolution reaction (HER) still has limitations, mainly including high overpotential, low current density and insufficient stability. Therefore, the development of efficient, low-cost and stable HER electrocatalytic materials is of great significance to improve the efficiency of electrolytic water splitting. Although precious metal electrocatalysts (such as Pt) exhibit excellent electrocatalytic activity, their high cost limits their large-scale application. Therefore, non-precious metal catalysts based on transition metals have become a research hotspot. However, the existing non-precious metal catalysts still need to be further optimized in HER performance, which is a challenge facing current technology. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a P-CoNiMoO@Co 2 P-Ni 2 The P core-shell structure catalyst and its preparation method and application are aimed at solving the problems of high cost, low activity and poor stability in electrocatalytic water decomposition.

[0004] To achieve the above object, the present invention provides a P-CoNiMoO@Co 2 P-Ni 2 The preparation method of the P core-shell structure catalyst comprises the following steps: Step 1: Nickel substrate treatment: remove surface oxide layer and oil stains; Step 2, preparation of cobalt nickel molybdate precursor: dissolving ammonium molybdate and cobalt salt in distilled water, stirring to form a clear solution; transferring the solution to a hydrothermal reactor, and performing a hydrothermal reaction with the treated nickel substrate to generate a cobalt nickel molybdate precursor. After the hydrothermal reaction is completed, the nickel substrate is removed, rinsed and dried; Step 3: Phosphating treatment: The precursor obtained in step 2 is treated with red phosphorus in an argon / hydrogen mixed atmosphere to form P-CoNiMoO@Co 2 P-Ni 2 P core-shell structure catalyst.

[0005] Furthermore, the nickel substrate treatment method in step 1 adopts ultrasonic treatment with dilute hydrochloric acid, ethanol and distilled water.

[0006] Furthermore, the cobalt salt is one or more of cobalt nitrate, cobalt sulfate or cobalt chloride.

[0007] Furthermore, the nickel substrate in step 2 also provides a nickel source required for the hydrothermal reaction.

[0008] Furthermore, the concentration of the cobalt salt in step 2 is 0.01-0.2 mol·L -1 , the molar ratio of cobalt and molybdenum is 1:0.5~3.

[0009] Furthermore, in step 2, the temperature of the hydrothermal treatment is 100-160°C, and the time is 4-14 h.

[0010] Furthermore, the phosphating temperature of step 3 is 400-600 °C, the calcination time is 2-6 h, and the heating rate is 2-10 °C min -1 The volume ratio of hydrogen in the argon / hydrogen mixed atmosphere is 2%~20%.

[0011] Furthermore, in step 3, the ratio of the area of ​​the nickel substrate to the amount of red phosphorus is: 1 cm 2 : 0.05~1g.

[0012] On the other hand, the present invention also provides a P-CoNiMoO@Co prepared by the above method. 2 P-Ni 2 P core-shell catalyst. The catalyst is a rod-shaped structure array grown on the surface of a nickel substrate. The shell is a cobalt phosphide-nickel phosphide heterostructure, and the core is phosphorus-doped cobalt nickel molybdate. The different components of the core and shell work synergistically to significantly improve its catalytic performance.

[0013] In another aspect, the present invention provides P-CoNiMoO@Co 2 P-Ni 2 Application of P core-shell structure catalysts in hydrogen evolution reaction by water electrolysis.

[0014] The beneficial effects of the present invention are as follows: (1) Structural advantages: P-CoNiMoO@Co 2 P-Ni 2 The P core-shell structure catalyst significantly improves the activity of the electrocatalytic hydrogen evolution reaction through the synergistic effect of the inner core and the outer shell. The rod-shaped array structure increases the specific surface area and exposes more active sites.

[0015] (2) Improved electrocatalytic performance: The catalyst exhibits low hydrogen evolution overpotential and excellent electrochemical stability; (3) Simple preparation: The hydrothermal method is combined with phosphating treatment. The process is simple and controllable, suitable for large-scale production.

[0016] (4) Low cost: The raw materials are easily available and inexpensive. Compared with precious metal catalysts, it has a significant cost advantage and is suitable for industrial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 This is a scanning electron microscope image of the cobalt nickel molybdate precursor prepared in Example 1 of the present invention; Figure 2 P-CoNiMoO@Co prepared in Example 1 of the present invention 2 P-Ni 2 SEM images of P; Figure 3 P-CoNiMoO@Co prepared in Example 1 of the present invention 2 P-Ni 2 Transmission electron microscopy image of P; Figure 4 P-CoNiMoO@Co prepared in Example 1 of the present invention 2 P-Ni 2 High-resolution transmission electron microscopy image of P; Figure 5 P-CoNiMoO@Co prepared in Example 1 of the present invention 2 P-Ni 2 X-ray powder diffraction pattern of P; Figure 6 P-CoNiMoO@Co prepared in Example 1 of the present invention 2 P-Ni 2 HER performance diagram of P; Figure 7 P-CoNiMoO@a-CoNiP prepared in Comparative Examples 1 and 2 of the present invention x and a group of physical characterization images of P-CoNiMoO; Figure 8 P-CoNiMoO@Co prepared in Example 1 of the present invention 2 P-Ni 2 HER stability test diagram of P; DETAILED DESCRIPTION

[0019] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0020] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0021] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0022] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to the skilled artisan. The present invention description and examples are exemplary only.

[0023] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0024] Example 1 Step 1: Nickel substrate treatment: A 2 cm × 5 cm nickel substrate was immersed in 3M hydrochloric acid, distilled water, and anhydrous ethanol for ultrasonic treatment, each for 5 minutes. After being rinsed with distilled water several times, it was placed in a vacuum drying oven and dried at 60°C for 12 hours for later use.

[0025] Step 2: Preparation of cobalt nickel molybdate precursor: 0.8 mmol ammonium molybdate (NH 4 ) 6 Mo 7 O 24 ·4H 2 O) and 3.2 mmol cobalt nitrate (Co(NO 3 ) 2 6H2 O) was dissolved in 80 mL of distilled water, where the concentration of cobalt salt was 0.04 mol·L -1 , the molar ratio of cobalt to molybdenum is 1:1.75. After stirring for 30 minutes to obtain a clear solution, transfer it to a 100 mL hydrothermal kettle. Add the nickel substrate treated in step 1 to the hydrothermal kettle, set it to 150 ° C for 5 hours, cool it to room temperature, take out the nickel substrate, rinse it with distilled water and anhydrous ethanol several times, and put it in a 60 ° C oven to dry for 12 hours to obtain a cobalt nickel molybdate precursor.

[0026] Step 3: Phosphation of cobalt nickel molybdate precursor: The cobalt nickel molybdate precursor obtained in step 2 was placed in a tube furnace together with 1.0 g of red phosphorus and heated to 500 °C at a heating rate of 5 °C min -1 , and in an argon / hydrogen mixed atmosphere (H 2 The volume fraction of 10% was kept warm for 2 hours, and after cooling to room temperature, the sample was taken out, washed with distilled water and ethanol, and dried to obtain P-CoNiMoO@Co 2 P-Ni 2 P core-shell structure catalyst.

[0027] Example 2 Step 1: Nickel substrate treatment: A 2 cm × 5 cm nickel substrate was immersed in 3M hydrochloric acid, distilled water, and anhydrous ethanol for ultrasonic treatment, each for 5 minutes. After being rinsed with distilled water several times, it was placed in a vacuum drying oven and dried at 60°C for 12 hours for later use.

[0028] Step 2: Preparation of cobalt nickel molybdate precursor: 0.6 mmol ammonium molybdate (NH 4 ) 6 Mo 7 O 24 ·4H 2 O) and 2.4 mmol cobalt nitrate (Co(NO 3 ) 2 6H 2 O) was dissolved in 80 mL of distilled water, where the concentration of cobalt salt was 0.03 mol·L -1 , the molar ratio of cobalt to molybdenum is 1:1.75. After stirring for 30 minutes to obtain a clear solution, it was transferred to a 100 mL hydrothermal kettle. The nickel substrate treated in step 1 was added to the hydrothermal kettle and set to 150 °C for hydrothermal treatment for 5 hours. After cooling to room temperature, the nickel substrate was taken out, rinsed with distilled water and anhydrous ethanol several times, and placed in an oven at 60 °C for 12 hours to obtain a cobalt nickel molybdate precursor.

[0029] Step 3: Phosphation of cobalt nickel molybdate precursor: The cobalt nickel molybdate precursor obtained in step 2 was placed in a tube furnace together with 0.5 g red phosphorus and heated to 600 °C at a heating rate of 2 °C min -1 , and in an argon / hydrogen mixed atmosphere (H 2 After cooling to room temperature, the sample was taken out, washed with distilled water and ethanol, and dried to obtain P-CoNiMoO@Co 2 P-Ni 2 P core-shell structure catalyst.

[0030] Example 3 Step 1: Nickel substrate treatment: A 2 cm × 5 cm nickel substrate was immersed in 3M hydrochloric acid, distilled water, and anhydrous ethanol for ultrasonic treatment, each for 5 minutes. After being rinsed with distilled water several times, it was placed in a vacuum drying oven and dried at 60°C for 12 hours for later use.

[0031] Step 2: Preparation of cobalt nickel molybdate precursor: 0.8 mmol ammonium molybdate (NH 4 ) 6 Mo 7 O 24 ·4H 2 O) and 2.4 mmol cobalt nitrate (Co(NO 3 ) 2 6H 2 O) was dissolved in 80 mL of distilled water, where the concentration of cobalt salt was 0.03 mol·L -1 , the molar ratio of cobalt to molybdenum is 1:2.33. After stirring for 30 minutes to obtain a clear solution, transfer it to a 100 mL hydrothermal kettle. Add the nickel substrate treated in step 1 to the hydrothermal kettle and set the hydrothermal treatment at 120 °C for 10 hours. After cooling to room temperature, take out the nickel substrate, rinse it with distilled water and anhydrous ethanol several times, and put it in an oven at 60 °C to dry for 12 hours to obtain a cobalt nickel molybdate precursor.

[0032] Step 3: Phosphation of cobalt nickel molybdate precursor: The cobalt nickel molybdate precursor obtained in step 2 was placed in a tube furnace together with 1.0 g of red phosphorus and heated to 500 °C at a heating rate of 2 °C min -1 , and in an argon / hydrogen mixed atmosphere (H 2 After cooling to room temperature, the sample was taken out, washed with distilled water and ethanol, and dried to obtain P-CoNiMoO@Co 2 P-Ni 2 P core-shell structure catalyst.

[0033] Physical characterization: P-CoNiMoO@Co obtained in Example 1 2 P-Ni 2 The P core-shell structure catalyst and precursor were physically characterized, and the results are as follows: SEM image of cobalt nickel molybdate precursor ( Figure 1 ) shows that the precursor is a smooth rod-like structure array with a diameter of several microns. 2 P-Ni 2 SEM images of P Figure 2 ) shows that the rod-like structure after phosphating treatment maintains the original array, but the surface becomes rough, forming stacked flakes and obvious cracks, which is conducive to the penetration of electrolyte and the rapid release of bubbles. Transmission electron microscopy image ( Figure 3 ) further confirmed the core-shell structure, in which the outer shell is translucent and the inner core is dark, indicating the successful synthesis of the core-shell structure. High-resolution transmission electron microscopy image ( Figure 4 ) show that the lattice spacing of the outer shell is 0.287 nm and 0.202 nm, corresponding to Co 2 The (110) crystal plane of P and Ni 2 The (201) crystal plane of P proves that the outer shell is Co 2 P-Ni 2 P heterostructure. X-ray diffraction pattern shows ( Figure 5 ), the main components include Co 2 P (PDF# 54-0413), Ni 2 P (PDF# 03-0953), CoMoO 4 (PDF#21-0868) and NiMoO 4 (PDF#45-0142), indicating that the core of the catalyst is phosphorus-doped cobalt nickel molybdate (P-CoNiMoO), and the shell is a cobalt phosphide-nickel phosphide heterojunction (Co 2 P-Ni 2 P).

[0034] Application of water electrolysis hydrogen evolution reaction: P-CoNiMoO@Co obtained in Example 1 2 P-Ni 2 P was tested for activity and stability. (1) Activity: A standard three-electrode system was used to test P-CoNiMoO@Co in 1 M KOH solution. 2 P-Ni 2The polarization curves obtained by linear sweep voltammetry (LSV) (Figure 6) show that the catalyst can drive 10 mA·cm in the hydrogen evolution reaction with only 24 mV and 114 mV overpotential. - ² and 100 mA·cm - ² Current density. (2) Stability: at -100mA·cm - At a current density of 2, the catalyst can continue to operate stably for 100 h without obvious activity decay ( Figure 7 ).

[0035] Comparative Example 1 The difference from Example 1 is that in step 3, 1 g of sodium hypophosphite is used as the phosphorus source instead of red phosphorus, and argon atmosphere is used instead of argon / hydrogen mixed atmosphere.

[0036] Physical characterization results: The physical characterization of the obtained catalyst is as follows Figure 8 (ac) Shown: X-ray powder diffraction spectrum ( Figure 8 a) Displays that there is no Co 2 P and Ni 2 P phase; SEM image ( Figure 8 b) shows the existence of flocculent nanosheet structures on the surface; TEM analysis ( Figure 8 c) shows that there is an amorphous layer several nanometers thick on the outer surface and 0.33 nm lattice fringes in the inner region, corresponding to CoMoO 4 and NiMoO 4 Therefore, we obtained a phosphorus-doped cobalt nickel molybdate coated with an amorphous cobalt nickel phosphide thin layer, named P-CoNiMoO@a-CoNiP x .

[0037] P-CoNiMoO@a-CoNiP x The electrochemical activity test of the catalyst showed that in the hydrogen evolution reaction, to obtain 10 mA cm - ² and 100 mA·cm - ², the overpotentials required are 41mV and 155mV respectively ( Figure 6 ), which is less active than P-CoNiMoO@Co in Example 1 2 P-Ni 2 P catalyst (24 mV vs. 114 mV).

[0038] Comparative Example 2 The difference from Example 1 is that in step 3, 1 g of sodium hypophosphite is used as the phosphorus source instead of red phosphorus, the argon atmosphere is replaced by an argon / hydrogen mixed atmosphere, and the insulation temperature is 350°C.

[0039] Physical characterization results: The physical characterization of the obtained catalyst is as follows Figure 8 (df) shown; X-ray powder diffraction spectrum ( Figure 8 d) Confirmed the retention of the cobalt nickel molybdate phase and no formation of Co 2 P and Ni 2 P phase; SEM image ( Figure 8 e) shows a smooth rod surface, indicating minimal phosphorus attack. TEM analysis ( Figure 8 f) shows that the rod-like structure is well preserved, with no obvious contrast between the translucent and dark areas. Under this condition, we obtained phosphorus-doped cobalt nickel molybdate, named P-CoNiMoO.

[0040] The electrochemical activity test of P-CoNiMoO catalyst showed that at a current density of 10 mA·cm - ² and 100mA·cm - ², the overpotentials required for the hydrogen evolution reaction are 84 mV and 223 mV respectively ( Figure 6 ), which has lower activity than the P-CoNiMoO@Co prepared in Example 1 2 P-Ni 2 P catalyst (24 mV vs. 114 mV).

[0041] Compared with the catalysts in Comparative 1 and Comparative 2, P-CoNiMoO@Co 2 P-Ni 2 The core-shell structure of P significantly improves the electrocatalytic activity and stability of the catalyst. Specifically, the core-shell structure not only provides more active sites, but also enhances the electron and proton transport capacity of the catalyst. The synergistic effect of the core-shell significantly improves the catalytic activity of the hydrogen evolution reaction. This shows that the core-shell structure has significant advantages in optimizing catalyst performance, making P-CoNiMoO@Co 2 P-Ni 2 P becomes an excellent HER electrocatalyst.

[0042] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a P-CoNiMoO@Co2P-Ni2P core-shell structure catalyst, characterized in that: The following steps are involved: Step 1: Nickel substrate treatment: remove surface oxide layer and oil stains; Step 2, preparation of cobalt nickel molybdate precursor: dissolving ammonium molybdate and cobalt salt in distilled water and stirring to form a clear solution; The solution and the nickel substrate treated in step 1 are subjected to a hydrothermal reaction, during which the nickel substrate also provides a nickel source, to finally obtain a cobalt nickel molybdate precursor, and then the nickel substrate is rinsed and dried; Step 3, phosphating treatment: Under an argon / hydrogen mixed atmosphere, the cobalt nickel molybdate precursor obtained in step 2 is phosphated with red phosphorus to obtain a P-CoNiMoO@Co2P-Ni2P core-shell structure catalyst.

2. The preparation method according to claim 1, characterized in that: The concentration of cobalt salt in step 2 is 0.01~0.2 mol·L -1 , the molar ratio of cobalt and molybdenum is 1:0.5~3.

3. The preparation method according to claim 1, characterized in that: The temperature of the hydrothermal reaction in step 2 is 100-160° C. and the time is 4-14 h.

4. The preparation method according to claim 1, characterized in that: The phosphating temperature of step 3 is 400~600℃, the holding time is 2~6 h, and the heating rate is 2~10℃min -1 The volume ratio of hydrogen in the argon / hydrogen mixed atmosphere is 2%~20%.

5. The preparation method according to claim 1, characterized in that: The ratio of the area of ​​the nickel substrate to the amount of red phosphorus used in step 3 is 1 cm 2 : 0.05~1g.

6. The P-CoNiMoO@Co2P-Ni2P core-shell structure catalyst prepared according to claims 1 to 5, characterized in that The shell is a cobalt phosphide-nickel phosphide heterostructure, and the core is phosphorus-doped cobalt nickel molybdate.

7. Application of a P-CoNiMoO@Co2P-Ni2P core-shell structure catalyst in hydrogen evolution reaction.

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