Doping regulation and control method and application of noble metal loaded nickel molybdate heterostructure bifunctional electrocatalyst

Abstract

The invention relates to a doping regulation and control method and application of a noble metal loaded nickel molybdate heterostructure bifunctional electrocatalyst, and belongs to the technical field of energy and electrochemical catalysis. According to the preparation method, nickel foam is pretreated and then immersed in an aqueous solution containing nickel salt, molybdate and ammonium fluoride, then a fluorine-doped nickel molybdate nanorod precursor is obtained through a hydrothermal synthesis method, and ruthenium and nickel salt are introduced through an impregnation method; and finally, performing thermal reduction in a hydrogen and argon mixed atmosphere to obtain the ruthenium-nickel alloy loaded fluorine-doped nickel molybdate nanostructure. The work function difference of ruthenium-nickel alloy and nickel molybdate is effectively reduced through fluorine doping, the interface potential barrier is reduced, electron transfer is accelerated, and the electrocatalytic activity and stability are enhanced, so that the material shows excellent performance in hydrogen evolution reaction (HER) and urea oxidation reaction (UOR) in alkaline fresh water and seawater, low-energy-consumption hydrogen production is realized, and the preparation method is simple and easy to implement. And powerful support is provided for sustainable energy technology development.

Description

TECHNICAL FIELD

[0001] The application relates to a doping regulation method and application of a noble metal loaded nickel molybdate heterostructure bifunctional electrocatalyst, and belongs to the technical field of energy and electrochemical catalysis. BACKGROUND

[0002] With the intensification of global energy crisis, it is increasingly critical to seek efficient water splitting electrocatalysts. Hydrogen is a potential energy carrier due to its excellent energy density and environmental friendliness. Among various hydrogen production methods, water electrolysis driven by renewable energy is one of the feasible ways to produce green hydrogen. However, freshwater resources are scarce, accounting for only a small part of the earth's water resources, while seawater accounts for 96.53%, which provides a more abundant and sustainable choice for hydrogen production from seawater.

[0003] However, seawater electrolysis faces many complex problems, among which chloride ions (Cl - ) not only cause electrode corrosion, but also easily cause undesirable chlorine evolution reaction. This is because the theoretical oxygen evolution reaction (OER) potential is 1.23V, but the overpotential required by existing OER catalysts is often more than 200mV, which exceeds the chlorine evolution potential, reducing energy efficiency. To solve this problem, using small molecule oxidation processes such as UOR to replace anode OER has become an effective strategy to reduce anode potential. Urea oxidation has a low oxidation potential (only 0.37V vs. RHE), and urea is a common water pollutant. Combining it with water electrolysis can achieve the dual benefits of pollution control and hydrogen production. However, UOR requires a catalyst with high activity and selectivity due to the complex six-electron transfer mechanism, which leads to slow kinetics.

[0004] Nickel molybdate as a catalyst has many advantages, such as abundant active sites, adjustable electronic properties of Mo's multivalent oxidation state, and unique nanostructure that can increase surface area and improve mass transfer. However, its inherent HER activity is limited, and Mo dissolution during the HER process can affect stability and reusability. Although various strategies have been used to improve it, such as element doping, oxygen vacancy creation, and conversion into nitrides or phosphides, it is still difficult to achieve high bifunctional catalytic performance for both HER and UOR. Introducing hetero catalysts such as noble metal or alloy loading is an effective solution, but there are problems such as interface compatibility and charge transfer resistance. Therefore, developing an efficient electrocatalyst that can overcome these problems is of great significance for achieving efficient and sustainable hydrogen production from seawater. SUMMARY

[0005] The purpose of the present application is to solve the problems existing in the prior art, and to provide a doping regulation method and application of a noble metal loaded nickel molybdate heterostructure bifunctional electrocatalyst, which realizes efficient and stable urea-assisted seawater splitting for hydrogen production.

[0006] To achieve the above object, the application provides the following technical scheme:

[0007] First, the noble metal loaded nickel molybdate heterostructure is doped and regulated by a hydrothermal method and an immersion reduction method to obtain a ruthenium-nickel alloy loaded fluorine-doped nickel molybdate bifunctional catalyst. The existing technology has the problem of high interface barrier of the nickel molybdate loaded alloy catalyst without fluorine doping, and fluorine doping can optimize the electronic structure of the heterojunction, so that the catalyst has excellent HER and UOR performance.

[0008] The specific steps are as follows:

[0009] Step one, synthesis of fluorine-doped nickel molybdate precursor: dissolve nickel salt, molybdenum salt and fluoride in 20-40 mL ultrapure water and stir for 20-40 minutes, then transfer the solution to a 40-60 mL polytetrafluoroethylene lined autoclave together with foamed nickel, react at 150-170 DEG C for 8-12 hours, cool to room temperature, take out the sample, wash with ultrapure water several times and dry at 50-70 DEG C, and finally sinter at 400-500 DEG C for 1.5-2.5 hours;

[0010] Step two, preparation of ruthenium-nickel alloy loaded fluorine-doped nickel molybdate: immerse the fluorine-doped nickel molybdate precursor in a solution containing ruthenium salt and nickel salt for 15-25 minutes, the volume of the solution is 10-20 mL, and after drying, reduce it at 400-500 DEG C under H2 / Ar atmosphere for 1.5-2.5 hours.

[0011] Preferably, the nickel salt is nickel nitrate, and the concentration is 0.8-1.2 mmol; the molybdenum salt is ammonium molybdate tetrahydrate, and the concentration is 0.12-0.16 mmol; the fluoride is ammonium fluoride, and the addition amount can be adjusted in the range of 0.2-0.6 mmol to optimize the regulation effect of fluorine doping on the electronic structure of the catalyst and improve the catalytic performance; the ruthenium salt is ruthenium chloride, and the nickel salt is nickel chloride, and the concentration of each is 0.12-0.18 mmol.

[0012] Preferably, the foamed nickel substrate in step one is cut into a square with an area of 2*4 cm.

[0013] Preferably, the foamed nickel substrate in step one needs to be pretreated, including: sequentially washing with 2-4 M hydrochloric acid, acetone, ethanol and ultrapure water for 15-25 minutes, and then drying at 50-70 DEG C.

[0014] Alternatively, the sintering atmosphere in step one can be air or O2, which aims to fully convert the material into an oxide and crystallize it.

[0015] In addition, the application also provides a use of the above-mentioned ruthenium-nickel alloy loaded fluorine-doped nickel molybdate bifunctional electrocatalyst in urea-assisted seawater decomposition and hydrogen production.

[0016] Compared with the prior art, the present application has the following advantages:

[0017] 1. The present application prepares a ruthenium-nickel alloy loaded fluorine-doped nickel molybdate bifunctional electrocatalyst by a hydrothermal method and an impregnation reduction method, characterized in that the catalyst presents a three-dimensional hierarchical structure, in which ruthenium-nickel alloy nanoparticles are uniformly anchored on the surface of fluorine-doped nickel molybdate nanorods, and fluorine doping enhances the interface interaction by reducing the work function difference between the ruthenium-nickel alloy and the nickel molybdate, making it exhibit high efficient catalytic performance and good stability in hydrogen evolution reaction and urea oxidation reaction in alkaline fresh water and seawater.

[0018] 2. The application of the ruthenium-nickel alloy loaded fluorine-doped nickel molybdate bifunctional electrocatalyst in urea-assisted seawater decomposition for hydrogen production, as claimed in claim 1, is characterized in that the ruthenium-nickel alloy loaded fluorine-doped nickel molybdate is used as a cathode and anode catalyst in a two-electrode system for urea-assisted seawater decomposition for hydrogen production, which realizes high current density hydrogen evolution reaction at a lower voltage in an alkaline electrolyte containing urea, effectively resists seawater corrosion and maintains long-term stability, has high Faraday efficiency and good commercial application value. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the specific embodiments or prior art description will be briefly introduced below.

[0020] Figure 1 X-ray diffraction pattern of the ruthenium-nickel alloy loaded fluorine-doped nickel molybdate prepared in Example 1 of the present application;

[0021] Figure 2 High-resolution transmission electron microscopy analysis result of the ruthenium-nickel alloy loaded fluorine-doped nickel molybdate prepared in Example 1 of the present application;

[0022] Figure 3 F1s XPS spectrum of the catalyst prepared in Example 1 and Comparative Example 2 of the present application;

[0023] Figure 4 Polarization curve of the HER performance of Example 1-3 and Comparative Example 1-3 of the present application.

[0024] Figure 5 Polarization curve of the UOR performance of Example 1-3 and Comparative Example 1-3 of the present application.

[0025] Figure 6 Constant-current stability test curve of Example 1 of the present application, showing its stability in long-time operation. DETAILED DESCRIPTION

[0026] The application will be further described in conjunction with the following examples without limiting the scope of the application thereto.

[0027] Example 1

[0028] 1. Synthesis of fluorine-doped nickel molybdate precursor: 1 mmol of nickel nitrate, 0.143 mmol of ammonium molybdate tetrahydrate and 0.5 mmol of ammonium fluoride were dissolved in 30 mL of ultrapure water and stirred for 30 minutes. The solution was transferred to a 50 mL Teflon-lined autoclave with pretreated nickel foam (2 cm x 4 cm) and reacted at 160 °C for 10 hours. After cooling to room temperature, the sample was removed, washed with ultrapure water several times and dried at 60 °C, and finally sintered at 450 °C for 2 hours.

[0029] 2. Preparation of fluorine-doped nickel molybdate supported on ruthenium-nickel alloy: The fluorine-doped nickel molybdate precursor prepared above was immersed in a 15 mL solution containing 0.15 mmol of ruthenium chloride and 0.15 mmol of nickel chloride for 20 minutes, dried and reduced at 450 °C under H2 / Ar atmosphere (5% H2, 95% Ar) for 2 hours to obtain a fluorine-doped nickel molybdate catalyst supported on ruthenium-nickel alloy.

[0030] Example 2

[0031] 1. Synthesis of fluorine-doped nickel molybdate precursor: 1 mmol of nickel nitrate, 0.143 mmol of ammonium molybdate tetrahydrate and 0.25 mmol of ammonium fluoride were dissolved in 30 mL of ultrapure water and stirred for 30 minutes. The solution was transferred to a 50 mL Teflon-lined autoclave with pretreated nickel foam (2 cm x 4 cm) and reacted at 160 °C for 10 hours. After cooling to room temperature, the sample was removed, washed with ultrapure water several times and dried at 60 °C, and finally sintered at 450 °C for 2 hours.

[0032] 2. Preparation of fluorine-doped nickel molybdate supported on ruthenium-nickel alloy: The fluorine-doped nickel molybdate precursor prepared above was immersed in a 15 mL solution containing 0.15 mmol of ruthenium chloride and 0.15 mmol of nickel chloride for 20 minutes, dried and reduced at 450 °C under H2 / Ar atmosphere (5% H2, 95% Ar) for 2 hours to obtain a fluorine-doped nickel molybdate catalyst supported on ruthenium-nickel alloy.

[0033] Example 3

[0034] 1. Synthesis of nickel molybdate precursor: 1 mmol of nickel nitrate and 0.143 mmol of ammonium molybdate tetrahydrate were dissolved in 30 mL of ultrapure water and stirred for 30 minutes. The solution was transferred to a 50 mL Teflon-lined autoclave with pre-treated nickel foam (2 cm x 4 cm) and reacted at 160 °C for 10 hours. After cooling to room temperature, the sample was removed, washed with ultrapure water several times and dried at 60 °C, and finally sintered at 450 °C for 2 hours.

[0035] 2. Preparation of ruthenium nickel alloy supported fluorine-doped nickel molybdate: The fluorine-doped nickel molybdate precursor prepared above was immersed in a 15 mL solution containing 0.15 mmol of ruthenium chloride and 0.15 mmol of nickel chloride for 20 minutes, dried and reduced at 450 °C under H2 / Ar atmosphere (5% H2, 95% Ar) for 2 hours to obtain a ruthenium nickel alloy supported fluorine-doped nickel molybdate catalyst.

[0036] Comparative Example 1

[0037] 1. Synthesis of fluorine-doped nickel molybdate precursor: 1 mmol of nickel nitrate, 0.143 mmol of ammonium molybdate tetrahydrate and 0.5 mmol of ammonium fluoride were dissolved in 30 mL of ultrapure water and stirred for 30 minutes. The solution was transferred to a 50 mL Teflon-lined autoclave with pre-treated nickel foam (2 cm x 4 cm) and reacted at 160 °C for 10 hours. After cooling to room temperature, the sample was removed, washed with ultrapure water several times and dried at 60 °C, and finally sintered at 450 °C for 2 hours.

[0038] 2. Preparation of ruthenium supported fluorine-doped nickel molybdate: The fluorine-doped nickel molybdate precursor prepared above was immersed in a 15 mL solution containing 0.15 mmol of ruthenium chloride for 20 minutes, dried and reduced at 450 °C under H2 / Ar atmosphere (5% H2, 95% Ar) for 2 hours to obtain a ruthenium supported fluorine-doped nickel molybdate catalyst.

[0039] Comparative Example 2

[0040] Synthesis of fluorine-doped nickel molybdate: 1 mmol of nickel nitrate, 0.143 mmol of ammonium molybdate tetrahydrate and 0.5 mmol of ammonium fluoride were dissolved in 30 mL of ultrapure water and stirred for 30 minutes. The solution was transferred to a 50 mL Teflon-lined autoclave with pre-treated nickel foam (2 cm x 4 cm) and reacted at 160 °C for 10 hours. After cooling to room temperature, the sample was removed, washed with ultrapure water several times and dried at 60 °C, and finally sintered at 450 °C for 2 hours. A fluorine-doped nickel molybdate catalyst was obtained.

[0041] Comparative Example 3

[0042] Synthesis of nickel molybdate: 1 mmol of nickel nitrate and 0.143 mmol of ammonium molybdate tetrahydrate were dissolved in 30 mL of ultrapure water and stirred for 30 minutes. The solution, along with pretreated nickel foam (2 cm × 4 cm), was transferred to a 50 mL polytetrafluoroethylene-lined autoclave and reacted at 160 °C for 10 hours. After cooling to room temperature, the sample was removed, washed several times with ultrapure water, dried at 60 °C, and finally sintered at 450 °C for 2 hours to obtain the nickel molybdate catalyst.

[0043] To verify the technical effects of each embodiment and comparative example, the following experiments were conducted.

[0044] Material characterization analysis:

[0045] 1. Crystal structure verification (corresponding) Figure 1 )

[0046] like Figure 1 As shown, the diffraction peaks at 14.2°, 25.6°, and 29.8° in the XRD pattern are assigned to the (110), (021), and (220) crystal planes of NiMoO4 (JCPDS No. 86-0361). The weak peak at 43.1° matches the (111) crystal plane of the RuNi alloy (PDF#65-7645), indicating successful loading of the ruthenium-nickel alloy. No fluoride characteristic peaks were detected, proving that F exists in the form of lattice doping.

[0047] 2. Microstructure and elemental distribution (corresponding to) Figure 2 )

[0048] High-resolution transmission electron microscopy (HRTEM) Figure 2 The lattice spacing of 0.210 nm (the (002) crystal plane of RuNi alloy) and 0.616 nm (the (110) crystal plane of NiMoO4) was measured. There was no lattice distortion at the interface, indicating that the alloy is strongly coupled with the substrate.

[0049] 3. Surface chemical state analysis (corresponding to) Figure 3 )

[0050] XPS Atlas ( Figure 3 The results show that 683.6 eV (MF bond) and 687.1 eV (OMF bond) in the F 1s spectrum prove that fluorine doping successfully substituted some hydroxyl sites.

[0051] Electrochemical performance analysis:

[0052] 1. HER performance (corresponding) Figure 4 )

[0053] In 1M KOH ( Figure 4 Example 1, at a current density of 1 Acm -2The overpotential is only 248 mV, which is reduced by 366 mV compared with Example 3 (undoped).

[0054] 2. UOR performance (corresponding Figure 5 )

[0055] In the electrolyte containing 0.33 M urea (see Figure 5 ), Example 1 reaches 1 A cm -2 at only 1.59 V. Example 3 (undoped) can only reach 655 mA cm -2 at the same potential.

[0056] 3. Stability verification (corresponding Figure 6 )

[0057] The constant current test (see Figure 6 ) shows that Example 1 has an overpotential fluctuation of <5% at 100 mA cm -2 under the environment of 1 M KOH + seawater for 1000 hours of continuous operation, which meets the industrial durability requirements.

[0058] In summary, the ruthenium-nickel alloy loaded fluorine-doped nickel molybdate catalyst prepared by the present application optimizes the heterojunction electron transport through fluorine doping, and exhibits high-efficiency bifunctional catalytic activity (HER overpotential 248 mV@1A cm -2 , UOR potential 1.59 V@1A cm -2 ) and long-term stability (decay <5% for 1000 hours) in the alkaline seawater and urea environments, providing a high-performance and low-cost catalytic material solution for seawater electrolysis hydrogen production and urea wastewater co-production, and having significant industrial application potential.

Claims

1. A method for controlling the doping of a noble metal-supported nickel molybdate heterostructure bifunctional electrocatalyst, characterized in that, Includes the following steps: Step 1: Synthesis of fluorine-doped nickel molybdate precursor: Dissolve nickel salt, molybdenum salt and fluoride in 20-40 mL of ultrapure water and stir for 20-40 minutes. Then, transfer the solution together with nickel foam to a 40-60 mL high-pressure reactor lined with polytetrafluoroethylene. React at 150-170 °C for 8-12 hours. After cooling to room temperature, remove the sample, wash it several times with ultrapure water and dry it at 50-70 °C. Finally, sinter it at 400-500 °C for 1.5-2.5 hours. Step 2: Preparation of fluorine-doped nickel molybdate supported on ruthenium-nickel alloy: The fluorine-doped nickel molybdate precursor is immersed in a solution containing ruthenium salt and nickel salt for 15-25 minutes, with a solution volume of 10-20 mL. After drying, it is reduced at 400-500℃ for 1.5-2.5 hours under H2 / Ar atmosphere.

2. The preparation method according to claim 1, characterized in that: The nickel salt is nickel nitrate with a concentration of 0.8-1.2 mmol; the molybdenum salt is ammonium molybdate tetrahydrate with a concentration of 0.12-0.16 mmol; the fluoride is ammonium fluoride, the amount of which can be adjusted in the range of 0.3-0.7 mmol, to optimize the effect of fluorine doping on the electronic structure of the catalyst and improve catalytic performance; the ruthenium salt is ruthenium chloride, and the nickel salt is nickel chloride, both with a concentration of 0.12-0.18 mmol.

3. The preparation method according to claim 1, characterized in that: The pretreatment of the foam substrate described in step one includes: washing with hydrochloric acid, acetone, ethanol and ultrapure water at a concentration of 2-4M for 15-25 minutes in sequence, followed by drying at 50-70°C.

4. The preparation method according to claim 1, characterized in that: The sintering atmosphere in step one can be either air or O2, with the aim of fully converting the material into oxides and crystallizing it.

5. A bifunctional electrocatalyst of ruthenium-nickel alloy supported on fluorine-doped nickel molybdate, prepared by the method described in claim 1, characterized in that: The catalyst exhibits a three-dimensional hierarchical structure in which ruthenium-nickel alloy nanoparticles are uniformly anchored on the surface of fluorine-doped nickel molybdate nanorods. Fluorine doping enhances the interfacial interaction by reducing the work function difference between the ruthenium-nickel alloy and nickel molybdate, thus enabling it to exhibit high catalytic performance and good stability in hydrogen evolution reaction and urea oxidation reaction in alkaline fresh water and seawater.

6. The application of the ruthenium-nickel alloy-supported fluorine-doped nickel molybdate bifunctional electrocatalyst of claim 1 in urea-assisted seawater decomposition for hydrogen production, characterized in that: The ruthenium-nickel alloy supported on fluorine-doped nickel molybdate is used as the cathode and anode catalyst in a two-electrode system for urea-assisted seawater decomposition to produce hydrogen. In an alkaline urea-containing electrolyte, it achieves a high current density hydrogen evolution reaction at a relatively low voltage, while effectively resisting seawater corrosion and maintaining long-term stability. It has high Faraday efficiency and good commercial application value.

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