Method for in-situ synthesis of nickel phosphate-molybdenum phosphide / nickel molybdenum oxide catalyst by two-step method and application of nickel phosphate-molybdenum phosphide / nickel molybdenum oxide catalyst

Abstract

The invention belongs to the technical field of catalyst preparation, and particularly relates to a method for in-situ synthesis of a nickel phosphate-molybdenum phosphide / nickel molybdenum oxide catalyst through a two-step method and application of the nickel phosphate-molybdenum phosphide / nickel molybdenum oxide catalyst. The preparation method comprises the following steps: by taking a nickel source and a molybdenum source as reactants and taking foamed nickel as a carrier, carrying out hydrothermal reaction to obtain foamed nickel on which Ni and Mo grow; a phosphorus source is used as a reactant, foamed nickel on which Ni and Mo grow is used as a growth substrate, phosphorus atoms are doped through chemical vapor deposition, and the nickel phosphate-molybdenum phosphide / nickel molybdenum oxide catalyst is obtained. The catalyst has extremely low hydrogen evolution overpotential (53 mV) under the current density of 10 mA cm <-2 >, has extremely excellent hydrogen evolution reaction kinetics, and has the characteristics of easiness in preparation, low cost, no pollution and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation, and more specifically relates to a method for in-situ synthesizing nickel phosphate-molybdenum phosphide / nickel molybdenum oxide catalyst by a two-step method and its application. Background Art

[0002] Hydrogen is considered a promising approach to address the energy crisis due to its high energy density and environmental harmlessness. Alkaline water electrolysis can achieve efficient and high-purity hydrogen production, and thus has received increasing attention.

[0003] Currently, platinum-based catalysts have excellent catalytic performance in the hydrogen evolution reaction of alkaline water electrolysis. However, due to their high price, the large-scale application of such catalysts is limited. In some existing technologies, nickel molybdenum oxide is used as a catalyst for the hydrogen evolution reaction of electrolyzed water. However, the internal resistance of nickel molybdenum oxide is large, resulting in a low charge transfer rate and a decrease in hydrogen evolution performance with the increase of current density. Moreover, in a reducing environment, a reduction reaction occurs on the surface of nickel molybdenum oxide, and nickel and molybdenum are reduced to lower valence states or even metallic states, and the loss of lattice oxygen leads to structural collapse. The original oxide structure is reconstructed, and the composition of the active phase and structure formed by the reconstruction is difficult to control, resulting in performance degradation. Therefore, how to provide a hydrogen evolution catalyst with excellent catalytic performance, structural stability, and low cost has become a difficult problem that needs to be overcome by those skilled in the art. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for in-situ synthesizing nickel phosphate-molybdenum phosphide / nickel molybdenum oxide catalyst by a two-step method and its application, so as to enable two transition metals Ni and Mo to grow in-situ on nickel foam in a hydrothermal-vapor deposition manner and perform phosphorus atom doping, so as to solve the problems existing in the above-mentioned prior art.

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

[0006] One of the technical solutions of the present invention: provides a method for in-situ synthesizing nickel phosphate-molybdenum phosphide / nickel molybdenum oxide catalyst by a two-step method, and the steps include:

[0007] Using a nickel source and a molybdenum source as reactants and nickel foam as a carrier, through a hydrothermal reaction, nickel foam grown with Ni and Mo is obtained;

[0008] Using a phosphorus source as a reactant and the nickel foam grown with Ni and Mo as a growth substrate, phosphorus atom doping is carried out by chemical vapor deposition to obtain the nickel phosphate-molybdenum phosphide / nickel molybdenum oxide catalyst.

[0009] In this invention, NiMoO4 is in-situ generated on the surface of nickel foam through hydrothermal reaction, and then doped with phosphorus atoms to synthesize a heterostructure of nickel phosphate - molybdenum phosphide on the surface of NiMoO4, showing a scallion-like microstructure. The formation of this heterostructure promotes the formation of an interfacial electric field. Nickel phosphate (usually an n-type semiconductor) combines with molybdenum phosphide (a p-type semiconductor) to form a p-n heterojunction. An internal electric field is generated at the interface due to the Fermi level difference, significantly reducing the charge recombination probability.

[0010] Benefiting from the synthesis of the heterostructure, Mo atoms in molybdenum phosphide interact with Ni of nickel phosphate through the heterointerface, 2+ adjusting the position of the d-band center of Mo, reducing the adsorption free energy of hydrogen intermediates and making it close to the thermoneutral value, thereby enhancing the rate of the hydrogen molecule synthesis step in the hydrogen evolution reaction. And the high electronegativity of phosphate groups (PO3 3- ) can induce the electrons of Ni 2+ to transfer to molybdenum phosphide, enhancing the electron-deficiency of Ni sites and promoting the adsorption and dissociation of OH - . At the same time, due to the formation of the heterostructure, a large number of oxygen vacancies are generated at the heterojunction, further exposing the unsaturated coordination bonds. Benefiting from the synergistic effect between nickel phosphate and molybdenum phosphide, in the hydrogen evolution reaction, adsorption and dissociation preferentially occur on the surface of molybdenum phosphide, generating H + and OH - . Nickel phosphate promotes the formation of H2 by adsorbing H at the nickel sites. At the same time, the porous layered structure of nickel phosphate can protect molybdenum phosphide from electrolyte erosion and extend the catalyst life.

[0011] Furthermore, the nickel source includes NiCl2·6H2O and / or Ni(NO3)2·6H2O.

[0012] Furthermore, the molybdenum source includes (NH4)6Mo7O 24 ·4H2O / or and MoO3.

[0013] Furthermore, the molar ratio of the nickel source to the molybdenum source is 1 - 5:1.

[0014] Furthermore, the temperature of the hydrothermal reaction is 100 - 200 °C and the time is 5 - 10 h.

[0015] Furthermore, the phosphorus source includes NaH2PO2·H2O.

[0016] Furthermore, the heating rate of the chemical vapor deposition is 1 - 5 °C / min, the temperature is 350 - 400 °C, and the time is 1 - 3 h.

[0017] The second technical solution of the present invention: Provide a nickel phosphate - molybdenum phosphide / nickel molybdenum oxide catalyst, which is prepared by the above - mentioned preparation method.

[0018] The third technical solution of the present invention: Provide an application of the above - mentioned nickel phosphate - molybdenum phosphide / nickel molybdenum oxide catalyst in alkaline water electrolysis for hydrogen evolution.

[0019] The fourth technical solution of the present invention: Provide a method for alkaline water electrolysis for hydrogen evolution, which uses the above - mentioned nickel phosphate - molybdenum phosphide / nickel molybdenum oxide catalyst to catalyze alkaline water electrolysis for hydrogen evolution.

[0020] The fifth technical solution of the present invention: Provide a method for improving the catalytic activity and stability of a nickel molybdenum oxide catalyst, and the steps include:

[0021] Using a phosphorus source as a reactant and a nickel molybdenum oxide catalyst (NiMoO4) as a growth substrate, and performing phosphorus atom doping through chemical vapor deposition to obtain the nickel phosphate - molybdenum phosphide / nickel molybdenum oxide catalyst, thereby improving the catalytic activity and stability of the nickel molybdenum oxide catalyst.

[0022] Furthermore, the phosphorus source includes NaH2PO2·H2O.

[0023] Furthermore, the heating rate of the chemical vapor deposition is 1 - 5 °C / min, the temperature is 350 - 400 °C, and the time is 1 - 3 h.

[0024] The transition metal hydrogen evolution catalyst (nickel phosphate - molybdenum phosphide / nickel molybdenum oxide catalyst) prepared by the present invention is relatively stable in an alkaline solution, and due to the synergistic effect between transition metals, it shows good catalytic activity in the hydrogen evolution reaction in an alkaline solution. Among them, the Gibbs free energy of hydrogen adsorption of transition metals Ni and Mo is second only to that of Pt - based materials. In terms of cost, Ni and Mo metals also have great advantages compared to Pt. Therefore, the transition metal hydrogen evolution catalyst prepared by the present invention has great potential in electrocatalytic hydrogen evolution.

[0025] The present invention uses nickel foam as a carrier. Nickel foam presents a porous structure in terms of structure, has a very high specific surface area, and has excellent electrical conductivity, so it is often used as a catalyst substrate. In an alkaline solution, metallic nickel has a smaller hydrogen adsorption free energy and exchange current density than other transition metals. Due to the dissolution effect of molybdenum (when a solid substance contacts a solvent, its surface molecules or ions will gradually enter the solvent), therefore, the loading of nickel-molybdenum bimetal will make the catalyst have extremely high hydrogen evolution catalytic activity. At the same time, by doping additional elements, the stability and catalytic activity of the catalyst are increased. The electronegativity of phosphorus atoms enables it to extract electrons from metal atoms, making them play a role as a base for capturing positively charged protons in the electrochemical process of the hydrogen evolution reaction. Therefore, the doping of phosphorus elements in the present invention can reduce the electron density around Ni-Mo and generate abundant empty d orbitals to promote the adsorption of hydroxide ions and protons, ultimately achieving the purpose of improving the stability of the hydrogen evolution catalyst and enhancing the catalytic activity.

[0026] The present invention discloses the following technical effects:

[0027] The present invention uses nickel foam with a special three-dimensional porous structure as a substrate, which not only has excellent electrical conductivity but also can load more catalysts. At the same time, the heterojunction formed by nickel phosphate-phosphide molybdenum / nickel molybdenum oxide in the catalyst can bring a large number of vacancy defects, which can adsorb hydrogen atoms and transfer charges in time to form hydrogen gas.

[0028] The nickel phosphate-phosphide molybdenum / nickel molybdenum oxide catalyst prepared by the present invention (under the conditions of using 1 mol·L -1 KOH as the electrolyte, a graphite rod as the counter electrode, and a reference electrode of Hg / HgO), has an extremely low hydrogen evolution overpotential (53 mV) at a current density of 10 mA cm -2 , and has extremely excellent hydrogen evolution reaction kinetics, as well as characteristics such as easy preparation, low cost, and no pollution. In addition, the synthesis of transition metal phosphides and phosphates caused by the doping of phosphorus elements not only improves the catalytic activity of the catalyst, but also greatly improves its surface charge transfer resistance. At the same time, the performance of the catalyst in the response current test is also excellent. Generally speaking, the nickel phosphate-phosphide molybdenum / nickel molybdenum oxide catalyst synthesized based on the present invention has excellent hydrogen evolution activity and excellent stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0030] Figure 1 It is the SEM image of the pretreated nickel foam in Example 1.

[0031] Figure 2 SEM image of nickel foam grown with Ni and Mo in Example 1.

[0032] Figure 3 SEM image of nickel phosphate - molybdenum phosphide / nickel molybdenum oxide catalyst prepared in Example 1.

[0033] Figure 4 XRD pattern of nickel phosphate - molybdenum phosphide / nickel molybdenum oxide catalyst prepared in Example 1.

[0034] Figure 5 Comparison chart of polarization hydrogen evolution curves of PAN - MoP / NiMoO4 / NF, NiMoO4 / NF and NF.

[0035] Figure 6 Comparison chart of Nyquist curves of PAN - MoP / NiMoO4 / NF, NiMoO4 / NF and NF.

[0036] Figure 7 Stable response current curve diagram of PAN - MoP / NiMoO4 / NF. Detailed implementation mode

[0037] Now, various exemplary embodiments of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics and implementation schemes of the present invention.

[0038] It should be understood that the terms described in the present invention are only for describing specific implementation modes and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0039] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can 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 related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0040] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the present invention specification, which are obvious to those skilled in the art. Other embodiments obtained from the present invention specification are obvious to those skilled in the art. The present invention specification and examples are merely exemplary.

[0041] Regarding the use of "comprising", "including", "having", "containing", etc. in this article, they are all open-ended terms, that is, they are intended to include but not limited to.

[0042] It should be noted that the aspects not detailed in the present invention are all conventional operation means in the art and are not the focus of the present invention.

[0043] The raw materials and reagents involved in the specific embodiments of the present invention are all commercially available products.

[0044] In the specific embodiments of the present invention, the normal temperature and room temperature, unless otherwise specified, both refer to 20 - 30 °C.

[0045] Example 1

[0046] Preparation steps of nickel phosphate - molybdenum phosphide / nickel molybdenum oxide catalyst:

[0047] S1. Pretreat the nickel foam (2×4×0.15 cm), ultrasonically treat it with HCl solution (4 mol·L -1 ), deionized water, and absolute ethanol for 20 min each, and then dry it in a vacuum drying oven at 60 °C for 30 min;

[0048] S2. Dissolve NiCl2·6H2O and (NH4)6Mo7O 24 ·4H2O in deionized water and stir to make it fully dissolved to obtain a mixed solution;

[0049] Among them, the concentration of NiCl2·6H2O in the mixed solution is 0.02 M, and the concentration of (NH4)6Mo7O 24 ·4H2O is 0.01 M;

[0050] S3. Transfer the mixed solution in step S2 to a 100 mL polytetrafluoroethylene liner, and at the same time vertically place the nickel foam pretreated in step S1 into the liner, and carry out a hydrothermal reaction at 150 °C for 6 h, then rinse and dry to obtain nickel foam grown with Ni and Mo;

[0051] S4. Place the nickel foam grown with Ni and Mo in step S3 in a porcelain boat, place NaH2PO2·H2O upstream of it, then put it into a tube furnace, and under a nitrogen atmosphere, heat it from room temperature to 400 °C at a heating rate of 3 °C / min, and keep it at this temperature for 2 h. Subsequently, rinse it successively with deionized water and absolute ethanol, and dry it in a vacuum drying oven to obtain the nickel phosphate-phosphomolybdenum / nickel molybdenum oxide catalyst (where the proportion of nickel is 19.42%, molybdenum is 38.08%, phosphorus is 5.17%, and oxygen is 37.33%).

[0052] Example 2

[0053] Compared with Example 1, the difference is that the concentration of NiCl2·6H2O in the mixed solution in step S2 is 0.03 M.

[0054] Example 3

[0055] Compared with Example 1, the difference is that the concentration of NiCl2·6H2O in the mixed solution in step S2 is 0.04 M.

[0056] Example 4

[0057] Compared with Example 1, the difference is that the temperature raised from room temperature in step S4 is 350 °C.

[0058] Comparative Example 1

[0059] Compared with Example 1, the difference is that phosphorus doping is not carried out. The specific steps are as follows:

[0060] S1. Pretreat the nickel foam (2×4×0.15 cm), ultrasonically treat it with HCl solution (4 mol·L -1 ), deionized water, and absolute ethanol for 20 min each, and then dry it in a vacuum drying oven at 60 °C for 30 min;

[0061] S2. Dissolve NiCl2·6H2O and (NH4)6Mo7O 24 ·4H2O in deionized water and stir to make it fully dissolve to obtain a mixed solution;

[0062] Among them, the concentration of NiCl2·6H2O in the mixed solution is 0.02 M, and the concentration of (NH4)6Mo7O 24 ·4H2O is 0.01 M;

[0063] S3. Transfer the mixed solution in step S2 to a 100 mL polytetrafluoroethylene liner, and at the same time vertically place the nickel foam pretreated in step S1 into the liner, and carry out a hydrothermal reaction at 150 °C for 6 h, and then rinse and dry it to obtain a nickel molybdenum oxide catalyst.

[0064] Test Example

[0065] Figure 1 It is the SEM image of the nickel foam pretreated in Example 1. It can be seen from the figure that the surface of the nickel foam is smooth.

[0066] Figure 2 It is the SEM image of the nickel foam grown with Ni and Mo in Example 1. It can be seen from the figure that after the growth of the nickel-molybdenum bimetal on the surface of the nickel foam, a micro-rod-like microstructure is presented.

[0067] Figure 3 It is the SEM image of the nickel phosphate-phosphomolybdenum / nickel molybdenum oxide catalyst prepared in Example 1. The figure shows that after phosphidation, spikes grow at the top of the micro-rods, forming a scallion-like shape.

[0068] Figure 4 It is the XRD pattern of the nickel phosphate-phosphomolybdenum / nickel molybdenum oxide catalyst prepared in Example 1. It can be seen from the figure that the XRD pattern of the nickel phosphate-phosphomolybdenum / nickel molybdenum oxide catalyst (PAN-MoP / NiMoO4 / NF) shows the successful synthesis of nickel phosphate and phosphomolybdenum.

[0069] Next, the nickel phosphate-phosphomolybdenum / nickel molybdenum oxide catalyst (PAN-MoP / NiMoO4 / NF) prepared in Example 2 is used as the working electrode to illustrate its performance.

[0070] The catalysts prepared in Example 2 (PAN-MoP / NiMoO4 / NF) and Comparative Example 1 (NiMoO4 / NF), as well as the pretreated nickel foam (NF), are used as the working electrodes, and the electrochemical performance test is carried out on a CHI760E electrochemical workstation using a three-electrode system. The results are as Figures 5 - 7 shown.

[0071] Specifically: Using 1 mol·L -1 KOH as the electrolyte, a graphite rod as the counter electrode, a reference electrode of Hg / HgO, and the catalysts prepared in Example 2 and Comparative Example 1 and the pretreated nickel foam as the working electrodes.

[0072] Figure 5 It is the comparative chart of the polarization hydrogen evolution curves of PAN-MoP / NiMoO4 / NF, NiMoO4 / NF, and NF. It can be seen from the figure that at a current density of 10 mA cm -2 the phosphidated PAN-MoP / NiMoO4 / NF (53 mV) has a much lower hydrogen evolution overpotential compared to NiMoO4 / NF (198 mV) and NF (222 mV), indicating that PAN-MoP / NiMoO4 / NF has excellent catalytic activity in HER.

[0073] Figure 6 Nyquist curve comparison diagrams of PAN-MoP / NiMoO4 / NF, NiMoO4 / NF, and NF. It can be seen from the figure that for the phosphated catalyst, the surface charge transfer resistance is extremely small, only 0.06 Ω, which means that PAN-MoP / NiMoO4 / NF has high intrinsic activity. In addition, it has a strong response ability to current, small polarization loss at high current density, and can achieve stable output of large current. At the same time, the efficiency of converting electrical energy into chemical energy is high, and the system energy consumption is reduced.

[0074] Figure 7 Stable response current curve diagram of PAN-MoP / NiMoO4 / NF. It can be seen from the figure that this catalyst can work stably under variable current conditions, with strong dynamic adaptability and fast interfacial mass transfer rate. Variable current stability is a rigid requirement for industrial scenarios.

[0075] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. For the same and similar parts between the embodiments, reference can be made to each other.

[0076] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for in-situ synthesizing nickel phosphate-molybdenum phosphide / nickel molybdenum oxide catalyst by a two-step method, the steps comprising: Using a nickel source and a molybdenum source as reactants and nickel foam as a carrier, through hydrothermal reaction, nickel foam grown with Ni and Mo is obtained; Using a phosphorus source as a reactant and the nickel foam grown with Ni and Mo as a growth substrate, phosphorus atom doping is carried out by chemical vapor deposition to obtain the nickel phosphate-molybdenum phosphide / nickel molybdenum oxide catalyst.

2. The method according to claim 1, wherein The nickel source includes NiCl2·6H2O and / or Ni(NO3)2·6H2O; and / or, the molybdenum source includes (NH4)6Mo7O 24 ·4H2O and / or MoO3.

3. The method according to claim 1, wherein The molar ratio of the nickel source to the molybdenum source is 1-5:

1.

4. The method according to claim 1, wherein The temperature of the hydrothermal reaction is 100-200 °C and the time is 5-10 h.

5. The method according to claim 1, wherein The phosphorus source includes NaH2PO2·H2O.

6. The method according to claim 1, characterized in that The heating rate of the chemical vapor deposition is 1-5 °C / min, the temperature is 350-400 °C, and the time is 1-3 h.

7. A nickel phosphate-molybdenum phosphide / nickel molybdenum oxide catalyst, characterized in that, The nickel phosphate-molybdenum phosphide / nickel molybdenum oxide catalyst is prepared by the method according to any one of claims 1-6.

8. An application of the nickel phosphate-molybdenum phosphide / nickel molybdenum oxide catalyst according to claim 7 in alkaline electrolytic water hydrogen evolution.

9. A method for hydrogen evolution by alkaline electrolyzed water, characterized in that, The method uses the nickel phosphate-molybdenum phosphide / nickel molybdenum oxide catalyst according to claim 7 to catalyze alkaline electrolytic water hydrogen evolution.

10. A method for improving the catalytic activity and stability of a nickel molybdenum oxide catalyst, characterized in that the steps Comprising: Using a phosphorus source as a reactant and a nickel molybdenum oxide catalyst as a growth substrate, phosphorus atom doping is carried out by chemical vapor deposition to obtain a nickel phosphate-molybdenum phosphide / nickel molybdenum oxide catalyst, improving the catalytic activity and stability of the nickel molybdenum oxide catalyst.

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