Carbon and nitrogen doped polyoxometalate catalyst, and preparation method and application thereof

Abstract

This application discloses a carbon-nitrogen-doped polyoxometalate catalyst, its preparation method, and its application, belonging to the field of electrocatalytic water splitting for hydrogen production technology. The carbon-nitrogen-doped polyoxometalate catalyst provided in this application includes nickel foam and a Finke-type carbon-nitrogen-doped polyoxometalate in situ grown on the surface of the nickel foam; the Finke-type carbon-nitrogen-doped polyoxometalate is Finke-type Ni4PMo9OCN; the catalyst is a three-dimensional flower-like aggregate formed by the assembly of nanopillars. The catalyst prepared in this application, through carbon-nitrogen doping with Finke-type molybdenum polyoxometalate, not only changes the d-band electronic state density and chemical environment of Ni and Mo, optimizing the electronic structure, but also significantly increases the active surface area, achieving a significant improvement in electrocatalytic performance; it also possesses the advantages of excellent stability and can be directly used as a working electrode, and has wide applications in electrocatalytic hydrogen evolution.

Description

Technical Field

[0001] This application belongs to the field of electrocatalytic water splitting for hydrogen production technology, and particularly relates to a carbon-nitrogen doped polyoxometalate catalyst, its preparation method and application. Background Technology

[0002] Hydrogen energy is a clean, efficient, and renewable secondary energy source that holds promise for playing a positive role in addressing a range of major global challenges, including global warming, air pollution, and energy shortages. Water electrolysis for hydrogen production is considered a promising green and efficient technology, offering advantages such as a simple process, zero pollution, and high-purity hydrogen. Therefore, developing electrocatalysts with high catalytic activity and stability to improve the efficiency of water electrolysis for hydrogen production provides a research foundation for the future development of sustainable and clean hydrogen energy.

[0003] Polyacids are nanoscale clusters composed of transition metals (such as W, Mo, and V) and oxygen atoms. Their active sites, such as metal atoms and oxygen bridges, can have their electronic structure precisely controlled through atomic-level doping with elements like cobalt, nickel, and copper. This allows for the preparation of highly efficient electrocatalysts suitable for water splitting and redox reactions in fuel cells. For example, prior art patent application CN117070990 A discloses a NiP2-Mo8P5@NF hydrogen evolution electrocatalyst, fabricated by forming a heterojunction of NiP2 and Mo8P5 supported on a nickel foam matrix, exhibiting excellent electrocatalytic hydrogen evolution performance under alkaline conditions.

[0004] However, the heterojunction electrocatalysts described above have the following problems: First, the heterojunction structure is prone to phase separation due to weakening of interfacial interactions during long-term electrolysis, resulting in the loss of active sites and affecting the durability of catalytic performance; second, the electron transport efficiency is limited, which seriously restricts the full play of catalytic activity, and the preparation process is harsh and not conducive to industrial production. Summary of the Invention

[0005] This application discloses a carbon-nitrogen doped polyoxometalate, its preparation method and application, aiming to solve the technical problems of insufficient catalytic activity and poor stability of existing heterojunction electrocatalysts during use.

[0006] To achieve the above objectives, the technical solution of this application is:

[0007] The first aspect of this application provides a carbon-nitrogen-doped polyoxometalate catalyst, including nickel foam and nanopillar Finke-type carbon-nitrogen-doped polyoxometalate;

[0008] The nano-column Finke-type carbon-nitrogen-doped polyoxometalate is grown in situ on the surface of the nickel foam and forms a three-dimensional flower-like aggregate structure.

[0009] The nanopillar-shaped Finke-type carbon-nitrogen doped polyoxometalate was selected as Finke-type Ni4PMo9OCN.

[0010] In conjunction with the first aspect, preferably, the outer surface of the nanopillar Finke-type carbon-nitrogen doped polyoxometalate has rough protrusions.

[0011] The second aspect of this application provides a method for preparing the carbon-nitrogen-doped polyoxometalate catalyst described in the first aspect, the method comprising:

[0012] An aqueous solution of sodium molybdate was reacted in a mixed solvent of phosphoric acid and glacial acetic acid to yield Na8(HPMo9O). 34 );

[0013] The Na8(HPMo9O) 34 Aqueous solutions of nickel nitrate and nickel-iron foam were subjected to a hydrothermal reaction, filtered, and then vacuum dried to obtain Finke-type polyacid Ni4PMo9.

[0014] Under a nitrogen atmosphere, the Finke-type polyoxometalate Ni4PMo9, dicyandiamide, and iron powder are placed in sequence and calcined at high temperature, then cooled to room temperature to obtain the carbon-nitrogen doped polyoxometalate catalyst.

[0015] Preferably, in conjunction with the second aspect, the molar ratio of sodium molybdate to phosphoric acid is 12:1.

[0016] Preferably, in conjunction with the second aspect, the nickel nitrate and Na8(HPMo9O) 34 The molar ratio of ) is (4-6):1.

[0017] Preferably, in conjunction with the second aspect, the nickel nitrate and Na8(HPMo9O) 34 The molar ratio of ) is 4:1.

[0018] In conjunction with the second aspect, preferably, the hydrothermal reaction is carried out at a temperature of 120-180 ℃ for a time of 8-12 h.

[0019] Preferably, in conjunction with the second aspect, the mass ratio of the Finke-type polyacid Ni4PMo9 to dicyandiamide is 1:1.5.

[0020] In conjunction with the second aspect, preferably, the high-temperature calcination temperature is 600 ℃ and the time is 2 h.

[0021] The third aspect of this application provides the application of carbon-nitrogen-doped polyoxometalate catalysts prepared by the preparation method described in the second aspect in electrocatalytic hydrogen evolution.

[0022] Compared with the prior art, the advantages or beneficial effects of the embodiments of this application include at least the following:

[0023] The carbon-nitrogen-doped polyoxometalate catalyst provided in this application achieves significant improvements in catalytic performance by in-situ growing nanopillar-shaped Finke-type carbon-nitrogen-doped polyoxometalate (Finke-type Ni4PMo9OCN) on the surface of nickel foam and forming a three-dimensional flower-like aggregate structure. This is achieved by altering the d-band electronic state density and chemical environment of Ni and Mo, thereby adjusting the intensity of MH and reducing its oxygen affinity, optimizing the electronic structure of the electrocatalyst, accelerating electron transfer between substances, and reducing the hydrogen binding free energy. Furthermore, it significantly increases the reactive surface area of ​​the catalyst, thereby greatly increasing the contact area with the electrolyte and effectively enhancing the catalyst's reactivity and catalytic efficiency. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 SEM image of Al-carbon-nitrogen-doped polyoxometalates prepared in the embodiments of this application;

[0026] Figure 2 SEM image of Finke-type polyacid Ni4PMo9 prepared in the embodiments of this application;

[0027] Figure 3 The elemental mapping distribution of Al-carbon-nitrogen-doped polyoxometalates prepared in the embodiments of this application;

[0028] Figure 4 Elemental composition diagram of Al-carbon-nitrogen-doped polyoxometalates prepared in the embodiments of this application;

[0029] Figure 5 XRD pattern of Al-carbon-nitrogen-doped polyoxometalates prepared in the embodiments of this application;

[0030] Figure 6 Raman spectra of Al-carbon-nitrogen-doped polyoxometalates prepared in the embodiments of this application;

[0031] Figure 7 LSV polarization curves of the B1-catalyst, A1-carbon-nitrogen-doped polyoxometalate, and A2-carbon-nitrogen-doped polyoxometalate prepared for the embodiments of this application in 1 M KOH solution for hydrogen evolution test;

[0032] Figure 8Overpotential histograms of the B1-catalyst, A1-carbon-nitrogen-doped polyoxometalate, and A2-carbon-nitrogen-doped polyoxometalate prepared for the embodiments of this application in 1 M KOH solution for hydrogen evolution test;

[0033] Figure 9 LSV polarization curves of the B1-catalyst, A3-polyoxometalate, A4-polyoxometalate, and A5-polyoxometalate prepared for the embodiments of this application in 1 M KOH solution for hydrogen evolution test;

[0034] Figure 10 Overpotential histograms of hydrogen evolution tests in 1 M KOH solution for B1-catalyst, A3-polyoxometalate, A4-polyoxometalate, and A5-polyoxometalate prepared for the embodiments of this application.

[0035] Figure 11 LSV polarization curves of A1-carbon-nitrogen-doped polyoxometalate, B1-catalyst, B2-catalyst and Pt / C (20%) prepared for the embodiments of this application in 1 M KOH solution for hydrogen evolution test;

[0036] Figure 12 Tafel slope curves of hydrogen evolution tests of A1-carbon-nitrogen-doped polyoxometalate, B1-catalyst, B2-catalyst and Pt / C (20%) prepared for the embodiments of this application in 1 M KOH solution;

[0037] Figure 13 Overpotential histogram of A1-carbon-nitrogen-doped polyoxometalate, B1-catalyst, B2-catalyst and Pt / C (20%) prepared for the embodiments of this application in 1 M KOH solution for hydrogen evolution test;

[0038] Figure 14 ESCA plots of hydrogen evolution test in 1 M KOH solution for A1-carbon-nitrogen-doped polyoxometalate, B1-catalyst and B2-catalyst prepared for the embodiments of this application;

[0039] Figure 15 Stability test results of Al-carbon-nitrogen-doped polyoxometalates prepared in the embodiments of this application in an AEM electrolytic cell;

[0040] Figure 16 SEM images of carbon-nitrogen-doped polyoxometalates prepared in the embodiments of this application after cyclic testing in an AEM electrolytic cell;

[0041] Figure 17 The elemental mapping distribution of the carbon-nitrogen-doped polyoxometalate prepared in the embodiments of this application after cyclic testing in an AEM electrolytic cell. Detailed Implementation

[0042] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0043] In the following description of this embodiment, the term "and / or" is used to describe the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, B existing alone, and A and B existing simultaneously. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0044] In the following description of this embodiment, the term "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0045] Those skilled in the art should understand that, in the following description of the embodiments of this application, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0046] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0047] It should be noted that all raw materials and / or reagents in the embodiments of this application were purchased commercially or prepared using conventional methods well known to those skilled in the art. The commercial Pt / C (20%) catalyst was purchased from Sigma-Aldrich; the foamed nickel was purchased from Lizhiyuan Technology Co., Ltd.; and the reaction raw materials such as nickel nitrate and ferric nitrate were purchased from Shanghai Aladdin Chemical Reagent Co., Ltd.

[0048] In a first aspect, embodiments of this application provide a carbon-nitrogen-doped polyoxometalate catalyst, including nickel foam and nano-pillar Finke-type carbon-nitrogen-doped polyoxometalate;

[0049] The nano-column Finke-type carbon-nitrogen-doped polyoxometalate is grown in situ on the surface of the nickel foam and forms a three-dimensional flower-like aggregate structure.

[0050] The nanopillar-shaped Finke-type carbon-nitrogen doped polyoxometalate was selected as Finke-type Ni4PMo9OCN.

[0051] In one aspect, it can change the d-band electronic state density and chemical environment of Ni and Mo, thereby adjusting the strength of MH and reducing its oxygen affinity, optimizing the electronic structure of the electrocatalyst, accelerating the electron transfer ability between substances, reducing the hydrogen binding free energy, and achieving a significant improvement in catalytic performance. In another aspect, it significantly increases the reactive surface area of ​​the catalyst, thereby greatly increasing the contact area with the electrolyte, thus effectively enhancing the catalyst's reactive activity and catalytic efficiency.

[0052] It should be noted that the Finke-type polyacid (K) produced in this application... 10 [Ni4(H2O)2(PMo9O 34 Using [2] as the research object, carbonitrided Finke-type molybdenum polyacid (Ni4PMo9OCN) was synthesized in a tube furnace under a saturated nitrogen atmosphere. Leveraging the molecular designability of polyacids, nickel was fixed in clusters on the polyacid framework, forming a binary alloy with the strongest hydrogen evolution catalytic activity—the Ni-Mo alloy. Ni atoms can alter the d-band electronic state density and chemical environment of Ni and Mo, thereby adjusting the intensity of MH and reducing its oxygen affinity. C coating provides a carbon layer to protect the stability of the electrode material while improving conductivity.

[0053] It should be noted that a nano-column-shaped carbon-nitrogen-doped polyoxometalate—Finke-type molybdenum polyacid (Ni4PMo9OCN)—was synthesized. This catalyst exhibits a nano-column structure and has rough small protrusions on its surface, thereby increasing the active area of ​​the reaction. This structural characteristic helps to enhance the reaction activity and catalytic efficiency.

[0054] Secondly, embodiments of this application provide a method for preparing the carbon-nitrogen-doped polyoxometalate catalyst described in the first aspect, the method comprising:

[0055] An aqueous solution of sodium molybdate was reacted in a mixed solvent of phosphoric acid and glacial acetic acid to yield Na8(HPMo9O). 34 );

[0056] The Na8(HPMo9O) 34 Aqueous solutions of nickel nitrate and nickel-iron foam were subjected to a hydrothermal reaction, filtered, and then vacuum dried to obtain Finke-type polyacid Ni4PMo9.

[0057] Under a nitrogen atmosphere, the Finke-type polyoxometalate Ni4PMo9, dicyandiamide, and iron powder are placed in sequence and calcined at high temperature, then cooled to room temperature to obtain the carbon-nitrogen doped polyoxometalate catalyst.

[0058] In this embodiment, the preferred molar ratio of sodium molybdate to phosphoric acid is 12:1. Excess phosphoric acid is used to ensure the successful production of Finke-type polyacid Ni4PMo9.

[0059] In the embodiments of this application, the nickel nitrate and Na8(HPMo9O) 34 The molar ratio of the two compounds is (4-6):1, more preferably 4:1. This is achieved through a simple one-step hydrothermal reaction of Finke-type polyacids (K... 10 [Ni4(H2O)2(PMo9O 34 [2] The carbonitrided polyoxometalate—Finke-type molybdenum polyoxometalate (Ni4PMo9OCN)—was loaded onto nickel foam and then carbonitrated in a tube furnace to prepare structurally stable nano-columnar carbonitrided polyoxometalate. Iron powder was added in this application to prevent oxidation.

[0060] It should be noted that the preparation method provided in this application is simple, produces no waste, is environmentally friendly, and has a novel structure, providing a practical strategy for developing high-performance, low-cost, and corrosion-resistant HER water electrolysis materials.

[0061] Thirdly, this application also provides the application of the carbon-nitrogen-doped polyoxometalate catalyst prepared by the method described in the second aspect in the electrocatalytic hydrogen evolution reaction. The carbon-nitrogen-doped polyoxometalate catalyst, as described above, possesses excellent reactivity and catalytic efficiency, good stability, and the advantage of being directly usable as a working electrode. Therefore, when the carbon-nitrogen-doped polyoxometalate catalyst prepared in this application is used in the alkaline electrolysis of water for the hydrogen evolution reaction, it exhibits good electrocatalytic performance.

[0062] The technical solution of this application will be further described below with reference to specific embodiments.

[0063] Example 1

[0064] This embodiment provides a method for preparing Al-carbon-nitrogen-doped polyoxometalate catalysts, specifically including:

[0065] S101: Dissolve 12 g Na2MoO4 in 15 ml of water, then add 0.3 ml H3PO4 and 2.2 ml glacial acetic acid to the solution sequentially. After vigorous stirring and filtration, a white crystalline precipitate is obtained, yielding Na8(HPMo9O) 34 );

[0066] S102: Weigh 4 mmol NiNO3·6H2O and dissolve it in 100 mL of deionized water. Add 1 mmol Na8(HPMo9O) to the above mixed solution. 34 (Nitrogen nitrate and Na8(HPMo9O)) 34 The molar ratio of the two components was 4:1, and the mixture was stirred until homogeneous. The solution was transferred to a polytetrafluoroethylene autoclave, and a piece of nickel-iron foam was placed inside. The autoclave was heated at 180 °C for 8 hours. After the autoclave cooled naturally to room temperature, the nickel-iron foam was rinsed several times with deionized water and dried in a vacuum drying oven at 60 °C for later use. This yielded Finke-type polyacid-supported Ni4PMo9 on nickel foam.

[0067] S103: Weigh dicyandiamide into a quartz boat, and place it in a tube furnace in the following order: 1 g Finke-type polyoxometalate Ni4PMo9, 1.5 g dicyandiamide, and 0.4 g reduced iron powder (the mass ratio of Finke-type polyoxometalate Ni4PMo9 to dicyandiamide is 1:1.5). Under a saturated nitrogen atmosphere, the temperature is increased to 600 ℃ at a programmed rate of 3 ℃ / min, and then held for 120 min for high-temperature nitriding. After the tube furnace cools down to room temperature naturally, Al-carbon-nitrogen doped polyoxometalate—Finke-type molybdenum polyoxometalate (Ni4PMo9OCN) is obtained.

[0068] Example 2

[0069] This embodiment provides a material preparation method, component ratio, preparation operation, and process parameters that are basically the same as those in Example 1. The difference is that in this embodiment, the mass ratio of Finke-type polyacid Ni4PMo9 to dicyandiamide is 1:1 (1 g Finke-type polyacid Ni4PMo9, 1 g dicyandiamide), which yields A2-carbon nitrogen-doped polyoxometalate.

[0070] Example 3

[0071] This embodiment provides a material preparation method, component ratio, preparation operation, and process parameters that are basically the same as in Example 1. The difference lies in the nickel nitrate and Na8(HPMo9O) used in this embodiment. 34 The molar ratio of 6 mmol NiNO3·6H2O to 1 mmol Na8(HPMo9O) is 6:1. 34 Without carbonitriding, A3-polyoxometalate is obtained.

[0072] Example 4

[0073] This embodiment provides a material preparation method, component ratio, preparation operation, and process parameters that are basically the same as in Example 1. The difference lies in the nickel nitrate and Na8(HPMo9O) used in this embodiment. 34The hydrothermal reaction was carried out for 12 hours without carbonitriding treatment, thus obtaining A4-polyoxometalate.

[0074] Example 5

[0075] This embodiment provides a material preparation method, component ratio, preparation operation, and process parameters that are basically the same as in Example 1. The difference lies in the nickel nitrate and Na8(HPMo9O) used in this embodiment. 34 The molar ratio of the two components is 6:1, the hydrothermal reaction time is 12 h, and no carbonitriding treatment is performed to obtain A5-polyoxometalate.

[0076] Meanwhile, to verify the electrochemical performance of the carbon-nitrogen-doped polyoxometalate catalysts prepared in the above embodiments, this application provides the following comparative examples for detailed illustration.

[0077] Comparative Example 1

[0078] This comparative example provides a material preparation method, component ratio, preparation operation, and process parameters that are basically the same as those in Example 1. The difference is that the third carbon and nitrogen doping step is not performed in this comparative example. The Finke-type polyacid Ni4PMo9 obtained in the second step is compared and referred to as B1-catalyst (Ni4PMo9O).

[0079] Comparative Example 2

[0080] This comparative example provides a method for preparing the B2-catalyst (PMo9CN), specifically including:

[0081] S501: Dissolve 12 g Na2MoO4 in 15 ml of water, then add 0.3 ml H3PO4 and 2.2 ml glacial acetic acid to the solution sequentially. After vigorous stirring and filtration, a white crystalline precipitate is obtained, yielding Na8(HPMo9O) 34 );

[0082] S502: Weigh the keggin type polyacid Na8 (HPMo9O 34 Dissolve the compound in 100 mL of deionized water, transfer the liquid to a polytetrafluoroethylene autoclave, place a piece of treated nickel foam inside, and heat at 180 °C for 8 h. After the autoclave has cooled to room temperature, rinse the reacted nickel foam several times with deionized water and dry it in a vacuum drying oven at 60 °C for later use. This yields Finke-type polyacid-supported PMo9 on nickel foam.

[0083] S503: Weigh dicyandiamide into a quartz boat, and place it in a tube furnace in the order of Finke-type polyacid PMo9, dicyandiamide, and reduced iron powder. Under a saturated nitrogen atmosphere, the temperature is increased to 600 ℃ by a programmed heating rate of 3 ℃ / min, and then held for 120 min for high-temperature nitriding. After the tube furnace cools down to room temperature naturally, B2-catalyst (PMo9CN) is obtained.

[0084] Comparative Example 3

[0085] This comparative example uses commercial platinum-carbon Pt / C (20%) for direct comparison.

[0086] To verify the morphology and structure of the carbon-nitrogen-doped polyoxometalate catalyst prepared in the embodiments of this application, the structure of the electrocatalyst prepared in the embodiments was characterized, and the results were as follows: Figure 1-2 As shown.

[0087] according to Figure 1 It can be seen that, Figure 1 In the electrocatalyst, it can be clearly observed that Finke-type carbon-nitrogen doped polyoxometalates grow on nickel foam; Figure 1 b) clearly shows the three-dimensional flower-like aggregates formed by the assembly of nano-columns; Figure 1 c) After carbon and nitrogen doping, the surface of the nanopillars has obvious small protrusion structures, which increases their contact area with the electrolyte.

[0088] according to Figure 2 It can be seen that, Figure 2 a) and Figure 2 b) and Figure 1 The structures are basically the same. Figure 2 c) It is undoped of carbon and nitrogen and has a smooth and flat surface.

[0089] To verify the composition of the carbon-nitrogen-doped polyoxometalate catalyst prepared in the embodiments of this application, elemental mapping distribution and content tests were performed on the electrocatalyst structure prepared in the embodiments. The results are as follows: Figure 3-5 As shown.

[0090] according to Figure 3 and 4 It is evident that N, O, Ni, Mo, and C elements coexist in the carbon-nitrogen-doped polyoxometalate catalyst.

[0091] according to Figure 5 It can be seen that its characteristic peaks include the (002) characteristic crystal plane (13.67°) of 2H type molybdenum disulfide, the (100) characteristic crystal plane of molybdenum disulfide—32.46°, the (110) characteristic crystal plane of β type nickel sulfide—18.60°, the (021) characteristic crystal plane of nickel sulfide—35.90°, etc.

[0092] Meanwhile, the active specific surface area of ​​the carbon-nitrogen-doped catalyst was characterized, and the surface area of ​​the carbon-nitrogen-doped polyoxometalate catalyst was 25.520 m². 2 / g, while the surface area of ​​the B1-catalyst (Ni4PMo9O) is 0.1268 m². 2 / g, it can be seen that carbon and nitrogen doping significantly increases the active specific surface area of ​​the catalyst, thereby effectively improving the electrochemical performance of the catalyst.

[0093] Meanwhile, the prepared catalyst was subjected to Raman spectroscopy, according to... Figure 6 It was found that Mo=O bonds were formed in in-situ Raman spectroscopy: 1. Enhanced electron transfer: The oxygen atom in the Mo=O bond has high electronegativity, which attracts electrons from molybdenum atoms, reducing the electron cloud density around the molybdenum atoms and thus promoting electron transfer from molybdenum atoms to nickel atoms in the alloy. This electron transfer can accelerate the transfer of electrons between the electrode surface and the reaction intermediates, reduce the charge transfer resistance in the HER process, improve the reaction kinetic rate, and promote water dissociation and proton supply. 2. The presence of Mo=O bonds may promote hydrogen spillover. On the alloy surface, hydrogen atoms adsorbed on molybdenum atoms can more easily spill over to nickel atoms or other active sites through the bridging effect of Mo=O bonds, thereby accelerating hydrogen diffusion and reaction and improving HER efficiency. This hydrogen spillover effect can effectively solve the problem that protons cannot be transferred to the active sites exposed on the catalyst surface in a timely and sufficient manner under high current density. 3. Stabilized surface structure: Mo=O bonds can enhance the surface structural stability of nickel-molybdenum-nitrogen alloys, making them less prone to aggregation, dissolution, or structural deformation during long-term reactions, thereby maintaining the catalytic performance of the catalyst. Meanwhile, the oxygen atoms in the Mo=O bond can also form chemical bonds with other atoms on the alloy surface, further improving the alloy's oxidation resistance and reducing catalyst deactivation caused by oxidation during the HER reaction.

[0094] Catalyst deactivation occurs during the HER reaction due to oxidation. To verify the efficient application of the carbon-nitrogen-doped polyoxometalate Ni4PMo9OCN prepared in the embodiments of this application in anion exchange water electrolysis, a three-electrode system test device was assembled using the Finke-type Ni4PMo9OCN catalyst prepared in the embodiments as the cathode, a platinum-carbon electrode as the anode, and 1 M KOH solution as the electrolyte. The electrolytic water electrolysis performance was tested, and the electrocatalytic hydrogen evolution performance was tested in 1.0 mol / L potassium hydroxide solution at an operating temperature of 25 °C. The results are as follows: Figures 7 to 17 As shown. All voltages are relative to a standard hydrogen electrode.

[0095] It should be noted that nickel-iron LDH is obtained by dissolving nickel nitrate and ferric nitrate in 100 ml of deionized water at a molar ratio of 3:1, transferring the solution to a polytetrafluoroethylene autoclave, placing a piece of foamed nickel-iron in the autoclave, and heating at 120 °C for 12 h.

[0096] This study aims to test the oxygen reduction activity of the prepared catalysts, including Ni4PMo9OCN, Ni4PMo9O without carbonitridation, PMo9CN carbonitrided with keggin-type polyacids, and commercial platinum-carbon Pt / C (20%)-10 mg. All electrochemical tests were performed at room temperature using a CS350M electrochemical workstation (Wuhan Koster Instruments Co., Ltd.) with a three-electrode setup. The three-electrode system used catalyst-containing nickel foam (NF) as the working electrode (1 × 1 cm²). 2 A new saturated Hg / HgO electrode was used as the reference electrode, and a platinum sheet was used as the counter electrode. Linear sweep voltammetry (LSV) measurements for the HER assay were performed in 1.0 M KOH solution at a scan rate of 10 mV·s. -1 .

[0097] according to Figure 7 As can be seen from the comparison diagram of precursors without carbonitriding, the linear sweep voltammetry (LSV) curves of the B1-catalyst, A1-carbonitrid doped polyoxometalate, and A2-carbonitrid doped polyoxometalate prepared in this application show that the A1-carbonitrid doped polyoxometalate exhibits the best HER performance.

[0098] according to Figure 8 It can be seen that when the current density is 100 mA·cm -2 At that time, the overpotential of A1-carbon-nitrogen-doped polyoxometalate-Finke type molybdenum polyacid (Ni4PMo9OCN) prepared in this application was 60 mV, the overpotential of B1-catalyst (Ni(4mmol)-Mo 180° 8h) was 308 mV, and the overpotential of A2-carbon-nitrogen-doped polyoxometalate was 177 mV.

[0099] according to Figure 9 As can be seen, the linear sweep voltammetric curves (LSV curves) of the B1-catalyst, A3-polyoxometalate, A4-polyoxometalate, and A5-polyoxometalate prepared in this application were used to screen out the optimal reaction conditions. Among them, the B1-catalyst represents nickel nitrate and Na8(HPMo9O) 34 The optimal performance is achieved when the molar ratio of the two components is 4:1 and the reaction time is 8 h.

[0100] according to Figure 10 It can be seen that when the current density is 100 mA·cm -2At that time, the overpotential of the B1-catalyst prepared in this application was 308 mV, the overpotential of the A3-polyoxometalate was 334 mV, the overpotential of the A4-polyoxometalate was 329 mV, and the overpotential of the A5-polyoxometalate was 345 mV, thus the optimal reaction conditions were screened.

[0101] according to Figure 11 It is evident that the Al-carbon-nitrogen-doped polyoxometalate—Finke-type molybdenum polyoxometalate (Ni4PMo9OCN) prepared in this application exhibits the best HER performance in the linear sweep voltammetry (LSV) curve.

[0102] according to Figure 12 As can be seen, the Tafel slope of the Al-carbon-nitrogen-doped polyoxometalate—Finke-type molybdenum polyacid (Ni4PMo9OCN) prepared in this application is as low as 66.54 mV·dec. -1 The Tafel slope of the B1-catalyst (Ni4PMo9) is as low as 164.10 mV·dec. -1 The Tafel slope of the B2-catalyst (PMo9CN) was as low as 163.45 mV·dec. -1 The Tafel slope for Pt / C (20%) is as low as 129.04 mV·dec -1 .

[0103] according to Figure 13 It can be seen that when the current density is 10 mA·cm -2 At the same time, the overpotential of Al-carbon-nitrogen-doped polyoxometalate-Finke type molybdenum polyacid (Ni4PMo9OCN) prepared in this application is 6 mV, the overpotential of B1-catalyst (Ni4PMo9O) is 180 mV, the overpotential of B2-catalyst (PMo9CN) is 130 mV, and the overpotential of Pt / C (20%) is 124 mV.

[0104] according to Figure 14 As can be seen from the double-layer capacitance diagram (Cdl), it is evident that Al-carbon-nitrogen-doped polyoxometalate—Finke-type molybdenum polyacid (Ni4PMo9OCN)—has superior electrochemical hydrogen evolution performance.

[0105] Electrochemical test results indicate that in the HER alkaline water electrolysis reaction, the overpotential of the Ni4PMo9OCN catalyst after 90% IR compensation is 10 mA·cm⁻¹. -2 Under these conditions, only 6 mV, 1000 mA·cm -2 The voltage is only 204 mV, and the Tafel slope is as low as 66.54 mV·dec. -1Compared to the non-carbonitrified polyacid Ni4PMo9O catalyst, Ni4PMo9OCN exhibits a faster charge transfer rate, a higher electrocatalytic active surface area, and stable electrochemical durability. Furthermore, compared to the non-carbonitrified polyacid Ni4PMo9O catalyst, the cdl value in the ESCA plot is significantly increased, nearly 25 times. This is due to the formation of small protrusions on the surface after carbonitrification, which increases the contact area with the electrolyte.

[0106] To verify the cycling stability of the carbon-nitrogen-doped polyoxometalate Ni4PMo9OCN prepared in the embodiments of this application in anion-exchange electrolysis of water, this experimental example uses a self-assembled electrolyzer. Related tests were conducted at 25 °C using a CT6000A Landian electrochemical workstation (Wuhan Landian Co., Ltd.). Using nickel-iron LDH as the anode, Ni4PMo9OCN as the cathode, a PiperION self-supporting thick 60 μm anion exchange membrane as the diaphragm, and 1 M KOH solution as the electrolyte, the electrolyzer device was assembled. Its electrode alkaline water electrolysis hydrogen production stability performance was tested at 60 °C, and the results are as follows: Figure 15 As shown.

[0107] according to Figure 15 It can be seen that in the self-assembled AEM electrolytic cell at 60 ℃, 25 A (10000 A / m) 2 At the current density, the voltage is only 2.11 V, and the electrolyzer operates stably for over 750 h with a performance degradation of only 3.34%. Compared with traditional transition metal catalysts, the experimental results show that Al-carbon nitrogen-doped polyoxometalate-Finke type molybdenum polyacid (Ni4PMo9OCN) has more stable anion exchange water electrolysis catalytic performance.

[0108] Furthermore, after reacting in the electrolytic cell for 750 h, the Al-carbon-nitrogen-doped polyoxometalate was subjected to SEM and mapping tests, and the test results are as follows: Figure 16-17 As shown.

[0109] according to Figure 16 and 17 It can be seen that after 750 h of cyclic reaction, the material still maintains a columnar structure, and the surface is rougher and more granular, which is conducive to further expanding the active surface area of ​​the reaction. Furthermore, a comparison of the elemental ratios before and after the reaction revealed that a large amount of molybdenum dissolved out, which may be due to the formation of high-valence MoO4. - This is more beneficial for improving the conductivity of the material.

[0110] The B1-catalyst (Ni4PMo9O) electrocatalyst prepared in Comparative Example 1 differs from the Finke-type molybdenum polyacid (Ni4PMo9OCN) obtained in Example 1 in that it was not carbon-nitrogen doped. Carbon-nitrogen doping reduces the overpotential, Tafel slope, and electrochemical impedance of the electrocatalyst. The B2-catalyst (PMo9CN) obtained in Comparative Example 2 differs from the Finke-type molybdenum polyacid (Ni4PMo9OCN) obtained in Example 1 in that it did not introduce a Ni source. Due to the synergistic effect between Ni and Mo, the H adsorption energy is optimized, and there are many active sites and surface defects, thereby improving its hydrogen evolution performance. Comparative Example 3 uses commercial platinum-carbon Pt / C (20%) for direct comparison. The Finke-type molybdenum polyacid (Ni4PMo9OCN) provided in this application is significantly superior in electrochemical performance.

[0111] Therefore, this application provides a carbon-nitrogen-doped polyoxometalate catalyst, comprising nickel foam and a Finke-type carbon-nitrogen-doped polyoxometalate in situ grown on the surface of the nickel foam; the Finke-type carbon-nitrogen-doped polyoxometalate is Finke-type Ni4PMo9OCN. On one hand, the synergistic effect between Ni and Mo optimizes the H adsorption energy; carbon-nitrogen doping alters the d-band electronic state density and chemical environment of Ni and Mo, thereby adjusting the intensity of MH and reducing its oxygen affinity, optimizing the electronic structure of the electrocatalyst, accelerating the electron transfer ability between substances, reducing the hydrogen binding free energy, effectively improving atom utilization, and achieving a significant improvement in catalytic performance, showing broad application prospects in electrocatalytic hydrogen evolution.

[0112] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0113] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this application.

Claims

1. A method for preparing a carbon-nitrogen-doped polyoxometalate catalyst, characterized in that, The preparation method includes: An aqueous solution of sodium molybdate was reacted in a mixed solvent of phosphoric acid and glacial acetic acid to yield Na8(HPMo9O). 34 ); The Na8(HPMo9O) 34 Aqueous solutions of nickel nitrate and nickel foam were subjected to hydrothermal reaction, filtered, and then vacuum dried to obtain Finke-type polyacid Ni4PMo9. Under a nitrogen atmosphere, the Finke-type polyoxometalate Ni4PMo9, dicyandiamide, and iron powder were placed in sequence and calcined at high temperature, then cooled to room temperature to obtain the carbon-nitrogen doped polyoxometalate catalyst. The nickel nitrate and Na8(HPMo9O) 34 The molar ratio of (4-6):1; The hydrothermal reaction is carried out at a temperature of 120-180℃ for 8-12 hours. The mass ratio of the Finke-type polyacid Ni4PMo9 to dicyandiamide is 1:1.

5.

2. The method for preparing the carbon-nitrogen-doped polyoxometalate catalyst according to claim 1, characterized in that, The molar ratio of sodium molybdate to phosphoric acid is 12:

1.

3. The method for preparing the carbon-nitrogen-doped polyoxometalate catalyst according to claim 1, characterized in that, The nickel nitrate and Na8(HPMo9O) 34 The molar ratio of ) is 4:

1.

4. The method for preparing the carbon-nitrogen-doped polyoxometalate catalyst according to claim 1, characterized in that, The high-temperature calcination was carried out at 600°C for 2 hours.

5. A carbon-nitrogen-doped polyoxometalate catalyst prepared by the method described in any one of claims 1-4, characterized in that, Including nickel foam and Finke-type carbon-nitrogen doped polyoxometalates in nanopillars; The nano-column Finke-type carbon-nitrogen-doped polyoxometalates are grown in situ on the surface of the nickel foam and form a three-dimensional flower-like aggregate structure. The nanopillar-shaped Finke-type carbon-nitrogen doped polyoxometalate is Finke-type Ni4PMo9OCN.

6. The carbon-nitrogen-doped polyoxometalate catalyst according to claim 5, characterized in that, The outer surface of the nanopillar-shaped Finke-type carbon-nitrogen doped polyoxometalate has rough protrusions.

7. The application of a carbon-nitrogen-doped polyoxometalate catalyst prepared by any of the methods described in claims 1-4 in electrocatalytic hydrogen evolution.

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