A bifunctional cobalt-nickel-phosphorus catalyst, a preparation method and application thereof

Abstract

The present application relates to the technical field of electrocatalysis, and provides a bifunctional cobalt-nickel-phosphorus catalyst as well as a preparation method and application thereof. The present application uses cobalt nitrate hexahydrate, nickel nitrate hexahydrate, urea and ammonium fluoride as reaction raw materials, dissolves the raw materials, then adds a pretreated nickel foam substrate, and then performs a hydrothermal reaction at 120-140 DEG C. The obtained product is washed and dried to obtain a precursor. The precursor is subjected to a gas phase phosphorization treatment with sodium hypophosphite as a phosphorus source to obtain a bifunctional CoNiP / NF catalyst. The CoNiP / NF catalyst prepared by the present application exhibits a low hydrogen evolution overpotential and excellent electrocatalytic activity in full pH hydrogen evolution, and also exhibits a low hydrogen evolution overpotential and excellent catalytic activity in hydrazine hydrate oxidation reaction, and is a bifunctional catalyst applied to electrocatalytic hydrogen evolution and hydrazine hydrate oxidation.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalysis technology, and particularly relates to a bifunctional cobalt-nickel-phosphorus catalyst, its preparation method, and its application. Background Technology

[0002] Hydrogen energy, as a promising clean energy source, has shown great application potential in energy conversion and efficient storage. Water electrolysis for hydrogen production, due to its green and efficient characteristics, is considered one of the key pathways for large-scale hydrogen production in the future. However, the core challenge currently lies in developing electrocatalysts that combine high efficiency and high stability to ensure long-term reliability and economic viability in industrial applications. With the continuous growth of global demand for clean energy, the development of efficient and stable electrocatalysts has become crucial for driving the development of hydrogen energy technology. In recent years, transition metal phosphides have shown great application potential in the electrocatalytic hydrogen evolution reaction (HER) due to their metalloid conductivity, suitable hydrogen adsorption free energy, and abundant tunable electronic structure. Among them, cobalt-based phosphides, with their unique electronic orbital configuration and high catalytic activity, are important candidate materials to replace noble metal catalysts; while nickel-based phosphides occupy an important position in transition metal phosphide systems due to their excellent chemical stability, abundant active sites, and lower cost. However, simple cobalt-based or nickel-based phosphides still have significant limitations in practical applications. Single-component cobalt phosphides often suffer from sluggish kinetics due to excessive hydrogen adsorption, while single-component nickel phosphides have relatively insufficient active sites and electron transport efficiency. Neither can simultaneously meet the industrial requirements of efficient hydrogen evolution and long-term stable operation. By constructing cobalt-nickel phosphide (CoNiP) through a multi-component composite of cobalt and nickel, the synergistic electronic regulation and lattice distortion effects between the two metals are utilized to synergistically optimize the Fermi level and hydrogen adsorption free energy of the material. This significantly increases the density of active sites and improves overall conductivity, thereby achieving a breakthrough in electrocatalytic hydrogen evolution performance.

[0003] Despite the theoretical advantages of CoNiP multi-phosphide catalysts, a series of key technical challenges remain to be overcome before their industrial application can be realized. First, the current research focus remains on how to construct CoNiP catalysts with high specific surface area and porous hierarchical structures through precise control of the preparation process and microstructure to fully expose active sites and accelerate mass transfer. Second, maintaining the crystal structure integrity and surface chemical stability of CoNiP catalysts under the mainstream alkaline / neutral electrolyte environment, inhibiting the leaching and reconstruction of metal elements, and thus slowing down catalytic performance degradation, is a core bottleneck restricting their practical application. Therefore, developing a highly efficient CoNiP-based electrocatalyst that combines high activity, high conductivity, and strong structural stability is of great significance for promoting the practical application of water electrolysis for hydrogen production. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a bifunctional cobalt-nickel-phosphorus catalyst, its preparation method, and its application, aiming to solve the problems mentioned in the background art.

[0005] In a first aspect, the present invention provides a method for preparing a bifunctional cobalt-nickel-phosphorus catalyst, using cobalt nitrate hexahydrate, nickel nitrate hexahydrate, urea and ammonium fluoride as reactants, adding a pretreated foamed nickel substrate after dissolution, and then carrying out a hydrothermal reaction at 120-140°C. The resulting product is washed and dried to obtain a precursor, and the precursor is subjected to gas-phase phosphating treatment using sodium hypophosphite as a phosphorus source to obtain a bifunctional CoNiP / NF catalyst (bifunctional cobalt-nickel-phosphorus catalyst).

[0006] Furthermore, the specific steps include: Step S1: The nickel foam substrate is ultrasonically cleaned with hydrochloric acid, ethanol and deionized water respectively to remove surface oxides and impurities, and a pretreated nickel foam substrate is obtained. Step S2: Dissolve cobalt nitrate hexahydrate, nickel nitrate hexahydrate, urea and ammonium fluoride in deionized water and stir continuously until fully dissolved. Then pour the solution into a polytetrafluoroethylene liner, place the pretreated nickel foam substrate inside, and carry out a hydrothermal reaction at 120-140℃ for 6-8 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature. Then wash it alternately with deionized water and anhydrous ethanol, and dry it to obtain the CoNi / NF precursor. Step S3: Place the CoNi / NF precursor in a ceramic boat, add sodium hypophosphite upstream of the tube furnace and the CoNi / NF precursor downstream, and program the temperature to 300-350℃ under inert gas protection, hold for 2-4 hours for phosphating treatment to obtain the bifunctional CoNiP / NF catalyst.

[0007] Further, step S1 specifically involves immersing the nickel foam substrate sequentially in 2-3M hydrochloric acid, anhydrous ethanol, and deionized water, performing ultrasonic cleaning for 15 minutes each, and then drying it in a vacuum drying oven at 60°C to obtain the pretreated nickel foam substrate.

[0008] Further, in step S2, the ratio of cobalt nitrate hexahydrate: nickel nitrate hexahydrate: urea: ammonium fluoride: deionized water is 2 mmol: 2 mmol: 2 mmol: 10 mmol: 80 mL.

[0009] Further, step S2 specifically involves dissolving cobalt nitrate hexahydrate, nickel nitrate hexahydrate, ammonium fluoride, and urea in deionized water, stirring continuously until completely dissolved, and then immersing the solution into the prepared nickel foam substrate; placing it in a sealed stainless steel high-pressure reactor lined with polytetrafluoroethylene, and carrying out a hydrothermal reaction at 120°C for 6 hours. After the reaction is completed, the reaction system is allowed to cool naturally to room temperature, and is washed three times alternately with deionized water and anhydrous ethanol, and finally dried under vacuum at 60°C for 10 hours to obtain the CoNi / NF precursor.

[0010] Furthermore, in step S3, the temperature rise rate of the programmed temperature rise is 2℃ / min.

[0011] Further, step S3 specifically involves placing the CoNi / NF precursor in a ceramic boat, adding 1g of sodium hypophosphite upstream of a tube furnace, and adding the CoNi / NF precursor downstream. The temperature is then programmed to reach 350℃ under inert gas protection at a heating rate of 2℃ / min, and held at that temperature for 2 hours for phosphating treatment, ultimately obtaining a bifunctional CoNiP / NF catalyst.

[0012] Furthermore, the inert gas is nitrogen or argon.

[0013] Secondly, the present invention also provides a bifunctional cobalt-nickel-phosphorus catalyst, which is prepared by a method for preparing a bifunctional cobalt-nickel-phosphorus catalyst, and has a nanoflower structure, wherein the nanoflower structures are interconnected to form a three-dimensional porous network structure.

[0014] Thirdly, the present invention also provides the application of a bifunctional cobalt-nickel-phosphorus catalyst in hydrogen evolution and hydrazine hydrate oxidation in a full-pH electrolyte.

[0015] The present invention has the following beneficial effects: (1) The preparation method is simple, the process is easy to control, the cycle is short, the cost is low, the production efficiency is high, and it is suitable for industrial production. Moreover, it can make the catalyst maintain stability and activity in a full pH environment, and the improved corrosion resistance ensures the reliability of the catalyst in long-term use. The prepared CoNiP / NF catalyst exhibits a low hydrogen evolution overpotential and excellent catalytic activity in electrocatalytic hydrogen evolution, and also exhibits a low overpotential and excellent catalytic activity in the oxidation of hydrazine hydrate. It is a bifunctional catalyst for electrocatalytic hydrogen evolution and oxidation of hydrazine hydrate. By replacing the traditional oxygen evolution reaction (OER) with the oxidation of hydrazine hydrate, not only is the reaction efficiency improved, but also the environmental friendliness is enhanced, and high-value-added products are generated.

[0016] (2) Adding appropriate concentrations of ammonium fluoride and urea to the hydrothermal reaction system can achieve a good synergistic effect. Urea slowly hydrolyzes under hydrothermal conditions, continuously and uniformly releasing hydroxide ions, gently increasing the pH of the system, avoiding rapid aggregation caused by local strong alkali, which is conducive to the formation of products with good dispersibility, high crystallinity, and regular morphology. It can also act as a ligand to regulate the anisotropic growth of crystals. However, when the amount of urea is too large, it will cause the product to crystallize too strongly or become a mixed phase. The fluoride ions dissociated from ammonium fluoride can act as a mild etching agent to selectively etch specific crystal faces and induce the formation of hollow, porous or highly active crystal face exposed nanostructures. It can also act as a mineralizer to promote the dissolution and recrystallization of precursors and reduce reaction conditions. Some fluoride ions can also be incorporated into the lattice in situ to achieve fluorine doping, optimize the electronic structure and stability of the material. The combination of the two can not only accurately control the morphology, crystal phase and pore structure of the product, but also improve the crystallinity, specific surface area and electrochemical properties of the material. It is a commonly used and efficient composite control strategy in the hydrothermal synthesis of nanofunctional materials.

[0017] (3) Through the synergistic effect of cobalt and nickel, and the doping of phosphorus, the electronic structure and reaction pathway of the catalyst are further optimized, promoting rapid electron transfer and significantly improving the overall catalytic efficiency. The introduction of cobalt effectively modulates the electronic structure of nickel-based materials, enhancing the adsorption and dissociation capabilities of hydrogen, thereby improving catalytic activity. The combination of cobalt and nickel-based materials, and the introduction of phosphorus, not only enhance the conductivity of the catalyst, but also significantly improve its catalytic activity, making the catalyst exhibit higher efficiency and stability in electrochemical reactions. Attached Figure Description

[0018] Exemplary embodiments of the present invention can be more fully understood by referring to the following figures: Figure 1 This is a scanning electron microscope image of the bifunctional CoNiP / NF catalyst prepared in Example 1 of the present invention.

[0019] Figure 2 This is a scanning electron microscope image of the bifunctional CoNi / NF catalyst prepared in Comparative Example 1 of this invention.

[0020] Figure 3 This is an image showing the elemental (Co) distribution of the CoNiP / NF catalyst prepared in Example 1 of this invention.

[0021] Figure 4 This is an image showing the elemental (Ni) distribution of the CoNiP / NF catalyst prepared in Example 1 of this invention.

[0022] Figure 5 This is an image showing the elemental (P) distribution of the CoNiP / NF catalyst prepared in Example 1 of this invention.

[0023] Figure 6 The LSV curves and 45-hour stability of the catalysts prepared in Comparative Examples 1, 2, 3 and 1 of this invention under alkaline conditions (1M KOH) are shown below. Figure 6 In the figure, A represents the LSV curve. Figure 6 B in the equation represents stability analysis.

[0024] Figure 7 The LSV curves and stability over 60 hours of the catalysts prepared in Comparative Examples 1, 2, 3, and 1 are shown. Figure 7 In the figure, A represents the LSV curve. Figure 7 B in the equation represents stability analysis.

[0025] Figure 8 The LSV curves and 18-hour stability of the catalysts prepared in Comparative Examples 1, 2, 3 and 1 are shown. Figure 8 In the figure, A represents the LSV curve. Figure 8 B in the equation represents stability analysis.

[0026] Figure 9 The LSV curves and 70-hour stability of the catalysts prepared in Comparative Examples 1, 2, 3, and 1 are shown. Figure 9 In the figure, A represents the LSV curve. Figure 9 B in the equation represents stability analysis.

[0027] Figure 10 The bifunctional CoNiP / N catalyst prepared for Example 1 of the invention was tested at 100 mA cm⁻¹. -2 Potential displacement diagrams (HzOR and OER) under current density.

[0028] Figure 11 LSV diagrams of the bifunctional CoNiP / N catalyst prepared in Example 1 of the invention under the following conditions: anode basic, cathode basic, anode basic, cathode acidic, anode basic, cathode neutral, anode hydrazine hydrate basic, cathode neutral, anode hydrazine hydrate basic, cathode acidic, and anode hydrazine hydrate basic, cathode basic. Figure 11 (A in the text), and the stability in a flow cell (cathode acidic, anode alkaline hydrazine hydrate) at 50 mA ( Figure 11 (B in the middle).

[0029] Figure 12 This is a comparison diagram of the LSV of the catalysts prepared in Example 1 and Comparative Example 4 of the present invention. Detailed Implementation

[0030] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0032] This invention provides a method for preparing a bifunctional cobalt-nickel-phosphorus catalyst. Cobalt nitrate hexahydrate, nickel nitrate hexahydrate, urea, and ammonium fluoride are used as reactants. After dissolution, a pretreated nickel foam substrate is added, and a hydrothermal reaction is carried out at 120-140°C. The resulting product is washed and dried to obtain a precursor. The precursor is then subjected to gas-phase phosphating treatment using sodium hypophosphite as a phosphorus source to obtain a bifunctional CoNiP / NF catalyst (bifunctional cobalt-nickel-phosphorus catalyst).

[0033] In some embodiments, the following steps are specifically included: Step S1: The nickel foam substrate is ultrasonically cleaned with hydrochloric acid, ethanol and deionized water respectively to remove surface oxides and impurities, and a pretreated nickel foam substrate is obtained. Step S2: Dissolve cobalt nitrate hexahydrate, nickel nitrate hexahydrate, urea and ammonium fluoride in deionized water and stir continuously until fully dissolved. Then pour the solution into a polytetrafluoroethylene liner, place the pretreated nickel foam substrate inside, and carry out a hydrothermal reaction at 120-140℃ for 6-8 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature. Then wash it alternately with deionized water and anhydrous ethanol, and dry it to obtain the CoNi / NF precursor. Step S3: Place the CoNi / NF precursor in a ceramic boat, add sodium hypophosphite upstream of the tube furnace and the CoNi / NF precursor downstream, and program the temperature to 300-350℃ under inert gas protection, hold for 2-4 hours for phosphating treatment to obtain the bifunctional CoNiP / NF catalyst.

[0034] In some embodiments, step S1 specifically involves immersing the nickel foam substrate sequentially in 2-3M hydrochloric acid, anhydrous ethanol, and deionized water, performing ultrasonic cleaning for 15 minutes each, and then drying it in a vacuum drying oven at 60°C to obtain a pretreated nickel foam substrate.

[0035] In some embodiments, in step S2, the ratio of cobalt nitrate hexahydrate: nickel nitrate hexahydrate: urea: ammonium fluoride: deionized water is 2 mmol: 2 mmol: 2 mmol: 10 mmol: 80 mL.

[0036] In some embodiments, step S2 specifically involves: dissolving cobalt nitrate hexahydrate, nickel nitrate hexahydrate, ammonium fluoride, and urea in deionized water, stirring continuously until completely dissolved, and then immersing the solution into the treated nickel foam substrate; placing the solution in a sealed stainless steel high-pressure reactor lined with polytetrafluoroethylene, and performing a hydrothermal reaction at 120°C for 6 hours; after the reaction is completed, waiting for the reaction system to cool naturally to room temperature, washing it three times alternately with deionized water and anhydrous ethanol, and finally drying it under vacuum at 60°C for 10 hours to obtain the CoNi / NF precursor.

[0037] In some embodiments, in step S3, the temperature rise rate is 2°C / min.

[0038] In some embodiments, step S3 specifically involves: placing the CoNi / NF precursor in a ceramic boat, adding 1g of sodium hypophosphite upstream of a tube furnace, and adding the CoNi / NF precursor downstream. The temperature is then programmed to 350°C at a heating rate of 2°C / min under inert gas protection, and held at that temperature for 2 hours for phosphating treatment, ultimately obtaining a bifunctional CoNiP / NF catalyst.

[0039] In some embodiments, the inert gas is nitrogen or argon.

[0040] In some embodiments, the present invention provides a bifunctional cobalt-nickel-phosphorus catalyst, which is prepared by a method for preparing a bifunctional cobalt-nickel-phosphorus catalyst, and has a nanoflower structure, wherein the nanoflower structures are interconnected to form a three-dimensional porous network structure.

[0041] In some embodiments, the present invention provides the application of a bifunctional cobalt-nickel-phosphorus catalyst in hydrogen evolution and hydrazine hydrate oxidation in a full-pH electrolyte.

[0042] Example 1: (1) The nickel foam substrate was immersed in 3M hydrochloric acid, anhydrous ethanol and deionized water in sequence, and ultrasonically cleaned for 15 min each. Then it was dried in a vacuum drying oven at 60℃ to obtain the pretreated nickel foam substrate. (2) Dissolve 2 mmol of cobalt nitrate hexahydrate, 2 mmol of nickel nitrate hexahydrate, 2 mmol of urea, and 10 mmol of ammonium fluoride in 80 mL of deionized water and stir continuously for 3 hours to ensure complete dissolution. Then transfer the solution to a stainless steel high-pressure reactor lined with polytetrafluoroethylene and immerse it in the pretreated nickel foam substrate. After sealing the stainless steel high-pressure reactor, carry out a hydrothermal reaction at 120 °C for 6 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature. Then wash it three times with deionized water and anhydrous ethanol respectively. Finally, dry it under vacuum at 60 °C for 12 hours to obtain the CoNi / NF precursor. (3) Place the CoNi / NF precursor in a ceramic boat, add 1 gram of sodium hypophosphite upstream, and heat it to 350°C under nitrogen protection at a heating rate of 2°C / min. Then, keep it at this temperature for 2 hours for pyrolysis treatment to finally obtain the bifunctional CoNiP / NF catalyst.

[0043] Scanning electron microscopy (SEM) images of the bifunctional CoNiP / NF tandem catalyst prepared in Example 1 are shown below. Figure 1 As shown, the bifunctional CoNiP / NF catalyst possesses a nanosheet stack composed of cobalt and nickel sources. This unique morphology not only provides abundant active sites for the electrocatalytic hydrogen evolution reaction but also promotes electron transport, exhibiting excellent stability and environmental friendliness. This ensures the uniformity of the catalytic active sites, thereby significantly improving the overall performance of the catalyst.

[0044] Example 2: (1) The nickel foam substrate was sequentially immersed in 2M hydrochloric acid, anhydrous ethanol and deionized water, and ultrasonically cleaned for 15 min each, and then dried in a vacuum drying oven at 60℃. The pretreated nickel foam substrate was obtained. (2) Dissolve 2 mmol of cobalt nitrate hexahydrate, 2 mmol of nickel nitrate hexahydrate, 2 mmol of urea, and 10 mmol of ammonium fluoride in 80 mL of deionized water and stir continuously for 3 hours to ensure complete dissolution. Then transfer the solution to a stainless steel high-pressure reactor lined with polytetrafluoroethylene and immerse it in the pretreated nickel foam substrate. After sealing the stainless steel high-pressure reactor, carry out a hydrothermal reaction at 120 °C for 8 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature. Then wash it three times with deionized water and anhydrous ethanol respectively. Finally, dry it under vacuum at 60 °C for 10 hours to obtain the CoNi / NF precursor. (3) The CoNi / NF precursor was placed in a ceramic boat and heated to 300℃ under nitrogen protection at a heating rate of 2℃ / min. The temperature was then maintained at this temperature for 4 hours for pyrolysis treatment to finally obtain the bifunctional CoNiP / NF catalyst.

[0045] Example 3: (1) The nickel foam substrate was sequentially immersed in 3M hydrochloric acid, anhydrous ethanol and deionized water, and ultrasonically cleaned for 15 min each, and then dried in a vacuum drying oven at 60℃. The pretreated nickel foam substrate was obtained. (2) Dissolve 2 mmol of cobalt nitrate hexahydrate, 2 mmol of nickel nitrate hexahydrate, 2 mmol of urea, and 10 mmol of ammonium fluoride in 80 mL of deionized water and stir continuously for 3 hours to ensure complete dissolution. Then transfer the solution to a stainless steel high-pressure reactor lined with polytetrafluoroethylene and immerse it in the pretreated nickel foam substrate. After sealing the stainless steel high-pressure reactor, carry out a hydrothermal reaction at 120 °C for 7 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature. Then wash it three times with deionized water and anhydrous ethanol respectively. Finally, dry it under vacuum at 60 °C for 10 hours to obtain the CoNi / NF precursor. (3) The CoNi / NF precursor was placed in a ceramic boat and heated to 300℃ under nitrogen protection at a heating rate of 2℃ / min. The temperature was then maintained at this temperature for 4 hours for pyrolysis treatment to finally obtain the bifunctional CoNiP / NF catalyst.

[0046] Comparative Example 1: (1) The nickel foam substrate was sequentially immersed in 3M hydrochloric acid, anhydrous ethanol and deionized water, and ultrasonically cleaned for 15 min each, and then dried in a vacuum drying oven at 60℃. The pretreated nickel foam substrate was obtained.

[0047] (2) Dissolve 2 mmol of cobalt nitrate hexahydrate, 2 mmol of nickel nitrate hexahydrate, 2 mmol of urea, and 10 mmol of ammonium fluoride in 80 mL of deionized water and stir continuously for 3 hours to ensure complete dissolution. Then transfer the solution to a stainless steel high-pressure reactor lined with polytetrafluoroethylene and immerse it in the pretreated nickel foam substrate. After sealing the stainless steel high-pressure reactor, carry out a hydrothermal reaction at 120 °C for 6 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature. Then wash it three times alternately with deionized water and anhydrous ethanol. Finally, dry it under vacuum at 60 °C for 10 hours to obtain the CoNi / NF precursor.

[0048] Comparative Example 2: (1) The nickel foam substrate was sequentially immersed in 3M hydrochloric acid, anhydrous ethanol and deionized water, and ultrasonically cleaned for 15 min each, and then dried in a vacuum drying oven at 60℃. The pretreated nickel foam substrate was obtained. (2) Dissolve 2 mmol of cobalt nitrate hexahydrate, 2 mmol of urea, and 10 mmol of ammonium fluoride in 80 mL of deionized water and stir continuously for 3 hours to ensure complete dissolution. Then transfer the solution to a stainless steel high-pressure reactor lined with polytetrafluoroethylene and immerse it in a pretreated nickel foam substrate. After sealing the stainless steel high-pressure reactor, perform a hydrothermal reaction at 120°C for 6 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature. Then wash the system three times alternately with deionized water and anhydrous ethanol. Finally, dry the system under vacuum at 60°C for 10 hours to obtain the Co / NF precursor. (3) The Co / NF precursor was placed in a ceramic boat and heated to 350°C under nitrogen protection at a heating rate of 2°C / min. The temperature was then maintained at this temperature for 2 hours for pyrolysis treatment to finally obtain the bifunctional CoP / NF catalyst.

[0049] Comparative Example 3: (1) The nickel foam substrate was sequentially immersed in 3M hydrochloric acid, anhydrous ethanol and deionized water, and ultrasonically cleaned for 15 min each, and then dried in a vacuum drying oven at 60℃. The pretreated nickel foam substrate was obtained. (2) Dissolve 2 mmol of nickel nitrate hexahydrate, 2 mmol of urea, and 10 mmol of ammonium fluoride in 80 mL of deionized water and stir continuously for 3 hours to ensure complete dissolution. Then transfer the solution to a stainless steel high-pressure reactor lined with polytetrafluoroethylene and immerse it in the pretreated nickel foam substrate. After sealing the stainless steel high-pressure reactor, carry out a hydrothermal reaction at 120°C for 6 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature. Then wash it three times with deionized water and anhydrous ethanol respectively. Finally, dry it under vacuum at 60°C for 10 hours to obtain the Ni / NF precursor. (3) The Ni / NF precursor was placed in a ceramic boat and heated to 350°C under nitrogen protection at a heating rate of 2°C / min. The temperature was then maintained at this temperature for 2 hours for pyrolysis treatment to finally obtain the bifunctional NiP / NF catalyst.

[0050] Comparative Example 4: (1) The nickel foam substrate was sequentially immersed in 3M hydrochloric acid, anhydrous ethanol and deionized water, and ultrasonically cleaned for 15 min each, and then dried in a vacuum drying oven at 60℃. The pretreated nickel foam substrate was obtained. (2) Dissolve 2 mmol of cobalt nitrate hexahydrate, 2 mmol of nickel nitrate hexahydrate and 2 mmol of urea in 80 mL of deionized water and stir continuously for 3 hours to ensure complete dissolution. Then transfer the solution to a stainless steel high-pressure reactor lined with polytetrafluoroethylene and immerse it in the pretreated nickel foam substrate. After sealing the stainless steel high-pressure reactor, carry out a hydrothermal reaction at 120 °C for 6 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature. Then wash it three times with deionized water and anhydrous ethanol respectively. Finally, dry it under vacuum at 60 °C for 10 hours to obtain the CoNi / NF precursor. (3) The CoNi / NF precursor was placed in a ceramic boat and heated to 350°C under nitrogen protection at a heating rate of 2°C / min. The temperature was then maintained at this temperature for 2 hours for pyrolysis treatment to finally obtain the bifunctional CoNiP / NF catalyst.

[0051] The LSV comparison results of the catalysts prepared in Example 1 and Comparative Example 4 are as follows: Figure 12 As shown in the figure, the results indicate that the absence of ammonium fluoride significantly reduces the hydrogen evolution performance of the catalyst.

[0052] Analysis of test results: The scanning electron microscope image of Comparative Example 1 (CoNi-NF) is as follows: Figure 2 As shown, the scanning electron microscope image of Example 1 (CoNiP-NF) is presented. Figure 1 As can be seen, the CoNiP-NF catalyst prepared in Example 1 possesses a nanoflower structure, with the nanoflowers interconnected to form a three-dimensional porous network structure. In the electrocatalytic hydrogen evolution reaction, the three-dimensional porous network structure allows the electrolyte to fully wet the catalyst surface and fully contact the active sites. The abundant pores provide unobstructed channels for hydrogen generation and escape, effectively preventing the adsorption and accumulation of hydrogen on the catalyst surface, thereby suppressing the overpotential rise of the hydrogen evolution reaction and significantly improving the efficiency of the hydrogen evolution reaction. In the hydrazine hydrate oxidation reaction, the hierarchical porous system allows hydrazine hydrate molecules to rapidly diffuse into the catalyst interior, fully contacting and reacting with the active sites. The microscopic wrinkles and protrusions on the surface of the nanospheres further increase the adsorption capacity for hydrazine hydrate molecules, promoting the reaction.

[0053] The elemental distribution diagram of Example 1 (CoNiP-NF) is shown below. Figure 3 — Figure 5 As can be seen, Co, Ni, and P all exhibit a uniform spatial distribution on the sample surface, with no obvious elemental segregation or local enrichment. This indicates that the hydrothermal synthesis and subsequent phosphating process did not cause uneven elemental distribution, further confirming the successful preparation of the CoNiP catalyst and the uniformity of its elemental composition.

[0054] The LSV curves of Comparative Example 1 (CoNi-NF), Comparative Example 2 (CoP-NF), Comparative Example 3 (NiP-NF), and Example 1 (CoNiP-NF) under alkaline conditions (1M KOH) are shown below. Figure 6 As shown, compared to Comparative Examples 1-3, the CoNiP-NF catalyst prepared in Example 1 exhibits a lower hydrogen evolution overpotential in alkaline electrolyte and maintains excellent stability for up to 45 hours.

[0055] Comparative Example 1 (CoNi-NF), Comparative Example 2 (CoP-NF), Comparative Example 3 (NiP-NF), and Example 1 (CoNiP-NF) under acidic conditions ( The LSV curve is as follows: Figure 7 As shown, compared to Comparative Examples 1-3, the CoNiP-NF catalyst prepared in Example 1 exhibits a lower hydrogen evolution overpotential in the acidic electrolyte and can maintain stability for more than 60 hours.

[0056] The LSV curves of Comparative Example 1 (CoNi-NF), Comparative Example 2 (CoP-NF), Comparative Example 3 (NiP-NF), and Example 1 (CoNiP-NF) under neutral conditions (1M PBS) are shown in the figure. Figure 8 As shown, compared to Comparative Examples 1-3, the CoNiP-NF catalyst prepared in Example 1 exhibits a lower hydrogen evolution overpotential in neutral electrolyte and can maintain stability for nearly 20 hours.

[0057] The LSV curves of Comparative Example 1 (CoNi-NF), Comparative Example 2 (CoP-NF), Comparative Example 3 (NiP-NF), and Example 1 (CoNiP-NF) in 1M KOH + 0.5M N2H4 are shown below. Figure 9 As shown, compared to Comparative Examples 1-3, the CoNiP-NF catalyst prepared in Example 1 exhibits a lower hydrogen evolution overpotential in HzOR and can maintain long-term stability for more than 70 hours.

[0058] To illustrate the significant advantages of hydrazine oxidation at the electrocatalytic level, Comparative Example 1 (CoNi-NF), Comparative Example 2 (CoP-NF), Comparative Example 3 (NiP-NF), and Example 1 (CoNiP-NF) were compared. Potential displacement at current density (HzOR and OER) such as Figure 10 As shown. It can be seen that, compared with Comparative Examples 1-3, the CoNiP-NF catalyst prepared in Example 1, when the current density reaches... At that time, the HzOR overpotential of the CoNiP / NF catalyst electrode was only 0.043 V vs .RHE, which is significantly negatively shifted by 1.617 V vs .RHE compared to the OER overpotential of the same electrode (1.66 V vs .RHE). This huge potential difference indicates that replacing the traditional OER reaction with the hydrazine oxidation pathway can effectively overcome the energy barrier limitation of the alkaline electrolysis system.

[0059] To further investigate the performance of hydrogen evolution at the cathode and hydrazine hydrate oxidation at the anolyte at all pH, flow cell tests were conducted using the material from Example 1 (CoNiP-NF). Figure 11 As shown in Figure A, this demonstrates the excellent performance of the acid-base asymmetric system. Furthermore, long-term stability tests were conducted on this acid-base asymmetric system, as shown in Figure A. Figure 11 As shown in B, it indicates that it has good stability.

[0060] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a bifunctional cobalt-nickel-phosphorus catalyst, characterized in that, Cobalt nitrate hexahydrate, nickel nitrate hexahydrate, urea and ammonium fluoride were used as reactants. After dissolution, a pretreated nickel foam substrate was added, and then a hydrothermal reaction was carried out at 120-140℃. The resulting product was washed and dried to obtain a precursor. The precursor was then subjected to gas-phase phosphating treatment with sodium hypophosphite as the phosphorus source to obtain a bifunctional CoNiP / NF catalyst.

2. The preparation method according to claim 1, characterized in that, Specifically, the following steps are included: Step S1: The nickel foam substrate is ultrasonically cleaned with hydrochloric acid, ethanol and deionized water respectively to remove surface oxides and impurities, and a pretreated nickel foam substrate is obtained. Step S2: Dissolve cobalt nitrate hexahydrate, nickel nitrate hexahydrate, urea and ammonium fluoride in deionized water and stir continuously until fully dissolved. Then pour the solution into a polytetrafluoroethylene liner, place the pretreated nickel foam substrate inside, and carry out a hydrothermal reaction at 120-140℃ for 6-8 hours. After the reaction is completed, wait for the reaction system to cool naturally to room temperature. Then wash it alternately with deionized water and anhydrous ethanol, and dry it to obtain the CoNi / NF precursor. Step S3: Place the CoNi / NF precursor in a ceramic boat, add sodium hypophosphite upstream of the tube furnace and the CoNi / NF precursor downstream, and program the temperature to 300-350℃ under inert gas protection, hold for 2-4 hours for phosphating treatment to obtain the bifunctional CoNiP / NF catalyst.

3. The preparation method according to claim 2, characterized in that, Step S1 is as follows: The nickel foam substrate is sequentially immersed in 2-3M hydrochloric acid, anhydrous ethanol and deionized water, and ultrasonically cleaned for 15 minutes each. Then it is dried in a vacuum drying oven at 60℃ to obtain the pretreated nickel foam substrate.

4. The preparation method according to claim 3, characterized in that, In step S2, the ratio of cobalt nitrate hexahydrate: nickel nitrate hexahydrate: urea: ammonium fluoride: deionized water is 2 mmol: 2 mmol: 2 mmol: 10 mmol: 80 mL.

5. The preparation method according to claim 4, characterized in that, Step S2 is as follows: Cobalt nitrate hexahydrate, nickel nitrate hexahydrate, ammonium fluoride and urea are dissolved in deionized water and stirred continuously until completely dissolved. Then, the solution is immersed in the prepared nickel foam substrate. The solution is placed in a sealed stainless steel high-pressure reactor lined with polytetrafluoroethylene and subjected to a hydrothermal reaction at 120°C for 6 hours. After the reaction is completed, the reaction system is allowed to cool naturally to room temperature. The system is then washed three times alternately with deionized water and anhydrous ethanol. Finally, the system is dried under vacuum at 60°C for 10 hours to obtain the CoNi / NF precursor.

6. The preparation method according to claim 5, characterized in that, In step S3, the temperature rise rate of the programmed temperature rise is 2℃ / min.

7. The preparation method according to claim 6, characterized in that, Step S3 is as follows: the CoNi / NF precursor is placed in a ceramic boat, 1g of sodium hypophosphite is placed upstream of the tube furnace, and the CoNi / NF precursor is placed downstream. The temperature is programmed to rise to 350℃ at a heating rate of 2℃ / min under inert gas protection, and held at that temperature for 2 hours for phosphating treatment, finally obtaining the bifunctional CoNiP / NF catalyst.

8. The preparation method according to claim 7, characterized in that, The inert gas is nitrogen or argon.

9. A bifunctional cobalt-nickel-phosphorus catalyst, characterized in that, The catalyst is prepared by any one of the bifunctional cobalt-nickel-phosphorus catalysts according to claims 1-7, and has a nanoflower structure. The nanoflower structures are interconnected to form a three-dimensional porous network structure.

10. The application of the bifunctional cobalt-nickel-phosphorus catalyst according to claim 9 in hydrogen evolution and hydrazine hydrate oxidation in full pH electrolyte.

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