Molybdenum-doped nickel phosphide electrode and preparation method and application thereof

Abstract

The invention belongs to the technical field of electrochemistry, and particularly relates to a molybdenum-doped nickel phosphide electrode and a preparation method and application thereof. The preparation method comprises the following steps: dissolving soluble nickel salt, ammonium fluoride and urea in water to obtain a mixed solution; soaking foamed nickel in the mixed solution for hydrothermal reaction to obtain a precursor Ni (CO3) OH / NF; dipping the precursor Ni (CO3) OH / NF in a molybdenum salt solution for solvothermal reaction to obtain Mo-Ni (OH) 2 / NF; and carrying out high-temperature phosphating reaction on the Mo-Ni (OH) 2 / NF and a phosphorus source in an inert atmosphere to obtain the molybdenum-doped nickel phosphide electrode. By adopting a step-by-step doping method, the problems of overlapping of catalytic active sites and low catalytic efficiency caused by simultaneous addition of a nickel source and a molybdenum source in the prior art are solved, and the specific surface area of the molybdenum-doped nickel phosphide electrode is remarkably increased, so that the catalytic sites are more uniformly distributed on the surface of the molybdenum-doped nickel phosphide electrode, and the catalytic efficiency is greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of electrochemistry, and in particular to a molybdenum-doped nickel phosphide electrode and a preparation method and application thereof. Background Art

[0002] As a clean and sustainable way to produce hydrogen, water electrolysis technology has shown great significance in the context of global energy structure transformation and climate change. Hydrogen energy, with its high energy density, zero pollution and easy storage, is recognized as an ideal alternative energy option.

[0003] In the exploration of efficient methods to obtain hydrogen energy, electrolysis of hydrogen technology stands out, and the improvement of catalytic efficiency is highly dependent on the rational selection of catalysts. However, the development of water electrolysis hydrogen production technology still faces many challenges, including low hydrogen production efficiency, high overpotential required for the reaction, and high overall equipment costs. In particular, platinum, rhodium, and palladium precious metal catalysts, despite their excellent performance, are difficult to be widely used due to their high prices, which undoubtedly limits the commercialization of water electrolysis hydrogen production technology.

[0004] In the field of hydrogen energy research, molybdenum-doped nickel phosphide catalysts have broad application prospects, especially in the fields of hydrogen storage and hydrogen fuel cells. The main advantage of molybdenum-doped nickel phosphide catalysts lies in the regulatory effect of molybdenum atoms on the electronic properties of the catalyst surface. Molybdenum doping can introduce new electronic states, thereby changing the electron density and orbital distribution on the catalyst surface. This change helps to improve the adsorption capacity of molybdenum-doped nickel phosphide catalysts for hydrogen, thereby improving the catalytic activity. In addition, molybdenum doping can also improve the stability of nickel phosphide catalysts. However, in the molybdenum-doped nickel phosphide electrodes currently prepared by adding nickel source and molybdenum source at the same time, nickel and molybdenum form nickel clusters and molybdenum clusters, respectively, resulting in the overlap and stacking of molybdenum metal catalytic sites and nickel metal catalytic sites, which in turn makes the catalytic efficiency low, limiting its large-scale application in water electrolysis hydrogen production technology. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a molybdenum-doped nickel phosphide electrode and a preparation method and application thereof. The present invention prepares a precursor Ni(OH)2 / NF by a hydrothermal method, then dopes the precursor Ni(OH)2 / NF with molybdenum to obtain Mo-Ni(OH)2 / NF; finally, mixes Mo-Ni(OH)2 / NF with a phosphorus source and performs a high-temperature phosphating reaction to obtain a molybdenum-doped nickel phosphide electrode. The present invention adopts a step-by-step doping method to make the precursor Ni(CO3)OH / NF have a larger specific surface area, and then dopes molybdenum atoms into the lattice of nickel atoms, so that the catalytic sites of the molybdenum-doped nickel phosphide electrode obtained by the present invention are evenly distributed, and then the catalytic efficiency of the molybdenum-doped nickel phosphide electrode is improved, overcoming the problems of overlapping and stacking of molybdenum catalytic sites and nickel catalytic sites and low catalytic efficiency caused by nickel and molybdenum forming nickel clusters and molybdenum clusters respectively in the molybdenum-doped nickel phosphide electrode prepared by adding nickel source and molybdenum source at the same time in the prior art.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] The first object of the present invention is to provide a method for preparing a molybdenum-doped nickel phosphide electrode, comprising the following steps:

[0008] Soluble nickel salt, ammonium fluoride and urea are dissolved in water to obtain a mixed solution; wherein the molar ratio of the soluble nickel salt, ammonium fluoride and urea is 0.5-1.5:4:5.

[0009] The metal foam is immersed in the mixed solution and subjected to a hydrothermal reaction to obtain a precursor Ni(CO3)OH / NF. In the hydrothermal reaction, urea and water are thermally decomposed to generate ammonia water to make the mixed solution weakly alkaline. At the same time, urea is thermally decomposed to obtain carbonate ions. Under weakly alkaline conditions, ammonium fluoride is used as a directing agent. Under the guiding effect of ammonium fluoride, nickel ions react with carbonate ions and hydroxide ions in the mixed solution to generate basic nickel carbonate, which is attached to the metal foam. - Embedded into the layered structure of basic nickel carbonate to obtain Ni(CO3)OH / NF.

[0010] The precursor Ni(CO3)OH / NF is immersed in a molybdenum salt solution and subjected to a solvothermal reaction. During the solvothermal reaction, molybdenum ions diffuse into Ni(CO3)OH / NF and replace part of the nickel atoms to obtain Mo-Ni(OH)2 / NF.

[0011] The Mo-Ni(OH)2 / NF and the phosphorus source are placed at the upper and lower ends of a muffle furnace respectively, and a high-temperature phosphating reaction is carried out in an inert atmosphere. During the high-temperature phosphating reaction, the PH3 gas generated by the decomposition of the phosphorus source at the upper end undergoes an oxidation-reduction reaction with the Ni(OH)2 in the Mo-Ni(OH)2 / NF at the lower end to obtain a molybdenum-doped nickel phosphide electrode.

[0012] Preferably, the concentration of molybdenum ions in the molybdenum salt solution is 0.2 mmol / L to 0.8 mmol / L; wherein, if the concentration of molybdenum ions is too low, the doping effect is poor, and if the concentration is too high, alloys are formed.

[0013] Preferably, the hydrothermal reaction conditions are: hydrothermal reaction at 90° C. to 150° C. for 5 h to 8 h.

[0014] Preferably, the conditions for the high temperature phosphating reaction are: heating to 250° C. to 350° C. at 2° C. / min for phosphating for 1 h to 3 h.

[0015] Preferably, the soluble nickel salt is selected from nickel nitrate, nickel chloride or nickel sulfate; among them, compared with nickel chloride and nickel sulfate, nitrate is more stable in the chemical reaction of multiple metal ions and will not easily combine with other metal ions to form precipitation like chloride or sulfate ions.

[0016] Preferably, the molybdenum salt in the molybdenum salt solution is selected from Na2MoO4·2H2O or potassium molybdate.

[0017] Preferably, the metal foam is selected from nickel foam, titanium foam or copper foam.

[0018] Preferably, the phosphorus source is selected from sodium hypophosphite or red phosphorus.

[0019] Preferably, the Mo-Ni(OH)2 / NF is dried before the high temperature phosphating reaction. The drying conditions are: drying at 120°C to 150°C for 6h to 12h. 。

[0020] Preferably, the mass ratio of Mo-Ni(OH)2 / NF to the phosphorus source is 1:3-10; if the amount of the phosphorus source is too low, the molybdenum-doped nickel phosphide electrode will exhibit metallization-rich characteristics, making the structure of the molybdenum-doped nickel phosphide electrode easily change during the catalytic reaction, thereby reducing its stability; if the amount of the phosphorus source is too much, the molybdenum-doped nickel phosphide electrode will be phosphide-rich, and the presence of a large number of PP bonds will weaken the conductivity of the molybdenum-doped nickel phosphide electrode, thereby reducing its catalytic efficiency.

[0021] The second object of the present invention is to provide a molybdenum-doped nickel phosphide electrode prepared by the above preparation method.

[0022] Preferably, in the molybdenum-doped nickel phosphide electrode, molybdenum atoms are doped into the crystal lattice of nickel atoms.

[0023] Preferably, a molybdenum-doped nickel phosphide electrode is prepared, wherein molybdenum-doped nickel phosphide is attached to the foam metal, the molybdenum-doped nickel phosphide is a nanosheet array, the nanosheets form a burr-like three-dimensional structure, there are protruding molybdenum-doped nickel phosphide nanoparticles on the surface of the nanosheets, and the surface of the three-dimensional structure is uniformly distributed with cavities.

[0024] The third object of the present invention is to provide the use of the above-mentioned molybdenum-doped nickel phosphide electrode in preparing a negative electrode for catalytic hydrogen evolution reaction.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The present invention provides a method for preparing a molybdenum-doped nickel phosphide electrode, wherein a soluble nickel salt, ammonium fluoride and urea are dissolved in water to obtain a mixed solution; wherein the molar ratio of the soluble nickel salt, ammonium fluoride and urea is 0.5-1.5:4:5; a foamed metal is immersed in the mixed solution for hydrothermal reaction to obtain a precursor Ni(CO3)OH / NF; during the hydrothermal reaction, urea and water are thermally decomposed to generate ammonia water to make the mixed solution weakly alkaline, and urea is thermally decomposed to obtain carbonate ions; under weakly alkaline conditions, ammonium fluoride is used as a directing agent, and the F of ammonium fluoride is - with Ni 2+ The formation of complexes changes the Ni 2+ Under the guidance of ammonium fluoride, nickel ions react with carbonate ions and hydroxide ions in the mixed solution to form basic nickel carbonate, which is attached to the foam metal. - Embedded into the layered structure of basic nickel carbonate and maintaining the stability of the layered structure to obtain Ni(CO3)OH / NF; immersing the precursor Ni(CO3)OH / NF in a molybdenum salt solution and performing a solvothermal reaction. During the solvothermal reaction, molybdenum ions diffuse into Ni(CO3)OH / NF and replace part of nickel atoms to obtain Mo-Ni(OH)2 / NF; placing Mo-Ni(OH)2 / NF and a phosphorus source at the upper and lower ends of a muffle furnace respectively, and performing a high-temperature phosphating reaction in an inert atmosphere. During the high-temperature phosphating reaction, PH3 gas generated by the decomposition of the phosphorus source at the upper end undergoes an oxidation-reduction reaction with the Mo-Ni(OH)2 / NF at the lower end to obtain a molybdenum-doped nickel phosphide electrode.

[0027] 2. The precursor Ni(CO3)OH / NF of the present invention has a large specific surface area and a regular layered structure, which is conducive to the uniform doping of molybdenum atoms and the uniform distribution of catalytic sites; the molybdenum atoms are uniformly doped into the lattice of nickel atoms, avoiding the phenomenon that nickel and molybdenum atoms agglomerate to form nickel clusters and molybdenum clusters respectively, so that the molybdenum catalytic sites and nickel catalytic sites are completely exposed, thereby effectively overcoming the problem of the prior art that the catalytic sites of the molybdenum-doped nickel phosphide electrode prepared by simultaneously adding a nickel source and a molybdenum source overlap and stack, resulting in low catalytic efficiency.

[0028] In addition, the high-temperature phosphating reaction of Mo-Ni(OH)2 / NF with phosphorus source does not change the overall structure of the precursor Ni(CO3)OH / NF and the doping state of molybdenum atoms. Therefore, the molybdenum-doped nickel phosphide electrode can maintain the uniformity of the catalytic sites and high catalytic efficiency.

[0029] 3. The molybdenum-doped nickel phosphide electrode provided by the present invention exhibits higher activity and stability in the catalytic hydrogen evolution reaction. When the phosphating concentration is 0.8 mmol / L, the molybdenum-doped nickel phosphide electrode exhibits better catalytic hydrogen evolution performance, and the current density is 100 mA / cm 2 When , the overpotential is 278mV. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 These are morphology characterization pictures of the 0.8Mo-NiP / NF electrode of Example 4 of the present invention at different magnifications, wherein (a) is a picture at a lower magnification, and (b) is a picture at a higher magnification.

[0031] Figure 2 This is the XRD spectrum of Ni(CO3)OH / NF of Example 2 of the present invention.

[0032] Figure 3 This is the XRD spectrum of Mo-Ni(OH)2 / NF of Example 3 of the present invention.

[0033] Figure 4 This is the XRD spectrum of the Mo-NiP / NF electrode of Example 4 of the present invention.

[0034] Figure 5 Ni(CO3)OH / NF, Mo-Ni(OH) 2 / LSV and EIS test diagrams of NF and Mo-NiP / NF electrodes, where (a) is the Ni(CO3)OH / NF, Mo-Ni(OH) 2 / LSV test diagram of NF and Mo-NiP / NF electrodes, (b) is the Ni(CO3)OH / NF, Mo-Ni(OH) 2 / EIS test graphs of NF and Mo-NiP / NF electrodes.

[0035] Figure 6 These are the LSV and EIS test graphs of Ni(CO3)OH / NF and Mo-Ni(OH)2 / NF of Examples 1 to 4 of the present invention, wherein (a) is the LSV test graph of Ni(CO3)OH / NF and Mo-Ni(OH)2 / NF of Examples 1 to 4, and (b) is the EIS test graph of Ni(CO3)OH / NF and Mo-Ni(OH)2 / NF of Examples 1 to 4.

[0036] Figure 7These are the LSV and EIS test graphs of the Ni(CO3)OH / NF and Mo-NiP / NF electrodes of Examples 1 to 4 of the present invention, wherein (a) is the LSV test graph of the Ni(CO3)OH / NF and Mo-NiP / NF electrodes of Examples 1 to 4, and (b) is the EIS test graph of the Ni(CO3)OH / NF and Mo-NiP / NF electrodes of Examples 1 to 4. DETAILED DESCRIPTION

[0037] The technical solution of the present invention will be clearly and completely described below in combination with the data in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] It should be noted that the professional terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the following embodiments of the present invention can be purchased from the market or prepared by existing methods. Among them, nickel nitrate hexahydrate, ammonium fluoride and sodium molybdate dihydrate are all analytically pure and purchased from Shanghai Hushi; urea and sodium hypophosphite are both analytically pure, and potassium hydroxide has a purity of 91% and is purchased from Aladdin.

[0039] Currently, molybdenum-doped nickel phosphide catalysts have shown good application potential in the fields of hydrogen storage and hydrogen fuel cells. However, the existing technology, that is, the molybdenum-doped nickel phosphide electrode prepared by adding nickel source and molybdenum source at the same time, has the disadvantage of overlapping catalytic active sites, which directly leads to a decrease in catalytic efficiency, thus limiting the large-scale promotion and application of molybdenum-doped nickel phosphide electrodes in water electrolysis hydrogen production technology.

[0040] In view of the problems existing in the prior art, the present invention provides a method for preparing a molybdenum-doped nickel phosphide electrode, comprising the following steps: dissolving a soluble nickel salt, ammonium fluoride and urea in water to obtain a mixed solution; wherein the molar ratio of the soluble nickel salt, ammonium fluoride and urea is 0.5-1.5:4:5; immersing a foamed metal in the mixed solution and performing a hydrothermal reaction to obtain a precursor Ni(CO3)OH / NF; in the hydrothermal reaction, urea and water are thermally decomposed to generate ammonia water to make the mixed solution weakly alkaline, and at the same time, urea is thermally decomposed to obtain carbonate ions; under weakly alkaline conditions, ammonium fluoride is used as a guiding agent, and under the guiding effect of ammonium fluoride, nickel ions react with carbonate ions and hydroxide ions in the mixed solution to generate basic nickel carbonate, which is attached to the foamed metal, and F -Embedded into the layered structure of basic nickel carbonate to obtain Ni(CO3)OH / NF; The precursor Ni(CO3)OH / NF is immersed in a molybdenum salt solution and subjected to a solvothermal reaction. During the solvothermal reaction, molybdenum ions diffuse into Ni(CO3)OH / NF and replace part of nickel atoms to obtain Mo-Ni(OH)2 / NF; Mo-Ni(OH)2 / NF and a phosphorus source are placed at the upper and lower ends of a muffle furnace respectively, and a high-temperature phosphating reaction is carried out in an inert atmosphere to obtain a molybdenum-doped nickel phosphide electrode.

[0041] The present invention adopts a step-by-step doping method to uniformly dope molybdenum atoms into the lattice of nickel atoms, effectively avoiding the problem of overlapping and stacking of molybdenum catalyst points and nickel catalytic sites caused by simultaneous addition of nickel source and molybdenum source in the prior art, and effectively improving the catalytic efficiency of the molybdenum-doped nickel phosphide electrode.

[0042] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0043] Example 1

[0044] A method for preparing a molybdenum-doped nickel phosphide electrode comprises the following steps:

[0045] S1. Dissolve 0.9683 g of nickel nitrate hexahydrate, 0.4937 g of ammonium fluoride and 1.0008 g of urea in 60 mL of deionized water to obtain a mixed solution.

[0046] S2. Immerse 1 cm×3 cm nickel foam in the mixed solution, then put the mixed solution into a reactor and perform a hydrothermal reaction at 100° C. for 6 h to obtain the precursor Ni(CO3)OH / NF.

[0047] S3. The precursor Ni(CO3)OH / NF was immersed in an aqueous solution consisting of 0.4 mmol Na2MoO4·2H2O and 30 mL ionized water, and then transferred to the inner lining of a reactor with a capacity of 100 mL, and subjected to solvothermal reaction in an oven at 140°C for 6 h to obtain Mo-Ni(OH)2 / NF, recorded as 0.4Mo-Ni(OH)2 / NF.

[0048] S4. Place Mo-Ni(OH)2 / NF and 1 g of sodium hypophosphite at the lower and upper ends of the muffle furnace respectively, heat the muffle furnace to 350°C at a heating rate of 2°C / min, keep it for 2 hours under argon flow, and then cool it to room temperature to obtain a Mo-NiP / NF electrode, recorded as 0.4Mo-NiP / NF.

[0049] Example 2

[0050] A method for preparing a molybdenum-doped nickel phosphide electrode, which has the same preparation steps as those in Example 1, except that the amount of Na2MoO4·2H2O in S2 is replaced from 0.24 mmol to 0.2 mmol, and the mass of sodium hypophosphite in S3 is replaced from 1 g to 0.2 g, comprising the following steps:

[0051] S1. Dissolve 0.9683 g of nickel nitrate hexahydrate, 0.4937 g of ammonium fluoride and 1.0008 g of urea in 60 mL of deionized water to obtain a mixed solution;

[0052] S2. Immerse 1 cm×3 cm nickel foam in the mixed solution, then put the mixed solution into a reactor and perform a hydrothermal reaction at 100° C. for 6 h to obtain the precursor Ni(CO3)OH / NF.

[0053] S3. The precursor Ni(CO3)OH / NF was immersed in an aqueous solution consisting of 0.2 mmol Na2MoO4·2H2O and 30 mL ionized water, and then transferred to the inner lining of a reactor with a capacity of 100 mL, and subjected to solvothermal reaction in an oven at 140°C for 6 h to obtain Mo-Ni(OH)2 / NF, which was recorded as 0.2Mo-Ni(OH)2 / NF.

[0054] S4. Place Mo-Ni(OH)2 / NF and 0.2 g of sodium hypophosphite at the lower and upper ends of the muffle furnace respectively, heat the muffle furnace to 350°C at a heating rate of 2°C / min, keep it for 2 hours under argon flow, and then cool it to room temperature to obtain a Mo-NiP / NF electrode, recorded as 0.2Mo-NiP / NF.

[0055] Example 3

[0056] A method for preparing a molybdenum-doped nickel phosphide electrode, which has the same preparation steps as those in Example 1, except that the amount of Na2MoO4·2H2O in S2 is replaced from 0.4 mmol to 0.6 mmol, and the mass of sodium hypophosphite in S3 is replaced from 1 g to 0.6 g, comprising the following steps:

[0057] S1. Take 0.9683 g of nickel nitrate hexahydrate, 0.4937 g of ammonium fluoride and 1.0008 g of urea and dissolve them in 60 mL of ionized water to obtain a mixed solution; immerse 1 cm × 3 cm of nickel foam in the mixed solution, and then put the mixed solution in a reactor and perform a hydrothermal reaction at 100 ° C for 6 hours to obtain the precursor Ni(CO3)OH / NF.

[0058] S2. The precursor Ni(CO3)OH / NF was immersed in an aqueous solution consisting of 0.6 mmol Na2MoO4·2H2O and 30 mL ionized water, and then transferred to the inner lining of a reactor with a capacity of 100 mL, and subjected to solvothermal reaction in an oven at 140°C for 6 h to obtain Mo-Ni(OH)2 / NF, recorded as 0.6Mo-Ni(OH)2 / NF.

[0059] S3. Place Mo-Ni(OH)2 / NF and 0.6 g of sodium hypophosphite at the lower and upper ends of the muffle furnace respectively, heat the muffle furnace to 350°C at a heating rate of 2°C / min, keep it for 2 hours under argon flow, and then cool it to room temperature to obtain a Mo-NiP / NF electrode, recorded as 0.6Mo-NiP / NF.

[0060] Example 4

[0061] A method for preparing a molybdenum-doped nickel phosphide electrode, which has the same preparation steps as those in Example 1, except that the amount of Na2MoO4·2H2O in S2 is replaced from 0.4 mmol to 0.8 mmol, and the mass of sodium hypophosphite in S3 is replaced from 1 g to 0.8 g, comprising the following steps:

[0062] S1. Dissolve 0.9683 g of nickel nitrate hexahydrate, 0.4937 g of ammonium fluoride and 1.0008 g of urea in 60 mL of deionized water to obtain a mixed solution.

[0063] S2. Immerse 1 cm×3 cm nickel foam in the mixed solution, then put the mixed solution into a reactor and perform a hydrothermal reaction at 100° C. for 6 h to obtain the precursor Ni(CO3)OH / NF.

[0064] S3. The precursor Ni(CO3)OH / NF was immersed in an aqueous solution consisting of 0.8 mmol of Na2MoO4·2H2O and 30 mL of ionized water, and then transferred to the inner lining of a reactor with a capacity of 100 mL, and subjected to solvothermal reaction in an oven at 140°C for 6 h to obtain Mo-Ni(OH)2 / NF, which was recorded as 0.8Mo-Ni(OH)2 / NF.

[0065] S4. Place Mo-Ni(OH)2 / NF and 0.8 g of sodium hypophosphite at the lower and upper ends of the muffle furnace respectively, heat the muffle furnace to 350°C at a heating rate of 2°C / min, keep it for 2 hours under argon flow, and then cool it to room temperature to obtain a Mo-NiP / NF electrode, recorded as 0.8Mo-NiP / NF.

[0066] Example 5

[0067] A method for preparing a molybdenum-doped nickel phosphide electrode comprises the following steps:

[0068] S1. Dissolve 0.9683 g of nickel nitrate hexahydrate, 0.4937 g of ammonium fluoride and 1.0008 g of urea in 60 mL of deionized water to obtain a mixed solution.

[0069] S2. Immerse 1 cm×3 cm nickel foam in the mixed solution, then put the mixed solution into a reactor and perform a hydrothermal reaction at 90° C. for 5 h to obtain the precursor Ni(CO3)OH / NF.

[0070] S3. The precursor Ni(CO3)OH / NF was immersed in an aqueous solution consisting of 0.4 mmol of Na2MoO4·2H2O and 30 mL of ionized water, and then transferred to the inner lining of a reactor with a capacity of 100 mL, and subjected to a solvothermal reaction in an oven at 120°C for 8 h to obtain Mo-Ni(OH)2 / NF.

[0071] S4. Place Mo-Ni(OH)2 / NF and 1 g of sodium hypophosphite at the lower and upper ends of the muffle furnace respectively, heat the muffle furnace to 250°C at a heating rate of 2°C / min, keep it under argon flow for 3 hours, and then cool it to room temperature to obtain a Mo-NiP / NF electrode.

[0072] Example 6

[0073] A method for preparing a molybdenum-doped nickel phosphide electrode comprises the following steps:

[0074] S1. Dissolve 0.9683 g of nickel nitrate hexahydrate, 0.4937 g of ammonium fluoride and 1.0008 g of urea in 60 mL of deionized water to obtain a mixed solution.

[0075] S2. Immerse 1 cm×3 cm nickel foam in the mixed solution, then put the mixed solution into a reactor and perform a hydrothermal reaction at 150° C. for 8 h to obtain the precursor Ni(CO3)OH / NF.

[0076] S3. The precursor Ni(CO3)OH / NF was immersed in an aqueous solution consisting of 0.4 mmol of Na2MoO4·2H2O and 30 mL of ionized water, and then transferred to the inner lining of a reactor with a capacity of 100 mL, and subjected to a solvothermal reaction in an oven at 140°C for 6 h to obtain Mo-Ni(OH)2 / NF.

[0077] S4. Place Mo-Ni(OH)2 / NF and 1 g of sodium hypophosphite at the lower and upper ends of the muffle furnace respectively, heat the muffle furnace to 350°C at a heating rate of 2°C / min, keep it under argon flow for 1 hour, and then cool it to room temperature to obtain a Mo-NiP / NF electrode.

[0078] observe Figure 1 Figures (a) and (b) show that the 0.8Mo-NiP / NF electrode exhibits three-dimensional structural characteristics, with numerous and uniform cavities distributed on its surface, providing abundant sites for the attachment of molybdenum-doped nickel phosphide, which also means that the 0.8Mo-NiP / NF electrode has a large specific surface area. Figure 1 In (a), it is observed that there are protruding molybdenum-doped nickel phosphide attached to the surface of the 0.8Mo-NiP / NF electrode, with a diameter of about 2μm, which is the result of the size effect of molybdenum ions during the high-temperature phosphating reaction. The presence of these particles not only significantly increases the specific surface area of ​​the 0.8Mo-NiP / NF electrode, but also increases the number of its active sites, which helps to improve the overall performance of the 0.8Mo-NiP / NF electrode.

[0079] Depend on Figure 1 In (b), a large number of uniform burr-like structures were observed on the surface of nickel foam. This feature further expanded the specific surface area of ​​the 0.8Mo-NiP / NF electrode. The larger specific surface area has a positive effect on improving the overall performance of the 0.8Mo-NiP / NF electrode. At the same time, the increase in surface cavities also had a significant impact on the performance of the 0.8Mo-NiP / NF electrode. First, the increase in cavities improved the adsorption capacity of the 0.8Mo-NiP / NF electrode, enabling it to exhibit better performance during the adsorption and separation process; second, this porous structure helps to reduce the weight of the 0.8Mo-NiP / NF electrode, which is of great significance for reducing device weight, reducing energy consumption, and improving the performance of the 0.8Mo-NiP / NF electrode. In addition, the presence of cavities is also conducive to providing more active sites, thereby enhancing the catalytic activity of the 0.8Mo-NiP / NF electrode, which has an important impact on the process of catalytic oxidation, reduction, and decomposition reactions.

[0080] observe Figure 2 It was concluded that two significant and sharp diffraction peaks can be seen at 44.8° and 52.3°, which are attributed to the metallic nickel component in the Ni(CO3)OH / NF-based nickel foam. In addition, Ni(CO3)OH / NF exhibits obvious diffraction peaks at 19.4°, 33.1°, 39.1°, 52.1°, 59.2°, and 621°. After comparing these diffraction peaks with the standard card Ni(OH)2 (PDF#14-0117), it was confirmed that these diffraction peaks correspond to the (001), (100), (101), (001), and (102) crystal planes of Ni(OH)2, respectively.

[0081] observe Figure 3It was found that Mo-Ni(OH)2 / NF showed significant diffraction peaks at 9.2°, 33.1°, 39.1°, 52.1°, 59.2°, and 62.1°. After comparing these diffraction peaks with the standard card Ni(OH)2 (PDF#14-0117), it was confirmed that these diffraction peaks corresponded to the (001), (100), (101), and (102) crystal planes of Ni(OH)2, respectively. Figure 2 and Figure 3 The XRD spectrum shows that the intensities and positions of these diffraction peaks remain highly consistent, which indicates that the doping of molybdenum does not significantly change the crystal structure of Ni(OH)2.

[0082] observe Figure 4 It was concluded that characteristic peaks of Ni(OH)2 and NiO were generated in the Mo-NiP / NF electrode. After high-temperature phosphating reaction, the diffraction peak of MoNiP8 appeared in the XRD spectrum. The formation of NiO is attributed to the chemical reaction of Ni with oxygen in the air under high temperature conditions. Further, in an environment containing a small amount of PH3 gas, NiO will be converted into Ni3P, but due to the relative lack of phosphorus content, only Ni3P is formed. Among them, the diffraction peak intensity of metallic nickel in nickel foam is significant, which masks other diffraction peaks with lower crystallinity. In the XRD spectrum, there are several more prominent diffraction peaks, located at approximately 40.1°, 44.2°, 54.2°, and 66.2°, respectively. By comparing with the standard card PDF#50-1191, it is confirmed that these diffraction peaks correspond to the (110), (201), (210), (210) and (310) crystal planes of MoNiP8, respectively, Figure 4 In addition, there are some unmarked diffraction peaks in the XRD spectrum, which also correspond to the crystal plane of MoNiP8 (PDF#50-1191). This is because a specific molybdenum-nickel-phosphorus compound structure phase is formed during the high-temperature phosphating reaction, which produces these additional diffraction peaks.

[0083] at the same time, Figure 4 The diffraction peak in the graph shows a slight shift, which is attributed to the successful integration of molybdenum into the matrix of nickel foam in the form of doping. XRD test verification proves that the present invention successfully prepares molybdenum-doped nickel phosphide electrode, which is composed of Ni(CO3)OH / NF and MoNiP8.

[0084] observe Figure 5 Figure (a) shows that under the same current density conditions, compared with Ni(CO3)OH / NF and Mo-Ni(OH) 2 / NF, the 0.8Mo-NiP / NF electrode prepared in Example 4 exhibits a lower hydrogen evolution overpotential. Specifically, when the current density of the working electrode reaches 100 mA / cm 2 The Mo-NiP / NF electrode only needs an overpotential of 278mV. This is because the dense and fine burr structure formed on the surface of the Mo-NiP / NF electrode after the high-temperature phosphating reaction greatly increases the number of electron attachment sites and the effective reaction area, making the Mo-NiP / NF electrode more efficient than the Mo-Ni(OH) 2 / NF and Ni(CO3)OH / NF showed more outstanding performance in electrocatalytic hydrogen evolution. In addition, the size of the arc in the impedance diagram reflects the impedance of the electrochemical process. That is to say, the smaller the impedance arc, the smaller the impedance of the electrode to the electrochemical process, the greater the current density of the electrode in the electrochemical process, and the higher its catalytic activity. Figure 5 As shown in Figure (b), Mo-NiP / NF electrode is better than Mo-Ni(OH) 2 / NF has better catalytic activity.

[0085] from Figure 6 (a) shows that the electrode catalytic hydrogen evolution overpotential changes with the change of molybdenum doping amount. Among them, the 0.6Mo-Ni(OH)2 / NF electrode has a smaller hydrogen evolution overpotential at the same current density. Similarly, the observation Figure 6 (b) shows that the semicircle diameters of Ni(CO3)OH / NF and 0.2Mo-Ni(OH)2 / NF are larger, which means that the charge transfer resistance values ​​of Ni(CO3)OH / NF and 0.2Mo-Ni(OH)2 / NF are higher, and the electrical conductivity of 0.2Mo-Ni(OH)2 / NF is poor, which means that the electron transmission speed is slow during the reaction, resulting in poor electrochemical hydrogen evolution performance. 0.2Mo-Ni(OH)2 / NF is only slightly higher than Ni(CO3)OH / NF, mainly because only limited doping between molybdenum ions and nickel precursors has been carried out, and the defects of the original nickel precursor, such as few active sites and poor electrical conductivity, have not been improved; and with the increase of molybdenum ion concentration, the redox current and redox peak of Mo-Ni(OH)2 / NF are increasing, indicating that the electrochemical performance of Mo-Ni(OH)2 / NF improves with the increase of molybdenum ion concentration.

[0086] from Figure 7 (a) shows that the Mo doping amount has an important influence on the catalytic hydrogen evolution performance of the Mo-NiP / NF electrode. At the same current density, the smaller the overpotential, the better the catalytic hydrogen evolution performance of the electrode. Therefore, the 0.8Mo-NiP / NF electrode exhibits the best catalytic hydrogen evolution performance. Figure 5 and Figure 6Performance analysis shows that Mo doping significantly improves the catalytic performance of the catalytic electrode. Figure 7 (b) shows that as the Mo doping concentration increases, the Nyquist semicircle diameter decreases significantly with the increase of phosphorus concentration, indicating that its conductivity gradually increases and its catalytic activity gradually increases. This shows that molybdenum ion doping helps to improve the kinetic characteristics of the electrode reaction and makes the Mo-NiP / NF electrode have more outstanding electrochemical performance.

[0087] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

Claims

1. A method for preparing a molybdenum-doped nickel phosphide electrode, characterized in that: The following steps are involved: Dissolving soluble nickel salt, ammonium fluoride and urea in water to obtain a mixed solution; wherein the molar ratio of the soluble nickel salt, ammonium fluoride and urea is 0.5-1.5:4:5; The foamed metal is immersed in the mixed solution and subjected to a hydrothermal reaction. In the hydrothermal reaction, urea and water are thermally decomposed to generate ammonia water, making the mixed solution weakly alkaline. At the same time, urea is thermally decomposed to obtain carbonate ions. Under weakly alkaline conditions, ammonium fluoride is used as a directing agent. Under the guiding effect of ammonium fluoride, nickel ions react with carbonate ions and hydroxide ions in the mixed solution to generate basic nickel carbonate, which is attached to the foamed metal. - It is embedded into the layered structure of basic nickel carbonate to obtain the precursor Ni(CO3)OH / NF; The precursor Ni(CO3)OH / NF is immersed in a molybdenum salt solution and subjected to a solvothermal reaction. During the solvothermal reaction, molybdenum ions diffuse into the Ni(CO3)OH / NF and replace some nickel atoms to obtain Mo-Ni(OH)2 / NF. The Mo-Ni(OH)2 / NF and the phosphorus source are placed at the upper and lower ends of the muffle furnace respectively, and a high-temperature phosphating reaction is carried out in an inert atmosphere to obtain a molybdenum-doped nickel phosphide electrode.

2. The method for preparing a molybdenum-doped nickel phosphide electrode according to claim 1, characterized in that: The concentration of molybdenum ions in the molybdenum salt solution is 0.2mmol / L to 0.8mmol / L.

3. The method for preparing a molybdenum-doped nickel phosphide electrode according to claim 1, characterized in that: The conditions of the hydrothermal reaction are: hydrothermal reaction at 90°C to 150°C for 5h to 8h.

4. The method for preparing a molybdenum-doped nickel phosphide electrode according to claim 1, characterized in that: The conditions of the solvent thermal reaction are: reacting at 120°C to 140°C for 6h to 8h.

5. The method for preparing a molybdenum-doped nickel phosphide electrode according to claim 1, characterized in that: The conditions for high temperature phosphating reaction are: phosphating at 250°C to 350°C for 1h to 3h.

6. The method for preparing a molybdenum-doped nickel phosphide electrode according to claim 1, characterized in that: The mass ratio of Mo-Ni(OH)2 / NF to phosphorus source is 1:3-10.

7. The method for preparing a molybdenum-doped nickel phosphide electrode according to claim 1, characterized in that: The metal foam is selected from nickel foam, titanium foam or copper foam.

8. A molybdenum-doped nickel phosphide electrode obtained by the preparation method according to any one of claims 1 to 7.

9. The molybdenum-doped nickel phosphide electrode according to claim 8, characterized in that: In the molybdenum-doped nickel phosphide electrode, molybdenum atoms are doped into the lattice of nickel atoms.

10. Use of the molybdenum-doped nickel phosphide electrode according to claim 8 in preparing a negative electrode for hydrogen production reaction by electrolysis of water.

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