Iron-nickel co-doped ammonium phosphomolybdate, preparation method therefor, and use thereof

Abstract

The present invention belongs to the technical field of water electrolysis for hydrogen production, and particularly relates to iron-nickel co-doped ammonium phosphomolybdate, a preparation method therefor, and the use thereof. The iron-nickel co-doped ammonium phosphomolybdate uses a molybdate, a phosphate, a ferric salt and a nickel salt as starting materials, and is prepared under a mild condition of 40-80℃ by means of adjusting the proportion of the raw materials and the pH value of a solution, the obtained iron-nickel co-doped ammonium phosphomolybdate being used to manufacture an oxygen evolution electrode to be applied to water electrolysis for hydrogen production. Linear sweep voltammetry in a 0.5mol / L H2SO4 solution shows that the iron-nickel co-doped ammonium phosphomolybdate of the present invention exhibits an oxygen evolution overpotential of only 210 mV at 10mA / cm2, which is lower than the oxygen evolution overpotential 370mV of noble metal iridium oxide, the oxygen evolution Tafel slope in an acidic medium of the iron-nickel co-doped ammonium phosphomolybdate is smaller than the oxygen evolution Tafel slope of the noble metal IrO2, and the alternating-current impedance reaction resistance is lower than the oxygen evolution reaction resistance of the noble metal. The electrochemical characteristics enable the iron-nickel co-doped ammonium phosphomolybdate material to achieve obvious technical and cost advantages during PEM water electrolysis for hydrogen production.

Description

Iron-nickel co-doped ammonium phosphomolybdate and its preparation method and application Technical Field

[0001] The present invention relates to the technical field of hydrogen production by electrolysis of water, and in particular to iron-nickel co-doped ammonium phosphomolybdate, a preparation method thereof and an application thereof. Background Art

[0002] Hydrogen production by water electrolysis is an effective way to achieve the "dual carbon" strategy. At present, the main methods of hydrogen production by water electrolysis are alkaline water electrolysis (ALK), proton exchange membrane water electrolysis (PEM), anion exchange membrane water electrolysis (AEM) and solid oxide water electrolysis (SOEC). In these four water electrolysis hydrogen production modes, electrocatalytic materials are key materials for improving water electrolysis hydrogen production. In particular, the anodic oxygen evolution process involves a four-electron transfer reaction. Compared with hydrogen evolution, its reaction is more complex, involves more reaction steps, and has greater reaction resistance. Therefore, oxygen evolution electrocatalysts are the key core materials in the entire water electrolysis hydrogen production system. In the PEM mode of water electrolysis hydrogen production, oxygen is released after anodic oxidation, leaving acidic hydrogen ions. In an acidic environment and under high potential conditions, it is easy to corrode the electrode material, thereby destroying the structure of the electrode material and reducing the electrocatalytic activity. For this purpose, precious metal electrocatalysts are needed, but precious metals are expensive and difficult to popularize.

[0003] Among the four modes of hydrogen production by water electrolysis, the PEM mode has the following significant advantages: (1) High hydrogen purity and no pollution. The PEM mode uses a proton exchange membrane solid electrolyte, and the gas produced does not need to be de-alkali treated. The thickness of the cationic membrane is very small, and it is not easy to produce hydrogen reverse osmosis. The PEM mode only requires pure water, does not require any additives, does not contain corrosive liquids, and does not pollute the environment. (2) High conversion efficiency and energy saving. The electrodes of the PEM mode are tightly attached to both sides of the cationic membrane and its internal pores. It is a zero-distance catalytic electrode with a large electrode reaction area and high Coulomb efficiency. (3) The stack is light and small in size. The collector structure of the two-stage chamber in the PEM mode electrolyzer is compact and flexible, which makes the electrolyzer light and small in size. The weight is only about 1 / 3 of that of an ordinary electrolyzer with the same hydrogen production capacity. The advantage is zero electrode distance and small internal resistance. (4) Strong adaptability to current and voltage fluctuations of renewable energy sources. PEM water electrolysis for hydrogen production offers a fast response time and adaptability to dynamic operation, making it ideally suited to the uneven, intermittent, and fluctuating transmission of renewable energy sources (wind and solar). Therefore, research and development of electrode materials suitable for PEM applications is of great value. However, the acidic environment and high oxidizing potential of the PEM require expensive precious metals such as iridium or ruthenium, making widespread application of the PEM method challenging.

[0004] Patent application number 202211051214.2 discloses a method for preparing MoRuP-loaded carbon nanobelts, MoRuP-loaded carbon nanobelts and their applications, and reports the electrocatalytic hydrogen evolution performance under acidic and alkaline conditions. Despite this, these disclosed materials do not involve the preparation of iron-nickel co-doped ammonium phosphomolybdate and its application in electrolysis of water to produce hydrogen in acidic media. In order to overcome the shortcomings of the prior art, the present invention proposes an iron-nickel co-doped ammonium phosphomolybdate, a preparation method and its application in electrolysis of water to produce hydrogen and oxygen in acidic media. Summary of the Invention

[0005] The purpose of the present invention is to provide an iron-nickel co-doped ammonium phosphomolybdate and its preparation method and application, which can effectively solve the technical difficulties encountered in the electrolysis of water to produce hydrogen in acidic media and PEM mode.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] An iron-nickel co-doped ammonium phosphomolybdate, characterized in that the chemical formula is:

[0008] Fe x Ni y (NH4)3Mo( 12-x-y )PO 40 4H2O,

[0009] Wherein, x is the molar ratio of iron to molybdenum, and y is the molar ratio of nickel to molybdenum.

[0010] Preferably, the molar ratio x of iron to molybdenum is 3.0-7.0%, the molar ratio y of nickel to molybdenum is 2.0-6.0%, and the molar number of the phosphate is 1 / 12 of the total metal ions.

[0011] Furthermore, the iron-nickel co-doped ammonium phosphomolybdate is used in hydrogen production by water electrolysis.

[0012] Furthermore, the application is to grind the iron-nickel co-doped ammonium phosphomolybdate and then apply it on carbon paper to prepare an oxygen evolution electrode.

[0013] Preferably, the application is to mix and grind the iron-nickel co-doped ammonium phosphomolybdate with graphite and boron carbide, and then spray the mixture onto a cation exchange membrane to prepare an oxygen evolution electrode.

[0014] Furthermore, the oxygen evolution electrode is used to electrolyze water to produce hydrogen in neutral and acidic media.

[0015] A method for preparing iron-nickel co-doped ammonium phosphomolybdate comprises the following steps:

[0016] S1: dissolving molybdate in deionized water, dissolving phosphate in another container, and slowly adding the phosphate solution dropwise to the molybdate solution to form a reaction mixture A;

[0017] S2: Weigh iron salt and nickel salt and dissolve them in deionized water until they are completely dissolved to form solution B;

[0018] S3: adding solution B obtained in S2 dropwise to solution A under stirring at 40°C. After the addition is complete, adding concentrated nitric acid, maintaining the reaction system at 80°C and a pH between 1.0 and 2.0, heating and continuing stirring to obtain a precipitated product;

[0019] S4: The precipitated product is washed, filtered, and dried to obtain iron-nickel co-doped ammonium phosphomolybdate.

[0020] Preferably, the molybdate in S1 is any one, two or three of potassium molybdate, sodium molybdate and ammonium molybdate; the phosphate includes one, two or three of potassium hydrogen phosphate, sodium hydrogen phosphate, ammonium phosphate and / or potassium dihydrogen phosphate and sodium dihydrogen phosphate.

[0021] Preferably, the iron salt in S2 is any one of sulfate, nitrate and chloride.

[0022] Preferably, the nickel salt in S2 is any one of its sulfate, nitrate and chloride.

[0023] An iron-nickel co-doped ammonium phosphomolybdate is prepared from phosphate, molybdate, iron salt and nickel salt as starting materials by adjusting the ratio of the raw materials and the pH value of the solution under mild conditions of 40-80°C.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention provides a new electrocatalytic material, which realizes electrocatalytic oxygen evolution by using iron-nickel co-doped ammonium phosphomolybdate. The iron-nickel co-doped ammonium phosphomolybdate carbon paste electrode is used as the working electrode. The linear scanning in 0.5 mol / L H2SO4 solution is carried out at 10 mA / cm 2 The overpotential of oxygen evolution is only 200mV, while the overpotential of IrO2 electrode under the same conditions is 370mV; the Tafel slope of oxygen evolution of iron-nickel doped ammonium phosphomolybdate in acidic medium is 61.60mVdec -1 It is also lower than the Tafel value of IrO2 81.91mVdec -1 The AC impedance reaction resistance is also lower than the oxygen evolution reaction resistance of noble metals. These electrochemical properties give the iron-nickel co-doped ammonium phosphomolybdate material of the present invention significant technical and cost advantages in hydrogen production by water electrolysis in the PEM mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG1 is an XRD pattern of ammonium phosphomolybdate and iron-nickel co-doped ammonium phosphomolybdate designed by the present invention;

[0027] FIG2 is an XPS elemental analysis diagram of iron-nickel co-doped ammonium phosphomolybdate, a material designed according to the present invention;

[0028] FIG3 is an electron affinity spectrum of molybdenum element in the XPS elemental analysis diagram of iron-nickel co-doped ammonium phosphomolybdate designed as a material of the present invention;

[0029] FIG4 is an electron affinity spectrum of phosphorus in the XPS elemental analysis diagram of iron-nickel co-doped ammonium phosphomolybdate, a material designed according to the present invention;

[0030] FIG5 is an electron affinity spectrum of iron in the XPS elemental analysis diagram of iron-nickel co-doped ammonium phosphomolybdate, a material designed according to the present invention;

[0031] FIG6 is an electron affinity spectrum of nickel in the XPS elemental analysis diagram of iron-nickel co-doped ammonium phosphomolybdate, a material designed according to the present invention;

[0032] FIG7 is a linear sweep voltammogram of iron-nickel co-doped ammonium phosphomolybdate in 0.5 mol / L H2SO4;

[0033] FIG8 is a Tafel curve of iron-nickel co-doped ammonium phosphomolybdate in 0.5 mol / L H2SO4;

[0034] FIG9 is an AC impedance diagram of iron-nickel co-doped ammonium phosphomolybdate in 0.5 mol / L H2SO4. DETAILED DESCRIPTION

[0035] In order to make the purpose and advantages of the present invention more clearly understood, the present invention is described in detail below with reference to the following examples. It should be understood that the following text is only used to describe one or more specific embodiments of the present invention and does not strictly limit the scope of protection of the present invention.

[0036] Example 1

[0037] Preparation of iron-nickel co-doped ammonium phosphomolybdate:

[0038] Weigh 0.15g of sodium dihydrogen phosphate and dissolve it in 20mL of deionized water. Once completely dissolved, add 40mL of an aqueous solution of 2.3g of ammonium molybdate, stirring while adding. Separately, weigh a molybdate solution (4% nickel salt and 1% iron salt) and dissolve it in 20mL of deionized water to form Solution B. Maintaining the solution temperature at 40°C, slowly add Solution B dropwise to Solution A while stirring. After the addition is complete, add concentrated nitric acid, maintaining the pH of the reaction system between 1.0 and 2.0. Raise the temperature to 80°C and continue stirring for 18 hours to obtain the precipitated product. Wash, filter, and dry the desired iron-nickel co-doped ammonium phosphomolybdate.

[0039] Similarly, by changing the ratio of nickel and iron salts, pure ammonium phosphomolybdate co-doped with iron and nickel can be prepared, in which the molar ratio of iron salt to molybdate is 0.1-2.0%, the ratio of nickel salt to molybdate is 2.0-8.0%, and the molar number of phosphate is 1 / 12 of the total metal ions.

[0040] Example 2

[0041] The following experiments were conducted based on the iron-nickel co-doped ammonium phosphomolybdate and pure ammonium phosphomolybdate in Example 1, and the test results are shown in FIG1 .

[0042] XRD test of ammonium phosphomolybdate and iron-nickel co-doped ammonium phosphomolybdate:

[0043] The prepared samples were subjected to XRD test. Diffraction peaks appeared at 2θ = 10.97°, 15.40°, 21.82°, 26.82°, 30.95° and 36.52°, corresponding to the (110), (200), (220), (222), (400) and (332) crystal plane structures, which are consistent with (NH4)3PO4(MoO3) 12 The crystal structure of 4H2O (JCPDS No. 09-0412) is consistent with that of iron and nickel. The above test results indicate that the synthesized product is iron-nickel co-doped ammonium phosphomolybdate. The diffraction peak 2θ = 21.77° on the (220) crystal plane of undoped pure ammonium phosphomolybdate is shifted by 0.05° after doping, confirming that iron and nickel, with smaller ionic radii, are doped into the crystal structure of ammonium phosphomolybdate.

[0044] Example 3

[0045] According to the XRD test of ammonium phosphomolybdate and iron-nickel co-doped ammonium phosphomolybdate in Example 2, the test results are shown in Figures 2 to 6.

[0046] XPS elemental analysis of the prepared iron-nickel co-doped ammonium phosphomolybdate was performed. Carbon, nitrogen, oxygen, phosphorus, molybdenum, nickel, and iron were detected throughout the image, as shown in Figure 2. High-resolution electron affinities for molybdenum, phosphorus, iron, and nickel are shown in Figures 2 to 6, respectively. This demonstrates that nickel and iron have been doped into the ammonium phosphomolybdate crystals.

[0047] Example 4

[0048] Method for preparing oxygen evolution electrode by iron-nickel co-doped ammonium phosphomolybdate compound and application of iron-nickel co-doped ammonium phosphomolybdate in electrocatalytic oxygen evolution:

[0049] Take 56% by mass of graphite powder, add 40% of boron carbide, and then add 4.0% of iron-nickel co-doped ammonium phosphomolybdate, mix and dissolve in 30mL of deionized water, stir evenly to obtain a mixed suspension, evaporate at a certain temperature, take out after cooling and assemble into a carbon paste electrode. Using this electrode as the working electrode, a potential scan is performed in a 0.5mol / LH2SO4 solution at room temperature and pressure with a scan rate of 5mV / s. The instrument used is the Shanghai Chenhua CHI660D electrochemical workstation. The working electrode is prepared as follows: weigh 0.5g of the sample to be tested, grind it with an agate mortar, add 0.1mL of silicone oil thereto, and stir thoroughly to obtain a paste sample with fine particles and uniformity. Fill the sample into a polytetrafluoroethylene electrode tube and connect it to the three-electrode system with copper wire as a conductor. The electrode potential corresponding to the LSV test curve is calculated according to the formula E REH =E SCE +0.242+0.059pH(V) is converted into reversible electrode potential (RHE).

[0050] The obtained linear sweep voltammetry curve is shown in FIG7e, the measured Tafel curve is shown in FIG8e, and the measured AC impedance curve is shown in FIG9a.

[0051] As shown in Figure 8, the oxygen evolution overpotential of Fe-Ni doped ammonium phosphomolybdate in acidic medium is 210 mV, which is lower than the oxygen evolution overpotential of precious metal IrO2 (370 mV), and its Tafel slope is 66.34 mVdec. -1 It is also lower than IrO2's 81.91mVdec -1 , showing good acidic oxygen evolution characteristics.

[0052] Ammonium phosphomolybdate generated by co-doping with iron and nickel has the smallest reaction resistance, as shown in Table 1:

[0053] Table 1 AC impedance test results

[0054] In Table 1:

[0055] a: 4.0wt% ammonium phosphomolybdate doped with 4% nickel and 5% iron + 40% boron carbide + 56.0wt% carbon powder;

[0056] b: 40.0wt% ammonium phosphomolybdate doped with 5% iron + 60.0wt% carbon powder;

[0057] c: 40.0wt% ammonium phosphomolybdate doped with 4% nickel + 60.0wt% carbon powder;

[0058] d: 40.0wt% ammonium phosphomolybdate doped with 4% nickel and 6% iron + 60.0wt% carbon powder.

[0059] In summary, iron-nickel doped ammonium phosphomolybdate has good electrocatalytic oxygen evolution properties in acidic solution and can play an important role in hydrogen production by acidic water electrolysis.

[0060] It should be noted that:

[0061] In Figure 7, a is 40% pure ammonium phosphomolybdate + 60% graphite powder, b is 40% ammonium phosphomolybdate doped with 4% nickel + 60% graphite powder, c is 40% ammonium phosphomolybdate doped with 5% iron + 60% graphite powder, d is 40% ammonium phosphomolybdate doped with 4% nickel and 6% iron + 60% graphite powder, e is IrO2, and f is 4% ammonium phosphomolybdate doped with 4% nickel and 6% iron + 40% boron carbide + 56% carbon powder;

[0062] In Figure 8, a is 40% pure ammonium phosphomolybdate + 60% graphite powder, b is 40% ammonium phosphomolybdate doped with 5% iron + 60% graphite powder, c is 40% ammonium phosphomolybdate doped with 4% nickel + 60% graphite powder, d is 40% ammonium phosphomolybdate doped with 4% nickel and 6% iron + 60% graphite powder, e is IrO2, and f is 4% ammonium phosphomolybdate doped with 4% nickel and 6% iron + 40% boron carbide + 56% carbon powder;

[0063] In Figure 9, a is 4.0wt% ammonium phosphomolybdate doped with 4% nickel and 1% iron + 40% boron carbide + 56.0wt% carbon powder, b is 40.0wt% ammonium phosphomolybdate doped with 3% iron + 60.0wt% carbon powder, c is 40.0wt% ammonium phosphomolybdate doped with 4% nickel and 1% iron + 60.0wt% carbon powder, and d is 40.0wt% ammonium phosphomolybdate doped with 4% nickel + 60.0wt% carbon powder. The measured solution resistance Rs, reaction resistance Rct and double-layer capacitance related parameters CPE are shown in Table 1.

[0064] The above describes the embodiments of the present invention in detail with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. After knowing the contents described in the present invention, ordinary technicians in this technical field can make several equivalent changes and substitutions without departing from the principles of the present invention. These equivalent changes and substitutions should also be regarded as falling within the scope of protection of the present invention.

Claims

1. An iron-nickel co-doped ammonium phosphomolybdate, characterized in that: The chemical formula is: Fe x Ni y (NH4)3Mo (12-x-y) PO 40 4H2O, Wherein, x is the molar ratio of iron to molybdenum, y is the molar ratio of nickel to molybdenum, the molar ratio x of iron to molybdenum is 3.0-7.0%, the molar ratio y of nickel to molybdenum is 2.0-6.0%, and the molar number of the phosphate is 1 / 12 of the total metal ions.

2. The iron-nickel co-doped ammonium phosphomolybdate according to claim 1, characterized in that: The application of the iron-nickel co-doped ammonium phosphomolybdate in hydrogen production by water electrolysis.

3. The iron-nickel co-doped ammonium phosphomolybdate according to claim 2, characterized in that: The application is to grind the iron-nickel co-doped ammonium phosphomolybdate and then apply it on carbon paper to prepare an oxygen evolution electrode.

4. The iron-nickel co-doped ammonium phosphomolybdate according to claim 2, characterized in that: The application is to mix and grind the iron-nickel co-doped ammonium phosphomolybdate with graphite and boron carbide, and then spray the mixture onto a cation exchange membrane to prepare an oxygen evolution electrode.

5. The iron-nickel co-doped ammonium phosphomolybdate according to claim 3 or 4, characterized in that: The oxygen evolution electrode is used for electrolyzing water to produce hydrogen in neutral and acidic media.

6. A method for preparing the iron-nickel co-doped ammonium phosphomolybdate according to claim 1, characterized in that: The following steps are involved: S1: dissolving molybdate in deionized water, dissolving phosphate in another container, and slowly adding the phosphate solution dropwise to the molybdate solution to form a reaction mixture A; S2: Weigh iron salt and nickel salt and dissolve them in deionized water until they are completely dissolved to form solution B; S3: adding solution B obtained in S2 dropwise to solution A under stirring at 40°C. After the addition is complete, adding concentrated nitric acid, maintaining the reaction system at 80°C and a pH between 1.0 and 2.0, heating and continuing stirring to obtain a precipitated product; S4: The precipitated product is washed, filtered, and dried to obtain iron-nickel co-doped ammonium phosphomolybdate.

7. The preparation method according to claim 6, characterized in that The molybdate in S1 is any one, two or three of potassium molybdate, sodium molybdate and ammonium molybdate; the phosphate includes any one, two or three of potassium hydrogen phosphate, sodium hydrogen phosphate, ammonium phosphate and / or potassium dihydrogen phosphate and sodium dihydrogen phosphate.

8. The preparation method according to claim 6, characterized in that The iron salt in S2 is any one of sulfate, nitrate and chloride.

9. The preparation method according to claim 6, characterized in that The nickel salt in S2 is any one of its sulfate, nitrate and chloride.

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